ELEMENTS 


OF 


INOKGANIC   CHEMISTRY, 


INCLUDING    THE 


APPLICATIONS  OF  THE  SCIENCE  IN  THE  ARTS. 


f^M,  F.K.S.L.&E., 

LATE    PROFESSOR    OP    CHEMISTRY    Ilf    UNIVERSITY    CO  LLE  G  E,  L  OND  0  N  . 

"V%>  «4&$ 

X^/pTQ'ftp^TED    BY 

HENRY    WATTS,    B.A.,F.  C.S. 

AND 

ROBERT    BRIDGES.    M.  D., 
SECOND    AMERICAN, 

FROM  THE   SECOND  REVISED  AND  ENLARGED  LONDON   EDITION. 
COMPLETE  IN  ONE  VOLUME. 

WITH    TWO    HUNDRED    AND    THIRTY-THREE    ILLUSTRATIONS    ON    WOOD. 


PHILADELPHIA: 
HENRY    C.    LEA. 

1866. 


Entered,  according  to  the  Act  of  Congress,  in  the  year  1858,  by 

BLANCHARD    AND    LEA. 

the  Clerk's  Office  01  trie  District  Court  of  the  United  States  for  u*e  Eastern  District  of 

Pennsylvania. 

COLLINS,     PBISTE* 


AMERICAN  PUBLISHERS'  NOTICE. 


THE  publishers  have  much  pleasure  in  at  length  presenting 
Mr.  GRAHAM'S  Inorganic  Chemistry  complete.  The  first  portion 
(up  to  p.  430),  was  edited  in  1852  by  Dr.  BRIDGES;  the  remainder 
is  reproduced  without  alteration  from  the  English  edition,  issued 
a  few  months  since,  under  the  supervision  of  the  Author,  by  Mr. 
WATTS,  whose  elaborate  Supplement  will  be  found  to  bring  the 
subjects  embraced  in  the  first  portion,  on  a  level  with  the  most 
advanced  condition  of  the  science. 

The  Organic  portion  of  the  work,  issued  in  1843,  has  not 
been  reproduced  by  Mr.  GRAHAM,  nor  does  he,  in  his  "Ad- 
vertisement," hold  out  any  promise  of  its  revision  and  reappear- 
ance. The  present  volume,  therefore,  contains  all  that  the 
Author  has  seen  fit  to  reproduce,  being  the  whole  of  the  two 
volumes  of  the  London  edition. 

References  have  been  introduced  throughout  the  first  part,  to 
Articles  in  the  Supplement  which  modify  or  extend  the  remarks 
in  the  text. 

PHILADELPHIA,  April,  1858. 


ADVERTISEMENT.* 


THE  present  Volume  completes  the  Work  as  a  Treatise  upon 
Inorganic  Chemistry ;  and  it  is,  accordingly,  furnished  with  an 
Index  of  Contents,  which  applies  to  both  volumes. 

From  the  time  which  has  elapsed  since  the  first  publication 
of  these  Elements,  an  amount  of  alteration  and  addition  had 
become  necessary  for  properly  completing  a  new  edition,  which 
precluded  the  Author,  with  his  present  engagements,  from 
undertaking  the  task.  In  these  circumstances,  he  gladly  availed 
himself  of  the  assistance  of  Mr.  Watts,  who  has  supplied  a 
large  amount  of  new  matter,  including  the  Supplement,  and  has 
edited  the  volume  throughout  in  the  most  careful  and  conscien- 
tious manner.  The  most  conspicuous  changes  now  made,  by 
which  the  work  is  improved,  are  the  following : — 

1.  The  systematic  introduction  of  the  best  processes  for  the 
separation    and    quantitative    estimation   of  metals    and    other 
important  substances,  in  addition  to  the  description  of  their  pro- 
perties and  reactions.     The  new  methods  of  volumetric  analysis 
are  detailed,  with  the  description  and  applications  in  particular 
of  Bunsen's  General  Method. 

2.  In  the  Supplement,  in  which  the  subjects  treated  in  the 
first  volume  are  resumed  and  brought  down  to  the  present  time : 
The  determination  of  the  most  important  Physical  constants, 

*  The  observations  in  this  "Advertisement"  apply  to  the  second  volume  of  the  London 
edition,  which  forms  p.  431  to  end  of  the  present  volume. 

W 


vi  ADVERTISEMENT. 

viz.,  the  Mechanical  Equivalent  of  Heat;  the  relations  between 
the  Chemical  and  Magnetic  effects  of  the  Electric  Current,  arid 
the  reduction  of  its  force  to  Absolute  Mechanical  Measure;  also 
the  Measurement  of  the  Chemical  Action  of  Light.  The  Polar- 
ization of  Light  is  treated  in  sufficient  detail  for  the  wants  of 
the  Chemical  Student,  attention  being  especially  directed  to  the 
methods  of  Optical  Saccharimetry,  and  to  the  very  remarkable 
relations  between  Crystalline  Form  and  Molecular  Kotatory 
Power  discovered  by  Pasteur. 

3.  The  modern  views  of  the  constitution  and  classification  of 
Chemical   Compounds   are   explained   at   considerable    length, 
chiefly  according  to  Gerhardt's  Unitary  System.     This  includes 
the  classification  of  Organic  as  well  as  Inorganic  Compounds,  as 
indeed  every  general  system  of  classification  must  do.     In  the 
same  portion  of  the  work,  -the  formation  and  reactions  of  the 
principal  classes  of  organic  compounds  are  explained,  so  far  as 
appeared  necessary  to  the  general  understanding  of  their  mutual 
relations. 

4.  The  last  portion  of  the  Supplement  contains   the   most 
recently  discovered  facts  relating  to  the  Non-metallic  Elements, 
and  the  Metals  of  the  Alkalies  and  Earths,  a  prominent  place 
being  assigned  to  the  allotropic  modifications  of  certain  elements; 
viz.,  Boron,  Silicon,  Sulphur,  Selenium,  and  Phosphorus,  and  to 
the  methods  of  obtaining  the  alkali  and  earth-metals  in  the  free 

state. 

THOMAS  GKAHAM. 
ROYAL  MINT  :  December,  1857. 


PREFACE 

TO  THE   SECOND  EDITION, 
(PART  I.) 


IF  the  Inorganic  department  of  chemistry  has  not  recently  been  ex- 
panded in  the  same  vast  proportion  as  the  Organic  branch  of  the  science, 
still  the  former  has  been  far  from  stationary  of  late  years.  The  advance 
observed  is  partly  in  the  old  direction  of  enlarging  the  list  of  elements, 
partly  and  more  conspicuously  in  supplying  deficient  members  to  familiar 
series  of  compounds,  and  in  thus  enlarging  these  series, — as  in  the  com- 
pounds of  chlorine  with  oxygen,  and  of  sulphur  with  oxygen.  But  the 
most  important  feature  in  the  recent  progress  of  Inorganic  Chemistry 
has  been  the  rigorous  verification  which  numerical  data  of  all  kinds  have 
received,  whether  relating  to  physical  laws,  such  as  the  specific  heat  of 
substances,  or  to  chemical  properties  and  composition.  The  statement 
of  properties  and  relations  has  thus  acquired  a  fulness  and  precision  for 
many  substances,  which  contrasts  strongly  with  the  history  that  could  be 
offered  of  the  same  substances  even  but  a  very  few  years  ago.  The  cor- 
rection and  revision  of  every  minute  branch  of  the  science  was  never, 
indeed,  more  general  and  rapid  than  at  the  present  time.  The  enlarged 
means  of  practical  instruction  in  chemistry,  now  everywhere  provided  for 
the  student,  and  the  consequent  increase  in  the  number  of  able  investi- 
gators, have  no  doubt  contributed  much  to  this  result. 

Progress  of  this  description  cannot  fail  to  affect  the  theoretical  views 
of  chemists,  and  to  promote  sound  conclusions  by  affording  an  extended 
and  safe  foundation  for  reasoning,  in  a  body  of  well-established  facts. 
It  must  be  admitted  that  the  fundamental  views  respecting  the  constitu- 
tion of  salts  are  at  present  in  a  state  of  transition,  but  the  great  questions 
of  chemical  theory,  if  not  yet  solved,  have  at  least  been  correctly  enun- 
ciated, and  a  general  assent  obtained  to  the  facts  upon  which  they  rest. 

(vii) 


CONTENTS. 


CHAPTER  I. 

Heat  ......................  ...,...'  .......................................................................  PAGE  34 

Expansion  and  the  Thermometer  .......................................................................  34 

>  The  Thermometer  ............................  .  ............................................................  41 

Specific  Heat  ................................................................................................  48 

Communication  of  Heat  by  Conduction  ..............................................................  61 

Communication  of  Heat  by  Radiation  ...............................................................  53 

Transmission  of  Heat  through  Media,  and  the  effect  of  Screens  ..............................  65 

—  Equilibrium  of  Temperature  ............................................................................  57 

Fluidity  as  an  effect  of  Heat  ............................................................................  59 

Vaporization  ........................................................................................  .  .......  62 

^  Distillation  .......  .  ...................................................................  .  .......................  72 

Evaporation  in  Vacuo  ...............................................................  ......................  73 

Gases  ..........................................................................................................  77 

Effusion  of  Gases  ..........................................................................................  83 

Transpiration  of  Gases  ....................................................................................  85 

Diffusion  of  Gases  ..............  .  ...........................................................................  87 

Diffusion  of  Vapours  into  Air,  or  Spontaneous  Evaporation  ............  ..  .....................  90 

Hygrometers  ..............................................................................................  91 

Nature  of  Heat  ...............................................................  ,  ...........................  96 


CHAPTER  II. 
Light  ........................................................................................................       98 

CHAPTER  III. 

Chemical  Nomenclature  and  Notation  ..............................  .  .................................  101 

Table  of  Elementary  Substances  ........................................................  .  .............  102 

Nomenclature  of  Compounds  ........  ............................................................  106 

Formulas  of  Compounds  ..................................................................................  109 

Combining  Proportions  ....................................................................................  Ill 

Atomic  Theory  ..................................  .7  ........................................................  .  119 

Specific  Heat  of  Atoms  ............................................................  .  .....................  120 

Relations  between  Atomic  Weight  and  Volumes  ..................................................  125 

Table  of  Specific  Gravity  of  Gases  and  Vapours  ..........................................  .  ........  130 

Isomorphism  .................................................................................................  139 

Classification  of  Elements  ...  ............................................................................  144 

Allatropy  .......................................................................................  .  .............  150 

Isomerism  .................................................................................................  152 

(xi) 


Xll  CONTENTS. 

Arrangement  of  Elements  in  Compounds 154 

Formation  of  Salts  by  Substitution 166 

Salts  of  Ammonia 166 

Antithetic  or  Polar  Formulae 168 

Atomic  Volume  of  Solid  Bodies 171 

CHAPTER  IV. 

Chemical  Affinity 176 

Solution 177 

Order  of  Affinity  .-. 180 

Circumstances  which  affect  the  order  of  Decomposition 181 

Influence  of  Insolubility 182 

Formation  of  Compounds  by  Substitution 182 

Catalysis 186 

Chemical  Polarity  —  Illustrations  from  Magnetical  Polarity : 187 

Atomic  Representation  of  a  Double  Decomposition 189 

Action  of  an  Acid  on  two  Metals  in  Contact 190 

Polarity  of  the  Arrangement 192 

Simple  Voltaic  Circle 193 

Amalgamation  of  the  Zinc  Plate , 194 

Impurity  of  the  Zinc 195 

Compound  Voltaic  Circle 197 

Voltaic  Battery 198 

Solid  Elements  of  the  Voltaic  Circle 200 

Voltaic  Protection  of  Metals 201 

Liquid  Elements  of  the  Voltaic  Circle .' 202 

'  Transference  of  the  Ions 206 

Voltaic  Circles  without  a  Positive  Metal 208 

Theoretical  Considerations 211 

General  Summary 212 

Voltaic  Instruments • 218 

CHAPTER  V. 

SECT.  I.  — Oxygen 223 

Ozone 232 

SECT.  II.  — Hydrogen 232 

Protoxide  of  Hydrogen. — Water 237 

Binoxide  of  Hydrogen 242 

SECT.  III.— Nitrogen 243 

The  Atmosphere 245 

Analysis  of  Air 249 

Protoxide  of  Nitrogen 253 

Binoxide  of  Nitrogen 255 

Nitrous  Acid 257 

Peroxide  of  Nitrogen 258 

v  Nitric  Acid , 259 

Ammonia 264 

SECT  IV.  — Carbon 266 

Diamond. —  Graphite 267 

Varieties  of  Charco'al 268 

Carbonic  Acid  270 

Carbonic  Oxide 274 


CONTENTS.  Xlll 

Oxalic  Aeid 276 

Protocarburetted  Hydrogen 278 

Safety-lamp.— Coal-gas 280 

Structure  of  Flame .'. 283 

Bicarburetted  Hydrogen 285 

Gas  of  Oil. — Carbon  and  Nitrogen, —  Cyanogen 286 

SECT.  V.  — Boron 287 

Boracic  Acid 288 

SECT.  VI.  — Silicon 289 

Silica,  or  Silicic  Acid 290 

SECT  VII.  —  Sulphur 292 

Sulphurous  Acid 294 

Sulphuric  Acid . 295 

Sulphates 300 

Chlorosulphuric  Acid. — Nitrosulphuric  Acid 301 

Hyposulphuric  Acid 302 

Hyposulphurous  Acid 303 

Polythionic  Series '. 304 

Trithionic  Acid. — Tetrathionic  Acid. — Peutathionic  Acid '...  305 

Hydrosulphuric  Acid 306 

Bisulphide  of  Hydrogen 308 

Sulphur  and  Nitrogen. —  Sulphur  and  Carbon 309 

SECT.  VIII.  —  Selenium 311 

Selenious  Acid, —  Selenic  Acid * 312 

* 

SECT.     IX.  —  Phosphorus 313 

Oxide  of  Phosphorus 315 

Hypophosphorous  Acid 316 

Phosphorous  Acid 317 

Phosphoric  Acid ,.  318 

Phosphates 321 

Phosphorus  and  Hydrogen 326 

Phosphorus  and  Nitrogen... 328 

SECT.       X.  —  Chlorine 329 

Uses.— Chlorides 334 

Hydrochloric  Acid 335 

Hypochlorous  Acid 338 

Hypochlorites. —  Chloric  Acid 340 

Chlorates. — Perchloric  Acid 341 

Chlorous  Acid. — Peroxide  of  Chlorine 343 

Chlorine  and  Binoxide  of  Nitrogen 344 

Chloride  of  Nitrogen. —  Chlorides  of  Carbon 346 

Chloroxicarbonic  Gas. —  Chloride  of  Boron. —  Chloride  of  Silicon 347 

Chlorides  of  Sulphur 348 

Chlorides  of  Phosp'iPtig  349 

SECT.     JLl.  -  Bromine 350 

Hydrobromic  Acid. — tfromic  Acid. — Chloride  of  Bromine. —  Bromide  of 

Sulphur 351 

Bromide  of  Silicon 352 

SECT.    XII.  —  Iodine : 35l» 

Iodides. — Hydriodic  Acid '.'. 355 

lodic  Acid ..  356 


XIV  CONTENTS. 

lodates. — Periodic  Acid 357 

Periodates. — Iodide  of  Nitrogen. — Iodide  of  Sulphur. — Iodide  of  Phos- 
phorus.—  Chlorides  of  Iodine 358 

Bromides  of  Iodine ... 359 

SECT.  XIIL  — Fluorine.— Hydrofluoric  Acid 359 

Fluoride  of  Boron « 361 

Fluoride  of  Silicon ....  3&i 


CHAPTER  VI. 

Metallic  Elements. —  General  Observations. — Table  of  Metals 363 

Table  of  Fusibility  of  different  Metals 365 

Arrangement  of  Metallic  Elements 368 


ORDER  I. 
METALLIC  BASES  OF  THE  ALKALIES. 

SECT.        I. — Potassium 369 

Potassa,  or  Potash 372 

Peroxide  of  Potassium. —  Sulphides  of  Potassium 374 

Chloride  of  Potassium. — Iodide  of  Potassium. — Ferrocyanide  of  Potas- 
sium   375 

Ferricyanide  of  Potassium. —  Cyanide  of  Potassium  376 

Sulphocyanide  of  Potassium. —  Carbonate  of  Potassa 377 

Bicarbonate,  —  Sulphate,  —  Bisulphate,  —  Sesquisulphate, — Nitrate   of 

Potassa 378 

Gunpowder 379 

Deflagration  of  Gunpowder.  —  Chlorate  of  Potassa 380 

•"V--       Perchlorate  of  Potassa.— lodate  of  Potassa 381 

SECT.      II.  — Sodium— Soda 382 

Sulphides  of  Sodium, —  Chloride  of  Sodium 383 

Carbonate  of  Soda 384 

Alkalimetry 386 

Method  of  Gay-Lussac 388 

Bicarbonate  of  Soda 389 

Sesquicarbonate  of  Soda,  —  Double  Carbonate  of  Soda  and  Potassa. — 

Sulphite, — Hyposulphite  of  Soda 390 

Sulphate  of  Soda 391 

Preparation  of  Carbonate  from  Sulphate  of  Soda 392 

Bisulphate  of  Soda, — Nitrate  of  Soda 395 

Chlorate, — Phosphates  of  Soda, — Phosphate  of  Soda  and  Ammonia 396 

tPyrophosphate, — Metaphosphates, — Biborate  of  Soda *  397 
Silicates  of  Soda,— Glass 399 

Silicate  of  Soda  and  Lime, —  Silicates  of  Potassa  and  Lime  400 

Silicates  of  Potassa  and  Lead, —  other  Silicates 401 

Ultramarine 402 

BECT.     III.— Lithium 402 

Hydrate  of  Lithia, — Chloride  of  Lithium,  —  Carbonate, —  Sulphate, — 

Phosphate  of  Lithia 403 


CONTENTS.  XV 

ORDER   II. 

METALLIC    BASES    OP    THE    ALKALINE    EARTHS. 

SECT.        I. — Barium. — Baryta 403 

Hydrate  of  Baryta. — Binoxide  of  Barium 404 

Chloride^  of  jSarium. — Carbonate, —  Sulphate, — Nitrate  of  Baryta 405 

SECT.       II.  —  Strontium, —  Strontia, — Binoxide, — Chloride, — Carbonate,  —  Sulphate,  406 
Hyposulphate,— Nitrate  of  Strontia 407 

SECT.     III.  —Calcium, — Lime 407 

/    Protosulphide, — Phosphide, —  Chloride  of  Calcium 409 

Fluoride  of  Calcium, —  Carbonate  of  Lime 410 

Sulphite, — Hyposulphite, — Nitrate, — Phosphates  of  Lime 412 

Hypochlorite  of  Lime 413 

Chlorimetry 414 

SECT.      IV.  —  Magnesium, — Magnesia, —  Chloride  of  Magnesium 415 

Carbonate  of  Magnesia, —  Bicarbonate  of  Potassa  and  Magnesia 416 

Sulphate. — Hyposulphate  of  Magnesia 417 

Nitrate.— Phosphates.—  Borate.— Silicates  of  Magnesia 418 

ORDER  III. 
METALLIC  BASES  OP  THE  EARTHS. 

SECT.        I. — Aluminum, — Alumina 419 

Sulphide, —  Chloride, — Fluoride  of  Aluminum, —  Sulphate  of  Alumina..  421 

Sulphate  of  Alumina  and  Potassa 422 

Sulphate  of  Alumina  and  Ammonia, —  Sulphate  of  Alumina  and  Soda...  423 

Nitrate, — Phosphates, —  Silicates  of  Alumina 424 

Earthenware  and  Porcelain .-.-...» 426 

Stoneware ..*....k. 427 

SECT.       II. — Glucinum. —  Glucina. — Sulphate. —  Silicates  of  Glucina 428 

Yttrium. — Erbium. — Terbium. — Thorium 429 

Zirconium ..  430 


XVI  CONTENTS. 


ORDER  IV. 

METALS    PROPER,    HAVING    PROTOXIDES    ISOMORPHOUS    WITH 

MAGNESIA. 

SECT.        I. — Manganese 431 

"          II.— Iron.. 441 

"        III.— Cobalt.... 459 

«        IV.— Nickel 466 

"          V. — Zinc 47C 

"         VI. — Cadmium , : 474 

"      VII.— Copper 476 

"     VIII.— Lead 485 

ORDER  V. 

OTHER    METALS    PROPER,   HAVING   ISOMORPHOUS    RELATIONS 
WITH     THE     MAGNESIAN    FAMILY. 

SECT.        L— Tin 494 

"         II.— Titanium 601 

"        HI. — Chromium 505 

"         IV.— Vanadium 515 

«          V.— Tungsten 517 

«        VI. Molybdenum 521 

«      VII. Tellurium » 525 

ORDER  VI. 
METALS    ISOMORPHOUS    WITH    PHOSPHORUS. 

SECT.        I. — Arsenic 530 

«»          II. — Antimony 539 

'«       III.— Bismuth 548 

ORDER  VII. 

METALS   NOT   INCLUDED   IN   THE    FOREGOING  CLASSES,   WHOSE 
OXIDES   ARE   NOT  REDUCED   BY   HEAT  ALONE. 

SECT.        I. — Uranium 553 

II.— Cerium 558 

"        III.— Lanthanum 562 

«        IV. — Didymium , 564 

"         V. — Tantalum 566 

«        VI. — Columbium  (Niobium) 570 


CONTENTS.  XV11 


.    ORDER  VIII. 

METALS    WHOSE    OXIDES    ARE    REDUCED    TO    THE    METALLIC 
STATE    BY    HEAT    (NOBLE    METALS). 

SECT.        I. — Mercury « 573 

"         II.— Silver 591 

«       III.— Gold 600 

ORDER  IX. 
METALS    IN    NATIVE    PLATINUM. 

SECT.        I.— Platinum  ; 608 

»         II.— Palladium 619 

«<        III.— Iridium 622 

"         IV.— Osmium 627 

«          V.— Rhodium 630 

«'        VI. — Ruthenium ..  633 


1 


SUPPLEMENT. 

HEAT. 

Expansion  of  Solids 637 

Expansion  of  Liquids 638 

Specific  Heat 640 

Liquefaction , .7 642 

Latent  Heat  of  Vapours 643 

Tension  of  Vapours 645 

Conduction  of  Heat 649 

Mechanical  Equivalent  of  Heat 652 

Dynamical  Theory  of  Heat 654 

LIGHT. 

Polarization 658 

Change  of  Refrangibility  of  Light:  Fluorescence 671 

Spectra  exhibited  by  Coloured  Media 673 

Measurement  of  the  Chemical  Action  of  Light 675 

ELECTRICITY. 

Measurement  of  the  Force  of  Electric  Currents 679 

Ohm's  Formulae 680 

Electric  Resistance  of  Metals 682 

Reduction  of  the  Force  of  the  Current  to  absolute  Mechanical  Measure 684 

2 


\ 


XV111  CONTENTS. 


CHEMICAL  NOTATION  AND  CLASSIFICATION. 

Atoms  and  Equivalents 685 

Gerhardt's  Unitary  System 687 

Types  and  Radicals.  — Rational  Formulae 692 

Classification  of  Compounds  according  to  their  Chemical  Functions 696 

Water-type 697 

Hydrochloric-acid  type 707 

Ammonia-type 710 

Hydrogen-type 716 

RELATIONS  BETWEEN  CHEMICAL  COMPOSITION  AND 

DENSITY. 

Atomic  Volume  of  Liquids .". 720 

Atomic  Volume  of  Solids 728 

RELATIONS  BETWEEN  CHEMICAL  COMPOSITION  AND 
BOILING  POINT. 

Boiling  Points  of  Alcohols,  Fatty  Acids,  and  Compound  Ethers , 729 

CHEMICAL  AFFINITY. 

Influence  of  Mass  on  Chemical  Action. 730 

Mutual  Decomposition  of  Salts  in  Solution 733 

Decomposition  of  Insoluble  Salts  by  Soluble  Salts 735 

Chemical  Decomposition  explained  by  Atomic  Motion.., 737 

DIFFUSION  OF  LIQUIDS. 

Diffusion  of  Saline  Solutions 740 

Decomposition  of  Salts  by  Diffusion 743 

Diffusion  of  Salts  in  the  Soil , 745 

OSMOSE. 

x  Passage  of  Liquids  through  Porous  Earthenware 748 

n  «  «      Membrane 750 

Physiological  Effects  of  Osmose 750 

Diffusion  of  Gases  through  Porous  Septa. 751 

DEVELOPMENT   OF   HEAT   BY  CHEMICAL  COMBINATION. 

Heat  evolved  in  the  Combination  of  Bodies  with  Oxygen 751 

««         «  «  "  Chlorine 754 

«         ««  "  Acids  with  Bases 755 

«         <i  «  "  Water 756 

Calorific  Effects  of  the  Solution  of  Salts  in  Water 756 

Cold  produced  by  Chemical  Decomposition 767 


CONTENTS.  XIX 


NON-METALLIC  ELEMENTS. 

Oxygen  and  Hydrogen 759 

Nitrogen ,.  765 

Carbon 769 

Boron 773 

Silicon , 776 

Sulphur 780 

Selenium 783 

Phosphorus 785 

Chlorine 791 

Bromine 795 

Iodine „ 796 

Fluorine 800 

Bunsen's  Method  of  Volumetric  Analysis 801 

METALS  OF  THE  ALKALIES  AND  EARTHS. 

Potassium 805 

Sodium 806 

Ammonium 808 

Lithium 811 

Barium 812 

Strontium.. 814 

Calcium 815 

Magnesium 817 

Aluminium 818 

Glucinum 821 


LIST  OF  WOOD  CUTS. 


1.  Difference  of  Expansion  in  Solids...  35 

2.  Expansion  of  Merqury 87 

3.  Expansion  of  Water 38 

4.  5,  6.  Expansion  of  Water  above  and 

below  40° 39 

*  7,  8.  Air  Thermometers 41 

9.  Mode  of  Making  Thermometers 42 

10,11,12.  Scales  Compared 44 

13.  Daniel's  Pyrometer 45 

14.  Rutherford's  Self-registering  Ther- 

mometer   46 

15.  Six's 47 

16.  Vibration  between  metals  of  differ- 

ent Temperatures 52 

17.  Heating  of  Liquids 52 

18.  Circulation  in  Fluids  by  Caloric 52 

19.  Radiation  of  Caloric  53 

20.  Reflection  of  Cftloric 54 

21.  Measurement  of  Transmitted  Heat.  55 

22.  Papin's  Digester 65 

23.  Elastic  Force  of  Steam 67 

24.  Brix's  Calorimeter 69 

25.  Expansive  Force  of  Steam  in  contact 

with  Water 71 

26.  Expansive  Force  of  Steam 71 

27.  Cylinder  Boiler 72 

28.  Locomotive  Boiler 72 

29.  Distillation 72 

30.  Liebig's  Condenser  73 

31.  Glass  Condensing  Tube 73 

32.  Elastic  Force  of  Vapours 74 

33.  Water    Frozen   by   Evaporation   in 

Vacuo  75 

34.  Wollaston's  Cryophorus 75 

35.  Liquefaction  of  Gases 77 

36.  Thilorier's  Machine  for  Liquefying 

Carbonic  Acid 77 

37.  38.  Faraday's  Condensing  Tubes 79 

39.  Specific  Gravity  of  Gases 83 

40.  Transpiration  of  Gases 85 

41.  Diffusion  of  Gases 87 

42.  43.  Diffusion  Tubes 89 

44.  Wet  Bulb  Hygrometer 92 

45.  Daniel's  Hygrometer 94 


46,  47.  Regnault's  Condenser-hygrome- 
ter ....t 94 

48.  Madder  Stove 95 

49.  Drying  Oven 96 

50.  Refraction  of  Light 98 

51.  Solar  Spectrum 99 

62.  Different  Coloured  Spectra 100 

53.  Crystalline  Axes 143 

54.  Cube 143 

55.  Octohedron 143 

56.  Rhombic  Dodecahedron 143 

57.  Octohedron,  Solid  Angles  Truncated  144 

58.  Octohedron,  Edges  Truncated 144 

59.  Octohedron,  Doubly  Truncated 144 

60.  Magnetic  Polarity 187 

61-4.  Induced  Polarity 188 

65.  Induced  Polarity 189 

66.  Simple  Voltaic  Circle 190 

67.  Simple  Voltaic  Circle  in  Hydrochlo- 

ric Acid 190 

68.  Simple  Voltaic  Circle  and  Decom- 

posing Cell 191 

69.  Polarity  of  the  Voltaic  Circuit 192 

70.  Polarity  of  the  Closed  Circuit 194 

71.  Polarity  of  the  Impure  Zinc  in  Di- 

lute Acid 195 

72.  Polarity  of  the  Open  Voltaic  Cir- 

cuit   196 

73.  Polarity  of  the  Open  Voltaic  Cir- 

cuit   197 

74.  Polarity  of  the  Compound  Voltaic 

Circuit 197 

75.  76.  Polarity  of  the  Compound  Vol- 

taic Circuit 198 

77.  Voltaic  Battery  ; 199 

78.  Voltaic  Battery  and  Decomposing 

Cell 199 

79.  80.  Compound  Circles 202 

81.  Simple  Circle  with  two  Polar  Li- 

quids   205 

82.  Gas  Battery 209 

83.  84.  Thermo-electric  Pairs 215 

85.  Diamagnetic  Polarity 217 

86,  87.  Daniel's  Constant  Battery 218 

(xxi) 


XX11 


LIST    OF    WOOD    CUTS. 


88,  89,  90.  Grove's  Nitric  Acid  Battery  219 

91.  Bunsen  Battery 220 

92.  Bird   Battery    and   Decomposing 

Cell 220 

93.  94.  Volta-meter  and  Galvanometer  222 

95.  Preparation  of  Oxygen  from  Red 

Oxide  of  Mercury 223 

96.  Preparation  of  Oxygen  from  Black 

Oxide  of  Manganese 225 

97.  Mode  of  Transferring  Gases 225 

98.  Preparation  of  Oxygen  from  Chlo- 

rate of  Potassa 226 

99.  Combustion  in  Oxygen 227 

100.  Blowpipe  Flame  of  Lamp  urged 

by  Oxygen 231 

101.  Blowpipe  Flame  of  Coal-gas  urged 

by  Oxygen 231 

102    Decomposition  of  Water  by  Red- 
hot  Iron 233 

103.  Decomposition  of  Water  by  Zinc 

and  Sulphuric  Acid 234 

104.  Musical  Sound  from  Burning  Hy- 

drogen    235 

105.  Oxyhydrogen  Blowpipe 235 

106.  Safety-jet 236 

107.  Gas-bag 236 

108.  Synthesis  of  Water 237 

109.  Crystalline  form  of  Water 238 

110.  Water-filter 240 

111.  Preparation  of  Nitrogen 244 

112.  Snow  Crystals 249 

113.  Syphon  Eudiometer 249 

114.  Analysis  of  Atmospheric  Air 250 

115.  Preparation  of  Nitrous  Oxide 254 

,  117.  Preparation  of  Nitric  Acid..  261 

118.  Preparation  of  Solution  of  Am- 

monia   264 

119,  120.  Preparation  of  Gaseous  Am- 

monia   265,  266 

121,  122.  Preparation  of  Carbonic  Acid  271 

123.  Analysis  of  Carbonic  Acid 273 

124.  Preparation  of  Carbonic  Oxide  ...  275 

125.  Analysis  of  Oxalic  Acid  : 277 

126.  Collection   of  Light  Carburetted 

Hydrogen 278 

127.  Preparation  of  Light  Carburetted 

Hydrogen 279 

128.  Davy's  Safety-lamp 280 

Preparation  of  Coal-gas 281 

130,  181.   Graduation  of   Eudiometer 

Tubes 283 

132.  Structure  of  Flame 284 

133.  Preparation  of  Olefiant  Gas 285 

134.  Synthesis  of  Cyanogen 287 

135.  136.  Crystalline  Forms  of  Sulphur  293 
137,  138.  Preparation   of    Sulphurous 

Acid 294 

139.  Preparation  of  Sulphuric  Acid...  297 


140.  Formation    of    Crystals    of    the 

Leaden  Chamber 298 

141,  142.  Preparation  of  Hydrosulphu- 

ric  Acid 306,  307 

143,  144.  Preparation  of  Bisulphide  of 

Carbon 310 

145.  Preparation  of  Selenious  Acid 312 

146.  Preparation  of  Phosphoric  Acid..  319 

147.  Preparation  of  Phosphuretted  Hy- 

drogen   327 

148.  Preparation  of  Muriatic  Acid 329 

149.  160,  151.    Preparation    of   Chlo- 

rine   330,  331 

152.  Decomposition    of   Ammonia   by 

Chlorine 333 

153.  Preparation  of  Aqueous  Hydro- 

chloric Acid 835 

154.  Preparation  of  Hypochlorous  Acid  339 

155.  Preparation  of  Euchlorine 340 

156.  Combustion  of  Phosphorus  in  Per- 

oxide of  Chlorine 344 

157.  Preparation  of  Chloride  of  Boron  347 

158.  Preparation    of    Subchloride   of 

Sulphur 348 

159.  Preparation  of  Hydrobromic  Acid  351 

160.  Preparation  of  Iodine 353 

161.  Crystalline  form  of  Iodine 354 

162.  Preparation  of  Hydriodic  Acid ...  355 

163.  Preparation  of  Hydrofluoric  Acid  360 

164.  Preparation  of  Fluosilicic  Acid...  362 

165.  Preparation  of  Potassium 370 

166. -Receiver  for  Potassium 371 

167.  Crystalline  form  of  Ferrocyanide 

of  Potassium 375 

168.  Crystalline  form  of  Bicarbonate 

of  Potassa 378 

169.  Crystalline  form  of  Sulphate  of 

Potassa 378 

170.  Crystalline  form  of  Hydrated  Bi- 

sulphate  of  Potassa 378 

171.  Crystalline  form  of  Nitrate  of  Po- 

tassa   379 

172.  Crystalline  form  of  Carbonate  of 

Soda 384 

173.  Determination  of  the   Solubility 

of  Salts 385 

174,175.  Alkalimetry 386 

176.  Pipette 388 

177.  Burette 388 

178,179.  Apparatus  for  Freezing  Water  392 

180.  Reverberatory  Furnace 392 

181.  Soda  Furnace  393 

182.  Platinum  Loop  for  Blowpipe  Ex- 

periments   397 

183.  184.  Blowpipe  Flames 398 

185.  Burette 412 


LIST    OF    WOOD    C^TTS. 


XX111 


186.  Valuation  of  Bioxide  of  Manga- 

nese   438 

187.  Iron  Blast  Furnace 443 

188.  Iron  Puddling  Furnace 445 

189.  Muffles  for  the  Reduction  of  Zinc,  470 

190.  Silesian  Furnace  for  Zinc-ores 471 

191.  English         "  "       471 

192.  Reverberatory  Furnace  for  Roast- 

ing Copper  Pyrites 476 

193.  Tubes  for  Reduction-Test  of  Arse- 

nic   535 

194.  195.  Marsh's  Apparatus  for  Test- 

ing Arsenic 536 

196.  Bismuth  Furnace 548 

197,  198,  199.  Illyrian     Furnace    for 

Roasting  Cinnabar 573,  574 

200,  201.  Almaden  Furnace  for  Roast- 
ing Cinnabar 574,  575 

202.  Tubular   vessels    for  Condensing 

Mercury 575 

203.  Furnace  for  reducing  Mercury . ...  575 

204.  Amalgamation  of  Silver 592 

205.  Compression  of  Spongy  Platinum,  609 

206.  207,  208.    Joule's  Apparatus  for 

estimation    of    Mechanical 
Equivalent  of  Heat 653 

209.  Circular  Polarization 659 

210.  Diagram  of  Angle  of  Polarization,  659 
,211.  Nichol's  Prism 660 

212.  Polarization  by  Nichol's  Prism....  660 


213.  Diagram  of  Polarized  and  Unpo- 

larized  Light 661 

214.  Diagram  of  Polarized  Light 662 

215.  'Colours  of  Polarization 663 

216.  217.  Saccharimetry  by   Polariza- 

tion   664,  665 

218.  Compensator  for  Polarization 666 

219.  Tetartohedral  Crystal  of  Quartz...  668 

220.  Another    form    of    Tetartohedral 

Crystal  of  Quartz 668 

221.  Crystal  of  Racemate  of  Soda  and 

Ammonia 669 

222.  Another  form  of  Crystal  of  Race- 

mate  of  Soda  and  Ammonia,  669 

223.  Spectrum  produced  by  Sesquichlo- 

ride  of  Chromium 674 

224.  Spectrum  produced  by  Permanga- 

nate of' Potash 674 

225.  Apparatus    for    Measurement    of 

Chemical  Action  of  Light...  676 

226.  Galvanometer 679 

227.  Estimation  of  Magnetic  Deflection,  680 

228.  Wheatstone's  Rheostat 683 

229.  Diffusion  of  Liquids 740 

230.  Apparatus  for  determining  Diffu- 

sion Co-efficients 745 

231.  Osmometer 749 

232.  Fabre   and    Silbermann's   Calori- 

meter   752 

233.  Mercury-Calorimeter 752 


ELEMENTS   OF   CHEMISTRY. 


CHAPTER   I. 

HEAT, 

THE  objects  of  the  material  world  are  altered  in  their  properties  by  heat  in  a 
very  remarkable  manner.  The  conversion  of  ice  into  water,  and  of  water  into 
vapour,  by  the  application  of  heat,  affords  a  familiar  illustration  of  the  effects  of  this 
agent  in  changing  the  condition  of  bodies.  All  other  material  substances  are  equally 
under  its  influence ;  and  it  gives  rise  to  numerous  and  varied  phenomena,  demanding 
the  attention  of  the  chemical  inquirer. 

Heat  is  very  readily  communicated  from  one  body  to  another ;  so  that  when  hot 
and  cold  bodies  are  placed  near  each  other,  they  speedily  attain  the  same  temper- 
ature. The  obvious  transference  of  heat  in  such  circumstances  impresses  the  idea 
that  it  possesses  a  substantial  existence,  and  is  not  merely  a  quality  of  bodies,  like 
colour  or  weight ;  and  when  thus  considered  as  a  material  substance,  it  has  received 
the  name  caloric.  It  would  be  injudicious,  however,  to  enter  at  present  into  any 
speculation  on  the  nature  of  heat;  it  is  sufficient  to  remark  that  it  differs  from 
matter,  as  usually  conceived,  in  several  respects.  Our  knowledge  of  heat  is  limited 
to  the  different  effects  which  it  produces  upon  bodies,  and  the  mode  of  its  transmis- 
sion ;  and  these  subjects  may  be  considered  without  reference  to  any  theory  of  the 
nature  of  this  agent. 

The  subject  of  Heat  will  be  treated  of  under  the  following  heads :  — 

1.  Expansion,  the  most  general  effect  of  heat,  and  the  Thermometer. 

2.  Specific  heat. 

3.  The*  communication  of  heat  by  Conduction  and  Radiation. 

4.  Liquefaction,  as  an  effect  of  heat. 

5.  Vaporization,  or  the  gaseous  state,  as  an  effect  of  heat. 

6.  Speculative  notions  respecting  the  nature  of  heat. 

EXPANSION   AND   THE   THERMOMETER. 

All  bodies  in  nature,  solids,  liquids,  or  gases,  suffer  a  temporary  increase  of  dimen- 
sion when  heated,  and  contract  again  into  their  original  volume  on  cooling. 

1.  Expansion  of  solids.* — The  expansion  of  solid  bodies,  such  as  the  metals,  is 
by  no  means  considerable,  but  may  readily  be  made  sensible.  A  bar  of  iron  which 
fits  easily  when  cold  into  a  gauge,  will  be  found,  on  heating  it  to  redness,  to  have 
increased  sensibly  both  in  length  and  thickness.  The  expansion  and  contraction  of 
metals,  indeed,  and  the  immense  force  with  which  these  changes  take  place,  are 
matters  of  familiar  observation,  and  are  often  made  available  in  the  arts.  The  iron 
hoops  of  carriage  wheels,  for  instance,  are  applied  to  the  frame  while  they  are 
red  hot,  and  in  a  state  of  expansion,  and  being  then  suddenly  cooled  by  dashing 
water  upon  them,  they  contract,  and  bind  the  wood-work  of  the  wheel  with  great 
force.  The  expansion  of  solids,  however,  is  very  small,  and  requires  nice  measure- 
ment to  ascertain  its  amount.  The  expansion  in  length  only  has  generally  been 

»  [See  SitpplAnent,  p.  637.] 


34 


EXPANSION  OF   SOLIDS. 


determined,  but  it  must  always  be  remembered  that  the  body  expands  also  in  its  other 
dimensions  in  an  equal  proportion.  The  first  general  fact  observable  is,  that  the 
amount  of  dilatation  by  heat  is  different  in  different  bodies.  No  two  solids  expand 
alike.  The  metals  expand  most,  and  their  rates  of  expansion  are  best  known.  Rods 
of  the  undermentioned  substances,  on  being  heated  from  the  freezing  to  the  boiling 
point  of  water,  elongate  as  follows  :  — 


1     «    340 

Iron  Wire  

1     "       812 

Lead        

1     «    351 

1    "     1  000 

Tin  

1    «    516 

Glass  without  lead 

1     "    1142 

Silver  *  

1     «    524 

Platinum 

1     "    1167 

1    «    581 

Flint  Glass    ...          

.  .    1     "    1248 

Brass  t.  .  . 

.    1     "    584 

Black  Marble  fLuculliteV 

.    1     "    2833 

This  is  the  increase  which  these  bodies  sustain  in  length.  Their  increase  in 
general  bulk  is  about  three  times  greater.  Thus,  if  glass  elongates  1  part  in  1248 
from  the  freezing  to  the  boiling  point  of  water,  it  will  dilate  in  cubic  capacity  3  parts 
in  1248,  or  1  part  in  416.  The  expanded  bodies  return  to  their  original  dimensions 
on  cooling.  Wood  does  not  expand  much  in  length ;  hence  it  is  occasionally  used 
as  a  pendulum  rod.  For  the  same  reason  a  slip  of  marble,  of  the  variety  mentioned 
in  the  preceding  table,  was  employed  for  that  purpose,  in  constructing  the  clock  of 
the  Royal  Society  of  Edinburgh.  Glass  without  lead  expands  by  the  table  TT1T2 
part,  while  the  metal  platinum  expands  very  little  less,  yy'gy  Hence  the  possibility 
of  cementing  glass  and  platinum  together,  as  is  done  in  many  chemical  instruments. 
Other  metals  pushed  through  the  glass  when  it  is  red  hot  and  soft,  shrink  afterwards 
so  much  more  than  glass  on  cooling,  as  to  separate  from  it,  and  become  loose.  Zinc 
is  the  most  expansible  of  the  metals  j  it  expands  nearly  four  times  more  than  plati- 
num from  the  same  heat.  But  ice,  of  which  the  contraction  by  cold  has  been 
observed  for  30  or  40  degrees  under  the  freezing  point,  proves  to  be  more  dilatable 
even  than  the  metals,  the  rate  of  this  solid  being  in  the  proportion  of  ?jjth  part, 
while  that  of  zinc  is  ^gd  part  onlv.  (Brunner  (fils),  Ann.  de  Chim.  et  de  Phys., 
3  se>.  t.  14,  p.  377.) 

The  most  important  discovery,  in  a  theoretical  point  of  view,  that  has  been  made 
on  the  subject  of  the  dilatation  of  solids  by  heat,  is  the  observation  of  Professor  Mit- 
scherlich,  of  Berlin,  that  the  angles  of  some  crystals  are  affected  by  changes  of  tem- 
perature. This  proves  that  some  solids  in  the  crystalline  form  do  not  expand 
uniformly,  but  more  in  one  direction  than  in  another.  Indeed,  Mitscherlich  has 
shown  that  while  a  crystal  is  expanding  in  length  by  heat,  it  may  actually  be  con- 
tracting at  the  same  time  in  another  dimension.  An  angle  of  rhomboidal  calcareous 
spar  alters  eight  and  a  half  minutes  of  a  degree  between  the  freezing  and  boiling 
points  of  water.  But  this  unequal  expansion  does  not  occur  in  crystals  of  which  all 
the  sides  and  angles  are  alike,  as  the  cube,  the  regular  octohedron,  the  rhomboidal 
dodecahedron.  In  investigating  the  laws  of  expansion  among  solids,  it  is  advisable, 
therefore,  to  make  choice  of  crystallized  bodies.  For,  in  a  substance  not  regularly 
crystallized,  the  expansion  of  different  specimens  may  not  be  precisely  the  same,  as 
the  internal  structure  may  be  different.  Hence  the  expansions  of  the  same  sub- 
stance, as  given  by  different  experimenters,  do  not  always  exactly  correspond.  The 
same  glass  has  been  observed  to  dilate  more  when  in  the  form  of  a  solid  rod,  than 
in  that  of  a  tube ;  and  the  numerous  experiments  on  uncrystallized  bodies,  which  we 
possess,  have  afforded  no  ground  for  general  deductions. 

It  has  been  further  observed,  that  the  same  solid  is  more  expansible  at  high  than 
at  low  temperatures,  although  the  increase  in  the  rate  of  expansion  is  in  general  not 
considerable.  Thus,  if  we  mark  the  progress  of  the  dilatation  of  a  bar  of  iron  under 
a  graduated  heat,  we  find  that  the  increase  in  dimension  is  greater  for  one  degree  of 
heat  near  the  boiling  point  of  water,  than  for  one  degree  near  its  freezing  point. 
Solids  are  observed  to  expand  at  an  accelerated  rate,  in  particular,  when  heated  up 
to  near  their  fusing  points.  The  cohesion  or  attraction  which  subsists  between  the 


EXPANSION   OF   SOLIDS.  35 

particles  of  a  solid  is  supposed  to  resist  the  expansive  power  of  heat.  But  many 
solids  become  less  tenacious,  or  soften  before  melting,  which  may  account  for  their  in- 
creasing expansibility.  Platinum  is  the  most  uniform  in  its  expansions  of  the  metals. 

Such  changes  in  bulk,  from  variations  in  temperature,  take  place  with  irresistible 
force.  This  is  well  illustrated  in  an  experiment,  which  was  first  made  upon  a  gallery 
in  the  Museum  of  Arts  and  Manufactures  in  Paris,  in  order  to  preserve  it,  and  has 
been  successfully  repeated  in  many  other  buildings.  The  opposite  walls  of  the 
edifice  referred  to  were  bulging  outwards,  from  the  pressure  of  the  floors  and  roof, 
which  endangered  its  stability.  By  the  directions  of  an  ingenious  mechanic,  stout 
iron  rods  were  laid  across  the  building,  with  their  extremities  projecting  through  the 
opposite  walls  so  as  to  bind  them  together.  Half  the  number  of  the  rods  were  then 
strongly  heated  by  means  of  lamps,  and,  when  in  an  expanded  condition,  a  disc  on 
either  extremity  of  each  rod  was  screwed  firmly  up  against  the  external  surface  of 
the  wall.  On  afterwards  allowing  the  rods  to  cool,  they  contracted,  and  drew  the 
walls  to  which  they  were  attached  somewhat  nearer  together.  The  process  was 
several  times  repeated,  till  the  walls  were  restored  to  a  perpendicular  position. 

The  force  of  expansion  always  requires  to  be  attended  to  in  the  arts,  when  iron  is 
combined  in  any  structure  with  less  expansible  materials.  The  cope-stones  of  walls 
are  sometimes  held  together  with  clamps,  or  bars  of  iron  :  such  bars,  if  of  cast  iron, 
which  is  brittle,  often  break  on  the  first  frost,  from  a  tendency  to  contract  more  than 
the  stone  will  permit;  if  of  malleable  iron,  they  generally  crush  the  stone,  and 
loosen  themselves  in  their  sockets.  When  cast  iron  pipes  are  employed  to  conduct 
hot  air  or  steam  through  a  factory,  they  are  never  allowed  to  abut  against  a  wall  or 
an  obstacle  which  they  might  in  expanding  overturn.  Lead,  from  its  extreme 
softness,  is  permanently  expanded  when  repeatedly  heated  ;  a  waste  steam  pipe  of 
that  metal  being  elongated  several  inches  in  a  few  weeks. 

A  compound  bar,  made   by  riveting   or 

soldering  together  two  thin  plates  of  copper  FlG-  ** 

and  platinum,  affords  a  good  illustration  of 
unequal  expansion  by  heat.  The  copper 
plate,  being  much  more  expansible  than  pla- 
tinum, the  bar  is  bent  upon  the  application 
of  heat  to  it;  and  in  such  a  manner,  that 
the  copper  is  on  the  outside  of  the  curve. 
The  reverse  is  produced  when  the  bar  is  cooled. 
It  may  easily  be  conceived,  that  by  a  proper  ^ 
attention  to  the  expansions  of  the  metals  of 
which  it  is  composed,  a  bar  of  this  kind 

might  be  so  constructed,  that  although  it  was  heated  and  expanded,  its  extreme 
points  should  always  remain  at  the  same  distance  from  each  other,  the  lengthening 
being  compensated  for  by  the  bending.  The  balance-wheels  of  chronometers  are 
preserved  invariable  in  their  diameters,  at  all  temperatures,  by  a  contrivance  of  this 
kind.  It  has  also  been  applied  to  the  construction  of  a  thermometer  of  solid  mate- 
rials —  that  of  Breguet. 

When  hot  water  is  suddenly  poured  upon  a  thick  plate  of  glass,  the  upper  surface 
is  heated  and  expanded  before  the  heat  penetrates  to  the  lower  surface  of  the  plate. 
There  is  here  unequal  expansion,  as  in  the  slip  of  copper  and  platinum.  The  glass 
tends  to  bend,  with  the  hot  and  expanded  surface  on  the  outside  of  the  curve,  but 
is  broken  from  its  want  of  flexibility.  The  occurrence  of  such  fractures  is  best 
avoided  by  applying  heat  to  glass  vessels  in  a  gradual  manner,  so  as  to  occasion  no 
great  inequality  of  expansion ;  or  by  using  very  thin  vessels,  through  the  substance 
of  which  heat  is  rapidly  transmitted. 

This  effect  of  heat  on  glass  may  by  a  little  address  be  turned  to  advantage. 
Watch-glasses  are  cut  out  of  a  thin  globe  of  glass,  by  conducting  a  crack  in  a  proper 
direction,  by  means  of  an  iron  rod,  or  piece  of  tobacco  pipe,  heated  to  redness. 
Glass  vessels  damaged  in  the  laboratory  may  often  be  divided  in  the  same  manner 
and  still  made  available  for  useful  purposes. 


36  EXPANSION   OF   LIQUIDS. 

Both  cast  iron  and  glass  are  peculiarly  liable  to  accidents  from  unequal  expansion, 
when  in  the  state  of  flat  plates.  Plate  glass,  indeed,  can  never  be  heated  without 
risk  of  its  breaking.  The  flat  iron  plates  placed  across  chimneys  as  dampers,  are 
also  very  apt  to  split  when  they  become  hot,  and  much  inconvenience  has  often 
been  experienced  in  manufactories  from  this  cause.  A  slight  curvature  in  their  form 
has  been  found  to  protect  them  most  effectually. 

Expansion  of  liquids.* — In  liquids  the  expansive  force  of  heat  is  little  resisted 
by  cohesive  attraction,  and  is  much  more  considerable  than  in  solids.  This  fact  is 
strikingly  exhibited  by  filling  the  bulb  and  part  of  the  stem  of  a  common  thermo- 
meter tube  with  a  liquid,  and  applying  heat  to  it.  The  liquid  is  seen  immediately 
to  mount  in  the  tube. 

The  first  law,  in  the  case  of  liquids,  is  that  some  expand  much  more  considerably 
by  heat  than  others.  Thus,  on  being  heated  to  the  same  extent,  namely,  from  the 
freezing  to  the  boiling  point  of  water — 

Spirit  of  wine  expands i,  that  is,    9  measures  become  10 

Fixed  oils fr,      "       12  "  13 

Water ?/T7,    «       22  76  «  23-76 

Mercury 7i-3>     "      55'5  "  86  5 

Spirit  of  wine  is,  therefore,  six  times  more  expansible  by  heat  than  mercury  is. 
The  difference  in  the  heat  of  the  seasons  affects  sensibly  the  bulk  of  spirits.  In  the 
height  of  summer,  spirits  will  measure  5  per  cent,  more  than  in  the  depth  of  winter. 

The  new  liquids  produced  by  the  condensation  of  gases  appear  to  be  characterized 
.by  an  extraordinary  dilatability.  M.  Thilorier  has  observed,  that  fluid  carbonic  acid 
is  more  expansible  by  heat  than  air  itself;  heated  from  32°  to  86°,  twenty  volumes 
of  this  liquid  increase  to  twenty-nine,  which  is  a  dilatation  four  times  greater  than 
is  produced  in  air,  by  the  same  change  of  temperature.  (Annales  de  Chimie  et  de 
Physique,  t.  60,  p.  427.)  Mr.  Kemp  extended  this  observation  to  liquid  sulphurous 
acid  and  cyanogen,  which,  although  not  possessing  the  excessive  dilatability  of  liquid 
carbonic  acid,  are  still  greatly  more  expansible  than  ordinary  liquids.  Sir  D.  Brew- 
ster  had  several  years  before  discovered  certain  fluids  in  the  minute  cavities  of  topaz 
and  quartz,  which  seemed  to  bear  no  analogy  to  any  other  then  known  liquid  in 
their  extraordinary  dilatability.  They  do  not  appear  to  have  been  entirely  liquefied 
gases,  but  probably  were  so  in  part.  (Edinburgh  Phil.  Journ.  vol.  ix.  p.  94,  1824 ; 
vol.  xvi.  p.  11,  1845.) 

A  singular  correspondence  has  been  observed,  by  M.  Gay-Lussac,  ("Ann.  de  Chimie, 
t.  2,  p.  130,)  between  two  particular  liquids  —  alcohol  and  bisulphuret  of  carbon, 
in  the  amount  of  their  expansion  by  heat :  although  each  of  these  liquids  has  a 
peculiar  temperature  at  which  it  boils — 

Alcohol  at 173° 

Sulphuret  of  carbon  at 116° 

still  the  ratios  of  expansions  from  the  addition,  and  of  contraction  from  the  loss  of 
heat,  are  found  to  be  uniformly  the  same  in  these  two  liquids,  compared  at  the  same 
distance  from  their  respective  boiling  points.  A  similar  relation  has  lately  been 
observed  by  M.  Isidore  Pierre,  between  the  bromide  of  ethyl  and  bromide  of  methyl, 
and  between  the  iodide  of  ethyl  and  iodide  of  methyl,  which  does  not  appear  to  exist 
between  a  pair  of  isomeric  bodies,  which  were  also  compared, — namely,  the  formiate 
of  oxide  of  ethyl  and  the  acetate  of  oxide  of  methyl.  The  observations  made  with 
this  view  on  four  different  groups  of  liquids,  including  those  mentioned,  are  thus 
exhibited,  the  degrees  of  temperature  being  of  Fahrenheit's  scale  : '  — 

1  M.  Pierre  has  also  examined  the  dilatations  of  water,  oxide  of  ethyl  (ether),  and  chlo- 
ride of  ethyl.  The  results  he  has  already  published  are  the  most  exact  and  valuable  we 
possess  on  the  subject  of  the  dilatation  of  liquids ;  and  he  is  proceeding  with  his  experi- 
ments. Ann.  de  Chimie,  &c.,  3  s4rie,  t.  15,  p.  325.  1845. 

*  [See  Supplement,  p»  628.] 


EXPANSION   OF   LIQUIDS.  37 

CONTRACTION   OF   LIQUIDS   FROM   THE   BOILING   POINT   (PIERRE). 


NAMES   OF   THE   LIQUIDS. 

BOILING 
POINT. 

TEMPERATURES 

equidistant      from 
the    boiling    point 
for  each  group. 

between  the 
two    preced- 
ing tempera- 
tures. 

VOLUME 

at   boiling 
point. 

VOLUMES 

at  the  equi- 
distant tem- 
peratures. 

I.    GROUP. 

Sulphnret  of  carbon  .... 

118-22° 
172-94° 

—  22-72° 
32° 

140-94° 
140-94° 

1 
1 

0-913099 
0-914452 

151-34° 

—  104° 

140-94° 

1 

0-905819 

II.    GROUP. 

Bromide  of  ethyl    •  •    •  •• 

105-26° 

32° 

73-26° 

1 

0-944375 

Bromide  of  methyl  .    ... 

55-4° 

—  17-86° 

73-26° 

1 

0-944575 

III.    GROUP. 

Todicle  of  ethyl   

158° 

32° 

126° 

1 

0-918704 

110-84° 

—  15-16° 

126° 

1 

0-916643 

IV.    GROUP. 

Formiate  of  oxide  of  ethyl 

127-22° 

—  20-12° 

107-1° 

1 

0-910223 

Acetate  of  oxide  of  methyl 

139-10° 

—  15-8° 

107-1° 

1 

0-918750 

32° 

I  have  only  to  add  the  following  results  obtained  by  M.  Muncke,  of  St.  Peters- 
burgh:1— 

EXPANSION   OF   LIQUIDS,   VOLUME   AT   32°   FAHR.   BEING   1. 

Solution  of  ammonia  (sp.  gr.  0-9465)  ...  1-0198810  at  113°  (45°  Centig.) 

Hydrochloric  acid  (sp.  gr.  1-1978) 1-0253598  "  " 

Nitric  acid  (sp.  gr.  1-4405)  1-0479512  "     " 

1-1148853  at  212°  (100°  Centig.) 

Sulphuric  acid  (sp.  gr.  1-836) 1-0578495  at  212° 

»     1-1388577  at  446°  (230°  Centig.) 

Rectified  petroleum  (sp.  gr.  0-7813)  1-1060059  at  203°  (95°    Centig.) 

Almond  oil         1-0787005  at  212°  (100°  Centig.) 

The  second  law  is,  that  liquids  are  progressively  more  expansible  at  higher  than 
at  lower  temperatures.  This  is  less  the  case  with  mercury,  perhaps,  than  with  any 
other  liquid.  The  expansions  of  that  liquid  are,  indeed,  so  uniform,  as  to  render  it 
extremely  proper  for  the  construction  of  the  thermometer,  as  will  afterwards  appear. 
The  rate  of  expansion  of  mercury  was  determined  with  extraordinary  care  by  Du- 
long  and  Petit. 


From     0°  to  100°  Centigrade,  mercury  expands  1  measure  on  55 
"     100°    "  200°         "  "  "         1  " 

"    200°   "  300°  .      "  "  "         1          4< 


4 

53 


According  to  the  same  ex- 
perimenters, the  expansion  of 
mercury,  confined  in  glass 
tubes,  is  only  1  on  64-8.  The 
dilatation  of  the  glass  causes 
the  capacity  of  the  instrument 
to  be  enlarged,  so  that  the 
whole  expansion  of  the  mer- 
cury is  not  indicated.  The 
only  mode  in  which  the  error 
introduced  by  the  expansion 
of  the  enclosing  vessel  can  be 


FIG.  2. 


,2 


1  See  the  Handwb'rterbuch  der  Chemie  of  Liebig,  Poggendorff,  and  Wohler,  vol.  i.  p.  632 
article  Ausdehnung  (Dilatation). 


38  EXPANSION  OF  LIQUIDS. 


avoided,  in  ascertaining  the  expansion  of  liquids,  is  that  practised  by  Dulong  and 
Petit :  namely,  heating  the  liquid  in  one  limb  of  a  syphon  (see  fig.  2),  and  observing 
how  high  it  rises  above  the  level  of  the  same  liquid  in  the  other  limb,  kept  at  a 
constant  temperature.  The  columns  of  course  balance  each  other,  and  the  shorter 
column  of  dense  fluid  supports  a  longer  column  of  dilated  fluid.  All  other  inodea 
of  obtaining  the  absolute  expansions  of  liquids  are  fallacious. 

No  progress  has  yet  been  made  in  discovering  the  law  by  which  expansions  of 
liquids  are  regulated;  for  the  complicated  mathematical  formulae  of  Biot,  Dr.  Young, 
and  others,  are  mere  general  expressions  for  these  expansions,  which  proceed  upon 
no  ascertained  physical  principle.  Some  theory  must  be  formed  of  the  constitution 
of  liquids,  before  we  can  hope  to  account  for  their  expansions. 

Count  Rumford  ascertained  the  contraction  of  water  for  every  22 1  degrees,  in 
cooling  from  212°  to  32°.  The  results  are  as  follows  :  — 

2000  measures  of  water  contract  — 
In  cooling  22i  degrees,  or  from  212° 


°12°  to  189i0 

ures. 

189£  "107   

]6-2 

167   "  144^  .... 

13-8 

144  a  "  1°2 

11-5 

122   "   99£  

9-3  ;, 

99^  "   77   

7-1 

77   «  '  54£ 

•••-  3-9 

544  «   32 

.  0-2 

The  expansion  of  water  by  heat  is  subject  to  a  remarkable  peculiarity,  which 
occasions  it  to  be  extremely  irregular,  and  demands  special  notice.     This  liquid,  in 
a  certain  range  of  temperature,  becomes  an  exception  to  the  very  general  law  that 
bodies  expand  by  heat.     When  heat  is  applied  to  ice-cold  water,  or  water  at  the 
temperature  of  32°,  this  liquid,  instead  of  expanding,  contracts  by  every  addition 
of  heat,  till  its  temperature  rises  to  40°,  at  or  very  near  which 
FIG.  3.  temperature  water  is  as  dense  as  it  can  be.    And,  conversely, 

when  water  of  the  temperature  of  40°  is  exposed  to  cold,  it 
actually  expands  with  the  progress  of  the  refrigeration.  Water 
may,  with  caution,  be  cooled  20  or  25  degrees  below  its 
freezing  point,  in  the  fluid  form,  and  still  continue  to  expand. 
It  is  curious  that  this  liquid,  in  a  glass  bulb,  expands  'as  nearly 
as  possible  to  the  same  amount  on  each  side  of  40°,  when 
either  heated  or  cooled  the  same  number  of  degrees.  Hence, 
when  cooled  to  36°  it  rises  to  the  same  point  in  the  stem  as 
when  heated  to  44° ;  at  32°  it  stands  at  the  same  point  as  at 
48°;  at  20°,  at  the  same  point  as  at  60°,  temperatures  (fig. 
3).  The  expansion  of  water  by  cold,  under  40°,  is  certainly 
not  very  great,  being  little  more  than  1  part  in  10,000  at 
32° ;  hence  it  was  early  suspected  that  it  might  be  an  illusion, 
from  the  contraction  of  the  glass  bulb  (in  which  the  experi- 
ment was  always  made)  forcing  up  the  water  in  the  stem. 
But  all  grounds  of  objection  on  this  score  have  been  removed 
by  the  mode  in  which  the  experiment  has  subsequently  been 
conducted,  particularly  in  the  researches  of  the  late  Dr.  Hope, 
of  Edinburgh,  on  this  subject.  (Phil.  Trans,  vol.  v.  p.  379.) 
Dr.  Hope  carried  a  deep  glass  jar,  filled  with  water  of  the 
temperature  of  50°,  into  a  very  cold  room ;  and  having  im- 
^^^^^^  mersed  two  small  thermometers  in  the  water,  one  near  the 

— :^^^^*~^  surface,  and  the  other  at  the  bottom  of  the  jar,  watched  their 

indications  as  the  cooling  proceeded.  The  thermometer  above  indicated  a  tempera- 
ture higher  by  several  degrees  than  the  thermometer  below,  til]  the  temperature  fell 
to  40°,  that  is,  the  chilled  water  fell  as  usual  to  the  bottom  of  the  jar,  or  became 
denser  as  it  lost  heat,  as  illustrated  in  fig.  4.  At  40°  the  two  thermometers  were 


EXPANSION   OF   LIQUIDS. 


39 


FIG.  4. 

In  cooling 
above  40°. 


FIG.  5. 


FIG.  6. 

In  cooling 
below  40°. 


for  some  time  steady  (fig.  5),  but 
as  the  cooling  proceeded  beyond 
that  point,  the  instrument  in  the 
higher  situation  indicating  the 
lower  temperature,  (fig.  6);  or 
the  water  now  as  it  became  colder, 
became  lighter,  and  rose  to  the 
top.  A  better  demonstration  of 
the  fact  in  question  could  not  be 
devised. 

Great  pains  have  been  taken 
by  several  philosophers  to  deter- 
mine  the  exact  temperature  of  this  turning  point  at  which  water  possesses  its  maxi- 
mum density.  By  the  elaborate  experiments  of  both  Hallstrom  and  of  Muncke  and 
Stampfer,  as  calculated  by  Hallstrom,  this  point  is  39°-38,  or  4°-l  Centigrade. 
Rudberg  has  more  recently  obtained  4°-02  O,  and  Despretz  4°-00  C.,  or  89°-2 
Fahr.,  the  number  now  generally  taken.  Sir  C.  Blagden  and  Mr.  Gilpin  had  made 
it  39°.  Dr.  Hope  had  estimated  it  at  39£°. ! 

When  salt  is  dissolved  in  water,  the  temperature  of  maximum  density  becomes 
lower  and  lower,  in  proportion  to  the  quantity  of  salt  in  solution,  and  sinking  below 
the  freezing  point  of  the  liquid,  the  anomaly  disappears.  This  is  the  reason  why 
the  property  in  question  cannot  be  observed  in  sea  water. 

There  is  a  solid  body  which  presents  the  only  other  known  parallel  case  of  pro- 
gressive contraction  by  heat;  this  is  Rose's  fusible  metal,  which  is  an  alloy  of — 

2  parts  by  weight  of  Bismuth 
1  part     "          "       "   Lead 
1     «        "          <«       '•    Tin 

A  bar  of  this  metal  expands  progressively,  like  other  bodies,  till  it  attains  the  tem- 
perature of  111° ;  it  then  rapidly  contracts  by  the  continued  addition  of  heat,  and 
at  156°  attains  its  maximum  density,  occupying  less  space  than  it  does  at  the  freez- 
ing point  of  water.  It  afterwards  progressively  expands,  melting  at  201°.  It  may 
be  remarked,  however,  of  this  body,  that  it  is  a  chemical  compound,  of  a  kind  in 
which  a  change  of  constitution  is  very  likely  to  occur  from  a  change  in  temperature ; 
and  that  it  cannot,  therefore,  be  fairly  compared  with  water. 

The  dilatation  which  water  undergoes  below  39°  has  been  supposed  to  be  con- 
nected with  its  sudden  increase  in  volume  in  freezing,  for  ice  is  lighter  than  water, 
bulk  for  oulk,  in  the  proportion  of  92  to  100.  The  water,  it  is  said,  may  begin  to 
pass  partially  into  the  solid  form  at  39°,  although  the  change  is  not  complete  till 
the  temperature  sinks  to  32°.  But  such  an  assumption  is  altogether  gratuitous,  and 
improbable  in  the  extreme. 

The  extraordinary  irregularity  in  the  dilatation  of  water  by  heat  is  not  only  curious 
in  itself,  but  also  of  the  utmost  consequence  in  the  economy  of  nature.  When  the 
cold  sets  in,  the  surface  of  our  rivers  and  lakes  is  cooled  by  the  contact  of  the  cold 
air  and  other  causes.  The  superficial  water  so  cooled,  sinks  and  gives  place  to 
warmer  water  from  below,  which,  chilled  in  its  turn,  sinks  in  lik;e  manner.  The 
progress  of  cooling  in  the  lake  goes  on  with  considerable  rapidity,  so  long  as  the 
cold  water  descends  and  exposes  that  not  hitherto  cooled.  But  this  circulation, 
which  accelerates  the  cooling  of  a  mass  of  water  in  so  extraordinary  a  degree,  ceases 
entirely  when  the  whole  water  has  been  cooled  down  to  the  temperature  of  40°, 
which  is  still  eight  degrees  above  the  freezing  point.  Thereafter  the  chilled  surface 
water  expands  as  it  loses  its  heat,  and  remains  at  the  top,  from  its  lightness,  while 
the  cold  is  very  imperfectly  propagated  downwards.  The  surface  in  the  end  freezes, 
and  the  ice  may  thicken,  but  at  the  depth  of  a  few  feet  the  temperature  is  not  under 


1  For  tables  of  the  volume  of  water  at  different  temperatures,  see  Appendix  1. 


40  EXPANSION   OF   GASES. 

40°,  which  is  high  when  compared  with  that  frequently  experienced,  even  in  this 
climate,  during  winter. 

If  water  continued  to  become  heavier,  until  it  arrived  at  the  freezing  temperature, 
the  whole  of  it  would  be  cooled  to  that  point  before  ice  began  to  be  formed;  and  the 
consequence  would  be,  that  the  whole  body  of  water  would  rapidly  be  converted  into 
ice,  to  the  destruction  of  every  being  that  inhabits  it.  Our  warmest  summers  would 
make  but  little  impression  upon  such  masses  of  ice ;  and  the  cheerful  climate,  which 
we  at  present  enjoy,  would  be  less  comfortable  than  the  frozen  regions  of  the  pole. 
.Upon  such  delicate  and  beautiful  adjustments  do  the  order  and  harmony  of  the  uni- 
verse depend. 

Expansion  of  gases.  —  The  expansion  by  heat  in  the  different  forms  of  matter  is 
exceedingly  various. 

By  being  heated  from  32°  to  212°, 

1000  cubic  inches  of  iron  become  1004 
1000  «  water     «        1045 

1000  "  air          «       1366 

Gases  are,  therefore,  more  expansible  by  heat  than  matter  in  the  other  two  condi- 
tions of  liquid  and  solid.  The  reason  is,  that  the  particles  of  air  or  gas,  far  from 
being  under  the  influence  of  cohesive  attraction,  like  solids  or  liquids,  are  actuated 
by  a  powerful  repulsion  for  each  other.  The  addition  of  heat  mightily  enhances  this 
repulsive  tendency,  and  causes  great  dilatation. 

The  rate  of  the  expansion  of  air  and  gases  from  increase  of  temperature,  was  long 
involved  in  considerable  uncertainty.  This  arose  from  the  neglect  of  the  early 
experimenters  to  dry  the  air  or  gas  upon  which  they  operated.  The  presence  of  a 
little  water  by  rising  in  the  state  of  steam  into  the  gas,  on  the  application  of  heat, 
occasioned  great  and  irregular  expansions.  But  in  1801,  the  law  of  the  dilatation 
of  gases  was  discovered  by  M.  Glay-Lussac,  of  Paris,  and  by  our  countryman,  Dr. 
Dalton,  independently  of  each  other.  It  was  discovered  by  these  philosophers  that 
all  gases  experience  the  same  increase  in  volume  by  the  application  of  the  same 
degree  of  heat,  and  that  the  rate  of  expansion  continues  uniform  at  all  temperatures. 

Dr.  Dalton  confined  a  small  portion  of  dry  air  over  mercury  in  a  graduated  tube. 
He  marked  the  quantity  by  the  scale,  and  the  temperature  by  the  thermometer. 
He  then  placed  the  whole  in  circumstances  where  it  was  uniformly  heated  up  to  a 
certain  temperature,  and  observed  the  expansion.  Gay-Lussac's  apparatus  was  more 
complicated,  but  calculated  to  give  very  precise  results.  He  found  that  1000  volumes 
of  air,  on  being  heated  from  82°  to  212°,  become  1375,  which  agreed  very  closely 
with  Dalton's  result.  The  expansion  was  lately  corrected  by  Rudbcrg,  who  found 
that  1000  volumes  of  air  expand  to  1365. 

The  still  more  recent  and  exact  researches  of  Magnus  and  of  Regnault  give  as 
the  expansion  of  air  from  32°  to  212°,  Jfl-fof,  or  ±$  of  its  volume  at  32°.  The 
dilatation  for  every  degree  of  Fahrenheit  is  0-002036  (Regnault) ;  or  7 ^r.¥  part. 

It  follows,  consequently,  that  air  at  the  freezing  point  expands  ?£-,  part  of  its 
bulk  for  every  added  degree  of  heat  on  Fahrenheit's  scale  :  that  is  — 

491  cubic  inches  of  air  at  32°  become 

492  "  "          33° 

493  "  «          84°,  &c. 

increasing  one  cubic  inch  for  every  degree.     A  contraction  of  one  cubic  inch  occurs 
for  every  degree  below  32°. 

i  491  cubic  inches  of  air  at  32°  become 

490  "  "  31° 

489  "  "          30° 

488  "  "          29°,  &c. 

We  can  easily  deduce,  from  this  law,  the  expansion  which  a  certain  volume  of  gas 
at  a  given  temperature  will  undergo,  by  heating  it  up  to  any  particular  temperature; 


THE   THERMOMETER. 


41 


or  the  contraction  that  will  result  from  cooling.1  Air  of  the  temperature  of  freezing 
water,  has  its  volume  doubled  when  heated  491  degrees,  and  when  heated  982  de- 
grees, or  twice  as  intensely,  its  volume  is  tripled,  which  is  the  effect  of  a  low  red  heat. 
A  slight  deviation  from  exact  uniformity  in  the  expansion  of  different  gases  was 
established  by  the  rigorous  experiments  of  both  Magnus  (Ann.  de  Chim.  &c.  3  ser. 
t.  4,  p.  330;  et  t.  6,  p.  353)  and  Regnault  (ibid.  t.  4,  p.  5  ;  et  t.  6,  p.  370).  The 
more  easily  liquefied  gases,  which  exhibit  a  sensible  departure  from  the  law  of 
Mariotte,  are  more  expansible  by  heat  than  air,  as  will  appear  by  the  following 

table  :  — 

Expansion  upon  1  volume  from 
NAMES  OF  THE  GASES.  32°  to  212°. 

REGNAULT.  MAGNUS. 

Atmospheric  air  ..........................................  0-36650  ..................  0-366508 

Hydrogen  ..................................................  0-36678  ..................  0-365659 

Carbonic  acid  .............................................  0-36896  ..................  0-369087 

Sulphurous  acid  ..........................................  0-36696  ..................  9-385618 

Nitrogen  ...................................................  0-36682 

Nitrous  oxide  .............................................  0-36763 

Carbonic  oxide  ................  .  ..........................  0-36667 

Cyanogen  ..................................................  0-36821 

Hydrochloric  acid  .......................................  0-36812 

The  expansion  is  also  found  to  be  sensibly  greater  when  the  gas  is  in  a  compressed 
than  when  in  a  rare  state  ;  and  the  results  above  strictly  apply  only  to  the  gases 
ander  the  atmospheric  pressure. 

THE   THERMOMETER, 

An  instrument  for  indicating  variations  in  the  intensity  of  heat,  or  degrees  of  tem- 
perature, by  their  effect  in  expanding  some  body,  was  invented  more  than  two  cen- 
turies ago,  and  has  received  successive  improvements. 

The  expansions  of  solids  are  too  minute  to  be  easily  measured,  and  cannot,  there- 
fore, be  conveniently  applied  to  mark  degrees  of  heat.  Air  and  gases,  on  the  other 
hand,  are  so  much  dilated  by  a  slight  increase  of  heat,  that  they  are  not  calculated 
for  ordinary  purposes.  The  first  thermometer  constructed,  however,  that  of  Sanc- 
torio,  was  an  air  one.  A  glass  tube,  open  at  one  end,  with  a  bulb 
blown  upon  the  other  (fig.  7),  was  slightly  heated,  so  as  to  expel 
a  portion  of  the  air  from  it,  and  then  the  open  end  of  the  tube 
was  dipped  under  the  surface  of  a  coloured  fluid,  which  was  al- 
lowed  to  rise  into  the  tube,  as  the  air  cooled  and  contracted. 
When  heat,  the  heat  of  the  hand  for  instance,  is  applied  to  the 
bulb,  the  air  in  it  is  expanded,  and  depresses  the  column  of  co- 
loured fluid  in  the  tube.  A  useful  modification  of  the  air  ther- 
mometer, for  researches  of  great  delicacy,  was  contrived  by  Sir 
John  Leslie,  under  the  name  of  the  Differential  Thermometer. 
In  this  instrument  two  close  bulbs  are  connected  by  a  syphon 
containing  a  coloured  liquid  (fig.  8).  If  both  bulbs  be  equally 
heated,  the  air  in  each  is  equally  expanded,  and  the  liquid  be- 
tween them  remains  stationary.  But  if  the  upper  bulb  only  be 
heated,  then  the  air  in  that  bulb  is  expanded,  and  the  column 
of  liquid  depressed.  It  is,  therefore,  the  difference  of  tempera- 
ture between  the  two  bulbs  which  is  indicated. 

1  As  491  cubic  inches  of  air  at  32°  become  459  cubic  inches  at  0°,  air  may  be  stated  to 
expand  ¥j¥th  part  of  its  volume  at  the  zero  of  Fahrenheit  for  each  degree.  That  is,  459 
volumes  of  air  at  0°  become  at  50°,  459  +  50  volumes,  or  509  volumes  ;  at  60°,  459  +  60 
volumes,  or  519  volumes.  Hence  the  expansion  of  100  volumes  of  air  from  50°  to  60°  is 
obtained  by  the  proportion  — 

Meas."  at  50°.        Meas.  at  60°.        Meas.  at  50°.        Meas.  at  60°. 
509  :  519  ::  100          :          101-96 


FIG.  8. 


^-^ 
C     ) 


42  THE   THERMOMETER. 

But  liquids  fortunately  are  intermediate  in  their  expansions  between  solids  and 
gases,  and  when  contained  in  a  glass  vessel  of  a  proper  form,  the  changes  of  bulk 
which  they  undergo  can  be  indicated  to  any  degree  of  precision. 

A  hollow  glass  stem  or  tube  is  selected,  the  calibre  or  bore  of  which  may  be  of 
any  convenient  size,  but  must  be  uniform,  or  not  wider  at  one  place  than  another. 
Tubes  of  very  narrow  bore,  and  which  are  called  capillary,  the  bore  being  like  a 
hair  in  magnitude,  are  now  alone  employed.  Such  tubes  are  made  by  rapidly  draw- 
ing out  a  hollow  mass  of  glass  while  soft  and  ductile  under  the  influence  of  heat. 
The  central  cavity  still  continues,  becoming  the  bore  of  the  tube,  and  would  not 
cease  to  exist  although  the  tube  were  drawn  out  into  the  finest  thread.  From  the 
mode  in  which  capillary  tubes  are  made,  their  equality  of  bore,  and  suitableness  for 
thermometers,  cannot  always  be  depended  upon.  The  bore  is  frequently  conical,  or 
wider  at  one  end  than  at  the  other.  It  is  tested  by  drawing  up  into  the  tube  a  little 
mercury,  as  much  as  fills  a  few  lines  of  the  cavity.  The  little  column  is  then  moved 
progressively  along  the  tube,  and  its  length  accurately  measured,  at  every  stage,  by 
a  pair  of  compasses.  The  column  will  measure  the  same  in  every  part  of  the  tube, 
provided  the  bore  does  not  alter.  Not  more  than  one-sixth  part  of  the  tubes  made 
are  found  to  possess  this  requisite. 

Satisfied  with  the  regularity  of  the  bore,  the  thermometer-maker  softens  one 
extremity  of  the  tube,  and  blows  a  ball  upon  it.  This  is  not  done  by  the  mouth, 
which  would  moisten  the  interior,  by  introducing  watery  vapour,  but  by  means  of  an 
elastic  bag  of  caoutchouc,  which  is  fitted  to  the  open  end  of  the  tube.  He  then 
marks  off  the  length  which  the  thermometer  ought  to  have,  and  above  that  point 
expands  the  tube  into  a  second  bulb  a  little  larger  than  the  first.  It  has  the  form 

of  fig.  9.  After  cooling,  the  open  extremity 

FlG-  9-  of  the  tube  is  plunged  into  distilled  and 

well-boiled  mercury,  and  one  of  the  bulbs 
heated  so  as  to  expel  air  from  it.  During 
the  cooling,  the  mercury  is  drawn  up  and 
rises  into  the  ball  a.  It  is  made  to  pass 
from  thence  into  the  ball  b,  by  turning 
the  instrument,  so  that  b  is  undermost, 
and  then  expelling  the  air  from  that  bulb 
by  applying  heat  to  it,  after  which  the 
mercury  descends,  from  the  effect  of  cool- 
ing. The  ball  b,  being  entirely  filled  with  mercury,  and  a  portion  left  in  a,  the 
tube  is  supported  by  an  iron  wire,  as  represented  in  the  figure,  over  a  charcoal  fire, 
where  it  is  heated  throughout  its  whole  length,  so  as  to  boil  the  mercury,  the  vapour 
of  which  drives  out  all  the  air  and  humidity,  and  the  balls  contain  at  the  end  nothing 
but  the  metal  and  its  vapour.  The  open  end  of  the  tube,  which  must  not  be  too 
hot,  is  then  touched  with  sealing-wax,  which  is  drawn  into  the  tube  on  melting,  and 
solidifies  there  on  protecting  that  end  of  the  tube  from  the  heat.  That  being  done, 
the  thermometer  is  immediately  withdrawn  from  the  fire,  and  being  held  with  the 
end  sealed  with  wax  uppermost,  during  the  cooling  the  ball  b,  and  the  portion  of 
the  tube  below  the  ball  a,  are  filled  with  mercury.  After  cooling,  the  instrument  is 
inclined  a  little,  and  by  warming  the  lower  ball,  a  portion  of  mercury  is  expelled 
from  it,  so  that  the  mercury,  may  afterwards  stand  at  a  proper  height  in  the  tube 
when  the  instrument  is  cold.  The  tube  is  then  melted  with  care  by  the  blow-pipe 
flame  below  the  ball  a,  and  closed,  or  hermetically  sealed,  as  in  c.  The  thermometer 
is  in  this  way  properly  filled  with  mercury,  and  contains  no  air.  ^ 

We  have  now  an  instrument  in  which  we  can  nicely  measure  and  compare  any 
ehange  in  the  bulk  of  the  included  fluid  metal.  Having  previously  made  sure  of 
the  equality  of  the  bore,  it  is  evident  that  if  the  mercury  swells  up  and  rises  two, 
three,  four,  or  five  inches  in  the  tube,  it  has  expanded  twice,  thrice,  four,  or  five 
times  more  than  if  it  had  risen  only  one  inch  in  the  tube.  By  placing  a  graduated  scale 


THE    THERMOMETER.  43 

against  the  tube,  we  can  therefore  learn  the  quantity  of  expansion  by  simple  in- 
spection. 

In  order  to  have  a  fixed  point  on  the  scale,  from  which  to  begin  counting  the 
expansion  of  mercury  by  heat,  we  plunge  the  bulb  of  the  thermometer  into  melting 
ice,  and  put  "a  mark  on  the  stem  at  the  point  to  which  the  mercury  falls.  However 
frequently  we  do  so  with  the  same  instrument,  we  shall  find  that  the  mercury  always 
falls  to  the  same  point.  This  is,  therefore,  a  fixed  starting  point.  We  obtain  an- 
other fixed  point  by  plunging  the  thermometer  into  boiling  water.  With  certain 
precautions,  this  point  will  be  found  equally  fixed  on  every  repetition  of  the  experi- 
ment. The  most  important  of  these  precautions  is,  that  the  barometer  be  observed 
to  stand  at  80  inches,1  when  the  boiling  point  is  taken.  It  will  afterwards  be 
explained  that  the  boiling  point  of  water  varies  with  the  atmospheric  pressure  to 
which  it  is  subject  at  the  time. 

Thermometers  which  are  properly  closed,  and  contain  no  air,  can  be  inverted 
without  injury,  and  the  mercury  falls  into  the  tube,  producing  a  sound  as  water 
does  in  the  water-hammer.  When  the  instrument  contains  air,  the  thread  of  mer- 
cury is  apt  to  divide  on  inversion,  or  from  other  circumstances.  When  this  accident 
occurs,  it  is  best  remedied  by  attaching  a  string  to  the  upper  end  of  the  instrument, 
and  whirling  it  round  the  head.  The  detached  little  column  of  mercury  generally 
acquires  in  this  way  a  centrifugal  force,  which  enables  it  to  pass  the  air,  and  rejoin 
the  mercury  in  the  bulb. 

When  the  glass  of  the  bulb  is  thin,  it  is  proper  to  seal  the  tube  as  described,  and 
to  retain  it  for  a  few  weeks  before  marking  upon  it  the  fixed  points.  Thermometers, 
however  carefully  graduated  at  first,  are  found  in  a  short  time  to  stand  above  the 
mark  in  melting  ice,  unless  this  precaution  be  attended  to.  Old  instruments  often 
err  by  as  much  as  half  a  degree,  or  even  a  degree  and  a  half,  in  this  way.2  The 
effect  is  supposed  to  arise  from  the  pressure  of  the  atmosphere  upon  the  bulb, 
which,  when  not  truly  spherical,  seems  to  yield  slightly,  and  in  a  gradual  manner. 
The  chance  of  this  defect  may  be  avoided  by  giving  the  bulb  a  certain  thickness. 
Mr.  Crichton's  thermometers,  of  which  the  freezing  point  has  not  altered  in  forty 
years,  were  all  made  unusually  thick  in  the  glass.  But  this  thickness  has  the 
disadvantage  of  diminishing  the  sensibility  of  the  instrument  to  the  impression  of 
heat. 

We  have  in  this  way  the  expansion  marked  off  on  the  tube,  which  takes  place 
between  the  freezing  and  boiling  points  of  water.  On  the  thermometer  which  is 
used  in  this  country,  and  called  Fahrenheit's,  this  space  is  subdivided  into  180  equal 
parts,  which  are  called  degrees.  This  division  appears  empirical,  and  different  reasons 
are  given  why  it  was  originally  adopted.  But  as  Fahrenheit,  who  was  an  instru- 
ment-maker in  Amsterdam,  kept  his  process  for  graduating  thermometers  a  secret, 
we  can  only  form  conjectures  as  to  what  were  the  principles  that  guided  him. 

It  is  more  convenient  to  divide  the  space  between  the  freezing  and  boiling  of 
water  into  100  equal  parts,  which  was  done  in  the  instrument  of  Celsius,  a  Swedish 
philosopher.  This  division  was  adopted  at  a  later  period  in  France,  under  the 
designation  of  the  Centigrade  scale,  and  is  now  generally  used  over  the  continent. 
The  freezing  point  of  water  is  called  0,  or  zero,  and  the  boiling  point  100.  But  in 
our  scale,  the  point  is  arbitrarily  called  32°,  or  the  32d  degree ;  and  consequently 
the  boiling  point  is  32  added  to  180,  or  the  212th  degree.3 

1  More  exactly  29-92  inches,  that  is,  760  millimetres  ;  the  latter  number  being  universally 
assumed  on  the  continent  as  the  standard  height  of  the  barometer. 

2  Many  thermometers  cannot  be  heated  60  or  80  degrees,  without  a  sensible  displacement 
of  the  zero  point,  as  remarked  by  Regnault  (Ann.  de  Chimie,  &c.,  3  se>.,  t.  6,  p.  378),  and 
by  Is.  Pierre  (Ib.  8  ser.,  t.  5,  p.  427;  et  t.  15,  p.  332;,  who  indicate  the  extraordinary  pre- 
cautions requisite  in  the  construction  of  thermometers  for  accurate  research. 

3  A  simple  rule  may  be  given  for  converting  Centigrade  degrees  into  degrees  Fahrenheit. 
"CO  degrees  Centigrade  being  equal  to  180  degrees  Fahrenheit,  10  degrees  C.  =  18  degrees 


44 


THE    THERMOMETER. 


The  scale  can  easily  be  prolonged  to  any  extent,  above  or  below  these  points,  by 
marking  off  equal  lengths  of  the  tube  for  180  degrees,  either  above  or  below  the 
space  first  marked.  The  degrees  of  contraction  below  zero,  or  0°,  are  marked  by 
the  minus  sign  ( — ),  and  called  negative  degrees,  in  order  to  distinguish  them  from 
degrees  of  the  same  name  above  zero,  or  positive  degrees.  Thus,  47°  means  the 
47th  degree  above  zero,  — 47°,  the  47th  degree  under  zero. 

The  only  other  scale  in  use  is  that  of  Reaumur,  in  the  north  of  Germany.  The 
expansion  between  the  freezing  and  boiling  of  water  is  divided  into  80  parts  in  this 
thermometer.  The  relation  between  the  three  scales  is  illustrated  in  the  following 
diagram. 


FIQ.  10. 

Fahrenheit's 

scale. 


FIG.  11. 

Centigrade 

scale. 


FIG.  12. 

Reaumur's 

scale. 


The  zero  of  our  scale  is  32 
degrees  below  the  freezing 
point  of  water,  and  the  expan- 
sions of  mercury  are  available 
in  the  thermometer  from  — 39° 
to  600° ;  but  about  the  latter 
degree,  mercury  rises  in  the 
tube  in  the  state  of  vapour,  so 
as  to  derange  the  indications, 
and  at  about  660°  it  boils,  and 
can  no  longer  be  retained  in 
the  glass  vessel ;  while  at  the 
former  low  point  it  freezes  or 
becomes  solid.  For  degrees  of 
cold  below  the  freezing  point 
of  mercury,  we  must  be  guided 
by  the  contractions  of  alcohol 
or  spirits  of  wine,  a  liquid 
which  has  not  been  frozen  by 
any  degree  of  cold  we  are  capa- 
ble of  producing.  There  is  no 
reason,  however,  for  believing 
that  we  have  ever  descended  more  than  160  or  170  degrees  below  zero  of  Fahren- 
heit. 

The  zero  of  these  scales  has,  therefore,  no  relation  to  the  real,  zero  of  heat,  or 
point  at  which  bodies  have  lost  all  heat.  Of  this  point  we  know  nothing,  and  there 
is  no  reason  to  suppose  that  we  have  ever  approached  it.  The  scale  of  temperature 
may  be  compared  to  a  chain,  extended  both  upwards  and  downwards  beyond  our 
sight.  We  fix  upon  a  particular  link,  and  count  upwards  and  downwards  from  that 
link,  and  not  from  the  beginning  of  the  chain. 

The  means  of  producing  heat  are  much  more  at  our  command,  but  we  have  no 
measure  of  it,  of  easy  application  and  admitted  accuracy,  above  the  boiling  point 
of  mercury.  Recourse  has  been  had  to  the  expansion  of  solids  at  high  tempera- 
tures, and  various  pyrometers,  or  "measures  of  fire/'  have  been  proposed.  Professor 

F.,  or  5  degrees  C.  =  9  degrees  F. ;  multiply  the  Centigrade  degrees  by  9,  and  divide  by  6, 
and  add  32.     Thus  to  find  the  degree  F.  corresponding  with  50°  C. 

50 
9 

5)450 

90 
add  32 


Or  the  50°  C.  corresponds  with  the  122°  F. 
For  facility  of  reference  a  table  of  the  corresponding  degrees  is  given  in  Appendix  IL 


THE    THERMOMETER. 
FIG.  13. 


45 


Darnell's  pyrometer  is  a  valuable  instrument  of  this  kind,  of  which  the  indications 
result  from  the  difference  in  the  expansion  by  heat  of  an  iron  or  platinum  bar,  and 
a  tube  of  well-baked  black-lead  ware,  in  which  the  bar  is  contained.  The  metallic 
bar  a  is  shorter  than  the  tube,  and  a  short  plug  of  earthenware  b  is  placed  in  the 
mouth  of  the  tube  above  the  iron  bar,  and  so  secured  by  a  strap  of  platinum  foil 
and  a  little  wedge,  that  it  slides  with  difficulty  in  the  tube.  By  the  expansion  of 
the  metallic  bar,  the  plug  of  earthenware  is  pushed  outwards,  and  remains  in  its 
new  position  after  the  contraction  of  the  metallic  bar  on  cooling.  The  expansion 
of  the  iron  bar  thus  obtained,  is  measured  by  adapting  to  the  instrument  an  index, 
c,  which  traverses  a  circular  scale,  before  and  after  the  earthenware  plug  has  been 
moved  outwards  by  the  expansion  of  the  metallic  bar.  The  degrees  marked  on  the 
scale  are  in  each  instrument  compared  experimentally  with  those  of  the  mercurial 
scale,  and  the  ratio  marked  on  the  instrument,  so  that  its  degrees  are  convertible 
into  those  of  Fahrenheit,  (Philosophical  Transactions,  1830-31).  An  air  thermo- 
meter, of  which  the  bulb  and  tube  were  of  metal,  has  also  been  employed  to  explore 
high  temperatures.  In  the  old  pyrometer  of  Wedgwood,  the  degree  of  heat  was 
estimated  by  the  permanent  contraction  which  it  produced  upon  a  pellet  of  pipe- 
clay j  but  the  indications  of  this  instrument  are  fallacious,  and  it  has  long  gone  out 
of  use. 

The  applicability  of  the  mercurial  thermometer  to  measure  degrees  of  heat,  de- 
pends upon  two  important  circumstances,  which  involve  the  whole  theory  of  the 
instrument : — 

1st.  The  hollow  glass  ball,  with  its  fine  tube  of  uniform  bore,  is  a  nice  fluid 
measure.  The  ball  and  part  of  the  stem  being  filled  with  a  fluid,  the  slightest 
change  in  the  bulk  of  the  fluid,  which  may  arise  from  the  application  of  heat  or  of 
cold  to  it,  is  conspicuously  exhibited  by  the  rise  or  fall  of  the  fluid  column  in  the 
stem.  No  more  delicate  measure  of  the  bulk  of  an  included  fluid  could  be  de- 
vised. 

2d.  It  fortunately  happens  that  the  expansions  of  mercury,  which  can  thus  be 
measured  so  accurately,  are  proportional  to  the  quantities  of  heat  which  produce 
them.  But  the  mode  in  which  this  is  proved  requires  a  little  attention.  Suppose 
we  had  two  reservoirs,  one  containing  cold,  and  the  other  hot  water.  Plunge  a 
thermometric  bulb  containing  mercury  first  into  the  cold  water,  and  mark  at  what 
point  in  the  stem  the  mercury  stands.  Then  plunge  it  into  the  hot  water,  and 
mark  also  the  point  to  which  the  mercury  now  rises  in  the  stem.  We  can  obviously 


i6  THE    THERMOMETER. 

make  a  heat  which  will  be  half  way  exactly  between  the  hot  and  cold  water,  by 
taking  the  same  quantity  of  the  hot  and  cold  water,  and  mixing  them  together. 
Now,  does  this  half  heat  produce  a  half  expansion  in  mercury  ?  On  trial  we  find 
that  it  does.  In  the  mixture  of  equal  parts  of  the  hot  and  cold  water,  the  mercury 
stands  exactly  half  way  between  the  marks,  supposing  the  experiment  to  be  con- 
ducted with  the  proper  precautions.  This  proves  that  the  dilatations  of  mercury 
are  proportional  to  the  intensity  of  the  heat  which  produces  them.  In  the  mercu- 
rial thermometer,  therefore,  quantities  or  degrees  of  expansion  may  be  taken  to 
indicate  quantities  or  degrees  of  heat ;  and  that  is  the  principle  of  the  instrument. 

The  same  correspondence  exists  between  the  expansions  of  air  and  the  quantities 
of  heat  which  produce  them.  Indeed,  in  air,  the  correspondence  is  rigidly  exact, 
while  in  mercury  it  is  only  a  close  approximation.  Thus  Dulong  and  Petit  found 
that  the  boiling  point  of  mercury  was, 

As  measured  by  mercury  in  a  syphon 680° 

"         "         the  air  thermometer  (true  temp.) 662° 

"         "        mercury  in  glass  (Mr.  Crichton)  660° 

A  short  table  exhibiting  the  increasing  rate  of  the  expansions  of  mercury  has 
already  been  given,  but  glass  expands  in  a  ratio  increasing  quite  as  rapidly  as  this 
metal  j  so  that  the  greater  expansion  of  the  mercury  in  the  thermometer  at  high 
temperatures  is  fortunately  corrected  by  the  increasing  capacity  of  the  glass  bulb.1 

Fixed  oils  and  spirit  of  wine  do  not  deviate  far  from  uniformity  in  their  expan- 
sions, at  least  at  low  temperatures,  and  therefore  are  sometimes  used  as  thermometric 
liquids.  Spirit  of  wine  thermometers,  however,  are  often  found  to  vary  6  or  8  de- 
grees from  each  other  at  temperatures  so  low  as  — 30°  or — 40°. 

Thermometers  have  been  devised  which  indicate  the  highest  and  lowest  tempera- 
ture which  has  occurred  between  two  observations,  or  are  self-registering.     A  ther- 
mometer, which  was  invented  by 

FlG- 14«  Dr.  Rutherford,  is  of  this  kind. 

This  instrument  consists,  properly 
speaking,  of  two  thermometers, 
one,  a,  of  spirit  of  wine,  and  the 
other,  b,  of  mercury,  which  are 
placed  in  the  position  represented 
in  the  figure,  their  stems  being 
horizontal.  The  thermometer  b 
*  intended  to  indicate  the  maximum  temperature.  It  contains,  in  advance  of  the 
mercury,  a  short  piece  of  iron  wire,  which  the  mercury  carries  forward  with  it  in 
dilating,  and  which  remains  in  its  advanced  position,  marking  the  highest  tempera- 
ture that  has  occurred,  when  the  mercury  withdraws.  The  minimum  temperature 
is  indicated  by  the  spirit  of  wine  thermometer  a,  which  contains,  immersed  in  the 
spirit,  a  small  cylinder  of  ivory,  or  enamel,  which,  by  a  slight  inclination  of  the  instru- 
ment, falls  to  the  surface  of  the  liquid  without  being  able  to  pass  out  of  it.  When  the 
thermometer  sinks,  the  ivory  is  carried  back  in  the  spirit ;  but  when  the  temperature 
rises,  the  alcohol  only  advances,  leaving  the  ivory  where  it  was.  Its  extremity  most 
distant  from  the  bulb  then  indicates  the  lowest  temperature  to  which  the  thermo- 
meter had  been  exposed.  Before  another  observation  is  made,  the  ivory  must  be 
brought  again  to  the  surface  of  the  alcohol  by  a  slight  percussion  of  the  instru- 
ment. 

Another  self-registering  instrument,  known  in  London  as  Six's,  has  the  great 
advantage  over  the  preceding  instrument  of  being  much  less  liable  to  go  out  of 
order.  It  consists  of  one  thermometer  only  (fig.  15),  filled  with  colourless  spirit 
of  wine,  having  a  large  cylindrical  bulb.  The  stem  is  twice  bent,  and  contains  a 
column  of  mercury,  b,  in  the  lower  bend,  which  is  in  contact  with  the  alcohol,  and 

1  In  a  note  on  the  Comparison  of  the  Air  and  Mercurial  Thermometers ;  by  M.  Eegnault 
Annales  de  Chimie,  &c.  3  se>.  t.  6,  p.  470. 


THE    THEKMOMETEE. 


47 


advances  or  recedes  with  it.  On  either  side  of  this  mercury 
there  is  placed  a  little  iron  cylinder,  or  index,  c  and  c?,  which 
has  a  fine  hair  projecting  from  it,  so  as  to  press  against  the 
sides  of  the  tube,  and  cause  the  cylinder  to  move  with  a  little 
difficulty.  These  iron  cylinders,  which  have  flattened  ends 
covered  with  a  vitreous  matter,  are  brought  into  contact  with 
the  mercury  by  means  of  a  magnet,  and  are  pushed  along 
by  the  column  of  mercury,  when  the  latter  is  moved  by 
the  alcohol.  The  minimum  temperature  is  indicated  by  c, 
and  the  maximum  by  d.  The  tube  is  expanded  at  e,  and 
sealed  after  filling  that  space  partly  with  alcohol,  for  no 
other  purpose  than  to  facilitate  the  movement  of  the 
index;  d. 

Our  notions  of  the  range  of  temperature  acquire  all  their 
precision  from  the  use  of  the  thermometer.  Cold,  for  in- 
stance, is  allowed  a  substantial  existence,  as  well  as  heat,  in 
popular  language.  What  is  cold  ?  it  is  the  absence  of  heat,  as 
darkness  is  the  absence  of  light.  The  absence  of  heat,  how- 
ever, is  never  complete,  but  only  partial.  Water,  after  it  is 
frozen  into  ice,  cold  as  it  is  in  relation  to  our  bodies,  has  not 
lost  all  its  heat,  for  it  is  easy  to  cool  a  thermometer  far  below 
the  temperature  of  ice,  and  have  it  in  such  a  condition  as  that 
it  shall  acquire  heat,  and  be  expanded  by  contact  with  ice ; 
thus  proving  that  the  ice  contains  heat.  Spirits  of  wine  have 
not  beea  frozen  at  the  lowest  temperature  that  has  hitherto 
been  attained;  but  even  then  this  liquid  possesses  heat,  and 
there  is  no  doubt  that  if  a  sufficiently  large  portion  of  its 
heat  were  withdrawn,  it  would  freeze  like  other  bodies. 
The  following  are  interesting  circumstances  in  the  range  of 
temperature  — 


FIG.  15. 


—220°  Fair. 

—166° 

—150° 

—122° 

—105° 

—  71° 

—  91° 

—  56° 

—  70° 

—  58° 

—  47° 

—  39° 

—  30° 

—  7° 
+  7° 

20° 

32° 

50°-7 

81°-5 

98° 


151°-34 

172°-94 

212° 

442° 

594o 

662° 

980° 


Greatest  artificial  cold  measured.     (Natterer.) 

(Faraday.) 

Liquid  nitrous  oxide  freezes.  « 

Liquid  sulphuretted  hydrogen  freezes.     " 
Liquid  sulphurous  acid  freezes.  " 

Liquid  carbonic  acid  freezes.  " 

Greatest  artificial  cold  measured  by  Walker. 
Greatest   natural  cold    observed    by  a    "verified"    thermometer. 

(Sabine.) 

Greatest  natural  cold  observed  at  Fort  Reliance  by  Back.  Doubtful 
Estimated  temperature  of  planetary  space.     (Fourier.) 
Sulphuric  ether  freezes. 
Mercury  freezes. 

Liquid  cyanogen  freezes.     (Faraday.) 
A  mixture  of  equal  parts  of  alcohol  and  water  freezes. 
A  mixture  of  one  part  of  alcohol  and  three  parts  of  water  freezes. 
Strong  wine  freezes. 
Ice  melts. 

Mean  temperature  of  London. 
Mean  temperature  at  the  Equator. 
Heat  of  the  human  blood. 
Highest  natural  temperature  observed — of  a  hot  wind  in  Upper 

Egypt     (Burckhardt.) 
Wood-spirit  boils.     (Is.  Pierre.) 
Alcohol  boils.  " 

Water  boils. 
Tin  melts. 
Lead  melts. 
Mercury  boils. 
Red  heat.     (Daniell.) 


48  SPECIFIC  HEAT. 

1141°  Fahr.  Heat  of  a  common  fire.  (Daniell.) 

1869°         "  Brass  melts.  " 

2283°         "  Silver  melts.  " 

3479°         "  Cast  iron  melts.  " 


SPECIFIC    HEAT.* 

Equal  bulks  of  different  substances,  such  as  water  and  mercury,  require  the  addi- 
tion of  different  quantities  of  heat  to  produce  the  same  change  in  their  temperature. 
This  appears  evident  from  a  variety  of  circumstances.  If  two  similar  glass  bulbs, 
like  thermometers,  one  containing  mercury  and  the  other  water,  be  immersed  at  the 
same  time  in  a  hot  water-bath,  it  will  be  found  that  the  mercury  bulb  is  heated 
up  to  the  temperature  of  the  water-bath  in  half  the  time  that  the  water  bulb  requires; 
and  if  the  two  bulbs,  after  having  both  attained  the  temperature  of  the  water-bath, 
be  removed  from  it  and  exposed  to  the  air,  the  mercury  bulb  will  cool  twice  as 
rapidly  as  the  other.  These  effects  must  arise  from  the  mercury  absorbing  only 
half  the  quantity  of  heat  which  the  water  does  in  being  heated  up  to  the  same  degree 
in  the  water-bath,  and  from  having,  consequently,  only  half  the  quantity  of  heat  to 
lose  in  the  subsequent  cooling.  Again,  if  we  mix  equal  measures  of  water  at  70° 
and  130°,  the  temperature  of  the  whole  will  be  100° ;  or  the  hot  measure  of  water, 
in  losing  30°,  elevates  the  temperature  of  the  cold  measure  by  an  equal  amount. 
But  if  we  substitute  for  the  hot  water,  in  this  experiment,  an  equal  measure  of 
mercury  at  130°,  on  mixing  it  with  the  measure  of  water  at  70°,  the  temperature 
of  the  whole  will  not  be  100°,  but  more  nearly  90°.  Here  the  mercury  is  cooled 
from  130°  to  90°,  or  loses  40°  of  heat,  which  have  been  transferred  to  the  water, 
but  which  raise  the  temperature  of  the  latter  only  20°,  or  from  70°  to  90°.  To 
heat  the  measure  of  water  at  70°  to  100°,  we  must  mix  with  it  two,  or  a  little  more 
than  two,  equal  measures  of  mercury  at  130°,  although  one  measure  of  water  at 
130°  would  answer  the  purpose.  If,  therefore,  two  measures  of  mercury,  by  losing 
30°  of  temperature,  heat  only  one  measure  of  water  30°,  it  follows  that  hot  mercury 
possesses  only  half  the  heat  of  equally  hot  water ;  or  that  water  requires  double  the 
quantity  of  heat  that  is  required  by  mercury,  to  raise  it  a  certain  number  of  degrees. 
This  is  expressed  by  saying  that  water  has  twice  the  capacity  for  heat  that  mercury 
possesses.1 

It  is  more  convenient  to  express  the  capacities  of  different  bodies  for  heat,  with 
reference  to  equal  weights  than  equal  measures  of  the  bodies.  On  accurate  trial,  it 
is  found  that  a  pound  of  water  absorbs  thirty  times  more  heat  than  a  pound  of  mer- 
cury, in  being  heated  the  same  number  of  degrees :  the  capacity  of  water  for  heat  is, 
therefore,  thirty  times  greater  than  that  of  mercury.  The  capacities  of  these  two 
bodies  are  in  the  relation  of  1000  to  33;  and  it  is  convenient  to  express  the  capaci- 
ties for  heat  of  all  bodies,  in  relation  to  that  of  water,  as  1000.  Such  numbers  are 
the  specific  heats  of  bodies. 

There  are  two  methods  usually  followed  in  determining  capacity  for  heat.  The 
first,  which  was  that  practised  by  MM.  Dulong  and  Petit,  consists  in  allowing  dif- 
ferent substances  to  cool  the  same  number  of  degrees  in  circumstances  which  are 
exactly  similar;  to  inclose  them,  for  instance,  in  a  polished  silver  vessel,  containing 
the  bulb  of  a  thermometer  in  its  centre,  and  to  place  this  vessel  under  a  bell-jar  in 
which  a  vacuum  is  made.  The  time  which  the  different  substances  take  to  cool, 
enables  us  to  calculate  the  quantity  of  heat  which  they  give  out.  The  second,  or 
method  of  mixture,  consists  in  heating  up  the  metal  or  other  substance  to  212°,  and 
then  throwing  it  into  a  vessel  containing  a  considerable  weight  of  cold  water,  to 
which  a  quantity  of  heat  will  be  communicated,  and  a  rise  of  temperature  occasioned 
proportional  to  the  capacity  for  heat  of  the  substance.  The  following  table  contains 
results  of  M.  Regnault,  which  closely  coincide  with  the  prior  determinations  of  Du- 
long and  Petit :  — 

*  [See  Supplement,  p.  640.] 


SPECIFIC   HEAT.  49 

Substances.  Specific  heat  of 

equal  weights. 

Water 1000 

Ice1 613 

Oil  of  turpentine,  at  63-5°  Fahr 4262 

«  «  at  50°         "    414 

Wood  charcoal 2412 

Sulphur 203 

Glass 198 

Diamond 1472 

Iron 113-79 

Nickel 108-63 

Cobalt 106-96 

Zinc 95-55 

Copper 95-15 

Arsenic 81-40 

Silver 57-01 

Tin 56-23 

Iodine 54-12 

Antimony : 50-77 

Gold 32-44 

Platinum 32-43 

Mercury 33-32 

Lead 31-40 

Bismuth 30-84 

The  method  of  cooling  gives  results  so  exact,  as  to  allow  the  detection  of  an  in- 
crease of  capacity  with  the  temperature.  The  capacity  of  iron,  when  tried  between 
32°  and  212°,  as  was  the  case  with  all  the  bodies  in  the  table,  was  110;  but  115 
between  32°  and  392°,  and  126  between  32°  and  662°.  It  hence  follows,  that 
the  capacity  for  heat,  like  dilatation,  augments  in  proportion  as  the  temperature  is 
elevated.  Dulong  and  Petit  likewise  established  a  relation  between  the  capacity 
for  heat  of  metallic  bodies  and  the  proportion  by  weight  in  which  they  combine 
with  oxygen,  or  any  other  substance,  which  will  again  be  adverted  to. 

Of  all  liquid  or  solid  bodies,  water  has  much  the  greatest  capacity  for  heat. 
Hence  the  sea,  which  covers  so  large  a  proportion  of  the  globe,  is  a  great  magazine 
of  heat,  and  has  a  beneficial  influence  in  equalizing  atmospheric  temperature. 
Mercury  has  a  small  specific  heat,  so  that  it  is  quickly  heated  or  cooled,  another 
property  which  recommends  it  as  a  liquid  for  the  thermometer,  imparting,  as  it 
does,  great  sensibility  to  the  instrument. 

The  determination  of  the  specific  heat  of  gases  is  a  problem  involved  in  the 
greatest  practical  difficulties ;  so  that  notwithstanding  its  having  occupied  the  at- 
tention of  some  of  the  ablest  chemists,  our  knowledge  on  the  subject  is  still  of  the 
most  uncertain  nature.  It  has  been  concluded  by  Delarive  and  Marcet  (Annales 
de  Ch.  et  de  Ph.  t.  35,  p.  5 ;  t.  41,  p.  78 ;  and  t.  75,  p.  113),  and  by  Mr.  Hay- 
craft  (Edinburgh  Phil.  Journ.  vol.  x.  p.  351),  that  the  specific  heat  of  all  gases  is 
the  same  for  equal  volumes.  But  this  opinion  has  been  controverted  by  Dulong 
(Annales  de  Ch.  et  de  Ph.  t.  41,  p.  113),  by  Dr.  Apjohn  (Transactions  of  the 
Royal  Irish  Academy,  1837),  and  by  Suermann  (Ann.  de  Ch.  et  de  Ph.  t.  63,  p. 
315),  who  have  followed  Delaroche  and  Berard  in  this  inquiry  (Annales  de  Chimie, 
t.  75 ;  or  Annals  of  Philosophy,  vol.  ii.)  Their  method  was  to  transmit  known 
quantities  of  the  gases,  heated  to  212°  in  an  uniform  current,  through  a  serpentine 
tube,  surrounded  by  water,  the  temperature  of  which  was  observed,  by  a  delicate 
thermometer  at  the  beginning  and  end  of  the  process.  The  results  obtained  by 
the  different  experimenters  are  contained  in  the  following  table  :  — 

1  Ed.  Desains,  Annales  de  Chimie  et  de  Physique,  3me  se>.  t.  14,  p.  306  (1845).     By  an- 
other method,  the  number  465  was  obtained.     The  capacity  of  ice  is,  therefore,  sensibly 
one-half  that  of  water.     This  is  a  valuable  paper,  which  will  be  refei-red  to  with  advantage. 

2  Regnault,  ibid.  t.  ix.  pp.  339  and  324. 

4 


50 


SPECIFIC   HEAT. 

SPECIFIC    HEAT   OF    GASES. 


Name  of  the  gas. 

Capacity 
for  equal 
volumes. 
Air=l. 

Capacity  for  equal 
weights. 

Authority. 

Air  =  l. 

Water  =1. 

Air  

1-0000 

0-8080 
0-9765 
0-9954 

1-0000 

0-9033 
1-0000 
1-3979 
1-4590 
1-0000 
1-0000 
1-0005 
1-0480 
1-9600 
0-9925 
0-9960 
1-0000 
1-0340 
I  -0000 
1-0655 
1-1750 
1-1950 
1-2220 
1-2583 
1  -0000 
1  -0000 
1-0000 
1-0000 
1-0229 
1-1600 
1-1930 
1-3503 
1-7000 
1-0000 
1-0000 
1.0660 
1-5310 
1-5530 
1-5300 

1-0000 

0-7328 

0-8848 
0-9028 

0-9069 

12-3401 
14-4930 
20-3121 
21-2064 
0-4074 
1-0318 
1-0293 
1-0741 
3-1360 
1-0253 
1-0239 
1-0802 
1-0805 
0-6557 
0-6925 

0-7838 

0-8280 
0-4507 
0-8485 
0-7925 
0-6557 
0-7354 

0-7827 
0-8878 
0-9616 
1-6968 
0-5547 

l'-5763 

0-2669 
0-3046 
0-1956 
0-2361 
0-2750 

5 

Delaroche  and  Berard. 
Suermann. 
Apjohn. 
Delaroche  and  Berard. 
Suermann. 
Delarive  and  Marcet,   Hay- 
craft,  Dulong. 
Delaroche  and  Berard. 
D.  and  M.,  Haycraft,  Dulong. 
Suermann. 
"Apjohn. 
Delarive  and  Marcet. 
Delaroche  and  Berard. 
Suermann. 
Apjohn. 
Delaroche  and  Berard. 
Suermann. 
Apjohn. 
D.  and  M.,  Dulong. 
Delaroche  and  Berard. 
Haycraft. 
Suermann. 
Dulong. 
Apjohn. 
Delarive  and  Marcet. 
Delaroche  and  Berard. 
Delarive  and  Marcet. 
«                    « 
««                    « 
<«                    <« 
Suermann. 
Dulong. 
Apjohn. 
Delaroche  and  Berard. 
Delarive  and  Marcet. 
«                    t< 
«                    « 
Haycraft. 
Dulong. 
Delaroche  and  Berard. 
Delarive  and  Marcet. 

Oxygen  

3-2936 
6-1892 

Chlorine  

0-2754 
0-3138 

0-8470 
0-3123 

Nitrogen  

Steam  

Carbonic  oxide  

Carbonic  acid     . 

0-2884 
0-2i24 

Sulphurous  acid 

0-2210 

Sulphuretted  hydrog  . 
Hydrochloric  acid  
Nitrous  oxide 



Nitric  oxide  

0-2240 

0-2369 
0-4207 

Cyanogen    

Olefiant  gas  

It  will  be  observed,  that  the  capacity  for  heat  of  steam,  as  well  as  of  ice,  is  less 
than  that  of  an  equal. weight  of  water.  Hence  the  specific  heat  of  a  body  may 
change  with  its  physical  state.  Delaroche  and  Berard  likewise  observed  that  the 
capacity  of  a  gas  is  increased  by  its  rarefaction.  When  the  volume  of  a  gas  is 
doubled,  by  withdrawing  half  the  pressure  upon  it,  its  specific  heat  is  not  quite  so 
much  as  doubled.  This  is  the  reason  why  a  gas  becomes  cold  in  expanding.  In 
the  expanded  state  it  requires  more  heat  to  sustain  it  at  its  former  temperature, 
from  the  augmentation  which  has  occurred  in  its  capacity.  Air  expanded  into 
double  its  volume  is  cooled  40  or  50  degrees;  and  it  has  its  temperature  raised  to 
that  extent  by  compression  into  half  its  volume ;  suddenly  condensed  to  one-fifth 
of  its  volume  by  a  piston  in  a  small  cylinder,  so  much  heat  is  evolved  as  to  causo 
the  ignition  of  a  readily  inflammable  substance,  such  as  tinder. 


CONDUCTION   OF   HEAT. 


51 


COMMUNICATION    OF    HEAT   BY   CONDUCTION    AND    RADIATION. 

1.  Conduction* — When  one  extremity  of  a  bar  of  iron  is  plunged  into  a  fire, 
the  heat  passes  through  the  bar  in  a  gradual  manner,  being  communicated  from 
particle  to  particle,  and  after  passing  through  the  whole  length  of  the  bar,  may 
arrive  at  the  other  extremity.  Heat,  when  conveyed  in  this  way,  is  said  to  be 
conducted. 

In  solid  substances,  the  phenomenon  of  the  conduction  of  heat  is  so  simple  and 
familiar,  that  little  need  be  said  on  the  subject.  Different  solid  substances  vary 
exceedingly  from  each  other  in  their  power  to  conduct  heat.  Dense  or  heavy  sub- 
stances are  generally  good  conductors,  while  light  and  porous  bodies  conduct  heat 
imperfectly.  Hence  the  universal  use  of  substances  of  the  latter  class  for  the 
purposes  of  clothing.  Count  Rumford  observed,  that  the  finer  the  fabric  of  woollen 
cloth  is,  the  more  imperfectly  does  it  conduct  (Phil.  Trans.  1792).  The  down  of 
the  eider-duck  appears  to  be.  unrivalled  in  this  respect.  Bad  conductors  are  also 
the  most  suitable  for  keeping  bodies  cool,  protecting  them  from  the  access  of  heat. 
Hence  to  preserve  ice  in  summer,  we  wrap  it  in  flannel.  Among  good  conductors 
of  heat,  the  metals  are  the  best.  The  relative  conducting  power  of  several  bodies 
is  expressed  by  the  numbers  in  the  following  table,  from  the  experiments  of 
Despretz  (Ann.  de.  Ch.  et  Ph.  t.  xxxvi.  p.  422)  :  — 


Gold 1000 

Silver 973 

Copper 898 

Iron 374-3 

Zinc 363 


Tin 303-9 

Lead 179-6 

Marble 23-6 

Porcelain 14-2 

Clay 11-4 


Glass  is  an  imperfect  conductor,  for  we  can  fuse  the  point  of  a  glass  rod  in  a 
lamp,  holding  it  within  an  inch  of  the  extremity.  On  the  contrary,  we  find  it  dif- 
ficult to  heat  any  part  of  a  thick  metallic  wire  to  redness  in  a  lamp,  owing  to  the 
rapidity  with  which  the  heat  is  carried  away  by  the  contiguous  parts. 

The  following  table  of  the  conducting  power  of  various  materials  used  in  the 
construction  of  houses,  as  observed  by  Mr.  Hutchinson,  is  of  considerable  utility 
for  practical  purposes.  The  substances  are  arranged  in  the  order  in  which  they 
resist  most  the  passage  of  heat ;  the  warmest  substances,  which  are  most  valuable 
in  construction,  being  placed  first.1 


Name  of  Substance. 

Conducting 
power  referred 
to  that  of  slate 
=  100.' 

Name  of  Substance. 

Conducting 
power  referred 
to  that  of  slate 
-100. 

Plaster  and  Sand  

18-70 
19-01 
20-26      • 
20-88 
22-44 
25-55 
27-61 
33-66 
45-19 
56-38 
58-27 
60-14 

Bath  Stone 

61-08 
61-70 
71-36 
72-92 
75-10 
75-41 
76-35 
95-36 
100-00 
110-94 
521-34 

Keene's  Cement  

Fire  Brick 

Plaster  of  Paris  

Painswick  Stone  (H.  P.).. 
Malm  Brick 

Roman  Cement  

Beech  Wood  

Portland  Stone 

Lath  and  Plaster  

Lunelle  Marble 

Fir  Wood  

Bolsover  Stone  (H.  P.)... 
Norfal  Stone  (H.  P.)  

Slate 

Oak  Wood  

Asphalt  

Chalk  (soft)  

Napoleon  Marble  ,. 

Lead  

Stock  Brick  

'New  Experiments  on  Building  Materials,  by  J.  Hutchinson:  Taylor  and  Walton.  The 
three  substances  marked  H.  P.  are  the  building  stones  employed  in  the  construction  of  *he 
New  Houses  of  Parliament. 

*  [Sec  Supplement,  p.  649.] 


52 


CONDUCTION   OF   HEAT. 


Fio.  17. 


Certain  vibrations  were  observed  by  Mr.  Trevelyan  to  take  place  between  metallic 
masses  having  different  temperatures,  occasioning  particular  sounds,  which  appear 
to  be  connected  with  the  conducting  power  of  the  metal  (Phil.  Mag.  3d  Series,  vol. 
iii.  321).  Thus,  if  a  heated  curved  bar  of  brass  £,  be  laid 
upon  a  cold  support  of  lead  Z,  of  which  the  surface  is  flat,  as 
represented  in  the  figure,  the  brass  bar,  while  communicating 
its  heat  to  the  lead,  is  thrown  into  a  state  of  vibration,  accom- 
panied with  a  rocking  motion  and  the  production  of  a  musical 
note,  like  that  of  the  glass  harmonicon.  The  rocking  motion 
of  the  brass  bar,  accidentally  commenced,  appears  to  be  con- 
tinued from  a  repulsion  which  exists  between  heated  surfaces, 
enhanced  in  this  case  by  the  low  conducting  power  of  the  lead, 
which  allows  its  surface  to  be  strongly  heated  by  the  brass.  Professor  Forbes  finds 
that  the  most  intense  vibrations  are  produced  between  the  best  conductors  and  the 
worst  conductors  of  heat,  the  latter  being  the  cold  bodies  (Edinburgh  Phil.  Trans, 
vol.  xii.) 

Our  ordinary  conceptions  of  the  actual  temperature  of  different  bodies  are  much 
affected  by  their  conducting  power.  If  we  apply  the  hand,  at  the  same  time,  to  a 
good  and  to  a  bad  conductor,  such  as  a  metal  and  a  piece  of  wood,  which  are  exactly 
of  the  same  temperature  by  the  thermometer,  the  good  conductor  will  feel  colder 
or  hotter  than  the  other,  from  the  greater  rapidity  with  which  it  conducts  away  heat 
from,  or  communicates  heat,  to  our  body,  according  as  the  temperature  of  the  metal 
and  wood  happens  to  be  above  or  below  that  of  the  hand 
applied  to  them. 

The  diffusion  of  heat  through  liquids  and  gases  is 
effected,  in  a  great  measure,  by  the  motion  of  their  par- 
ticles among  each  other.  When  heat  is  applied  to  the 
lower  part  of  a  mass  of  liquid,  the  heated  portions  become 
lighter  than  the  rest,  and  ascend  rapidly,  conveying  or  car- 
rying the  heat  through  the  mass  of  the  fluid.  In  a  glass 
flask,  for  instance,  containing  water,  with  which  a  small 
quantity  of  any  light  insoluble  powder  has  been  mixed,  a 
circulation  of  the  fluid  may  be  observed  upon  the  application 
of  the  flame  of  a  lamp  to  the  bottom  of  the  vessel,  the 
heated  liquid  rising  in  the  centre  of  the  vessel,  and  after- 
wards descending  near  its  sides,  as  represented  in  the  an- 
nexed figure.  But  when  heat  is  applied  to  the  surface  of 
a  liquid,  this  circulation  does  not 
occur,  and  the  heat  is  propagated 
very  imperfectly  downwards.  It 
has  even  been  doubted  whether 
liquids  conduct  heat  downwards  at 
all,  or,  indeed,  in  any  other  way 
than  by  conveying  it  as  above 
described.  It  can  be  proved, 

however,  that  heat  passes  downwards  in  fluid  mercury,  and 
hence  it  is  probable  that  all  liquids  possess  a  slight  conduct- 
ing power  similar  to  that  of  solids. 

Let  the  endless  tube  represented  in  the  accompanying' 
figure  be  supposed  to  be  entirely  filled  with  water,  and 
the  heat  of  a  fire  be  applied  to  the  lower  portion  of  it  at 
<i,  which  is  twisted  into  a  spiral  form,  the  water  will  im- 
mediately be  set  in  motion,  and  made  to  circulate  through 
the  tubo,  from  the  expansion  and  ascent  of  the  portion  in 
a,  and  the  whole  of  the  water  in  the  tube  will  be  brought 
in  succession  to  the  source  of  heat.  The  tube  may  be  led 


HADIATION    OF    HEAT. 


53 


into  an  apartment  above  d,  and  being  twisted  into  another  spiral  at  b,  a  quantity  of 
the  heat  of  the  circulating  water  will  be  discharged  in  proportion  to  the  extent  of 
surface  of  tube  exposed.  Water  of  a  temperature  considerably  above  212°  is  made 
to  circulate  in  this  manner  through  a  very  strong  drawn-iron  tube  of  about  one  inch 
in  diameter,  for  the  purpose  of  heating  houses  and  public  buildings.  A  slight 
waste  of  the  water  is  found  to  occur,  so  that  it  is  necessary  to  introduce  a  small 
quantity  every  few  weeks  by  an  opening  and  stopcock  c,  in  the  upper  part  of  the 
tube.  Tubes  of  larger  calibre,  with  water  circulating  below  the  boiling  point,  are 
likewise  much  used  for  warming  large  buildings. 

Air  and  gases  are  very  imperfect  conductors.  Heat  appears  to  be  propagated 
through  them  almost  entirely  by  conveyance,  tne  heated  portions  of  air  becoming 
lighter,  and  diffusing  the  heat  through  the  mass  in  their  ascent,  as  in  liquids. 
Hence,  in  heating  an  apartment  by  hot  air,  the  hot  air  should  always  be  introduced 
at  the  floor  or  lowest  part.  The  advantage  of  double  windows  for  warmth  depends 
in  a  great  measure  on  the  sheet  of  air  confined  between  them,  through  which  heat 
is  very  slowly  transmitted.  In  the  fur  of  animals,  and  in  clothing,  a  quantity  of 
air  is  detained  among  the  loose  fibres,  which  materially  enhances  their  non-coriduct- 
ing  property.  In  dry  air,  the  human  body  can  resist  a  temperature  of  250°  without 
inconvenience,  provided  it  is  not  brought  into  contact  with  good  conductors  at  the 
same  time. 

Radiation  of  Heat.  —  Heat  is  also  emitted  from  the  surface  of  bodies  in  the  form 
of  rays,  which  pass  through  a  vacuum,  air,  and  certain  other  transparent  media, 
with  the  velocity  of  light.  It  is  not  necessary  that  a  body  be  heated  to  a  visible 
redness  to  enable  it  to  discharge  heat  in  this  manner.  Rays  of  heat,  unaccompanied 
by  light,  continue  to  issue  from  a  hot  body  through  the  whole  process  of  its  cooling, 
till  it  sinks  to  the  actual  temperature  of  the  air  or  surrounding  medium.  The 
circumstance  that  bodies  suspended  in  a  perfect  vacuum  cool  rapidly  and  completely, 
without  the  intervention  of  conduction,  places  the  fact  of  the  dissipation  of  heat  by 
radiation,  at  low  temperatures,  beyond  a  doubt. 

The  most  valuable  observations  which  we  possess  on  this  subject,  wore  published 
by  Sir  John  Leslie,  in  his  Essay  on  Heat,  in  1804.  Leslie  proved  that  the  rate  of 
cooling  of  a  hot  body  is  more  influenced  by  the  state  of  its  surface  than  by  the 
nature  of  its  substance.  He  filled  a  bright  tin  globe  with  hot  water,  and  observed 
its  rate  of  cooling  in  a  room  of  which  the  air  was  undisturbed.  A  thermometer 
placed  in  the  water  cooled  half  way  to  the  temperature  of  the  apartment  in  156 
minutes.  The  experiment  was  repeated,  after  covering  the  globe  with  a  thin  coating 
of  lamp-black.  The  whole  now  cooled  to  the  same  extent  as  in  the  first  experiment, 
in  81  minutes  j  the  rapidity  of  cooling  being  nearly  doubled  merely  by  this  change 
of  surface. 

An  experiment  of  Count  Rum  ford  is  even  more  singular.  Water,  of  the  same 
temperature,  was  allowed  to  cool  in  two  similar  brass  cylinders,  one  of  which  was 
covered  by  a  tight  investiture  of  linen,  and  the  other  left  naked.  The  covered 
vessel  cooled  10°  in  36 \  minutes,  while  the  naked  vessel  required  55  minutes ;  or 
the  covering,  of  linen,  like  the  coating  of  lamp-black,  greatly  expedited  the  cooling, 
instead  of  retarding  the  escape  of  heat,  as  might  be  expected.  The  cooling  was 
accelerated  in  the  same  manner, 
when  the  cylinder  was  coated 
with  black  or  white  paint,  or 
smoked  by  a  candle. 

In  determining  the  radiating 
power  of  different  surfaces, 
Leslie  generally  made  use  of 
square  tin  canisters,  of  which 
the  surfaces  were  variously 
coated,  and  which  he  filled  with 
hot  water.  Instead  of  watching 


54 


RADIATION    OF    HEAT. 


the  rate  of  cooling,  as  in  the  experiments  already  mentioned,  he  presented  the  side 
of  a  canister,  having  its  surface  in  any  particular  condition,  to  a  concave  metallic 
mirror,  which  concentrated  the  heat  falling  upon  it  into  a  focus,  where  the  bulb  of 
an  air  thermometer  was  placed  to  receive  it,  as  represented  in  figure  19.  The 
differential  thermometer  answered  admirably  for  this  purpose,  as  from  its  con- 
struction it  is  unaffected  by  the  temperature  of  the  room,  while  the  slightest  change 
in  the  temperature  of  the  focal  spot  is  immediately  indicated  by  it. 

Two  metallic  mirrors  were 

occasionally  used  in  conducting  Fl°- 

these  experiments.  The  mir- 
rors being  arranged  so  as  to 
face  each  other  (fig.  20),  with 
their  principal  axes  in  the  same 
line;  when  a  lighted  lamp  or 
hot  canister  is  placed  in  the 
focus  of  one  mirror,  the  inci- 
dent rays  are  reflected  by  that 
mirror  against  the  other,  and 
collected  in  its  focus. 

The  following  table  exhibits  the  relative  radiating  power  of  various  substances 
with  which  the  surface  of  the  canister  was  coated,  as  indicated  by  the  effect  upon 
the  differential  thermometer : — 


Lamp-black   100 

Water  by  estimate  100+ 

Writing-paper  98 

Sealing-wax  95 

Crown  glass  90 


Plumbago 75 

Tarnished  lead  45 

Clean  lead  19 

Iron,  polished   15 

Tin  plate,  gold,  silver,  copper  12 


It  thus  appears  that  lamp-black  radiates  five  times  more  of  the  heat  of  boiling 
water  than  clean  lead,  and  eight  times  more  than  bright  tin.  The  metals  have  tht 
lowest  radiating  power,  which  arises  from  their  brightness  and  smoothness.  If 
allowed  to  tarnish,  their  radiating  power  is  greatly  increased.  Thus  the  radiating 
power  of  lead  with  its  surface  tarnished  is  45,  and  with  its  surface  bright,  only  19 ; 
but  glass  and  porcelain  radiate  most  powerfully,  although  their  surface  is  smooth. 
When  the  actual  radiating  surface  is  metallic,  it  is  not  affected  in  a  sensible  manner 
by  the  substance  under  it.  Thus,  glass  covered  with  gold-leaf  possesses  the  radiating 
power  of  a  bright  metal. 

It  is  placed  beyond  doubt,  by  the  recent  experiments  of  Prof.  A.  D.  Bache,  that 
the  radiating  power  of  any  surface  is  not  affected  by  its  colour,  at  least  in  an  appre- 
ciable degree.  Hence,  no  particular  colour  of  clothes  can  be  recommended  for 
superior  warmth  in  winter.  But  the  absorbent  powers  of  bodies  for  the  heat  of  the 
sun  depend  entirely  upon  their  colour.  (Journ.  Franklin  Inst.,  May  and  Novem- 
ber, 1835.) 

The  faculty  which  different  surfaces  possess  of  absorbing  or  of  reflecting  heat 
radiated  against  them,  is  connected  with  their  own  radiating  power.  Those  surfaces 
which  radiate  heat  freely,  such  as  lamp-black,  glass,  &c.,  also  absorb  a  large  propor- 
tion of  the  heat  falling  upon  them,  and  reflect  little  of  it;  while  surfaces  which 
have  a  feeble  radiating  and  absorbing  faculty,  such  as  the  bright  metals,  reflect  a 
large  proportion,  as  they  absorb  little,  and  form  the  most  powerful  reflectors.  So 
that  the  good  absorbents  are  found  at  the  top,  and  the  good  reflectors  at  the  bottom 
of  the  preceding  table.  The  efficiency  of  a  reflector  depending  upon  its  low  absorb- 
ing power,  reflectors  of  glass  are  totally  useless  in  conducting  experiments  upon 
radiant  heat  Metallic  reflectors  remain  cold,  although  they  collect  much  he*  t  in 
their  foci. 

These  laws  of  the  radiation  of  heat  admit  of  some  practical  applications.  If  we 
wish  to  retard,  as  much  as  possible,  the  cooling  of  a  hot  fluid  or  other  substance,  in 
what  sort  of  vessel  should  we  inclose  it  ?  In  a  metallic  vessel,  of  which  the  surface 


RADIATION    OF    HEAT. 


55 


is  not  dull  and  sooty,  but  clean  and  highly  polished ;  for  it  has  been  observed,  that 
hot  water  cools  twice  as  fast  in  a  tin  globe  of  which  the  surface  is  covered  with  a 
thin  coating  of  lamp-black,  as  in  the  same  globe  when  the  surface  is  bright  and 
clean.  Hence  the  advantage  of  bright  metallic  covers  at  table,  and  the  superiority 
of  metallic  tea-pots  over  those  of  porcelain  and  stone-ware. 


TRANSMISSION    OF   RADIANT    HEAT    THROUGH    MEDIA,   AND    THE   EFFECT    OP 

SCREENS. 

It  has  been  shown  by  Dulong  and  Petit,  that  hot  bodies  radiate  equally  in  all 
gases,  or  exactly  as  they  radiate  in  a  vacuum.  Hot  bodies  certainly  cool  more 
rapidly  in  some  gases  than  in  others ;  but  this  is  owing  to  the  mobility  and  conduct- 
ing powers  of  the  gases  being  different. 

Light  of  every  colour,  and  from  every  source,  is  equally  transmitted  by  all  trans- 
parent bodies  in  the  liquid  or  solid  form ;  but  this  is  not  true  of  heat.  The  heat  of 
the  sun  passes  through  any  transparent  body  without  loss ;  but  of  heat  from  terres- 
trial sources,  a  certain  variable  proportion  only  is  allowed  to  pass,  which  increases  as 
the  temperature  of  the  radiant  body  is  elevated.  Thus,  it  was  observed  by  Dela- 
roche  that,  from  a  body  heated  to  182°,  only  140th  of  all  the  heat  emitted  passed 
through  a  glass  screen:  from  a  body  at  346°,  l-16th  of  the  whole;  and  from  a 
body  at  960°,  so  large  a  proportion  as  l-4th  appeared  to  pass  through  a  glass  screen. 
M.  Melloni  has,  within  the  last  few  years,  greatly  extended  our  knowledge  respecting 
the  transmission  of  heat  through  media,  in  a  series  of  the  most  profound  researches.1 
In  his  experiments,  he  made  use  of  the  thermo-electric  pile  to  detect  changes  of 
temperature ;  an  instrument  which,  in  his  hands,  exhibited  a  sensibility  to  the  im- 
pressions of  heat  vastly  greater  than  that  of  the  most  delicate  mercurial  or  air  ther- 
mometer. 

His  instrument,  or  the  thermo-multiplier.  (fig.  21),  consists  of  an  arrangement 
of  thirty  pairs  of  bismuth  and  antimony  bars-contained  in  a  brass  cylinder,  t,  and 


/H 


having  the  wires  from  its  poles  connected  with  an  extremely  delicate  magnetic  gal- 
vanometer, n.  The  extremities  of  the  bars  at  b  being  exposed  to  any  source  of 
radiant  heat,  such  as  the  copper  cylinder  d,  heated  by  the  lamp  /,  while  the  tempe- 
rature of  the  other  extremities  of  the  bars  at  c  is  not  changed,  an  electric  current 
passes  through  the  wires  from  the  poles  of  the  pile,  and  causes  the  magnetic  needle 
of  the  galvanometer  to  deflect.  The  force  of  the  electric  current  increases  in  pro- 
portion to  the  difference  of  the  temperatures  of  the  two  ends,  b  and  c,  that  is,  in 


1  The  complete  series  of  Melloni's  Memoirs  is  given  in  Taylor's  Scientific  Memoirs,  Vols. 
I.  aud  II. 


56  RADIATION    OF    HEAT. 

proportion  to  the  quantity  of  heat  falling  upon  b  ;  and  the  effect  of  this  current 
upon  the  needle,  or  the  deviation  produced,  is  proportional  to  the  force  of  the  cur- 
rent, and  consequently  to  the  heat  itself;  at  least,  Melloni  finds  this  correspondence 
to  be  exact  through  the  whole  arc,  from  zero  to  20°,  when  the  needle  is  truly  astatic. 
Melloni  proved  that  heat,  which  has  passed  through  one  plate  of  glass,  becomes 
less  subject  to  absorption  in  passing  through  a  second.  Thus,  of  1000  rays  of  heat 
from  an  oil  flame,  451  rays  being  intercepted  in  passing  through  four  plates  of  glass 
of  equal  thickness — 

381  rays  were  intercepted  by  the  first  plate. 
43  "  "  by  the  second. 

18  "  "  by  the  third. 

9  "  «          by  the  fourth. 

457 

The  rays  appear  to  lose  considerably  when  they  enter  the  first  layers  of  a  transpa- 
rent medium ;  but  that  portion  of  heat,  which  has  forced  its  passage  through  the 
first  layers,  may  penetrate  to  a  great  depth.  Transparent  liquids  are  found  to  be 
less  penetrable  to  radiant  heat  than  solids. 

The  capacity  which  bodies  possess  of  transmitting  heat  does  not  depend  upon 
their  transparency ;  or  bodies  are  not  at  all  transparent  to  heat  in  the  same  propor- 
tion that  they  are  transparent  to  light.  Thus,  plates  of  the  following  transparent 
minerals,  having  a  common  thickness  of  0-1081  of  an  inch,  allowed  very  different 
proportions  of  the  heat  from  the  flame  of  an  argand  oil-lamp  to  pass  through  them. 

Of  100  incident  rays  there  were  transmitted  : — 

By  Rock-salt 92  rays. 

Mirror  glass 62 

Rock-crystal 62 

Iceland  spar 62 

Rock-crystal,  smoky  and  brown 57 

Carbonate  of  lead 52 

Sulphate  of  barytes v.  33 

Emerald 29 

Gypsum 20 

Fluor  spar 15 

Citric  acid 15 

Rochelle  salt 12 

Alum 12 

Sulphate  of  copper 0 

A  piece  of  smoky  rock-crystal,  so  brown  that  the  traces  of  letters  on  a  printed 
page  covered  by  it  could  not  be  seen,  and  which  was  fifty-eight  times  thicker  than  a 
transparent  plate  of  alum,  transmitted  19  rays,  while  the  alum  transmitted  only  6. 
One  substance,  which  is  perfectly  opaque,  a  kind  of  black  glass  used  for  the  polari- 
zation of  light  by  reflection,  was  found  by  Melloni  to  allow  a  considerable  quantity 
of  rays  of  heat  to  pass  through  it.  He  applied  the  term  diathermanous  to  bodies 
which  transmit  heat,  as  diaphanous  is  applied  to  bodies  which  transmit  light.  Of 
all  diaphanous  or  transparent  bodies,  water  is  in  the  least  degree  diathermanous. 
With  the  exception  of  the  opaque  glass  referred  to  above,  all  diathermanous  bodies 
belong  also  to  the  class  of  diaphanous  bodies ;  for  those  kinds  of  metal,  wood  and 
marble,  which  totally  obstruct  the  passage  of  light,  obstruct  that  of  heat  also. 

The  proportion  of  heat  from  various  sources  which  radiates  through  a  plate  of 
glass  l-50th  of  an  inch  in  thickness,  was  observed  by  Melloni  to  be  as  follows  : — 

Of  100  rays  Transmitted.     Absorbed. 

From  the  flame  of  an  oil-lamp  there  were 54 

"     red  hot  platinum 37  63 

"     blackened  copper,  heated  to  732°  F 12 

«  «  "  "  212° 0  100 

But  the  power  of  transmission  of  rock-salt  is  the  same  for  heat  from  all  these 


RADIATION    OF    HEAT.  57 

sources,  or  for  heat  of  all  intensities ;  92  per  cent,  of  the  incident  heat  being  trans- 
mitted by  that  body,  whether  it  be  the  heat  radiated  from  the  hand  or  from  a  bright 
argand  lamp.  Rock-salt  stands  alone  in  this  respect  among  diathermanous  bodies. 
This  substance  may  be  cut  into  lenses  or  prisms,  and  be  used  in  concentrating  heat 
of  the  very  lowest  intensity,  or  in  decomposing  it  by  double  refraction,  in  the  same 
manner  as  glass  is  employed  with  the  light  of  the  sun.  Indeed,  rock-salt  has 
become  quite  invaluable  in  researches  upon  the  transmission  of  heat. 

It  thus  appears  that  a  body  at  different  temperatures  emits  different  species  of 
rays  of  heat,  which  may  be  sifted  or  separated  from  each  other  by  passing  them 
through  certain  transparent  media.  They  are  all  emitted  simultaneously,  and  in 
different  proportions,  by  flame ;  but  in  heat  from  sources  of  lower  intensity  some  of 
them  are  always  absent.  The  calorific  rays  of  the  sun  are  chiefly  of  the  kind  which 
passes  through  glass ;  but  Melloni  shows  that  the  other  species  are  not  altogether 
wanting.  The  rays  of  heat  emitted  by  the  sun  and  other  luminous  bodies  are  quite 
different  rays  from  the  rays  of  light  with  which  they  are  accompanied. 

Of  the  equilibrium  of  temperature.  —  When  several  bodies  of  various  tempera- 
tures, some  cold  and  some  hot,  are  placed  near  each  other,  their  temperatures  gra- 
dually approximate,  and,  after  a  certain  period  has  elapsed,  they  are  found  all  to  be 
of  one  and  the  same  temperature.  To  account  for  the  production  and  continuation 
of  this  equilibrium  of  temperature,  it  is  necessary  to  assume  that  all  bodies  are  at 
all  times  radiating  heat  in  great  abundance  in  all  directions,  although  their  tempe- 
rature does  not  exceed  or  even  falls  below  the  temperature  of  the  atmosphere. 
Hence,  there  is  an  incessant  interchange  of  heat  between  neighbouring  bodies;  and 
a  general  equalization  of  temperature  is  produced  when  every  object  receives  as 
much  radiated  heat  as  it  emits. 

This  theory,  which  was  first  proposed  by  Prevost,  of  Geneva,  enables  us  to 
account  for  the  apparent  radiation  of  cold.  Cold,  we  know,  is  a  negative  quality, 
being  merely  the  absence  of  heat,  -and  cannot  therefore  be  radiated.  Yet,  when  a 
lump  of  ice  is  placed  in  the  focus  of  a  reflecting  mirror,  a  thermometer  in  the  focus 
of  the  opposite  conjugate  mirror  is  chilled.  To  account  for  this  phenomenon  we 
must  remember  that  the  temperature  of  the  thermometer  is  stationary  only  so  long 
as  it  receives  as  much  heat  as  it  radiates.  It  is  in  that  state  before  the  experiment 
is  made  with  the  ice;  for  the  air  or  any  object  which  may  happen  to  be  in  the  other 
focus  is  of  the  same  temperature  as  the  ball  of  the  thermometer.  But  it  is  evident 
that  the  moment  ice  is  introduced  into  one  focus  less  heat  will  be  sent  from  that  to 
the  other  focus  than  was  previously  transmitted,  and  than  is  necessary  to  sustain 
the  thermometer  at  a  constant  temperature.  The  thermometer  ball,  therefore, 
giving  out  as  much  heat  as  formerly,  and  receiving  less  in  return,  must  fall  in  tem- 
perature. This  is  an  experiment  in  which  the  thermometer  ball  is  in  fact  the 
hot  body. 

The  doctrine  of  the  radiation  of  heat  is  happily  applied  to  account  for  the  depo- 
sition of  dew.  A  considerable  refrigeration  of  the  surface  of  the  ground  below  the 
temperature  of  the  air  resting  upon  it,  amounting  to  10  or  20  degrees,  occurs  every 
calm  and  clear  night,  and  is  caused  by  the  radiation  of  heat  from  the  earth  (which 
is  a  good  radiator)  into  empty  space.  Now,  on  becoming  colder  than  the  air  above 
it,  the  ground  will  condense  the  moisture  of  the  air  in  contact  with  it,  and  be 
covered  with  dew.  For  the  air,  however  clear,  is  never  destitute  of  watery  vapour, 
and  the  quantity  of  vapour  which  air  can  retain  depends  upon  its  temperature ;  air 
at  52°,  for  instance,  being  capable  of  retaining  l-86th  of  its  volume  of  vapour, 
while  at  32°  it  can  retain  no  more  than  1-1 50th  of  its  volume.  The  greatest 
difference  between  the  temperature  of  the  day  and  night  takes  place  in  spring 
and  autumn,  and  these  are  the  seasons  in  which  the  most  abundant  dews  are 
deposited. 

That  the  deposition  of  dew-drops  depends  entirely  upon  radiation  is  fully  established 
by  the  following  circumstances :  —  1.  It  is  on  clear  and  calm  nights  only  that  dew 
is  observed  to  fall.  When  the  sky  is  overcast  with  clouds,  no  dew  is  formed;  for 


58  RADIATION    OF   HEAT. 

then  the  heat  which  radiates  from  the  earth  is  returned  by  the  clouds  above,  and  pre- 
vented from  escaping  into  space ;  so  that  the  ground  never  becomes  colder  than  the 
air.  2.  The  slightest  screen,  such  as  a  thin  cambric  handkerchief,  stretched  between 
pins,  at  the  height  of  several  inches  above  the  ground,  is  sufficient  to  protect  the 
objects  below  it  from  this  chilling  effect  of  radiation,  and  to  prevent  the  formation 
of  dew  or  of  hoar-frost  upon  them.  This  fact  was  well  known  to  gardeners,  and 
they  had  long  availed  themselves  of  it  in  protecting  their  tender  plants  from  frost, 
before  the  laws  of  the  radiation  of  heat  came  to  be  explained.  8.  Dr.  Wells  proved 
by  numerous  experiments  that  the  quantity  of  dew  which  condenses  on  different  ob- 
jects exposed  in  the  same  circumstances  is  proportional  to  the  radiating  power  of 
those  substances.  Thus,  when  a  polished  plate  of  metal  and  a  quantity  of  wool  are 
exposed  together  in  favourable  circumstances,  scarcely  a  trace  of  dew  is  to  be  ob- 
served on  the  metal,  while  a  large  quantity  condenses  in  the  wool,  the  latter  sub- 
stance being  incomparably  the  best  radiator,  and  therefore  falling  to  a  much  lower 
temperature  than  the  metal. 

The  same  theory  has  been  applied  to  explain  a  process  for  making  ice  followed  by 
the  Indian  natives  near  Calcutta.  In  that  climate  the  temperature  of  the  air  rarely 
falls  below  40°  in  the  coldest  nights ;  but  the  sky  is  clear,  and  a  powerful  radiation 
takes  place  from  the  surface  of  the  ground.  Hence,  water  contained  in  shallow  pans 
imbedded  in  straw  is  often  sheeted  over  with  ice  by  a  night's  exposure.  The  water 
is  certainly  cooled  by  radiation  from  its  surface,  and  not  by  evaporation ;  for  the 
process  succeeds  best  when  the  pans  are  placed  in  shallow  trenches  dug  in  the 
ground,  an  arrangement  which  retards  evaporation;  and  no  ice  forms  in  windy 
weather,  when  evaporation  is  greatest. 

The  morning  frosts  of  autumn  are  first  felt  in  sequestered  situations,  as  in  ravines 
closed  on  all  sides,  or  along  the  low  courses  of  rivers,  where  the  cooling  of  the 
earth's  surface  by  radiation  is  in  the  least  degree  checked  by  the  movement  of  the 
air  over  it.  These  are  also  the  very  situations  upon  which  the  sun's  rays  produce 
the  greatest  effect  in  summer. 

Reverting  again  to  the  subject  of  conduction  of  heat  through  solid  bodies,  it  may 
now  be  stated,  that  there  is  every  reason  to  believe  that  heat  is  propagated,  even  in 
that  case,  in  a  manner  not  unlike  radiation.  Heat,  in  its  passage  through  a  bar  of  iron, 
is  probably  radiated  from  particle  to  particle ;  for  the  material  atoms,  of  which  the  bar 
consists,  are  not  supposed  to  be  in  absolute  contact,  although  held  near  each  other 
by  a  strong  attraction.  Radiation,  as  observed  in  air  or  a  vacuum,  may  thus  pass 
into  conduction  in  solids,  without  any  breach  of  continuity  in  the  natural  law  to 
which  heat  in  motion  is  subject.  Baron  Fourier  proceeds  upon  such  an  hypothesis 
in  his  mathematical  investigation  of  the  law  of  cooling  by  conduction  in  solid 
bodies.1 

We  are  now  in  a  condition  to  advert  with  advantage  to  the  equilibrium  of  the 
temperature  of  the  earth.  There  can  be  no  doubt  of  the  existence,  in  this  globe  of 
ours,  of  a  central  heat.  At  a  depth  under  the  surface  of  the  earth,  not  in  general 
exceeding  twenty  feet,  the  thermometer  is  perfectly  stationary,  not  being  affected  by 
the  change  of  the  seasons;  but  at  greater  depths  the  temperature  progressively  rises. 
M.  Cordier,  to  whom  we  are  indebted  for  a  most  profound  investigation  of  this  inte- 
resting subject,  considers  the  two  following  conclusions  to  be  established  by  all  the  ob- 
servations on  temperature  which  have  been  made  at  considerable  depths.  1st.  That 
below  the  stratum  where  the  annual  variations  of  the  solar  heat  cease  to  be  sensible,  a 
notable  increase  of  temperature  takes  place  as  we  descend  into  the  interior  of  the  earth. 
2dly.  That  a  certain  irregularity  must  be  admitted  in  the  distribution  of  the  subter- 
raneous heat,  which  occasions  the  progressive  increase  of  temperature  to  vary  at  differ- 
ent places.  Fifteen  yards  has  been  provisionally  assumed  as  the  average  depth  which 

1  See  a  report  by  Professor  Kelland,  On  the  present  state  of  our  Theoretical  and  Experi- 
mental Knowledge  of  the  Laws  of  the  Conduction  of  Heat,  in  the  Reports  of  the  British 
Association  for  the  Advancement  of  Science,  for  1841,  p.  1. 


.  FLUIDITY. 


59 


corresponds  to  an  increase  of  one  degree  Fahrenheit.  This  is  about  116  degrees  for 
each  mile.  Admitting  this  rate  of  increase,  we  have  at  the  depth  of  SOj  miles 
below  the  surface  a  temperature  of  3500°,  which  would  melt  cast  iron,  and  which  is 
amply  sufficient  to  melt  the  lavas,  basalts,  and  other  rocks,  which  have  actually  been 
erupted  from  below  in  a  fluid  state.  But  this  central  heat  has  long  ceased  to  affect 
the  surface  of  the  earth.  Fourier  demonstrates,  from  the  laws  of  conduction,  that 
although  the  crust  of  the  globe  were  of  cast  iron,  heat  would  require  myriads  of 
years  to  be  transmitted  to  the  surface  from  a  depth  of  150  miles.  But  the  crust  of 
the  globe  is  actually  composed  of  materials  greatly  inferior  to  cast  iron  in  conducting 
power.  The  temperature  of  the  surface  of  the  globe  now  depends  upon  the  amount 
of  heat  which  it  receives  from  the  sun,  compared  with  the  heat  radiated  away  from 
its  surface  into  free  space.  There  is  reason  to  believe  that  no  material  change  has 
occurred  in  the  quantity  of  heat  received  from  the  sun  during  the  historical  epoch. 
The  radiation  from  the  surface  of  the  earth  has  its  limit  in  the  temperature  of  the 
planetary  space  in  which  it  moves,  which  Fourier  deduces,  from  calculation,  to  lie 
between  — 58°  and  — 76°,  and  which  Schwanberg,  from  a  calculation  on  totally 
different  principles,  estimates  at  — 58°. 6;  a  close  coincidence.  This  low  temper- 
ature appears  to  be  attained  in  the  long  absence  of  the  sun  during  a  polar  winter, 
as  Captain  Parry  found  the  thermometer  to  fall  so  low  as  — 55°  or  — 56°  at  Mel- 
ville Island;  and  Captain  Back  has  recorded  a  temperature  observed  on  the  North 
American  continent  so  low  as  —  70°. 


FLUIDITY  AS  AN  EFFECT  OF  HEAT. 

One  of  the  general  effects  of  heat  upon  bodies  has  already  been  adverted  to, 
namely  its  power  of  causing  them  to  expand,  which  demanded  our  earliest  attention, 
as  it  involves  the  principle  of  the  thermometer.  But  heat,  besides  effecting  changes 
in  the  bulk,  is  capable  of  effecting  changes  in  the  condition  of  bodies.  Matter  is 
presented  to  us  in  three  very  dissimilar  conditions,  or  forms,  namely,  in  the  solid, 
liquid,  and  gaseous  forms.  It  is  believed  that  no  body  is  restricted  to  any  of  these 
forms,  but  that  the  state  of  bodies  depends  entirely  upon  the  temperature  in  which 
they  are  placed.  In  the  lowest  temperatures,  they  are  all  solid,  in  higher  tempe- 
ratures they  are  converted  into  liquids,  and  in  the  highest  of  all  they  become  elastic 
gases.  The  particular  temperatures  at  which  bodies  undergo  these  changes  are 
exceedingly  various,  but  they  are  always  constant  for  the  same  body.  The  first 
effect,  then,  of  heat  on  the  state  of  bodies  is  the  conversion  of  solids  into  liquids ;  or 
heat  is  the  cause  of  fluidity. 

Some  substances,  in  liquefying,  pass  through  an  intermediate  condition,  in  which 
it  is  difficult  to  say  whether  they  are  liquids  or  solids.  Thus  tallow,  wax,  and  several 
other  bodies,  pass  through  every  possible  degree  of  softness  before  they  attain  com- 
plete fluidity.  Such  bodies,  however,  are  in  general  mixtures  of  two  or  more  sub- 
stances, which  crystallize  imperfectly.  But  ice,  and  the  great  majority  of  bodies, 
pass  immediately  from  the  solid  into  the  liquid  state.  The  temperatures  at  which 
bodies  undergo  this  change  are  exceedingly  various. 


Melts  at 

Lead 594° 

Bismuth 476 

Tin 442 

Sulphur 232 

Wax 142 

Spermaceti 112 

Phosphorus 108 

Tallow 92 

Oil  of  anise .    50 


Olive  oil, 

Ice 

Milk 

Wines..., 


Melts  at 
.      36° 
.      32 
.      30 
20 


Oil  of  turpentine 14 

Mercury — 39 

Liquid  ammonia — 46 

Ether...  ,..—47 


If  the  bodies  are  in  the  fluid  form,  they  freeze  upon  being  cooled  below  the  tempe- 
ratures set  against  them. 


60  FLUIDITY.     . 

It  may  be  added,  in  reference  to  this  table,  first,  that  in  certain  circumstances 
liquids  can  be  cooled  down  several  degrees  below  their  usual  freezing  point  before 
they  begin  to  congeal.  Thus  we  may  succeed,  by  taking  certain  precautions,  in 
cooling  a  small  quantity  of  water,  in  a  glass  tube,  so  low  as  the  temperature  8°,  or 
even  as  5°,  without  its  freezing ;  that  is,  24  or  27  degrees  under  its  proper  freezing 
poipt  32°.  The  water  must  be  cooled  without  the  slightest  agitation,  and  no  sand 
or  angular  body  be  in  contact  with  it ;  for  the  instant  any  solid  body  is  dropped  into 
water  cooled  below  its  freezing  point,  or  a  tremor  is  communicated  to  it,  congelation 
commences,  and  the  temperature  of  the  liquid  starts  up  to  32°.  But,  on  the  other 
hand,  we  cannot  heat  a  solid  the  smallest  fraction  of  a  degree  above  its  proper  melt- 
ing point,  without  occasioning  liquefaction.  Hence  it  is  not  the  freezing  of  water, 
but  the  melting  of  ice,  which  takes  place  with  rigorous  constancy  at  82°  Fahrenheit. 

All  salts  dissolved  in  water  have  the  effect  of  lowering  the  freezing  temperature 
of  that  liquid.  Common  culinary  salt  appears  to  depress  this  point  lower  than  any 
other  saline  body ;  and  the  effect  appears  to  be  closely  proportional  to  the  quantity 
of  salt  in  solution.  A  solution  of  1  part  of  salt  in  4  of  water  freezes  at  4° ;  and 
sea-water,  which  contains  l-30th  of  its  weight  of  salt,  freezes  at  28°. 

But  the  principal  fact  to  be  adverted  to  in  liquefaction  is  the  disappearance  of  a 
large  quantity  of  heat  during  the  change.  Heat  pours  into  a  body  during  its  melt- 
ing, without  raising  its  temperature  in  the  most  minute  degree.  This  heat,  which 
enters  the  body  and  becomes  insensible  or  latent,  serves  merely  to  melt  the  body. 
We  are  indebted  to  Dr.  Black  for  this  observation,  which  involves  consequences  of 
greater  importance  than  any  other  announcement  in  the  theory  of  heat. 

Before  Dr.  Black's  views  were  made  known,  fluidity  was  considered  as  produced 
by  a  very  small  addition  to  the  quantity  of  heat  which  a  body  contains,  when  it  is 
once  heated  up  to  its  melting  point.  But  if  we  attend  to  the  manner  in  which  ice 
and  snow  melt,  when  exposed  to  the  air  of  a  warm  room,  we  can  perceive  that, 
however  cold  they  may  be  at  first,  they  are  soon  heated  up  to  their  melting  point, 
and  begin  at  their  surface  to  be  changed  into  water.  Now,  if  the  complete  change 
of  these  bodies  into  water  required  only  the  farther  addition  of  a  very  small  quan- 
tity of  heat,  a  mass  of  them,  though  of  considerable  size,  ought  all  to  be  melted  in  a 
few  minutes  or  seconds  more,  the  heat  continuing  to  be  communicated  from  the  air 
around.  But  masses  of  ice  and  snow  melt  with  extreme  slowness,  especially  if  they 
be  of  a  large  size,  as  are  those  collections  of  ice  and  wreaths  of  snow  that  are  formed 
in  some  places  during  winter.  These,  after  they  begin  to  melt,  often  require  many 
weeks  of  warm  weather,  before  they  are  totally  dissolved  into  water.  The  slow 
manner  in  which  ice  melts  in  ice-houses  is  also  familiarly  known. 

By  examining  what  happens  in  these  cases,  it  may  easily  be  perceived  that  a  very 
great  quantity  of  heat  must  enter  the  melting  ice,  to  form  the  water  into  which  it  is 
changed,  and  that  the  length  of  time  necessary  for  the  collection  of  so  much  heat 
from  surrounding  bodies  is  the  reason  of  the  slowness  with  which  the  ice  is  liquefied. 
When  melting  ice  is  suspended  in  warm  air,  the  entrance  of  heat  into  it  is  made 
sensible  by  a  stream  of  cold  air  descending  constantly  from  the  ice,  which  n.ay  be 
perceived  by  the  hand.  It  is,  therefore,  evident  that  the  melting  ice  receives  heat 
very  fast;  but  the  only  effect  of  this  heat  is  to  change  it  into  water,  which  is  not  in 
the  least  sensibly  warmer  than  the  ice  was  before.  A  thermometer  applied  to  the 
drops  or  small  streams  of  water  as  they  come  immediately  from  the  melting  ice1, 
will  point  to  the  same  degree  as  when  applied  to  the  ice  itself.  A  great  quantity  of 
the  heat,  therefore,  which  enters  into  the  melting  ice,  has  no  other  effect  than  that 
of  giving  it  fluidity.  The  heat  appears  to  be  absorbed  or  concealed  within  the  water, 
and  cannot  be  detected  by  the  thermometer. 

When  ice  is  melted  by  means  of  warm  water,  this  absorption  of  heat  is  made 
exceedingly  obvious.  Thus,  on  mixing  a  pound  of  water  at  172°  with  a  pound  of 
snow  at  32°,  the  snow  is  all  melted,  and  the  mixture  is  two  pounds  of  water  of  the 
temperature  of  32°.  In  being  cooled  down  from  172°  to  32°,  the  hot  water  loses 
140  degrees  of  heat,  which  convert  the  snow  into  water,  indeed,  but  produce  no 


FLUIDITY.  61 

rise  of  temperature  in  the  mixture  above  the  32  degrees  originally  possessed  by 
the  snow. 

Dr.  Black  proved  that  the  heat  which  disappears  in  this  manner  is  not  extinguished 
or  destroyed,  but  remains  latent  in  the  water  so  long  as  it  is  fluid,  and  is  extricated 
again  when  it  freezes. 

In  water  that  has  been  cooled  below  its  usual  freezing  point,  when  the  congelation 
is  once  determined,  quantities  of  icy  spiculse  are  produced  in  proportion  to  the  de- 
pression of  temperature,  whilst  at  the  same  instant  the  temperature  of  ice  and  water 
starts  up  to  82°.  The  heat  which  thus  appears  was  previously  latent  in  that  portion 
of  the  water  which  is  frozen.  The  same  disengagement  of  latent  heat  may  be  con- 
veniently illustrated  by  means  of  a  supersaturated  solution  of  sulphate  of  soda, 
formed  by  dissolving,  at  a  high  temperature,  three  pounds  of  the  salt  in  two  pounds 
of  water.  When  this  liquid  is  allowed  to  cool  undisturbed,  and  with  a  stratum  of 
oil  on  its  surface,  it  remains  fluid,  although  containing  a  much  greater  quantity  of 
salt  in  solution  than  the  water  could  dissolve  at  the  temperature  to  which  it  has 
fallen.  But  the  suspended  congelation  of  the  salt  being  determined  by  the  intro- 
duction of  any  solid  substance  into  the  solution,  the  temperature  then  often  rises  30 
and  even  40  degrees,  while  crystals  of  sulphate  of  soda  shoot  rapidly  through  the 
liquid. 

Wax,  tallow,  sulphur,  and  all  other  solid  bodies,  are  melted  in  the  same  manner 
as  water,  by  the  assumption  of  a  certain  dose  of  heat.  The  latent  heat  which  the 
following  substances  possess  in  the  fluid  form  was,  with  the  exception  of  water,  de- 
termined by  Dr.  Irvine. 

Latent  heat. 

Water  142  degrees.1 

Sulphur  145 

Lead 162 

Bees'-wax  175 

Zinc 493 

Tin    500 

Bismuth  550 

Even  in  the  solid  form  certain  bodies  admit  of  a  variation  in  their  structure  and 
properties  from  the  assumption  or  loss  of  latent  heat.  Dr.  Black  made  it  appear 
probable  that  metals  owe  their  malleability  and  ductility  to  a  quantity  of  latent  heat 
combined  with  t'hem.  When  hammered  they  become  hot  from  the  disengagement 
of  this  heat,  and  at  the  same  time  become  brittle.  Their  malleability  is  restored  by 
heating  them  again  in  a  furnace.  Sugar,  it  is  well  known,  may  exist  as  a  transparent 
and  colourless  body,  with  the  physical  properties  of  glass,  or  as  a  white  and  opaque, 
because  a  granular  or  crystalline  mass.  The  transition  from  the  glassy  to  the  granular 
state  is  attended  by  a  very  remarkable  evolution  of  heat,  which  appears  to  have 
escaped  the  notice  of  scientific  men.  If  melted  sugar  be  allowed  to  cool  to  about 
100°,  and  then,  while  it  js  still  soft  and  viscid,  be  rapidly  and  frequently  extended 
and  doubled  up,  till  at  last  it  consists  of  threads,  as  in  drawn  sugar,  the  temperature 
of  the  mass  quickly  rises  so  as  to  become  insupportable  to  the  hand.  After  this 
liberation  of  heat,  the  sugar  on  again  cooling  is  no  longer  a  glass,  but  consists  of 
minute  crystalline  grains,  and  has  a  pearly  lustre.  The  same  change  may  occur  in  a 
gradual  manner,  as  when  a  clear  stick  of  barley-sugar  becomes  white  and  opaque  in 
the  atmosphere;  but  then  we  have  no  means  of  observing  the  escape  of  the  latent 
heat  on  which  the  change  depends.  It  may  be  inferred  that  glass  itself,  like  trans- 
parent barley-sugar,  owes  its  peculiar  constitution  and  properties  to  the  permanent 
retention  of  a  certain  quantity  of  latent  heat.  Of  this  heat  glass  can  be  deprived 
by  keeping  it  long  in  a  soft  state :  it  then  becomes  granular,  and,  passing  into  the 
condition  of  Reaumur's  porcelain,  loses  all  the  characters  of  glass. 

It  is  not  unlikely  that  the  dimorphism  of  a  body,  or  its  property  to  assume  two 
different  crystalline  forms,  may  likewise  depend  upon  the  retention  of  a  certain 

1  De  la  Provostaye  and  Regnault,  Annales  de  Chimie,  &c.,  3  se>.  t  8,  p.  1. 


62  VAPORIZATION". 

quantity  of  latent  heat  by  the  body  in  the  one  form,  and  not  in  the  other.  Thus, 
sulphur  assumes  two  forms,  one  on  cooling  from  a  state  of  fusion  by  heat,  another 
in  crystallizing  at  a  lower  temperature,  and  probably  with  the  retention  of  less  latent 
heat,  from  a  solution  of  sulphuret  of  carbon.  In  charcoal  and  plumbago,  again,  we 
have  carbon  which  has  assumed  the  solid  form  at  a  high  temperature,  and  possibly 
with  the  fixation  of  a  quantity  of  latent  heat  which  does  not  exist  in  the  diamond, 
another  form  of  the  same  body. 

When  a  solid  body  is  melted  by  the  intervention  of  some  affinity,  without  heat 
being  applied  to  it,  cold  is  generally  produced.  Thus,  most  salts  occasion  a  reduction 
of  temperature,  in  the  act  of  dissolving  in  water,  which  requires  them  to  become 
fluid.  Nitre,  for  instance,  cools  the  water  in  which  it  is  dissolved  15  or  18  degrees. 
A  mixture  of  five  parts  of  sal  ammoniac  and  five  of  nitre,  both  finely  powdered, 
dissolved  in  nineteen  parts  of  water,  may  reduce  its  temperature  from  50°  to  10°, 
or  considerably  below  the  freezing  point  of  pure  water.  These  salts  are  necessitated, 
by  their  affinity  for  water,  to  dissolve  when  mixed  with  it,  and  to  become  fluid,  a 
change  which  implies  the  assumption  of  latent  heat.  Most  of  our  artificial  processes 
for  producing  cold  are  founded  upon  this  disappearance  of  heat  during  liquefaction. 
A  very  convenient  process  for  freezing  a  little  water,  without  the  use  of  ice,  is  to 
drench  finely  powdered  sulphate  of  soda  with  the  undiluted  hydrochloric  acid  of  the 
shops.  The  salt  dissolves  to  a  greater  extent  in  this  acid  than  in  water,  and  the 
temperature  may  sink  from  50°  to  0°.  The  vessel  in  which  the  mixture  is  made 
becomes  covered  with  hoar  frost,  and  water  in  a  tube  immersed  in  the  mixture  is 
speedily  frozen. 

The  same  affinity  between  salts  and  water  may  be  taken  advantage  of  to  cause 
the  liquefaction  of  ice.  On  mixing  snow  with  a  third  of  its  weight  of  salt,'  the 
snow  is  instantly  melted,  and  the  temperature  sinks  nearly  to  0°.  It  was  in  this 
way  that  Fahrenheit  is  supposed  to  have  obtained  the  zero  of  his  scale.  Ices  for 
the  table  are  always  made  in  summer  by  mixing  roughly  pounded  ice  and  salt  toge- 
ther, and  immersing  the  cream,  or  other  liquid  to  be  frozen,  contained  in  a  thin 
metallic  pan,  in  the  cold  brine  which  is  produced  by  the  melting  of  the  ice. 

The  liquefaction  of  snow  by  means  of  the  salt,  chloride  of  calcium,  occasions  a 
still  greater  degree  of  cold.  To  prepare  this  salt,  marble  or  chalk  is  dissolved  in 
hydrochloric  acid,  and  the  solution  evaporated  by  a  temperature  not  exceeding  300°. 
It  should  be  stirred,  as  it  becomes  dry  at  this  temperature ;  and  is  obtained  in  a 
crystalline  powder,  being  the  combination  of  chloride  of  calcium  with  two  atoms  of 
water.  When  three  parts  of  this  salt  are  mixed  with  two  of  dry  snow,  the  tem- 
perature is  reduced  from  32°  to  — 50°.  In  attempting  to  freeze  mercury  by  means 
of  this  mixture,  it  is  advisable  to  make  use  of  not  less  than  three  or  four  pounds  of 
the  materials.  When  the  materials  are  divided,  and  the  mercury  is  first  cooled  con- 
siderably by  one  portion,  it  rarely  fails  in  being  frozen  when  transferred  into  another 
portion  of  the  mixture.  For  producing  still  more  intense  degrees  of  cold,  the  eva- 
poration of  highly  volatile  liquids,  of  liquid  carbonic  acid,  for  instance,  affords  the 
most  efficient  means. 

VAPORIZATION. 

We  have  now  to  consider  the  second  general  effect  of  heat — Vaporization,  or  the 
conversion  of  solids  and  liquids  into  vapour.  Vapours,  of  which  steam  is  the  most 
familiar  to  us,  are  light,  expansible,  and  generally  invisible  gases,  resembling  air 
completely  in  their  mechanical  properties,  while  they  exist,  but  subject  to  be  con- 
densed into  liquids  or  solids  by  cold.  Water  undergoes  a  great  expansion  when 
converted  into  steam,  a  cubic  inch  of  water  becoming,  in  ordinary  circumstances,  a 
cubic  foot  of  steam ;  or,  more  strictly,  one  cubis  inch  of  water,  when  converted  into 
steam,  expands  into  1694  cubic  inches. 

This  change,  like  fluidity,  is  produced  by  the  addition  of  heat  to  the  body  which 
undergoes  it.  But  a  much  larger  quantity  of  heat  enters  into  vapours  than  into 
liquids,  into  steam  than  into  water.  If,  over  a  steady  fire,  a  certain  quantity  of  ice- 


VAPORIZATION.  63 

cold  water  requires  one  hour  to  bring  it  to  the  boiling  point,  it  will  require  a  con- 
tinuance of  the  same  heat  for  five  hours  more  to  boil  it  off  entirely.  Yet  liquids  do 
not  become  hotter  after  they  begin  to  boil,  however  long,  or  with  whatever  violence 
the  boiling  is  continued :  for  if  a  thermometer  be  plunged  into  water,  and  the  point 
marked  where  it  stands  at  the  beginning  of  the  boiling,  it  will  be  found  to  rise  no 
higher,  although  the  boiling  be  continued  for  a  long  time. 

This  fact  is  of  importance  in  domestic  economy,  particularly  in  cookery;  and 
attention  to  it  would  save  much  fuel.  Soups,  &c.,  made  to  boil  in  a  gentle  way,  by 
the  application  of  a  moderate  heat,  are  just  as  hot  as  when  they  are  made  to  boil  on 
a  strong  fire  with  the  greatest  violence ;  when  water  in  a  copper  is  once  brought  to 
the  boiling  point,  the  fire  may  be  reduced,  as  having  no  further  effect  in  raising  its 
temperature,  and  a  moderate  heat  being  sufficient  to  preserve  it. 

The  steam  from  boiling  water,  when  examined  by  the  thermometer,  is  found  to 
be  no  hotter  than  the  water  itself.  What,  then,  becomes  of  all  the  heat  which  is 
communicated  to  the  water,  since  it  is  neither  indicated  in  the  steam  nor  in  the 
water  ?  It  enters  into  the  water,  and  converts  it  into  steam,  without  raising  its 
temperature.  As  much  heat  disappears  as  is  capable  of  raising  the  temperature  of 
the  portion  of  water  converted  into  steam  1000  degrees,  or,  what  is  the  same  thing, 
as  would  raise  the  temperature  of  one  thousand  times  as  much  water  by  one  degree. 
This  is  now  generally  assumed  to  be  the  amount  of  the  latent  heat  of  steam.  I)r. 
Black  found  it  to  be  about  960  degrees,  Mr.  Watt  940  degrees,  and  Lavoisier  rather 
more  than  1000  degrees. 

Several  circumstances  may  be  remarked  during  the  occurrence  of  this  change  in 
water.  On  heating  water  gradually  in  a  vessel,  we  first  observe  minute  bubbles  to 
form  in  the  liquid,  and  rise  through  it,  which  consist  of  air.  As  the  temperature 
increases,  larger  bubbles  are  formed  at  the  bottom  of  the  vessel,  which  rise  a  little 
way  in  the  liquid,  and  then  contract  and  disappear,  producing  a  hissing  or  simmering 
sound.  But,  as  the  heating  goes  on,  these  bubbles,  which  are  steam,  rise  higher 
and  higher  in  the  liquid,  till  at  last  they  reach  its  surface  and  escape,  producing  a 
bubbling  agitation,  or  the  phenomenon  of  ebullition.  The  whole  process  of  boiling 
is  beautifully  seen  in  a  glass  vessel.  It  will  be  remarked  that  steam  itself  is 
invisible;  it  only  appears  when  condensed  again  into  minute  drops  of  water  by 
mixing  with  the  cold  air. 

It  was  first  observed  by  Gay-Lussac,  that  liquids  are  converted  more  easily  into 
vapour  when  in  contact  with  angular  and  uneven  surfaces,  than  when  the  surfaces 
which  they  touch  are  smooth  and  polished.  He  also  remarked  that  water  boils  at 
a  temperature  two  degrees  higher  in  glass  than  in  metal ;  so  that  if  into  water,  in  a 
glass  flask,  which  has  ceased  to  boil,  a  twisted  piece  of  cold  iron  be  dropped,  the 
boiling  is  resumed :  it  is  only  in  vessels  of  metal  that  the  boiling  point  is  regular, 
and  should  be  taken  in  graduating  thermometers.  It  has  been  remarked  by  Mr. 
Scrymgeour,  of  Glasgow,  that  if  oil  be  present  with  water,  the  boiling  point  of  the 
water  is  raised  a  few  degrees,  in  any  kind  of  vessel.  A  much  greater  elevation  of 
the  boiling  point  has  been  observed  by  M.  Marcet,  (Ann.  de  Chimie,  &c.,  3  ser. 
t.  5,  p.  449),  in  a  glass  flask,  having  its  inner  surface  coated  with  a  thin  film  of 
shellac,  in  which  the  temperature  often  rises  to  221°,  or  even  higher,  before  a  burst 
of  vapour  occurs;  it  then  sinks  a  few  degrees,  after  which  it  rises  again.1  The 
reason  why  water  in  these  circumstances  does  not  pass  into  vapour  at  its  usual  boil- 
ing point,  is  not  distinctly  understood.  The  water  appears  to  be  in  a  precarious 
state  of  equilibrium,  as  in  the  other  analogous  case,  when  cooled  with  caution  in  a 
smooth  glass  vessel  considerably  under  its  usual  freezing  point.  The  introduction 
of  an  angular  body  into  the  water  is  sufficient,  in  either  instance,  to  induce  the  sus- 

1  The  author  has  quoted  incorrectly  the  results  of  Marcet's  experiments,  as  referred  to 
above.  The  statements  made,  are  to  the  effect  that  in  glass  vessels  deprived  of  all  foreign 
matter  on  their  surface,  a  marked  elevation  of  the  temperature  of  ebullition  may  be  obtained, 
distilled  water  not  boiling  below  105°  C.  (221°  F.) ;  but  in  vessels  coated  with  shellac  or  sul- 
phur, this  temperature  is  inferior  by  some  tenths  of  a  degree  to  that  in  metal  vessels.  — R.  B 


64  VAPORIZATION. 

pended  change.  The  same  irregular  deviation  of  the  boiling  point  in  glass  vessels 
takes  place  in  other  liquids  as  well  as  water,  and  in  some  of  them  to  a  much  greater 
extent. 

There  is  a  curious  circumstance  in  regard  to  boiling,  which  is  a  matter  of  common 
observation  in  some  shape  or  other.  When  a  little  water  (a  few  drops)  is  thrown 
into  a  metallic  cup  considerably  above  the  boiling  point  of  water,  the  liquid  assumes 
a  spheroidal  form,  and  rolls  about  the  cup  like  melted  crystal,  without  visible  ebul- 
lition, being  only  slowly  dissipated.  The  cause  of  the  phenomenon  appears  to  be 
this.  Water  exhibits  an  attraction  for  the  surface  of  almost  all  solids  at  low  tempe- 
ratures, and  wets  them.  Fluid  mercury  exhibits  the  opposite  property,  or  a  repul- 
sion for  most  surfaces.  The  attraction  of  water  for  surfaces  brings  it  into  the  closest 
contact  with  them,  and  greatly  promotes  the  communication  of  heat  by  a  heated 
vessel  to  the  water  contained  in  it.  But  heat  appears  to  develope  a  repulsive  power 
in  bodies,  and  it  is  probable  that  above  a  particular  temperature  the  heated  metal 
no  longer  possesses  this  attraction  for  water.  The  water,  not  being  attracted  to  the 
surface  of  the  hot  metal,  and  induced  to  spread  over  it,  is  not  rapidly  heated,  and 
therefore  boils  off  slowly.  A  rude  method  of  judging  of  the  degree  of  heat  is 
founded  on  the  same  principle,  and  is  seen  familiarly  exemplified  in  the  laundry. 
The  heat  of  the  smoothing  iron  is  judged  of  by  its  effects  upon  a  drop  of  saliva  let 
fall  upon  it.  If  the  drop  do  not  boil,  but  run  along  the  surface  of  the  metal,  the 
iron  is  considered  sufficiently  hot ;  but  if  the  drop  adheres  and  is  rapidly  dissipated, 
the  temperature  is  considered  low. 

The  spheroidal  ebullition  of  liquids,  which  was  first  examined  by  Leidenfrost,  in 
1756,  has  lately  received  from  M.  Boutigny  some  striking  experimental  illustra- 
tions (Annales  de  Chirnie,  &c.,  3  ser.  t.  ix.  p.  350  ;  et  t.  xi.  p.  16).  He  has  ob- 
served that  water  may  pass  into  spheroidal  ebullition  at  any  temperature  above  340°, 
and  remain  in  that  state  till  the  temperature  falls  to  288° ;  then  it  moistens  the 
metallic  capsule  in  which  the  experiment  is  made,  and  evaporates  rapidly.  The 
corresponding  temperatures  at  which  alcohol  and  ether  pass  into  the  spheroidal  form 
in  a  heated  capsule  were  found  to  be  proportional  to  their  points  of  ebullition  ;  the 
temperature  for  the  first  being  273°,  and  for  the  second  142°.  The  ball  of  a  ther- 
mometer being  plunged  in  liquids  while  in  the  spheroidal  state,  indicated  the  tem- 
peratures—  in  water,  of  205-7°;  in  absolute  alcohol,  of  167 -9°;  in  ether,  93-6°; 
in  hydrochloric  ether,  50-9°;  in  sulphurous  acid,  13-1°;  which  are  all  several 
degrees  below  the  ordinary  temperatures  of  ebullition  of  these  liquids.  When  dis- 
tilled water  is  allowed  to  fall  drop  by  drop  into  sulphurous  acid  in  the  spheroidal 
state,  the  water  is  immediately  congealed  into  a  spongy  mass  of  ice,  even  when  the 
containing  capsule  is  visibly  red-hot. 

The  temperature  at  which  any  liquid  boils  is  not  fixed  (like  the  melting  point  of 
solids),  but  depends  entirely  upon  a  particular  circumstance, — the  degree  of  pressure 
to  which  the  liquid  is  at  the  time  subject.  Liquids  are  in  general  subject  to  the 
pressure  of  the  atmosphere ;  for  although  the  air  is  an  exceedingly  light  substance, 
being  815  times  lighter  than  water,  yet  by  reason  of  its  great  quantity  and  height, 
it  comes  to  weigh  with  considerable  force  upon  the  earth.  This  is  called  the  atmo- 
spheric pressure,  and  amounts  to  about  fifteen  pounds  upon  each  square  inch  of 
surface.  The  force  with  which  air  presses  upon  a  man  of  ordinary  size  has  been 
estimated  at  fifty  tons;  yet,  from  all  the  cavities  of  the  animal  frame  being  filled 
with  equally  elastic  air,  we  support  this  great  pressure  without  being  sensible  of  it; 
indeed,  we  should  suffer  the  greatest  inconvenience  from  its  sudden  removal.  Now 
the  pressure  of  the  atmosphere  is  not  always  the  same  at  the  same  place,  but  is 
found  by  the  barometer  to  vary  within  the  limits  of  one-tenth  of  the  whole  pressure. 
This  difference  affects  the  boiling  point  to  the  extent  of  4£  degrees.  Thus,  when 
the  height  of  the  mercury  in  the  barometer  is  expressed  by  the  numbers  in  the 
first  column,  water  boils  at  the  temperatures  placed  against  them  in  the  second 
column. 


VAPORIZATION.  65 

Barometer  in  inches  of  mercury.  Water  boils. 

27-74 208° 

28-29 209 

28-84  210 

29-41  211 

29-92  212 

30-6 213 

On  this  account  the  pressure  of  the  atmosphere  must  be  attended  to  in  fixing  the 
boiling  point  of  water  on  thermometers.  Water  boils  at  212°  only  when  the  pres- 
sure of  the  atmosphere  is  equivalent  to  a  column  of  29-92  inches  of  mercury. 

The  pressure  of  the  atmosphere  will  be  greatest  at  the  level  of  the  sea,  and  will 
diminish  as  we  ascend  to  any  height  above  it,  for  then  we  have  less  of  the  atmo- 
sphere above  and  pressing  upon  us,  part  of  it  being  below  us.  Hence,  water  boils 
on  the  tops  of  mountains  at  a  considerably  lower  temperature  than  at  their  bases. 
On  the  top  of  Mont  Blanc,  which  is  the  pinnacle  of  Europe,  water  was  observed  by 
Saussure  to  boil  at  184°.  In  deep  pits,  on  the  other  hand,  water  requires  a  higher 
temperature  to  boil  it  than  at  the  surface  of  the  earth.  An  instrument  has  been 
constructed  for  ascertaining  the  heights  of  mountains  on  this  principle.  It  consists 
essentially  of  a  thermometer,  graduated  with  great  care  about  the  boiling  point  of 
water,  by  means  of  which  the  temperature  at  which  water  boils  at  different  altitudes 
can  be  ascertained  with  minute  accuracy.  A  difference  of  one  degree  of  temperature 
is  occasioned  by  an  ascent  of  about  550  feet,  and  the  depression  of  the  boiling  point 
is  accurately  proportional  to  the  elevation  above  the  earth's  surface,  according  to  the 
observations  of  Prof.  Forbes  (Edinburgh  Phil.  Trans,  xv.  409). l 

When  the  pressure  on  liquids  is  removed  by  artificial  means,  they  boil  at  greatly 
reduced  temperatures.  This  may  be  done  by  placing  them  under  the  receiver  of  an 
air-pump,  and  exhausting.  When  the  whole  air  is  withdrawn,  liquids  in  general 
boil  at  about  145°  under  the  temperature  which  they  require  to  make  them  boil 
when  subject  to  the  atmospheric  pressure.  In  a  good  vacuum  water  will  boil  at  67°. 
This  fact  is  also  illustrated  by  a  simple  experiment  which  any  one  may  perform.  A, 
flask,  containing  boiling  water,  is  closed  with  a  cork,  while  the  upper  part  is  filled 
with  steam.  The  boiling  in  the  flask  may  be  renewed  by  plunging  it  into  cold 
water;  and  the  colder  the  water  the  brisker  will  the  ebullition  become.  But  the 
boiling  is  instantly  checked  by  removing  the  flask  from  the  cold  water  and  immers- 
ing it  in  very  hot  water.  On  corking  the  flask  the  ebullition  ceased  from  the  pres- 
sure exerted  by  the  confined  steam  upon  the  surface  of  the  water;  but  on  plunging 
the  flask  into  cold  water,  the  steam  was  condensed,  and  the  water  began  to  boil 
under  the  reduced  pressure.  On  removing  the  flask  to  the  hot 
water,  the  steam  above  ceased  to  be  condensed,  and  by  its  pres-  FlG<  2^- 

sure  stopped  the  boiling.  On  the  other  hand,  in  a  Papin's  di- 
gester, which  is  a  tight  and  strong  kettle  with  a  safety  valve, 
water  may  be  raised  to  3  or  400°  without  ebullition :  but  the 
instant  that  this  great  pressure  is  removed,  the  boiling  com- 
mences with  prodigious  violence. 

The  facility  with  which  liquids  boil  under  reduced  pressure  is 
frequently  taken  advantage  of  in  the  arts,  in  concentrating  liquors 
which  would  be  injured  in  flavour  or  colour  by  the  heat  necessary 
to  boil  them  under  the  pressure  of  the  atmosphere.  Mr.  Howard 
applied  this  principle  in  concentrating  the  syrup  of  sugar,  which 
is  apt  to  be  browned  when  made  to  boil  under  the  usual  pressure. 
He  thus  boiled  syrup  at  150°,  applying  heat  to  it  in  a  pan  co- 
vered by  an  air-tight  lid,  and  pumping  off  the  air  and  steam  from  the  upper  part 

1  For  the  most  recent  minute  determinations  of  the  boiling  point  of  water,  under  varia- 
tions of  atmospheric  pressure,  see  the  memoir  of  M.  Regnault;  Ann.  de  Chimie,  &c.,  3  se'rie, 
t.  xiv.  p.  196.     A  simple  portable  apparatus  for  the  experiment  is  also  described  there. 
5 


DO  VAPORIZATION. 

of  the  pan  by  means  of  a  steam-engine.  This  was  the  most  essential  part  of  his 
patent  process,  by  which  nearly  the  whole  of  the  loaf  sugar  consumed  in  this  country 
has  been  manufactured  for  many  years. 

In  the  same  apparatus  vegetable  infusions  may  be  inspissated,  or  reduced  to  the 
state  of  extracts,  for  medical  purposes,  with  great  advantage.  When  an  extract  is 
prepared  in  the  ordinary  way,  by  boiling  down  an  infusion  or  expressed  juice  in  an 
open  vessel  under  atmospheric  pressure,  a  considerable  and  variable  proportion  of  the 
active  principle  is  always  destroyed  by  the  high  temperature  and  exposure  to  the 
air.  But  the  extract  is  not  injured  when  the  infusion  or  juice  is  evaporated  at  a 
low  temperature,  and  without  access  of  air,  and  is  generally  found  to  be  a  more  active 
medicine. 

The  temperatures  at  which  different  liquids  are  converted  into  vapour  are  exceed- 
ingly various  j  but  other  things  remaining  the  same,  the  boiling  temperature  is  con- 
stant for  any  particular  liquid.  The  following  table  exhibits  the  boiling  points  of  a 
tew  liquids,  in  which  that  point  has  been  determined  with  precision :  — 

Boiling  point. 

Hydrochloric  ether 52° 

Ether 96 

Sulphuret  of  carbon 118 

Ammonia  (sp.  gr.  0-945) 140 

Alcohol 173 

Water 212 

Nitric  acid  (sp.  g.  1-42) 248 

Crystallized  chloride  of  calcium 302 

Oil  of  turpentine 314 

Naphtha 320 

Phosphorus 554 

Sulphuric  acid  (sp.  gr.  1-843) 620 

Whale  oil 630 

Mercury 662 

The  boiling  point  of  water  is  uniformly  elevated  by  the  solution  of  salts  in  the 
fluid ;  but  much  more  so  by  some  salts  than  others.  Tables  have  been  constructed 
of  the  boiling  points  of  saline  liquors,  which  are  of  useful  application  when  it  is 
wished  to  maintain  a  steady  temperature  somewhat  above  212°.  Thus,  water  satu- 
rated with  common  salt  (100  water  to  30  salt),  boils  at  224° ;  saturated  with  nitrate 
of  potash  (100  water  to  74  salt),  it  boils  at  238° ;  saturated  cold  with  chloride  of 
calcium,  at  264°. 

When  steam  from  water  is  confined,  it  increases  in  temperature,  and  acquires 
great  force ;  and  the  experiment  can  only  be  performed  with  safety  in  a  boiler  pos- 
sessed of  a  safety-valve.  This  is  a  small  lid  in  the  upper  part  of  the  boiler,  properly 
loaded,  according  to  the  force  of  the  steam  to  be  generated.  The  steam  of  boiling 
water  occasions*  a  severe  scald,  if  allowed  to  condense  upon  the  body.  But  when 
steam  from  water  under  pressure,  or  "high  pressure"  steam,  which  maybe  of  a 
much  higher  temperature  than  boiling  water,  issues  into  the  air,  the  hand  may  be 
directly  exposed  to  it  with  impunity ;  and  a  thermometer  placed  in  it  shows  that  its 
temperature  is  greatly  below  that  of  boiling  water.  This  singular  property  of  high 
pressure  steam  is  connected  with  the  great  expansion  which  it  undergoes  on  escaping 
into  the  air  from  the  vessel  in  which  it  was  confined ;  elastic  bodies  having  a  ten- 
dency, when  escaping  from  a  state  of  compression,  to  fly  asunder,  not,  only  to  their 
original  dimensions,  but  beyond  them.  The  steam  is  greatly  expanded,  and  at  the 
same  time  mixed  with  air,  which  prevents  it  from  afterwards  collapsing.  Now,  after 
being  incorporated  with  several  times  its  bulk  of  air,  steam  is  not  easily  condensed, 
but  becomes  low-pressure  steam,  and  may  have  its  condensing  point  reduced  from 
above  212°  to  120°  or  130°.  Hence  the  heat  which  it  is  capable  of  communicating, 
while  condensing  upon  the  hand  held  in  it,  is  of  much  less  intensity  than  that  of 
ordinary  steam,  and  inadequate  to  occasion  scalding. 


VAPORIZATION. 


67 


Steam,  when  heated  by  itself,  apart  from  the  liquid  which  produced  it,  does  not 
possess  a  greater  elasticity  than  an  equal  bulk  of  air  confined  and  heated  to  the 
same  degree,  and  may  be  heated  to  the  temperature  at  which  the  containing  vessel 
becomes  red  hot,  without  acquiring  great  elastic  force.  But  if  water  be  present, 
then  more  and  more  steam  continues  to  rise,  adding  its  elastic  force  to  that  of  the 
vapour  previously  existing,  so  that  the  pressure  becomes  excessive. 

The  elastic  force  of  steam  at  temperatures  above 
212°  is  determined  by  heating  water  in  a  stout  glo- 
bular vessel  containing  mercury,  m,  (see  fig.  23,) 
and  water,  w,  and  having  a  long  glass  tube,  1 t, 
screwed  into  it,  open  at  both  ends,  and  dipping  into 
the  mercury,  with  a  scale,  a,  divided  into  inches, 
applied  to  it.  The  globular  vessel  has  two  other 
openings,  into  one  of  which  a  stopcock,  b,  is  screwed, 
and  into  the  other  thermometer,  /,  having  its  bulb 
within  the  globe.  The  water  is  boiled  in  this  ves- 
sel for  some  time,  with  the  stopcock  open  so  as  to 
expel  all  the  air.  On  shutting  the  stopcock,  and 
continuing  the  heat,  the  temperature  of  the  inte- 
rior, as  indicated  by  the  thermometer,  now  rises 
above  212°,  at  which  it  was  stationary  while  the 
steam  generated  was  allowed  to  escape.  The  steam 
in  the  upper  part  of  the  globe  becomes  denser, 
more  and  more  steam  being  produced,  and  forces 
the  mercury  to  ascend  in  the  gauge  tube,  ty  to  a 
height  proportional  to  the  elastic  force  of  the  steam. 
The  height  of  the  mercurial  column  is  taken  to 
express  the  elastic  force  or  pressure  of  the  steam 
produced  at  any  particular  temperature  above  212°. 
The  weight  of  the  atmosphere  itself  is  equivalent 
to  a  column  of  mercury  of  30  inches,  and  this  pres- 
sure has  been  overcome  by  the  steam  at  212°, 
before  it  began  to  act  upon  the  mercurial  gauge. 
For  every  thirty  inches  that  the  mercury  is  forced 
up  in  the  gauge  tube  by  the  steam,  it  is  said  to 
have  the  pressure  or  elastic  force  of  another  atmo- 
sphere. Thus,  when  the  mercury  in  the  tube 
stands  at  thirty  inches,  the  steam  is  said  to  be  of 
two  atmospheres ;  at  45  inches,  of  two  and  a  half 
atmospheres;  at  60  inches,  of  three  atmospheres, 
and  so  on. 

Experiments  have  been  made  on  the  elastic  force  of  steam  by  Professor  Robison, 
Mr.  Southern,  Mr.  Watt,  and  others  j  but  all  preceding  results  have  been  superseded 
by  those  of  a  commission  of  the  French  Academy,  consisting  of  MM.  Dulong  and 
Arago,  appointed  by  the  French  government  to  investigate  the  subject,  from  its 
importance  in  connexion  with  the  steam  engine  (Annales  de  Chimie,  &c.  2  s4r. 
t.  xliii.  p.  74).  Their  results,  which  are  expressed  in  the  following  table, 
were  obtained  by  experiment,  up  to  a  pressure  of  25  atmospheres.  The  higher 
pressures  were  calculated  by  extending  the  progression  observed  at  lower  tempe- 
ratures :  — 


68 


VAPORIZATION. 


Elasticity  of  Steam 

taking  Atmospheric 

Pressure  as  Unity. 

1 


Temp.  Fahr. 


212.0 
1£  ............................  233.96 

2  ............................  250.52 

2£  ............................  263.84 

3  ............................  275.18 

3£  ............................  285.08 

4  ............................  293.72 

4J  ............................  300.28 

5  ............................  307.5 

5£...  .........................  314.24 

6  ............................  320.36 

6£  ............................  326.26 

7  ............................  331.20 

1\  ............................  336.50 

8  ............................  341.78 

9  ............................  350.78 

10  ............................  358.28 

11  ............................  366.85 

12  ............................  374.00 


Elasticity  of  Steam 

taking  Atmospheric  Temp.  Fahr 

Pressure  as  Unity. 

13 386.66 

14 386.94 

15 392.46 

16 398.48 

17 40382 

18 408.92 

19 413.78 

20 418.46 

21 422.96 

22 427.28 

23 431.42 

24 435.56 

25 439.34 

30 457.16 

35 472.73 

40 486.59 

45 499.14 

50 510.60 


Some  curious  experiments  were  made  by  M.  Cagniard  de  la  Tour  on  the  vapour 
from  various  liquids  at  very  high  temperatures,  and  under  great  pressures.  He 
filled  a  small  glass  tube  in  part  with  ether,  alcohol,  or  water,  and  sealed  it  her- 
metically. The  tube  was  then  exposed  to  heat,  till  the  liquid  passed  entirely  into 
vapour.  Ether  became  gaseous  in  a  space  scarcely  double  its  volume  at  a  tempera- 
ture of  320°,  and  the  vapour  exerted  a  pressure  of  no  more  than  38  atmospheres. 
Alcohol  became  gaseous  in  a  space  about  thrice  its  volume  at  the  temperature  of 
404$°,  with  a  pressure  of  about  139  atmospheres.  Water  acted  chemically  on  the 
glass,  and  broke  it  ;  but  adding  a  little  carbonate  of  soda  to  it,  the  water  became 
gaseous  in  a  space  four  times  its  volume  at  the  temperature  at  which  zinc  melts,  or 
about  648°.  These  results  are  singular,  in  so  far  as  the  pressure  or  elastic  force  of 
the  vapours  proves  to  be  much  smaller  than  that  which  corresponds  with  their  cal- 
culated density.  It  thus  appears  that  highly  compressed  vapours  lose  a  portion  of 
their  elasticity,  or  yield  more  to  a  certain  pressure  than  air,  by  calculation,  would  do. 

A  measure  is  obtained  of  the  quantity  of  latent  heat  in  steam  by  observing  the 
degree  to  which  it  heats  up  a  mass  of  water  when  condensed  in  it.  Cold  water  is 
easily  made  to  boil  by  placing  the  open  end  of  a  pipe  from  a  steam-boiler  in  it,  and 
causing  the  steam  to  blow  through  it  for  a  sufficient  time.  If  a  measured  quantity 
of  water  at  32°,  amounting  to  11  cubic  inches,  is  heated  up  to  212°  in  this  manner, 
it  is  found  that  the  volume  is  increased  to  13  cubic  inches  by  the  condensed  steam. 
Consequently,  11  cubic  inches  of  water  are  heated  up  from  32°  to  212°,  or  one 
hundred  and  eighty  degrees,  by  2  cubic  inches  of  water  in  the  form  of  steam.  But 
if,  for  comparison,  2  cubic  inches  of  boiling  hot  water  be  substituted  for  the  steam, 
and  added  to  11  cubic  inches  of  cold  water,  the  temperature  of  the  latter  is  raised 
no  more  than  about  twenty-eight  degrees.  In  both  experiments,  however,  the  tem- 
perature of  the  steam,  and  of  the  boiling  water  added,  was  the  same,  or  212°  ;  the 
difference  of  their  heating  effects  depends  entirely  upon  the  latent  heat  which  the 
former  possesses,  in  addition  to  its  sensible  temperature,  and  abandons  to  the  cold 
water  on  condensing. 

In  the  condensing  experiment  2  cubic  inches  of  water  in  the  form  of  steam  raised 
the  temperature  of  11  cubic  inches  of  water  one  hundred  and  eighty  degrees,  or  1 
of  steam  raised  the  temperature  of  5£  of  water  to  that  amount.  As  it  follows  that 
one  part  of  steam  would  heat  one  part  of  water,  5£  times  180,  or  990  degrees,  it 
appears  that  steam  possesses  as  much  heat  latent  as  might  raise  its  own  temperature 
to  that  amount  on  becoming  sensible. 

The  latest,  and  probably  most  exact,  determinations  which  we  possess  of  the 
'atent  heat  of  the  vapours  of  water,  and  other  liquids,  are  those  of  M.  Brix,  of 


VAPORIZATION. 


69 


FIQ.  24. 


Berlin,  (Poggendorff's  Annalen,  Iv.)  He  employed  the  apparatus  represented  in 
Fig.  24.  The  refrigeratory  to  contain  the  cold  condensing  water  consists  of  a 
cylindrical  vessel,  A  C,  3  inches  in  diameter  and  3  inches  deep.  The  steam  from 
a  small  retort  E,  does  not  pass  directly  into 
the  water  of  the  refrigeratory,  but  is  con- 
veyed by  the  spout  M  into  an  inner  hollow 
cylinder  E  G,  of  a  ring-formed  basis,  which 
has  an  opening  into  the  atmosphere  by  the 
tube  L,  by  which  the  air  it  contains  finds 
vent  on  the  arrival  of  the  vapour.  The 
condensing  water  is  agitated  by  means  of  a 
thin  disc  of  metal  B,  attached  to  a  vertical 
rod,  the  upper  end  of  which  passes  through 
the  cover  of  the  refrigeratory.  A  known 
quantity  of  cold  water  being  introduced  into 
this  refrigeratory,  its  temperature  is  accu- 
rately observed  by  the  including  thermo- 
meter. In  conducting  the  experiments  it 
was  arranged  that  the  temperature  of  the 
condensing  water  should  at  first  be  a  few 
degrees  below  that  of  the  atmosphere,  and 
vapour  was  thrown  into  the  inner  receiver 
by  boiling  a  weighed  portion  of  liquid  hi  R, 
till  the  temperature  of  the  condensing  water 
rose  as  many  degrees  above  that  point.  The 
weight  of  liquid  distilled  is  then  found  by 
weighing  the  retort  R  with  what  remains  in 
it,  and  ascertaining  the  loss ;  and  the  latent 
heat  calculated  by  increasing  the  rise  of 
temperature  observed  in  the  refrigeratory,  in  the  same  proportion  as  the  weight  of 
the  condensing  water  in  the  refrigeratory  exceeds  that  of  the  liquid  distilled  from 
the  retort. 

The  following  are  the  mean  results  which  M.  Brix  obtained  by  this  method, 
several  experiments  being  made  upon  each  liquid : — 

Equal  weights.  Latent  heat  of  vapour. 

Water 972     degrees. 

Alcohol 385.2       « 

Ether 162  " 

Oil  of  turpentine 133.2       " 

Oil  of  lemons 144          " 

Despretz,  who  at  an  earlier  period  had  also  made  very  careful  experiments  on 
several  of  the  same  liquids,  gave  the  following  estimations  of  latent  heat : — 

Equal  weights.  Latent  heat  of  vapour. 

Water ....^ 955.8  degrees. 

Alcohol 374.4       " 

Ether 174.6       " 

Oil  of  turpentine 138.6       " 

Dulong  obtained  for  the  latent  heat  of  the  vapour  of  water  977.4  degrees. 

It  is  to  be  further  remarked,  that  equal  weights  of  these  liquids  yield  very  dif- 
ferent volumes  of  vapour,  owing  to  the  different  specific  gravities  of  the  latter ;  and 
the  densest  vapours  appear  to  have  generally  the  least  latent  heat.  According  to 
the  table  of  M.  Brix,  the  latent  heat?  of  the  vapour  of  water  is  972  degrees,  while 
that  of  the  vapour  of  alcohol  is  385  degrees :  or  water-vapour  has  for  equal  weights 
about  2.5  times  more  latent  heat  than  alcohol-vapour.  The  specific  gravity  of 
alcohol- vapour,  on  the  other  hand,  is  about  2.5  times  greater  than  that  of  water- 


70  VAPORIZATION. 

vapour,  taking  the  former  at  1589.4,  and  the  latter  at  622 ;  consequently,  equal 
volumes  of  these  two  vapours  possess  equal  quantities  of  latent  heat. 

If  the  latent  heat  of  different  vapours  be  proportional  to  their  volume,  as  these 
numbers  seem  to  indicate,  the  same  bulk  of  vapour  will  be  produced  from  all 
liquids  with  the  same  expenditure  of  heat;  and  hence  there  can  be  no  advantage 
in  substituting  any  other  liquid  for  water,  as  a  source  of  vapour,  in  the  steam- 
engine. 

The  latent  heat  of  the  vapour  of  water  itself  increases  with  its  rarity  at  low  tem- 
peratures, and  diminishes  with  its  increasing  density  at  high  temperatures.  Water 
may  easily  be  made  to  boil  in  a  vacuum  at  the  temperature  of  100°,  but  the  steam 
produced  is  much  more  expanded  and  rare  than  that  produced  at  212°,  and  has  a 
greater  latent  heat.  Hence  there  is  no  fuel  saved  by  distilling  in  vacuo.  It  has 
been  shown,  by  Mr.  Sharpe,  of  Manchester,  that  whatever  be  the  temperature  of 
steam,  from  212°  upwards,  if  the  same  weight  of  it  be  condensed  by  water,  the 
temperature  of  the  water  will  always  be  raised  the  same  number  of  degrees  j  or  the 
latent  and  sensible  heat  of  steam,  added  together,  amount  to  a  constant  quantity. 
We  may  hence  deduce  a  simple  rule  for  ascertaining  the  latent  heat  of  steam  at  any 
particular  temperature.  The  sensible  heat  of  steam  at  212°  maybe  assumed  at  212 
degrees,  neglecting  the  heat  which  it  has  below  zero  Fahrenheit,  and  the  latent  heat 
of  such  steam  is  972  degrees,  of  which  the  sum  is  1184  degrees.  To  calculate  the 
latent  heat  of  steam  at  any  particular  temperature  above  212°,  subtract  the  sensible 
heat  from  this  constant  number  1184.  Thus  the  latent  heat  of  steam  at  300°  is 
1184 — 300,  or  884  degrees.  The  same  relation  between  the  latent  and  sensible 
heat  of  vapour  appears  to  exist  at  temperatures  below  212°,  and  the  latent 
heat  of  vapour,  below  that  temperature,  may  therefore  be  calculated  by  the  same 
rule.* 

Latent  heat  of 
Temperature.  Equal  Weights  of  Steam. 

0° 1184  degrees. 

32° 1152 

100° 1084 

150° 1034 

212° T 972 

250° 934 

The  latent  heat  of  other  vapours,  such  as  that  of  alcohol,  ether,  and  oil  of  turpen- 
tine, has  been  found  by  Despretz  to  vary  according  to  the  same  law. 

From  the  large  quantity  of  heat  which  steam  possesses,  and  the  facility  with 
which  it  imparts  it  to  bodies  colder  than  itself,  it  is  much  used  as  a  vehicle  for  the 
communication  of  heat.  The  temperature  of  bodies  heated  by  it  can  never  be  raised 
above  212° ;  so  that  it  is  much  preferable  to  an  open  fire  for  heating  extracts  and 
organic  substances,  all  danger  of  empyreuma  being  avoided.  When  applied  to  the 
cooking  of  food,  the  steam  is  generally  conveyed  into  a  shallow  tin  box,  in  the  upper 
surface  of  which  are  cut  several  round  apertures,  of  such  sizes  as  admit  exactly  the 
pans  with  the  materials  to  be  heated.  The  pans  are  thus  surrounded  by  steam, 
which  condenses  upon  them  with  great  rapidity,  till  their  temperature  rises  to  within 
a  degree  or  two  of  212°.  For  some  purposes,  a  pan  containing  the  matters  to  be 
heated  is  placed  within  another  and  similar  larger  one,  and  steam  admitted  between 
the  two  vessels.  Manufactured  goods  also  are  often  dried  by  passing  them  once 
over  a  series  of  metallic  cylinders,  or  of  square  boxes  filled  with  steam.  Factories 
are  now  very  generally  heated  by  steam,  conveyed  through  them  in  cast-iron  pipes. 
It  has  been  found  by  practice  that  the  boiler  to  produce  steam  for  this  purpose  must 
have  one  cubic  foot  of  capacity  for  every  2,000  cubic  feet  of  space  to  be  heated  to  a 
temperature  of  70°  or  80° ;  and  that  of  the  conducting  steam  pipe,  one  square  foot 
of  surface  must  be  exposed  for  every  200  cubic  feet  of  space  to  be  heated. 

The  expansion  of  water  into  steam  is  used  as  a  moving  power  in  the  steam 
engine.  The  application  is  made  upon  two  different  principles,  both  of  which  may 

*  [See  Supplement,  p.  643.] 


VAPORIZATION. 


71 


be  illustrated  by  the  little  instrument  depicted  on  the  margin.  FiQ-  25. 

It  consists  of  a  glass  tube,  about  an  inch  in  diameter,  slightly 
expanded  into  a  bulbous  form  at  one  extremity,  and  open  at 
the  other  (fig.  25) ;  a  piston  is  made,  by  twisting  tow  about 
the  end  of  a  piece  of  straight  wire,  which  must  be  fitted  tightly 
in  the  tube  by  the  use  of  grease.  Upon  heating  a  little  water 
in  the  bulb  below  piston  p,  steam  is  generated,  which  raises 
the  piston  to  the  top  of  the  cylinder.  Here  the  simple  elastic 
form  of  the  steam  is  the  moving  power ;  and  in  this  manner 
steam  is  employed  in  the  high  pressure  engine.  The  greater 
the  load  upon  the  piston,  and  the  more  the  steam  is  confined, 
the  greater  does  its  elastic  force  become.  Again  :  the  piston 
being  at  the  top  of  the  cylinder,  if  we  condense  the  steam 
with  which  the  cylinder  is  filled,  by  plunging  the  bulb  in 
cold  water,  a  vacuum  is  produced  below  the  piston,  which  is 
now  forced  down  to  the  bottom  of  the  cylinder  by  the  pres- 
sure of  the  atmosphere.  In  this  second  part  of  the  experiment,  the  power  is 
acquired  by  the  condensation  of  the  steam,  or  the  production  of  a  vacuum ;  and 
this  is  the  principle  of  the  common  condensing  engine.  In  the  first  efficient  form 
of  the  condensing  engine  (that  of  Newcomen)  the  steam  was  condensed  by  injecting 
a  little  cold  water  below  the  piston,  which  then  descended,  from  the  pressure  of  the 
atmosphere  upon  its  upper  surface,  exactly  as  in  the  instrument.  But  Mr.  Watt 
introduced  two  capital  improvements  into  the  construction  of  the  condensing  engine  j 
the  first  was,  the  admitting  steam,  instead  of  atmospheric  air,  to  press  down  the 
piston  through  the  vacuous  cylinder,  which  steam  itself  could  afterwards  be  con- 
densed, and  a  vacuum  produced  above  the  piston,  of  which  the  same  advantage 
might  be  taken  as  of  the  vacuum  below  the  piston.  The  second  was,  the  effecting 
the  condensation  of  the  steam,  not  in  the  cylinder  itself,  which  was  thereby  greatly 
cooled,  and  occasioned  the  waste  of  much  steam  in  being  heated  again  at  every 
stroke ;  but  in  a  separate  air-tight  chamber,  called  the  condenser,  which  kept  cool 
and  vacuous.  Into  this  condenser  the  steam  is  allowed  to  escape  from  above  and 
from  below  the  piston  alternately,  and  a  vacuum  is  obtained  without  ever  reducing 
the  temperature  of  the  cylinder  below  212°. 

A  third  improvement  in  the  employment  of  steam  as  a  moving  power  consists  in 
using  it  expansively;  a  mode  of  application  which  will  be  best  understood  by  being 
explained  in  a  particular  case.  Let  it  be  supposed  that  a  piston,  loaded  with  one 
ton,  is  raised  four  feet  by  filling  the  cylinder  in  which  it  moves  with  low-pressure 
steam,  or  steam  of  the  tension  of  one  atmosphere. 
An  equivalent  effect  may  be  produced  at  the  same 
expense  of  steam,  by  filling  one-fourth  of  the  cylin- 
der with  steam  of  the  tension  of  four  atmospheres, 
and  loading  the  piston  with  four  tons,  which  will 
be  raised  one  foot.  But  the  piston  being  raised  4.. 
one  foot  by  steam  of  four  atmospheres,  and  in  the 
position  represented  in  fig.  26,  the  supply  of  steam 
may  be  cut  off,  and  the  piston  will  continue  to  be 
elevated  in  the  cylinder  by  the  simple  expansion 
of  the  steam  below  it,  although  with  a  diminishing 
force.  When  the  piston  has  been  raised  another 
foot  in  the  cylinder,  or  two  feet  from  the  bottom,  ^ 
the  volume  of  the  steam  will  be  doubled,  and  its 
tension  consequently  reduced  from  four  to  |,  or 

two  atmospheres.    At  a  height  of  three  feet  in  the  1 

cylinder,  the  piston  will  have  steam  below  it  of  the 
tension  of  %  or  1|  atmosphere,  and  when  the  pis- 
ton is  elevated  four  feet,  or  reaches  the  top  of  the 


FIG.  -26. 


4.  or  1  atmoa. 


or2 


4  atmoa. 


72 


VAPORIZATION. 


FIG.  27. 


Fio.  28. 


cylinder,  the  tension  of  the  steam  below  it  will  still  be  £ ,  or  one  atmosphere.    The 
piston  has,  therefore,  been  raised  to  a  height  of  three  feet,  with  a  force  progressively 

diminishing  from  four  atmospheres  to  one, 
or  with  an  average  force  of  two  atmospheres, 
by  means  of  a  power  acquired  without  any 
consumption  of  steam ;  but  by  the  expansion 
merely  of  steam  that  had  already  produced  its 
usual  effect.1 

The  boiler  used  to  produce  the  steam  is 
constructed  of  different  forms.  The  cylinder 
boiler,  of  which  a  section  is  given  in  fig.  27,  was 
found  the  most  economical  for  the  great  steam- 
engines  at  the  Cornish  mines,  and  its  use  is 
extending  in  other  quarters.  It  consists  of 
two  cylinders,  one  within  the  other,  the 
smaller  cylinder  containing  the  fire,  and  the 
space  between  the  two  cylinders  being  occu- 
oied  by  the  water.  The  outer  cylinder  may  be  six  feet  in  diameter,  and  is  often 
Ifty  or  sixty  feet  in  length.  The  heated  air  from  the  fire,  after  traversing  the 

inner  cylinder,  is  conducted  under  the  boiler  by 
the  flues  0,  0,  before  it  is  conveyed  to  the 
chimney. 

In  the  locomotive  steam-engines,  where  the 
principal  object  is  to  generate  steam  in  a  small 
and  compact  apparatus  with  great  rapidity,  a 
different  construction  is  adopted.  Here  the 
boiler  consists  of  two  parts,  a  square  box  with 
a  double  casing  (of  which  a  section  or  end 
view  is  given  in  figure  28),  which  contains 
the  fire  f,  surrounded  by  a  thin  shell  of 
water  in  the  space  e  e,  between  the  casings; 
and  a  cylinder  «,  through  the  lower  part  of 
which  pass  a  number  of  copper  tubes  of  small 
size,  which  communicate  at  one  end  with  the 
fire-box,  and  at  the  other  with  the  chimney,  and 
form  a  passage  for  the  heated  air  from  the  fire 
to  the  chimney.  By  means  of  these  tubes,  the 
object  is  accomplished  of  exposing  to  a  source 
of  heat  the  greatest  possible  quantity  of  surface 
in  contact  with  the  water.  (See  Dr.  Lardner 
on  the  Steam-Engine  :  Cabinet  Cyclopoedia.) 

The  subject  of  distillation  is  a  natural  sequel 
to  vaporization ;  but  it  is  unnecessary  to  enter 
into  much  detail.  The  principal  point  to  be 
attended  to  is  the  most  efficient  mode  of  con- 
densing the  vapour.  Figure  29  represents  the 
ordinary  arrangement  in  distilling  a  liquid  from 
a  retort  a,  and  condensing  the  vapour  in  a  glass 
flask  b,  which  is  kept  cool  by  water  dropping 
upon  it  from  a  funnel  above,  c.  The  condensing 
flask  is  covered  by  bibulous  paper,  so  that  the 

be  made 


o     o 


o     o     O 


o     o 


Fm.  29. 


water   falling  upon    it   may 


to  pass 


1  For  the  mathematical  theory  of  the  steam-engine,  see  a  Memoir  on  the  Motive  Power  of 
Heat,  by  E.  Clapeyron,  Taylor's  Scientific  Memoirs,  vol.  i.  p.  347  ;  a  Memoir  on  the  Heat 
and  Elasticity  of  Gases  and  Vapours,  by  C.  Holtzmann,  ibid.  vol.  iv.  p.  109;  Experiments 
on  the  Expansive  Force  of  Steam,  by  Prof.  G.  Magnus,  ibid.  p.  218  ;  and  on  the  Force  requi- 
site for  the  Production  of  Vapours,  by  the  same,  ibid.  p.  235. 


VAPORIZATION.  73 

equally  over  its  surface,  and  it  is  supported  in  a  basin  likewise  containing  cold 


water. 


But  a  much  superior  instrument  to  the  condensing  flask  is  the  condensing  tube 
of  Professor  Liebig  (fig.  30).     This  is  a  plain  glass  tube,  1 1,  about  thirty  inches  in 


Fio.  30. 


length,  and  one  inch  internal  diameter,  which  is  enclosed  in  a  larger  tube,  b,  of 
brass  or  tin-plate,  about  two  feet  long  and  two  inches  in  diameter,  the  ends  of 
which  are  closed  by  perforated  corks,  made  fast  by  a  mixture  of  white  and  red  lead 
with  a  drying  oil,  a  resinous  cement  being  useless  for  such  a  junction.  Or,  the 
lower  opening  may  be  contracted  by  a  collar  of  tin-plate,  not  much  wider  than  the 
glass  tube,  and  the  two  be  united  by  a  strong  ring  of  sheet  caoutchouc.  A  constant 
supply  of  cold  condensing  water  from  a  vessel  a  is  introduced  into  the  space  between 
the  two  tubes,  being  conveyed  to  the  lower  part  of  the  instrument  by  the  funnel 
and  tube  /,  and  flowing  out  from  the  upper  part  by  the  tube  j.  The  condensed 
liquid  drops  quite  cool  from  the  lower  extremity  of  the  glass  tube,  where  a  vessel 
c  is  placed  to  receive  it.  The  spiral  copper  tube  or  worm  which  is  used  for  conden- 
sing in  the  common  still  is  commonly  made  longer  than  is  necessary,  and,  from  its 
form,  cannot  be  examined  and  cleared  like  a  straight  tube.  Much  vapour  may  be 
condensed  by  a  small  extent  of  surface,  provided  it  is  kept  cold  by  an  ample  supply 
of  condensing  water. 

Both  the  outer  and  inner  tube 

81*  may  be  of  glass  in  the  condensing 

apparatus  which  has  been  described, 
and  then  the  small  tubes  to  bring 
and  carry  off  the  condensing  water 
may  be  made  to  pass  through  open- 
ings in  the  corks,  which  they  fit,  as 
represented  in  figure  31. 


EVAPORATION   IN   VACUO. 


Water  rises  rapidly  in  vapour  into  a  vacuous  space,  without  the  appearance  of 
ebullition,  at  all  temperatures,  even  at  32°,  and  greatly  lower.  Its  elastic  force  in- 
creases as  the  temperature  is  elevated,  till  at  212°  it  is  equal  to  that  of  the  atmo- 
sphere, or  capable  of  supporting  a  column  of  mercury  thirty  inches  in  height. 


VAPORIZATION. 


FIG.  32. 
432 


Various  other  solid  and  liquid  substances  emit  vapour  in 
similar  circumstances;  such  as  camphor,  alcohol,  ether,  and 
oil  of  turpentine.  Such  bodies  are  said  to  be  volatile,  and 
other  bodies,  such  as  marble,  the  metals,  &c.  which  do  not 
emit  a  sensible  vapour  at  the  temperature  of  the  air,  are  said 
to  be  fixed.  All  bodies  which  boil  at  low  temperatures 
belong,  to  the  volatile  class.  An  accurate  estimate  of  the 
volatility  of  different  bodies  is  obtained  by  determining  the 
elastic  force  of  the  vapour  which  they  emit  in  the  vacuous 
space  above  the  column  of  mercury  in  the  barometer.  If 
we  pass  up  a  bubble  of  air  into  the  vacuum  of  the  barome- 
ter, above  the  mercurial  column,  standing  at  the  time  at  a 
height  of  30  inches,  the  mercury  is  depressed,  we  may  sup- 
pose, to  the  level  of  29  inches,  or  by  one  inch.  This  would 
indicate  that  the  air,  by  rising  above  the  mercury,  has  been 
expanded  into  thirty  times  its  former  bulk,  or  that  the 
elastic  force  of  this  rare  air  is  equal  to  a  column  of  one 
inch  of  mercury.  The  elastic  force  of  vapour  is  estimated 
in  the  same  manner.  A  few  drops  of  the  liquid  operated 
upon  are  passed  up  into  the  vacuum  above  the  mercurial 
column,  which  is  depressed  in  proportion  to  the  elastic  force 
of  the  vapour.  The  depression  produced  by  various  liquids 
is  very  different,  as  illustrated  in  the  annexed  figure,  repre- 
senting four  barometer  tubes,  in  which  the  mercury  is  at  its 
proper  height  in  No.  1 ;  is  depressed  by  the  vapour  of 

'  '  water  of  the  temperature  60°  in  No.  2 ;  and  by  alcohol  and 

ether  at  the  same  temperature  in  Nos.  3  and  4  respectively. 

The  depression  of  the  mercurial  column  produced  by  water  at  every  degree  of 
temperature,  between  32°  and  212°,  was  first  determined  by  Dr.  Dalton,  afterwards 
by  M.  Kaemtz,  (Kaemtz,  Meteorology,  edited  by  C.  Walker,  p.  69),  and  again  quite 
recently  by  M.  Regnault,  (Annales  de  Chimie,  3d  ser.  t.  xi.  p.  333 ;  and  t.  xv.  p. 
139).  The  following  selected  observations  prove  that  the  elasticity  increases  at  a 
very  rapid  rate  with  the  temperature. 


VAPOUR  OF  WATER  IN  VACUO  (Regnault). 


Temperature. 


Tension  in  Millimeters  and  English 
inches  of  Mercury. 


Centig.  Fahr.  Millimeters.  English  Inches. 

—30°  —22°  0-365  0-0144 

—25°  —13°  0-553  0-0218 

—20°  —4°  0-841  0-0331 

—15°  —5°  1-284 0-0506 

—10°  14°  1-963  0-0818 

—5°  23°  3-004 0-1233 

0°  32°  4-600 0-1811 

5°  41°  6-534 0-2573 

10°  50°  9-165  0-3608 

16°  59°  12-699  0-5000, 

20°  68°  17-391  0-6847 

25°  77°  23-550 0-9272 

30°  86°  31-548 1-2421 

35°  95°  41-827  1-6468 

60°  140°  148-791  5-8583 

85°  185°  433-041  7-0488 

100°  212°  760-000 29-9220 

The  vapours  of  other  liquids  increase  in  density  and  elastic  force  with  the  tern- 


VAPORIZATION.  75 

perature,  as  well  as  the  vapour  of  water ;  but  each  vapour  appears  to  follow  a  rate 
of  progression  peculiar  to  itself.1 

The  assumption  of  latent  heat  by  such  vapours  is  evinced  in  some  processes  for 
producing  cold.  Water  may  be  frozen  by  the  evaporation  of  ether  in  the  air-pump, 
and  a  cold  produced  of  55  degrees  under  the  zero  of  Fahrenheit  by  the  evaporation 
of  that  fluid.  The  ether  vapour  derives  its  store  of  latent  heat  from  the  remaining 
fluid  and  contiguous  bodies,  which  being  robbed  of  their  heat,  suffer  a  great  refri- 
geration. To  sustain  the  evaporation  of  this  fluid,  it  is  necessary  to  withdraw  the 
vapour  as  it  is  produced  by  continual  pumping.  The  volatile  liquid,  sulphuret  of 
carbon,  substituted  for  ether,  produces  even  greater  effects. 

On  the  same  principle  is  founded  Leslie's  elegant  process  for  the  freezing  of  water 
by  its  own  evaporation,  within  the  exhausted  receiver  of  an  air-pump,  the  evapora- 
tion being  kept  up  by  the  absorbent  power  of  sulphuric  acid.  (Supp.  Encycloped. 
Britt.,  Art.  Cold).  A  little  water  in  a  cup  of  porous  stone-ware  is  supported  over  a 
,-,  00  shallow  basin  containing  sulphuric  acid  (fig.  33).  All 

±IG.  oo.  ,1      ,     •  .  i  IT- 

that  is  necessary  is  to  produce  a  good  exhaustion  at 
first :  the  processes  of  evaporation  and  absorption  then 
go  on  spontaneously,  in  an  uninterrupted  manner. 
Various  bodies,  which  have  a  powerful  attraction  for 
watery  vapour,  may  be  used  as  absorbents,  such  as 
parched  oatmeal,  the  powder  of  mouldering  whinstone, 
and  even  dry  sole  leather,  by  means  of  any  one  of  which  a  small  quantity  of 
water  may  be  frozen,  during  summer,  in  the  exhausted  receiver  of  an  air-pump.  No 
substance,  however,  is  superior,  in  this  respect,  to  concentrated  sulphuric  acid.  When 
this  liquid  becomes  too  dilute  to  act  powerfully  as  an  absorbent,  it  may  be  rendered 
again  fit  for  use,  by  boiling  it  and  driving  off  the  water.  Ice  might  be  procured  in 
quantity,  in  a  warm  climate,  by  this  process.  The  necessary  vacuum  would  be  most 
easily  commanded,  on  the  large  scale,  by  allowing  the  receivers  to  communicate  with 
a  strong  drum,  filled  with  steam  which  could  be  condensed. 

In  the  Cryophurus  of  Dr.  Wollaston,  water  is  also  frozen  by  its  own  evaporation. 
This  instrument  consists  of  two  glass  bulbs,  connected  by  a  tube,  and  containing  a 
„      o4  portion  of  water,  as  represented  in 

the  figure.  The  air  is  first  entirely 
expelled  from  the  instrument  by 
boiling  the  water,  in  both  bulbs,  at 
the  same  time,  and  allowing  the 
steam  to  escape  by  a  small  opening 
at  the  extremity  of  the  little  projecting  tube  e.  While  the  instrument  is  entirely 
filled  with  steam,  the  point  of  e  is  fused  by  the  blow-pipe  flame,  and  the  opening 
hermetically  closed.  In  experimenting  with  this  instrument,  the  water  is  all  poured 
into  one  bulb,  and  the  other,  or  empty  bulb,  placed  in  a  basin  containing  a  mixture 
of  ice  and  salt.  The  vapour  in  the  cooled  bulb  is  condensed,  but  its  place  is  sup- 
plied by  vapour  from  the  water  in  the  other  bulb.  A  rapid  evaporation  takes  place 
in  the  water  bulb,  and  condensation  in  the  empty  bulb,  till  the  water  in  the  former 
bulb  is  cooled  so  low  as  to  freeze.  The  instrument  derives  its  name  of  the  cryophorus, 
or  frost-bearer,  from  this  transference  of  the  cold  of  the  bulb  in  the  freezing  mixture 
to  the  bulb  at  a  distance  from  it. 

The  question  arises,  do  those  bodies  which  evaporate  at  a  moderate  temperature 
continue  to  evaporate  at  all  temperatures,  however  low.  The  opinion  has  prevailedt 

1  For  the  tension  of  the  vapour  of  mercury  at  different  temperatures,  see  a  memoir  of  M. 
Avogadro,  Annales  de  Chimie,  £c.,  t.  xlix.  p.  369.  For  other  vapours,  the  article  Dnmpfi 
in  the  Handworterbuch  der  Chemie,  &c.  of  Liebig,  Poggendorff,  and  Wohler;  and  the  me- 
moir by  Mr.  Faraday,  On  the  Liquefaction  and  Solidification  of  Bodies  generalb 
Gases,  (Philos.  Trans.  1845,  p.  155). 


76  VAPORIZATION". 

that  bodies  which  are  decidedly  vaporous  at  high  temperatures,  such  as  sulphuric 
acid  and  mercury,  never  cease  to  evolve  vapour,  however  far  their  temperature  may 
be  depressed,  although  the  quantity  emitted  becomes  less  and  less,  till  it  ceases  to 
be  appreciable  by  our  senses.  Even  fixed  bodies,  such  as  metals,  rocks,  &c.,  have 
been  supposed  to  allow  an  escape  of  their  substance  into  air  at  the  ordinary  temper- 
ature ;  and  hence  the  atmosphere  has  been  supposed  to  contain  traces  of  the  vapours 
of  all  the  bodies  with  which  it  is  in  contact.  Certain  researches  of  Mr.  Faraday, 
published  in  the  Philosophical  Transactions  for  1826,  on  the  existence  of  a  limit  to 
vaporization,  establish  the  opposite  conclusion.  Mercury  was  found  to  yield  a  small 
quantity  of  vapour  during  summer,  at  a  temperature  varying  from  60°  to  80°,  but 
in  winter  no  trace  of  vapour  could  be  detected.  Mr.  Faraday  has  proved  that 
several  chemical  agents,  which  may  be  volatized  by  a  heat  between  300°  and  400°, 
did  not  undergo  the  slightest  evaporation  when  kept  in  a  confined  space  with  water 
during  four  years. 

Bodies,  therefore,  cease  all  at  once  to  emit  vapour,  at  some  particular  temperature. 
In  mercury,  this  temperature  lies  between  40°  and  60°  Fahrenheit.  But  a  pro- 
gressive and  endless  diminution  of  vaporizing  power  is  certainly  more  natural  than 
an  abrupt  cessation.  What  puts  a  stop  to  vaporization  ?  it  may  be  asked.  Liquids, 
we  know,  have  a  certain  attraction  for  their  own  particles,  evinced  in  their  disposition 
to  collect  into  drops.  The  particles  of  solids  are  attracted  more  powerfully,  and 
cohere  strongly  together.  Mr.  Faraday  is  of  opinion,  that  when  the  vaporizing 
power  becomes  weak,  at  low  temperatures,  it  may  be  overcome  and  negatived  com- 
pletely by  this  cohesive  attraction,  and  no  escape  of  particles  in  the  vaporous  form 
be  permitted. 

This  supposition  is  conformable  with  the  views  of  corpuscular  philosophy  which 
were  entertained  by  Laplace.  According  to  that  profound  philosopher,  the  form  of 
aggregation  which  a  body  affects  depends  upon  the  mutual  relation  of  three  forces : 
1.  The  attraction  of  each  particle  for  the  other  particles  which  surround  it,  which 
induces  them  to  approach  as  near  as  possible  to  each  other.  2.  The  attraction  of 
each  particle  for  the  heat  which  surrounds  the  other  particles  in  its  neighbourhood. 
3.  The  repulsion  between  the  heat  which  surrounds  each  particle,  and  that  which 
surrounds  the  neighbouring  particles  —  a  force  which  tends  to  disunite  the  particles 
of  bodies.  When  the  first  of  these  forces  prevails,  the  body  is  solid ;  if  the  quantity 
of  heat  augments,  the  second  force  becomes  dominant,  the  particles  then  move 
among  each  other  with  facility,  and  the  body  is  liquid.  While  this  is  the  case,  the 
particles  are  still  retained  by  the  attraction  for  the  neighbouring  heat,  within  the 
limits  of  the  space  which  the  body  formerly  occupied,  except  at  the  surface,  where 
the  heat  separates  them,  that  is  to  say,  occasions  evaporation,  till  the  influence  of 
some  pressure  prevents  the  separation  from  being  effected.  When  the  lieat  increases 
to  such  a  degree  that  the  reciprocal  repulsive  force  prevails  over  the  attraction  of  the 
particles  for  one  another,  they  disperse  in  all  directions,  as  long  as  they  meet  no 
obstacle,  and  the  body  assumes  the  gaseous  form.  Berzelius  adds  the  reflection,  that 
if,  in  that  gaseous  state  into  which  Cagnard  de  la  Tour  reduced  some  volatile  liquids, 
the  pressure  does  not  correspond  with  the  result  of  calculation,  that  difference  may 
depend  on  this :  that,  as  the  particles  have  not  an  opportunity  to  recede  much,  the 
two  first  forces  continue  always  to  act,  and  oppose  the  tension  of  the  gas,  which  does 
not  establish  itself  in  all  its  power  unless  when  the  particles  are  so  distant  from 
each  other  as  to  be  out  of  the  sphere  of  the  influence  of  these  forces.  (Trait£  de 
Chimie,  par  J.  J.  Berzelius,  t.  i.  p.  85). 


GASES. 


77 


GASES. 


Permanent  gases,  such  as  atmospheric  air,  unquestionably  owe  their  elastic  state 
to  the  possession  of  latent  heat.  But  the  theory  of  the  similar  constitution  of  gases 
and  vapours,  although  supported  by  strong  analogies,  was  not  generally  adopted  by 
chemists,  till  it  was  experimentally  confirmed  by  Faraday,  who  first  liquefied  several 
of  the  gases.  (Philosophical  Transactions,  1823,  pp.  160,  189  ;  and  1845,  p.  155). 
His  method  was  to  generate  the  gas  in  one  end  of  a  strong  glass  tube,  bent  in  the 

middle,  as  represented  (fig.  35);  and  hermeti- 
Fl°-  35<  cally  sealed.     The  gas  accumulating  in  a  con- 

fined space,  comes  to  exert  a  prodigious  pressure  ; 
an  effect  of  which  is,  that  a  portion  of  the  gas 
itself  condenses  into  a  liquid  in  the  end  of  the 
tube  most  remote  from  the  materials,  which  is 
kept  cool  with  that  view.  Considerable  danger  is  to  be  apprehended  by  the  operator 
in  conducting  such  experiments,  from  the  bursting  of  the  glass  tubes,  and  the  face 
ought  always  to  be  protected  by  a  wire-gauze  mask  from  the  effects  of  an  explosion. 
The  names  of  the  gases  which  were  liquefied  in  this  manner,  are  sulphurous  acid, 
cyanogen,  chlorine,  ammoniacal  gas,  sulphuretted  hydrogen,  carbonic  acid,  muriatic 
acid,  and  nitrous  oxide  ;  which  required  a  degree  of  pressure  varying,  in  the  different 
gases,  from  two  atmospheres,  in  the  first  mentioned,  to  fifty  atmospheres,  in  the  last 
mentioned  gas,  at  the  temperature  of  45°.  The  liquefaction  of  several  of  these 
gases  has  since  been  effected  by  the  application  of  cold  alone,  without  compression. 

The  principle  of  Faraday's  condensing  tube  has  been  embodied  in  the  machine  of 
Thilorier  for  the  liquefaction  of  carbonic  acid  gas.  (Annales  de  Chimie,  &c.  1835, 
Ix.  427,  432).  It  consists  (fig.  86)  of  two  similar  cylindrical  vessels  of  wrought 
iron,  made  exceedingly  strong,  of  the  capacity  of  about  three-fourths  of  a 
gallon,  each  of  which  is  provided  with  a  peculiarly  constructed  stopcock,  being  a 
spherical  plug  of  lead  on  a  spindle  which  can  be  screwed  down,  by  turning  the 
handle  above,  into  a  spherical  cavity  of  brass-work,  having  at  its  base  a  tubular 
opening  into  the  cylinder,  which  is  thus  closed.  There  is  also  a  connecting  tube  of 
copper,  the  ends  of  which  can  be  attached  by  screws  to  the  discharging  orifices  of 
the  stopcocks,  so  as  to  unite  the  two  cylinders  when  necessary.  The  stopcock  being 

FIG.  36. 


78  GASES. 

removed  from  one  of  the  cylinders  a,  which  is  called  the  generator,  a  charge  is  in 
troduced,  consisting  of  two  pounds  of  pulverulent  bicarbonate  of  soda  and  three* 
pounds  of  water  at  the  temperature  of  90°.  After  stirring  these  well  together  with 
a  wooden  rod,  a  quantity  amounting  to  one  pound  three  ounces  of  undiluted  oil  of 
vitriol  is  added,  the  latter  being  contained  in  a  long  cylindrical  vessel  of  brass,  suffi- 
ciently narrow  to  enter  the  generator,  into  which  it  is  carefully  let  down  by  a  hook 
without  spilling.  The  stopcock  being  now  applied  to  the  mouth  of  the  generator, 
and  firmly  screwed  down  upon  it,  with  the  intervention  of  a  leaden  washer,  the 
generator  is  turned  round  upon  its  supporting  pivots,  so  as  completely  to  invert  it : 
the  brass  measure  within  is  thus  canted  over,  and  the  acid  which  it  contained  mixed 
with  the  solution  of  soda.  The  carbonic  acid  of  the  salt,  which  amounts  to  half  its 
weight,  is  thus  disengaged,  and  accumulates  with  great  elastic  force  in  the  vacant 
part  of  the  generator.  The  charge  of  gas  is  then  transferred  to  the  other  large 
cylinder,  which  is  used  as  a  receiver,  by  attaching  it  to  the  generator  by  the  con- 
necting tube,  and  after  the  lapse  of  five  minutes,  opening  the  stopcocks  of  both.  It 
is  advisable  to  have  a  woollen  case  or  bag  about  the  receiver,  to  hold  fragments  of 
ice  for  cooling  it.  The  cylinders  may  again  be  separated,  after  shutting  the  stop- 
cocks, and  the  same  operations  repeated.  After  two  or  three  charges  of  gas  are 
conveyed  into  the  receiver,  the  pressure  of  the  latter  becomes  sufficient  to  liquefy 
the  gas ;  and  after  five  or  six  charges  the  receiver  may  contain  several  pints  of  liquid 
carbonic  acid.  The  receiver  being  finally  detached  is  set  aside,  and  the  liquid  it 
contains  preserved  for  use. 

When  this  highly  volatile  liquid  is  allowed  to  escape  into  air  it  evaporates  so 
readily  that  one  portion1  is  instantly  resolved  into  gas,  and  another  portion  is  cooled 
so  low  by  the  heat  thus  abstracted  as  to  freeze.  From  the  stopcock  of  the  receiver, 
a  small  tube,  shown  in  the  figure,  descends  to  near  the  bottom  and  dips  into  the 
liquid ;  so  that  upon  opening  the  former  it  is  the  liquid,  and  not  gaseous  carbonic 
acid,  which. escapes.  A  nozzle,  being  applied  to  the  receiver,  the  stream  of  liquid 
is  directed  into  a  small  cylindrical  box  of  thin  copper,  with  hollow  wooden  han- 
dles, which  is  soon  filled  with  solid  carbonic  acid,  in  the  form  of  a  white  substance 
like  snow,  or  more  closely  resembling  anhydrous  phosphoric  acid,  from  its  opacity 
and  entire  want  of  crystallization. 

Solid  carbonic  acid  is  a  very  bad  conductor  of  heat,  and  may,  therefore,  be  handled 
without  injury,  although  its  temperature  is  supposed  to  be  so  low  as  — 100°  C.,  or 
— 148°  Fahr. ;  and  also  preserved  in  the  air  for  hours,  if  a  considerable  mass  of  it 
in  a  glass  vessel  be  placed  within  another  similar  and  larger  glass  vessel,  with  any 
non-conducting  material  between  them.  When  applied  to  produce  cold,  in  order 
to  give  it  contact  the  solid  carbonic  acid  is  mixed  with  a  little  ether,  with  which  it 
unites  and  forms  a  soft  semifluid  mass  like  half  melted  snow,  capable  of  abstracting 
heat  and  evaporating  rapidly,  by  means  of  which  mercury  can  be  frozen  in  large 
quantities,  and  an  alcohol  thermometer  sunk  in  the  open  air  so  low  as  — 135° 
(Thilorier).  The  apparatus  of  Thilorier  forms  thus  an  invaluable  cold-producing 
machine. 

Mr.  Faraday  has  since  produced  a  still  lower  degree  of  cold  by  placing  a  bath 
of  Thilorier's  mixture  of  solid  carbonic  acid  and  ether  in  the  receiver  of  an  air- 
pump,  from  which  the  air  and  gaseous  carbonic  acid  were  rapidly  removed.  The 
bath  consisted  of  an  earthenware  dish  of  the  capacity  of  four  cubic  inches  or  more, 
which  was  fitted  into  a  similar  dish  somewhat  larger,  with  three  or  four  folds  of  dry 
flannel  intervening ;  with  the  mixture  in  the  inner  dish  such  a  bath  lasted  for  twenty 
or  thirty  minutes,  retaining  solid  carbonic  acid  the  whole  time.  An  alcohol  thermo- 
meter placed  in  the  bath,  merely  covered  with  paper,  fell  to  — 106°;  and  in  the 
air-pump  receiver,  exhausted  to  within  1-2  inch  mercury  of  a  vacuum,  the  thermo- 
meter fell  to  — 166° ;  or  a  cold  of  60  degrees  additional  was  produced  by  promot- 
ing the  evaporation  in  this  manner.  At  this  low  temperature  the  solid  carbonic 
acid  mixed  with  ether,  was  not  more  volatile  than  water  at  the  temperature  of  86°, 
or  alcohol  at  ordinary  temperatures. 


GASES.  79 

By  combining  this  extreme  cooling  power  with  the  effect  of  mechanical  pressure 
upon  gases,  several  most  interesting  results  were  obtained.  To  produce  the  pres- 
sure, Mr.  Faraday  employed  two  condensing  syringes,  fixed  to  a  table,  the  first 
having  a  piston  of  an  inch  in  diameter,  and  the  second  a  piston  of  only  half  an  inch 
in  diameter;  and  these  were  so  associated  by  a  connecting  pipe,  that  the  first  pump 
forced  the  gas  into  and  through  the  valves  of  the  second,  and  then  the  second  eould 
be  employed  to  throw  forward  this  gas,  already  condensed  to  ten  or  twenty  atmo- 
spheres, into  its  final  recipient,  the  condensing  tube,  at  a  much  higher  pressure. 

The  condensing  tubes  were  of  green  bottle-glass,  being  from  |th  to  ith 
of  an  inch  external  diameter,  and  from  ^d  to  J^th  of  an  inch  in  thick-  Fia-  37- 
ness.  They  were  of  two  kinds,  about  nine  and  eleven  inches  in  length : 
one,  in  form  of  an  inverted  syphon  (fig.  37),  could  have  the  bend  cooled 
by  immersion  into  a  cold  bath,  and  the  other,  horizontal  (fig.  38),  having 
a  curve  downward  near 

one  end  to  be  cooled  in  FlG-  38> 

the  same  manner.  Into  =, 

the  longest  leg  of  the  ;N 

syphon  tube,  and   the  ^^^^ 

straight  part  of  the  ho- 
rizontal tube,  minute  pressure  gauges  were  introduced  when  required. 
The  caps,  stopcocks,  and  connectors,  were  attached  to  the  tubes  by  com- 
mon cement,1  and  the  screw  joints  made  tight  by  leaden  washers. 

With  the  apparatus  described,  olefiant  gas,  which  had  not  previously 
been  liquefied,  was  condensed  into  a  colourless  transparent  fluid,  but  did  not  become 
solid  at  the  lowest  temperature.  The  tension  of  its  vapour  was  4 '6  atmospheres  at 
— 105°,  and  26-9  atmospheres  at  0°  Fahr.;  but  Mr.  Faraday  is  doubtful  whether 
the  condensed  fluid  can  be  considered  as  one  uniform  body.  Hydriodic  acid  gas, 
which  is  easily  liquefied,  having  a  tension  of  2-9  atmospheres  only  at  0°  Fahr.,  was 
found  to  freeze  at  — 60°,  and  to  form  a  clear,  colourless  solid,  resembling  ice.  Hy- 
drobromic  acid .  became  a  solid  crystalline  body  at  — 124°.  Fluosilicic  acid  gas 
liquefied  under  a  pressure  of  about  9  atmospheres,  at  about  160°  below  zero,  and 
was  then  clear,  transparent,  colourless,  and  very  fluid,  like  hot  ether ;  it  did  not 
freeze  at  any  temperature  to  which  it  could  be  submitted ;  it  has  since  been  solidi- 
fied by  M.  Natterer.  The  results  obtained  with  fluoboric  acid  were  similar.  Phos- 
phuretted  hydrogen,  subjected  to  high  pressure,  was  condensed  into  a  colourless 
liquid  by  the  most  intense  degree  of  cold  attainable,  but  was  not  solidified  by  any 
temperature  applied. 

Of  gaseous  bodies  previously  condensed,  hydrochloric  acid  did  not  freeze  at 
the  lowest  attainable  temperature;  the  tension  of  its  vapour  was  1-8  atmospheres  at 
— 100°,  15-04  atmospheres  at  0°,  26-20  atmospheres  at  32°,  and  30-67  atmospheres 
at  40°.  Sulphurous  acid  became  a  crystalline,  transparent,  and  colourless  solid 
body  at  — 105° ;  the  pressure  of  the  vapour  of  liquid  sulphurous  was  0-726  atmo- 
spheres at  0°  Fahr.,  1-53  atmospheres  at  32°,  2  atmospheres  at  46°-5,  3  atmo- 
spheres at  68°,  4  atmospheres  at  85°,  5  atmospheres  at  98°,  and  6  atmospheres 
at  110°. 

Sulphuretted  hydrogen  solidified  at  — 122°,  forming  a  white  crystalline  trans- 
lucent substance,  more  like  nitrate  of  ammonia  solidified  from  the  melted  state,  or 
camphor,  than  ice.  The  pressure  of  the  vapour  from  the  solid  is  not  more,  pro- 
bably, than  0-8  of  an  atmosphere,  so  that  the  liquid  allowed  to  evaporate  in  the  air 
would  not  solidify  as  carbonic  acid  does.  The  tension  of  sulphuretted  hydrogen 
vapour  was  1-02  atmosphere  at  — 100°,  2  atmospheres  at  — 58°,  6-1  atmospheres 
at  0°,  9-94  atmospheres  at  30°,  and  14-6  atmospheres  at  52°,  which  form  a  pro- 
gression considerably  different  from  that  of  water  or  carbonic  acid. 

1  Five  parts  of  resin,  one  part  of  yellow  bees'-wax,  and  one  part  of  red  ochre,  by  weight, 
melted  together. 


80 


GASES. 


Mr.  Faraday  observed,  that  when  carbonic  acid  is  melted  and  resolidified  by  a 
bath  of  low  temperature,  it  appears  as  a  clear  transparent  crystalline  colourless  body, 
like  ice.  It  melts  at  — 70°  or  — 72°,  and  the  solid  carbonic  acid  is  heavier  than 
the  liquid  bathing  it.  The  solid  or  liquid  carbonic  acid,  at  this  temperature,  has  a 
pressure  of  5*33  atmospheres.  Hence  the  facility  with  which  liquid  carbonic  acid, 
when  allowed  to  escape  into  air,  exerting  only  a  pressure  of  one  atmosphere,  freezes 
a  part  of  itself  by  the  evaporation  of  another  part.  The  following  are  the  pressures 
of  the  vapours  of  carbonic  acid  which  Mr.  Faraday  has  obtained  :  — 


CARBONIC   ACID    VAPOUR. 


Temp.  Fahr. 


Tension  in 
Atmospheres. 
_111<> 1-14 

—  107 1-36 

—  95  2-28 

_  83  3-60 

—  75  4-60 

—  56  6-97 

_  34  12-50 

—  23  15-45 


Temp.  Fahr.  Tension  in 

Atmospheres. 

—15° 17-80 

—  4   21-48 

0   22-84 

5   24-75 

10   26-82 

15   29-09 

23    33-15 

32   38-50 


Nitrous  oxide  was  obtained  solid,  as  a  beautiful  clear  crystalline  colourless  body, 
by  a  temperature  estimated  at  about  — 150°,  when  the  pressure  of  its  vapour  was 
less  than  one  atmosphere.  Mr.  Faraday  believes  that  liquid  nitrous  oxide  may  be 
used  instead  of  carbonic  acid,  to  produce  degrees  of  cold  far  below  those  which  the 
latter  body  can  supply.  This  idea  was  verified  by  M.  Natterer,  who  has  liquefied 
nitrous  oxide,  and  several  other  gases,  by  mechanical  compression.  He  found  that 
liquid  nitrous  oxide  may  be  mixed  with  sulphuret  of  carbon  in  all  proportions,  and 
on  placing  a  mixture  of  these  two  liquids  under  the  receiver  of  an  air-pump,  he  saw 
an  alcohol  thermometer  fall  to  — 140°  C.,  or  — 220°  Fahr. ;  at  this  extremely  low 
temperature  neither  chlorine  nor  the  sulphuret  of  carbon  lost  its  fluidity.  He  also- 
succeeded  in  freezing  liquid  fluosilicic  acid  by  the  same  means  (Poggendorff's  An- 
nalen,  t.  xii.  p.  132  :  and  Liebig's  Annalen,  t.  liv.  p.  254).  The  tension  of  its 
vapour  was  observed  by  Faraday  to  be,  atmosphere  at  — 125°,  19-34  atmospheres  at 
0°,  and  334  atmospheres  at  35°. 

Liquid  cyanogen,  when  cooled,  becomes  a  transparent  crystalline  solid,  as  Bussy 
and  Bunsen  had  previously  observed,1  which  liquefies  at  — 30°.  The  tension  of  its 
vapour  was  1-25  atmospheres  at  0°,  2-37  atmospheres  at  32°,  and  6-9  atmospheres 
at  63°. 

Ammonia  formed  a  white,  translucent,  crystalline  solid,  melting  at  — 103°.  The 
density  of  the  liquid  was  0-731  at  60°;  its  tension  2-48  atmospheres  at  0°,  444 
atmospheres  at  32°,  and  6.9  atmospheres  at  60°. 

Arsenietted  hydrogen,  which  was  liquefied  by  Dumas  and  Soubeiran,  did  not 
solidify  at  — 166°.  The  tension  of  its  vapour  was  0-94  atmospheres  at  — 75°, 
5-21  atmospheres  at  0°,  8-95  atmospheres  at  32°,  and  13-19  atmospheres  at  60°. 

The  following  gases  showed  no  signs  of  liquefaction  when  cooled  by  the  carbonic 
acid  bath  in  vacuo,  at  the  pressure  expressed :  — 

Atmospheres. 

Hydrogen  at 27 

Oxygen 58-5 

Nitrogen 50 

Nitric  oxide 50 

Carbonic  oxide 40 

Coal  gas 32 

Several  gases  were  submitted  by  M.  Gr.  Aime*  to  still  higher  pressures,  rising  for 
nitrogen  and  hydrogen  gases  to  220  atmospheres,  by  immersion  in  the  depths  of  the 


1  For  Bunsen's  results  on  the  liquefaction  of  several  of  the  gases,  see  Bibliotheque  Univer- 
selle,  1839,  t.  xxxii.  p.  185. 


GASES.  81 

isea,  where  the  results  under  pressure  could  not  be  observed  (Annales  de  Chimie, 
&c.  1843,  3d  ser.  t.  viii.  p.  275).  Most  of  them  were  diminished  in  bulk  in  a  ratio 
greatly  exceeding  the  pressure ;  but  this  has  been  shown  to  be  often  the  case  whilst 
the  substance  retains  the  gaseous  form.  No  sufficient  evidence  of  the  liquefaction 
of  any  of  the  gases  just  enumerated  has  yet  been  produced.  The  same  may  be  said 
of  light  carburetted  hydrogen.  At  the  lowest  temperatures  attainable,  alcohol,  ether, 
sulphuret  of  carbon,  chloride  of  phosphorus,  and  chlorine,  also  retained  the  liquid 
form. 

Sir  H.  Davy  threw  out  the  idea  that  the  prodigious  elastic  force  of  the  liquid 
gases  might  be  used  as  a  moving  power.  Bat  supposing  the  application  practicable, 
it  may  be  doubted,  from  what  we  know  of  the  constancy  of  the  united  sum  of  the 
latent  and  sensible  heat  of  high  pressure  steam,  whether  any  saving  of  heat  would 
be  effected  by  such  an  application  of  the  vapours  of  these  fluids. 

All  gases  whatever  are  absorbed  and  condensed  by  water  in  a  greater  or  less 
degree,  in  which  case  they  certainly  assume  the  liquid  form.  The  quantity  con- 
densed is  widely  different  in  the  different  gases ;  and  in  the  same  gas  the  quantity 
condensed  depends  upon  the  pressure  to  which  the  gas  is  subject,  and  the  tempera- 
ture of  the  absorbing  water.  Dr.  Henry  proved  that  with  carbonic  acid  gas  the 
volume  absorbed  by  water  is  the  same,  whatever  be  the  pressure  to  which  the  gas  is 
subject.  Hence,  we  double  the  weight  or  quantity  of  gas  absorbed,  by  subjecting 
it,  in  contact  with  water,  to  the  pressure  of  two  atmospheres }  and  this  practice  is 
adopted  in  impregnating  water  with  carbonic  acid,  to  make  soda-water.  The  colder 
the  water,  the  greater  also  the  quantity  of  gas  absorbed. 

In  the  physical  theory  of  gases,  they  are  assumed  to  be  expansible  to  an  indefinite 
extent,  in  the  proportion  that  pressure  upon  them  is  diminished,  and  to  be  con- 
tractible  under  increased  pressure  exactly  in  proportion  to  the  compressing  force  — 
the  well-known  law  of  Mariotte.  The  bulk  of  atmospheric  air  has  been  found 
rigidly  to  correspond  with  this  law,  when  it  was  expanded  to  300  volumes,  and  also 
when  compressed  into  l-25th  of  its  primary  volume.  But  there  is  reason  to  doubt 
whether  the  law  holds  with  absolute  accuracy,  in  the  case  of  a  gas  either  in  a  state 
of  extreme  rarefaction,  or  of  the  greatest  density.  Thus  atmospheric  air  does  not 
appear  to  be  indefinitely  expansible,  as  the  law  of  Mariotte  would  require ;  for  there 
is  certainly  a  limit  to  the  earth's  gaseous  atmosphere,  and  it  does  not  expand  into  all 
space.  Dr.  Wollaston  supposed  that  the  material  particles  of  air  are  not  indefinitely 
minute,  but  have  a  certain  magnitude  and  weight.  These  particles  are  under  the 
influence  of  a  powerful  mutual  repulsion,  as  is  always  the  case  in  gaseous  bodies, 
and,  therefore,  tend  to  separate  from  each  other;  but  as  this  repulsive  force  dimi- 
nishes as  the  distance  of  the  particles  from  each  other  increases,  Dr.  Wollaston 
imagined  that  the  weight  of  the  individual  particles  might  come  at  last  to  balance 
it,  and  thus  prevent  their  further  divergence.  On  this  view,  which  is  probable  on 
other  grounds,  the  expansion  of  a  gas,  caused  by  the  removal  of  pressure,  will  cease 
at  a  particular  point  of  rarefaction,  and  the  gas  not  expanding  farther,  will  come  to 
have  an  upper  surface,  like  a  liquid.  The  earth's  atmosphere  has  probably  an  exact 
limit,  and  true  surface. 

The  deviation  from  the  law  of  Mariotte,  in  gases  under  a  greater  pressure  than 
that  of  the  atmosphere,  has  been  distinctly  observed  in  the  more  liquefiable  gases. 
Thus,  Professor  Oersted,  of  Copenhagen,  found  that  sulphurous  acid  gas  diminishes, 
under  increased  pressure,  more  rapidly  than  common  air.  The  volumes  of  atun> 
spheric  air  and  of  the  gas  were  equal  at  the  following  pressures : — 

Pressure  upon  air  in  Pressure  upon  sulphurous 

atmospheres.  gas  in  atmospheres. 

1         1 

1.176 1.173 

2.821 2.782 

3.319 3.189 

6 


82  GASES. 

It  will  be  observed  that  less  pressure  always  suffices  to  reduce  tlie  sulphurous  acid 
gas  to  the  same  bulk  than  is  required  by  air.  If  the  pressure  upon  the  air  and  gas 
were  made  equal,  then  the  gas  would  be  compressed  into  less  bulk  than  the  air,  and 
deviate  from  the  law  of  Mariotte.  Despretz  observed  an  equally  conspicuous  devia- 
tion from  this  law  under  increasing  pressures,  in  several  other  gases,  particularly 
sulphuretted  hydrogen,  cyanogen,  and  ammonia,  which  are  all  easily  liquefied. 
There  is  no  reason,  however,  to  suppose  that  any  partial  liquefaction  of  the  gases 
occurs  under  the  pressure  applied  to  them  in  such  experiments.  They  remain 
entirely  gaseous,  and  their  superior  compressibility  must  be  referred  to  a  law  of 
their  constitution.  It  is  the  phenomenon  beginning  to  show  itself  in  a  gas  under 
moderate  pressure,  which  was  observed  in  all  its  excess  by  Cagnard  de  la  Tour,  in 
the  vapours  confined  by  him  under  great  pressure  (page  68). 

Those  gases  which  exhibit  this  deviation  must  occupy  less  bulk  than  they  ought 
to  do  under  the  pressure  of  the  atmosphere  itself;  which  may  be  the  reason  why 
the  liquefiable  gases  are  generally  found  by  experiment  specifically  heavier  than  they 
ought  by  theory  to  be. 

M.  Regnault -accordingly  finds,  that  at  the  temperature  of  32°,  and  under  more 
feeble  pressures  than  that  of  the  atmosphere,  carbonic  acid  deviates  from  the  law  of 
Mariotte  in  a  marked  manner ;  while  it  appears  to  follow  that  law  when  heated  to 
212°  under  more  feeble  pressures  than  that  of  the  atmosphere. 

The  density  of  carbonic  acid  at  33°  (air  =  1000)  was  :— 

Under  the  pressure  of  760  millimeters  (30  inches)..  1529.10 

374.13 1523.66 

224.17 1521.45 

The  density  of  the  gas  at  212°  (that  of  air  at  the  same  temperature  being  1000) 
was: — 

Under  the  pressure  of  760  millimeters  (30  inches)..  1524.18 
338.39 1524.10 

The  theoretical  density  of  carbonic  acid,  calculated  in  a  manner  which  shall  be 
afterwards  explained,  and  taking  for  the  atomic  weight  of  carbon  the  number  6,  is 
1520.24 ;  to  which  the  numbers  for  the  density  of  the  gas  under  greatly  reduced 
pressures  appear  to  be  converging.  M.  Regnault  verified  at  the  same  time  the 
exactness  of  the  law  of  Mariotte  for  atmospheric  air.  (Annales  de  Ch.,  xiv.  227, 
and  234). 

Such  are  the  most  remarkable  features  which  gases  exhibit  in  relation  to  pressure 
and  temperature.  These  properties  are  independent  of  the  specific  weights  of  the 
gases,  which  are  very  different  in  the  various  members  of  the  class,  and  they  are 
but  little  connected  with  the  nature  of  the  particular  substance  or  material  which 
exists  in  the  gaseous  form.  But  when  gases  differing  in  composition  are  presented 
to  each  other,  a  new  property  of  the  gaseous  state  is  developed,  namely,  the  forcible 
disposition  of  dissimilar  gases  to  intermix,  or  to  diffuse  themselves  through  each 
other.  This  is  a  property  which  interferes  in  a  great  variety  of  phenomena,  and  is 
no  less  characteristic  of  the  gaseous  state  than  any  we  have  considered.  It  appears 
in  the  spontaneous  diffusion  of  gases  through  each  other,  and  in  the  diffusion  of 
vapours  into  gases,  or  the  ascent  of  vapours  from  volatile  bodies  into  air  and  othei 
gases,  of  which  the  spontaneous  evaporation  of  water  into  the  air  is  an  instance. 
Related  closely  to  this  subject,  and  preliminary  to  its  consideration,  is  the  passage 
of  different  gases  into  a  vacuum,  through  a  small  aperture,  which  takes  place  with 
different  degrees  of  facility;  with  their  rates  of  transmission  by  capillary  tubes. 
The  whole  may  be  briefly  treated  under  the  heads  of,  (1)  Effusion  of  gases  (their 
pouring  out),  by  which  I  express  their  passage  into  a  vacuum  by  a  small  aperture  in. 
a  thin  plate ;  (2)  Transpiration  of  gases,  or  their  passage  through  tubes  of  fine  bore 
of  greater  or  less  length ;  (3)  The  diffusion  of  gases ;  and  (4)  Evaporation  in  air. 


EFFUSION    OF    GASES. 


83 


FIQ.  39. 


EFFUSION   OF   GASES. 

The  specific  weights,  or  weights  of  an  equal  measure,  of  the  different  gases  vary 
exceedingly.  The  numbers  representing  these  weights  are  always  referred  to  the 
weight  of  a  gas,  generally  air,  as  1  or  1000,  instead  of  water,  which  is  the  standard 
comparison  for  liquids  and  solids.  The  operation  of  taking  the  specific  gravity  of  a 
gas  is  simple  in  principle,  but  the  accurate  execution  of  it  is  attended  with  great  prac- 
tical difficulties.  A  light  glass  globe  g  (fig.  39) 
from  50  to  100  cubic  inches  in  capacity,  is  weighed 
full  of  air,  then  exhausted  by  an  air-pump  and 
weighed  empty,  the  loss  being  taken  as  the  weight 
of  its  volume  of  air.  It  is  then,  in  its  exhausted 
state,  united  with  a  bell-jar  c,  containing  the  gas 
to  be  weighed  and  standing  over  a  mercurial 
trough,  by  a  union  screw  between  the  stopcocks  d 
and  e  of  the  two  vessels ;  and  filled  with  the  gas, 
which  rushes  from  the  jar  to  the  vacuous  globe  on 
opening  both  stopcocks.  A  supply  of  gas  is  con- 
veyed to  the  jar  by  the  bent  tube  b,  after  being 
deprived  of  moisture  by  passing  through  a  drying 
tube  a,  containing  fragments  of  chloride  of  calcium. 
The  globe  is  again  weighed  when  full  of  gas  of  the  atmospheric  pressure  and  tem- 
perature, and  the  weight  of  a  volume  of  the  gas  obtained  by  deducting  the  weight 
of  the  vacuous  globe.  The  specific  gravity  is  then  calculated  by  the  proportion,  as 
the  weight  of  air  first  found,  to  the  weight  of  gas,  so  1.000  (density  of  air),  to  a 
number  which  expresses  the  density  of  the  gas  required.  MM.  Dumas  and  Bous- 
singault,  in  their  late  careful  observations  of  the  density  of  oxygen,  nitrogen,  and 
hydrogen,  employed  a  capacious  glass  globe,  of  which  the  cubic  contents  were  first 
ascertained  by  measuring  in  an  accurate  manner  the  volume  of  water  required  to  fill 
it  (Annales  de  Chimie,  3d  ser.  viii.  201).  In  the  refined  experiments  of  M.  Regnault, 
lately  published,  a  light  glass  balloon  of  about  ten  litres  or  616  cubic  inches  in 
capacity,  was  employed  as  the  weighing  globe.  It  was  counterpoised,  when  weighed, 
by  a  similar  globe  formed  of  the  same  glass ;  by  which  arrangement  numerous  and 
somewhat  uncertain  corrections  for  variations  in  the  density,  temperature,  and  hygro- 
metric  state  of  the  air,  during  the  continuance  of  an  experiment,  the  film  of  moisture 
which  adheres  to  glass,  and  the  displacement  of  air  by  the  solid  materials  of  the 
balloon,  were  entirely  avoided.  (Ibid.,  1845,  3d  se>.  t.  iv.  211). 

The  following  tables  exhibit  the  specific  gravity  of  those  gases  to  which  reference 
will  most  frequently  be  made,  air  being  taken  as  the  standard  of  comparison  in  the 
first  table,  and  oxygen  in  the  second.  To  each  specific  gravity  is  added,  in  a  second 
column,  the  square  root  of  the  number,  and  in  a  third  column  1  divided  by  the 
square  root,  or  the  reciprocal  of  the  square  root. 

TABLE  I.   DENSITY  OF  GASES,  AIR— 1. 


DENSITY. 

SQUARE  ROOT 
OF 
DENSITY. 

1 

SQUARE  ROOT. 

AUTHO- 
RITY. 

Nitrogen  

0-97137 

0-9856 

1-0147 

RegnQiUlt. 

1-10563 

1-0515 

0-9510 

0-06926 

0-2632 

3-7994 

Carbonic  acid  

1-52901 

1-2365 

0-8087 

Carbonic  oxide  

0-9712 

1-9855 

1-0147 

Calculated 

Light  carburetted  hydrogen  
Olefiant  gas  

0-5549 
0-9712 

0-7449 
0-9855 

1-3424 
1-0147 

1-5261 

1  -2353 

0-8095 

Nitric  oxide  

1-0405 

1-0205 

0-9799 

Sulphuretted  hydrogen  

1-1793 

1-0860 

0-9208 

Chlorine  

2-4573 

1-6676 

0-6379 

« 

84 


EFFUSION    OF    GASES. 


TABLE   II.      DENSITY    OP   GASES,    OXYGEN  =  1. 


OASES. 

DENSITY. 

SQUARE 
ROOT  OP 
DENSITY. 

1 

SQUARE   ROOT. 

AUTHORITY. 

Air  

0-9038 

0-9507 

1-0518 

Regnault. 

Nitrogen   . 

0-8785 

0-93,73 

1-0669 

Hydrogen  

0-6626 

0-2502 

3-9968 

Carbonic  acid 

1-3830 

1-1760 

0-8503 

Carbonic  oxide  

0-8750 

0-9354 

1-0691 

Calcu  ated 

Light  carburetted  hydrogen  CH2 
Olefiant  gas   

0-5000 
0-8750 

0-7071 
0-9354 

1.4142 
1-0691 

1-3750 

1-1705 

0-8545 

Nitric  oxide 

0-9375 

0-%82 

1-0328 

Sulphuretted  hydrogen    . 

1-0625 

1-0308 

8-9701 

2-2129 

1-4876 

0-6722 

A  jar  on  the  plate  of  an  air-pump  is  kept  vacuous  by  continued  exhaustion,  and 
a  measured  quantity  of  air,  or  any  other  gas,  allowed  to  find  its  way  into  the  vacuous 
jar  through  a  minute  aperture  in  a  thin  metallic  plate,  such  as  platinum  foil,  made 
by  a  fine  steel  point,  and  not  more  than  l-300dth  of  an  inch  in  diameter.  With  an 
imperfect  exhaustion,  it  is  found  that  the  velocity  with  which  the  gas  flows  into  the 
jar  rapidly  increases  till  the  aspiration  power  or  degree  of  exhaustion  amounts  to 
about  one-third  of  an  atmosphere.  Higher  degrees- of  exhaustion  do  not  produce  a 
corresponding  increase  of  velocity,  and  the  difference  of  an  inch  of  the  mercurial 
column  of  the  gauge  barometer  scarcely  affects  the  rate  at  which  the  gas  enters, 
when  the  vacuum  is  nearly  complete,  and  the  pressure  to  which  the  gas  is  subject 
approaches  that  of  a  whole  atmosphere.  By  a  perforated  plate  such  as  described,  60 
cubic  inches  of  dry  air  entered  the  vacuous,  or  nearly  vacuous  air-pump  receiver,  in 
about  1000  seconds,  and  in  successive  experiments  the  time  of  passage  did  not  vary 
more  than  one  or  two  seconds. 

The  time  of  passage  into  a  vacuum  of  a  constant  volume  varied  in  the  different 
gases,  the  lightest  passing  in  the  shortest  time.  The  time  corresponded  very  closely 
for  each  gas  with  the  square  root  of  its  density.  Thus  the  square  root  of  the  density 
of  oxygen  being  1-0515,  and  that  of  air  1,  (Table  I.),  the  time  of  passage  of  the 
constant  volume  of  oxygen  was  observed  to  be  1-0519,  1-0519,  1-0506,  1-0502,  in 
experiments  made  on  different  occasions,  the  time  of  passage  of  the  same  volume  of 
air  being  1.  Compared  with  the  time  of  the  passage  of  a  constant  volume  of  oxygen 
taken  as  1,  the  time  of  hydrogen  was  0-2631,  instead  of  0-25  (Table  II.) ;  the  time 
of  nitrogen  was  0-9365  and  0-9345,  instead  of  0-9373 ;  the  time  of  carbonic  oxide, 
of  which  the  theoretical  density  is  the  same  as  the  last  gas,  was  0-9345,  instead  of 
0.9354;  of  carburetted  hydrogen  0-7023,  instead  of  0-7071;  of  carbonic  acid 
1-1675,  instead  of  1-1705.  The  time  of  nitrous  oxide  was  always  the  same,  as 
nearly  as  could  be  observed,  as  that  of  carbonic  acid ;  while  these  two  gases  have 
the  same  specific  gravity.  For  gases  which  do  not  differ  greatly  from  air  in  specific 
gravity,  the  times  correspond  so  closely  with  the  law,  that  the  densities  of  these 
gases,  it  appears,  might  be  deduced  as  accurately  from  an  effusion  experiment  as  by 
actually  weighing  them.  The  sensible  deviation  from  the  law  in  the  times  of  both 
the  very  light  and  very  heavy  gases  can  be  shown  to  be  occasioned  by  the  tubularity 
of  the  aperture  arising  from  the  unavoidable  thickness  of  the  metallic  plate. 

The  times  of  passage  into  a  vacuum  of  equal  volumes  of  different  gases  varying, 
then,  as  the  square  root  of  their  densities,  the  velocities  of  passage  will  consequently 
be  in  the  inverse  proportion,  or  as  1  divided  by  the  square  root  of  the  gas.  This  is 
the  physical  law  of  the  passage  of  fluids  generally  under  pressure,  which  has  been 
long  established  for  liquids  of  different  densities  by  observation,  but  had  not  pre- 
viously received  an  experimental  verification  in  the  case  of  gases. 


TRANSPIRATION    OF    GASES. 


85 


Mixtures  of  nitrogen  and  oxygen  in  different  proportions  were  found  to  have  the 
mean  rate  of  their  constituent  gases.  This  is  also  true  of  mixtures  of  carbonic  acid, 
nitrous  oxide,  and  carbonic  oxide,  with  each  other  or  with  the  preceding  gases.  But 
hydrogen  and  carburetted  hydrogen  lose  more  or  less  of  their  peculiar  rate,  and  pass 
slower,  when  mixed  with  other  gases.  Thus  the  time  of  passage  of  a  mixture  of 
equal  volumes  of  oxygen  and  hydrogen  is  Og7255 ;  instead  of  0-6315,  the  mean  of 
the  times,  1  and  0-2631,  of  those  gases  individually.  Supposing  the  rate  of  the 
oxygen  in  the  mixture  to  remain  unchanged,  and  that*  the  alteration  takes  place  on 
the  hydrogen  exclusively,  then  the  time  of  passage  of  the  hydrogen  has  increased 
from  0-2631  to  0-4510,  or  been  nearly  doubled.  But  it  is  in  mixtures  where  the 
proportion  of  hydrogen  is  large  compared  with  that  of  the  other  gas,  that  the  de- 
parture from  the  mean  velocity  is  most  conspicuous.  Thus  the  addition  of  half  a 
per  cent,  of  air  or  oxygen  has  an  effect  in  retarding  the  passage  of  hydrogen  at  least 
three  times  greater  than  what  it  should  produce  from  its  greater  density  by  calcula- 
tion. The  time  of  the  effusion  of  hydrogen  thus  becomes  a  delicate  test  of  the 
purity  of  that  gas.  This  want  of  mechanical  equivalency  in  hydrogen  mixtures  is 
exceedingly  remarkable,  being  a  marked  departure  from  the  usual  uniformity  of 
gaseous  properties. . 


TRANSPIRATION    OF    GASES. 


The  arrangement  exhibited  (fig.  40),  was  adopted  in  examining  the  rates  of  passage 
of  different  gases  into  a  vacuum  through  a  capillary  tube.     The  gas  is  taken  from  a 


Fio.  40. 


counterpoised  bell-jar,  standing  over  the  water  of  a  pneumatic  trough,  and  passed 
first  by  a  flexible  tube  to  a  U-shaped  drying  tube  filled  with  fragments  of  chloride 
of  calcium;  in  order  to  be  deprived  of  aqueous  vapour  before  entering  the  capillary 


86  TRANSPIRATION    OF    GASES. 

glass  tube  a.  The  last  is  connected  by  means  of  a  tube  of  block  tin  with  a  receiver 
on  the  plate  of  an  air-pump,  provided  with  a  gauge  barometer  6,  as  represented. 
Gas  is  allowed  to  enter  the  exhausted  receiver  by  the  capillary  tube,  and  the  time 
observed  which  the  gauge  barometer  requires  to  fall  a  certain  number  of  inches  from 
the  admission  of  a  constant  volume. 

It  is  found  that  for  a  tube  of  any  given  diameter,  the  times  of  passage  of  different 
gases  approximate  the  more  closely  to  their  respective  times  of  effusion,  the  more 
the  tube  is  shortened  and  iflade  to  approximate  to  an  aperture  in  a  thin  plate. 
While,  as  the  tube  is  elongated,  a  deviation  from  those  rates  is  observed,  which  is 
rapid  with  the  first  additions  in  length,  but  becomes  gradually  less ;  and,  finally, 
with  a  certain  length  of  tube,  the  gases  attain  rates  of  which  the  relation  remains 
constant,  or  nearly  so,  for  any  farther  increase  of  length.  The  same  relation  in 
velocity  between  the  different  gases  is  then  found  to  extend  also  through  a  con- 
siderable range  of  pressure,  as  from  one  to  one-tenth  of  an  atmosphere. 

The  ultimate  rates  of  transpiration  differ  considerably  from  the  rates  of  effusion 
of  the  same  gases,  and  have  no  uniform  relation  to  their  density.  Of  all  the  gases 
tried,  oxygen  passes  with  least  velocity  through  a  capillary  tube.  The  time  of  pas- 
sage into  a  vacuum,  under  the  atmospheric  pressure,  of  a  volume  of  oxygen  being  1, 
that  of  air  was  0.9010,  of  nitrogen  0.8704,  and  carbonic  oxide  0.8671.  The  trans- 
piration times  of  these  gases  approach  so  closely  to  their  specific  gravities,  as  will  be 
seen  by  Table  II.,  as  to  lead  to  the  inference  that  the  transpiration  times  are  directly 
as  the  density  for  these  gases.  Nitric  oxide  appears  to  coincide  in  transpiration  time 
with  nitrogen,  although  denser,  the  specific  gravity  of  the  former  being  the  mean 
between  the  densities  of  the  nitrogen  and  oxygen.  The  transpiration  time  of  car- 
bonic acid  approached  very  closely  to  0.75,  or  three-fourths  of  that  of  oxygen. 
Nitric  oxide,  which  has  the  same  specific  gravity  as  carbonic  acid,  coincides  perfectly 
with  that  gas  also  in  time  of  transpiration.  The  densities  of  these  two  gases  are  to 
that  of  oxygen  as  22  to  16,  but  their  times  of  transpiration  are  to  the  time  of  trans- 
piration of  oxygen,  as  12  to  16. 

The  transpiration  time  of  hydrogen,  by  several  capillary  tubes,  varied  but  very 
little  from  0.44,  the  time  of  oxygen  being  1.  The  number  for  hydrogen  therefore 
approaches  0.4375,  which  is  7-16ths  of  the  oxygen  time.  The  time  of  light  car- 
buretted  hydrogen  was  also  remarkably  constant  at  0.550  to  0.555;  which  approach, 
although  not  very  closely,  to  0.5625,  or  9-16ths  of  the  oxygen  time.  Olefiant  gas 
has  probably  sensibly  the  same  specific  gravity  as  nitrogen  and  carbonic  oxide,  but 
it  is  much  more  transpirable  than  these  gases ;  the  transpiration  time  of  olefiant  gas 
being  found  so  low  as  0.512.  This  result  is  not  inconsistent  with  the  true  number 
for  olefiant  gas,  being  0.5,  or  one-half  the  time  of  oxygen;  for  the  gas  operated  upon 
was  found  always  to  contain  either  a  trace  of  a  heavy  hydrocarbon,  or  a  few  per  cent, 
of  carbonic  oxide,  both  of  which  increase  the  time  of  transpiration.  Hydrogen  with 
five  per  cent,  of  air  was  less  rapidly  transpired  than  olefiant  gas,  the  time  of  that 
mixture  being  0.5237. 

The  transpiration  time  of  mixtures  of  the  following  gases  was  exactly  the  mean 
of  the  times  of  the  mixed  gases,  namely,  oxygen,  nitrogen,  hydrogen,  carbonic  oxide, 
nitrous  oxide,  and  carbonic  acid ;  but  the  transpiration  time  of  hydrogen  and  car- 
buretted  hydrogen,  particularly  the  former,  is  greatly  increased  when  these  gases  are 
in  a  state  of  mixture  with  each  other,  or  with  gases  of  the  former  class.  Thus  the 
transpiration  time  of  a  mixture  of  equal  volumes  of  oxygen  and  hydrogen  was  0.9008, 
instead  of  0.72,  the  mean  time  of  the  two  gases.  The  transpiration  time  of  hydrogen 
in  such  a  mixture  is  as  high  as  0.8016;  or,  its  transpiration  is  then  less  rapid  than 
that  of  pure  carbonic  acid. 

The  effusion  of  a  given  measure  of  air  into  a  vacuum  takes  place  always  in  the 
same  time,  whatever  may  be  its  density,  from  one-fourth  of  an  atmosphere  up  to  two 
atmospheres.  But  the  transpiration  of  air  of  different  densities  was  observed  to  take 
place  in  times  which  are  inversely  as  the  densities ;  or,  the  denser  air  is,  the  more 
rapidly  is  a  given  volume  of  it  transpired.  Hence  the  transpiration  of  air  and  all 


DIFFUSION    OF    GASES.  87 

rases  is  greatly  affected  by  variations  of  the  barometer ;  the  higher  the  barometer 
the  more  quickly  are  the  gases  transpired.  The  difference  in  this  respect  separates 
completely  the  phenomena  of  effusion  and  transpiration.  Nor  can  the  phenomena 
of  transpiration  be  an  effect  of  friction,  for  the  greater  the  density  of  air,  the  more 
should  its  passage  be  resisted  by  friction.  The  transpirability  of  a  gas  appears  to  be 
a  constitutional  property,  like  its  density,  or  its  combining  volume ;  and  the  investi- 
gation is  of  peculiar  interest  from  supplying  a  new  class  of  constants  for  the  gases, 
namely,  their  coefficients  of  transpiration.  The  rates  of  transpiration  of  different 
gases  were  further  observed  to  be  the  same  through  a  fine  capillary  tube  of  copper 
of  eleven  feet  in  length,  and  a  mass  of  dry  stucco,  as  through  capillary  tubes  of  glass. 

DIFFUSION   OF   GASES. 

When  a  light  and  heavy  gas  are  once  mixed  together,  they  do  not  exhibit  any 
tendency  to  separate  again,  on  standing  at  rest ;  differing  in  this  respect  from  mixed 
liquids,  many  of  which  speedily  separate,  and  arrange  themselves  according  to  their 
densities,  the  lightest  uppermost,  and  the  heaviest  undermost  —  as  in  the  familiar 
example  of  oil  and  water,  unless  they  have  combined  together.  This  peculiar  pro- 
perty of  gases  has  repeatedly  been  made  the  subject  of  careful  experiment.  Common 
air,  for  instance,  is  essentially  a  mixture  of  two  gases,  differing  in  weight  in  the  pro- 
portion of  971  to  1105;  but  the  air  in  a  tall  close  tube  of  glass  several  feet  in  length, 
kept  upright  in  a  still  place,  has  been  found  sensibly  the  same  in  composition  at  the 
top  and  bottom  of  the  tube,  after  a  lapse  of  months.  Hence,  there  is  no  reason  to 
imagine  that  the  upper  strata  of  the  air  differ  in  composition  from  the  lower;  or  that 
a  light  gas,  such  as  hydrogen,  escaping  into  the  atmosphere,  will  rise,  and  ultimately 
possess  the  higher  regions ;  —  suppositions  which  have  been  the  groundwork  of 
meteorological  theories  at  different  times. 

The  earliest  observations  we  possess  on  this  subject  are  those  of  Dr.  Priestley,  to 
whom  pneumatic  chemistry  stands  so  much  indebted.  Having  repeated  occasion  to 
transmit  a  gas  through  stoneware  tubes  surrounded  by  burning  fuel,  he  perceived 
that  the  tubes  were  porous,  and  that  the  gas  escaped  outwards  into  the  fire ;  while  at 
the  same  time  the  gases  of  the  fire  penetrated  into  the  tube,  although  the  gas  within 
the  tube  was  in  a  compressed  state. 

Dr.  Dalton,  however,  first  perceived  the  important  bearings  of  this  pro-  FIG.  41. 
perty  of  aerial  bodies,  and  made  it  the  subject  of  experimental  inquiry.  * 
He  discovered  that  any  two  gases,  allowed  to  communicate  with  each  other, 
exhibit  a  positive  tendency  to  mix  or  to  penetrate  through  each  other,  even 
in  opposition  to  the  influence  of  their  weight.  Thus,  a  vessel  h,  contain- 
ing a  light  gas  (hydrogen),  being  placed  above  a  vessel  c,  containing  a 
heavy  gas  (carbonic  acid),  and  the  two  gases  allowed  to  communicate  by  a 
narrow  tube,  as  represented  (fig.  41),  an  interchange  speedily  took  place 
of  a  portion  of  their  contents,  which  it  might  be  supposed  that  their  rela- 
tive position  would  have  prevented.  Contrary  to  the  solicitation  of  gra- 
vity, the  heavy  gas  continued  spontaneously  to  ascend,  and  the  light  gas 
to  descend,  till  in  a  few  hours  they  became  perfectly  mixed,  and  the  pro- 
portion of  the  two  gases  was  the  same  in  the  upper  and  lower  vessels. 
This  disposition  of  different  gases  to  intermix,  appeared  to  Dr.  Dalton  so 
decided  and  strong,  as  to  justify  the  inference  that  different  gases  afforded 
no  resistance  to  each  other ;  but  that  one  gas  spreads  or  expands  into  the 
space  occupied  by  another  gas,  as  it  would  rush  into  a  vacuum.  At  least, 
that  the  resistance  which  the  particles  of  one  gas  offer  to  those  of  another 
is  of  a  very  imperfect  kind,  to  be  compared  to  the  resistance  which  stones  in  the 
channel  of  a  stream  oppose  to  the  flow  of  running  water.  Such  is  Dalton's  theory 
of  the  miscibility  of  the  gases.  (Manchester  Memoirs,  Vol.  V.) 

In  entering  upon  this  inquiry,  I  found,  first,  that  gases  diffuse  into  the  atmosphere, 
and  into  each  other,  with  different  degrees  of  ease  and  rapidity.  This  was  observed 


88  DIFFUSION    OF    GASES. 

by  allowing  each  gas  to  diffuse  from  a  bottle  into  the  air  through  a  narrow  tube, 
taking  care,  when  the  gas  was  lighter  than  air,  that  it  was  allowed  to  escape  from 
the  lower  part  of  the  vessel,  and  when  heavier  from  the  upper  part,  so  that  it  had, 
on  no  occasion,  any  disposition  to  flow  out,  but  was  constrained  to  diffuse  in  oppo- 
sition to  the  effect  of  gravity.  "The  result  was,  that  the  same  volume  of  different 
gases  escapes  in  times  which  are  exceedingly  unequal,  but  have  a  relation  to  the 
specific  gravity  of  the  gas.  The  light  gases  diffuse  or  escape  most  rapidly :  thus, 
hydrogen  escapes  five  times  quicker  than  carbonic  acid,  which  is  twenty-two  times 
heavier  than  that  gas.  Secondly,  in  an  intimate  mixture  of  two  gases,  the  most 
diffusive  gas  separates  from  the  other,  and  leaves  the  receiver  in  the  greatest  propor- 
tion. Hence,  by  availing  ourselves  of  the  tendencies  of  mixed  gases  to  diffuse  with 
different  degrees  of  rapidity,  a  sort  of  mechanical  separation  of  gases  may  be  effected. 
The  mixture  must  be  allowed  to  diffuse  for  a  certain  time  into  a  confined  gaseous  or 
vaporous  atmosphere,  of  such  a  kind  as  may  afterwards  be  condensed  or  absorbed 
with  facility.  (Quarterly  Journal  of  Science,  New  Series,  Vol.  V.) 

But  the  nature  of  the  process  of  diffusion  is  best  illustrated  when  the  gases  com- 
municate with  each  other  through  minute  pores  or  apertures  of  insensible  magnitude. 

A  singular  observation  belonging  to  this  subject  was  made  by  Professor  Dobe- 
reiner,  of  Jena,  on  the  escape  of  hydrogen  gas  by  a  fissure  or  crack  in  glass  receivers. 
Having  occasion  to  collect  large  quantities  of  that  light  gas,  he  had  accidentally 
made  use  of  a  jar  which  had  a  slight  fissure  in  it.  He  was  surprised  to  find  that 
the  water  of  the  pneumatic  trough  rose  into  this  jar  one  and  a  half  inches  in  twelve 
hours  j  and  that  after  twenty-four  hours  the  height  of  the  water  was  two  inches  two- 
thirds  above  the  level  of  that  in  the  trough.  During  the  experiment,  neither  the 
height  of  the  barometer  nor  the  temperature  of  the  place  had  sensibly  altered. 
(Annales  de  Chimie  et  de  Physique,  1825.)  He  ascribed  the  phenomenon  to  capil- 
lary action,  and  supposed  that  hydrogen  only  is  attracted  by  the  fissures,  and  escapes 
through  them  on  account  of  the  extreme  smallness  of  its  atoms.  It  is  unnecessary 
to  examine  this  explanation,  as  Dobereiner  did  not  observe  the  whole  phenomenon. 
On  repeating  the  experiment,  and  varying  the  circumstances,  it  appeared  to  me  that 
hydrogen  never  escapes  outwards  by  the  fissure  without  a  certain  portion  of  air  pene- 
trating at  the  same  time  inwards,  amounting  to  between  one-fourth  and  one-fifth  of 
the  volume  of  the  hydrogen  which  leaves  the  receiver.  It  was  found  by  an  instru- 
ment which  admits  of  much  greater  precision  than  the  fissured  jar,  that  when  hydro- 
gen gas  communicates  with  air  through  such  a  chink,  the  air  and  hydrogen  exhibit 
a  powerful  disposition  to  exchange  places  with  each  other ;  a  particle  of  air,  how- 
ever, does  not  exchange  with  a  particle  of  hydrogen  of  the  same  magnitude,  but  of 
3.83  times  its  magnitude.  We  may  adopt  the  word  diffusion-volume,  to  express 
this  diversity  of  disposition  in  gases  to  interchange  particles,  and  say  that  the  diffu- 
sion-volume of  air  being  1,  that  of  hydrogen  gas  is  3.83.  Now  every  gas  has  a  dif- 
fusion-volume peculiar  to  itself,  and  depending  upon  its  specific  gravity.  Of  those 
gases  which  are  lighter  than  air,  the  diffiision-volume  is  greater  than  1,  and  of  those 
which  are  heavier,  the  diffusion-volume  is  less  than  1.  The  diffusion  volumes  are, 
indeed,  inversely  as  the  square  root  of  the  densities  of  the  gases.  Hence  the  times 
of  the  effusion  and  diffusion  of  gases  follow  the  same  law.* 

Exact  results  are  obtained  by  means  of  a  simple  instrument,  which  may  be  called 
a  diffusion  tube,  and  which  is  constructed  as  follows.  A  glass  tube,  open  at  both 
ends,  is  selected,  half  an  inch  in  diameter,  and  from  six  to  fourteen  inches  in  length. 
A  cylinder  of  wood,  somewhat  less  in  diameter,  is  introduced  into  the  tube,  so  as  to 
occupy  the  whole  of  it,  with  the  exception  of  about  one-fifth  of  an  inch  at  one  extre- 
mity, which  space  is  filled  with  a  paste  of  Paris  plaster,  of  the  usual  consistence  for 
casts.  In  the  course  of  a  few  minutes  the  plaster  sets,  and  on  withdrawing  the 
wooden  cylinder  the  tube  forms  a  receiver,  closed  by  an  immoveable  plate  of  stucco, 
In  the  wet  state,  the  stucco  is  air-tight ;  it  is  therefore  dried,  either  by  exposure  to 
the  air  for  a  day,  or  by  placing  it  in  a  temperature  of  200°  for  a  few  hours ;  and  is 
thereafter  found  to  be  permeable  by  gases,  even  in  the  most  humid  atmosphere,  if 

*  [See  Supplement,  p.  751.] 


DIFFUSION    OF    GASES. 


89 


FIG.  43. 


FIQ.  42. 


not  positively  wetted.  When  such  a  diffusion-tube,  six  inches  in  length,  is  filled 
with  hydrogen  over  mercury,  the  diffusion,  or  exchange  of  air  for  hydrogen,  instantly 
commences  through  the  minute  pores  of  the  stucco, 
and  proceeds  with  so  much  force  and  velocity,  that 
within  three  minutes  the  mercury  attains  a  height 
in  the  receiver  of  more  than  two  inches  above  its 
level  in  the  trough;  within  twenty  minutes,  the 
whole  of  the  hydrogen  has  escaped.  In  conducting 
such  experiments  over  water,  it  is  necessary  to  avoid 
wetting  the  stucco.  With  this  view,  before  filling 
the  diffusion-tube  with  hydrogen,  the  air  is  with- 
drawn by  placing  the  tube  upon  the  short  limb  of 
an  empty  syphon  (see  figure  42),  which  does  not 
reach,  but  comes  within  half  an  inch  of  the  stucco, 
and  then  sinking  the  instrument  in  the  water  trough, 
so  that  the  air  escapes  by  the  syphon,  with  the 
exception  of  a  small  quantity,  which  is  noted.  The 
diffusion  tube  is  then  filled  up,  either  entirely  or  to 
a  certain  extent,  with  the  gas  to  be  diffused. 

The  ascent  of  the  water  in  the  tube,  when  hy- 
drogen is  diffused,  forms  a  striking  experiment. 
But  in  experiments  made  with  the  purpose  of 
determining  the  proportion  between  the  gas  diffused 
and  the  air  which  replaces  it,  it  is  necessary  to  guard 
against  any  inequality  of  pressure,  by  placing  the 
diffusion  tube  in  a  jar  of  water  as  in  figure  43, 
and  filling  the  jar  with  water  in  proportion  as  it  rises  in  the  tube. 

In  this  instrument  we  may  substitute  many  other  porous  substances  for  the  stucco; 
but  few  of  them  answer  so  well.  Dry  and  sound  cork  is  very  suitable,  but  permits 
the  diffusion  to  go  on  very  slowly,  not  being  sufficiently  porous ;  so  do  thin  slips  of 
many  granular  foliated  minerals,  such  as  flexible  magnesian  limestone.  Charcoal, 
woods,  unglazed  earthenware,  dry  bladder,  may  all  be  used  for  the  same  purpose. 

It  can  be  shown,  on  the  principles  of  pneumatics,  that  gases  should  rush  into  a 
vacuum  with  velocities  corresponding  to  the  numbers  which  have  been  found  to 
express  their  diffusion  volumes;  that  is,  with  velocities  inversely  proportional  to  the 
square  root  of  the  densities  of  the  gases.  The  law  of  the  diffusion  of  gasses  has  on 
this  account  been  viewed  by  my  friend,  Mr.  T.  S.  Thomson,  of  Clitheroe,  as  a  con- 
firmation of  Dr.  Dalton's  theory,  that  gases  are  inelastic  towards  each  other  (L.  Ed. 
and  D.,  Phil.  Mag.  3d  series,  iv.  321).  It  must  be  admitted  that  the  ultimate 
result  in  diffusion  is  in  strict  accordance  with  Dalton's  law,  but  there  are  certain 
circumstances  which  make  me  hesitate  in  adopting  it  as  a  true  representation  of  the 
phenomenon,  although  it  affords  a  covenient  mode  of  expressing  it.  1.  It  is  sup- 
posed, on  that  law,  that  when  a  cubic  foot  of  hydrogen  gas  is  allowed  to  communi- 
cate with  a  cubic  foot  of  air,  the  hydrogen  expands  into  the  space  occupied  by  the 
air,  as  it  would  do  into  a  vacuum,  and  becomes  two  cubic  feet  of  hydrogen  of  half 
density.  The  air,  on  the  other  hand,  expands  in  the  same  manner  into  the  space 
occupied  by  the  hydrogen,  so  as  to  become  two  cubic  feet  of  air  of  half  density. 
Now  if  the  gases  actually  expanded  through  each  other  in  this  manner,  cold  should 
be  produced,  and  the  temperature  of  the  mixed  gases  should  fall  40  or  45  degrees. 
But  not  the  slightest  change  of  temperature  occurs  in  diffusion,  however  rapidly  the 
process  is  conducted.  2.  Although  the  ultimate  result  of  diffusion  is  always  in  con- 
formity with  Dalton's  law,  yet  the  diffusive  process  takes  place  in  different  gases 
with  very  different  degrees  of  rapidity.  Thus,  the  external  air  penetrates  into  a 
diffusion  tube  with  velocities  denoted  by  the  following  numbers,  1277,  623,  302, 
according  as  the  diffusion  tube  is  filled  with  hydrogen,  with  carbonic  acid,  or  with 
chlorine  gas.  Now,  if  the  air  were  rushing  into  a  vacuum  in  all  these  cases,  why 


90  DIFFUSION    OF    VAPOURS. 

should  it  not  always  enter  it  with  the  same  velocity  ?  Something  more,  therefore, 
must  be  assumed  than  that  gases  are  vacua  to  each  other,  in  order  to  explain  the 
whole  phenomena  observed  in  diffusion. 

Passage  of  gases  through  membranes.  —  In  connexion  with  diffusion,  the  passage 
of  gases  through  humid  membranes  may  be  noticed.  If  a  bladder,  half  filled  with 
air,  with  its  mouth  tied,  be  passed  up  into  a  large  jar  filled  with  carbonic  acid  gas, 
standing  over  water,  the  bladder,  in  the  course  of  twenty- four  hours,  becomes  greatly 
distended,  by  the  insinuation  of  the  carbonic  acid  through  its  substance,  and  may 
even  burst,  while  a  very  little  air  escapes  outwards  from  the  bladder.  But*  this  is 
not  simple  diffusion.  The  result  depends  upon  two  circumstances  :  first,  upon  car- 
bonic acid  being  a  gas  easily  liquefied  by  the  water  in  the  substance  of  the  mem- 
brane,—  the  carbonic  acid  penetrates  the  membrane  as  a  liquid;  secondly,  this  liquid 
is  in  the  highest  degree  volatile,  and,  therefore,  evaporates  very  rapidly  from  the 
inner  surface  of  the  bladder  into  the  air  confined  in  it.  The  air  in  the  bladder 
comes  to  be  expanded  in  the  same  manner  as  if  ether  or  any  other  volatile  fluid  was 
admitted  into  it.  The  phenomenon  was  observed  by  Dalton  in  its  simplest  form. 
Into  a  very  narrow  jar,  half  filled  with  carbonic  acid  gas  over  water,  he  admitted  a 
little  air.  The  air  and  gas  were  accidentally  separated  by  a  water-bubble,  and  thus 
prevented  from  intermixing.  But  the  carbonic  gas  immediately  began  to  be  liquified 
by  the  film  of  water,  and  passing  through  it,  evaporated  into  the  air  below.  The 
air  was  in  this  way  gradually  expanded,  and  the  water-bubble  ascended  in  the  tube. 
Here  the  particular  phenomenon  in  question  was  observed  to  take  place,  but  without 
the  intervention  of  membrane.  It  is  to  be  remembered  that  the  thinnest  film  of 
water  or  any  liquid  is  absolutely  impermeable  to  a  gas  as  such. 

.  In  the  experiments  of  Drs.  Mitchell  and  Faust,  and  others,  in  which  gases  passed 
through  a  sheet  of  caoutchouc,  it  is  to  be  supposed  that  the  gases  were  always  lique- 
fied in  that  substance,  and  penetrated  through  it  in  a  fluid  form.  Indeed,  few  bodies 
are  more  remarkable  than  caoutchouc  for  the  avidity  with  which  they  imbibe  various 
liquids.  The  absorption  of  ether,  of  naphtha,  of  oil  of  turpentine,  softening  the  sub- 
stance of  the  caoutchouc,  without  dissolving  it,  may  be  referred  to.  It  is  likewise 
always  those  gases  which  are  more  easily  liquified  by  cold  or  pressure  that  pass  most 
readily  through  both  caoutchouc  and  humid  membranes.  Dr.  Mitchell  found  that 
the  time  required  for  the  passage  of  equal  volumes  of  different  gases  through  the 
same  membrane,  was 

1    minute,  with  ammonia. 

minutes,  with  sulphuretted  hydrogen. 
"  cyanogen. 

carbonic  acid, 
nitrous  oxide, 
arsenietted  hydrogen. 


28 


113 
160 


olefiant  gas. 
hydrogen, 
oxygen, 
carbonic  oxide. 


and  a  much  greater  time  with  nitrogen. 


DIFFUSION   OF  VAPOURS   INTO   AIR,    OR   SPONTANEOUS   EVAPORATION. 

Volatile  bodies,  such  as  water,  rise  into  air  as  well  as  into  a  vacuum,  and  obviously 
according  to  the  law  by  which  gases  diffuse  through  each  other.  Thus,  if  a  small 
quantity  of  the  volatile  liquid  ether  be  conveyed  into  two  tall  jars  standing  over 
water,  one  half  filled  with  air,  and  the  other  with  hydrogen  gas,  the  air  and  hydrogen 
immediately  begin  to  expand,  from  the  ascent  of  the  ether-vapour  into  them,  and 
the  two  gases  in  the  end  have  their  volume  increased  exactly  in  the  same  proportion. 
But  the  hydrogen  gas  undergoes  this  expansion  in  half  the  time  that  the  air  requires; 


SPONTANEOUS  EVAPORATION.  91 

that  is  to  say,  ether-vapour  follows  the  usual  law  of  diffusion  in  penetrating  more 
rapidly  through  the  lighter  gas. 

We  are  indebted  to  Dr.  Dalton  for  the  discovery  that  the  evaporation  of  water  has 
the  same  limit  in  air  as  in  a  vacuum.  Indeed,  the  quantity  of  vapour  from  a  vola- 
tile body  which  can  rise  into  a  confined  space,  is  the  same,  whether  that  space  be  a 
vacuum,  or  be  already  filled  with  air  or  gas,  in  any  state  of  rarefaction  or  condensa- 
tion. The  vapour  rises,  and  adds  its  own  elastic  force,  such  as  it  exhibits  in  a 
vacuum,  to  the  elastic  force  of  the  other  gases  or  vapours  already  occupying  the  same 
space/  Hence,  it  is  only  necessary  to  know  what  quantity  of  any  vapour  rises  into 
a  vacuum  at  any  particular  temperature ;  —  the  same  quantity  rises  into  air.  Thus 
the  vapour  from  water,  which  rises  into  a  vacuum  at  80°,  depresses  the  mercurial 
column  one  inch,  or  its  tension  is  one-thirtieth  of  the  usual  tension  of  the  air. 
Now,  if  water  at  80°  be  admitted  into  dry  air,  it  will  increase  the  tension  of  that  air 
by  l-30th,  if  the  air  be  confined;  or  increase  its  bulk  by  l-30th,  if  the  air  be  allowed 
to  expand.  M.  Regnault  has,  indeed,  observed  that  the  tension  of  the  vapour  of 
water  in  air,  and  in  pure  nitrogen  gas,  is  always  a  little  more  feeble  (2  or  3  per 
cent.)  than  in  a  vacuum  for  the  same  temperature,  (Annales  de  Ch.  et  Ph.,  xv.  137); 
from  which  may  be  inferred  the  existence  of  some  physical  obstacle  to  the  full  diffu- 
sion of  vapours,  of  which  the  nature  is  at  present  unknown.  The  density  of  the 
vapour  of  water  in  air  saturated  with  it  may  also  be  taken  as  the  same  as  it  has  been 
found  in  a  vacuum,  or  622  (air  =  1000),  M.  Regnault  having  observed  it  to  deviate 
not  more  than  one-hundredth  part  from  that  density,  at  all  temperatures  between 
32°  and  72°  Fahr.  —  (Ibid.,  p.  160). 

The  spontaneous  evaporation  of  water  into  air  is  much  affected  by  three  circum- 
stances : — 1.  The  previous  state  of  dryness  of  the  air  —  for  a  certain  fixed  quantity 
only  of  vapour  can  rise  into  air,  as  much  as  into  the  same  space  if  vacuous;  and  if 
a  portion  of  that  quantity  be  already  present,  so  much  the  less  will  be  taken  up  by 
the  air ;  and  no  evaporation  whatever  takes  place  into  air  which  contains  this  fixed 
quantity,  and  is  already  saturated  with  humidity.  2.  By  warmth  —  for  the  higher 
the  temperature  the  more  considerable  is  the  quantity  of  vapour  which  rises  into  any 
accessible  space.  Thus  water  emits  so  much  vapour  at  40°  as  expands  the  air  in  con- 
tact with  it  1-1 14th  part,  and  at  60°  as  much  as  expands  air  l-57th  part,  or  double 
the  quantity  emitted  at  the  lower  temperature.  Hence,  humid  hot  air  contains  a 
much  greater  portion  of  moisture  than  humid  cold  air.  4.  The  evaporation  of 
water  is  greatly  quickened  by  the  removal  of  the  incumbent  air  in  proportion  as  it 
becomes  saturated ;  and  hence  a  current  of  air  is  exceedingly  favourable  to  evapo- 
ration. 

When  air  saturated  with  humidity  at  a  high  temperature  is  cooled,  it  ceases  to  be 
able  to  sustain  the  large  portion  of  vapour  which  it  possesses,  and  the  excess  assumes 
the  liquid  form,  and  precipitates  in  drops.  Many  familiar  appearances  depend  upon 
the  condensation  of  the  vapour  in  the  atmosphere.  When  a  glass  of  cold  water,  for 
instance,  is  brought  into  a  warm  room,  it  is  often  quickly  covered  with  moisture. 
The  air  in  contact  with  the  glass  is  chilled,  and  its  power  to  retain  vapour  so  much 
reduced  as  to  occasion  it  to  deposit  a  portion  upon  the  cold  glass.  It  is  from  the 
same  cause  that  water  is  often  seen  in  the  morning  running  down  in  streams  upon 
the  inside  of  the  glass  panes  of  bed-room  windows.  The  glass  has  the  low  tempera- 
ture of  the  external  air,  and  by  contact  cools  the  warm  and  humid  air  of  the  apart- 
ment so  as  to  occasion  the  precipitation  of  its  moisture.  Hence  also,  when  a  warm 
thaw  follows  after  frost,  thick  stone  walls  which  continue  to  retain  their  low  tempe- 
rature are  covered  by  a  profusion  of  moisture. 

Hygrometers.  —  As  water  evaporates  at  all  temperatures,  however  low,  the  atmo 
sphere  cannot  be  supposed  to  be  ever  entirely  destitute  of  moisture.  The  proportion 
present  varies  with  the  temperature,  the  direction  of  the  wind,  and  other  circum- 
stances, but  is  generally  greater  in  summer  than  in  winter.  There  are  various 
means  by  which  the  moisture  in  the  air  may  be  indicated,  and  its  quantity  estimated, 
affording  principles  for  the  construction  of  different  hygroscopes  or  hygrometers. 


92 


HYGROMETERS. 


FIG.  44. 


1.  The  chemical  method  consists  in  passing  a  known  measure  of  air  over  a 
highly  hygrometric  substance,  such  as  chloride  of  calcium,  contained  in  a  glass  tube, 
which  has  been  weighed;  the  increase  of  weight  is  that  of  the  vapour  absorbed. 
The  experiment  admits  of  being  made  with  rigorous  accuracy,  but  is  seldom  had 
recourse  to,  except  to  check  other  methods  which  are  more  expeditious,  but  less 
certain.1 

2.  Many  solid  substances  swell  on  imbibing  moisture,  and  contract  again  on  dry- 
ing :  such  as  wood,  parchment,  hair,  and  most  dry  organic  substances.     The  hygro- 
meter of  Deluc  consisted  of  an  extremely  thin  piece  of  whalebone,  which  in  expand- 
ing and  contracting  moved  an  index.     The  principle  of  this  instrument  is  illustrated 
in  the  transparent  shavings  of  whalebone  cut  into  figures,  which  bend  and  crumple 
up  when  laid  upon  the  warm  hand.     Saussure  made  use  of  human  hair  boiled  in  a 
solution  of  carbonate  of  soda,  as  a  hygrometric  body,  and  it  appears  to  answer  better 
than  any  other  substance  of  the  class.     Regnault  does  no.t  make  any  essential  change 
in  the  construction  of  Saussure,  but  prefers  to  deprive  the  hairs  of  unctuous  matter 
by  leaving  them  for  twenty-four  hours  in  a  tube  filled  with  ether.     They  preserve  in 
this  way  all  their  tenacity,  and  acquire  at  the  same  time  nearly  as  much  sensibility 
as  if  they  had  been  prepared  by  an  alkali.     He  finds  that  each  instrument  must  be 
graduated  experimentally  by  placing  it  in  a  confined  space  with  air  kept  in  a  known 
state  of  humidity  by  the  presence  of  dilute  sulphuric  acid  of  several  degrees  of 
Strength,  which  he  indicates,  and  supplies  tables  of  their  tension  at  different  tempe- 
ratures (Ann.  de  Ch.,  t.  xv.  p.  173).     Of  this  instrument,  which  is  so  convenient  in 
a  great  many  circumstances,  he  speaks  more  highly  than  physicists  generally  of  late, 
but  at  the  same  time  remarks  that  it  requires  great  circumspection  in  the  observer, 
and  that  the  occasional. verification  of  the  instrument  by  means  of  the  solutions  first 
employed  in  graduating  it  is  indispensable. 

8.  The  degree  of  dryness  of  the  air  may  be  judged 
of  by  the  rapidity  of  evaporation.  Leslie  made  use  of 
his  differential  thermometer  as  a  hygrometer,  covering 
one  of  the  bulbs  with  muslin,  and  keeping  it  constantly 
moist  by  means  of  a  wet  thread  from  a  cup  of  water 
placed  near  it.  The  evaporation  of  the  moisture  cools 
the  ball,  and  occasions  the  air  in  it  to  contract.  This 
instrument  gives  useful  information  in  regard  to  the 
rapidity  of  evaporation,  or  the  drying  power  of  the  air, 
but  does  not  indicate  directly  the  quantity  of  moisture 
in  the  air.  The  wet-bulb  hygrometer,  more  commonly 
used,  acts  on  the  same  principle,  but  consists  of  two 
similar  and  very  delicate  mercurial  thermometers,  the 
bulb  of  one  of  which  (a)  is  kept  constantly  moist,  while 
the  bulb  of  the  other  (6)  is  dry.  The  wet  thermometer 
always  indicates  a  lower  temperature  than  the  dry  one, 
unless  when  the  air  is  fully  saturated  with  moisture, 
and  no  evaporation  from  the  moist  bulb  takes  place. 
In  making  an  observation,  the  instrument  is  generally 
placed,  not  in  absolutely  still  air,  but  in  an  open  win- 
dow where  there  is  a  slight  draught. 

The  indications  of  the  wet-bulb  hygrometer,  or  psy- 
chrometer,  are  discovered  by  simple  inspection.  It  is,  therefore,  a  problem  of  the 
greatest  importance  to  deduce  from  them  the  dew  point,  or  the  tension  of  the  vapour 
in  the  air,  by  an  easy  rule.  Could  this  inference  be  made  with  certainty,  the  wefc- 
bulb  hygrometer  is  so  commodious  that  it  would  supersede  all  others.  I  shall  place 

»  The  present  and  following  methods  of  hygroraetry,  and  all  the  experimental  data  required, 
have  lately  received  a  full  and  critical  revision  from  M.  Regnault,  of  the  greatest  value. 
See  his  "Etudes  sur  1'Hygrometrie,"  Annales  de  Chimie,  &c.,  1835,  3  se>.  t.  xv.  p.  129. 


SPONTANEOUS  EVAPORATION.  93 

below  a  formula  for  this  purpose,  which  has  been  used  for  several  years  in  the  north 
of  Europe,  and  the  same  as  it  has  been  recently  modified.1 

4.  The  most  simple  mode  of  ascertaining  the  absolute  quantity  of  vapour  in  the 
air  is  to  cool  the  air  gradually,  and  note  the  degree  of  temperature  at  which  it  begins 
to  deposit  moisture,  or  ceases  to  be  capable  of  sustaining  the  whole  quantity  of  vapour 
which  it  possesses.  The  air  is  saturated  with  vapour  for  this  particular  degree  of 
temperature,  which  is  called  its  dew-point.  The  saturating  quantity  of  vapour  for 
the  degree  of  temperature  indicated  may  then  be  learned  by  reference  to  a  table  of 
the  tension  of  the  vapour  of  water  at  different  temperatures.2  It  is  the  absolute 
quantity  of  vapour  which  the  air  at  the  time  of  the  observation  possesses.  The 
dew-point  may  be  ascertained  most  accurately  by  exposing  to  the  air  a  thin  cup  of 
silver  or  tin-plate  containing  water  so  cold  as  to  occasion  the  condensation  of  dew 
upon  the  metallic  surface.  The  water  in  the  cup  is  stirred  with  the  bulb  of  a  small 
thermometer,  and  as  the  temperature  gradually  rises,  the  degree  is  noted  at  which 
the  dew  disappears  from  the  surface  of  the  vessel.  The  temperature  at  which  this 
occurs  may  be  taken  as  the  dew-point.  Water  may  generally  be  cooled  sufficiently 
in  summer  to  answer  for  an  experiment  of  this  kind  by  dissolving  pounded  sal- 
ammoniac  in  it. 

The  dew-point  may  be  observed  much  more  quickly  by  means  of  the  elegant 
hygrometer  of  the  late  Mr.  Daniell.  (Daniell's  Meteorological  Essays,  p.  147). 
This  instrument  (see  figure  45)  consists  of  two  glass  balls,  a  and  b,  connected  by  a 
syphon,  and  containing  a  quantity  of  ether,  from  which  the  air  has  been  expelled 
by  the  same  means  as  in  the  cryophorus  of  Dr.  Wollaston  (page  75).  One  of  the 
arms  of  the  syphon  tube  contains  a  small  thermometer,  with  its  scale,  which  should 
be  of  white  enamel ;  the  bulb  of  the  thermometer  descends  into  the  ball,  £,  at  the 
extremity  of  this  arm,  and  is  placed,  not  in  the  centre  of  the  ball,  but  as  near  as 
possible  to  some  point  of  its  circumference.  A  zone  of  this  ball  is  gilt  and  bur- 
nished, so  that  the  deposition  of  dew  may  easily  be  perceived  upon  it.  The  other' 
ball,  a,  is  covered  with  muslin.  When  an  observation  is  to  be  made,  this  last  ball 
is  moistened  with  ether,  which  is  supplied  slowly  by  a  drop  or  two  at  a  time.  It  is 
cooled  by  the  evaporation  of  the  ether,  and  becomes  capable  of  condensing  the 
vapour  of  the  included  fluid,  and  thereby  occasions  evaporation  in  the  opposite  ball, 
6,  containing  the  thermometer.  The  temperature  of  the  ball,  b,  should  be  thus 

1  The  psychrometer  was  first  suggested  by  Gay-Lussac  (Annales  de  Chimie,  &c.,  t.  xxi. 
p.  91),  and  its  application  particularly  studied  by  Dr.  E.  H.  August,  of  Berlin,  (Ueber  die 
Fortschritte  der  Hygrometrie),  1830,  and  Dr.  Apjohn  (Philosophical  Magazine,  1838,  &c.)     To 
obtain  the  tension  of  vapour  in  the  atmosphere  from  the  two  temperatures  observed,  the 
following  formula  is  given  by  Dr.  August,  neglecting  some  very  small  quantities : — 

0.568  (t  —  t') 

*=/' .h; 

640  —  t' 

where  t  and  tf  are  temperatures  (Centigrade)  of  the  dry  and  wet  thermometers,  /'  the  ten- 
sion of  vapour  in  air  saturated  at  the  temperature  2',  h  the  height  of  the  barometer,  and 
640  —  t'  the  latent  heat  of  aqueous  vapour.  Some  of  the  numerical  data  are  modified  by 
M.  Regnault,  and  the  formula  becomes: — 

0.429  (*—*') 

*=/' 5 .h; 

610—*' 
Or, 

0.480  (t  —  f) 

*=/' ,*. 

616  —  t 

The  last  co-efficient  0.480  he  finds  to  give  a  coincidence  almost  perfect  between  the  calcu 
lated  and  true  results,  when  the  air  is  not  more  than  four-tenths  saturated.  Otherwise  the 
first  coefficient  0.429  is  least  objectionable.  (Annales,  &c.,  xv.  pp.  202  and  226). 

2  A  table  by  M.  Regnault  for  this  purpose  will  be  given  in  an  Appendix.     [See  Supplement, 
p.  646.] 


94 


HYGROMETERS. 


FIG.  45. 


reduced  in  a  gradual  manner,  so  that  the  degree  of  the  ther- 
mometer at  which  dew  begins  to  be  deposited  on  the  metallic 
part  of  the  surface  of  the  ball  may  be  observed  with  preci- 
sion. The  temperature  of  b  being  thereafter  allowed  to  rise, 
the  degree  at,  which  the  dew  disappears  from  its  surface  may 
likewise  be  noted.  It  should  not  differ  much  from  the  tem- 
perature of  the  deposition,  and  will  probably  give  the  dew- 
point  more  correctly  j  although,  strictly  speaking,  the  mean 
between  the  two  observations  should  be  the  true  dew-point. 
It  is  convenient  to  have  a  second  thermometer  in  the  pillar 
of  the  instrument,  for  observing  the  temperature  of  the  air 
at  the  time. 

M.  Regnault  proposes  a  modification  of  DanielPs  hygro- 
meter, under  the  name  of  the  Condenser-hygrometer,  (An- 
nales  de  Chimie,  et  Ph.  t.  xv.  PI.  2),  which  appears  to  be 
the  most  perfect  instrument  of  the  class.  It  consists  of  a 
thimble,  a  b  c,  (figure  46),  made  of  silver,  very  thin,  and 
perfectly  polished,  1-8  inch  in  depth,  and  8-10ths  of  an  inch 
in  diameter,  which  is  fitted  tightly  upon  a  glass  tube,  c  d, 
open  at  both  ends.  The  tube  has  a  small  lateral  tubulure,  t 


FIG.  46. 


FIG.  47. 


The  upper  opening  of  the  tube  is  closed 
by  a  cork,  which  is  traversed  by  the  stem 
of  a  very  sensible  thermometer  occupying 
its  axis ',  the  bulb  of  the  thermometer  is 
in  the  centre  of  the  silver  thimble.  A 
very  thin  glass  tube,  f  g,  open  at  both 
ends,  traverses  the  same  cork,  and  de- 
'scends  to  the  bottom  of  the  thimble. 
Ether  is  poured  into  the  tube  as  high  as 
m  n,  and  the  tubulure  t  is  placed  in  com- 
munication by  means  of  a  leaden  tube 
with  an  aspirator  jar  six  or  eight  pints  in 
capacity,  filled  with  water.  The  aspirator 
jar  is  placed  near  the  observer,  while  the 
condenser-hygrometer  is  kept  as  far  from 
his  person  as  is  desirable. 

On  allowing  water  to  run  from  the 
aspirator  jar,  air  enters  by  the  tube  gft 
passing  bubble  by  bubble  through  the 
ether,  which  it  cools  by  carrying  away 
vapour '}  the  refrigeration  is  the  more  ra- 
pid, the  more  freely  the  water  is  allowed 
to  flow ;  and  the  whole  mass  of  ether  pre- 
sents a  sensibly  uniform  temperature,  as 
it  is  briskly  agitated  by  the  passage  of  the 
bubbles  of  air.  The  temperature  is  suffi- 
ciently lowered  in  less  than  a  minute  to 
determine  an  abundant  deposit  of  dew. 
The  thermometer  is  then  observed  through 
a  little  telescope ;  suppose  that  it  is  read 
off  at  50°.  This  temperature  is  evidently 
somewhat  lower  than  what  corresponds 

exactly  to  the  air's  humidity.    By  closing  •"'"  •••'" inim-mm 

the  stopcock  of  the  aspirator  the  passage  of  air  is  stopped,  the  dew  disappears 
in  a  few  seconds,  and  the  thermometer  again  rises.  Suppose  that  it  marks  52°  : 
thia  degree  is  above  the  dew-point.  The  stopcock  of  the  aspirator  is  then  opened 


SPONTANEOUS  EVAPORATION. 


95 


very  slightly,  so  as  to  determine  the  passage  of  a  very  small  stream  of  air  bubbles 
through  the  ether.  If  the  thermometer  continues,  notwithstanding,  to  rise,  the 
stopcock  is  opened  further,  and  the  thermometer  brought  down  to  51°. 8  :  by 
shutting  the  stopcock  slightly,  it  is  easy  to  stop  the  falling  range,  and  make  the 
thermometer  remain  stationary  at  51°. 8  as  long  as  is  desired.  If  no  dew  forms 
after  the  lapse  of  a  few  seconds,  it  is  evident  that  51°. 8  is  higher  than  the  dew- 
point.  It  is  brought  down  to  51°. 6,  and  maintained  there  by  regulating  the  flow. 
The  metallic  surface  being  now  observed  to  become  dim  after  a  few  seconds,  it  is 
concluded  that  51°. 6  is  too  low,  while  51°. 8  was  too  high.  A  still  greater  approxi- 
mation even  may  be  made,  by  now  finding  whether  51°. 7  is  above  or  below  the 
point  of  condensation.  These  operations  may  be  executed  in  a  very  short  time,  after 
a  little  practice ;  three  or  four  minutes  being  found  sufficient,  by  M.  Regnault,  to 
determine  the  dew-point  to  within  about  T\yth  of  a  degree  Fahr.  A  more  considera- 
ble fall  of  temperature  may  be  obtained  by  means  of  this  than  the  original  instru- 
ment of  Daniell,  with  the  consumption  of  a  much  less  quantity  of  ether;  indeed, 
that  liquid  may  be  dispensed  with  entirely,  and  alcohol  substituted  for  it.  The 
thermometer,  T,  to  observe  the  temperature  of  the  air  during  the  experiment,  is 
placed  in  a  second  similar  glass  tube  and  thimble  a'  #',  also  under  the  influence  of 
the  aspirator,  but  containing  no  ether. 

In  evaporating  by  means  of  hot  air,  as  in  drying  goods  in  the  ordinary  bleachers' 
stove,  which  is  heated  by  flues  from  a  fire  carried  along  the  floor,  it  should  be  kept 
in  mind  that  a  certain  time  must  elapse  before  air  is  saturated  with  humidity.  Mr. 
Daniell  has  observed  that  a  few  cubic  inches  of  dry  air  continue  to  expand  for  an 
hour  or  two,  when  exposed  to  water  at  the  temperature  of  the  air.  At  high  tem- 
peratures, the  diffusion  of  vapour  into  air  is  more  rapid ;  but  still  it  is  not  at  all 
instantaneous.  Hence,  in  such  a  drying  stove,  means  ought  to  be  taken  to  repress 
rather  than  to  promote  the  exit  of  the  hot  air ;  otherwise  a  loss  of  heat  will  be 
occasioned  by  the  escape  of  the  air,  before  it  is  saturated  with  humidity.  The 
greatest  advantage  has  been  derived  from  closing  such  a  stove  as  perfectly  as  possible 
at  the  top,  and  only  opening  it  after  the  goods  are  dried  and  about  to  be  removed, 
in  order  to  allow  of  a  renewal  of  the  air  in  the  chamber  between  each  operation. 
In  evaporating  water  by  heated  air,  the  vapour  itself  carries  off  exactly  the  same 
quantity  of  heat  as  if  it  were  produced  by  boiling  the  water  at  212°,  while  the  air 
associated  with  it  likewise  requires  to  have  its  temperature  raised,  and  therefore 
occasions  an  additional  consumption  of  heat.  Hence  water  can  never  be  evaporated 
by  air  in  a  drying  stove  with  so  small  an  expenditure  of  fuel  as  in  a  close  boiler. 

When  bodies  to  be  dried  do  not  part  with  their  moisture  freely,  but  in  a  gradual 
manner,  as  is  the  case  with  roots,  and  most  organic  substances,  the  hot  air  to  dry 
them  may  be  greatly  economised  by  a  particular  mode  of  applying  it,  which  is 

practised  in  the  madder-stove.  The  principle  of 
this  drying  stove  is  illustrated  by  the  annexed 
figure,  in  which  a  b  represent  a  tight  chamber, 
having  two  openings,  one  near  the  roof,  by  which 
hot  air  is  admitted  into  the  chamber,  and  another 
at  the  bottom,  by  which  the  air  escapes  into  the 
tall  chimney  c.  The  chamber  contains  a  series 
of  stages,  from  the  floor  to  the  roof,  on  the  lowest 
c  of  which,  sacks,  half  filled  with  the  damp  madder 
roots,  are  first  placed.  In  proportion  as  the  roots 
dry,  the  bags  are  raised  from  stage  to  stage,  till 
they  arrive  at  the  highest  stage,  where  they  are 
exposed  to  the  air  when  hottest  and  most  desic- 
cating. As  the  dried  roots  are  removed  from  the 
top,  new  roots  are  introduced  below,  and  passed 
through  in  the  same  manner.  Here  the  dry  and 


Fig.  48. 


96 


FIG.  49. 


NATURE    OF    HEAT. 

hot  air,  after  taking  all  the  moisture  which  the 
roots  on  the  highest  stage  will  part  with,  de- 
scends, and  is  still  capable  of  abstracting  a  se- 
cond quantity  of  moisture  from  the  roots  on  the 
next,  and  so  on,  as  it  proceeds,  till  it  passes  away 
into  the  chimney  absolutely  saturated  with  mois- 
ture, after  having  reached  the  bottom  of  the  cham- 
ber. 

It  is  frequently  an  object  to  dry  a  small  quantity 
of  a  substance  most  completely  (such  as  an  organic 
substance  for  analysis)  at  some  steady  temperature, 
such  as  212°.  This  is  effected  very  conveniently 
by  means  of  a  little  oven,  (figure  49),  consisting  of 
a  double  box  of  copper  or  tin-plate,  about  six 
inches  square,  with  water  between  the  casings, 
which  is  kept  in  a  state  of  ebullition  by  means  of  a 
gas  flame,  or  spirit  lamp. 


NATURE    OF    HEAT. 

It  is  convenient  to  adopt  the  material  theory  of  heat  in  considering  its  accumula- 
tion in  bodies,  and  in  expressing  quantities  of  heat  and  the  relative  capacities  of 
bodies  for  heat.  Indeed,  every  thing  relating  to  the  absorption  of  heat  suggests  the 
idea  of  its  substantial  existence;  for  heat,  unlike  light,  is  never  extinguished  when 
it  falls  upon  a  body,  but  is  either  reflected  and  may  be  farther  traced,  or  is  absorbed 
and  accumulated  in  the  body,  and  may  again  be  derived  from  it  without  loss.  But 
the  mechanical  phenomena  of  heat,  which  resemble  those  of  light,  may  be  explained 
with  equal  if  not  greater  advantage  by  assuming  an  undulatory  theory  of  heat,  cor- 
responding with  the  undulatory  theory  of  light.  A  peculiar  imponderable  medium 
or  ether  is  supposed  to  pervade  all  space,  through  which  undulations  are  propagated 
that  produce  the  impression  of  heat.  A  hot  radiant  body  is  a  body  possessing  the 
faculty  to  originate  or  excite  such  undulations  in  the  ether  or  medium  of  heat, 
which  spread  on  all  sides  around  it,  like  the  waves  from  a  pebble  thrown  into  still 
water.  Sound  is  propagated  by  waves  in  this  manner,  but  the  medium  in  which 
they  are  generally  produced,  or  the  usual  vehicle  of  sound,  is  the  air;  and  all  the 
experiments  on  the  reflection  and  concentration  of  heat,  by  concave  reflectors,  may 
be  imitated  by  means  of  sound.  Thus,  if  a  watch  instead  of  the  lamp  be  placed  in 
the  focus  of  one  of  a  pair  of  conjugate  reflecting  mirrors  (fig.  20,  p.  54),  the  waves 
of  air  occasioned  by  its  beating  emanate  from  the  focus,  strike  against  the  mirror, 
and  are  reflected  from  it,  so  as  to  break  upon  the  face  of  the  opposite  mirror,  are 
concentrated  into  .its  focus,  and  communicate  the  impression  of  sound  to  an  ear 
placed  there  to  receive  it.  The  transmission  of  heat  from  the  focus  of  one  mirror 
to  the  focus  of  the  other  may  easily  be  conceived  to  be  the  propagation  of  similar 
undulations  through  another  and  different  medium  from  air,  but  coexisting  in  the 
same  space. 

In  adopting  the  material  theory  of  heat,  we  are  under  the  necessity  of  assuming 
that  there  are  different  kinds  of  heat,  some  of  which  are  capable  of  passing  through 
glass,  such  as  the  heat  of  the  sun,  while  others,  such  as  that  radiating  from  the 
hand,  are  entirely  intercepted  by  glass.  But  on  the  undulatory  theory  the  different 
properties  of  heat  are  referred  to  differences  in  the  size  of  the  waves,  as  the  differ- 
ences of  colour  are  accounted  for  in  light.  Heat  of  the  higher  degrees  of  intensity, 
however,  admits  of  a  kind  of  degradation,  or  conversion  into  heat  of  lower  intensity, 
to  which  we  have  nothing  parallel  in  the  case  of  light.  Thus  when  the  calorific  rays 
of  the  sun,  which  are  of  the  highest  intensity,  pass  through  glass,  and  strike  a  black 
wall,  they  are  absorbed,  and  appear  immediately  afterwards  radiating  from  the  heated 
wall,  as  heat  of  low  intensity,  and  are  no  longer  capable  of  passing  through  glass. 


NATURE    OF    HEAT.  97 

It  is  as  yet  an  unsolved  problem  to  reverse  the  order  of  this  change,  and  convert 
heat  of  low  into  heat  of  high  intensity.  The  same  degradation  of  heat  or  loss  of 
intensity,  is  observed  in  condensing  steam  in  distillation.  The  whole  heat  of  the 
steam,  both  latent  and  sensible,  is  transferred  without  loss  in  that  process,  to  perhaps 
fifteen  times  as  much  condensing  water ;  but  the  intensity  of  the  heat  is  reduced 
from  212°  to  perhaps  100°  Fahr.  The  heat  is  not  lost;  for  the  fifteen  parts  of 
water  at  100°  are  capable  of  melting  as  much  ice  as  the  original  steam.  But  by  no 
quantity  of  this  heat  at  100°  can  temperature  be  raised  above  that  degree  :  no  means 
are  known  of  giving  it  intensity. 

If  heat  of  low  is  ever  changed  into  heat  of  high  intensity,  it  is  in  the  compression 
of  gaseous  bodies  by  mechanical  means.  Let  steam  of  half  the  tension  of  the  atmo- 
sphere, produced  at  180°,  in  a  space  otherwise  vacuous,  be  reduced  into  half  its 
volume,  by  doubling  the  pressure  upon  it,  and  its  temperature  will  rise  to  212°.  If 
the  pressure  be  again  doubled,  the  temperature  will  become  250°,  and  the  whole 
latent  heat  of  the  steam  will  now  possess  that  high  intensity.  When  air  itself  is 
rapidly  compressed  in  a  common  syringe,  we  have  a  remarkable  conversion  of  heat 
of  low  into  heat  of  very  high  intensity. 

It  may  be  imagined  that  the  elevation  of  temperature  produced  in  the  friction  of 
hard  bodies  has  a  similar  origin ;  that  it  results  from  the  conversion  of  heat  of  low 
intensity,  which  the  bodies  rubbed  together  possess,  into  Keat  of  high  intensity.  But 
it  would  be  necessary  further  to  suppose  that  a  supply  of  heat  of  low  intensity  to 
the  bodies  rubbed  can  be  endlessly  kept  up,  by  conduction  or  radiation,  from  conti- 
guous bodies,  as  there  is  certainly  no  limit  to  the  production  of  heat  by  means  of 
friction.* 

Count  Rumford,  by  boring  a  cylinder  of  cast  iron,  raised  the  temperature  of 
several  pounds  of  cold  water  to  the  boiling  point.  Sir  H.  Davy  succeeded  in  melting 
two  pieces  of  ice  in  the  vacuum  of  an  air-pump,  by  making  them  rub  against  each 
other,  while  the  temperature  of  the  air-pump  itself  and  the  surrounding  atmosphere 
was  below  32°.  M.  Haldot  observed  that  when  the  surface  of  the  rubber  was 
rough,  only  half  as  much  heat  appeared  as  when  the  rubber  was  smooth.  When 
the  pressure  of  the  rubber  was  quadrupled,  the  proportion  of  heat  evolved  was  in- 
creased seven-fold.  When  the  rubbing  apparatus  was  surrounded  by  bad  conductors 
of  heat,  or  by  non-conductors  of  electricity,  the  quantity  of  heat  evolved  was  dimi- 
nished. (Nicholson's  Journal,  xxvi.  30). 

According  to  Pictet,  a  piece  of  brass,  rubbed  with  a  piece  of  cedar  wood,  produced 
more  heat  than  when  rubbed  with  another  piece  of  metal ;  and  the  heat  was  still 
greater  when  two  pieces  of  wood  were  rubbed  together.  He  also  finds  that  solids 
alone  produce  heat  by  friction;  no  heat  appears  to  arise  from  the  friction  of  one 
liquid  upon  another  liquid,  or  upon  a  solid,  nor  by  the  friction  of  a  current  of  air 
or  gas  upon  a  liquid  or  solid. 

One  other  point  only  connected  with  the  nature  of  heat  remains,  to  which  there 
is  at  present  occasion  to  allude — the  existence  of  a  repulsive  property  in  heat. 
Such  a  repulsive  power  in  heated  bodies  is  inferred  to  exist  from  the  appearance  of 
extreme  mobility  which  many  fine  powders  assume,  such  as  precipitated  silica,  on 
being  heated  nearly  to  redness.  Professor  Forbes  also  attributes  to  such  a  repulsion 
the  vibrations  which  take  place  between  metals  unequally  heated,  and  the  production 
of  tones,  to  which  allusion  has  already  been  made.  But  this  repulsive  power  was 
rendered  conspicuous,  and  even  measurable,  by  Dr.  Baden  Powell,  in  the  case  of 
glass  lenses,  of  very  slight  convexity,  pressed  together.  On  the  application  of  heat, 
a  separation  of  the  glasses,  through  extremely  small  but  finite  spaces,  was  indicated 
by  a  change  in  the  tints  which  appear  between  the  lenses,  and  which  depend  upon 
the  thickness  of  the  included  plate  of  air.  This  repulsion  between  heated  surfaces 
appears  to  be  promoted  by  whatever  tends  to  the  more  rapid  communication  of  heat 
(Phil.  Trans.  1834,  p.  485). 

7  *  [See  Supplement,  p.  652.] 


98  LIGHT. 


CHAPTER   II. 

LIGHT. 

THE  mechanical  properties  of  light  constitute  the  science  of  optics,  and  belong, 
therefore,  to  physics,  and  not  to  chemistry.  But  it  may  be  useful,  by  a  short  re- 
capitulation, to  recal  them  to  the  memory  of  the  reader. 

1.  The  rays  of  light  emanate  with  so  great  velocity  from  the  sun,  that  they 
occupy  only  7£  minutes  in  traversing  the  immense  space  which  separates  the  earth 
from  that  luminary.     They  travel  at  the  rate  of  192,500  miles  in  a  second,  and 
would,  therefore,  move  through  a  space  equal  to  the  circumference  of  our  globe  in 
l-8th  of  a  second.     They  are  propagated  continually  in  straight  lines,  and  spread 
or  diverge  at  the  same  time ;  so  that  their  density  diminishes  in  the  direct  propor- 
tion of  the  squares  of  their  distance  from  the  sun.     Hence,  if  the  earth  were  at 
double  its  present  distance  from  the  sun,  it  would  receive  only  one-fourth  of  the 
light;  at  three  times  its  present  distance,  one-ninth;  at  four  times  its  present  dis- 
tance, one-sixteenth,  &c. 

2.  When  the  solar  rays  impinge  upon  a  body,  they  are  reflected  from  its  surface, 
and  bound  oft0,  as  an  elastic  ball  striking  against  the  same  surface  in  the  same  direction 
would  do ;  or  they  are  absorbed  by  the  body  upon  which  they  fall,  and  disappear, 
being  extinguished ;  or  lastly,  they  pass  through  the  bod}^  which  in  that  case  is 
transparent  or  diaphanous.     In  the  first  case,  the  body  becomes  visible,  appearing 
white,  or  of  some  particular  colour,  and  we  see  it  in  the  direction  in  which  the  rays 
reach  the  eye.     In  the  second  case,  the  body  is  invisible,  no  light  proceeding  from 
it  to  the  eye ;  or  it  appears  black,  if  the  surrounding  objects  are  illuminated.     In 
tlie  third  case,'  if  the  body  be  absolutely  transparent,  it  is  invisible,  and  we  see 
through  it  the  object  from  which  the  light  was  last  reflected.     But  light  is  often 
greatly  affected  in  passing  through  transparent  bodies. 

3.  If  light  enter  such  media,  of  uniform  density,  perpendicularly  to  their  surface, 
its  direction  is  not  altered ;  but  in  passing  obliquely  out  of  one  medium  into  another, 
it  undergoes  a  change  of  direction.     If  the  second  medium  be  denser  than  the  first, 
the  ray  of  light  -is  bent,  or  refracted,  nearer  to  the  perpendicular ;  but  in  passing 
out  from  a  denser  into  a  rarer  medium,  it  is  refracted  from  the  perpendicular. 

Thus,  when  the  ray  of  light  r,  passing  through 
^ia*  ^'  the  air,  falls  obliquely  upon  a  plate  of  glass  at 

the  point  «,  instead  of  continuing  to  move  in 
the  same  straight  line  a  b,  it  is  bent  towards 
— I     the  perpendicular  at  a,  and  proceeds  in  the 
direction  a  c.     The  ray  is  bent  to  the  side  on 
which  there  is  the  greatest  mass  of  glass.     On 
passing  out  from  the  glass  into  the  air,  a  rarer 
medium,  at  the  point  c,  the  ray  has  its  direction 
again  changed,  and  in  this  case  from  the  per- 
pendicular, but  still  towards  the  mass  of  glass.     The  amount  of  refraction,  generally 
speaking,  is  proportional  to  the  density  of  a  body,  but  combustible  bodies  possess  a 
higher  refracting  power  than  corresponds  to  their  density.     Hence  the  diamond, 
melted  phosphorus,  naphtha,  and  hydrogen  gas,  exhibit  this  effect  upon  light  in  a 
f  greater  degree  than  other  transparent  bodies.     Dr.  Wollaston  had  recourse  to  this 
refracting  power  as  a  test  of  the  purity  of  some  substances.     Thus,  genuine  oil  of 
cloves  had  a  refracting  power  expressed  by  the  number  1535,  while  that  of  an  im- 
pure specimen  was  not  more  than  1498. 

4.  In  passing  through  many  crystallized  bodies,  such  as  Iceland  spar,  a  certain 

of  light  is  refracted  in  the  usual  way,  and  another  portion  undergoes  UD 


LIGHT. 


99 


extraordinary  refraction,  in  a  plane  parallel  to  the  diagonal  which  joins  the  two 
obtuse  angles  of  the  crystal.  Such  bodies  are  said  to  refract  doubly,  and  exhibit  a 
double  image  of  any  body  viewed  through  them. 

5.  Reflected  and  likewise  doubly  refracted  light  assume  new  properties.   Common 
light,  by  being  reflected  from  the  surface  of  glass,  or  any  bright  surface  non-metallic, 
is  more  or  less  of  it  converted  into  what  is  called  polarized  light.     If  it  be  reflected 
at  one  particular  angle  of  incidence,  56°. 45',  it  is  all  changed  into  polarized  light; 
and  the  further  the  angle  of  reflection  deviates  from  56°,  on  either  side,  the  less  is 
polarized,  and  the  more  remains  common  light.     56°  is  the  maximum  polarizing 
angle  for  glass ;  52°. 45'  for  water.     The  light  is  said  to  be  polarized,  from  certain 
properties  which  it  assumes,  which  seem  to  indicate  that  the  ray,  like  a  magnetic 
bar,  has  sides  in  which  reside  peculiar  powers.     One  of  these  new  properties  is,  that 
when  it  falls  upon  a  second  glass  plate,  it  is  not  reflected  in  the  same  way  as  com- 
mon light.     If  the  plane  of  the  second  reflector  is  perpendicular  to  the  first,  and 
the  ray  fall  at  an  angle  of  56°,  it  is  not  reflected  at  all,  it  vanishes;  but  if  parallel, 
it  is  entirely  reflected.     Polarized  light  appears  to  possess  some  most  extraordinary 
properties,  in  regard  to  vision,  of  useful  application.     It  is  said  that  a  body  which 
is  quite  transparent  to  the  eye,  and  which  appears  upon  examination  to  be  as  homo- 
geneous in  its  structure  as  it  is  in  its  aspect,  will  yet  exhibit,  under  polarized  light, 
the  most  exquisite  organization.     As  an  example  of  the  utility  of  this  agent  in 
exploring  mineral,  vegetable,  and  animal  structures,  Sir  I).  Brewster  refers  to  the 
extraordinary  structure  of  the  minerals  apophyllite  and  analcime ;  to  the  symmetrical 
and  figurate  disposition  of  siliceous  crystals  in  the  epidermis  of  equisetaceous  plants, 
and  to  the  wonderful  variations  of  density  in  the  crystalline  lenses,  and  the  integu- 
ments of  the  eyes  of  animals,  which  polarized  light  renders  visible.     (Rep.  of  the 
British  Association,  vol.  i.     Report  upon  Optics,  by  Sir.  D.  Brewster.) 

6.  Decomposition  of  light. —  When  a  beam  of  light  from  the  sun  is  admitted 

FIG.  61. 


t ,',' 


into  a  dark  room,  by  a  small  aperture  r  in  a  window-shutter,  and  is  intercepted  in 
its  passage  by  a  wedge  or  solid  angle  of  glass  a  ft  c,  it  is  refracted  as  it  enters,  and 
a  second  time  as  it  issues  from  the  glass ;  and  instead  of  forming  a  round  spot  of 
white  light,  as  it  would  have  done  if  allowed  to  proceed  in  its  original  direction  r  t, 
it  illuminates  with  several  colours  an  oblong  space  of  a  white  card  ef,  properly 
placed  to  receive  it.  The  solid  wedge  of  glass  is  called  a  prism,  and  the  oblong 
coloured  image  on  the  card,  the  solar  spectrum.  Newton  counted  seven  bands  of 
different  colours  in  the  spectrum,  which,  as  they  succeed  each  other  from  the  upper 
part  of  the  spectrum  represented  in  the  figure,  are  violet,  indigo,  blue,  green,  yellow, 
orange,  and  red.  The  beam  of  light  admitted  by  the  aperture  in  the  window-shutter 
has  been  separated  in  passing  through  the  prism  into  rays  of  different  colours,  and 
this  separation  obviously  depends  upon  the  rays  being  unequally  refrangible.  Tho 
blue  rays  are  more  considerably  refracted  or  deflected  out  of  their  course,  in  passing 
through  the  glass,  than  the  yellow  rays,  and  the  yellow  rays  than  the  red.  Hence 
the  violet  end  is  spoken  of  a's  the  most  refrangible,  and  the  red  as  the  least  refran- 
gible end  of  the  spectrum. 


100  LIGHT. 

The  coloured  bands  of  the  spectrum  differ  in  width,  and  are  shaded  into  each 
other;  and  it  is  not  to  be  supposed  that  there  are  really  rays  of  seven  different 
colours.  Sir  D.  Brewster  has  established,  in  his  analysis  of  solar  light,  that  there 
are  rays  of  three  colours  only,  blue,  yellow,  and  red,  which  were  well  known  to  artists 
to  be  the  three  primary  colours  of  which  all  others  are  compounded. 

A  certain  quantity  of  white  light,  and  a  portion  of  each  of  the  primary  lays, 
may  be  found  at  every  point  from  the  top  to  the  bottom  of  the  spectrum.     But 
each  of  the  primary  rays  predominates  at  a  particular  part  of  the  spectrum.     This 
point  is,  for  the  blue  rays,  near  the  top  of  the  spectrum ;  for  the  yellow  rays,  some- 
what below  the  middle ;  and  for  the  red  rays,  near  the  bottom  of  the  spectrum. 
Hence,  there  exist  rays  of  each  colour  of  every  degree 
of  refrangibility ;  but  the  great  proportion  of  the  yellow 

Blue  Yellow  Red  ravs  is  m0re  refrangible  than  the  red,  and  the  great 
spectrum,  spectrum,  spectrum.  proportion  Of  the  blue  more  refrangible  than  either  the 
yellow  or  red.  The  compound  spectrum  which  we 
observe  is  in  fact  produced  by  the  superposition  of 
three  simple  spectra,  a  blue,  a  yellow,  and  a  red  spec- 
trum. The  distribution  of  the  rays  in  each  of  these 
simple  spectra  is  represented  by  the  shading  in  the 
annexed  figures.  Of  the  seven  different  coloured  bands 
into  which  Newton  divided  the  spectrum,  not  one  is  a 
pure  colour.  The  orange  is  produced  by  a  predomi- 
nance of  the  yellow  and  red  rays ;  the  green,  by  the 
yellow  and  blue  rays,  and  the  indigo  and  violet  are 
essentially  blue;  with  different  proportions  of  red  and 
yellow.1 

By  placing  a  second  prism  a  d  c,  in  a  reversed  position,  in  contact  with  the  first 
prism,  the  colours  disappear,  and  we  have  a  spot  of  white  light,  as  if  both  prisms 
were  absent.  The  three  coloured  rays  of  the  spectrum,  therefore,  produce  white 
light  by  their  union. 

On  examining  the  solar  spectrum,  Dr.  Thomas  Young  observed  that  it  is  crossed 
by  several  dark  lines ;  that  is,  that  there  are  interruptions  in  the  spectrum,  where 
there  is  no  light  of  any  colour.  Fraunhofer  subsequently  found  that  the  lines  in 
the  spectrum  of  solar  light  were  much  more  numerous  than  Dr.  Young  had  ima- 
gined, while  the  spectrum  of  artificial  white  flames  contains  all  the  rays  which  are 
thus  wanting.  One  of  the  most  notable  is  a  double  dark  line  in  the  yellow,  which 
occurs  in  the  light  of  the  sun,  moon,  and  planets.  In  the  light  of  the  fixed  stars, 
Sirius  and  Castor,  the  game  double  line  does  not  occur;  but  one  conspicuous  dark 
line  in  the  yellow,  and  two  in  the  blue.  The  spectrum  of  Pollux,  on  the  contrary, 
is  the  same  as  that  of  the  sun.  Now  a  very  recent  discovery  of  Sir  D.  Brewster 
has  given  these  observations  an  entirely  chemical  character.  He  has  found  that 
the  white  light  of  ordinary  flames  requires  merely  to  be  sent  through  a  certain 
gaseous  medium  (nitrous  acid  vapour)  to  acquire  more  than  a  thousand  dark  lines  in 
its  spectrum.  He  is  hence  led  to  infer  that  it  is  the  presence  of  certain  gases  in 
the  atmosphere  of  the  sun  which  occasions  the  observed  deficiencies  in  the  solar 
spectrum.  We  may  thus  have  it  yet  in  our  power  to  study  the  nature  of  the  com- 
bustion which  lights  up  the  suns  of  other  systems.  Dr.  Miller,  by  subjecting  the 
spectrum  to  the  absorptive  influences  of  chlorine,  iodine,  bromine,  perchloride  of 
manganese,  and  other  coloured  vapours,  brought  into  view  numerous  dark  bands 
not  previously  observed.  The  spectra  of  coloured  flames  were  also  marked  by  pecu- 
liar lines. 

The  rays  of  heat  are  distributed  very  unequally  throughout  the  luminous  spectrum; 
most  heat  being  found  associated  with  the  red  or  least  refrangible  luminous  rays,  and 

1  Sir  David  Brewster,  On  a  New  Analysis  of  the  Solar  Light,  indicating  three  primary 
colours,  forming  coincident  spectra  of  equal  length.  Edinburgh  Phil.  Trans,  vol.  xii.  p.  123. 


CHEMICAL    NOMENCLATURE    Afrl)    Nd'TA^TIO^    '     101 


least  with  the  violet  rays.  Indeed,  when  the  solar  beam  is  decomposed  by  a  prism 
of  a  highly  diathermanous  material,  such  as  rock  salt,  the  rays  of  heat  are  found  to 
extend,  and  to  have  their  point  of  maximum  intensity  considerably  beyond  the 
visible  spectrum,  on  the  side  of  the  red  ray.  Hence,  although  there  are  calorific 
rays  of  all  degrees  of  refrangibility,  the  great  proportion  of  them  are  even  less  re- 
frangible than  the  least  refrangible  luminous  rays.  It  is  to  be  observed  that  the 
least  refrangible  rays  are  absorbed  in  greatest  proportion  in  passing  through  bodies 
which  are  not  highly  diathernmnous  ;  such  as  crown-glass,  and  water.  Hence 
prisms  of  these  substances,  allowing  only  the  more  refrangible  rays  of  heat  to  pass, 
give  a  spectrum  which  is  hottest  in  the  red.  or  perhaps  even  in  the  yellow  ray,  and 
possesses  little  or  no  heat  beyond  the  border  of  the  red  ray.  The  inequality  in 
refrangibility  existing  between  the  rays  of  heat  and  of  light  is  decisive  of  the  fact 
that  they  are  peculiar  rays,  that  can  be  separated,  although  associated  together  in 
the  sunbeam.  Indeed,  Melloni  finds  that  light  from  both  solar  and  terrestrial  sources 
is  divested  of  all  heat  by  passing  successively  through  water,  and  a  glass  coloured 
green  by  oxide  of  copper,  being  incapable  as  it  issues  from  these  media  of  affecting 
the  most  delicate  thermoscope. 

The  light  of  the  sun  is  capable  of  inducing  certain  chemical  changes  which  de- 
pend neither  upon  its  luminous  nor  calorific  rays,  but  upon  the  presence  of  what  are 
called  chemical  rays.  Thus,  under  the  influence  of  light,  chlorine  gas  is  capable  of 
decomposing  water,  combining  with  its  hydrogen,  and  liberating  oxygen  ;  the  chlo- 
rine in  the  freshly  precipitated  chloride  of  silver  appears  to  be  liberated,  and  the 
colour  of  the  salt  changes  from  white  to  black  from  the  formation  of  a  subchloride. 
Photographic  impressions  are  obtained  on  paper  by  means  of  this  and  other  salts  of 
silver,  particularly  the  bromide  and  iodide,  which  are  still  more  sensitive  to  light. 
A  polished  plate  of  silver,  covered  with  the  thinnest  film  of  iodide,  is  employed  to 
receive  the  image  in  the  daguerreotype.  The  moist  chloride  of  silver  is  darkened 
more  rapidly  by  the  violet  than  by  the  red  rays  of  the  spectrum  ;  but  this  change 
is  produced  upon  it  even  when  carried  a  little  way  out  of  the  visible  spectrum  on 
the  side  of  the  violet  ray.  The  rays  found  in  that  situation  are,  therefore,  more 
refrangible  than  any  other  kind  of  rays  in  the  spectrum.  Their  characteristic  effect 
is  to  promote  those  chemical  decompositions  in  which  oxygen  is  withdrawn  from 
water  and  other  oxides  ;  and  hence  they  are  sometimes  named  de-oxidizing  rays. 
These  rays  were  likewise  supposed  to  communicate  magnetism  to  steel  needles 
exposed  to  them  ;  but  this  opinion  is  no  longer  tenable. 

[The  subjects  of  Polarization  and  the  Chemical  Action  of  Light  will  be  found 
in  the  Supplement,  p.  658.] 


CHAPTER   III. 
SECTION  I. 

CHEMICAL    NOMENCLATURE   AND    NOTATION. 

THERE  are  fifty-nine  substances  at  present  known,  which  are  simple,  or  contain 
one  kind  of  matter  only.  Their  names  are  given  in  the  following  table,  together 
with  certain  useful  numbers  which  express  the  quantities  by  weight,  according  to 
which  the  different  elements  combine  with  each  other.  The  letter  or  symbol  an- 
nexed to  the  name  is  employed  to  represent  these  particular  quantities  of  the  ele- 
ments, or  the  chemical  equivalents. 


102         CHEMICAL    NOMENCLATURE    AND    NOTATION. 

TABLE   OF   ELEMENTARY   SUBSTANCES, 

WITH  THEIR  CHEMICAL  EQUIVALENTS. 
***  For  the  authorities  for  the  numbers  in  this  table,  see  note  at  page  104. 


Names  of 
Elements. 

00 

1 

I 

Equivalents. 

Hydrogen 
=1. 

Oxy.=100. 
H.=12-5. 

Aluminum  

Antimony 
(Stibium) 

Al 

Sb 
As 
Ba 

Bi 

B 
Br 
Cd 
Ca 

C 
Ce 
Cl 

Cr 

Co 
Cu 

D 
F 
Gl 
Au 
H 
I 
Ir 

Fe 
Ln 

13-69 

129-03 
75 
68-64 

70-95 

10-90 
78-26 
55-74 
20 

6 
46 
35-50 

28-15 
29-52 
31-66 

49-6 
18-70 
26-50 
98-33 
1 
126-36 
98-68 

28 
48 

171-17 

1612-90 
937-50 
858-01 

886-92 

136-20 
978-30 
696-77 
250-00 

75-00 
575 
443-75 

351-82 
'  368-99 
395-70 

620 
233-80 
331-26 
1229-16 
12-50 
1579-50 
1233-50 

350-00 
600 

{A12  03,  alumina. 
A12  C13,  chloride  of  aluminum. 
A12  03,  3S03,  sulphate  of  alumina. 
(  Sb03,  oxide  of  antimony. 
f  Sb05,  antimonic  acid. 
J  As03,  arsenious  acid. 
\  As05,  arsenic  acid. 
/  BaO,  baryta. 
\  BaCl,  chloride  of  barium. 
{BiO,  oxide  of  bismuth. 
BiO,  N05,  nitrate  of  bismuth. 
BiCl,  chloride  of  bismuth. 
(  BOg,  boric  or  boracic  acid. 
\  BF13,  fluoboric  acid. 
(  Br05,  bromic  acid. 
|  BrH,  hydrobromic  acid. 
(  CdO,  oxide  of  cadmium.         [mium. 
\  CdS,  sulphide  or  sulphuret  of  cad- 
(  CaO,  lime. 
\  CaCl,  chloride  of  calcium. 
{CO,  carbonic  oxide. 
C02,  carbonic  acid. 
CS2,  sulphide  or  sulphuret  of  carbon. 
(  CeO,  oxide  of  cerium. 
\  Ce203,  sesquioxide  of  cerium. 
{CK)5,  chloric  acid. 
CIO  7,  perchloric  acid. 
C1H,  hydrochloric  acid. 
{Cr03,  chromic  acid. 
Cr203,  sesquioxide  of  chromium. 
Cr203,  3S03,  sulphate  of  chromium. 
(  CoO,  oxide  of  cobalt. 
(  Co203,  sesquioxide  of  cobalt. 
{Cu20,  suboxide  of  copper. 
CuO,  oxide  of  copper. 
CuO,  S03,  sulphate  of  copper. 

(  HF,  hydrofluoric  acid. 
\  BF3,  fluoboric  acid. 
^  G12O3,  glucina. 
f  G12C13,  chloride  of  glucin.um. 
/  Au20.  oxide  of  gold. 
\  Au203,  sesquioxide  of  gold. 
/HO,  water. 
\  H02,  binoxide  of  hydrogen. 
(  10,  iodic  acid. 
\  HI,  hydriodic  acid. 
j  IrO,  protoxide  of  iridium. 
\  Ir203,  sesquioxide  of  iridium. 
{FeO,  protoxide  of  iron. 
Fe203,  sesquioxide  of  iron,     [of  iron. 
Fe203,  3S03,  sulphate  of  sesquioxide 
LnO,  oxide  of  lanthanum. 

Arsenic  

Barium  

Bismuth  

Bromine  

Cadmium  

Calcium  

Carbon            

Cerium   

Chlorine      

Chromium  

Cobalt  

Copper  (Cuprum). 
Didyrnium  

Fluorine  

Glucinum  

Gold  (Aurum)  
Hydrogen  

Iodine..  

Iridium  

Iron  (Ferrum)  
Lanthanum  

CHEMICAL    NOMENCLATURE    AND    NOTATION. 


103 


Name  of 
Elements. 

tn 
"3 

1 
J? 

Equivalents. 

Hydrogen 
=1. 

Oxy.=100. 
H.  =  12-5. 

Lead  (Plumbum).. 
Lithium   

Pb 
Li 
Mg 

Mn 

Hg 

Mo 

Ni 

103-56 
643 
12-67 

27-67 

100-07 

47-88 
29-57 

14 

99-56 
8 

53-27 

82-02  . 

98-68 
39-00 

52-11 
52-11 

39-57 

21-35 
108-00 
22-97 
43-84 
16 
92-30 
66-14 
59-59 
58-82 
24-29 

1294-50 
80-37 
158-35 

345-90 

1250-9 

598-52 
369-68 

175-00 

1244-49 
100-00 

665-90 

400-3 

1233-50 

487-50 

651-39 
651-39 
494-58 

266-82 
1350-00 
287-17 
548-02 
200-00 
1153-72 
801-76 
744-90 
735-29 
303-66 

(  PbO,  oxide  of  lead. 
\  PbCl,  chloride  of  lead. 
/  LiO,  oxide  of  lithium. 
\  LiCl,  chloride  of  lithium. 
/  MgO,  magnesia, 
t  MgCl,  chloride  of  magnesium, 
j"  MnO,  protoxide  of  manganese, 
j  Mn02,  binoxide  of  manganese. 
1  Mn03,  manganic  acid. 
l_Mn207,  permanganic  acid. 
f  Hg20,  suboxide  (black  oxide). 
J  HgO,  oxide  (red  oxide), 
j  Hg2Cl,  subchloride  (calomel). 
[  HgCl,  chloride  (sublimate). 
M03,  molybdic  acid, 
f  NiO,  protoxide  of  nickel. 
\  Ni203,  sesquioxide  of  nickel. 

{N05,  nitric  acid. 
N02,  binoxide  of  nitrogen. 
NH3,  ammonia. 
Os04,  osmic  acid. 

(  PdO,  protoxide  of  palladium. 
\  Pd02,  peroxide  of  palladium. 

{P05,  phosphoric  acid. 
P03,  phosphorous  acid. 
PH3,  phosphuretted  hydrogen. 
/  PtO,  protoxide  of  platinum. 
\  Pt02,  binoxide  of  platinum. 
KO,  potassa. 
KC1,  chloride  of  potassium. 
RO,  protoxide  of  rhodium. 
R203,  sesquioxide  of  rhodium. 
Ru203,  sesquioxide  of  ruthenium. 
Se03,  selenic  acid. 
SeH,  hydroselenic  acid. 
Si03,  silicic  acid,  or  silica. 
SiF3,  fluosilicic  acid. 
AgO,  oxide  of  silver. 
AgCl,  chloride  of  silver. 
NaO,  soda. 
NaCl,  chloride  of  sodium. 
SrO,  strontium. 
SrCl,  chloride  of  strontium. 
S03,  sulphuric  acid. 
SH,  hydrosulphuric  acid. 
TaO,  oxide  of  tantalum. 
Ta03,  tan  tali  c  acid. 
S  Te03,  telluric  acid. 
)  TeH,  hydrotelluric  acid. 
S  ThO,  oxide  of  thorium. 
)  ThCl,  chloride  of  thorium. 
S  SnO,  protoxide  of  tin. 
(  Sn02,  binoxide  of  tin. 
S  Ti02,  titanic  acid. 
)  TiCl2,  bichloride  of  titanium. 

Magnesium  
Manganese      • 

Mercury  (Hydrar- 
ffvrum)  ... 

Molybdenum 

Nickel  

Niobium     

Nitrogen  or  azote. 
Osmium  

N(or 
Az) 

Os 
0 

Pd 

Palladium  

Phosphorus  

P 

Pt 
K 

R 
Ru 

Se 

Si 
Ag 
Na 
Sr 
S 
Ta 
Te 
Th 
Sn 
Ti 

Platinum 

Potassium 
(Kalium)  

Rhodium 

Ruthenium  

Selenium 

Silicium  

Silver  (Argentum) 

Sodium 
(Natronium)  

Strontium 

Tantalum  or 
Columbium  

Telurium 

Tin  (Stannum)  
Titanium  . 

104 


CHEMICAL    NOMENCLATURE    AND    NOTATION. 


Name  of 
Elements. 

Symbols. 

Equivalents. 

Hydrogen 
=1. 

Oxy.=100. 
H.  =  12-5. 

Tungsten 
(Wolfram)  

W 

U 
V 
Y 

Zn 
Zr 

94-64 

60 
68-55 
32-20 

32-52 
33-62 

1183-00 

750 
856-89 
402-51 

406-59 
420-20 

W03,  tungstic  acid.                  ^.^ 

(  UO,  oxide  of  uranium  (urane  of  Pe- 
f  U203,  uranic  acid. 
VO3,  vanadic  acid. 
J  YO,  yttria. 
^  YC1,  chloride  of  yttrium. 
<j  ZnQ,  oxide  of  zinc. 
)  ZnCl,  chloride  of  zinc. 
\  Zr203,  zirconia. 
I  Zr2Cl3,  chloride  of  zirconium. 

Uranium  . 

Vanadium  

Yttrium.-  

Zinc 

Zirconium  

*.£*  The  numbers  in  the  preceding  table  are,  with  several  exceptions,  those  of  Berzelius. 
The  equivalent  of  carbon  has  lately  been  reduced,  Avith  the  general  concurrence  of  chemists, 
from  76-44,  on  the  oxygen  scale,  to  75,  and  hydrogen  made  12-5  exactly,  chiefly  from  the 
experiments  of  M.  Dumas  on  the  combustion  of  carbon  and  hydrogen  gas  by  means  of  oxy- 
gen and  oxide  of  copper,  in  his  refined  arrangement  for  organic  analysis  (Ann.  de  Chimie, 
3  ser.  t.  i.  p.  5).  For  nitrogen,  M.  Pelouze  obtained,  by  two  analyses  of  sal-ammoniac,  the 
numbers  175-58  and  174-78  ;  M.  Marignac  obtained  for  the  same  element  the  number  175-25, 
from  the  analysis  of  nitrate  of  silver;  and  Dr.  T.  Anderson  has  been  led  to  nearly  the  same 
result,  by  an  analysis  of  the  nitrate  of  lead.  These  results  permit  the  adoption  of  175  as 
the  equivalent  of  nitrogen:  the  old  number  was  177-04. 

The  equivalents  of  chlorine,  potassium,  and  silver,  the  most  fundamental  numbers  in  the 
table,  which  were  determined  by  Berzelius  with  remarkable  precision,  have  received  small 
corrections  from  M.  Marignac.  Seven  experiments  were  made  by  the  latter  chemist  on  the 
decomposition  of  chlorate  of  potash  by  heat,  in  each  of  which  from  800  to  1100  grains  of  the 
salt  were  employed,  which  gave  him  from  39.155  to  39.167  per  cent,  of  oxygen;  he  adopts 
39.161,  the  actual  result  of  two  experiments.  Berzelius  had  obtained,  thirty  years  before, 
39.15.  Pelouze  has  also  obtained  identically  the  same  result  (Poggendorff's  Annalen,  Iviii. 
171).  On  the  other  trarid,  100  parts  of  silver  required  for  precipitation  from  solution  of 
nitrate,  69.062  parts  of  chloride  of  potassium  (mean  of  six  experiments) ;  the  maximum  was 
69.067,  and  the  minimum  69.049;  while  the  precipitated  chloride  of  silver  amounted  after 
fusion  to  132.84  parts,  as  the  mean  of  five  experiments,  of  which  the  maximum  was  132.844, 
and  the  minimum  132.825  parts  (Marignac).  These  experiments,  from  which  the  equiva- 
lents are  deduced,  obtain  the  unqualified  approbation  of  Berzelius,  who  gives  the  numbers 
reduced  to  equivalents  as  they  appear  below.  (Rapport  Annuel  sur  le  Progres  de  la  Chimie, 
par  J.  Berzelius,  Paris,  1845,  p.  32). 


Chlorine 

Potassium 

Silver 


Marignac.'  Berzelius  (old  numbers). 

443.20  442.65 

488.94 489.92 

1349.01 1351.61 


Finally,  M.  Maumen6  has  investigated  the  same  three  important  equivalents ;  decom- 
posing the  chlorate  of  potash  by  heat',  and  by  guarding  against  certain  minute  sources  of 
inaccuracy,  raising  the  proportion  of  oxygen  from  100  salt  to  39.209;  also  decomposing  the 
fused  chloride  of  silver  by  hydrogen  gas,  and  analyzing  the  oxalate  and  acetate  of  silver. 
The  experiments  of  this  chemist  appear  to  be  executed  with  a  degree  of  exactness  which 
can  scarcely  be  exceeded,  and  lead  to  conclusions  of  the  highest  interest,  as  they  give  num- 
bers which  approach  so  closely  to  multiples  of  6.25,  the  half  equivalent  of  hydrogen,  that 
the  differences  may  be  safely  considered  as  falling  within  the  unavoidable  errors  of  observa- 
tion, and  the  multiple  numbers  assumed  as  the  true  numbers  for  the  three  equivalents  in 
question,  (Annales,  &c.  1846,  3  s6r.  xviii.  41).  The  results  are: — 

Maumene'.  Multiple  Numbers. 

Chlorine 443.669 443.75  =  6.25  X    71 

Potassium 487.004 487.50=    «    X    78 

Silver 1350.322 1350.00=    "    X  216 

The  following  short  table  contains  numbers  lately  obtained  by  M.  Pelouze,  for  several 
elements,  differing  sensibly  from  the  numbers  of  Berzelius,  for  which  they  are  substituted, 
and  multiples  of  6.25,  to  which  they  all  closely  approximate. 


CHEMICAL    NOMENCLATURE    AND    NOTATION. 


105 


Sodium  
Barium  
Strontium  
Silicium  
Phosphorus  ... 
Arsenic  ... 

Berzelius. 
290.90  .... 
856.88.... 
547.29.... 
277.29.... 
392.29  .... 
940.08  ... 

Pelouze. 
287.17  
858.03  
548.02  
266.82  
400.30  
...  937.50  ... 

Multiples  < 
287.50  =  6.. 
856.25  = 
550.00  = 
268.75  = 
400.00  = 
937.50  = 

)f  6.25. 
25  X    46 
X  187 
X    88 
X    43 
X    64 
*  150 

The  equivalent  of  sodium  was  determined  from  the  quantity  of  chloride  of  sodium  required 
to  precipitate  200  parts  of  silver  from  the  nitrate.  Barium,  strontium,  silicium,  phosphorus, 
and  arsenic,  in  a  similar  manner,  also  by  the  quantity  of  silver  which  their  chlorides  pre-' 
cipitated. 

The  equivalent  of  calcium  is  taken  at  250,  after  Dumas ;  MM.  Erdmann  and  Marchand 
have  confirmed  this  equivalent;  Berzelius  himself  reduces  his  first  number  from  256.02  to 
251.94.  Sulphur  and  mercury  are  also  after  Erdmann  and  Marchand:  Berzelius  has,  on 
recalculating  his  old  results,  reduced  the  number  for  sulphur  from  201.17  to  200.8. 

The  equivalent  of  iron  was  lately  found  349.80  by  MM.  Swanberg  and  Norlin,  and  their 
results  confirmed  by  Berzelius,  who  now  obtains  350.27  and  350.369  (instead  of  339.21,  the 
old  equivalent) :  an  intermediate  number  350  is  adopted  in  the  table. 

The  number  for  zinc  is  that  of  M.  Axel  Erdmann,  who  took  unusual  pains  in  purifying 
the  metal:  it  is  412.63  according  to  M.  Favre,  and  414  according  to  M.  Jacquelain;  the 
number  of  Berzelius  is  403.23. 

The  number  for  uranium  is  that  adopted  by  M.  Peligot;  it  has  been  found  746.36  by 
M.  Wertheim,  and  742.875  by  Ebelmen. 

The  number  for  gold  is  that  lately  deduced  by  Berzelius  from  an  analysis  of  the  double 
chloride  of  gold  and  potassium  (Poggendorff's  Annalen,  Ixv.  314) ;  it  replaces  his  former 
number  1243.01.  Those  of  cerium  and  ruthenium  are  by  Hermann  (Annuaire  de  Chimie, 
1835,  p.  130).  M.  Rammelsberg  has  adopted  for  the  former  metal  574.7,  and  M.  Beringer 
577  ;  the  number  of  M.  Hermann  is  intermediate.  Ruthenium,  the  new  metal  from  native 
platinum,  is  considered  by  its  discoverer,  Prof.  Haus,  to  be  isomorphous  with,  and  to  have 
the  same  equivalent  as,  rhodium,  from  the  composition  of  the  double  sesqui-chloride  of 
ruthenium  and  potassium,  2  K  Cl  -|-  Ru2Cls. 

No  data  exist  for  fixing  the  equivalents  of  the  metallic  elements  lately  discovered,  whese 
names  appear  in  the  table,  namely,  didymium  found  with  lanthanum  in  cerite  (Mosander) ; 
niobium  and  pelopium  in  the  tantalite  of  Bavaria  (H.  Rose). 


Names  of 
Elements. 

Symbols. 

Equivalents. 

"^-N 
A            '^\ 

b'        OUT        $ 

I 

Hydrogen 
=  1. 

Oxy.=100. 
H.=12-5. 

Ar 
Do 
E 
II 
No 
Tb 

79.72 
60.4 

997.4 
753. 

Do»0,,  sesquioxide  of  donarium. 

^sJ^Qx^X 

I102,  ilmenic  acid. 

Donarium               . 

Erbium  

Ilinenium  

Terbium... 

[The  elements  given  in  the  above  table  have  been  made  known  since  the  publication  of 
this  part  of  the  original  work.  Aridium  by  Ulgren,  Donarium  by  Bergemann,  Erbium  and 
Terbium  by  Mosander,  Ilmenium  by  Hermann,  and  Norium  by  Svanberg.  The  equivalents, 
as  far  as  ascertained,  are  given  on  the  authority  of  the  discoverers.  — R.  B.] 

In  the  class  of  simple  substances  are  placed  all  those  bodies  which  are  not  known 
to  be  compound,  on  the  principle  that  whatever  cannot  be  decomposed  or  resolved 
by  any  process  of  chemistry  into  other  kinds  of  matter,  is  to  be  considered  as  simple. 
They  are  the  only  bodies  the  names  of  which  are  at  present  independent  of  any  rule. 
An  attempt  was,  indeed,  made  on  the  first  introduction  of  a  systematic  nomenclature, 
to  make  the  names  of  several  of  them  significant ;  but  some  confusion  in  regard  to 
their  derivatives  was  found  to  be  the  consequence  of  this,  and  many  of  them  being 
familiar  substances,  were  almost  of  necessity  allowed  to  retain  the  names  they  bear 
in  common  language :  such  as,  sulphur,  tin,  silver,  and  the  other  metals  known  in 
the  arts.  To  newly  discovered  elements,  however,  such  names  were  applied  as  were 
suggested  by  any  striking  physical  property  they  possessed,  or  remarkable  circum- 


106         CHEMICAL    NOMENCLATURE    AND    DOTATION. 

stance  in  their  history.  The  names  of  the  newer  metals,  platinum,  potassium,  vana- 
dium, &c.,  have  a  common  termination,  which  serves  to  distinguish  them  as  metals. 
Another  class  of  elementary  bodies,  resembling  each  other  in  certain  particulars,  is 
marked  in  a  similar  manner;  namely,  that  composed  of  chlorine,  iodine,  bromine, 
and  fluorine. 

The  names  of  compound  bodies  are  contrived  to  express  their  composition,  and 
the  class  to  which  they  belong,  and  are  founded  on  a  distribution  of  compounds  into 
three  orders,  namely,  first,  compounds  of  one  element  with  another  element ;  as,  for 
instance,  oxygen  with  sulphur  in  sulphuric  acid,  or  oxygen  with  sodium  in  soda, 
which  are  called  binary  compounds.  Secondly,  combinations  of  binary  compounds 
with  each  other,  as  of  sulphuric  acid  with  soda  in  Glauber's  salt,  and  the  salts  gene- 
rally, which  are  termed  ternary  compounds.  And  thirdly,  combinations  of  salts 
with  one  another,  or  double  salts,  such  as  alum,  which  are  quaternary  compounds. 

1. — Of  the  compounds  of  the  first  order,  the  greater  number  known  to  the  original 
framers  of  the  chemical  nomenclature  contained  oxygen  as  one  of  their  two  consti- 
tuents; and  hence  an  exclusive  importance  was  attached  to  that  element.  Its  com- 
pounds with  the  other  elementary  bodies  may  be  divided  by  their  properties  into : 
(a)  the  class  of  neutral  bodies  and  bases ;  and  ( b)  the  class  of  acids. 

(a).  To  members  of  the  first  class  the  generic  term  oxide  was  applied,  the  first 
syllable  of  oxygen,  with  a  termination  (ide~)  indicative  of  combination;  to  which  the 
name  of  the  other  element  was  joined  to  express  the  specific  compound.  Thus  a 
compound  of  oxygen  and  hydrogen  is  oxide  of  hydrogen;  of  oxygen  and  potassium, 
oxide  of  potassium  ;  of  which  compounds,  the  first,  or  water,  is  an  instance  of  a 
neutral  oxide ;  and  the  second,  or  potash,  of  a  base  or  alkaline  oxide.  But  the 
same  elementary  body  often  combines  with  oxygen  in  more  than  one  proportion, 
forming  two  or  more  oxides ;  to  distinguish  which  the  Greek  prefix  (joro/o,  Ttpw-roj, 
first)  is  applied  to  the  oxide  containing  the  leastfr" proportion  of  oxygen;  deuto 
(Sfui'Epoj,  second)  to  the  oxide  containing  more  oxygen  than  the  protoxide ;  and 
trito  (Vpttfos,  third)  to  the  oxide  containing  still  more  oxygen  than  the  deutoxide ; 
which  last  oxide,  if  it  contains  the  largest  proportion  of  oxygen  with  which  the 
element  can  unite  to  form  an  oxide,  is  more  commonly  named  the  peroxide ;  from 
per,  the  Latin  particle  of  intensity.  Thus,  the  three  compounds  of  the  metal 
manganese  and  oxygen  are  distinguished  as  follows  : — 

Composition. 
Names.  Manganese.  Oxygen. 

Protoxide  of  manganese 100 28.91 

Deutoxide  of  manganese 100 43.36 

Peroxide  of  manganese 100 57.82 

As  the  prefix  per  implies  simply  the  highest  degree  of  oxidation,  it  may  be  applied 
to  the  second  oxide  where  there  are  only  two,  as  in  the  oxides  of  iron,  the  second  oxide 
of  which  is  called,  indifferently,  the  deutoxide  or  peroxide  of  iron.  M.  Thenard,  in 
his  Traite*  de  Chimie,  avoids  the  use  of  the  term  deutoxide,  and  confines  the  appli- 
cation of  peroxide  to  such  of  these  oxides  as,  like  the  peroxide  of  manganese,  do  not 
combine  with  acids.  He  applies  the  names  sesquioxide  and  binoxide  to  oxides, 
which  are  capable  of  combining  with  acids,  and  contain  respectively,  once  and  a 
half  and  twice  as  much  oxygen  as  the  protoxides  of  the  same  metal.  He  has  thus 
the  protoxide,  sesquioxide,  and  peroxide  of  manganese,  the  protoxide  and  sesqui- 
oxide of  iron,  the  protoxide  and  binoxide  of  tin,  &c.  This  distinction  is  useful,  and 
will  be  adopted  in  the  present  work.  Certain  inferior  oxides,  which  do  not  combine, 
with  acids,  are  called  suboxides ;  such  as  the  suboxide  of  lead,  which  contains  less 
oxygen  than  the  oxide  distinguished  as  the  protoxide  of  the  same  metal. 

The  compounds  of  chlorine  and  several  other  elements  are  distinguished  in  the 
same  manner  as  the  oxides.  Such  elements  resemble  oxygen  in  several  respects, 
particularly  in  the  manner  in  which  their  compounds  are  decomposed  by  electricity. 


CHEMICAL    NOMENCLATURE    AND    NOTATION.        107 

Chlorine,  for  example,  like  oxygen,  proceeds  to  the  positive  pole,  and  is  therefore 
classed  with  oxjgen  as  an  electro-negative  substance,  in  a  division  of  elements 
grounded  on  their  electrical  relations.  Thus,  with  the  other  elementary  bodies, 

Oxygen forms oxides, 

Chlorine " chlorides, 

Bromine " bromides, 

Iodine "      iodides, 

Fluorine "      fluorides, 

Sulphur "      sulphides  (or  sulphurets), 


Phosphorus 

Carbon 

Nitrogen .... 
Hydrogen... 
Cyanogen  (N  C 
Sulphion  (S 


*C2) 
04).. 


phosphides  (or  phosphurets), 
carbides  (or  carburets), 
nitrides, 

,  hydrides, 

.  cyanides, 

.  sulphionides. 


As  cyanogen  and  sulphion,  although  compound  bodies,  comport  themselves  in  their 
combinations  like  electro-negative  elements,  their  compounds  are  named  in  the  same 
manner  as  the  oxides. 

When  several  chlorides  of  the  same  metal  exist,  they  are  distinguished  by  the 
same  numerical  prefixes  as  the  oxides.  Thus  we  have  the  protochloride  and  the 
sesquichloride  of  iron  \  the  protochloride,  and  the  bichloride  of  tin.  The  compounds 
of  sulphur  greatly  resemble  the  oxides,  but  they  have  been  generally  named  sul- 
phurets, and  not  sulphides  or  sulphurides.  Bcrzelius,  indeed,  applies  the  term  sul- 
phuret  to  such  binary  compounds  of  sulphur  only  as  are  basic  and  correspond  with 
basic  oxides ;  while  sulphide  is  applied  by  him  to  such  as  are  acid,  or  correspond 
with  acid  oxides.  Hence,  he  has  the  sulphuret  of  potassium,  and  the  sulphide  of 
arsenic  and  sulphide,  of  carbon.  Compounds  of  chlorine  are  distinguished  by  him 
into  chlorurets  and  chlorides,  on  the  same  principle;  thus  he  speaks  of  the  chloruret 
of  potassium,  and  of  the  chloride  of  phosphorus.  But  these  distinctions  have  not 
served  any  important  purpose,  while  besides  conducing  to  perspicuity  it  is  an  object 
of  some  consequence  in  a  systematic  point  of  view  to  allow  the  termination  ide, 
already  restricted  to  electro-negative  substances,  to  apply  to  all  of  them  without 
exception. 

The  combinations  of  metallic  elements  among  themselves  are  distinguished  by 
the  general  term  alloys,  and  those  of  mercury  as  amalgams. 

(b).  The  binary  compounds  of  oxygen  which  possess  acid  properties  are  named 
on  a  different  principle.  Thus  the  acid  compound  of  titanium  and  oxygen  is  called 
titanic  acid;  of  chromium  and  oxygen,  chromic  acid;  or  the  name  of  the  acid  is 
dejived  from  that  of  the  substance  in  combination  with  oxygen,  with  the  termina- 
tion ic.  Where  the  same  element  was  known  to  form  two  acid  compounds  with 
oxygen,  the  termination  ous  was  applied  to  that  which  contained  the  least  proportion 
of  oxygen,  as  in  sulphurous  and  sulphuric  acids.  On  the  discovery  of  an  acid  com- 
pound of  sulphur  which  contained  less  oxygen  than  that  already  named  sulphurous 
acid,  it  was  called  hyposulphurous  acid,  (from  the  Greek  vrto,  under);  and  another 
new  compound,  intermediate  between  the  sulphurous  and  sulphuric  acids,  was  named 
hyposulphuric  acid.  On  the  same  principle,  an  acid  containing  a  greater  proportion 
of  oxygen  than  that  already  named  chloric  acid,  was  named  hyper  chloric  acid,  (from 
the  Greek  vrtsp,  over ;)  but  now  more  generally  perchloric  acid.  The  names  of  the 
different  acid  compounds  of  oxygen  and  sulphur,  which  have  been  referred  to  for 
illustration,  with  the  relative  proportions  of  oxygen  which  they  contain,  are  ab 
follows : 

Composition. 
Names.  Sulphur.  Oxygen. 

Hyposulphurous  acid  100 50 

Sulphurous  acid 100  100 

Hyposulphuric  acid  100 125 

Sulphuric  acid 100 150 


108          CHEMICAL   NOMENCLATURE    AND    NOTATION. 

The  same  system  is  adopted  for  all  analogous"  acids.  An  acid  of  chlorine,  con- 
taining more  oxygen  than  chloric  acid,  is  named  perchloric  acid,  and  other  similar 
compounds,  which  all  contain  an  unusually  large  proportion  of  oxygen,  are  distin- 
guished in  the  same  manner;  as  periodic  acid,  and  permanganic  acid.  The  per- 
chloric acid  is  also  sometimes  called  oxichloric  ;  but  this  last  term  does  not  seem  so 
suitable  as  the  first. 

Another  class  of  acids  exists  in  which  sulphur  is  united  with  the  other  element 
in  the  place  of  oxygen."  The  acids  thus  formed  are  called  sulphur  acids.  The 
names  of  the  corresponding  oxygen  acids  are  sometimes  applied  to  these,  with  the 
prefix  sulph,  as  sul.pharsenious  and  sulpharsenic  acids,  which  resemble  arsenious 
and  arsenic  acids  respectively  in  composition,  but  contain  sulphur  instead  of  oxygen. 

Lastly,  certain  substances,  such  as  chlorine,  sulphur  and  cyanogen,  form  acids 
with  hydrogen,  which  are  called  hydrogen  acids,  or  hydradds.  In  these  acid  com- 
pounds the  names  of  both  constituents  appear,  as  in  the  terms  hydrochloric  acid, 
hydro  sulphuric  acid,  and  hydrocyanic  acid.  Thenard  has  proposed  to  alter  these 
names  to  chlorhydric,  sulphohydric-,  and  cyanhydric  acids}  which  in  some  respects 
are  preferable  terms. 

2. —  Compounds  of  the  second  order,  or  salts,  are  named  according  to  the  acid 
they  contain,  the  termination  ic  of  the  acid  being  changed  into  ate,  and  ous  into  ite. 
Thus  a  salt  of  sulphuric  acid  is  a  sulphate ;  of  sulphurous  acid,  a  sulphite ;  of  hypo- 
sulphurous  acid,  a  hyposulphite;  of  hyposulplmric  acid,  a  hyposulphate ;  and  of 
perchloric  acid,  a  per chlorate  ;  and  the  name  of  the  oxide  indicates  the  species  —  as 
sulphate  of  oxide  of  silver,  or  sulphate  of  silver ;  for  the  oxide  of  the  metal  being 
always  understood,  it  is  unnecessary  to  express  it,  unless  when  more  than  one  oxide 
of  the  same  metal  combines  with  acids,  as  sulphate  of  protoxide  of  iron,  and  sul- 
phate of  sesquioxide  of  iron.  These  salts  are  often  called  protosulphate  and  per- 
sulphate of  iron?  where  the  prefixes  proto  and  per  refer  to  the  degree  of  oxidation 
of  the  iron.  The  two  oxides  of  iron  are  named  ferrous  oxide  and  ferric  oxide  by 
Berzelius,  and  the  salts  referred  to,  the  ferrous  sulphate,  and  the  ferric  sulphate. 
The  names  stannous  sulphate  and  stannic  sulphate  express  in  the  same  way  the 
sulphate  of  the  protoxide  of  tin,  and  the  sulphate  of  the  peroxide  of  tin.  But  such 
names,  although  truly  systematic,  and  replacing  very  cumbrous  expressions,  involve 
too  great  a  change  in  chemical  nomenclature  to  be  speedily  adopted.  Having  found 
its  way  into  common  language,  chemical  nomenclature  can  no  longer  be  altered 
materially  without  great  inconvenience.  It  must  be  learned  as  a  language,  and  not 
be  viewed  and  treated  as  the  expression  of  a  system.  A  sw/>er-sulphate  contains  a 
greater  proportion  of  acid  than  the  sulphate  or  neutral  sulphate  ]  a  fo'-sulphate  twice 
as  much,  and  a  ses<?m-sulphate  once  arid  a  half  as  much  as  the  neutral  sulphate ; 
while  a  swi-sulphate  contains  a  less  proportion  than  the  neutral  salt  j  the  prefixes 
referring  in  all  cases  to  the  proportion  of  acid  in  the  salt,  or  to  the  electro-negative 
ingredient,  as  with  oxides.  The  excess  of  base  in  sub-salts  is  sometimes  indicated 
by  Greek  prefixes  expressive  of  quantity,  as  cZi-chromate  of  lead,  Ins-acetate  of 
lead  j  but  this  deviation  is  apt  to  lead  to  confusion.  If  a  precise  expression  for  such 
subsalts  were  required,  it  would  be  better  to  say,  the  bibasic  subchromate  of  lead, 
the  tribasic  subacetate  of  lead.  But  the  names  of  both  acid  and  basic  salts  are  less 
in  accordance  with  correct  views  of  their  constitution,  than  the  names  of  any  other 
class  of  compounds. 

Combinations  of  water  with  other  oxides  are  called  hydrates :  as  hydrate  of  pot- 
assa,  hydrate  of  boracic  acid. 

3. — In  the  names  of  quarternary  compounds  or  of  double  salts,  the  names  of  the 
constituent  salts  are  expressed,  thus  : —  Sulphate  of  alumina  and  potash  is  the  com- 
pound of  sulphate  of  alumina  and  sulphate  of  potash ;  the  name  of  the  acid  being 
expressed  only  once,  as  it  is  the  same  in  both  of  the  constituent  salts.  The  name 
alum,  which  has  been  assigned  by  common  usage  to  the  same  double  salt,  is  like- 
wise received  in  scientific  language.  The  chloride  of  platinum  and  potassium  ex- 
presses, in  the  same  way,  a  compound  of  chloride  of  platinum  and  chloride  of 


CHEMICAL   NOMENCLATURE   AND   NOTATION.  109 

potassium.     An  oxichloride,  such  as  the  oxichloride  of  mercury,  is  a  compound  of 
the  oxide  with  the  chloride  of  the  same  metal. 

The  first  ideas  of  a  chemical  nomenclature  are  due  to  Guyton  de  Morveau,  whose 
views  were  published  in  1782  ;  but  the  chief  merit  of  the  construction  of  the  valua- 
ble system  in  use  is  justly  assigned  to  Lavoisier,  who  reported  to  the  French  Aca- 
demy on  the  subject,  in  the  name  of  a  committee,  in  1787.  It  has  not  been 
materially  modified  or  expanded  since  its  first  publication.  The  present,  or  Lavoi- 
sierian  nomenclature,  does  not  furnish  precise  expressions  for  many  new  classes  of 
compounds,  the  existence  of  which  was  not  contemplated  by  its  inventors,  and  many 
of  its  names  express  theoretical  views  of  the  constitution  of  bodies  which  are  doubt- 
ful, and  not  admitted  by  all  chemists'.  But  its  deficiencies  are  supplied,  and  the 
composition  of  bodies  more  accurately  represented,  in  certain  written  expressions,  or 
chemical  formulae,  which  are  also  employed  to  denote  particular  substances,  and 
which  form  a  valuable  supplement  to  the  nomenclature  still  generally  used.  These 
formulae  are  constructed  on  the  simplest  principles,  and  besides  supplying  the  defi- 
ciencies of  the  nomenclature,  they  at  once  exhibit  to  the  eye  the  composition  of 
bodies,  and  afford  a  mechanical  aid  in  observing  relations  in  composition,  of  the 
same  kind  as  the  use  of  figures  in  the  comparison  of  arithmetical  sums. 

Symbols  of  the  elements. — Each  elementary  substance  is  represented  by  the  initial 
letter  of  its  Latin  name,  as  will  be  seen  by  reference  to  the  table  of  elementary  sub- 
stances, page  102 ;  but  when  the  names  of  two  or  more  elements  begin  with  the 
same  letter,  a  second  in  a  smaller  character  is  added  for  distinction ;  thus  oxygen  is 
represented  by  the  letter  0,  the  metal  osmium  by  Os,  fluorine  by  F,  and  iron  (ferrum) 
by  Fe ;  small  letters,  it  is  to  be  observed,  never  being  significant  of  themselves,  but 
employed  only  in  connexion  with  the  large  letters  as  distinctive  adjuncts.  These 
symbols  represent,  at  the  same  time,  certain  relative  quantities  of  the  elements,  the 
letter  0  expressing  not  oxygen  indefinitely,  but  100  parts  by  weight  of  oxygen,  and 
Fe  350  parts  by  weight  of  iron,  or  any  other  quantities  of  these  two  substances 
which  are  in  the  proportion  of  these  numbers :  8  parts  of  oxygen,  for  instance,  and 
28  of  iron.  It  will  immediately  be  explained  that  the  elementary  bodies  combine 
with  each  other  in  certain  proportional  quantities  only,  which  are  expressed  by  one 
or  other  indifferently  of  the  two  series  of  numbers  placed  against  the  names  of  the 
elements  in  the  table  referred  to.  These  quantities  are  conveniently  spoken  of  as 
the  combining  proportions,  the  equivalent  quantities,  or  the  equivalents  of  the  ele- 
ments. The  symbol,  or  letter,  of  itself  representing  one  equivalent  of  the  element, 
several  equivalents  are  represented  by  repeating  the  symbol,  or  by  placing  figures 
before  it  j  thus  Fe  Fe,  or  2  Fe,  and  3  0,  mean  two  equivalents  of  iron  and  three 
of  oxygen.  Or  small  figures  are  placed  either  above  or  below  the  symbol,  and  to 
the  right ;  thus  Fe2,  and  O3,  or  Fe2  03,  are  of  the  same  value  as  the  former  expres- 
sions, but  are  used  only  when  symbols  are  placed  together  in  the  formulae  of  com- 
pounds. Two  equivalents  of  an  element  are  sometimes  expressed  by  placing  a  dash 
through,  or  under  its  symbol,  but  such  abbreviations  will  not  be  made  use  of  in  the 
present  work. 

Formulae,  of  compounds.  —  The  collocation  of  symbols  expresses  combination : 
thus  Fe  0  represents  a  compound  of  one  equivalent  or  proportion  of  iron,  and  one 
of  oxygen,  or  the  protoxide  of  iron ;  S03,  a  compound  of  one  equivalent  of  sulphur, 
and  three  of  oxygen  —  that  is,  one  equivalent  of  sulphuric  acid ;  and  sulphate  of 
iron  itself,  consisting  of  one  equivalent  of  each  of  the  preceding  compounds,  may. 
be  represented  as  follows : 

FeO       S03,  or 

FeO  +  SO3,  or 

FeO,     SO3. 

The  sign  plus  (-{-)  or  the  comma,  being  introduced  in  the  second  and  third  formula), 
to  indicate  a  distribution  of  the  elements  of  the  salt  into  its  two  proximate  consti- 


110          CHEMICAL   NOMENCLATURE   AND   NOTATION. 

tuents,  oxide  of  iron,  and  sulphuric  acid,  which  is  not  so  distinctly  indicated  in  the 
first  formula.  It  may  often  be  advantageous  to  make  use  of  both  the  comma  and 
the  plus  sign  in  the  same  formula,  and  then  it  would  be  a  beneficial  practice  to  use 
them  as  in  the  following  formula  for  the  double  sulphate  of  iron  and  potash  : 

FeO,  S03+K0,  S03, 

in  which  the  comma  is  employed  to  indicate  combination  more  intimate  in  degree,  or 
of  a  higher  order  than  the  plus  sign,  namely,  of  the  oxide  with  the  acid  in  each 
salt,  while  the  combination  of  the  two  salts  themselves  is  expressed  by  the  sign  + . 

The  small  figures  in  the  preceding  formulae  affect  only  the  symbol  or  letter  to 
which  they  are  immediately  attached.  Larger  figures  placed  before  and  in  the  same 
line  with  the  •  symbols  apply  to  the  compound  expressed  by  the  symbols.  Thus 
3  S  03,  means  three  equivalents  of  sulphuric  acid;  2  Pb  0,  two  equivalents  of  oxide 
of  lead.  But  the  interposition  of  the  comma  or  plus  sign  prevents  the  influence  of 
the  figure  extending  farther,  thus 

2  Pb  0,      Cr  08,  or 

2  Pb  0  +  Cr  03, 

is  two  proportions  of  oxide  of  lead,  and  one  of  chromic  acid,  or  the  sub-chromate 
of  lead.  To  make  the  figure  apply  to  symbols  which  are  separated  by  the  comma 
or  plus  sign,  it  is  necessary  to  enclose  all  that  is  to  be  affected  within  brackets, 
and  place  the  figure  before  them.  Thus, 

2  (Pb  0,  Cr  03) 

means  two  proportions  of  neutral  chromate  of  lead.  The  following  formulae  of  two 
double  salts  with  their  water  of  crystallization,  exhibit  the  application  of  these 
rules : — 

Iron-alum,  or  the  sulphate  of  peroxide  of  iron  and  potash : 
KO,  S03+Fe2  03,  3  S03-f24  HO 

Oxalate  of  peroxide  of  iron  and  potash : 

3  (K  0,  C2  03)  +  Fe2  03,  3  C2  03+6  HO. 

It  will  be  found  to  conduce  to  perspicuity,  to  avoid  either  connecting  two  formulas 
of  different  substances  not  in  combination,  by  the  sign  plus,  or  allowing  them  to  be 
separated  merely  by  a  comma,  as  the  plus  and  comma  between  symbols  or  formulae 
are  conventionally  understood  to  unite  the  formulae  into  one,  and  to  express  combi- 
nation ;  and  indeed  it  is  advisable  to  write  every  complete  formula  apart,  and  in  a 
line  by  itself,  if  possible. 

The  only  other  circumstance  to  be  attended  to  in  the  construction  of  such  formulae 
is  the  arrangement  of  the  symbols  or  letters,  which  is  not  arbitrary.  In  naming  a 
binary  compound,  such  as  oxide  of  iron,  chloride  of  potassium,  &c.,  we  announce 
first  the  oxygen  or  element  most  resembling  it  in  the  compound ;  that  is,  the  electro- 
negative ingredient ;  but  in  the  formulae  of  the  same  bodies,  it  is  the  other  or  the 
electro-positive  element  which  is  placed  first,  as  in  Fe  0,  and  K  Cl.  In  the  formulae 
of  salts,  it  is  likewise  the  basic  oxide  or  electro-positive  constituent  which  is  placed 
first,  and  not  the  acid.  Thus  the  sulphate  of  potash  is  K  0,  S  03,  atfd  not  S  03,  KO. 
Information  respecting  the  constitution  of  a  compound  may  often  be  expressed  in  its 
formula,  by  attending  to  this  rule.  Thus  sulphuric  acid  of  srjfecific  gravity  1.780, 
contains  two  proportions  of  water  to  one  of  acid,  but  by  giving  to  it  the  following 
formula : 

HO,  S03+H0,  .1 

we  express  that  one  proportion  only  of  water  is  combined  as  a  base1  with  the  acid, 
and  that  the  second  proportion  of  water,  the  formula  of  which  follows  that  of  the 
acid,  is  in  combination  with  this  sulphate  of  water. 

The  above  system  of  notation  is  complete,  and  sufficiently  convenient  for  repre- 
senting all  binary  compounds,  and  compounds  belonging  to  the  organic  department 
of  the  science,  in  the  formulae  of  which  the  ultimate  elements  only  are  expressed. 


COMBINING    PROPORTIONS.  Ill 

But  when  salts  and  double  salts  are  expressed,  the  formulas  sometimes  become  in- 
conveniently long.  They  may  often  be  greatly  abbreviated,  and  made  more  distinct, 
by  expressing  each  equivalent  of  oxygen  in  an  oxide  or  acid,  by  a  point  placed  ovei 
the  symbol  of  the  other  element,  thus : 

Protoxide  of  iron,  Fe. 

Sulphuric  acid,  S. 

Crystallized  sulphate  of  protoxide  of  iron,  Fe  S,  H  +  6H. 

Alum,  KS,  Ai'AlS3  +  24H. 

Felspar,  K  Si,  Al'Al  Si3. 

Oxalate  of  peroxide  of  iron  and  potash,  3K  CC  +  Fe  Fe,  3CC  +  6H. 

Such  formulae  are  more  compact,  and  more  easily  compared  with  each  other,  the 
relation  between  the  mineral  felspar  and  alum  without  its  water  of  crystallization, 
being  seen  at  a  glance  on  thus  placing  their  formulae  together;  the  one  having  the 
symbol  for  silicium,  the  other  that  for  sulphur,  but  everything  else  remaining  the 
same.  This  abbreviated  plan  also  exhibits  more  distinctly  the  relation  between  the 
equivalents  of  oxygen  in  the  different  constituents  of  a  salt,  which  is  always  im- 
portant. 

It  is  to  be  observed,  that  the  oxygen  expressed  by  the  points  placed  over  a  letter 
is  brought  under  the  influence  of  the  small  figure  attached  to  that  letter :  as,  for 
example,  S3  in  the  preceding  formula  of  alum,  means  three  equivalents  of  sulphuric 
acid ;  so  that  this  sign  has  the  same  value  as  if  it  were  written  3  S. 

Equivalents  of  sulphur  are  likewise  sometimes  expressed  by  commas  placed  over 
other  symbols,  as  the  trito-sulphuride  of  arsenic  by  As;  but  such  compounds  are 
not  of  constant  occurrence  like  the  oxides,  and  do  not  create  the  same  necessity  for 
a  new  and  arbitrary  symbol.  A  compound  body,  such  as  cyanogen,  which  combines 
with  a  numerous  series  of  other  bodies,  is  often  for  brevity  expressed  by  the  initial 
letter  or  letters  of  its  name,  as — 

Cyanogen  Cy, 

Ethyl E; 

and  the  organic  acids  are  sometimes  expressed  by  a  letter  in  the  same  way,  but  with 
the  minus  sign  ( — )  placed  over  it :  thus — 

Acetic  acid,  by  A, 
Tartaric  acid,  by  T. 

But  arbitrary  characters  of  this  kind  will  always  be  explained  on  the  occasion  of 
their  introduction. 

SECTION   II.  —  COMBINING   PROPORTIONS. 

All  analyses  prove  that  the  composition  of  bodies  is  fixed  and  invariable :  100 
parts  of  water  are  uniformly  composed  of  11.1  parts  by  weight  of  hydrogen,  and 
88.9  parts  of  oxygen,  its  constituents  never  varying  either  in  nature  or  proportion. 
This  and  other  substances  may  exist  in  an  impure  condition,  from  an  admixture  of 
foreign  matter,  but  their  own  composition  remains  the  same  in  all  circumstances. 
It  is  this  constancy  in  the  composition  of  bodies  which  gives  to  chemical  analyses 
all  their  value,  and  rewards  the  vast  care  necessarily  bestowed  upon  their  execution. 

An  examination  of  the  composition  of  a  class  of  bodies,  such  as  the  oxides,  con- 
taining an  element  in  common,  shows  that  any  one  element  unites  with  very  different 
quantities  of  the  other  elements.  Thus  in  each  of  the  five  oxides  of  which  the 
composition  is  given  on  page  112,  the  oxygen  and  other  constituents  appear  in  a 
different  relation  to  each  other : 


112 


COMBINING   PROPORTIONS. 
Composition  of  Oxides. 


Water. 

Oxide  of  Copper. 

Oxide  of  Zinc. 

Oxide  of  Lead. 

Oxide  of  Silver. 

Oxygen...  88.9 
Hydrogen  11  1 

Oxygen....  20.2 
Copper    .     79  8 

Oxygen  ...  19.1 
Zinc            80  9 

Oxygen    ...  7.2 
Lead  .    ..    92  8 

Oxygen  6.9 
Silver           93  1 

100 

100 

100 

100 

100 

But  the  relation  between  the  oxygen  and  the  other  constituent  in  these  oxides  will 
be  seen  more  distinctly  by  stating  their  composition  in  such  a  way  as  to  have  the 
oxygen  expressed  by  the  same  number  in  every  case,  or  made  equal  to  100  parts. 
Thus: 

Composition  of  Oxides. 


Water. 

Oxide  of  Copper. 

Oxide  of  Zinc. 

Oxide  of  Lead. 

Oxide  of  Silver. 

Oxygen  .  100 
Hydrogen  12  5 

Oxygen  100 
Copper          396 

Oxygen  ...  100 
Zinc             406 

Oxygen  ...  100 
Lead          1294 

Oxygen  100 
Silver          1350 

112.5 

496 

506 

1394 

1450 

From  which  it  follows,  that — 

12.5  parts  of  hydrogen, 
396      parts  of  copper, 
406      parts  of  zinc, 
1294 
1350 


V 


parts  of  lead, 
parts  of  silver, 

combine  with  100  parts  of  oxygen. 


These  numbers  prove  to  be  in  some  degree  characteristic  of  the  substances  to 
which  they  are  here  attached,  for  when  the  composition  of  the  sulphides  of  the 
same  substances  is  examined,  it  is  found  that  exactly  corresponding  quantities  of 
hydrogen,  copper,  &c.  likewise  combine  with  one  and  the  same  quantity  of  sulphur, 
although  not  with  100  parts  of  that  element  as  of  oxygen.  The  conclusion  from 
an  examination  of  the  sulphides  is,  that — 

12.5  parts  of  hydrogen, 
396      parts  of  copper, 
406      parts  of  zinc, 
1294      parts  of  lead, 
1350      parts  of  silver, 

combine  with  200  parts  of  sulphur. 

An  examination  of  the  chlorides  of  the  same  five  elements  likewise  proves,  that — 

12.5  parts  of  hydrogen, 
396     parts  of  copper, 
406     parts  of  zinc, 
1294     parts  of  lead, 
1350     parts  of  silver, 

combine  with  443.75  parts  of  chlorine. 

Hydrogen,  copper,  &c.,  are  indeed  found  to  unite  in  the  proportions  repeated  above, 
with  a  certain  or  constant  quantity  of  all  other  elements;  as,  for  example,  with  978 
bromine,  with  1580  iodine,  &c. 

On  extending  the  inquiry  to  other  substances,  it  appears  that  for  each  of  them  a 
number  may  be  found  which  expresses  in  like  manner  the  proportion  in  which  that 


COMBINING    PROPORTIONS.  113 

substance  unites  with  100  parts  of  oxygen,  200  of  sulphur,  443.73  of  chlorine,  &c. 
These  numbers  constitute  the  combining  proportions,  or  equivalent  quantities  of 
bodies,  which  are  introduced  in  the  table  of  the  names  of  the  elements  at  the  begin- 
ning of  this  chapter,  and  which  are  the  quantities  understood  to  be  expressed  by  the 
chemical  symbols  of  these  bodies. 

Any  series  of  numbers  may  be  chosen  for  the  combining  proportions,  provided  the 
true  relation  between  them  is  preserved,  as  in  the  first  series  of  numbers  given  in  the 
same  table,  which  are  all  12 }  times  less  than  the  numbers  of  the  second  series. 
Hydrogen  is  reduced  from  12.5  to  1,  oxygen  from  100  to  8,  sulphur  from  200  to  16  : 
altered  in  the  same  proportion,  copper  becomes  31.66,  zinc  32.52,  lead  103.56,  and 
silver  108.  This  series,  or  the  hydrogen  scale,  is  recommended  by  the  circumstance 
that  its  numbers  are  smaller  and  more  easily  recollected  than  those  of  the  other,  or 
oxygen  scale.  The  equivalents  of  several  of  the  most  important  elements  are  now 
also  generally  allowed  to  be  the  exact  multiples  of  the  equivalent  of  hydrogen,  so 
that  the  equivalent  of  the  latter  element  being  1,  the  equivalents  of  the  former  are 
accurately  expressed  by  entire  numbers;  —  carbon  by  6,  oxygen  by  8,  nitrogen  by 
14,  sulphur  by  16,  and  iron  by  28. 

Having  reference  to  the  oxygen  series,  it  is  said,  in  general  terms,  that  the  com- 
bining proportion  of  a  simple  substance  represents  the  quantity  of  that  substance 
which  combines  with  100  parts  of  oxygen  to  form  a  protoxide.  On  the  hydrogen 
scale,  which  I  shall  adopt,  the  definition  of  a  chemical  equivalent,  or  combining  pro- 
portion becomes  as  follows  : — The  combining  proportion  of  a  simple  substance  repre- 
sents the  quantity  of  that  substance  which  unites  with  8  parts  of  oxygen  to  form  a 
protoxide. 

The  first  law  of  combination  is,  that  "  bodies  unite  with  each  other  in  their  com- 
bining proportions  only,  or  in  multiples  of  them,  and  in  no  intermediate  proportions." 
This  law  may  be  illustrated  by  the  compounds  of  nitrogen  and  oxygen,  which  are 
five  in  number,  and  are  composed  as  follows : — 

Protoxide  of  nitrogen nitrogen  14,  oxygen  8. 

Deutoxide  of  nitrogen nitrogen  14,  oxygen  16. 

Nitrous  acid nitrogen  14,  oxygen  24. 

Peroxide  of  nitrogen nitrogen  14,  oxygen  32. 

Nitric  acid nitrogen  14,  oxygen  40. 

The  first  compound  consists  of  a  single  combining  proportion  of  each  of  its  consti- 
tuents. But  in  the  other  compounds,  a  single  proportion  of  nitrogen  is  united  with 
quantities  of  oxygen  which  correspond  exactly  with  two,  three,  four,  and  five  com- 
bining proportions  of  that  element.  In  the  greater  number  of  binary  compounds 
one  of  the  constituents  at  least  is  present  in  the  proportion  of  a  single  equivalent, 
like  the  nitrogen  in  this  series,  while  the  other  constituent,  generally  the  oxygen  in 
oxides,  and  the  electro-negative  element  in  other  compounds,  is  present  in  a  multiple 
of  its  combining  proportion.  But  the  number  of  equivalents  which  may  enter  into 
a  compound  is  subject  to  considerable  variation,  as  will  appear  from  the  following 
examples : — 


One  eq.  of  oxygen 

4- 

One  eq.  of  hydrogen,  forms  water. 

Two 

oxygen 

One 

hydrogen,  form  peroxide  of  hydrogen. 

One 

oxygen 

Two 

copper,    forms     suboxide  of  copper. 

One 

sulphur 

Three 

oxygen,        "         sulphuric  acid. 

Two 

sulphur 

Two 

oxygen,     form     hyposulphurous  acid. 

Two 

iron 

Three 

oxygen,       "         peroxide  of  iron. 

Two 

sulphur 

f 

Five 

oxygen,       "         hyposulphuric  acid. 

Two 

manganese 

+ 

Seven 

oxygen,       "         hy  permanganic  acid. 

Representing  the  constituents  of  a  binary  compound  by  A  and  B,  the  last  being 

the  oxygen  or  electro-negative  constituent,  the  most  frequent  combinations  are— 

A  +  B,  A-f  2B,  A  +  3B,  and  A  +  5B.     The  combination  of  2A-J-3B,  is  not  unfre- 

quent,  but  2A-J-B,  A-{-4B;  A  +  7B,  2A  +  2B,  or  2A  +  5B,  are  of  comparatively 

8 


114  COMBINING    PROPORTIONS. 

rare  occurrence.  Combination  between  two  elements  is  not  known  to  occur  in  more 
complicated  ratios  than  the  preceding,  if  the  compounds  of  carbon  and  hydrogen  be 
excepted,  which  are  numerous,  and  exhibit  great  diversity  of  composition,  like  the 
compounds  of  organic  chemistry  generally,  to  which  they  properly  belong. 

Combination  likewise  takes  place  among  bodies  which  are  themselves  compound, 
in  proportional  quantities,  which  are  fixed  and  determined  by  the  law,  that  "  the 
combining  number  of  a  compound  body  is  always  the  sum  of  the  combining  numbers 
of  its  constituents."  Thus  oil  of  vitriol,  which  contains  water  and  sulphuric  acid, 
is  composed  of  these  bodies  in  the  proportion  of — 

Water 9 

Sulphuric  acid 40 

in  which  the  combining  proportion  of  the  water  (9)  is  the  sum  of  the  equivalents 
of  its  constituents ;  namely,  of  oxygen  8,  and  of  hydrogen  1 ;  and  that  of  sulphuric 
acid  (40),  of  those  of  sulphur  16,  and  of  oxygen  24 ;  there  being  three  proportions 
of  oxygen  in  sulphuric  acid.  The  combining  proportion  of  oxide  of  zinc  is  40.52, 
the  sum  of  oxygen  8,  and  zinc  32.52 ;  and  the  compound  of  this  oxide  with  sul- 
phuric acid,  or  the  salt,  sulphate  of  zinc,  consists  of — 

Oxide  of  zinc 40.52 

Sulphuric  acid 40. 

80.52 

Of  potash,  the  combining  proportion  is  47 ;  or  oxygen  8,  added  to  potassium  39 ; 
and  to  this  proportion  of  potash  the  usual  proportion  of  sulphuric  acid  is  attached  in 
the  sulphate  of  potash,  which  is  composed  of — 

Potash  47 

Sulphuric  acid  40  "V 

87 

Of  these  salts  themselves,  the  combining  proportions  ought  to  be  the  sums  obtained 
by  the  addition  of  the  numbers  of  their  constituents ;  and  accordingly  the  double 
sulphate  of  zinc  and  potash  consists  of — 

Sulphate  of  zinc 80.52 

Sulphate  of  potash 87 

167.52 

Of  nitric  acid  the  constituents  are  one  eq.  of  nitrogen  14,  and  five  of  oxygen  40, 
making  together  54,  which  is  the  combining  proportion  of  that  acid,  and  is  found  to 
unite  with  9  water,  with  40.52  oxide  of  zinc,  and  with  47  potash ;  or  with  the  same 
quantities  of  these  oxides  as  combine  with  40  sulphuric  acid.  Carbonic  acid  is  com- 
posed of  one  proportion  of  carbon  6,  and  two  proportions  of  oxygen  16,  so  that  its 
combining  number  is  22 ;  in  which  proportion  it  unites  with  47  potash,  to  form 
carbonate  of  potash.  The  equivalent  quantities  of  all  other  acids  and  bases  corre- 

rnd  in  like  manner  with  the  numbers  deducible  from  their  composition.     Indeed, 
law  is  found  to  hold  in  compounds  of  every  class  and  character,  and  whether 
they  contain  few  or  many  equivalents  of  their  elements. 

Compound  bodies  likewise  unite  among  themselves  in  multiples  of  their  combining 
proportions,  as  well  as  in  single  equivalents.  Thus  47  potash  combine  with  52.15 
chromic  acid,  and  with  double  that  quantity,  or  104.30,  chromic  acid,  to  form  the 
yellow  and  red  chromates  of  potash ;  the  first  containing  one  equivalent,  and  the 
second  two  equivalents  of  acid.  The  occurrence  of  multiple  proportions  was  well 
illustrated  by  Dr.  Wollaston  in  the  carbonate  and  bicarbonate  of  potash.  A  quan- 
tity of  the  latter  salt  being  divided  into  equal  parts,  one-half  was  exposed  to  a  red 
heat,  by  the  effect  of  which  the  salt  lost  some  carbonic  acid  and  became  neutral  car- 


COMBINING    PROPORTIONS.  115 

bonate ;  and  both  portions  being  afterwards  decomposed  by  an  acid,  the  salt  in  its 
original  condition  was  found  to  afford  a  measure  of  carbonic  acid  gas  exactly  double 
of  that  yielded  by  the  portion  exposed  to  the  high  temperature.  By  experiments 
equally  simple  and  convincing,  he  proved  that  in  the  three  salts  formed  by  oxalic 
acid  and  potash,  the  quantities  of  acid  which  combine  with  the  same  quantity  of 
alkali  are  rigorously  among  themselves  as  the  numbers  1,  2,  and  4.  The  compo- 
sition of  all  other  super  and  sub-salts  is  found  to  be  in  conformity  with  the  same 
law,  one  of  the  constituents  being  always  present  in  the  proportion  of  two  or  more 
equivalents. 

The  combining  proportions  of  compound  bodies  depend  entirely,  therefore,  upon 
those  of  their  constituents,  or  upon  the  equivalents  of  the  elementary  bodies.  The 
mode  of  determining  these  fundamental  equivalents  generally  consists,  as  may  be 
anticipated,  in  ascertaining  the  quantity  of  any  element  which  exists  united  with  8 
parts  of  oxygen  in  the  protoxide  of  that  element,  which  quantity  is  viewed  as  a  single 
equivalent.  Thus,  of  hydrogen  and  lead,  the  protoxides  are  water  and  litharge,  in 
which  respectively  8  oxygen  are  associated  with  1  hydrogen  and  103.56  lead,  which 
numbers  are  therefore  single  equivalents  of  these  elementary  substances.  But  the 
difficulty  still  remains  to  know  what  is  a  protoxide ;  for  the  rule  is  not  followed  in 
all  cases  to  consider  that  oxide  of  an  element  as  the  protoxide  which  contains  the 
least  proportion  of  oxygen.  When  only  one  oxide  is  known,  it  is  presumed  to  be  a 
protoxide,  and  composed  of  single  equivalents,  unless  it  corresponds  in  properties 
with  a  higher  degree  of  oxidation  of  some  other  element  j  and  of  several  oxides  of 
the  same  element,  that  containing  least  oxygen  is  viewed  as  the  protoxide,  unless  a 
higher  oxide  has  better  claims  to  be  considered  as  such.  Hence  magnesia  and  oxide 
of  zinc  being  the  only  oxides  of  magnesium  and  zinc  known,  are  protoxides ;  and 
water,  litharge,  potash,  soda,  lime,  and  protoxide  of  iron,  which  are  all  the  lowest 
oxides  of  different  metals,  are  admitted  without  objection  to  be  protoxides,  and  be- 
come standards  of  comparison  for  this  class  of  bodies  ]  while  alumina,  the  only  oxide 
of  aluminum,  differing  entirely  from  the  protoxide  of  iron,  but  closely  resembling 
the  peroxide  of  that  metal,  is  considered  a  peroxide  of  similar  constitution,  or  to  con- 
tain three  equivalents  of  oxygen  and  two  of  metal.  Now  in  alumina  24  oxygen,  or 
three  equivalents,  are  united  with  27.38  aluminum,  one-half  of  which  number,  or 
13.69,  is  therefore  the  equivalent  of  aluminum.  The  true  protoxide  of  aluminum, 
if  it  is  capable  of  existing,  still  remains  to  be  discovered.  The  green  oxide  of  chro- 
mium, which  was  till  lately  the  lowest  degree  of  oxidation  known  of  that  metal,  was 
notwithstanding  considered  a  peroxide,  being  analogous  to  alumina  and  the  peroxide 
of  iron.  On  the  other  hand,  the  second  degree  of  the  oxidation  of  copper,  or  the 
black  oxide,  and  not  the  first  degree  of  oxidation  of  that  metal,  must  be  viewed  as 
the  protoxide,  or  as  composed  of  single  equivalents,  from  its  correspondence  with  the 
protoxide  of  iron  and  a  large  class  of  admitted  protoxides.  The  lower  degree  of 
oxidation  of  copper  or  the  red  oxide,  which  contains  only  half  the  proportion  of 
oxygen  in  the  black  oxide,  comes  therefore  to  be  considered  a  suboxide ;  a  com- 
pound of  two  equivalents  of  metal  and  one  of  oxygen.  For  reasons  somewhat  similar, 
the  higher  of  the  two  grades  of  oxidation  of  mercury,  or  the  red  oxide  of  that  metal, 
is  now  generally  received  as  the  protoxide,  and  the  ash-coloured  oxide  reputed  a 
suboxide.  These  suboxides  of  mercury  and  copper  are  capable  of  combining  with 
acids,  but  they  are  the  only  suboxides  which  possess  that  property.  It  is  the  cha- 
racter of  metallic  protoxides  to  form  salts  with  acids ;  and  of  several  oxides  of  the 
same  metal,  the  protoxide  is  always  the  most  powerful  base. 

Bodies  likewise  replace  each  other  in  combination,  in  equivalent  quantities. 
Thus  in  the  decomposition  of  water  by  chlorine,  which  occurs  in  certain  circum- 
stances, 35.5  parts  of  chlorine  unite  with  1  hydrogen  or  one  equivalent  of  that  body, 
to  form  hydrochloric  acid,  and  displace  at  the  same  time  and  liberate  8  parts  of 
oxygen.  Hence  the  number  35.5  represents  the  combining  proportion  of  chlorine, 
which  is  equivalent  in  combination  to,  or  can  be  substituted  for,  8  oxygen.  Again, 
in  decomposing  hydriodic  acid,  35.5  chlorine  unite  with  1  hydrogen,  and  liberate 
12G.36  iodine,  which  proportion  of  iodine  may  again  acquire  1  hydrogen,  by  decom- 


116  COMBINING    PROPORTIONS. 

posing  sulphuretted  hydrogen,  and  set  free  16  sulphur.  Hence  126.36  and  16  are 
the  equivalent  quantities  of  iodine  and  sulphur,  which  take  the  place  of  35.5  chlorine 
or  8  oxygen  in  combination  with  1  hydrogen. 

When  32.52  grains  of  zinc  are  introduced  into  a  solution  of  nitrate,  of  copper,  they 
dissolve,  acquiring  8  oxygen  and  54  nitric  acid,  and  become  nitrate  of  zinc,  while 
31.66  parts  of  metallic  copper  are  deposited,  which  had  previously  been  in  the  state 
of  nitrate,  and  in  combination  with  the  above-mentioned  quantities  of  oxygen  and 
nitric  acid,  and  the  solution  remains  otherwise  unaltered.  Zinc  throws  down  nearly 
all  the  metals  from  their  solutions  in  acids  in  the  same  manner,  and  if  the  quantity 
of  this  substance  introduced  into  the  solutions,  and  dissolved,  be  a  combining  pro- 
portion, as  in  the  instance  given,  the  quantities  of  the  metals  precipitated  will  also 
be  combining  proportions  of  those  metals.  The  quantity  of  zinc  employed  may  be 
varied,  but  the  quantity  of  other  metal  precipitated  will  still  be,  to  the  quantity  of 
zinc  dissolved,  in  the  ratio  of  the  combining  numbers  of  the  two  metals.  Lead, 
copper,  tin,  or  any  other  metal,  when  it  acts  like  zinc  as  a  precipitant,  likewise 
throws  down  equivalent  quantities  of  other  metals,  and  takes  their  place  in  the  pre- 
existing compound.  This  substitution  of  one  metal  for  another,  in  a  saline  com- 
pound, without  any  change  in  the  character  of  the  compound,  shows  how  justly  the 
combining  proportions  of  bodies  are  termed  their  equivalent  quantities  or  equivalents. 
The  metal  displaced,  and  that  substituted  for  it,  have  evidently  the  same  value  in 
the  construction  of  the  compound,  and  are  truly  equivalent  to  each  other. 

The  equivalent  proportions  of  such  oxides  as  are  bases  are  ascertained  by  finding 
what  quantity  of  each  saturates  the  known  combining  proportion  of  an  acid.  Thus, 
to  saturate  40  parts,  or  a  combining  proportion  of  sulphuric  acid,  the  following  pro- 
portions of  different  bases  are  requisite,  and  are  equivalent  in  producing  that  effect : 

Magnesia 20.67 

Lime 28 

Soda 31 

Protoxide  of  manganese 35.67 

Potassa 47 

Strontia 51.84 

Baryta 76.64 

Protoxide  of  lead 111.56 

Oxide  of  silver 116 

The  addition  of  these  bodies  to  sulphuric  acid  in  the  above  proportions  destroys 
its  sour  taste  and  other  properties  as  an  acid,  of  which  one  of  the  most  characteristic 
is  that  of  reddening  certain  vegetable  blue  colours,  such  as  litmus.  The  acid  is  said 
to  be  neutralized  or  saturated,  and  the  product  or  compound  formed  is  a  neutral  salt, 
which  does  not  alter  the  blue  colour  of  litmus.  Of  the  bases  mentioned,  magnesia 
has  the  greatest  saturating  power,  and  oxide  of  silver  the  least  j  the  proportion  of 
these  bases  necessary  to  saturate  the  same  quantity  of  sulphuric  acid  being  20.67  of 
the  former,  and  116  of  the  latter. 

Conversely,  the  equivalent  proportions  of  acids  are  the  quantities  which  neutralize 
the  known  equivalent  of  any  base  or  alkali.  Thus  47  parts  of  potassa,  or  a  com- 
bining proportion,  is  deprived  of  its  alkaline  properties,  —  of  which  the  most  obvious 
are  its  caustic  taste  and  power  to  restore  the  blue  colour  of  reddened  litmus,  —  by 
the  following  proportions  of  different  acids,  and  a  neutral  compound  or  salt  produced 
in  every  case  : — 

Sulphurous  acid 32 

Sulphuric  acid 40 

Hydrochloric  acid 36.5 

Nitric  acid 54 

Chloric  acid 75.5 

Hyperchloric  acid 91.5 

lodic  acid 166.36 

Hyperiodic  acid 182.36 


COMBINING  PROPORTIONS.  117 

It  thus  appears  that  the  acids  differ  as  widely  among  themselves  in  their  equivalent 
quantities  as  the  bases  do.  The  equivalent  of  either  an  acid  or  base  thus  deduced 
from  its  neutralizing  power  is  always  the  same  as  that  indicated  by  its  composition, 
namely  the  sum  of  the  equivalent  numbers  of  its  constituents.  As  the  bases  which 
saturate  acids  fully  are  all  protoxides,  it  also  necessarily  follows  that  100  parts  of 
oxygen  are  always  contained  in  the  proportion  of  base  which  neutralizes  the  equiva- 
lent of  an  acid. 

The  equivalents  of  both  acids  and  bases  are  likewise  observed  in  those  decompo- 
sitions in  which  one  acid  is  substituted  for  another  acid  in  combination,  or  one  base 
for  another  base.  Thus  an  equivalent  of  sulphuric  acid  is  found  to  disengage  the 
equivalent  quantity  exactly  of  sulphurous  acid  from  the  sulphite  of  soda,  of  nitric 
acid  from  the  nitrate  of  potash,  or  of  hydrochloric  acid  from  the  chloride  of  sodium, 
and  to  replace  it  in  combination  with  the  base,  forming  in  every  case  a  neutral  sul- 
phate. An  equivalent  of  potash  separates  in  like  manner  an  equivalent  of  magnesia, 
of  lime,  of  barytes,  or  of  protoxide  of  lead,  from  its  combination  with  an  acid.  The 
proportion  of  acid  or  base  necessary  to  produce  a  certain  amount  of  decomposition 
may  therefore  be  calculated  from  a  knowledge  of  the  equivalents  of  bodies;  and 
such  knowledge  comes  to  be  of  the  most  frequent  and  valuable  application  for  prac- 
tical purposes. 

But  the  substitution  of  equivalent  quantities  of  different  bodies  for  one  another  is 
most  strikingly  exhibited  in  the  decompositions  which  follow  the  mixture  of  certain 
neutral  salts.  An  equivalent  of  sulphate  of  magnesia  being  mixed  with  an  equiva- 
lent of  nitrate  of  barytes,  the  two  bases  exchange  acids,  the  original  salts  disappear 
completely,  and  two  new  salts  are  produced — the  sulphate  of  barytes,  which  is  inso- 
luble and  precipitates,  and  the  nitrate  of  magnesia,  which  remains  in  solution  ;  as 
represented  in  the  following  diagram,  in  which  the  equivalent  quantities  are  ex- 
pressed : — 

Before  decomposition.  After  decomposition. 

60.67  sulphate  of)  20.67  magnesia _--,  74.67  nitrate  of 


3hate  of)  20. 
da J  40 


magnesia j  40  sulphuric  acid /  magnesia. 

130.64  nitrate  of)  54  nitric  acid X*><> 

barytes J  76.64 ^^  116.64  sulphate 

of  barytes. 

After  a  double  decomposition  of  this  kind,  the  liquid  remains  neutral,  or  there  is 
no  redundancy  of  either  acid  or  base  •  because  each  of  the  new  salts  is  composed  of 
a  single  equivalent  of  acid  and  of  base,  like  the  salts  from  which  they  are  formed. 
If  one  of  the  salts  be  added  in  a  larger  proportion  than  its  equivalent  quantity,  the 
excess  does  not  interfere  with  the  decomposition,  and  remains  itself  unaffected,  the 
decomposition  proceeding  no  farther  than  the  equivalents  present.  Hence  the 
general  observation,  that  neutral  salts  continue  neutral  after  decomposition,  in  what- 
ever proportions  they  may  be  mixed. 

But  the  modes  of  fixing  the  equivalent  numbers  which  have  been  stated  are  inap- 
plicable to  several  elementary  bodies;  such  as  nitrogen,  phosphorus,  carbon,  boron, 
and  some  metals  of  which  the  protoxides  are  not  bases,  and  are  uncertain.  Nitrogen 
enters  into  nitric  acid,  of  which  acid  it  is  known  that  the  equivalent  is  54,  and  that  it 
contains  five  equivalents  or  40  parts  of  oxygen,  and  consequently  14  parts  of  nitrogen. 
It  is  doubtful,  however,  whether  14  represents  one  or  two  equivalents  of  nitrogen. 
But  the  equivalent  of  ammonia  likewise  contains  14  nitrogen,  and  a  less  proportion 
is  never  found  in  the  equivalent  of  any  other  compound  into  which  that  element 
enters.  The  number  14  is,  therefore,  the  least  combining  proportion  of  nitrogen, 
and  must  on  that  account  be  taken  as  one  equivalent.  The  equivalent  of  phos- 
phorus can  be  shown  on  the  same  principle  to  be  32,  that  of  arsenic  75,  and  that 
of  antimony  129,  as  given  in  the  tables,  and  not  the  halves  of  these  numbers,  as 
often  estimated.  These  three  bodies  agree  with  nitrogen  in  their  chemical  relations, 
and  the  numbers  recommended  represent  the  quantities  which  replace  14  of  nitrogen 


118  COMBINING    PROPORTIONS. 

in  analogous  compounds.  The  equivalent  of  carbon  may  be  deduced  from  the  known 
equivalent  of  its  compound,  carbonic  acid  :  but  the  equivalents  of  boron  and  silicium 
cannot  be  fixed  upon  with  the  same  certainty,  owing  to  the  doubt  which  hangs  over 
the  equivalents  of  boracic  and  silicic  acids. 

Of  the  facts  which  involve  the  principle  of  combination  in  definite  and  equivalent 
proportions,  the  last  mentioned  appears  to  have  been  the  first  observed  and  explained. 
Wenzel,  of  Freiberg  in  Saxony,  so  far  back  as  1777,  made  an  analysis  of  a  great 
variety  of  salts  with  surprising  accuracy,  which  enabled  him  to  perceive  that  the 
neutrality  which  is  observed  after  the  reciprocal  decomposition  of  neutral  salts  de- 
pends upon  this, —  that  the  quantities  of  different  acids  which  saturate  an  equal 
weight  of  one  baso  will  also  saturate  equal  weights  of  any  other  base. 

E-ichter  of  Berlin  confirmed  and  extended  the  observations  of  Wenzel,  attaching 
proportional  numbers  to  the  acids  and  bases,  and  remarking  for  the  first  time  that 
the  neutrality  does  not  change  during  the  precipitation  of  metals  by  each  other,  and 
also  that  the  proportion  of  oxygen  in  the  equivalents  of  bases  is  the  same  in  all,  and 
may  be  represented  by  100  parts.  But  the  first  foundations  of  a  complete  system 
of  equivalents,  embracing  both  simple  bodies  and  their  compounds,  were  laid  by 
Dalton,  at  the  same  time  that  he  announced  his  atomic  theory.  (New  System  of 
Chemical  Philosophy,  1807).  The  observation  that  the  equivalent  of  a  compound 
body  is  the  sum  of  the  equivalents  of  its  constituents,  and  the  discovery  of  combi- 
nation in  multiple  proportions,  are  peculiarly  his.  Dr.  Wollaston  afterwards  adapted 
the  more  important  equivalents  to  the  common  sliding  rule  of  Gunter,  by  means  of 
which,  proportions  can  be  observed  without  the  trouble  of  calculation.  This  instru- 
ment, which  is  known  under  the  name  of  the  scale  of  chemical  equivalents,  contri- 
buted largely  to  the  diffusion  of  the  knowledge  of  the  proportional  numbers,  but  is 
not  itself  of  much  practical  value. 

The  numerical  accuracy  of  the  equivalents  assigned  to  bodies  depends  entirely 
upon  the  exactness  of  the  chemical  analyses  from  which  they  are  deduced.  The 
generally  received  series  of  numbers,  which  is  adopted  in  this  work,  was  drawn  up 
by  Berzelius  from  data  supplied  in  a  great  measure  by  himself.  The  consideration 
of  the  laws  of  Wenzel  and  Richter,  which  were  long  overlooked  or  misunderstood, 
was  revived  by  him,  and  by  a  series  of  analytical  researches  unrivalled  for  their  ex- 
tent and  accuracy  he  first  impressed  upon  chemistry  the  character  of  a  science  of 
number  and  quantity,  which  is  now  its  highest  recommendation.  Several  of  Ber- 
zelius's  numbers  received  a  valuable  confirmation  from  Dr.  Turner,  whose  inquiries 
were  especially  directed  to  test  an  hypothesis  respecting  them  proposed  and  ably 
maintained  by  Dr.  Prout;  namely,  that  the  equivalents  of  all  the  elements  are 
multiplies  of  the  equivalent  of  hydrogen,  and  consequently  if  that  equivalent  be 
made  equal  to  1,  all  the  others  will  be  whole  numbers.  (Phil.  Trans.  1833,  p.  523). 
Dr.  Penny  took  a  part  in  the  same  inquiry,  (Ibid.  1839,  p.  13).  More  lately  labo- 
rious researches  have  been  undertaken  with  the  same  object  by  Dumas,  Marignac, 
Pelouze,  and  others,  whose  results  are  quoted  under  the  table  of  equivalents.  It 
appears  to  be  definitively  settled  that  the  equivalents  of  the  elements  are  not,  with- 
out exception,  multiples  of  the  equivalent  of  hydrogen.  The  number  for  chlorine 
(35-5)  is  conclusive  against  that  hypothesis.  At  the  same  time,  the  accurate  deter- 
minations of  the  equivalents  of  chlorine,  silver,  and  potassium,  by  Maumine,  lend 
positive  support  to  the  opinion  that  these  and  all  other  equivalents  are  multiples  of 
half  the  equivalent  of  hydrogen.  So  do  the  recent  determinations  of  carbon  and 
hydrogen  in  reference  to  oxygen,  and  those  of  nitrogen,  sodium,  iron,  and  calcium. 
The  number  for  lead  also,  upon  the  determination  of  which  extraordinary  pains  have 
been  bestowed  by  Berzelius  at  different  times,  namely  103-56,  is  favourable  to  the 
feame  view.  Now  these  are  the  equivalents  upon  which,  above  all  others,  our  know- 
ledge is  most  precise  and  certain. 

Might  not,  therefore,  the  equivalent  of  hydrogen  be  divided  by  two,  by  which 
chlorine  would  become  71  and  lead  207,  hydrogen  being  1  ?  The  multiple  relation 
would  not,  however,  be  established  by  dividing  the  equivalent  of  hydrogen,  for,  as 
is  justly  observed  by  Berzelius,  the  chemical  reasons  which  are  adduced  for  the 


ATOMIC     TIIEOHY. 


119 


division  of  the  equivalent  of  hydrogen  apply  with  equal  force  to  the  equivalent  of  chlo- 
rine, and  the  one  cannot  be  divided  without  dividing  the  other.  The  equivalent  of 
chlorine  would,  therefore,  still  remain  a  multiple  of  half  the  equivalent  of  hydrogen. 

SECTION    III. ATOMIC    THEORY. 

The  laws  of  combination,  and  the  doctrine  of  equivalents,  which  have  just  been 
considered,  are  founded  upon  experimental  evidence  only,  and  involve  no  hypothesis. 
The  most  general  of  these  laws  were  not  however  suggested  by  observation,  but  by 
a  theory  of  the  atomic  constitution  of  bodies,  in  which  they  are  included,  and  which 
affords  a  luminous  explanation  of  them.  The  partial  verification  which  this  theory 
has  received  in  the  establishment  of  these  laws  adds  greatly  to  its  interest,  and  is  a 
strong  argument  in  favour  of  its  truth.  It  is  the  atomic  theory  of  Dalton,  the 
essential  part  of  which  may  be  stated  in  a  few  words. 

Although  matter  appears  to  be  divided  and  comminuted  in  many  circumstances  to 
an  extent  beyond  our  powers  of  conception,  it  is  possible  that  it  may  not  be  indefinitely 
divisible }  that  there  may  be  a  limit  to  the  successive  division  or  secability  of  its  parts; 
a  limit  which  it  may  be  difficult  or  impossible  to  reach  by  experiment,  but  which  ne- 
vertheless exists.  Matter  may  be  composed  of  ultimate  particles  or  atoms,  which  are 
not  farther  divisible,  and  each  of  which  possesses  a  certain  absolute  and  possibly  appre- 
ciable weight.  Now  the  question  arises,  is  the  atom  in  every  kind  of  matter  of  the 
same  weight,  or  do  atoms  of  different  kinds  of  matter  differ  in  weight  ?  Are  the  ulti- 
mate particles,  for  instance,  to  which  charcoal  and  sulphur  are  reducible,  of  the  same 
or  different  weights  ?  Let  their  weights  be  supposed  to  be  different,  to  be  in  the  pro- 
portion of  the  equivalent  numbers  of  sulphur  and  charcoal,  which  thus  become  atomic 
weights,  and  so  of  the  atoms  of  other  elementary  bodies,  and  the  whole  laws  of  com- 
bination follow  by  the  simplest  reasoning.  The  atoms  of  the  elementary  bodies  may 
be  represented  to  the  eye  by  spheres  or  by  circles  in  which  their  symbols  are  inscribed 
to  distinguish  them,  as  in  the  following  examples,  with  their  relative  weights. 


Name. 


Atom. 


Weight  of  Atom. 


Oxygen  .. 
Hydrogen 
Nitrogen  . 
Carbon  ... 
Sulphur . . 
Lead 


...  1 
...14 
...  6 
...16 
103.56 


Chemical  combination  takes  place  between  the  atoms  of  bodies,  which  then  come 
into  juxtaposition;  and  in  decomposition  the  simple  atoms  separate  again  from  each 
other,  in  possession  of  their  original  properties.  The  atom  or  integrant  particle  of  a 
compound  body  is  an  aggregation  of  simple  atoms,  and  must  therefore  have  a  weight 
equal  to  the  sum  of  their  weights ;  as  will  be  obvious  from  the  exhibition  of  the  atomic 
constitution  of  a  few  compounds. 

Atom. 


Water  (oxide  of  hydrogen)  .. 

Protoxide  of  nitrogen 

Deutoxide  of  nitrogen 
Sulphuric  acid 
Oxide  of  lead 

Sulphate  of  lead 


Weight. 

1+8=9 

14  +     8  =  22 

14  +  16  =  30 

16  +  24  =  40 

103-56  +     8=111-56 

111-56+  40=151-56 


120  SPECIFIC    HEAT    OF    ATOMS. 

It  is  unnecessary  to  make  any  assumption  as  to  the  nature,  size,  form,  or  even 
actual  weight  of  the  atoms  of  elementary  bodies,  or  as  to  the  mode  in  which  they 
are  grouped  or  arranged  in  compounds.  All  that  is  known  or  likely  ever  to  be 
known  respecting  them  is  their  relative  weight.  The  atom  of  oxygen  is  eight  times 
heavier  than  that  of  hydrogen,  but  their  actual  weights  are  undetermined.  To  afford 
the  means  of  expressing  the  relative  weights  of  these  and  other  atoms,  a  number 
which  is  entirely  arbitrary  is  assigned  to  one  of  them,  namely  8  to  the  atom  of 
oxygen,  and  then  the  weight  of  the  atom  of  hydrogen  can  be  said  to  be  1,  of  nitro- 
gen 14,  of  carbon  6,  of  sulphur  16,  and  of  lead  103-56.  A  single  atom  of  water 
contains  one  atom  of  oxygen  (8),  and  one  of  hydrogen  (1),  and  must  therefore 
weigh  9 ;  an  atom  of  oxide  of  lead  contains  one  atom  of  oxygen  and  one  of  lead, 
which  weigh  together  111-56;  an  atom  of  sulphuric  acid,  one  atom  of  sulphur  and 
three  atoms  of  oxygen,  which  weigh  together  40 ;  and  an  atom  of  sulphate  of  lead, 
including  one  of  each  of  the  preceding  compound  atoms,  must  weigh  111-56  +  40, 
or  151-56. 

The  equivalent  quantities  being  now  represented  by  atoms,  it  necessarily  follows 
that  bodies  can  combine  in  these  quantities  or  multiples  of  them  only,  and  not  in 
intermediate  proportions,  for  atoms  do  not  admit  of  division.  In  a  series  of  several 
compounds  of  the  same  elements,  such  as  the  oxides  of  nitrogen,  which  was  formerly 
referred  to  in  illustration  of  combination  in  multiple  proportions  (page  113),  one  atom 
of  nitrogen  combines  with  one,  two,  three,  four  and  five  atoms  of  oxygen,  and  a 
simple  ratio  between  the  quantities  of  oxygen  in  these  compounds  is  the  conse- 
quence. The  equivalent  of  the  compound  body  also  is  the  sum  of  the  equivalents 
of  its  constituents,  for  the  weight  of  a  compound  atom  is  the  weight  of  its  consti- 
tuent atoms. 

By  the  juxtaposition,  separation,  and  exchange  of  one  atom  for  another  in  com- 
pounds, all  kinds  of  combination  and  decomposition  in  equivalent  quantities  may 
be  produced,  while  the  substitution  of  ponderable  masses  for  the  abstract  idea  of 
equivalents  renders  the  whole  changes  most  readily  conceivable. 

This  theory  being  adopted  as  a  useful,  while  it  is  at  the  same  time  a  highly  pro- 
bable representation  of  the  laws  of  combination,  its  terms  atom  or  atomic  weight 
may  be  used  as  synonymous  with  equivalent,  equivalent  quantity,  and  combining 
proportion. 

M.  Dumas  is  disposed  to  modify  the  atomic  theory  so  far  as  to  allow  the  divisi- 
bility of  the  atoms  or  ultimate  masses  in  which  a  body  enters  into  combination,  and 
to  suppose  that  they  are  groups  of  more  minute  atoms,  into  which  they  may  be 
divided  by  physical,  but  not  by  chemical  forces.  He  distinguishes  the  atoms  which 
correspond  with  equivalents  as  chemical  atoms,  and  allowing  them  to  represent  truly 
and  constantly  the  least  quantities  in  which  bodies  combine,  still  supposes  that  under 
the  influence  of  heat,  and  perhaps  other  physical  agencies,  these  molecules  may  be 
subdivided  into  atoms  of  an  inferior  order,  of  which,  for  example,  two,  four,  or  a 
thousand,  are  included  in  a  single  chemical  atom.  (Lemons  sur  la  Philosophic  Chi- 
mique,  professees  au  College  de  France,  par  M.  Dumas,  page  233).  But  surely 
such  a  view  is  entirely  subversive  of  the  atomic  theory.  It  is  principally  founded 
on  the  assumed  existence  of  a  similarity  between  atoms  in  their  capacity  for  heat, 
and  in  their  volume  while  in  the  gaseous  state. 

SPECIFIC    HEAT   OP   ATOMS. 

The  quantity  of  heat  necessary  to  raise  the  temperature  of  equal  weights  of 
different  bodies  a  single  degree,  varies  according  to  their  nature,  and  may  be  ex- 
pressed  by  numbers  which  are  the  capacities  for  heat  or  specific  heats  of  these  bodies 
(page  49).  This  difference  appears  in  the  numbers  for  several  simple  bodies  placed 
together  in  the  first  column  of  the  following  table,  among  which  no  relation  can  be 
perceived.  But  if  the  comparison  is  made  between  the  capacity  for  heat  not  of 
equal  weights,  but  of  atomic  weights  or  equivalent  quantities  of  the  same  bodies, 
as  in  the  second  and  third  columns  of  the  table,  then  the  numbers  for  several  bodies 


SPECIFIC    HEAT    OF    ATOMS. 


121 


are  found  to  be  nearly  the  same,  and  those  of  others  to  bear  a  simple  relation  to 
each  other. 

SPECIFIC    HEAT. 


_± 

I. 

Of  equal 
weights. 
Specific  heat 
of  same 
weight  of  water 
being  1. 

II. 

Of  atoms. 

Specific  heat 
of 
atom  of  water 
being  1. 

III. 

Of  atoms. 

Specific  heat 
of 
atom  of  lead 
being  1. 

IV. 

Atomic 
weights. 

Lead    

0-0293 

0-3372 

1  -0000 

103-56 

Tin  

0-0514 

0-3358 

0-9960 

58-82 

Zinc 

0-0927 

0-3321 

0-9850 

32-52 

Copper                        

0-0949 

0-3340 

0-9908 

31-66 

Nickel  

0-1035 

0-3404 

1-0095 

29-57 

Cobalt  

0-10696 

0-3508 

1-040 

29-52 

Iron 

0-1100 

0-3315 

0-9831 

28 

Platinum  

0-0314 

0-3443 

1-0211 

98-68 

Sulphur  

0-1880 

0-3359 

0-9963 

16 

0-0330 

0-3714* 

1-1015 

100-07 

Tellurium                    .  . 

0-05155 

0-3788 

1-123 

64-14 

Gold      

0-0298 

0-3292 

0-9765 

98-33 

Arsenic  

0-081 

0-6768 

2-0074 

75 

Silver 

0-0557 

0-6694 

1-9855 

108 

Phosphorus      ..         .. 

0-385 

1-3415 

3-9789 

32 

Iodine  

0-10824 

1-5197 

4-506 

126-36 

Carbon  

0-2411 

0-1698 

0-4766 

6 

Bismuth 

0-03084 

0-2190 

0-6494 

70-95 

Of  the  first  twelve  substances,  which  are  all  metals,  with  the  exception  of  sul- 
phur, the  capacities  of  the  atoms  approach  so  closely,  that  they  may  be  considered 
as  identical ;  their  capacities  appearing  to  be  all  nearly  one-third  of  that  of  the  atom 
of  water,  in  the  second  column;  and  nearly  coinciding  with  the  capacity  of  the 
atom  of  lead,  one  of  their  number  in  the  third  column.  The  weights  of  the  atoms 
themselves  are  added  in  a  fourth  column,  for  convenience  of  reference.  The  twelve 
substances  in  question,  taken  in  the  proportions  of  their  atomic  weights,  will,  there- 
fore, undergo  an  equal  change  of  temperature  on  assuming  an  equal  quantity  of 
heat.  The  two  metals  which  follow  in  the  table,  namely,  arsenic  and  silver,  appear 
to  have  an  equal  capacity  for  heat,  which  is  double  that  of  lead  and  the  class  which 
coincides  with  it,  while  the  capacity  of  phosphorus  is  four  times,  and  that  of  iodine 
four  and  a  half  times  greater  than  that  of  lead  and  its  class.  The  capacity  of  the 
atom  of  bismuth  appears  to  be  two-thirds,  and  that  of  carbon  to  be  one-half  of  the 
capacity  of  that  of  lead.  The  general  results  may  therefore  be  stated  as  follows : — 

Weight  of  Atom. 

Specific  heat  of  atom  of  lead 1  103-56 

tin 1  68-82 

zinc  1  32-52 

copper 1  31-66 

nickel 1  29-57 

cobalt 1  29-52 

iron  1  28 

platinum  1 98-68 

sulphur  1  4i.    16 

mercury 1  100-07 

tellurium  1  64-14 

gold 1 98-33 

arsenic 2  75 

silver  2  108 

phosphorus 4 32 

iodine  4$ 126-36 

bismuth  f 70-95 

carbon    .  ..  i  ...  6 


122 


SPECIFIC    HEAT    OF    ATOMS. 


Messrs.  Dulong  and  Petit,  whose  researches  supplied  the  greater  portion  of  these 
valuable  results,  drew  a  more  general  conclusion  from  them,  namely  that  all  atoms, 
or  at  least  all  simple  atoms,  have  the  same  capacity  for  heat,  and  that  those  atomic 
weights  which  are  inconsistent  with  that  supposition,  ought  to  be  altered  and  accom- 
modated to  it.  The  specific  heat  of  a  body  would  thus  afford  the  means  of  fixing 
its  atomic  weight.  Some  of  the  alterations  in  the  atomic  weights,  which  would 
follow  the  adoption  of  this  law,  might  be  advocated  upon  other  grounds  —  such  as 
halving  the  atomic  weight  of  silver,  doubling  that  of  carbon,  and  adding  one-half  to 
that  of  bismuth.  But  the  equivalent  of  phosphorus  would  require  to  be  divided  by 
four,  while  that  of  arsenic,  which  it  so  closely  represents  in  compounds,  is  divided 
only  by  two ;  changes  which  are  inadmissible. 

It  must  be  concluded,  then,  that  elementary  atoms  have  not  necessarily  the  same 
capacity  for  heat,  although  a  simple  relation  appears  always  to  exist  between  their 
capacities.  The  capacities  of  the  three  gaseous  elements,  oxygen,  hydrogen,  and 
nitrogen,  may  likewise  be  adduced  in  support  of  such  a  relation,  provided  they  are 
the  same  for  equal  volumes  of  the  gases,  agreeably  to  the  observations  of  Dulong. 
But  this  relation  can  only  be  looked  for  between  bodies  while  under  the  same  phy- 
sical condition,  and  perhaps  agreeing  in  other  circumstances  also,  for  the  capacity  for 
heat  of  the  same  body  is  known  to  vary  under  the  different  forms  of  solid,  liquid, 
and  gas ;  and,  indeed,  while  the  body  is  in  the  same  state,  its  capacity  appears  not 
to  be  absolutely  constant,  but  to  increase  perceptibly  to  elevated  temperatures  (page 
49). 

The  capacities  of  compound  atoms  have  also  been  submitted  to  a  sufficiently  ex- 
tensive examination  to  determine  that  simple  relations  subsist  among  them.  In  two 
classes  of  analogous  combinations,  the  capacities  of  the  atoms  for  heat  were  found 
by  M.  Neumann,  of  Konigsberg,  to  approach  so  closely,  that  they  may  be  admitted 
to  be  the  same,  the  differences  being  sufficiently  accounted  for  by  the  errors  of  obser- 
vation unavoidable  in  such  delicate  researches. 


OF   EQUAL 
WEIGHTS. 

Specific  heat  of 
same  weight  of 
water  being  1. 

OF   ATOMIC 
WEIGHTS. 

Specific  heat  of 
atom  of  water 
being  1. 

Carbonate  of  lime  

0-2044 

0-1148 

0-1080 

0-1181 

Carbonate  of  iron  

0-1819 

0-1156 

Carbonate  of  lead  

0-0810 

0-1200 

Carbonate  of  zinc  

0-1712 

0-1187 

Carbonate  of  strontia  

0-1445 

0  1184 

Dolomite  (carbonate  of  lime  and  magnesia)  

0-2111 

0-1121 

Mean  

0-1162 

A  small  class  of  sulphates  presented  a  similar  result  i — 


OF   EQUAL 
WEIGHTS. 

OF   ATOMIC 
WEIGHTS. 

0-1068 

0-1384 

Sulphate  of  lime  ... 

0-1854 

0-1412 

Sulphate  of  strontia  

0-1300 

0-1326 

Sulphate  of  lead  

0-0830 

0-1398 

Mean  

0-1380 

SPECIFIC    HEAT    OF    CARBON.  123 

The  numbers  in  the  second  column  of  both  tables  deviate  very  little  from  their  mean, 
but  there  is  no  obvious  relation  between  the  two  means.  Identity  in  capacity  for 
heat  is,  therefore,  to  be  looked  for  in  compound  atoms  of  the  same  nature,  and  which 
closely  agree  in  their  chemical  relations,  like  the  numbers  of  each  group,  but  not 
between  compound  atoms  which  are  differently  constituted. 

Our  information  on  this  subject  has  been  greatly  extended  of  late  by  the  valuable 
researches  of  M.  Regnault.1  The  atomic  heat  of  bodies,  as  it  is  named  by  this 
chemist,  is  obtained  by  multiplying  the  observed  specific  heat  of  each  body  by  its 
equivalent,  the  latter  being  taken  upon  the  oxygen  scale.  Now  this  product  is 
found  to  vary  for  the  metallic  elements  as  the  numbers  38  to  42,  a  greater  differ- 
ence than  can  result  from  errors  of  observation ;  so  that  the  law  of  atoms  is  not 
verified  in  an  absolute  manner.  But  if  it  is  considered  that  the  atomic  weights  of 
the  simple  substances  in  question  vary  at  the  same  time  from  200  to  1400,  the  law 
must  be  adopted,  as  at  least  closely  approximating  to  the  truth.  The  law  would 
probably  represent  the  results  of  observation  in  a  perfectly  rigorous  manner,  if  the 
specific  heat  of  each  body  could  be  taken  at  a  determinate  point  of  its  thermometrical 
scale,  and  the  specific  heat  be  further  disencumbered  of  all  the"  foreign  influences 
which  modify  the  observation,  —  such  as  the  state  of  softness,  with  the  assumption 
of  a  certain  portion  of  the  latent  heat  of  fusion,  which  many  bodies  exhibit  before 
melting  entirely,  —  and  the  heat  absorbed  to  produce  dilatation,  which  is  very  great 
in  gases,  much  more  feeble  in  solid  and  liquid  bodies,  but  which  can  in  no  case  be 
neglected  (Regnault).  An  increase  of  the  density  of  copper  also,  produced  by  ham- 
mering it,  is  found  by  Regnault  to  effect  a  sensible  diminution  of  its  specific  heat : 
the  latter  recovers  its  original  value  in  the  metal  after  being  heated. 

The  same  element,  in  different  conditions  as  to  crystalline  form,  hardness,  and 
aggregation,  may  vary  greatly  in  its  specific  heat,  as  is  observed  of  carbon  both  by 
Regnault,  and  by  Delarive  and  Marcet.  (Annales,  &c.,  t.  Ixxv.  p.  242).  The 
results  of  the  former  are  as  follows  : — 

SPECIFIC    HEAT   OF  VARIETIES    OF   CARBON. 

Animal  charcoal 0-26085 

Wood  charcoal 0-24150 

Coke  of  coal 0-20307 

Charcoal  from  anthracite 0-20146 

Graphite,  natural 0-20187 

Graphite  of  iron  furnaces 0-19702 

Graphite  of  gas  retorts 0-20360 

Diamond 0-14687 

The  calorific  capacity  of  this  body  is  the  more  feeble  in  proportion  as  its  state  of 
aggregation  is  greater :  it  is  an  instance  of  a  body  which  may  exist  with  calorific 
capacities  extending  through  a  very  wide  range. 

The  following  metallic  protoxides  of  the  formula  MO,2  protoxide  of  lead,  red  oxide 
of  mercury,  protoxide  of  manganese,  oxide  of  copper,  and  oxide  of  nickel,  have  an 
atomic  heat  varying  from  70-01  to  76-21,  of  which  the  mean  is  72.03;  these  num- 
bers being  the  observed  specific  heats  of  the  oxides  multiplied  by  their  atomic  weights : 
the  same  product  averages  about  40  in  the  elements.  The  atomic  heat  of  magnesia 
is  63-03,  and  of  oxide  of  zinc,  62-77,  expressed  in  the  same  manner,  which  agree 
very  closely  together,  but  differ  considerably  from  the  other  protoxides. 

The  protosulphurets,  of  the  formula  MS,  correspond  nearly  with  the  protoxides, — 
the  protosulphurets  of  iron,  nickel,  cobalt,  zinc,  lead,  mercury,  and  tin,  varying  from 
71-34  to  78-34;  with  a  mean  of  74-51,  while  the  mean  of  the  protoxides  is  72-03. 

Sesquioxides,  of  the  formula  M203,  give  for  the  product  of  their  specific  heats  by 
their  atomic  weights,  numbers  between  158-56  and  180*01;  with  an  average  of 
169-73 :  they  are  sesquioxide  of  iron,  sesquioxide  of  chromium,  arsenious  acid,  oxide 

1  On  the  specific  heat  of  simple  and  compound  bodies:  Annales  de  Chimie,  &c.,  t. 
p.  5,  and  3rd  se"r.  t.  i.  p.  129. 

2  M  representing  1  eq.  of  metal. 


124 


SPECIFIC    HEAT    OF    COMPOUNDS. 


of  antimony,  and  oxide  of  Bismuth,  represented  as  Bi203,  with  an  equivalent  of 
1003-6.  But  the  number  of  alumina  (A1203)  was  different,  being  in  the  form  of 
corundum  126-87,  and  the  saphire  139-61.  Two  corresponding  sulphureta  gave 
numbers  somewhat  higher  than  the  oxides,  namely,  sulphuret  of  antimony  186-21, 
and  sulphuret  of  bismuth  195-80,  of  which  the  mean  is  191-06. 

Two  oxides,  of  the  formula  M02,  namely,  binoxide  of  tin,  and  artificial  titanic 
acid,  gave  the  first  87'23,  and  the  second  8645.  The  bisulphuret  of  iron  (pyrites) 
gave  9645;  the  bisulphuret  of  tin  135-66;  the  sulphuret  of  molybdenum  12346; 
and  bisulphuret  of  arsenic  (AsS2)  174-51. 

Oxides,  of  the  form  M03,  gave  the  following  results:  tungstic  acid  118-38,  mo- 
lybdic  acid  118-96,  silicic  acid  11048,  boric  acid  103-52. 

The  subsulphuret  of  copper,  Cu2S,  gave  120-21;  and  the  sulphuret  of  silver, 
usually  represented  AgS,  gave  115-86. 

The  following  chlorides,  to  which  M.  Regnault  is  disposed  to  assign  the  common 
formula  M2C1,  gave  results  comprised  between  156-83  and  163-42,  with  a  mean  of 
158-64  —  chloride  of  sodium,  chloride  of  potassium,  chloride  of  silver,  subchloride 
of  copper,  and  sufcchloride  of  mercury.  The  corresponding  iodides  ranged  from 
162-30  to  169-38,  exclusive  of  the  iodide  of  silver,  which  was  180-45.  Of  corre- 
sponding bromides,  bromide  of  potassium  was  166-21,  bromide  of  silver  173-31,  and 
bromide  of  sodium  175-65. 

Protochlorides  of  the  formula  MCI,  namely,  chlorides  of  barium,  strontium,  cal- 
cium, magnesium,  lead,  mercury,  zinc,  and  tin,  were  comprised  between  114-72  and 
119-59;  with  a  mean  of  117-03.  The  protochloride  of  manganese  was  somewhat 
lower,  112-51. 

Of  volatile  bichlorides  (MC12),  bichloride  of  tin  gave  239-18,  and  chloride  of  tita- 
nium 227*63;  of  which  the  mean  is  233-40.  The  two  corresponding  chlorides  of 
arsenic  and  phosphorus,  MC13,  gave,  the  first  399-26,  and  the  second  359-86:  mean 
379-51. 

The  numbers  for  iodide  of  lead  and  iodide  of  mercury  (MI)  also  closely  approxi- 
mate, the  first  being  122-54,  and  the  second  119-36  :  mean  120-95.  The  fluoride 
of  calcium  (MF)  gave  105-31. 

The  principal  results  obtained  by  M.  Regnault  for  the  salts  are  thrown  together 
in  the  following  table.  The  equivalents  given  in  the  general  formula  are  those  of 
the  table  at  the  beginning  of  this  chapter. 


Name  of  the  salt. 

General 
formula, 
(M=l  eq.  of 
metal.) 

Product  of 
the  specific 
heats  by 
the  atomic 
weights. 

Mean. 

Nitrate  of  potassa  

MO-|-N06 

302-49 

Nitrate  of  soda  .  . 

297-13 

801-72 

Nitrate  of  silver  

u 

305-55 

« 

248-83 

Metaphosphate  of  lime  ... 

MO-{-P05 

248-64 

Chlorate  of  potassa  .  .. 

MO-j-C106 

321-04 

M04-AsOe 

317-30 

Pyrophosphate  of  potassa  

2MO-f-P06 

395-79 

^ 

Pyrophosphate  of  soda  

H 

382-22 

I  389-01 

Phosphate  of  lead 

u 

302-14 

Phosphate  of  lead..  

3MO-f-P05 

397-96 

Arseniate  of  lead  

3MO-f  As05 

409-37 

Sulphate  of  potassa  

MO-f-S08 

207-40 

> 

Sulphate  of  soda  

206-21 

v  206-80 

Sulphate  of  baryta                 . 

164-54 

Sulphate  of  strontia  

164-01 

Sulphate  of  lead 

165-39 

166-15 

Sulphate  of  lime  

168-49 

Sulphate  of  magnesia  

168-30 

VOLUMES    OF    ATOMS    IN    THE    GASEOUS    STATE. 


125 


Name  of  the  salt. 

General 
formula, 
(M=l  eq.  of 
metal.) 

Product  of 
the  specific 
heats  by 
the  atomic 
weights. 

Mean. 

M0  +  Cr03 

229-83 

Bichromate  of  potassa     .  .. 

MO-f  2Cr03 

358-67 

Biborate  of  potassa   

MO-j-2B08 

321-27 

. 

300-88 

V  311-07 

Biborate  of  lead              

M 

258-60 

Borate  of  potassa    

MO+BO, 

219-52 

^ 

212-60 

I  216-06 

« 

165-54 

Carbonate  of  potassa  

MO-fC02 

187-04 

. 

181-65 

I  184-35 

Carbonate  of  lime  (Iceland  spar)      

M0+C08 

131-61 

J 

Carbonate  of  lime  (arragonite)  

« 

131-56 

t< 

136-20 

« 

132-45 

Ditto  (white  chalk)  

« 

135-57 

f  134-40 

« 

135-99 

« 

133-58 

Carbonate  of  iron..., 

14 

138-16 

The  results  of  M.  Regnault  on  the  specific  heat  of  compound  bodies  are  of  great 
interest  with  regard  to  the  question  of  the  division  of  the  atomic  weights  of  certain 
elements,  to  which  reference  has  been  made.  They  establish  an  equally  close  rela- 
tion between  the  specific  heat  of  analogous  compounds  as  exists  among  elementary 
bodies.  The  general  law  is  announced  by  M.  Regnault  in  the  following  manner : — 
"In  all  compound  bodies,  of  the  same  atomic  composition  and  similar  chemical 
constitution,  the  specific  heats  are  in  the  inverse  proportion  of  the  atomic  weights." 
This  law  comprehends,  as  a  particular  case,  the  law  of  Dulong  and  Petit  for 
similar  bodies,  and  appears  to  be  verified  by  experiment  within  the  same  limits  as 
the  latter. 


RELATION   BETWEEN    THE   ATOMIC   WEIGHTS   AND   VOLUMES   OF   BODIES   IN   THE 

GASEOUS   STATE. 

Several  of  the  elementary  bodies  are  gases,  such  as  oxygen,  hydrogen,  nitrogen, 
and  chlorine,  and  the  proportions  in  which  they  combine  can  be  determined  by 
measure,  with  equal,  if  not  greater  facility  than  by  weight.  Now  a  relation  of  the 
simplest  nature  is  always  found  to  subsist  between  the  measures  or  volumes  in 
which  any  two  of  the  gaseous  elementary  bodies  unite.  This  arises  from  the  cir- 
cumstance that  the  specific  gravities  of  gases  either  correspond  exactly  with  their 
atomic  weights,  or  bear  a  simple  relation  to  them.  The  atom  of  chlorine  is  35$ 
times  heavier  than  that  of  hydrogen  j  and  chlorine  gas  is  also  35^  times  heavier 
than  hydrogen  gas,  so  that  the  combining  measures  of  these  two  gases,  which  corre- 
spond with  single  equivalents,  are  necessarily  equal.  The  atom  of  nitrogen,  and  its 
weight  as  a  gas,  being  both  14  times  greater  than  the  atom  and  weight  of  hydrogen 
gas,  their  combining  volumes  must  be  the  same. .  The  atom  of  oxygen  is  eight  times 
heavier  than  that  of  hydrogen,  but  oxygen  gas  is  16  times  heavier  than  hydrogen 
gas,  so  that  taken  in  equal  volumes  these  two  gases  are  in  the  proportion  by  weight  of 
two  equivalents  of  oxygen  to  one  of  hydrogen.  Hence,  in  the  combination  of  single 
equivalents  of  these  elements  to  form  water,  half  a  volume  or  measure  of  oxygen  gas 
unites  with  a  whole  volume  or  measure  of  hydrogen  gas.  One  volume  of  nitrogen 
also  unites  with  half  a  volume  of  oxygen,  and  with  a  whole  volume  of  the  same  gas, 
to  form  respectively  the  protoxide  and  deutoxide  of  nitrogen. 

The  exact  ratio  of  one  to  two  in  which  oxygen  and  hydrogen  gases  combine  bv 


126        VOLUMES   OF   ATOMS   IN   THE   GASEOUS   STATE. 


measure,  was  first  observed  by  Humboldt  and  Gay-Lussac  in  1805.  The  subject 
was  pursued  by  the  latter  chemist,  who  established  the  simple  ratios  in  which  gases 
generally  combine,  and  published  the  laws  observed  by  him,  or  his  Theory  of  Vo- 
lumes, shortly  after  the  announcement  of  the  Atomic  Theory  by  Dalton.  They 
afforded  new  and  independent  evidence  of  the  combination  of  bodies  in  definite  and 
also  in  multiple  proportions,  equally  convincing  as  the  observed  proportions  by 
weight  in  which  bodies  unite.  Gay-Lussac  likewise  observed  that  the  product  of  the 
union  of  two  gases,  if  itself  a  gas,  sometimes  retains  the  original  volume  of  its  con- 
stituents, no  contraction  or  change  of  volume  resulting  from  their  combination :  — 
thus  one  volume  of  nitrogen  and  one  volume  of  oxygen  form  two  volumes  of  deu- 
toxide  of  nitrogen ;  one  volume  of  chlorine  and  one  volume  of  hydrogen  form  two 
volumes  of  hydrochloric  acid  gas;  and  that  when  contraction  follows  combination, 
which  is  the  most  common  case,  the  volume  of  the  compound  gas  always  bears  a 
simple  ratio  to  the  volumes  of  its  elements.  Thus  two  volumes  of  hydrogen,  and 
one  of  oxygen,  form  two  volumes  of  steam  j  one  volume  of  nitrogen  and  three  of 
hydrogen  gas  form  two  volumes  of  ammoniacal  gas ;  one  volume  of  hydrogen  and 
one-sixth  of  a  volume  of  sulphur-vapour  form  one  volume  of  sulphuretted  hydro- 
gen gas.  In  these  and  all  other  statements  respecting  volumes,  the  gases  compared 
are  supposed  to  be  in  the  same  circumstances  as  to  pressure  and  temperature. 

The  uniformity  of  properties  observed  among  gases  in  compressibility  and  dilata- 
bility  by  heat,  has  appeared  to  many  chemists  to  indicate  a  similarity  of  constitution, 
and  to  favour  the  idea  that  they  all  contain  the  same  number  o"f  atoms  in  the  same 
volume.  May  not  equal  volumes  of  oxygen  and  hydrogen  gases,  for  instance,  be 
represented  by  an  equal  number  of  atoms  of  oxygen  and  hydrogen  respectively 
placed  at  equal  distances  from  each  other,  and  the  difference  of  sixteen  to  one  in  the 
densities  of  the  two  gases  arise  from  the  atom  of  oxygen  being  really  sixteen  times 
heavier  than  that  of  hydrogen  ?  Equal  volumes  of  gases  would  then  contain  an 
equal  number  of  atoms,  and  one,  two,  or  three  volumes  would  be  an  equivalent 
expression  to  one,  two,  or  three  atomic  proportions,  the  terms  volume  and  atom  be- 
coming of  the  same  import,  or  expressing  equal  quantities  of  bodies.  But  such  a 
view  is  obviously  inapplicable  to  compound  gases,  as  their  volume  has  a  variable 
relation  to  that  of  their  elements  j  and  its  adoption  would  require  grave  alterations 
to  be  made  in  the  atomic  weights  of  several  of  the  elements  themselves,  to  accom- 
modate those  weights  to  the  observed  densities  of  the  bodies  in  the  gaseous  state. 
This  will  be  seen  from  the  following  table,  in  which  the  volume  or  fractional  part 
of  a  volume  placed  against  each  element  always  contains  the  same  number  of  its 
presently  received  atoms.  These  volumes  are,  therefore,  the  equivalent  volumes  of 
the  elements,  and  may  be  viewed  as  representing  the  bulk  of  their  atoms  in  tho 
gaseous  state,  the  combining  measure  of  hydrogen  being  taken  as  two  volumes. 

ATOMS. 


Volume. 

Weight. 

2 

1 

2 

14 

Chlorine  

2 

35-5 

2 

98-26 

Iodine  

2 

126-36 

2 

100-07 

1 

8 

Phosphorus  . 

1 

32 

1 

75 

Sulohur... 

i 

16 

Of  the  first  six  bodies  enumerated,  equivalent  weights  occupy  each  two  volumes. 
It  was,  indeed,  the  observation  of  this  equality  between  the  atom  and  volume  in 


VOLUMES   OF   ATOMS   IN   THE   GASEOUS   STATE.        127 

these  gases,  that  led  to  the  supposition  of  that  relation  being  general.  But  the 
atoms  of  oxygen,  phosphorus,  and  arsenic,  occupy  only  one  volume,  and  would  re- 
quire to  be  doubled  to  fill  the  same  volume  as  the  preceding  class ;  or  the  latter 
rather  preserved  fixed,  and  the  former  class  divided  by  two.  The  present  atom  of 
sulphur  affords  only  one-third  of  a  volume  of  vapour,  and  must,  therefore,  be  multi- 
plied by  six  to  afford  two  volumes. 

It  will  be  found  conducive  to  perspicuity  to  apply  the  expression  combining  men- 
sure  to  the  volume  or  volumes  of  a  gas  which  enter  into  combination.  The  com- 
bining measure  of  oxygen  being  one  volume,  the  combining  measure  of  hydrogen 
and  its  class  will  be  two  volumes ;  or  the  atom  of  oxygen  gives  one,  and  the  atom 
of  hydrogen  two  volumes  of  gas.  Volumes  of  the  gases  may  be  represented  by 
equal  squares  with  their  relative  weights  inscribed,  the  numbers  having  reference  to 
the  number  assigned  to  the  oxygen  volume.  If  that  number  be  8,  or  the  atomic 
weight  of  oxygen,  as  in  column  1  of  the  table  which  follows,  then  the  number  to 
be  inscribed  in  each  of  the  two  volumes  forming  the  combining  measure  of  hydrogen 
will  be  0-5,  or  half  its  atomic  weight,  the  combining  measure  itself  having  the  full 
atomic  weight  of  hydrogen,  namely  1.  So,  of  other  gases,  the  combining  measure 
has  the  whole  atomic  weight,  which  is  divided  among  the  component  volumes.  But 
there  is  the  reason  for  preferring  the  number  1105 '6  to  8  for  the  standard  oxygen 
volume,  that  the  weight  of  a  volume  of  air  being  taken  as  1000,  that  of  an  equal 
volume  of  oxygen  is  1105-6;  and  consequently  the  corresponding  number  for  the 
volume  of  hydrogen,  69-3,  expresses  the  relation  in  weight  of  that  gas  also  to  air, 
and  so  do  the  corresponding  numbers  for  all  the  other  gases.  The  numbers  on  this 
scale,  which  express  the  relative  weights  of  a  volume  of  each  gas,  and  are  inscribed 
in  the  squares  of  column  2,  are  indeed  the  common  specific  gravities  of  the  gases. 

I.  II. 


AMMUQ  weigni.                        v 

/omumm 
measure. 

1 

V^OIllUI] 

Air  

1000 

. 

Oxygen                       1 

8 

1105-6 

Phosphorus               32 

32 

4422 

0-5 

69-3 

0.5 

69-3 

17-75 

2453 

17-75 

2453 

I 

The  dovDle  squares,  which  .represent  the  combining  measures  of  hydrogen  and 
chlorine,  arc  divided  into  volumes  by  dotted  lines,  to  show  that  the  division  is  ima- 


128       VOLUMES  OF   ATOMS  IN  THE   GASEOUS  STATE. 


ginary,  the  partition  of  a  combining  measure,  like  that  of  an  atom  which  it  repre- 
sents, being  impossible.  The  specific  gravities  of  gases  being  merely  the  relative 
weights  of  equal  volumes,  may  be  expressed  by  the  numbers  in  the  squares  of  the 
first  column;  and  the  specific  gravity  of  oxygen  being  accordingly  made  8,  the 
specific  gravity  of  any  other  gas  will  either  be  the  same  number  as  its  atomic  weight, 
or  an  aliquot  part  of  it.  Or  if  the  specific  gravity  of  oxygen  be  made  1  or  1000, 
the  relation  of  densities  to  atomic  weights  will  still  be  very  obvious.  (See  page  84). 

The  combining  measures  of  compound  gases,  although  variable,  have  still  a  con- 
stant and  simple  relation  to  each  other  —  such  as  1  to  1,  1  to  2,  or  2  to  3 ;  their 
elements  in  combining  suffering  either  no  condensation,  or  a  definite  and  very 
simple  change  of  volume.  Hence  the  density  of  a  compound  gas  may  often  be 
calculated  with  more  precision  from  the  densities  of  its  constituents,  and  a  knowledge 
of  the  change  of  volume,  if  any,  which  occurred  in  combination,  than  it  can  be 
determined  by  experiment. 

To  deduce  on  this  principle  the  specific  gravity  of  steam.  Water  consists  of  single 
equivalents  of  oxygen  and  hydrogen,  of  which  the  combining  measure  of  the  first 
is  one,  and  that  of  the  second  two  volumes.  These  three  volumes  weigh  1105-6  + 
69-3  -f  69-3  =  1244-2,  and  they  form  two  volumes  of  steam  ;  of  which  one  volume 
must,  therefore,  weigh  1244-2  divided  by  two,  or  622-1,  which  is,  consequently,  the 
calculated  specific  gravity  of  steam,  referred  to  that  of  air  as  1000.  The  relations  in 
volume  of  the  gases  before  and  after  combination  may  be  thus  exhibited : — 


Combining  measure,  or  one 
volume  of  oxygen. 


Combining  measure,  or  two 
volumes  of  hydrogen. 


Combining  measure,  or  two 
volumes  of  steam. 


69-3 

622-1 

69-3 

622-1 

1244-2 


1244-2 


It  thus  appears  necessary  to  inscribe  622-1  in  each  volume  of  steam,  to  make  up 
1244-2,  the  known  weight  of  the  two  volumes. 

In  the  formation  of  hydrochloric  acid  equal  measures  of  chlorine  and  hydrogen 
unite  without  condensation,  so  that  the  product  possesses  the  united  volumes  of  its 
constituent  gases. 


Comb 
of  hy 

ining  measure                         Combining  measure                           Combining  measure  of 
irogen,  or  two                          of  chlorine,  or  two                        hydrochloric  acid,  or  four 
volumes.                                            volumes.                                                volumes. 

69-3 

2453 

1261-1      1261-1 

69-3 

2453 

1261-1      1261-1 

5044-6 


6043-6 


The  specific  gravity  or  weight  of  a  single  volume  of  hydrochloric  acid  is,  therefore, 
obtained  by  dividing  5044-6  by  4,  and  is  1261-1. 

The  specific  gravity  of  the  vapour  of  an  elementary  body  which  there  are  no 
means  of  apcertoining  experimentally,  may  sometimes  be  calculated  from  the  known 
density  of  ?  gaseous  compound  containing  it.  The  density  of  carbon  vapour  may  be 


VOLUMES    OF    ATOMS    IN    THE    GASEOUS    STATE.       129 


thus  deduced  from  the  observed  density  of  carbonic  oxide  gas.  Assuming  that  the 
combining  measure  of  carbon  is  double  that  of  oxygen,  as  is  true  of  hydrogen  and 
several  other  elementary  bodies,  then  carbonic  oxide,  which  like  water  consists  of 
single  equivalents  of  its  constituents,  will  resemble  steam  in  its  constitution  also, 
and  be  composed  of  one  volume  of  oxygen  gas,  and  two  volumes  of  carbon  vapour 
condensed  into  two  volumes.  The  weight  of  a  single  volume  of  carbonic  oxide 
being  972'7,  two  volumes  (19454)  may  be  resolved,  as  shown  in  the  diagram 
below,  into  one  volume  of  oxygen,  1105-6,  and  two  volumes  of  carbon-vapour, 
839-8,  (1945-4  — 1105-6  =  839-8)  each  of  which  it  follows  must  weigh  419-9, 
or  420. 


Combining  measure,  or 

two  volumes  of  carbonic 

oxide. 


Combining  measure,  or 
one  volume  of  oxygen. 


Combining  measure,  or 

two  volumes  of  carbon 

vapour. 


972-7 


972-7 


1105-6 


419.9 


419-9 


1945-4 


1945-4 


But  the  density  420  thus  assigned  to  carbon  vapour  will  only  be  true  if  it  corre- 
sponds with  hydrogen  in  its  combining  measure;  but  the  combining  measure  of 
carbon  vapour  may  as  well  be  one-half  that  of  hydrogen,  like  that  of  phosphorus,  or 
one-sixth, -like  that  of  sulphur,  and  then  the  density  will  be  double  or  six  times  that 
supposed.  The  important  conclusion,  however,  that  the  density  of  carbon  vapour  is 
either  420,  or  some  multiple  or  sub-multiple  of  that  number,  is  quite  certain. 

The  following  Table  comprises  nearly  all  the  accurate  information  which  chemists 
at  present  possess  respecting  the  specific  gravities  of  gaseous  bodies.  The  bodies 
placed  first  in  the  table  are  generally  considered  as  belonging  to  the  inorganic,  and 
those  in  the  latter  part  to  the  organic  department  of  the  science.  They  are  all 
experimental  results,  with  the  exception  of  two  or  three  cases  which  are  calculated. 
The  specific  gravity  of  carbon-vapour  is  assumed  here  as  six-sixteenths  of  that  of 
oxygen  (1105-6). 


130      SPECIFIC    GRAVITIES    OF    GASES    AND    VAPOURS. 


TABLE  OF  SPECIFIC  GRAVITY  OF  GASES  AND  VAPOURS. 


Names  of  etabstances. 

Proportion  of  an  eq. 
in  1  volume. 

SPECIFIC  GRAVITY. 

Ob- 
servers. 

Air=l. 

Oxyg.=l.  H.=l. 

3S 
0 
P 

As 
H 

6617 
1105-63 
4355 
10600 
69-26 
414-61 
971-37 
2421-6 
5540 
8716 
6976 
622 
971-2 
1520.4 
1524-5 
3399 
2644-7 
1191-2 

5983-9 
1000 
3938-3 
9586-6 
62-6 
875 
878-5 
2189-9 
5009-7 
7882 
6308-5 
562-6 
875 
1375 
1378-6 
3564.8 
2391-6 
1077-3 

96 
16 
64 
150 
1 
6 
14 
35-5 
78 
126 
100-07 
9 
14 
22 
22 
49-5 
38 
17 

D. 
R. 
D. 
M. 
R. 
Calcul. 
R. 
G-L. 
M. 
D. 
D. 
R. 
Calc. 
C. 
B.  D. 

G-L. 
G.  T. 

Carbon  (hypothetical)  

2 

C 

2 
N 
2 
Cl 

T 

Br 

Nitrogen  

Bromine                                  • 

2 
I 

2 
Hg 

Mercury        •       ......     . 

Water  

2 
HO 

a 

CO 

Carbonic  oxide    • 

Protoxide  of  nitrogen  «... 

2 
NO 

Carbonic  acid                      . 

2 
C0a 

Chlof  ocarbonic  acid 

2 
COC1 

Sulphide  of  carbon  

2 

csa 

2 

HS 

T 

Hydrosulphuric  acid...  

SPECIFIC   GRAVITY   OF  GASES  AND  VAPOURS.         131 


Names  of  substances. 

Proportion  of  an  eq. 
in  1  volume. 

SPECIFIC  GRAVITY. 

\ 

Ob- 
servers. 

Air=l. 

Oxyg.=l. 

H.=l. 

CIO 
2 

NC2 
~2~ 
S02 
~2~ 
S03 
2 
S02C1 
~~2~~ 
SC12 
~2~ 

AsOg 

HO,  S03 

2998-4 
1806-4 
2193 
3000 
4665 
3685 
13850 
1680 
9800 
12160 
15630 
9199-7 
6876 
5510 
3680 
3600 
5939 
1247-4 

2693-4 
1633-7 
1983-1 
2713 
4219 
3332-7 
12526 
1519 
8862-3 
10996-6 
14134-6 
8389-4 
6181-9 
4982-9 
3329 
3255-5 
6370-7 
1128 

43-5 

26 
32 
40 
67-5 
51-5 
198 
24-5 
135-5 
178 
226 

77-3 

52-375 

18-25 

G-L. 
H-D 
M. 
R. 
D. 
M. 
B. 
M. 
M. 
M. 
D. 
D. 
M. 
C'. 
D. 
D. 
B.  A. 

Sulphurous  acid           •     ..   . 

Sulphuric  acid  (anhydrous).. 

Sulphate  of  water  at  848°  ... 

2 
HgCl 
2 
HgBr 

Bromide  of  mercury  

2 
Hgl 

2 
SnCl2 

Bichloride  of  tin  

2 

TiCl2 
~T~ 
HgS 
8 
PC15 
~8~ 
SiFl3 
3 
SiCl3 
3 
HC1 
~T 

Sulphuret  of  mercury  

Penta-chloride  of  phosphorus 
Fluoride  of  silicium  

Chloride  of  silicium  

Hydrochloric  acid  

132       SPECIFIC    GRAVITY    OF    GASES    AND    VAPOURS. 


Names  of  Substances. 

Proportion  of  an  eq. 
in  1  volume. 

SPECIFIC  GRAVITY. 

Ob- 
servers. 

Air  =  l. 

Oxy.=l. 

H.=l. 

HBr 

2731 
4443 
947-6 
2111 
1038-8 
1720 
596-7 
1214 
2695 
4875 
6300-6 
11160 
16100 
8350 
10140 
2312-4 
3942 
559-6 

2469-7 
4017-8 
856-9 
1908-9 
939-3 
1555-4 
539-6 
1097-8 
2437 
4408-5 
5697-7 
10092-1 
14560 
7551 
9170 
2091-2 
3564-8 
506-1 

39-5 
63-5 
13-5 
30-75 
15 
23 
8-5 
17-25 
39 
69-75 
91-5 

226-5 
136 
180 

8 

G-L 

Hydriodic  acid               ••  •  •• 

4 
HI 

T 

HCy 
~4~ 
CyCl 

Hydrocyanic  acid 

G-L. 
G-L. 
B'. 
C. 
B.  &A. 
D. 
D. 
D. 
D. 
J. 
M. 
M. 
M. 
J-D. 
D. 

Chloride  of  cyanogen 

Deutoxide  of  nitrogen  

4 
N02 
~4~ 
N04 

Peroxide  of  nitrogen  

Ammonia  

4 
NH3 
4 

ra, 

4 
AsH3 

Phosphuretted  hydrogen  .... 

Terchloride  of  phosphorus... 
Terchloride  of  arsenic  
Chloride  of  bismuth  

4 
PC13 
4 
AsCl3 
4 
BiCl 

Iodide  of  arsenic  

4 
Asl, 
4 
Hg2Cl 
4 
Hg2Br 

Subchloride  of  mercury  
Subbromide  of  mercury  
Fluoride  of  boron  

4 
BF, 
4 
BC13 
~4~ 
C2H4 

Carburetted  hydrogen  

4 

SPECIFIC  GRAVITY  OF  GASES  AND  VAPOURS.         133 


% 

Names  of  substances. 

Proportion  of  an  eq. 

SPECIFIC  GRAVITY. 

Ob- 
servers. 

in  1  volume. 

Air  =  1. 

Oxyg.=l. 

H.=l. 

Methylene  (?)  

C2H2 
4 
C4H4 
4 
C8H8 
4 
C32H32 
4 
Ci2H,2 

490 
985-2 
1892 
8007 
2875 
4071 
6061 
4528 
6741 
2770 
4765 
4891 
3230 
4242 
7110 
9476 
3965 
2805 

443 
891 
1711 
7240-8 
2600-8 
3681-5 
4576-6 
(  4072 
6096 
2505 
4309 
4422-8 
2921 
3836 
6429-7 
8569-3 
3582 
2836-5 

7 
14 
28 
112 
42 
63 
70 
64 
96 
39 
68 
68 
46 
60 
104 
136 
57 
40 

T.  S. 
F. 
D.  P. 
F". 
F. 
C". 
D. 
D. 
M. 
D. 
C". 
P.  W. 
P.  W. 
P.  W. 
R. 

it 

C". 

Olefiant  ffas           

Ole*ene  

Eloeene          

4 
C18H18 
4 

€20^20 

4 

C2oH8 
4 

C3oH,2 

4 
Ci2H6 
4 

C2QH.6 

~T~ 

C2oHi8 

~~T~ 

C,4H8 

Benzene  (benzole)  

Citrene  

Retinaphtha  

Retinile  

4 
C18H12 
4 
C32H16 
4 
Ci0H8 

C8H9 

2 

Ci2H8 

Sweet  oil  of  wine  

Volatile  sweet  oil  of  ether  ... 
Mesitylene  

4 

134       SPECIFIC    GRAVITY   OF    GASES    AND    VAPOURS. 


Names  of  Substances. 

Proportion  of  an  eq. 
in  1  volume. 

SPECIFIC  GRAVITY. 

Ob- 
servers. 

Air  =  l. 

Oxy.  =  l. 

H.=l. 

Wood-spirit       

C2H402 
4 
C2H30 
2 
C2H2C10 
:     2 
C2HC120 
6 
C2C130 
3 

C^HA 
4 
C2H3S 

C2C14 

1120 
1617 
3903 
2115 
4670 
1610 
6367 
5330 
5820 
8157 
1731 
3012 
1186 
4883 
4565 
2653 
2084 
5563 

1012-8 
1462-3 
3529-5 
1912-6 
4223-2 
1456 
5557-8 
4820 
5263-1 
7376-5 
1565-4 
2724 
1072-5 
4415-8 
4128-1 
2399-6 
1884-5 
2317-7 

16 
23 
57-5 
30-66 
62-75 
23 
94 
77 
83 
118-5 
25-25 
42-6 
16-5 
70-5 
63 
38-5 
30 
37 

D.  P. 
Id. 
R. 
R. 
Id. 
B. 
Id. 
R. 
Id. 
Id. 
D.  P. 
R. 
D.  P. 
Id. 
Id. 
Id. 
Id. 
Id. 

Methylic   ether   (monochlo- 

Methylic    ether    (bichlorin- 
ated)  

Methylic  ether  (perchlorin- 
ated)    

Formic  acid  at321°-8  F  
Sulphide  of  methyl  

Chloride  of  carbon  (another) 
Chloride  of  carbon  (another) 
Chloride  of  methyl  ........... 

4 
C4C14 
4 
C4C16 
4 
C2H3C1 
4 
C2H2C12 
~~~ 
C.H.F 
4 
C2H3I 

Chloride  of  methyl  (mono- 
chlorinated)  .  

Sulphate  of  methyl  

4 
C2H30,  S03 

Nitrate  of  methyl  

2 
C2H30,  N05 

Formiate  of  methyl  

2 
C2H30,  C2H03 

Acetate  of  methyl  

4 
C2H30,  C4H303 

4 

SPECIFIC  GRAVITY  OF  GASES  AND  VAPOURS.         135 


Names  of  substances. 

Proportion  of  an  eq. 
in  1  volume. 

SPECIFIC  GRAVITY. 

Ob- 
servers. 

Air  ==  1. 

0Xyg.=l. 

H.=l. 

i 

\fpthvlil 

C6H804 

2625 
1613 
2326 
2586 
3100 
2299 
3478 
4530 
5799 
6975 
5475 
2626 
3829 
4780 
5087 
7210 
5140 
3067 

2374 
1458-7 
2103-4 
2338-5 
2803-4 
2006-6 
3145-2 
4096-5 
5244-1 
6307-6 
4951-2 
2374-7 
3462-6 
4323 
4600-3 
6521 
4649 
2773-5 

38 
23 
31 
37 
45 
42-25 
49-5 
66-75 
84 
101-25 
77-5 
37-5 
54-25 
69 
73 
104 
72 
44 

M'. 
G-L. 
B. 
G-L. 
R. 
T. 
R. 
R. 
Id. 
Id. 
G-L. 
D.B'. 
D. 
E.  &B. 
D.B'. 
E. 
E.  &B. 
Id. 

[  Alcohol                      

4 

C4H602 

4 

C4H6S2 

Ether        

4 
C4H50 

Sulphuret  of  ethyl  

2 

C^HsS 
2 
C4H5C1 

Chloride  of  ethyl  

Chloride  of  ethyl  (monochlo- 

4 
C4H4C12 

4 

C4H3C13 
4 
C4H2C14 

Chloride  of  ethyl  (bichlori- 
nated)        

Chloride  of  ethyl  (trichlori- 

4 
C4HC15 
4 
C4H5I 
4 
C4H50,  N03 

Chloride   of  ethyl   (quadri- 
chlorinated)  

Nitrous  ether  

Chlorocarbonic  ether  

4 
C4H50,  C203C1 

Sulphurous  ether  

4 

C4H50,  S02 

Oxalic  ether  

2 
C4H50,  C203 

Silicic  ether  (tribasic)  
Boric  ether  (tribasic)  

2 
3C4H50,  Si03 

3 
3C4H50,  B03 

Acetic  ether  

4 
C4H50,  C4H303 

4 

136       SPECIFIC    GKAYITT    OF    GASES    AND    VAPOURS. 


Names  of  Substances. 

Proportion  of  an  eq. 
in  1  volume. 

SPECIFIC  GRAVITY. 

Ob- 
servers. 

Air=l. 

Oxy.=l. 

H.=l. 

C4H50,  C14H502 

5409 
6220 
4859 
10508 
3443 
6485 
5130 
4199 
1532 
7184 
2080 
5300 
2019 
4270 
4276 
6400 
5468 
3096 

4899 
5624-8 
4394-1 
9502-5 
3113-5 
5864-5 
4639-1 
3797-2 
1385-4 
6496-6 
1879-8 
4792-9 
1825-8 
3861-4 
3867-1 
5787-6 
4945-7 
2800 

71 
87 
70 
150 
49-5 
94 
73-75 
65-78 
22 
105 
30 
81-75 
29 
61 
61 
86 
76 
44-5 

Id. 
A. 
M. 
L.  &P. 
G-L.  D. 
R. 
D. 
D. 
L. 
B. 
C". 
D. 
Id. 
D.  M. 
P. 
D. 
Id. 
Id. 

4 
C4H50,  C4H303 

2 
C4H50,  C10H305 

4 
C4H50,  C14H1302 

2 
C4H3C1,  HC1 

Bromide  of  olefiant  gas  
Chloral                  

4 
C4H3Br,  HBr 

4' 
C4HC1302 

4 
C4HC13 
4 
C4H402 
4 
C4H6As 
2 
C4H404 
4 
C4HC1304 

Aldehyde  

Acetic  acid  at  482°  F  

4 
<W^ 
4 
C14H604 

Hydride  of  salicyl  

4 
C14H604 
~4 

^20H12^5 

4 

^20H16^2 

~4~ 
C6NH704 

Eugenic  acid  ••• 

Urethane  

4 

VOLUMES  OF  ATOMS   IN   THE   GASEOUS   STATE.        137 

After  the  name  of  each  substance  in  the  preceding  table  is  given  the  formula  of 
its  equivalent,  which  is  divided  by  the  number  of  volumes  of  vapour  which  the 
equivalent  gives  and  the  combining  measure  contains.  The  equivalent  thus  divided 
therefore  expresses  the  composition  of  a  single  volume  of  the  vapour.  The  first 
column  of  numbers  contains  the  specific  gravities  referred  to  air  as  1000;  the  second, 
in  which  the  specific  gravities  are  expressed  with  reference  to  that  of  oxygen  as 
1000,  is  obtained  by  dividing  the  former  specific  gravities  by  1105-6,  the  specific 
gravity  of  oxygen  gas.  In  the  third  column,  the  specific  gravities  are  referred  to 
hydrogen  as  1 ;  and  consequently  the  number  for  any  vapour  expresses  how  many 
times  that  vapour  is  heavier  than  hydrogen.  The  numbers  of  this  column  only  are 
obtained  by  calculation  from  the  equivalents,  and  are  therefore  the  theoretical  densi- 
ties :  if  divided  by  16  they  give  corresponding  theoretical  densities  on  the  scale  of 
oxygen  equal  to  1 ;  or  if  divided  by  14416  (the  number  of  times  which  air  is 
heavier  than  hydrogen)  they  give  the  theoretical  densities  on  the  scale  of  air  equal 
to  1.  The  letter  or  letters  in  the  last  column  refer  to  the  name  of  the  observer  on 
whose  authority  the  experimental  specific  gravities  of  the  first  and  second  columns 
of  numbers  are  given.1 

An  extraordinary  variation  in  the  specific  gravity  of  acetic  acid  at  different  tem- 
peratures was  observed  by  M.  Dumas,  which  is  confirmed  by  M.  Cahours  and  M. 
Bineau,  (Annales  de  Chiraie,  &o.  3e  ser.  t.  xviii.  p.  226),  and  the  anomaly  found  to 
extend  to  certain  acids  allied  to  the  acetic ;  namely  formic,  butyric,  and  valerianic 
acids.  Thus  the  vapour  of  acetic  acid  (H  0,  C4  H3  03),  has  a  specific  gravity  of 
3200  at  125°  Centig.,  2480  at  160°  C.,  2220  at  200°,  2090  at  230°,  2080  at  250°, 
and  retains  the  last  specific  gravity,  which  corresponds  with  the  theoretical  density 
of  four  volumes  from  one  equivalent,  at  higher  temperatures ;  the  observation  being 
made  up  to  338°  C.  This  vapour  has,  indeed,  been  observed  with  a  density  so  great 
as  3950,  under  reduced  pressure,  and  at  a  low  temperature,  namely  69°  Fahr.  The 
variation  is  probably  accounted  for  by  considering  the  acid  to  be  bibasic  at  low  tem- 
peratures, with  a  double  equivalent  and  double  density,  and  to  assume  progressively 
the  molecular  form  and  single  density  of  the  monobasic  acid,  as  the  temperature 
rises.  The  acid  undergoes  no  permanent  or  constitutional  alteration  at  the  highest 
of  the  temperatures  specified,  but  condenses  again  in  possession  of  all  its  usual  pro- 
perties. 

Butyric  acid  has  a  density  of  3680  at  177°  C.,  which  falls  to  3070  at  261°  C., 
and  remains  the  same  at  330°  C.  Valerianic  acid  gave  similar  results,  but  the 
variation  was  less  excessive  (Cahours). 

Formic  acid  vapour  was  observed  by  M.  Bineau  with  a  specific  gravity  as  high  as 
3230,  under  a  pressure  of  about  one-fiftieth  of  an  atmosphere,  and  at  the  tempera- 
ture of  51°  F.,  while  it  rarefied  to  1610  at  416°  Fahr.,  under  the  usual  atmospheric 
pressure.  The  two  sorts  of  molecular  groups  of  this  acid  correspond  respectively 
with  the  specific  gravities,  1590  and  3180;  in  the  first  case  the  ordinary  equivalent 
(C2  H  03-f  H  0)  gives  four,  and  in  the  second  two  equivalents  of  vapour. 

The  acetic  and  other  acids  of  this  class  were  formerly  supposed  to  give  three  vo- 
lumes of  vapour,  but  it  is  doubted  whether  the  proportions  of  three  and  six  volumes 
exist  at  all,  or  that  the  vaporous  molecule  of  compound  bodies  is  ever  divisible 
except  by  2,  4,  or  8.  Three  compounds  of  silicium  form  exceptions  to  this  rule— 
the  chloride  Si  C13,  and  the  corresponding  fluoride  and  ether,  which  give  three  vo- 
lumes. From  this  circumstance,  and  the  analogy  which  subsists  between  silicic 
acid,  and  the  titanic  acid  and  binoxide  of  tin,  it  has  been  proposed  to  diminish  the 

1  A  signifies  Felix  d'Arcet ;  B,  Bunsen ;  B',  Berard ;  BA,  Biot  and  Arago  ;  BD,  Berzelius 
andDulong;  C,  Colin;  C',  Cruikshanks;  C",  Cahours;  D,  Dumas;  DB,  Dumas  and  Bous- 
singault;  DB',  Dumas  and  P.  Boullay;  DP,  Dumas  and  Peligot;  E,  Ebehnen;  E  and  B, 
Ebelmen  and  Bouquet;  F',  Fremy;  G-L,  Gay-Lussac;  GT,  Gay-Lussac  and  Thenard;  L, 
Liebig ;  LP,  Liebig  and  Pelouze ;  M,  Mitscherlich ;  M',  Malaguti ;  P,  Piria ;  PW,  Peletier 
and  Walter ;  R,  Regnault ;  TS,  Theodore  de  Saussure.  The  table  itself  is  that  given  by  M 
Baudrimont  in  his  excellent  Traite"  de  Chimie,  somewhat  modified  and  extended. 


138         VOLUMES  OF   ATOMS   IN   THE   GASEOUS  STATE. 

equivalent  of  silicium  one-third,  representing  silicic  acid  by  Si  02 ;  and,  in  cou  se- 
quence, the  chloride  and  fluoride  of  silicium  and  silicic  ether  would  possess,  in  the 
state  of  vapour,  a  molecule  divisible  by  2.  Two  chlorinated  compounds  of  methyl 
and  the  sulphuret  of  mercury  are  the  only  other  substances  of  which  the  equivalents 
are  divided  in  the  table  by  6  or  3. 

The  specific  gravity  of  the  vapour  of  oil  of  vitriol  H  0,  S  03,  was  found  to  vary 
from  2500  at  630°  Fahr.,  to  1680  at  928°  Fahr.  This  substance  should  have  a 
density  of  1640  on  the  hypothesis  of  the  union  of  the  anhydrous  acid  and  water 
without  condensation ;  a  number  which  corresponds  sufficiently  well  with  observa- 
tions of  the  density  made  at  temperatures  above  750°  Fahr.  But  the  vapours  of 
the  acids  are  not  the  only  bodies  which  present  such  anomalies ;  the  oils  of  aniseed 
and  fennel,  which  are  perfectly  neutral,  offer  similar  results.  Thus  the  vapour  of 
the  oil  of  aniseed  varies  in  specific  gravity  from  5980  at  473°  Fahr.  to  5190  at  640° 
Fahr.;  its  theoretical  density  being  5180.  The  greater  part,  however,  of  the  com- 
pound ethers,  and  a  large  number  of  the  volatile  oils,  particularly  the  pure  hydro- 
carbon oils,  furnish,  at  from  60  to  80  degrees  above  the  boiling  point,  numbers 
which  accord  closely  with  theory. 

The  specific  gravity  of  the  pentachloride  of  phosphorus,  taken  by  M.  Mitscherlich 
at  335°  Fahr.,  is  represented  by  4850,  which  led  to  the  conclusion  that  the  molecule 
of  this  compound  gives  six  volumes  of  vapour.  But  M.  Cahours  finds  that  the 
density  of  this  vapour  varies  with  the  temperature,  from  4990  at  374°  to  3656  at 
621° :  about  554°  the  density  is  3680,  which  corresponds  with  eight  volumes  of 
vapour. 

From  these  tables,  it  appears  that  a  simple  relation  always  subsists  between  the 
combining  measures  of  different  bodies  in  the  gaseous  state : 

That  the  combining  measure  of  a  few  bodies  is  the  same  as  that  of  oxygen,  or 
one  volume ;  of  a  large  number,  double  that  of  oxygen,  or  two  volumes ;  and  of  a 
still  larger  number,  four  times  that  of  oxygen,  or  four  volumes ;  while  combining 
measures  of  other  numbers  of  volumes,  such  as  three  and  six,  or  of  fractional  por- 
tions of  one  volume,  such  as  one-third,  are  comparatively  rare : 

That  the  specific  gravity  of  a  gas  may  be  calculated  from  its  atomic  weight,  or  the 
atomic  weight  from  the  specific  gravity,  as  they  are  necessarily  related  to  each  other. 
Thus,  to  find  the  specific  gravity  of  a  vapour  like  that  of  phosphorus,  of  which  the 
combining  measure  is  one  volume,  or  the  same  as  that  of  oxygen.  The  specific 
gravities  of  two  bodies,  of  which  the  volumes  of  the  atoms  are  the  same,  must  ob- 
viously be  as  the  weights  of  these  atoms.  Hence,  8  and  32  being  the  atomic  weights 
of  oxygen  and  phosphorus,  and  1105-6,  the  known  specific  gravity  of  oxygen,  the 
specific  gravity  of  phosphorus  vapour  is  obtained  by  the  following  proportion — 

8  :  32  : :  1105-6  : 4422 
=  sp.  gr.  of  phosphorus  vapour. 

Secondly,  to  find  the  specific  gravity  of  a  vapour  like  that  of  fluorine,  of  which 
the  combining  measure  is  assumed  to  be  two  volumes,  or  double  that  of  oxygen. 
The  atomic  weight  of  fluorine  18-70, 

8  :  18-70  ::  1105-6:  2584-34  = 

twice  the  specific  gravity  of  fluorine,  being  the  weight  of  two  volumes,  and  the 
specific  gravity  required  is  1292-17. 

These  cases  are  examples  of  a  general  rule,  that  the  specific  gravity  of  a  body  in 
the  state  of  vapour  is  obtained  by  multiplying  the  atomic  weight  of  the  body  by 
1105-6,  the  specific  gravity  of  oxygen,  and  dividing  by  8.  '  The  number  thus  found 
must  then  be  divided  by  the  number  of  volumes  which  are  known  to  compose  the 
combining  measure  of  vapour. 

The  specific  gravities  thus  calculated  are  generally  more  accurate  than  those  ob- 
tained by  direct  experiment,  from  the  circumstance  that  the  operation  of  taking  the 
specific  gravity  of  a  gas  is  generally  less  susceptible  of  precision,  than  the  chemical 
analyses  on  which  the  atomic  weights  are  founded.  The  densities  of  vapours,  taken 


ISOMORPHISM.  139 

only  a  few  degrees  above  their  condensing  points,  are  generally  a  little  greater  than 
the  truth,  owing  to  a  peculiarity  in  their  physical  constitution  which  was  formerly 
explained  (page  81).  Of  such  bodies,  therefore,  the  theoretical  is  a  necessary  check 
upon  the  experimental  density. 

SECTION   IV. — RELATION   BETWEEN    THE   CRYSTALLINE   FORM   AND   ATOMIC 
CONSTITUTION   OF   BODIES  —  ISOMORPHISM. 

Bodies  on  passing  from  the  gaseous  or  liquid  to  the  solid  state  generally  present 
themselves  in  crystals,  or  regular  geometrical  figures,  which  are  the  larger  and  more 
distinct  the  more  slowly  and  gradually  they  are  produced.  Their  formation  is  readily 
observed  in  the  spontaneous  evaporation  of  a  solution  of  sea-salt,  or  in  the  slow 
cooling  of  a  hot  and  saturated  solution  of  alum,  which  salts  assume  the  forms  of  the 
cube  and  regular  octohedron.  The  crystalline  form  of  a  body  is  constant,  or  subject 
only  to  certain  geometrical  modifications  which  can  be  calculated,  and  is  most  ser- 
viceable as  a  physical  character  for  distinguishing  salts  and  minerals.  Between 
bodies  of  similar  atomic  constitution,  a  relation  in  form  has  been  observed  of  great 
interest  and  beauty,  which  now  forms  a  fundamental  doctrine  of  physical  science, 
like  the  subjects  of  atomic  weights  and  volumes  just  considered. 

Gay-Lussac  first  made  the  remark  that  a  crystal  of  potash-alum  transferred  to  a 
solution  of  ammonia-alum  continued  to  increase  without  its  form  being  modified, 
and  might  thus  be  covered  with  alternate  layers  of  the  two  alums,  preserving  its 
regularity  and  proper  crystalline  figure.  M.  Beudant  afterwards  observed  that  other 
bodies,  such  as  the  sulphates  of  iron  and  copper,  might  present  themselves  in  crystals 
of  the  same  form  and  angles,  although  the  form  was  not  a  simple  one  like  that  of 
alum.  But  M.  Mitscherlich  first  recognised  this  correspondence  in  a  sufficient  num- 
ber of  cases  to  prove  that  it  was  a  general  consequence  of  similarity  of  composition 
in  different  bodies.  To  the  relation  in  form  he  applied  the  term  isomorphism, 
(from  iao$}  equal,  and  i"°p<H,  shape),  and  distinguished  bodies  which  assume  the 
same  figure  as  isomorphous,  or  (in  the  same  sense)  as  similiform  bodies.  The  law 
at  which  he  arrived  is  as  follows  : — "  The  same  number  of  atoms  combined  in  the 
same  way  produce  the  same  crystalline  form ;  and  crystalline  form  is  independent 
of  the  chemical  nature  of  the  atoms,  and  determined  only  by  their  number  and  re- 
lative position/' 

This  law  has  not  been  established  in  all  its  generality,  but  perhaps  no  fact  is  cer- 
tainly known  which  is  inconsistent  with  it,  while  an  indisposition  which  certain 
classes  of  elements  have  to  form  compounds  at  all  similar  in  composition  to  those 
formed  by  other  classes,  limits  the  cases  for  comparison,  and  makes  it  impossible  to 
trace  the  law,  throughout  the  whole  range  of  the  elements,  in  the  present  state  of 
our  knowledge  respecting  them. 

The  relation  of  isomorphism  is  most  frequently  observed  between  salts,  from 
their  superior  aptitude  to  form  good  crystals.  Thus  the  arseniate  and  phosphate  of 
soda  are  obtained  in  the  same  form,  and  are  exactly  alike  in  composition,  each  salt 
containing  one  proportion  of  acid,  two  of  soda,  and  one  of  water  as  bases,  together 
with  twenty-four  atoms  of  water  of  crystallization.  With  a  different  proportion  of 
water  of  crystallization,  namely,  with  fourteen  atoms,  and  the  other  constituents 
unchanged,  the  crystalline  form  is  totally  different,  but  is  again  the  same  in  both 
salts.  For  every  arseniate,  there  is  a  phosphate  corresponding  in  composition,  and 
identical  in  form ;  the  isomorphism  of  these  two  classes  of  salts  is  indeed  perfect. 
The  arsenic  and  phosphoric  acids  contain  each  five  proportions  of  oxygen  to  one  of 
arsenic  and  phosphorus  respectively,  and  are  supposed  to  be  themselves  isomorphous, 
although  the  fact  cannot  be  demonstrated,  as  the  acids  do  not  crystallize.  The 
elements,  phosphorus  and  arsenic,  are  also  known  to  be  isomorphous:  and  the 
isomorphism  of  their  acids  and  salts  is  referred  to  the  isomorphism  of  the  elements 
themselves  j  isomorphous  compounds  in  general  appearing  to  arise  from  isomorphous 
elements  uniting  in  the  same  manner  with  the  same  substance. 


140  ISOMORPHISM. 

The  isomorphism  of  the  sulphate,  seleniate,  chromate,  and  manganate  of  the 
same  base  is  likewise  clear  and  easily  observed ;  each  of  the  acids  in  these  cases 
containing  three  proportions  of  oxygen  to  one  of  selenium,  sulphur,  chromium,  and 
manganese,  themselves  presumed  to  be  isomorphous. 

Of  bases,  the  isomorphism  of  the  class  consisting  of  magnesia,  oxide  of  zinc, 
oxide  of  cadmium,  and  the  protoxides  of  nickel,  iron  and  cobalt,  is  well  marked  in 
the  salts  which  they  form  with  a  common  acid,  and  is  particularly  observable  in  the 
double  salts  of  these  oxides,  such  as  the  sulphate  of  magnesia  and  potassa,  sulphate 
of  zinc  and  potassa,  sulphate  of  copper  and  potassa,  which  have  all -six  atoms  of 
water  and  a  common  form.  The  sulphates  themselves  of  these  bases  differ,  most 
of  them  affecting  seven  atoms  of  water  of  crystallization,  while  the  sulphate  of 
copper  affects  five ;  but  those  with  the  seven  may  likewise  be  crystallized  in  favour- 
able circumstances  with  five  atoms  of  water,  and  then  assume  the  form  of  the  copper 
salt,  thus  exhibiting  a  second  isomorphism  like  the  arseniate  and  phosphate  of  soda. 

The  sesquioxides  of  the  same  class  of  metals  with  alumina  and  the  sesquioxide 
of  chromium,  which  consist  of  two  atoms  of  metal  and  three  of  oxygen,  also  afford 
an  instructive  example  of  isomorphism,  particularly  in  their  double  salts.  The 
sulphate  of  the  sesquioxide  of  iron  with  sulphate  of  potassa  and  twenty-four  atoms 
of  water,  forms  a  double  salt  having  the  octohedral  form  of  sulphate  of  alumina  and 
potassa,  or  common  alum,  the  same  astringent  taste,  with  other  physical  and  chemical 
properties  so  similar,  that  the  two  salts  can  with  difficulty  be  distinguished  from 
each  other.  The  salt  is  called  iron  alum,  and  there  are  corresponding  manganese 
and  chrome  alums,  neither  of  which  contains  alumina,  but  the  sesquioxide  of  man- 
ganese and  sesquioxide  of  chromium  in  its  place,  with  the  proportions  of  acid  and 
water  which  exist  in  common  alum.  In  all  these  salts  another  substitution  may 
occur  without  change  of  form;  namely,  that  of  soda  or  oxide  of  ammonium  for  the 
potassa  in  the  sulphate  of  potassa,  giving  rise  to  the  formation  of  what  are  called 
soda  and  ammonia  alums. 

Certain  facts  have  been  supposed  to  militate  against  the  principles  of  isomorphism, 
which  require  consideration. 

1.  It  appears  that  the  corresponding  angles  of  crystals  reputed  isomorphous  are 
not  always  exactly  equal,  but  are  sometimes  found  to  differ  two  or  three  degrees, 
although  the  errors  of  observation  in  good  crystals  rarely  exceed  10'  or  20'  of  a 
degree.  But  it  has  been  shown  by  Mitscherlich  that  a  difference  may  exist  between 
the  inclinations  of  two  series  of  similar  faces  in  different  specimens  of  the  same 
salt,  of  59' ;  while  it  is  also  known  that  the  angles  of  a  crystal  alter  sensibly  in  their 
relative  dimensions  with  a  change  of  temperature  (page  34).  The  angles  of  crystals 
are,  therefore,  affected  in  their  values  within  small  limits  by  causes  of  an  accidental 
character,  and  absolute  identity  in  crystalline  form  may  require  the  concurrence  of 
circumstances  which  are  not  found  together  in  the  ordinary  modes  of  producing 
many  crystals,  which  are  still  truly  isomorphous. 

The  following  table  exhibits  the  inequalities  which  have  been  observed  between 
the  angles  of  certain  isomorphous  crystals : — 

Rhomboidal  form. 

Carbonate  of  manganese  (diallogite)  103° 

lime  (calc-spar) 105°  5' 

lime  and  magnesia  (dolomite)  106°  15' 

magnesia  (giobertite)  107°  25' 

iron  (spathic  iron)  107° 

zinc  (smithsonite) 107°  40/ 

Square  prismatic  with  rhomboidal  base. 

Carbonate  of  lime  (arragonite)  116°  & 

"  lead  (ceruse)  117° 

"  strontia  (strontianite)  117°  32' 

«  baryta  (witherite) 118°  57' 


ISOMORPHISM.  141 

Sulphate  of  baryta 101°  42' 

"  lead  (anglesite) 103°  42' 

"  strontia  (celestine)  104°  30' 

2.  It  appears  that  the  same  body  may  assume  in  different  circumstances  two 
forms  which  are  totally  dissimilar,  and  have  no  relation  to  each  other.    Thus  sulphur 
on  crystallizing  from  solution  in  the  bisulphide  of  carbon  or  in  oil  of  turpentine,  at 
a  temperature  under  100°,  forms  octohedrons  with  rhombic  bases,  but  when  melted 
by  itself  and  allowed  to  cool  slowly,  it  assumes  the  form  of  an  oblique  rhombic 
prism  on  solidifying  at  232°.     These  are  incompatible  crystalline  forms,  as  they 
cannot  be  derived  from  one  common  form.    Carbon  occurs  in  the  diamond  in  regular 
octohedrons,  and  in  graphite  or  plumbago  in  six-sided  plates,  forms  which  are  like- 
wise incompatible.    Sulphur  and  charcoal  have  each,  therefore,  two  crystalline  forms, 
and  are  said  to  be  dimorphous,  (from  &j,  twice,  and  pop^,  shape).     Carbonate  of 
lime  is  another  familiar  instance  of  dimorphism,  forming  two  mineral  species,  calc- 
spar  and  arragonite,  which  are  identical  in  composition,  but  differ  entirely  in  crystal- 
line form.     G.  Rose  has  shown  that  the  first  or  second  of  these  forms  may  be  given 
to  the  granular  carbonate  of  lime  formed  artificially,  according  as  it  is  precipitated 
at  the  temperature  of  the  air,  or  near  the  boiling  point  of  water.     Of  its  two  forms, 
carbonate  of  lime  most  frequently  affects  that  of  calc-spar :  but  carbonate  of  lead, 
which  assumes  the  same  two  forms,  and  is  therefore  isodimorphous  with  carbonate 
of  lime,  chiefly  affects  that  of  arragonite,  and  is  very  rarely  found  in  the  other  form. 
Had  these  carbonates,  therefore,  been  each  known  only  in  its  common  form,  their 
isomorphism  would  not  have  been  suspected, — an  important  observation,  as  the 
want  of  isomorphism  between  certain  other  bodies  may  be  caused  by  their  being 
really  dimorphous,  although  the  two  forms  have  not  yet  been  perceived.     Crystalli- 
zation in  three  forms  is  not  unknown  :  thus  titanic  acid  is  found  in  three  distinct 
forms,  as  the  minerals  rutile,  brookite,  and  anatase. 

3.  The  observation  of  the  isomorphism  of  bodies  is  of  the  greatest  value  as  an 
indication  that  they  possess  a  similar  constitution,  and  contain  a  like  number  of 
atoms  of  their  constituents.     But  it  must  be  admitted  that  the  most  perfect  coinci- 
dence in  form  is  likewise  observed  between  certain  bodies  which  are  quite  different 
in  composition.     Thus  bisulphate  of  potassa  is  dimorphous,  and  crystallizes  in  one 
of  the  two  forms  of  sulphur  (Mitscherlich).     Nitrate  of  potassa  in  common  nitre 
has  the  form  of  arragonite,  and  occurs  also,  there  is  reason  to  believe,  in  microscopic 
crystals  in  the  form  of  calc-spar.     Nitrate  of  soda,  again,  has  the  form  of  calc-spar. 
Permanganate  of  baryta  and  the  anhydrous  sulphate  of  soda  likewise  crystallize  in 
one  form.     Between  the  first  pair,  sulphur  and  bisulphate  of  potassa,  the  absence 
of  all  analogy  in  composition  is  sufficiently  obvious,  notwithstanding  their  isomor- 
phism.    Between  nitrate  of  potassa  and  carbonate  of  lime,  and  between  permanga- 
nate of  baryta  and  sulphate  of  soda,  there  is  no  similarity  of  composition,  on  the 
ordinary  view  which  is  taken  of  the  constitution  of  these  salts,  but  both  of  these 
pairs  have  been  assimilated,  in  speculative  views  of  their  constitution  proposed  by 
Mr.  Johnston  (Philos.  Mag.  third  series,  vol.  xii.  page  480)  in  regard  to  the  first 
pair,  and  by  Dr.  Clark  (Records  of  General  Science,  vol.  iv.  page  45)  in  regard  to 
the  second,  which  merit  consideration,  although  the  hypotheses  cannot  be  both  cor- 
rect, as  they  are  based  upon  incompatible  data.    To  these  may  be  added,  the  sulphate 
of  baryta  with  perchlorate  and  permanganate  of  potassa :  BaO,  S03  with  KO,  C107 
and  KO,  Mn2  07.     The  sulphide  of  antimony  with  sulphate  of  magnesia :  Sb  S3 
with  MgO,  S03  +  7HO.     Borax  with  augite,  labradorite  and  anorthite,  quartz  and 
chabasite,  rnohsite  and  eudialite,  anatase  and  apophyllite,  zircon  and  wernerite,  man- 
ganite  and  prehnite.     Copper  pyrites,  Cu  Fe  S2,  has  also  the  same  form  as  braunite 
or  sesquioxide  of  manganese,  Mn2  03.     Leucite  and  analcime  both  belong  to  the 
regular  system,  and  are  aluminous  silicates  of  similar  composition  ]  but,  while  the 
first  contains  one  equivalent  of  potassa,  the  other  contains  one  equivalent  of  soda 
+  2HO. 


142  ISOMORPHISM. 

The  nitrite  of  lead  has  the  same  octohedral  figure  as  the  nitrate  of  lead,  with  two 
atoms  of  oxygen  less  in  its  acid. 

Of  examples  of  identity  of  crystalline  form  without  any  well-established  relation 
in  composition,  many  others  might  be  quoted,  if  occurrence  in  the  simple  forms  of 
the  cube  and  regular  octohedron  should  be  allowed  to  constitute  isomorphism.  For 
example  :  carbon,  sea-salt,  arsenious  acid,  galena,  the  magnetic  oxide  of  iron,  and 
alum,  all  occur  in  octohedrons,  although  they  are  no  way  related  in  composition. 
But  these  simple  forms  are  so  common,  that  they  can  be  held  as  affording  no  proof 
of  isomorphism,  unless  in  cases  where  it  is  to  be  expected  from  admitted  similarity 
of  composition,  as  between  the  different  alums,  or  between  chrome  iron  and  the 
magnetic  oxide  of  iron,  Cr2  03,  FeO  and  Fe2  03,  FeO. 

But  notwithstanding  the  occurrence  of  such  apparently  fortuitous  coincidences  in 
form,  isomorphism  must  still  be  considered  as  the  surest  criterion  of  similarity  of 
composition  which  we  possess.  Truly  isomorphous  bodies  generally  correspond  in  a 
variety  of  other  properties  besides  external  form.  Arsenic  and  phosphorus  resemble 
each  other  remarkably  in  odour,  although  the  one  is  a  metal  and  the  other  a  non- 
metallic  body,  while  the  corresponding  arseniates  and  phosphates  agree  in  taste,  in 
solubility,  in  the  degree  of  force  with  which  they  retain  water  of  crystallization,  and 
in  various  other  properties.  The  seleniate  and  sulphate  of  soda,  with  ten  atoms  of 
water,  which  are  isomorphous,  are  both  efflorescent  salts,  and  correspond  in  solu- 
bility, even  so  far  as  to  agree  in  an  unwonted  deviation  from  the  usually  observed 
increasing  rate  of  solubility  at  high  temperatures,  both  salts  being  more  soluble  in 
water  at  100°  than  at  212°.  In  fact,  isomorphism  appears  to  be  always  accompanied 
by  many  common  properties,  and  to  be  the  feature  which  indicates  the  closest  rela- 
tionship between  bodies. 

It  will  afterwards  appear  that  the  more  nearly  bodies  agree  in  composition,  they 
are  the  more  likely  to  act  as  solvents  of  each  other,  or  to  be  miscible  in  the  liquid 
form.  An  attraction  for  each  other  of  the  same  character  is  probably  the  cause  of 
the  easy  blending  together  of  the  particles  of  isomorphous  bodies,  and  of  the  diffi- 
culty of  separating  them  after  they  are  once  dissolved  in  a  common  menstruum ; 
such  isomorphous  salts  as  the  permanganate  and  perchlorate  of  potassa  may,  indeed, 
crystallize  apart  from  the  same  solution,  owing  to  a  considerable  difference  of  solu- 
bility; and  potassa-alum  may  be  purified,  in  a  great  measure,  by  crystallization, 
from  iron-alum,  which  is  more  soluble,  and  remains  in  the  mother-liquor;  but  most 
isomorphous  salts,  such  as  the  sulphates  of  iron  and  copper,  or  the  iodide  and  chlo- 
ride of  potassium,  when  once  dissolved  together,  do  not  crystallize  apart,  but  com- 
pose homogeneous  crystals,  which  are  mixtures  of  the  two  salts  in  indefinite  propor- 
tions. This  intermixture  of  isomorphous  compounds  is  of  frequent  occurrence  in 
minerals,  and  was  quite  inexplicable,  and  appeared  to  militate  against  the  doctrine 
of  combination  in  definite  proportions,  till  the  power  of  isomorphous  bodies  to  re- 
place each  other  in  compounds  was  recognized  as  a  law  of  nature.  Thus,  in  garnet, 
which  is  a  silicate  of  alumina  and  lime,  A1203,  Si03-t-3CaO  Si03,  the  alumina  is 
found  often  wholly  or  in  part  replaced  by  an  equivalent  quantity  of  peroxide  of  iron; 
while  the  lime,  at  the  same  time,  may  be  exchanged  wholly  or  in  part  for  protoxide 
of  iron,  or  for  magnesia,  without  the  proper  crystalline  character  of  the  mineral 
being  destroyed.  Hence  the  composition  of  mineral  species  is  most  properly  ex- 
pressed by  general  formulae,  where  a  letter,  such  as  R,  expresses  an  equivalent  of 
metal  which  may  be  calcium,  magnesium,  manganese,  iron,  &c.  : — 

The  Pyroxenes  by  3RO,  2Si03. 

The  Epidotes  by  3RO,  2A1203,  3Si03. 

*^*  The  various  forms  of  crystals  were  first  happily  described  by  Professor  Weiss,  of 
Berlin,  by  reference  to  "crystalline  axes,"  which  are  three  straight  lines  passing  through 
the  same  point,  and  terminating  in  the  surfaces  or  angles  of  the  crystal.  The  simplest  case 
is  that  in  which  the  three  axes  cross  each  other  at  right  angles,  and  are  equal  in  length,  as 


ISOMORPHISM. 


143 


rf presented  (fig.  53) ;  c  being  the  vertical,  and  a  and  b  the  two  horizontal  axes.     A  crystal 
is  formed  by  applying  planes  in  three  principal  ways  to  these  axes. 

1.  By  applying  six  planes  so  that  each  shall  be  perpendicular  to  one  axis  and  parallel  to 
the 'other  two,  the  hexahedron,  or,  as  it  is  more  commonly  termed,  the  cube  (fig.  54),  is 
formed.  Here  the  axes  terminate  in  the  centre  of  each  of  the  six  faces  of  the  crystal. 


FIG.  63. 


FIG.  54. 


a 


\ 


2.  By  applying  one  plane  to  an  extremity  qf  each  of  the  three  axes,  as  to  the  points  a,  6, 
and  c  (fig.  63),  and  seven  planes  in  the  same  manner  to  other  extremities,  the  regular  octo- 
hedron  is  produced,  of  which  the  eight  faces  or  planes  are  all  equilateral  triangles  (fig.  55). 
The  axes  here  terminate  in  the  angles  of  the  crystal. 

3.  The  plane  may  be  applied  to  the  extremities  of  two  axes,  and  be  parallel  to  the  third, 
•which  will  require  twelve  planes  to  close  the  figure,  and  give  r'°e  to  the  rhombic  dodecahe- 
dron (fig.  56). 


FIG.  55. 


FIG.  56. 


In  these  three  principal  forms,  the  planes  are  applied  to  the  axes  at  equal  distances  from 
the  centre.  They  may  also  cut  the  axes  at  unequal  distances  from  the  centre,  giving  rise 
to  four  other  less  usual  forms. 

A  body  in  crystallizing  may  assume  any  of  these  forms,  the  only  thing  constant  being  the 
crystalline  axes.  Hence  common  salt  crystallizes  both  in  the  cube  and  octohedron,  although 
most  usually  in  the  former  figure  ;  and  the  magnetic  oxide  of  iron  both  in  the  octohedron 
and  rhombic  dodecahedron.  A  body  may  even  assume  several  of  these  forms  at  the  same 
time ;  that  is,  may  present  at  once  faces  of  the  cube,  octohedron,  and  dodecahedron.  Of 
the  octohedral  crystals  of  alum,  for  instance,  the  solid  angles  are  always  found  to  be  cut  or 
truncated  by  planes  which  belong  to  the  cube  of  the  same  axes  (fig.  57) ;  and  the  edges  of 
the  octohedron  in  the  same  salt  are  sometimes  removed  or  bevelled  by  the  faces  of  the  dode- 
cahedron (fig.  58).  Fig.  59  represents  a  combination  of  all  these  three  forms ;  and  similar 
or  even  more  complicated  combinations  are  often  found  in  nature. 


144 


ISOMORPHISM 


Fia.  57. 


Fia.  58. 


FIG.  59.  The  groups  of  forms   thus  associated,  by  being 

deducible  from  the  same  axes,  constitute  what  is 
called  a  "  system  of  crystallization."  Six  such  sys- 
tems are  enumerated  by  Weiss,  to  some  one  of  -which 
every  crystalline  body  belongs. 

1.  The  octohedral  or  regular  system  of  crystalli- 
zation, with  the  three  principal  axes  at  right  angles 
to  each  other,  and  equal  in  length.     It  is  that  already 
described. 

2.  The  square  prismatic,  with  the  axes  at  right 
angles,  but  two  only  of  them  equal  in  length. 

3.  The  right  prismatic,  with  the  axes  at  right  an- 
gles, but  unequal  in  length. 

4.  The  rhombohedral,  with  the   axes  equal,  and 
crossing  at  equal  but  not  right  angles. 

5.  The  oblique  prismatic,  with  two  of  the   axes 
intersecting  each  other  obliquely,  while  the  third  is 
perpendicular  to  both,  and  unequal  in  length. 

6.  The  doubly-oblique  prismatic,  with  all  three  axes  intersecting  each  other  obliquely, 
and  unequal. 

By  the  apposition  of  planes  to  these  diiferent  sets  of  crystalline  axes,  in  the  same  modes 
as  to  the  axes  of  the  regular  system,  series  of  forms  are  produced,  having  a  general  analogy 
in  all  the  systems,  but  specifically  diiferent. 

For  additional  information  on  the  subject  of  crystallography,  which,  although  highly  im- 
portant to  the  chemical  inquirer,  is  not  exactly  a  department  of  chemistry,  reference  may 
be  made  to  the  Essay  of  Dr.  Whewell,  in  the  Phil.  Trans,  for  1825 ;  to  an  Essay  by  Dr. 
Leeson,  in  the  Memoirs  of  the  Chemical  Society,  vol.  iii. ;  the  German.  Elements  of  Crystal- 
lography of  G.  Rose ;  the  Systems  of  Crystallography  of  Professor  Miller  and  Mr.  J.  J. 
Griffin ;  and  to  a  short  work  lately  published,  entitled  "  Elements  de  Crystallographie,  par 
M.  J.  Miiller,  traduits  de  1'Allemand  par  Jerome  Nickles,"  which  appears  to  be  well  adapted 
to  the  wants  of  the  chemist.  A  full  list  of  isomorphous  substances  is  given  by  M.  Gnielin 
in  his  invaluable  Handbuch  der  Chemie,  vol.  i.  p.  83. 

CLASSIFICATION   OF  ELEMENTS. 

The  extent  to  which  the  isomorphous  relations  of  bodies  have  been  traced,  will 
appear  on  reviewing  the  groups  or  natural  families  in  which  the  elements  may  be 
arranged,  and  observing  the  links  by  which  the  different  groups  themselves  are  con- 
nected ;  these  classes  not  being  abruptly  separated,  but  shading  into  each  other  in 
their  characters,  like  the  classes  created  by  the  naturalist  for  the  objects  of  the  or- 
ganic world. 

I.  Sulphur  Class.  —  This  class  comprises  four  elementary  bodies :  oxygen,  sul- 
phur, selenium,  tellurium.  The  three  last  of  these  elements  exhibit  the  closest 
parallelism  in  their  own  properties,  in  the  range  of  their  affinities  for  other  bodies, 
and  in  the  properties  of  their  analogous  compounds.  They  all  form  gases  with  one 
atom  of  hydrogen,  and  powerful  acids  with  three  atoms  of  oxygen,  of  which  the 


CLASSIFICATION   OF   ELEMENTS.  145 

salts,  the  sulphates,  seleniates,  and  tellurates  are  isomorphous ;  and  the  same  rela- 
tion undoubtedly  holds  in  all  the  corresponding  compounds  of  these  elements. 

Oxygen  has  not  yet  been  connected  with  this  group  by  a  certain  isomorphism  of 
any  of  its  compounds ',  but  a  close  correspondence  between  it  and  sulphur  appears, 
in  their  compounds  with  one  class  of  metals  being  alkaline  bases  of  similar  proper- 
ties, forming  the  two  great  classes  of  oxygen  and  sulphur  bases,  such  as  oxide  of 
potassium  and  sulphide  of  potassium ;  and  in  their  compounds  with  another  class 
of  elements  being  similar  acids,  giving  rise  to  the  great  classes  of  oxygen  and  sul- 
phur acids,  such  as  arsenious  and  sulphursenious  acids.  They  farther  agree  in  the 
analogy  of  their  compounds  with  hydrogen,  particularly  of  binoxide  of  hydrogen 
and  bisulphide  of  hydrogen,  both  of  which  bleach,  and  are  remarkable  for  their  in- 
stability ;  and  in  the  analogy  of  the  oxide,  sulphide,  and  telluride  of  ethyl,  and  of 
alcohol  and  mercaptan,  which  last  is  an  alcohol  with  its  oxygen  replaced  by  sulphur. 
This  class  is  connected  with  the  next  by  manganese,  of  which  manganic  acid  is 
isomorphous  with  sulphuric  acid,  and  consequently  manganese  with  sulphur. 

II.  Magnesian  Class. — This  class  comprises  magnesium,  calcium,  manganese, 
iron,  cobalt,  nickel,  zinc,  cadmium,  copper,  hydrogen,  chromium,  aluminum,  gluci- 
num,  vanadium,  zirconium,  yttrium,  thorinum.     The  protoxides  of  this  class,  in- 
cluding water,  form  analogous  salts  with  acids.     A  hydrated  acid,  such  as  crystallized 
oxalic  acid  or  the  oxalate  of  water,  corresponding  with  the  oxalate  of  magnesia  in 
the  number  of  atoms  of  water  with  which  it  crystallizes,  and  the  force  with  which 
the  same  number  of  atoms  is  retained  at  high  temperatures ;  hydrated  sulphuric  acid 
(HO,  S03  +  H0)  with  the  sulphate  of  magnesia  (MgO,  S03  +  H0).     The  isomor- 
phism of  the  salts  of  magnesia,  zinc,  cadmium,  and  the  protoxides  of  manganese, 
iron,  nickel,  and  cobalt,  is  perfect.     Water  (HO)  and  oxide  of  zinc  (ZnO)  have 
both  been  observed  in  thin  regular  six-sided  prisms ;  but  the  isomorphism  of  these 
crystals  has  not  yet  been  established  by  the  measurement  of  the  angles.     Oxide  of 
hydrogen  has  not,  therefore,  been  shown  to  be  isomorphous  with  these  oxides, 
although  it  greatly  resembles  oxide  of  copper  in  its  chemical  relations.    Lime  is  not 
so  closely  related  as  the  other  protoxides  of  this  group,  being  allied  to  the  following 
class.    But  its  carbonate,  both  anhydrous  and  hydrated,  its  nitrate,  and  the  chloride 
of  calcium,  assimilate  with  the  corresponding  compounds  of  the  group ;  while  to  its 
sulphate  or  gypsum,  CaO,  S03-}-2HO,  one  parallel  and  isomorphous  compound,  at 
least,  can  be  adduced,  a  sulphate  of  iron,  FeO,  S03+2HO  (Mitscherlich),  which  is 
also  sparingly  soluble  in  water,  like  gypsum.     Glucina  is  isomorphous  with  lime 
from  the  isomorphism  of  the  minerals  cuclase  and  zoisite  (Brooke). 

The  salts  of  the  sesquioxide  of  chromium,  of  alumina,  and  glucina,  are  isomor- 
phous with  those  of  sesquioxide  of  iron  (Fe2  03),  with  which  these  oxides  correspond 
in  composition  ~}  and  the  salts  of  manganic  and  chromic  acids  are  isomorphous,  and 
agree  with  the  sulphates.  The  vanadiates  are  believed  to  be  isomorphous  with  the 
chrpmates.  Zirconium  is  placed  in  this  class,  because  its  fluoride  is  isomorphous 
with  that  of  aluminum  and  that  of  iron,  and  its  oxide  appears  to  have  the  same 
constitution  as  alumina  j  and  yttrium  and  thorium,  solely  because  their  oxides,  sup- 
posed to  be  protoxides,  are  classed  among  the  earths. 

III.  Barium  Class.  —  Barium,  strontium,  lead.     The  salts  of  their  protoxides, 
baryta,  strontia,  and  oxide  of  lead,  are  strictly  isomorphous,  and  one  of  them  at 
least,  oxide  of  lead,  is  dimorphous,  and  assumes  the  form  of  lime,  and  the  preceding 
class  in  the  mineral  plumbocalcite,  a  carbonate  of  lead  and  lime  (Johnston).     But 
certain  carbonates  of  the  second  class  are  dimorphous,  and  enter  into  the  present 
class,  as  the  carbonate  of  lime  in  arragonite,  carbonate  of  iron  in  junckerite,  and 
carbonate  of  magnesia  procured  by  evaporating  its  solution  in  carbonic  acid  water  to 
dryness  by  the  water-bath  (Gr.  Rose),  which  have  all  the  common  form  of  carbonate 
of  strontia.     Indeed,  these  two  classes  are  very  closely  related. 

IV.  Potassium  Class. — The  fourth  class  consists  of  potassium,  ammonium,  so- 
dium, silver.     The  term  ammonium  is  applied  to  a  hypothetical  compound  of  one 
atom  of  nitrogen  and  four  of  hydrogen  (NH4),  which  is  certainly,  therefore,  not  an 

10 


146  ISOMORPHISM. 

elementary  body,  and  probably  not  even  a  metal,  but  which  is  conveniently  assimi- 
lated in  name  to  potassium,  as  these  two  bodies  occupy  the  same  place  in  the  two 
great  classes  of  potassa  and  ammonia  salts,  between  which  there  is  the  most  com- 
plete isomorphism.  Potassium  and  ammonium  themselves  are,  therefore,  isomor- 
phous.  The  sulphates  of  soda  and  silver  are  similiform,  and  hence  also  the  metals 
sodium  and  silver  j  but  their  isomorphism  with  the  preceding  pair  is  not  so  clearly 
established.  Soda  replaces  potassa  in  soda-alum,  but  the  form  of  the  crystal  is  the 
common  regular  octohedron ;  nitrate  of  potassa  has  also  been  observed  in  microscopic 
crystals,  having  the  arragonitic  form  of  nitrate  of  soda,1  which  is  better  evidence  of 
isomorphism,  although  not  beyond  cavil,  as  the  crystals  were  not  measured.  There 
are  also  grounds  for  believing  that  potassa  replaces  soda  in  equivalent  quantities  in 
the  mineral  chabasite,  without  change  of  form.  The  probable  conclusion  is,  that 
potassa  and  soda  are  isomorphous,  but  that  this  relation  is  concealed  by  dimorphism, 
except  in  a  very  few  of  their  salts. 

This  class  is  connected  in  an  interesting  way  with  the  other  classes  through  the 
second.  The  subsulphide  of  copper  and  the  sulphide  of  silver  appear  to  be  isomor- 
phous, (see  sulphide  of  silver,  under  silver,  in  this  work),  although  two  atoms  of 
copper  are  combined  in  the  one  sulphide,  and  one  atom  of  silver  in  the  other,  with 
one  atom  of  sulphur;  their  formulae  being — 

Cu2  S  and  Ag  S. 

Are  then  two  atoms  of  copper  isomorphous  with  one  atom  of  silver  ?  In  the  present 
state  of  our  knowledge  of  isomorphism,  it  appears  necessary  to  admit  that  they  are. 

The  fourth  class  will  thus  stand  apart  from  the  second,  which  is  represented  by  • 
copper,  and  also  from  the  other  classes  connected  with  the  second,  in  so  far  as  one 
atom  of  the  present  class  is  equivalent  to  two  atoms  of  the  other  classes  in  the  pro- 
duction of  the  same  crystalline  form.  This  discrepancy  may  be  at  once  removed  by 
halving  the  atomic  weight  of  silver,  and  thus  making  both  sulphides  to  contain  two 
atoms  of  metal  to  one  of  sulphur.  But  the  division  of  the  equivalents  of  sodium, 
potassium,  and  ammonium,  which  would  follow  that  of  silver,  and  the  consideration 
of  potassa  and  soda  as  suboxides,  are  assumptions  not  to  be  lightly  entertained. 

It  was  inferred  by  M.  Mosander,  that  lime  with  an  atom  of  water  is  isomorphous 
with  potassa  and  soda,  because  CaO  +  HO  appears  to  replace  KO  or  NaO  in  meso- 
type,  chabasite,  and  other  minerals  of  the  zeolite  family.  The  isomorphism  of 
natrolite  and  scolezite  is  so  explained  :  -NaO,  Ala  03,  2Si03,  2  HO  with  CaO,  A12  03, 
2Si03,  3HO.  On  the  other  hand,  it  is  strongly  argued  by  M.  T.  Scheerer,  that  one. 
equivalent  of  magnesia  is  isomorphous  with  three  equivalents  of  water,  from  the 
equality  of  the  forms  of  cordierite  and  a  new  mineral  aspasiolite,  the  first  containing 
MgO,  and  the  second  3 HO  in  its  place ;  and  from  a  review  of  a  considerable  number 
of  alumino-magnesian  minerals.  One  equivalent  of  oxide  of  copper,  however,  is 
supposed  to  be  replaced  by  two  equivalents  of  water.2 

V.  Chlorine  Class.  —  Chlorine,  iodine,  bromine,  fluorine.  These  four  elements 
form  a  well-defined  natural  family.  The  three  first  are  isomorphous  throughout  their 
whole  combinations  —  chlorides  with  bromides  and  iodides,  chlorates  with  bromates 
and  iodates,  perchlorates  with  periodates,  &c. ;  and  such  fluorides  also  as  can  be 
compared  with  chlorides  appear  to  affect  the  same  forms.  The  fluoride  of  calcium 
of  apatite,  CaF,  3(3CaO,  P05),  is  also  replaced  by  the  chloride  of  calcium.  It  is 
connected  with  the  second  class  through  perchloric  acid ;  the  perchlorates  being 
strictly  isomorphous  with  the  permanganates.  But  the  formulae  of  these  two  acids 
are — 

1  Frankenheim,  in  Poggenuorff 's  Annalen,  vol.  xl.  page  447.     See  also  a  paper  by  Professor 
Johnston  on  the  received  equivalents  of  potassa,  soda,  and  silver;   Phil.  Mag.  third  series, 
vol.  xii.  p.  324. 

2  Poggendorff's  Annalen  der '  Physik  und  Chemic,  t.  Ixviii.  p.  319.     Also,  Millon  and  Reiset's 
Annuaire  de  Chimie,  1847,  8vo.  Paris,  pp.  52  and  234. 


CLASSIFICATION   OF   ELEMENTS.  147 

Cl  07  and  Mn2  07, 

one  atom  of  chlorine  replacing  two  atoms  of  manganese.  Or,  this  class  has  the 
same  isomorphous  relation  as  the  preceding  class  to  the  others :  and  such  I  shall 
assume  to  be  its  true  relation.  Although  halving  the  atomic  weight  of  chlorine, 
which  would  give  two  atoms  of  chlorine  to  perchloric  acid,  is  not  an  improbable 
supposition,  still  it  would  lead  to  the  same  strange  conclusion  as  follows  the  division 
of  the  equivalent  of  sodium, —  namely,  that  chlorine  enters  into  its  other  com- 
pounds, as  well  as  into  perchloric  acid,  always  in  the  proportion  of  two  atoms; 
for  that  element  is  never  known  to  combine  in  a  less  proportion  than  is  expressed 
by  its  presently  received  equivalent.  Cyanogen  (C2  N),  although  a  compound  body, 
has  some  claim  to  enter  this  class,  as  the  cyanides  have  the  same  form  as  the  chlo- 
rides. 

VI.  Phosphorus  Class.  —  Nitrogen,  phosphorus,  arsenic,  antimony,  and  bismuth ; 
also  composing  a  well-marked  natural  group,  of  which  nitrogen  and  bismuth  are  the 
two  extremes,  and  of  which  the  analogous  compounds  exhibit  isomorphism.  These 
five  elements  all  form  gaseous  compounds  with  three  atoms  of  hydrogen;  namely, 
ammonia,  phosphuretted  hydrogen,  arsenietted  hydrogen,  &c.  The  hydriodates  of 
ammonia  and  of  phosphuretted  hydrogen  are  not,  however,  isomorphous.  Arsenious 
acid  and  the  oxide  of  antimony,  both  of  which  contain  three  atoms  of  oxygen  to  one 
of  metal,  are  doubly  isomorphous.  Arsenious  acid  also  is  capable  of  replacing  oxide 
of  antimony  in  tartrate  of  antimony  and  potassa  or  tartar  emetic,  without  change  of 
form ;  and  arsenic  often  substitutes  antimony  in  its  native  sulphide.  The  native 
sulphide  of  bismuth  (Bi  S3)  is  also  isomorphous  with  the  sulphide  of  antimony 
(Sb  S3).  Nitrous  acid  (NO3),  which  should  correspond  with  arsenious  acid  and 
oxide  of  antimony,  likewise  acts  occasionally  as  a  base,  as  in  the  crystalline  com- 
pound with  sulphuric  acid  of  the  leaden  chambers.  The  complete  isomorphism  of 
the  arseniates  and  phosphates  has  already  been  noticed.  But  phosphoric  acid  forms 
two  other  classes  of  salts,  the  pyrophosphates  and  metaphosphates,  to  which  arsenic 
acid  supplies  no  parallels. 

This  class  of  elements  is  connected  with  the  others  by  means  of  the  following 
links: — Bisulphide  of  iron  is  usually  cubic,  or  of  the  regular  system;  but  it  is 
dimorphous,  and,  in  spirkise,  it  passes  into  another  system,  and  has  the  form  of 
arsenide  of  iron ;  Fe  S2,  or  rather  Fe2  S4,  being  isomorphous  with  Fe2  As  S2.  Again, 
bisulphide  of  iron,  in  the  pentagonal-dodecahedron  of  the  regular  system,  is  isomor- 
phous with  cobalt-glance,  Fe2  S4  with  Co2  As  S2 :  so  that  one  equivalent  of  arsenic 
appears  to  be  isomorphous  with  2S.  This  is  also  supported  by  the  isomorphism  of 
the  sulphide  of  cadmium  and  sulphide  of  nickel  (Cd  S  and  Ni  S,  or  Cd2  S2  and  Ni2 
S2),  with  the  arsenide  of  nickel  (Ni2  As).  Tellurium  has  also  been  observed  in  the 
same  form  as  metallic  arsenic  and  antimony.  The  phosphorus  class  approximates 
also  to  the  chlorine  class ;  nitrogen  and  chlorine  both  forming  a  powerful  acid  with 
five  equivalents  of  oxygen,  nitric  acid,  and  chloric  acid ;  but  of  the  many  nitrates 
and  chlorates  which  can  be  compared,  no  two  have  proved  isomorphous.  Nor  do 
the  metaphosphates  appear  at  all  like  the  nitrates,  although  their  formulae  corre- 
spond. 

Nitrogen,  it  must  be  admitted,  is  but  loosely  attached  to  this  class.  It  is  greatly 
more  negative  than  the  other  members  of  the  class,  approaching  oxygen  in  that 
character,  with  which,  indeed,  nitrogen  might  be  grouped,  N  being  equivalent  to 
20.  For  while  phosphuretted  hydrogen  is  the  hydride  of  phosphorus,  or  has 
hydrogen  for  its  negative  and  phosphorus  for  its  positive  constituent,  ammonia  is 
undoubtedly  the  nitride  of  hydrogen,  or  has  nitrogen  for  its  negative  and  hydrogen 
for  its  positive  constituent.  The  one  should  be  written  PH3,  and  the  other  H3N — 
a  difference  in  constitution  which  separates  these  bodies  very  widely.  An  import- 
ant consequence  of  classing  nitrogen  with  oxygen  is,  that,  in  the  respective  series 
of  compounds  of  these  elements,  cyanogen  becomes  the  analogue  of  carbonic  oxide, 
C2N  being  equivalent  to  CO,  or  rather  C202. 


148  ISOMORPHISM. 

VII.  Tin  Class.  —  Tin,  titanium.     Connected  by  the  isomorphism  of  titanic 
acid  (Ti02)  in  rutile  with  peroxide  of  tin  (Sn02)  in  tin-stone.     Titanium  is  con- 
nected with  iron  and  the  second  class.     Ilmenite  and  other  varieties  of  titanic  iron 
which  have  the  crystalline  form  of  the  sesquioxide  of  that  metal,  —  namely,  that 
of  specular  iron,  and  also  of  corundum  (alumina),  —  are  mixtures  of  a  sesquioxide 
of  titanium  (Ti203)  with  sesquioxide  of  iron  (H.  Rose). 

VIII.  Gold  Class.  —  Gold,  which  is  isomorphous  with  silver  in  the  metallic 
state.     Gold  will  thus  be  connected,  through  silver,  with  sodium  and  the  fourth 
class. 

IX.  Platinum  Class.  —  Platinum,  indium,  osmium.      From  the  isomorphism 
of  their  double  chlorides.     The  double  bichloride  of  tin  and  chloride  of  potassium 
crystallizes  in  regular  octohedrons,  like  the  double  bichloride  of  platinum  and  potas- 
sium, and  other  double  chlorides  of  this  group ;  which,  although  not  alone  sufficient 
to  establish  an  isomorphous  relation  between  this  class  and  the  seventh,  yet  favours 
its  existence  (Dr.  Clark).     The  alloy  of  osmium  and  iridium  (IrOs)  is  isomorphous 
with   the   sulphide   of  cadmium   (CdS)   and   sulphide   of  nickel   (NiS)    (Breit- 
haupt). 

X.  Tungsten  Class.  —  Tungsten,  molybdenum,  tantalum,  niobium,  and  pelo- 
piurn.   From  the  isomorphism  of  the  tungstates  and  molybdates,  the  salts  of  tungstic 
and  molybdic  acids,  W03  and  Mo03.     Tantalic  acid  is  isomorphous  with  tungstic 
acid :    tantalite  (FeO,  Ta03)  with  wolfram  (FeO,  W03).     So  are  molybdic  and 
chromic  acids,  the  tungstate  of  lime,  tungstate  of  lead,  molybdate  of  lead,  and  chro- 
mate  of  lead  (in  the  least  usual  of  its  two  forms),  being  all  of  the  same  form.     This 
establishes  a  relation  between  molybdic,  chromic,  sulphuric,  and  other  analogous 
acids  (Johnston,  Phil.  Mag.  3d  series,  vol.  xii.  p.  387).     Niobium  and  pelopium 
are   introduced   into   this   class   as   they   replace   tantalum   in   the   tantalites  of 
Bavaria. 

XL  Carbon  Class.  —  Carbon,  boron,  silicium.  These  elements  are  placed  to- 
gether, from  a  general  resemblance  which  they  exhibit  without  any  precise  relation. 
They  are  not  known  to  be  isomorphous  among  themselves,  or  with  any  other  ele- 
ment. They  are  non-metallic,  and  form  weak  acids  with  oxygen,  —  the  carbonic, 
consisting  of  two  of  oxygen  and  one  of  carbon,  and  the  boric  and  silicic  acids,  which 
are  generally  viewed  as  composed  of  three  of  oxygen  to  one  of  boron  and  silicium. 
Silicic  acid  may,  perhaps,  replace  alumina  in  some  minerals,  but  this  is  un- 
certain. 

Of  the  elements  which  have  not  been  classed,  no  isomorphous  relations  are  known. 
They  are  mercury,  which  in  some  of  its  chemical  properties  is  analogous  to  silver, 
and  in  others  to  copper,  cerium,  didymium,  lanthanum,  lithium,  rhodium,  ruthe- 
nium, palladium,  and  uranium.  Ruthenium,  however,  is  believed  to  be  isomorphous 
with  rhodium,  from  the  correspondence  in  composition  of  their  double  chlorides. 
Didymium  and  lanthanum  are  also  probably  isomorphous  with  cerium,  as  they  ap- 
pear to  replace  that  metal  in  cerite. 

According  to  the  original  law  of  Mitscherlich,  that  isomorphism  depends  upon 
equality  in  the  number  of  atoms,  and  similarity  in  their  arrangement,  without  refer- 
ence to  their  nature,  the  elements  themselves  should  all  be  isomorphous.  Most  of 
the  metals  crystallize  in  the  simple  forms  of  the  cube  or  regular  octohedron,  which 
are  not  sufficient  to  establish  this  relation.  But  the  isomorphism  of  a  large  propor- 
tion, if  not  the  whole,  of  the  elements  may  be  inferred  from  the  isomorphism  of  their 
analogous  compounds.  Thus,  from  the  facts  just  adduced,  it  appears  that  the  mem- 
bers of  the  following  large  class  of  elements  are  linked  together  from  the  isomor- 
phism of  one  or  more  of  their  compounds.  This  large  class  may  be  subdivided  into 
smaller  classes,  between  the  members  of  which  isomorphism  is  of  more  frequent 
occurrence,  and  which  are  then  to  be  viewed  as  isomorphous  groups. 


CLASSIFICATION    OF   ELEMENTS. 


149 


1.  Sulphur 
Selenium 
Tellurium 


2.  Magnesium 
Calcium 
Manganese 
Iron 
Cobalt 
Nickel 
Zinc 

Cadmium 
Copper 
Chromium 
Aluminum 
Glucinum 
Vanadium 
Zirconium 


ISOMORPHOUS   ELEMENTS. 

3.  Barium 
Strontium 
Lead 


4.  Tin 
Titanium 


5.  Platinum 
Iridium 
Osmium 


6.  Tungsten 
Molybdenum 
Tantalum 


With  two  atoms  of  the 
preceding  elements. 

7.  Sodium 
Silver 
Gold 

Potassium 
Ammonium 

Chlorine 
Iodine 
Bromine 
Fluorine 

Cyanogen 

9.  Phosphorus 
Arsenic 
Antimony 
Bismuth 


The  tendency  of  discovery  is  to  bring  all  the  elements  into  one  class,  either  as  iso- 
morphous  atom  to  atom,  or  with  the  relation  to  the  others  which  sodium,  chlorine, 
and  arsenic  exhibit. 

But  must  not  isomorphism  be  implicitly  relied  upon  in  estimating  atomic  weights, 
and  the  alterations  which  it  suggests  be  adopted  without  hesitation  in  every  case  ? 
Chemists  have  always  been  most  anxious  to  possess  a  simple  physical  character  by 
which  atoms  might  be  recognised ;  and  equality  of  volume  in  the  gaseous  state, 
equality  of  specific  heat,  and  similarity  in  crystalline  form,  have  all  in  their  turn 
been  upheld  as  affording  a  certain  criterion.  The  indications  of  isomorphism  cer- 
tainly accord  much  better  than  those  of  the  other  two  criteria  with  views  of  the  con- 
stitution of  bodies  derived  from  considerations  purely  chemical,  and  are  indeed 
invaluable  in  establishing  analogy  of  composition  in  a  class  of  bodies,  by  supplying 
a  precise  character  which  can  be  expressed  in  numbers,  instead  of  that  general  and 
ill-defined  resemblance  between  allied  bodies,  which  chemists  perceived  by  an  ac- 
quired tact  rather  than  by  any  rule,  and  which  was  heretofore  their  only  guide  in 
classification.  Admitting  that  isomorphism  is  a  certain  proof  of  similarity  of  atomic 
constitution  within  a  class  of  elements  and  their  compounds,  it  may  still  be  doubted 
whether  the  relation  of  the  atom  to  crystalline  form  is  the  same  without  modifica- 
tion throughout  the  whole  series  of  the  elements,  or  whether  all  atoms  agree  exactly 
in  this  or  any  other  physical  character. 

Crystalline  form  and  the  isomorphous  relation  may  prove  not  to  be  a  reflection 
of  atomic  constitution,  or  immediately  and  necessarily  connected  with  it,  but  to  arise 
from  some  secondary  property  of  bodies,  such  as  their  relation  to  heat ;  in  which  a 
simple  atom  may  occasionally  resemble  a  compound  body,  as  we  find  sulphur  iso- 
morphous in  one  of  its  forms  with  bisulphate  of  potassa;  while  we  find  another  sim- 
ple atom,  potassium,  isomorphous  through  a  long  series  of  compounds  with  the 
group  of  five  atoms  which  constitute  ammonium.'  The  occurrence  of  dimorphism 
also,  both  in  simple  and  compound  bodies,  gives  to  crystalline  form  a  less  funda- 
mental character. 

Is  it  probable  that  sulphur  and  carbonate  of  lime  could  be  made  to  appear  in  sets 
of  crystals  which  are  wholly  unlike,  merely  by  a  slight  change  of  temperature,  if 
form  were  the  consequence  of  an  invariable  atomic  constitution  ?  Crystalline  form, 
then,  may  possibly  depend  upon  some  at  present  unknown  property  of  bodies,  which 
may  have  a  frequent  and  general,  but  certainly  not  an  invariable  relation  to  their 
atomic  constitution.  There  may  be  nothing  truly  inconsistent  with  the  principles 
of  isomorphism  in  one  atom  of  a  certain  class  of  elements  having  ^the  same  crystallo- 
graphic  value  as  two  atoms  of  another  class,  the  relation  which  has  been  assumed  to 


130  ALLATROPT. 

exist  between  the  sodium,  chlorine,  and  phosphorus  classes,  and  the  others,  par- 
ticularly when  the  classes  stand  apart,  arid  differ  in  their  properties  from  all  the 
others,  as  those  of  sodium  and  chlorine  do. 

SECTION    V. ALLATROPY. 

Many  solid,  and  a  few  liquid  bodies  admit  of  a  variation  of  properties,  and  may 
present  different  appearances  at  the  same  temperature. 

Dimorphism,  or  the  assumption  of  two  incompatible  crystalline  forms  by  the 
same  body,  in  different  circumstances,  has  already  been  noticed  as  occurring  with 
sulphur,  carbon,  carbonates  of  lime  and  lead,  bisulphate  of  potassa,  and  chromate 
of  lead.  It  is  also  observed  in  the  biphosphate  of  soda,  and  in  a  considerable  num- 
ber of  minerals.  The  sulphate  of  nickel  (NiO,  S03  +  7HO)  is  trimorphous ;  the 
other  salts  of  similar  composition,  such  as  sulphate  of  magnesia  and  sulphate  of 
zinc,  have  been  found  in  two  only  of  these  forms.  Dimorphous  crystals  may  differ 
in  density,  the  densities  of  calc-spar  and  arragonite,  the  forms  of  carbonate  of  lime 
being  2.719  and  2.949,  and  indeed  all  resemblance  in  properties  between  the  crys- 
tals may  be  lost,  as  in  diamond  and  graphite,  the  two  forms  of  carbon.  The  par- 
ticular form  assumed  by  sulphur  and  carbonate  of  lime,  which  may  be  made  to 
crystallize  in  either  of  their  forms  at  will,  is  found  to  depend  upon  the  degree  of 
temperature  at  which  the  solid  is  produced ;  carbonate  of  lime  being  precipitated, 
on  adding  chloride  of  calcium  to  carbonate  of  ammonia,  in  a  powder,  of  which  the 
grains  have  the  form  of  calc-spar  or  of  arragonite,  according  as  the  temperature  of 
the  solution  is  50°  or  150°  (Gr.  Rose,  Phil.  Mag.  3d  series,  vol.  xii.  p.  465).  A 
large  crystal  of  arragonite,  when  heated  by  a  spirit-lamp,  decrepitates,  and  falls  into 
a  powder  composed  of  grains  of  calc-spar.  Native  carbonate  of  iron  is  isodimorphous 
with  carbonate  of  lime;  as  spathic  iron  its  specific  gravity  is  3.872,  as  junckerite 
3.815.  The  crystals  of  sulphur  produced  at  the  higher  of  two  temperatures  be- 
come opaque  when  kept  for  some  days  in  the  air,  and  pass  spontaneously  into  the 
other  form ;  while  the  crystals  produced  at  the  lower  temperature  are  disintegrated 
and  changed  into  the  other  form  by  a  moderate  heat.  These  observations  are  im- 
portant, as  establishing  a  relation  between  dimorphism  and  solidification  at  different 
temperatures. 

A  considerable  variation  of  properties  is  likewise  often  observable  in  a  solid  which 
is  not  crystalline,  or  of  which  the  crystalline  form  is  indeterminate.  This  fact  has 
been  designated  allatropy  by  Berzelius  (from  d&*of  po^o^  of  a  different  nature) :  di- 
morphism, or  diversity  in  crystalline  form,  is,  therefore,  a  particular  case  of  alla- 
tropy. Sulphide  of  mercury  obtained  by  precipitating  corrosive  sublimate  by  hydro- 
sulphuric  acid,  is  black;  but  the  same  body,  when  sublimed  by  heat,  or  produced 
by  agitating  mercury  in  a  solution  of  the  persulphide  of  potassium,  forms  cinnabar, 
of  which  the  powder  is  the  red  pigment  vermilion ;  while  vermilion  itself,  if  heated 
till  sulphur  begins  to  sublime  from  it,  and  then  suddenly  thrown  into  cold  water, 
becomes  black ;  although,  if  allowed  to  cool  slowly,  it  remains  red.  Yet  it  is  of  the 
same  composition  exactly  in  the  black  and  red  states.  The  iodide  of  mercury  newly 
sublimed  is  of  a  lively  yellow  colour,  and  may  remain  so  for  a  long  time ;  but  it 
generally  begins  to  pass  into  a  fine  scarlet  on  cooling,  and  may  be  made  to  undergo 
this  change  of  colour  in  an  instant  by  strongly  pressing  it :  these,  however,  are  two 
different  crystalline  forms.  The  precipitated  sulphide  of  antimony  may  be  deprived 
of  the  water  it  contains,  at  the  melting  point  of  tin,  without  losing  its  peculiar 
orange  colour;  but,  when  heated  a  little  above  that  temperature,  it  shrinks,  and 
assumes  the  black  colour  and  metallic  lustre  of  the  native  sulphide,  without  any 
loss  of  weight.  Again,  the  black  sulphide,  when  heated  strongly  and  thrown  into 
water,  loses  its  metallic  lustre,  and  acquires  a  good  deal  of  the  appearance  of  the 
precipitated  sulphide.  Chromate  of  lead,  which  is  usually  yellow,  if  fused  and 
thrown  into  cold  water,  gives  a  red  powder.  The  nitrates  of  lead  are  sometimes 
white,  and  sometimes  yellow;  and  crystals  of  sulphate  of  manganese  are  often 


ALLATROPY.  151 

deposited  from  the  same  solution,  some  of  which  are  pink,  and  others  colourless, 
although  identical  in  composition. 

Such  differences  of  colour  are  permanent,  and  not  to  be  confounded  with  changes 
which  are  peculiar  to  certain  temperatures :  thus  oxide  of  zinc  is  of  a  lemon-yellow 
colour,  when  strongly  heated,  but  milk-white  at  a  low  temperature ;  the  oxide  of 
mercury  is  much  redder  at  a  high  than  at  a  low  temperature,  and  bichromate  of 
potassa,  which  is  naturally  red,  becomes  almost  black  when  fused  by  heat.  Even 
bodies  in  the  gaseous  state  are  liable  to  transient  changes  of  this  kind,  the  brown 
nitrous  fumes  being  nearly  colourless  below  zero,  and  on  the  other  hand  deepening 
greatly  in  colour  at  a  high  temperature. 

The  condition  of  glass  is  a  remarkable  modification  of  the  solid  form  assumed  by 
many  bodies.  Matter  in  this  state  is  not  crystallized,  and  on  breaking,  presents 
curved  and  not  plain  surfaces,  or  its  fracture,  in  mineralogical  language,  is  con- 
choidal,  and  not  sparry.  The  indisposition  to  crystallize,  which  causes  solidification 
in  the  form  of  glass,  is  more  remarkable  in  some  bodies,  such  as  phosphoric  and 
boracic  acids,  and  their  compounds,  than  in  others.  The  biphosphate  and  binarse- 
niate  of  soda  have  the  closest  resemblance  in  properties,  yet  when  both  are  fused  by 
a  lamp,  the  first  solidifies  on  cooling  into  a  transparent  colourless  glass,  and  the 
second  into  a  white  opake  mass  composed  of  interlaced  crystalline  fibres.  The 
phosphate  at  the  same  time  discharges  sensibly  less  heat  than  the  arseniate  in  solidi- 
fying, retaining  probably  a  portion  of  its  heat  of  fluidity,  or  latent  heat  in  a  state 
of  combination,  while  a  glass.  None  of  the  compounds  of  silicic  acid  and  a  single 
base,  such  as  soda  or  lime,  or  simple  silicate,  becomes  a  glass  on  cooling  from  a  state 
of  fusion,  with  the  exception  of  the  silicate  of  lead  containing  a  great  excess  of  oxide : 
they  all  crystallize.  But  a  mixture  of  the  same  silicates,  when  fused,  exhibits  a 
peculiar  viscosity  or  tenacity,  appears  to  have  lost  the  faculty  of  crystallizing,  and 
constantly  forms  a  glass.  The  varieties  of  glass  in  common  use  are  all  such  mix- 
tures of  silicates.  .Glass  is  sometimes  devitrified  when  kept  soft  by  heat  for  a  long 
time,  owing  to  the  separation  of  the  silicates  from  each  other,  and  their  crystalliza- 
tion ;  and  the  less  mixed  glasses  are  known  to  be  most  liable  to  this  change.  It  is 
probable  that  all  bodies  differ,  when  in  the  vitreous  and  in  the  crystalline  form,  in 
the  proportion  of  combined  heat  which  they  possess,  as  has  been  observed  of  melted 
sugar  (page  61)  in  these  two  conditions. 

Arsenious  acid,  when  fused  or  newly  sublimed,  appears  as  a  transparent  glass  of 
a  light  yellow  tint ;  but  left  to  itself,  it  slowly  becomes  opake  and  milk  white,  the 
change  commencing  at  the  surface  and  advancing  to  the  centre,  and  often  requiring 
years  to  complete  it,  in  a  considerable  mass.  The  arsenious  acid  is  no  longer  vitre- 
ous, being  changed  into  a  multitude  of  little  crystals,  whence  results  its  opacity ; 
and  it  has  altered  slightly  at  the  same  time  in  density  and  in  solubility.  But  the 
passage  from  the  vitreous  to  the  crystalline  state  may  take  place  instantaneously, 
and  give  rise  to  an  interesting  phenomenon  observed  by  H.  Rose.  The  vitreous 
arsenious  acid  seems  to  dissolve  in  dilute  and  boiling  hydrochloric  acid  without 
change,  but  the  solution  on  cooling  deposits  crystals  which  are  of  the  opake  acid, 
and  a  flash  of  light,  which  may  be  perceived  in  the  dark,  is  emitted  in  the  formation 
of  each  crystal.  This  phenomenon  depends  upon  and  indicates  the  transition,  for  it 
does  not  occur  when  arsenious  acid  already  opaque  is  substituted  for  vitreous  acid, 
and  dissolved  and  allowed  to  crystallize  in  the  same  manner. 

A  still  greater  change  than  those  described,  is  induced  upon  certain  "bodies  by 
exposure  to  a  high  temperature,  without  any  corresponding  change  in  their  compo- 
sition. Several  metallic  peroxides,  such  as  alumina,  sesquioxide  of  chromium  and 
binoxide  of  tin,  cease  to  be  soluble  in  acids  after  being  heated  to  redness.  The 
same  is  true  of  a  variety  of  salts,  such  as  many  phosphates,  tungstates,  antimoniates, 
and  silicates.  Many  of  these  bodies  contain  water  in  combination,  when  most 
readily  dissolved  by  acids,  which  constituent  is  dissipated  at  a  high  temperature,  but 
in  general  before  the  loss  of  solubility  occurs,  so  that  the  contained  water  alone  is 
not  the  cause  of  the  solubility.  Berzelius  remarked  an  appearance  often  observable 


152  ISOMEKISM. 

when  such  bodies  are  under  the  influence  of  heat,  and  in  the  act  of  passing  from 
the  soluble  to  the  insoluble  state.  They  suddenly  glow  or  become  luminous,  rising 
in  temperature  above  the  containing  vessel,  from  a  discharge  of  heat.  The  rare 
mineral  gadolinite,  which  is  a  silicate  of  yttria,  affords  a  beautiful  example  of  this 
change.  When  heated  it  appears  to  burn,  emits  light,  and  becomes  yellow,  but  un- 
dergoes no  change  in  weight.  Fluorspar,  and  many  other  crystalline  substances, 
exhibit  a  feeble  phosphorescence  when  heated,  which  has  no  relation  to  this  change, 
and  is  to  be  distinguished  from"  it. 

The  circumstance  most  certain  respecting  this  change  in  bodies,  which  affects  so 
deeply  their  chemical  properties,  is  that  the  bodies  do  not  contain  a  quantity  of  heat, 
after  the  change,  which  they  must  have  possessed  before  its  occurrence  in  a  com- 
bined or  latent  form.  No  ponderable  constituent  is  lost,  but  there  is  this  loss  of 
heat.  A  change  of  arrangement  of  the  particles,  it  is  true,  must  occur  at  the  same 
time  in  some  of  these  bodies,  such  as  is  observed  when  sulphite  of  soda  is  converted 
by  heat  into  a  mixture  of  sulphate  of  soda  and  sulphuret  of  sodium,  without  change 
of  weight;  but  it  would  be  difficult  to  apply  an  explanation  of  this  nature  to  oxides, 
such  as  alumina  and  binoxide  of  tin,  which  contain  only  two  constituents,  and  still 
more  so  to  an  element  such  as  carbon.  The  loss  of  heat  observed  will  afford  all  the 
explanation  necessary,  if  heat  be  admitted  as  a  constituent  of  bodies  equally  essential 
as  their  ponderable  elements.  As  the  oxide  of  chromium  possesses  more  combined 
heat  when  in  the  soluble  than  in  the  insoluble  state,  the  first  may  justly  be  viewed 
as  the  higher  caloride,  and  the  body  in  question  may  have  different  proportions  of 
this  as  well  as  of  any  other  constituent.  But  it  is  to  be  regretted  that  our  know- 
ledge respecting  heat  as  a  constituent  of  bodies  is  extremely  limited ;  the  definite 
proportion  in  which  it  enters  into  ice  and  other  solids  in  melting,  and  into  steam 
and  vapours,  has  been  studied,  and  also  the  proportion  emitted  during  the  combus- 
tion of  many  bodies,  which  has  likewise  proved  to  be  definite.  But  the  influence 
which  its  addition  or  subtraction  may  have  on  the  chemical  properties  of  a  body  is 
at  present  entirely  matter  of  conjecture.  The  phenomena  under  consideration  seem 
to  require  the  admission  of  heat  as  a  true  constituent  which  can  modify  the  proper- 
ties of  bodies  very  considerably ;  otherwise  a  great  physical  law  must  be  abandoned, 
namely,  that  "no  change  of  properties  can  occur  without  a  change  of  composition." 
But  if  heat  be  once  admitted  as  a  chemical  constituent  of  bodies,  then  a  solution  of 
the  presont  difficulties  may  be  looked  for,  for  nothing  is  more  certain  than  that  "  a 
change  in  composition  will  account  for  any  change  in  properties."  Heat  thus  com- 
bined in  definite  proportions  with  bodies,  and  viewed  as  a  constituent,  must  not  be 
confounded  with  the  specific  heat  of  the  same  bodies,  or  their  capacity  for  sensible 
heat,  which  may  have  no  relation  to  their  combined  heat. 

SECTION   VI.  —  ISOMERISM. 

In  such  changes  of  properties  as  have  already  been  described,  the  individuality 
of  the  body  is  never  lost.  But  numerous  instances  have  presented  themselves  of 
two  or  more  bodies  possessing  the  same  composition,  which  are  unquestionably  dif- 
ferent substances,  and  not  mutually  convertible  into  each  other.  Different  bodies 
thus  agreeing  in  composition,  but  differing  in  properties,  are  said  to  be  isomeric, 
(from  t'flo$,  equal,  and  ^poj,  part),  and  their  relation  is  termed  isomerism.  The  dis- 
covery of  such  bodies  excited  much  interest,  and  they  have  received  a  considerable 
share  of  the  attention  of  chemists.  But  the  result  of  a  careful  study  of  the  bodies 
associated  by  similarity  of  composition,  though  differing  in  properties,  has  been  upon 
the  whole  unfavourable  to  the  doctrine  of  isomerism.  Isomeric  bodies  have  in 
general  been  proved  by  the  progress  of  discovery  to  agree  in  the  relative  proportion 
of  their  constituents  only,  and  to  differ  either  in  the  aggregate  number  of  the  atoms 
composing  them,  or  in  the  mode  of  arrangement  of  these  atoms ;  and  although  new 
cases  of  isomerism  are  constantly  arising,  others  are  removed  as  they  come  to  admit 
of  explanation.  This  is  what  was  to  be  expected,  for  isomerism  in  the  abstract  is 


ISOMERISM.  153 

improbable  ;  a  difference  in  properties  between  bodies,  without  a  difference  in  their 
composition,  appearing  to  be  an  effect  without  a  sufficient  cause.  Hence,  the  term 
isomerisra  is  now  generally  employed  in  a  limited  sense,  to  indicate  simply  the 
identity  in  composition  of  two  or  more  bodies  as  expressed  in  the  proportion  of  their 
constituents  in  100  parts.  Several  classes  of  such  isomeric  bodies  may  be  formed. 

The  members  of  the  most  numerous  class  of  isomeric  bodies  differ  in  atomic  weight. 
Thus  we  know  at  present  three  gases,  three  or  four  liquids,  and  as  many  solids,  which 
all  consist  exactly  of  carbon  and  hydrogen,  in  the  proportion  of  one  atom  to  one 
atom,  or,  in  weight,  of  86  parts  of  carbon  and  14  of  hydrogen,  very  nearly.  These 
agree  in  ultimate  composition,  but  differ  completely  in  every  other  respect.  But  a 
representation  of  their  chemical  constitution  explains  at  once  the  cause  of  the  differ- 
ences they  present,  as  is  obvious  in  the  following  formulae  of  four  well  characterized 
members  of  this  isomeric  group  :  — 

Equivalents  and  combining  measure. 
Olefiantgas  ....................................  C4  H4  or  4  volumes. 

Gas  from  oil  ...................................  C8  H8  or  4  volumes. 

Naphthene  .....................................  C,6H16  or  4  volumes. 

Cetene  ..........................................  C32H32  or  4  volumes. 

It  thus  appears  that  the  atom  of  cetene  contains  twice  as  many  atoms  of  carbon  and 
hydrogen  as  the  atom  of  naphthene,  four  times  as  many  as  the  atom  of  the  gas  from 
oil,  and  eight  times  as  many  as  the  atom  of  olefiant  gas  ;  while  as  the  atom  of  all 
these  bodies  affords  the  same  measure  of  vapour,  or  four  volumes,  they  must  differ 
as  much  in  density  as  they  do  in  the  number  of  their  constituent  atoms.  It  is  not 
surprising,  therefore,  that  they  all  possess  different  and  peculiar  properties.  Several 
groups  of  bodies  might  be  selected  from  the  Table  at  page  130,  which  have  a  simi- 
lar relation  to  each  other,  the  number  of  their  atoms  being  different,  although  their 
relative  proportion  is  the  same  :  such  as  — 

Oil  of  lemons  .................................................  .  .  C10H8 

Oil  of  turpentine  ................................................  C2oH16 

and, 
Naphthaline  .....................................................  C20H8 

Paranaphthaline  .....................  * 


A  still  more  remarkable  case  is  presented  by  alcohol  and  the  ether  from  wood-spirit, 
in  which  there  is  identity  of  condensation  as  well  as  of  composition,  with  different 
equivalents.  The  vapours  of  these  two  liquids  have  in  fact  the  same  specific  gravity, 
and  contain,  under  equal  volumes,  equal  quantities  of  carbon,  hydrogen,  and  oxygen. 
But  we  know  that  they  are  of  a  different  type,  alcohol  being  the  hydrated  oxide  of 
ethyl,  and  ether  of  wood-spirit  the  oxide  of  methyl,  so  that  their  constitution  and 
rational  formulas  are  quite  different  :  — 

Alcohol  ................................................  C4H50  +  HO. 

Ether  of  wood-spirit  ..................................  C2H30. 

In  another  class  of  isomeric  bodies,  the  atomic  weight  may  be  equal,  as  well  as 
the  elementary  composition.  A  pair  belonging  to  this  class  are  known,  which  co- 
incide besides  in  the  specific  gravity  of  their  vapours.  The  composition  and  atom 
of  both  the  formiate  of  the  oxide  of  ethyl  (formic  ether)  and  the  acetate  of  oxide  of 
methyl,  may  be  represented  by  C6H504  :  the  density  of  both  their  vapours  is  2574  : 
and  what  is  very  remarkable,  these  bodies  in  their  ordinary  liquid  state  almost  co- 
incide in  properties,  the  density  of  formic  ether  being  0-916,  and  that  of  the  acetate 
of  methylene  0-919,  (density  of  water  being  =1.000),  while  the  first  boils  at  133°, 
and  the  last  at  1364°.  But  when  acted  on  by  alkalies,  their  products  are  entirely 
different,  the  one  affording  formic  acid  and  alcohol,  and  the  other  acetic  acid  and 
wood-spirit.  Each  of  the  isomeric  bodies  in  question  contains,  indeed,  two  dif- 


154   ARRANGEMENT  OF  ELEMENTS  IN  COMPOUNDS. 

fcrent  binary  compounds,  and  their  constitution  is  truly  represented  by  different; 
formulae  :  — 

Formiate  of  oxide  of  ethyl C4H50  +  C2H03 

Acetate  of  oxide  of  methyl C2H30  +  C4H303 

in  which  the  same  atoms  are  seen  to  be  very  differently  arranged.  The  term 
metameric  has  been  applied  to  bodies  so  related, 

The  last  class  of  isomeric  bodies  are  of  the  same  atomic  weights,  but  their  consti- 
tution or  molecular  arrangement  being  unknown,  their  isomerism  cannot  at  present 
be  explained.  It  can  scarcely  be  doubted,  however,  that  their  molecular  arrange- 
ment is  really  different. 

One  pair  of  such  isomeric  bodies  will  illustrate  the  coincidences  observed  not  at 
all  unfrequently  among  organic  substances.  The  racemic  and  tartaric  acids,  of 
which  the  composition  is  the  same,  exhibit  a  similarity  of  properties,  and  a  parallel- 
ism in  their  chemical  characters,  that  are  truly  astonishing.  These  acids  are  found 
together  in  the  grape  of  the  Upper  Rhine.  They  differ  considerably  in  solubility, 
the  racemic  being  the  least  soluble,  so  that  they  may  be  separated  from  each  other 
by  crystallization ;  and  the  racemic  acid  contains  an  atom  of  water  of  crystallization, 
which  is  not  found  in  the  crystals  of  tartaric  acid.  They  form  salts  which  corre- 
spond very  closely  in  their  solubility  and  other  properties.  The  bitartrate  and  bira- 
cemate  of  potassa  are  both  sparingly  soluble  salts :  the  tartrates  and  racemates  of 
lime,  lead,  and  barytes,  are  all  alike  insoluble.  Both  acids  form  a  double  salt  with 
soda  and  ammonia,  which  is  an  unusual  kind  of  combination.  But  what  is  most 
surprising,  crystals  of  these  double  salts  not  only  coincide  in  the  proportion  of  their 
water  and  other  constituents,  and  in  the  composition  of  their  acids,  but  also  in  exter- 
nal form,  having  been  observed  by  Mitscherlich  to  be  isomorphous.  A  nearer  ap- 
proach to  identity  could  scarcely  be  conceived  than  is  exhibited  by  these  salts,  which 
are,  indeed,  the  same  both  in  form  and  composition.  The  crystallized  acids  are  both 
modified  in  an  unusual  manner  by  heat,  and  form  three  classes  of  salts,  as  phosphoric 
acid  does.  The  formulae  of  both  acids  in  their  ordinary  class  of  salts  is  C8H4010-f 
two  atoms  of  base  (Fremy)  ]  but  by  no  treatment  can  the  one  acid  be  transmuted 
into  the  other.  Lastly,  every  organic  acid  produces  a  new  acid  by  destructive  dis- 
tillation, which  is  peculiar  to  it,  and  is  termed  its  pyr-acid.  Now  racemic  and 
tartaric  acid,  when  destroyed  by  heat,  agree  in  giving  birth  to  one  and  the  same 
pyr-acid. 

The  allatropy  of  elements  has  been  supposed  to  throw  light  upon  the  multiplica- 
tion of  series  of  compounds  arising  from  one  radical,  and  the  isomerism  of  certain 
compounds.  Fused  sulphur  passes  through  several  allatropic  conditions  as  its  tem- 
perature is  raised,  in  which  it  is  imagined  that  the  equivalent  of  the  element  may  be 
doubled,  tripled,  and  even  quadrupled  by  a  coalition  of  so  many  single  atoms  and 
the  formation  of  compound  atoms,  which  are  distinguished  as  a  sulphur,  |3  sulpnur, 
8  sulphur,  y  sulphur,  &c.  In  the  different  series  of  the  oxygen  acids  of  sulphur, 
containing  one,  two,  three,  and  four  equivalents  of  sulphur,  the  different  allatropic 
varieties  of  sulphur  are  imagined  to  exist.  Silicium  in  its  combustible  and  incom- 
bustible allatropic  conditions  may  thus  give  rise  to  different  silicic  acids,  and  alla- 
tropic borons  and  tungstens  to  the  isomeric  boric  and  tungstic  acids. 

SECTION   VII. ARRANGEMENT   OF   THE   ELEMENTS   IN    COMPOUNDS. 

The  names  of  some  compounds  imply  that  they  contain  other  compounds,  and  in-\ 
dicate  a  certain  atomic  constitution,  while  the  names  of  other  compounds  express 
no  particular  arrangement  of  their  constituent  atoms,  but  leave  it  to  be  inferred  that 
the  atoms  are  all  directly  combined  together.  Thus  sulphate  of  soda  implies  the 
continued  existence  of  sulphuric  acid  and  soda  in  the  salt,  while  nitric  acid,  or 
binoxide  of  hydrogen,  supposes  no  partition  of  the  compound  to  which  it  is  applied. 
But  it  is  to  be  remembered  that  the  original  framers  of  the  nomenclature  were 


CONSTITUTION   OF   SALTS.  155 

guided  more  by  facilities  of  an  etymological  nature,  in  constructing  such  terms,  than 
by  views  of  the  constitution  of  compounds. 

Of  a  binary  compound  containing  single  atoms  of  its  constituents,  there  cannot  be 
two  modes  of  representing  the  constitution;  but  where  one  of  the  constituents  is 
present  in  the  proportion  of  two  or  more  atoms,  several  hypotheses  can  always  be 
formed  of  their  mode  of  aggregation.  In  a  series  of  binary  combinations  of  the 
same  elements,  such  as  that  of  nitrogen  and  oxygen,  N015  N02,  N03,  N04,  N05, 
the  simplest  view  has  generally  been  taken,  namely,  that  it  is  the  elements  them- 
selves which  unite.  But  in  particular  cases  the  chemist  is  often  involuntarily  led 
into  another  opinion.  Thus  binoxide  of  nitrogen  is  so  often  a  product  of  the  decom- 
position of  nitric  acid,  that  the  acid  appears  more  like  a  compound  of  that  oxide  of 
nitrogen  with  oxygen,  than  a>  compound  of  nitrogen  itself  with  oxygen.  When  tho 
binoxide  of  hydrogen  was  first  discovered  by  Thenard,  he  was  led  by  the  whole  train 
of  its  properties  to  view  it  as  a  compound  of  water  and  oxygen,  into  which  it  is 
resolved  with  so  much  facility,  and  to  name  it  accordingly  oxygenated  water,  which 
it  may  be,  and  not  a  direct  combination  of  hydrogen  and  oxygen  ;  or  its  formula  be 
H0-|-0,  and  not  H02.  The  periodide  of  potassium,  and  the  other  analogous  com- 
pounds obtained  by  dissolving  iodine  in  metallic  iodides,  were  first  termed  iodurelted 
iodides  from  similar  considerations,  and  the  hyposulphites,  obtained  by  dissolving 
sulphur  in  sulphites,  sulphuretted  sulphites.  It  may  be  doubted  whether  chemists 
would  return  with  advantage  to  any  of  these  expressions,  the  views  of  composition 
which  they  indicate  being  uncertain,  and  not  offering  a  sufficient  inducement  to  de- 
part from  the  more  systematic  designations.  The  binoxide  of  hydrogen,  for  instance, 
may  be  easily  resolved  into  water  and  oxygen,  not  because  water  pre-exists  in  it,  but 
because  water  is  a  compound  of  great  stability,  and  is  formed  when  binoxide  of  hy- 
drogen is  decomposed.  Nitric  acid,  also,  is  as  likely  to  be  a  compound  of  quadoxide 
of  nitrogen  with  an  additional  atom  of  oxygen,  as  of  binoxide  of  nitrogen  with  three 
atoms  of  the  same  element. 

Certain  compound  bodies,  however,  have  been  observed  to  act  the  part  of  a  simple 
body  in  combination,  and  can  be  traced  through  a  series  of  compounds.  The  fol- 
lowing substances,  for  instance,  may  be  represented  with  considerable  probability  as 
compounds  of  carbonic  oxide,  as  in  the  formulae  :  — 

CO,          carbonic  oxide. 
CO  -f-  0,  carbonic  acid. 
CO  +  Cl,  chloroxicarbonic  acid. 
SCO  +  0,  oxalic-  acid. 

Carbonic  oxide  is  said  to  be  the  radical  of  this  series,  a  name  applied  to  any  com- 
pound which  is  capable  of  combining  with  simple  bodies,  as  carbonic  oxide  appears 
to  do  with  oxygen  and  chlorine  in  these  compounds.  Messrs.  Liebig  and  Wohler 
first  proved  by  decisive  experiments  that  such  a  radical  exists  in  the  benzoic  combi 
nations,  which  may  be  represented  thus  :  — 


Cj4H502  +  0,  benzoic  acid. 

C14H502  +  H,  essential  oil  of  bitter  almonds. 

Ci4H602+  Cl,  chloride  of  benzoyl,  &c. 

Cyanogen  was  the  first  recognised  member  of  the  class  of  compound  radicals,  of 
which  the  number  known  to  chemists  is  constantly  increasing,  and  which  appear  to 
pervade  the  whole  compounds  of  organic  chemistry.  In  combining  with  simple 
bodies,  radicals  act  the  part  of  other  simple  bodies,  such  as  metals,  chlorine,  oxygen, 
&c.,  which  they  replace  in  compounds. 

With  the  elements  themselves  compound  radicals  may  be  divided  into  two  great 
classes  :  — 

The  Basyl  class,  consisting  of  metals  the  oxides  of  which  are  bases,  hydrogen, 
the  corresponding  compound  radicals,  ammonium,  ethyl,  &c.  These  are  electro- 
positive bodies. 


156       ARRANGEMENT    OF    ELEMENTS    IN    COMPOUNDS. 

The  salt-radical  class  —  chlorine,  sulphur,  oxygen,  &c.,  with  cyanogen,  and  other 
compound  radicals  which  combine  with  metals  and  other  members  of  the  former 
class,  and  form  salts  or  compounds  partaking  of  the  saline  character.  Such  radicals 
are  also  termed  salogens ;  they  are  electro-positive. 

Constitution  of  salts.  —  Of  the  supposed  combinations  of  binary  compounds  with 
binary  compounds,  the  most  numerous  and  important  class  are  salts.  Sulphate  of 
soda  is  commonly  viewed  as  a  direct  combination  of  sulphuric  acid  and  soda,  each 
preserving  its  proper  nature  in  the  compound  ]  and  so  are  all  similar  compounds  of 
an  acid  oxide  with  a  basic  oxide.  An  oxygen  acid  is  allowed  to  exist  in  them,  and 
they  are  particularly  distinguished  as  "oxygen-acid  salts/'  But  an  opinion  was 
promulgated  long  ago  by  Davy,  that  these  salts  might  be  constituted  on  the  plan  of 
the  binary  compounds  of  the  former  class,  and  their  hyd rated  acids  on  the  plan  of  a 
hydrogen  acid ;  a  view  which  is  supported  by  many  analogies,  and  has  latterly  had 
a  preference  given  to  it  by  some  of  our  leading  chemical  authorities.  It  is,  there- 
fore, deserving  of  serious  consideration. 

One  class  of  acids,  the  hydrogen  acids,  and  the  salts  which  they  produce  with 
alkalies,  are  unquestionably  binary  compounds,  and  were  assumed  by  Davy  as  the 
types  of  acids  and  salts  in  general.  Hydrochloric  acid  is  composed  of  two  elements, 
chlorine  and  hydrogen,  and  with  soda  it  forms  water  and  chloride  of  sodium,  thus : — 


Soda '*1-1'~  ^     Chloride  of  sodium. 

the  hydrogen  of  the  acid  being  replaced  by  sodium  in  the  salt  formed.  Hydrocya- 
nic is  another  hydrogen  acid,  of  which  cyanide  of  sodium  is  a  salt.  In  general 
terms,  a  radical  (which  may  be  either  simple  or  compound,  like  chlorine  or  cyano- 
gen) forms  an  acid  with  hydrogen,  and  a  salt  with  sodium  or  any  other  metal. 

Hydrated  sulphuric  acid,  which  consists  of  sulphuric  acid  and  an  atom  of  water, 
HO-4-SOg,  is  represented  as  a  hydrogen  acid  by  transferring  the  oxygen  of  the 
water  to  the  sulphuric  acid  to  form  a  new  radical,  S04,  which  is  supposed  to  be  in 
direct  combination  with  the  remaining  atom  of  hydrogen,  as  H  -f  S04.  In  sulphate 
of  soda,  the  oxygen  of  the  soda  is  in  the  same  manner  transferred  to  the  acid,  or  the 
formula  of  the  salt  is  changed  from  NaO-j-S03  to  Na  +  S04.  To  S04,  the  salt- 
radical  of  sulphates,  the  name  sulphion  has  been  applied,  from  the  circumstance  that, 
in  the  voltaic  decomposition  of  a  sulphate,  S04,  travels  to  the  positive  pole,  and  the 
metal  or  hydrogen  to  the  negative  pole.  Its  compounds,  or  the  sulphates,  become 
sulpldonides.  The  hydrated  acid  and  its  soda  salt  are  thus  named  and  denoted  on 
the  two  views  of  their  constitution — 

I.    ON   THE   ACID   THEORY  I 

Hydrated  sulphuric  acid,  sulphate  of  oxide  of  hydrogen,  or 

hydric  sulphate H0  +  S03 

Sulphate  of  soda,  sulphate  of  oxide  of  sodium,  or  soda  sulphate     NaO  -f  S03 

II.    ON    THE    SALT-RADICAL    THEORY: 

Sulphionide  of  hydrogen II  +  S04 

Sulphionide  of  sodium Na+S04 

which  last  formulae  are  strictly  comparable  with  those  of  an  admitted  hydrogen  acid 
and  its  salt,  such  as — 

Hydrochloric  acid  or  chloride  of  hydrogen H  -f  Cl 

Chloride  of  sodium. Na-f-Cl 

or  as — 

Hydrocyanic  acid  or  cyanide  of  hydrogen H  -f  C2N" 

Cyanide  of  sodium Na  -f  C2N 


CONSTITITUTION  OP   SALTS.  157 

which  thus  appear  compounds  of  three  different  radicals,  chlorine  (Cl),  cyanogen 
(C2N),  and  sulphion  (S04),  with  the  same  elementary  bodies,  hydrogen  and  sodium. 
Sulphion  is  known  only  in  combination,  and  has  not  been  obtained  in  a  separate 
state  like  chlorine  and  cyanogen.  The  body,  sulphuric  acid,  S03,  which  may  be 
separated  from  some  sulphates,  and  can  exist  by  itself,  is  looked  upon  as  a  product 
of  the  decomposition  of  these  salts,  and  not  to  pre-exist  in  them,  so  that  a  secondary 
character  is  assigned  to  it. 

Hydrated  nitric  acid,  or  aqua  fortis,  becomes  a  hydrogen  acid  by  the  creation  of  a 
nitrate  radical,  nitration.  It  is  the  nitrationide  of  hydrogen  instead  of  the  nitrate 
of  water — 

H  +  N06,  instead  of  H0  +  N06. 

The  nitrate  of  potassa  becomes  the  nitrationide  of  potassium,  and  so  of  all  other 
nitrates. 

It  is  evident  that  the  same  view  is  applicable  to  hydrated  oxygen  acids  in  general, 
which  may  be  made  hydrogen  acids,  by  assuming  the  existence  of  a  new  salt-radical 
for  each,  containing  an  atom  more  of  oxygen  than  the  oxygen  acid  itself,  and  capable 
of  combining  directly  with  hydrogen  and  the  metals.  The  class  of  oxygen  acid  salts 
is  thus  abolished,  and  they  become  binary  compounds  like  the  chlorides  and  cyanides. 
Even  oxygen  acids  themselves  can  no  longer  be  recognized.  It  is  not  sulphuric  acid 
(S03),  but  what  was  former  viewed  as  its  compound  with  water,  that  is  the  acid, 
and  it  is  a  hydrogen  acid.  The  properties  which  characterize  acids  are  undoubtedly 
only  observed  in  the  hydrates  of  the  oxygen  acids.  Thus  the  anhydrous  sulphuric 
acid  does  not  redden  litmus,  and  exhibits  a  disposition  to  combine  with  salts,  such 
as  chloride  of  potassium  and  sulphate  of  potassa,  wither  than  with  bases.  The  liquid 
carbonic  acid  has  little  affinity  for  water,  does  not  combine  directly  with  lime,  but 
dissolves  in  alcohol,  ether,  and  essential  oils,  like  certain  neutral  bodies.  It  is  only 
when  associated  with  water  that  the  bodies  referred  to  exhibit  acid  properties,  and 
then  hydrogen  acids  may  be  prochiced.  I 

On  this  view,  it  is  obvious  that  the  acid  and  salt  are  really  bodies  of  the  same 
constitution,  hydrochloric  acid  being  the  chloride  of  hydrogen,  as  common  salt  is  the 
chloride  of  sodium,  and  sulphuric  acid  and  sulphate  of  soda  being  the  sulphionides 
of  hydrogen  and  of  sodium.  The  acid  reaction  and  sour  taste  are  not  peculiar  to 
the  hydrogen  compound,  and  do  not  separate  it  from  the  others ;  the  chloride,  sul- 
phionide,  and  nitrationide  of  copper  being  nearly  as  acid  and  corrosive  as  the  chlo- 
ride, sulphionide,  and  nitrationide  of  hydrogen,  and  clearly  bodies  of  the  same  cha- 
racter and.  composition  :  they  are  all  equally  salts  in  constitution.  The  term  "  acid" 
is  not  absolutely  required  for  any  class  of  bodies  included  in  the  theory,  and  might, 
therefore,  be  dropped,  if  it  were  not  that  an  inconvenience  would  be  felt  in  having 
no  common  name  for  such  bodies  as  anhydrous  sulphuric  acid  S03,  anhydrous  nitric 
acid  N05,  sulphurous  acid  S02,  carbonic  acid  C02,  &c.  To  these  substances,  which 
first  bore  the  name,  it  should  now  be  confined.  In  considering  the  generation  of 
salts,  three  orders  of  bodies  would  be  admitted,  as  in  the  following  tabular  exposition 
of  a  few  examples  : — 

I.  II.  III. 

The  Acid.  The  Salt-radical.  The  Salt. 

S03 S04  S04  +  H  or  a  metal. 

N05 N06 NO6  +  H  or  a  metal. 

NC2 NC2+H  or  a  metal. 

Cl     ClfH  or  a  metal.  { 

The  first  term  of  the  series,  or  "the  acid/'  is  wanting  in  the  last  two  examples; 
and  that  is  the  peculiarity  of  those  bodies  which  constituted  the  original  class  of 
hydrogen  acids  and  their  salts  :  while,  to  the  old  class  of  oxygen  acid  salts,  both  an 
acid  and  a  salt-radical  can  be  assigned,  as  in  the  first  two  examples. 
The  peculiar  advantages  of  the  salt-radical  theory  are — 


158     ARRANGEMENT   OF   THE   ELEMENTS  IN   COMPOUNDS. 

First :  That,  instead  of  two,  it  makes  but  one  great  class  -of  salts,  assimilating  in 
constitution  bodies  which  certainly  resemble  each  other  in  properties.  Chloride  of 
sodium  and  sulphate  of  soda  are  both  neutral,  and  possess  a  common  character, 
which  is  that  of  a  soda  salt ;  but  they  are  separated  widely  from  each  other  on  the 
view  of  their  constitution  which  is  expressed  in  their  names. 

Secondly :  It  accounts  for  a  remarkable  law  which  is  observed  in  the  construction 
of  salts ;  namely,  that  bases  always  combine  with  as  many  atoms  of  acid  as  they 
themselves  contain  of  oxygen  j  a  protoxide,  which  contains  one  atom  of  oxygen, 
combining  and  forming  a  neutral  salt  with  one  atom  of  an  oxygen  acid;  while  an 
oxide  which  contains  two  atoms  of  oxygen  to  one  of  metal,  like  binoxide  of  palla- 
dium, forms  a  neutral  salt  with  two  atoms  of  acid ;  and  an  oxide  of  three  atoms  ot 
oxygen  to  two  of  metal,  like  sesquioxide  of  iron,  forms  a  neutral  salt  with  three 
atoms  of  acid.  The  acid  and  oxygen  are  thus  always  together  in  the  exact  propor- 
tion to  form  the  salt-radical,  there  being  always  an  atom  of  oxygen  for  every  atom 
of  acid  in  the  salt.  This  will  appear  more  distinctly  in  the  following  formulae, 
which  exhibit  the  composition  of  the  neutral  sulphates  of  a  metal  in  four  different 
states  of  oxidation,  an  atom  of  metal  being  represented  by  K, : — 

FORMULAE   OP   NEUTRAL   SULPHATES. 

I.  II. 

As  consisting  of        As  consisting  of  Metal 
Oxide  and  Acid.  and  Salt-radica^ 

R0  +  S03  R  +  S04    as  in  sulphate  of  soda. 

R20-f  S03 R2-f  S04  as  in  sulphate  of  suboxide  of  mercury. 

R02  +  2S03 R-f-2S04  ...  as  in  sulphate  of  binoxide  of  palladium. 

RiOg-f  3S03 R2-f  3S04 as  in  sulphate  of  sesquioxide  of  iron. 

The  acid  is  seen  in  the  first  column  to  be  always  in  the  proper  proportion  to  form  a 
sulphionide  of  the  metal  in  the  second  column ;  and  these  sulphionides  correspond 
exactly  with  known  chlorides,  such  as  RC1,  R2C1,  RC12,  R2C13. 

Thirdly :  It  offers  a  more  simple  and  philosophical  explanation  of  the  action  of 
certain  metals  upon  acid  solutions,  and  of  the  decomposition  of  such  solutions  in 
other  circumstances.  Thus  when  zinc  is  introduced  into  hydrochloric  acid  (chloride 
of  hydrogen),  it  is  allowed  on  both  views,  that  the  metal  simply  displaces  the  hydro- 
gen which  is  evolved,  and  that  chloride  of  zinc  is  formed  in  the  place  of  chloride  of 
hydrogen.  In  the  same  way,  when  zinc  is  introduced  into  diluted  sulphuric  acid, 
which  contains  the  sulphionide  of  hydrogen  on  the  binary  theory,  hydrogen  is  simply 
displaced  and  evolved  as  before,  and  the  sulphionide  of  zinc  is  formed  in  the  place 
of  the  sulphionide  of  hydrogen.  The  metal  in  question  appears  to  be  incapable  of 
decomposing  pure  water  by  displacing  its  hydrogen  at  the  temperature  of  the  air ; 
but  this  fact  does  not  interfere  with  the  preceding  explanation,  as  zinc  may  have  a 
greater  affinity  for  sulphion  than  for  oxygen,  and,  therefore,  be  capable  of  decom- 
posing the  sulphionide,  but  not  the  oxide  of  hydrogen.  If  the  acid  solution,  how- 
ever, contains  sulphate  of  water,  as  it  does  on  the  old  view,  then  zinc  does  and  does 
not  decompose  water  j  decomposing  it  when  in  combination,  but  not  when  free.  It 
becomes  necessary  to  assume  that  the  presence  of  the  acid  enhances  the  affinity  of 
the  metal  for  the  oxygen  of  the  water,  in  a  manner  which  cannot  be  clearly  ex- 
plained j  for  the  solubility  of  oxide  of  zinc  in  the  acid,  to  which  the  influence  of 
the  acid  is  often  ascribed,  accounts  for  the  continuance  of  the  action,  by  providing 
for  the  removal  of  the  oxide,  rather  than  for  its  first  commencement.  The  pheno- 
mena of  the  decomposition  of  an  acid  solution  in  the  voltaic  circle,  are  also  most 
simply  explained  on  the  salt-radical  theory.  Oxide  of  hydrogen  and  sulphionide  of 
hydrogen,  are  both  binary  "electrolytes/'  which  are  decomposed  in  the  voltaic  circle 
in  the  same  manner,  although  not  with  equal  facility ;  the  common  element,  hydro- 
gen, proceeding  from  both  to  the  negative  electrode,  and  oxygen  in  the  one  case  and 
sulphion  in  the  other  to  the  positive  electrode.  The  sulphion  finds  water  there,  and 


CONSTITUTION    OF    SALTS.  159 

resolves  itself  into  sulphionide  of  hydrogen  and  free  oxygen.  The  decomposition 
of  the  sulphionide  of  sodium  or  any  other  salt  may  be  explained  in  the  same  simple 
manner ;  while  on  the  other  view,  it  must  be  assumed  that  a  simultaneous  transfer- 
ence between  the  electrodes  of  acid  and  alkali  with  the  oxygen  and  hydrogen  of 
water  takes  place ;  and  the  effect  of  the  acid  in  promoting  the  decomposition  of  the 
water  remains  unaccounted  for. 

When  a  metallic  oxide  is  dissolved  in  an  acid  solution,  as  oxide  of  zinc  in  diluted 
sulphuric  acid,  the  reaction  which  occurs  is  thus  explained  on  the  binary  theory : 

Sulphionide  of  J  Hydrogen --.  Water. 

hydrogen  . . .  {  Sulphion 


Oxide  of      ..  of  zinc; 


as  in  the  reaction  between  the  same  oxide  and  hydrochloric  acid  (page  156). 

The  chief  objections  to  the  salt-radical  theory,  are  — 

First  :  The  creation  of  so  many  hypothetical  radicals  ;  namely,  one  for  every  class 
of  oxygen-acid  salts.  But  it  is  to  be  remembered  that  the  great  proportion  of  oxygen 
acids,  such  as  acetic,  oxalic,  &c.  are  equally  of  an  ideal  character,  and  cannot  be 
exhibited  in  a  separate  state. 

Secondly  :  The  peculiarities  of  the  salts  of  phosphoric  acid  which  are  supposed  to 
be  inimical  to  the  new  view.  That  acid  forms  three  different  and  independent  classes 
of  salts,  containing  respectively  one,  two,  and  three,  equivalents  of  base  to  one  of 
acid.  On  the  binary  theory,  these  three  classes  of  salts  must  contain  three  different 
salt-radicals,  combined  respectively  with  one,  two,  and  three  equivalents  of  hydrogen 
or  metal.  The  three  phosphates  of  water  and  the  corresponding  phosphionides  of 
hydrogen  would  be  represented  as  follows  :  —  , 

I.  II.  III. 

H0  +  P05  ..................  2HO  +  P05  ..................  3HO  +  P06 

3H  +  P08 


Such  salt-radicals  and  such  compounds  with  hydrogen  startle  us,  from  their  novelty, 
but  it  may  be  questioned  whether  they  are  really  more  singular  than  the  anormal 
classes  of  phosphates,  containing  several  equivalents  of  base,  for  which  they  are 
substituted,  but  which  we  have  been  more  accustomed  to  contemplate.  All  the 
salt-radicals  known  in  a  separate  state,  such  as  chlorine  and  cyanogen,  combine  with 
one  equivalent  only  of  hydrogen,  or  are  monobasylous,  but  it  would  be  unfair  to 
assume  in  the  present  imperfect  state  of  our  knowledge  that  other  salt-radicals  may 
not  exist,  capable  of  combining  with  two  or  three  equivalents  of  hydrogen,  as  the 
phosphate-radicals  are  supposed  to  do.  The  existence  of  at  least  one  such  radical  is 
highly  probable,  as  will  afterwards  appear. 

In  conclusion,  it  may  be  stated  that  neither  view  of  the  constitution  of  the  oxygen- 
acid  salts,  (which  alone  are  affected  by  this  discussion),  rests  on  demonstrative  evi- 
dence ;  they  are  both  hypotheses,  and  are  both  capable  of  explaining  all  the  pheno- 
mena of  the  salts.  But  to  whichever  of  them  a  speculative  preference  is  given,  we 
can  scarcely  avoid  using  the  language  of  the  acid  theory,  in  the  present  state  of 
chemical  science. 

[Additional  objections  may  be  urged  against  the  salt-radical  theory  : 
As  long  as  it  is  applied  to  salts  constituted  according  to  the  law  that  "bases  always 
combine  with  as  many  atoms  of  acid  as  they  themselves  contain  of  oxygen/'  the 
subject  is  without  difficulty,  but  when  it  is  applied  to  anhydrous  compounds  contain- 
ing more  than  one  equivalent  of  acid,  it  fails,  or  necessitates  the  creation  of  as  many 
hypothetical  salt-radicals  as  there  are  examples  of  this  kind.  Thus,  the  anhydrous 
sulphates  of  potassa  and  soda,  the  chromates,  &c.  are  not  mere  combinations  of  one 
equivalent  of  the  base  with  one  and  more  equivalents  of  the  acid,  but  become  com- 
pounds of  a  metal  with  a  greater  number  of  salt-radicals.  The  neutral  chromate  of 


160    ARRANGEMENT   OF   THE   ELEMENTS  IN   COMPOUNDS. 

potassa,  KO,  O03,  is  on  the  salt-radical  theory ;  K,  Cr04,  the  bichromate ;  KO, 
2O03,  is  K,  Cr207;  and  the  terchromate,  KO,  3Cr03,  is  K,  Cr3010;  or  potassium 
combined  with  three  different  and  new  substances,  each  requiring  a  new  and  distinc- 
tive name.  Moreover,  the  theory  is  involved  in  the  same  difficulty  when  the  attempt 
is  made  to  apply  it  to  those  salts  which  are  exceptions  to  the  above  law,  or  in  which 
the  number  of  atoms  of  oxygen  in  the  base  does  not  correspond  with  the  number 
of  atoms  of  acid.  The  following  example  may  be  taken  from  the  salts  of  tartario 
acid,  which,  considered  as  bibasic,  has  the  formula  C8H4010,  for  which  the  conven- 
tional symbol  T  may  be  substituted,  and  we  shall  then  have  four  of  the  salts  repre- 
sented below,  on  the  old  and  new  views  of  their  constitution : 

KO,  HO.  T=K,  H.  T02, Cream  of  tartar. 

KO,  NaO.  T  =  K,  Na.  TO. Rochelle  salt. 

KO,  Fe203.JT=K,  Fe2JT04 Tartarized  iron. 

KO,  Sb03.  T=K,  Sb.  T04 Tartar  emetic. 

In  the  first  two  formulae  the  elements  are  readily  transposed  to  suit  either  view ; 
but  in  the  two  latter  a  new  hypothetical  salt-radical  appears,  endowed  with  new 
powers,  viz.  the  capability  of  combining  respectively  with  two  atoms  of  metallic- 
radical  K,  Sb,  and  with  three  atoms  of  radical  K,  Fe2. 

This  theory  explains  very  readily  the  reaction  which  takes  place  when  water  is 
decomposed  under  the  influence  of  readily  oxidated  metals  and  hydrated  acids,  by 
the  supposition  that  the  metal  replaces  the  hydrogen  of  the  combined  water.  But 
there  exist  acids  of  which  we  have  no  known  hydrate,  equivalent  for  equivalent, 
carbonic,  chromic,  &c.  acids.  These  being  destitute  of  combined  water  do  not  admit 
of  similar  substitution;  no  hydrogen  being  combined,  no  replacement  can  take 
place. 

Any  theory,  to  be  perfect,  must  include  all  known  cases;  and  hence,  if  this  hypo- 
thesis is  not  applicable  to  all  oxygen  salts,  to  the  same  extent  as  former  views,  it 
fails  in  its  promised  advantages.  It  has  not  yet  been  carried  out  or  exhibited  in 
detail  by  its  advocates,  which  would  seem  to  show  they  are  aware  of  its  difficulties, 
and  are  not  yet  prepared  to  obviate  them.  One  of  the  points  requiring  explanation 
is  the  supposition  in  some  of  the  examples  quoted,  that  potassium  and  oxygen,  two 
elements  occupying  the  extremes  of  the  electro-chemical  series,  can  be  placed  in  con- 
tact with  each  other  without  combining,  a  supposition  requiring  a  subversion  of 
chemical  affinity  which  does  not  correspond  with  known  facts. 

It  is  not  evident  why  "oxygen-acid  salts  alone  are  affected  by  this  discussion." 
The  compounds  of  sulphur,  selenium,  &c.  are  very  analogous  in  character;  and  as 
sulphur-acids,  combine  only  with  sulphur  bases,  the  same  transfer  of  sulphur  will 
be  here  required  as  of  oxygen  in  the  former  salts,  giving  rise  to  as  many  new  sul- 
phur salt-radicals  as  those  of  oxygen.  —  R.  B.] 

Without  deciding  definitively  in  favour  of  one  or  other  of  the  rival  theories,  it  is 
well  to  keep  in  view  that  the  great  class  of  salts  includes  compounds  which  differ 
essentially  in  their  capacity  of  analytical  decomposition.  A  certain  number  of  salts 
contain  salt-radicals  which  can  be  isolated,  others  oxygen-acids  which  can  be  isolated, 
while  others  have  yet  afforded  neither  salt-radical  nor  acid  in  a  separate  state.  Hence, 
they  may  be  classed  as — 

1.  Salts  of  isolable  salt-radicals  :  chlorides,  cyanides,  sulphocyanides,  &c. 

2.  Salts  of  isolable  acids :  sulphates,  nitrates,  carbonates,  &c. 

3.  Salts  which  contain  neither  an  isolable  salt-radical  nor  an  isolable  acid  :  ace- 
tates, hyposulphites,  &c.     Even  admitting  that  all  salts  have  the  same  constitution, 
the  capability  of  breaking  up  in  such  different  ways  must  affect  their  modes  of  de- 
composition in  different  circumstances,  and  produce  differences  in  properties  which 
render  such  distinctions  important. 

It  has  become  further  necessary  to  recognize  three  classes  of  oxygen-acid  salts, 
which  in  the  language  of  the  acid  theory  contain  one,  two,  and  three  equivalents  of 
base  to  one  of  acid. 


CONSTITUTION    OF   SAT-TS.  161 

1.  Monobasic  wits — The  great  proportion  of  acids,  such  as  sulphuric,  nitric, 
&c.  neutralize  but  one  equivalent  of  base,  or  moro  correctly  combine  in  the  propor- 
tion of  one  equivalent,  of  acid  to  each  equivalent  of  oxygen  in  the  base,  and  form, 
therefore,  monobasic  ?alts.     (See  formula)  of  the  neutral  sulphates,  page  158).   But 
this  is  not  inconsistent  with  an  acid  forming  two  series  of  salts  with  the  same  base 
or  class  of  isomorphous  bases.     Thus  there  appear  to  be  two  well-marked  classes  of 
sulphates  of  the  magnesian  oxides,  which  agree  in  Laving  one  equivalent  of  base, 
but  differ  essentially  in  the  proportions  of  combined  water  which  they  affect.     In 
one  series  the  sulphate  is  combined  with  one,  three,  five,  or  seven  equivalents  of 
water.     Copperas  (a  sulphate  of  iron),  Epsom  salt  (a  sulphate  of  magnesia),  blue 
vitriol  (a  sulphate  of  copper),  and  most  of  the  well-known  magnesian  sulphates, 
belong  to  this  class,  which  may  be  called  the  copperas  class  of  snlphates.     All  the 
members  of  it  are  very  soluble  in  water,  and  form  double  salts  with  sulphate  of 
potassa.     The  other  series  affect  two,  four,  and  six  equivalents  of  water.     They  are 
less  known,  but  appear  to  be  of  sparing  solubility,  and  to  be  incapable  of  forming 
double  salts  with  sulphate  of  potassa.     Gypsum  or  sulphate  of  lime  belongs  to  this 
class,  which  may,  therefore,  be  called  the  gypsum  class  of  magnesian  sulphates. 
Sulphate  of  iron  is  said  to  crystallize  from  solution  in  sulphuric  acid  with  two  equi- 
valents of  water,  with  the  crystalline  form  and  sparing  solubility  of  gypsum.     Dr. 
Kane  obtained  a  sulphate  of  copper  with  four  equivalents  of  water,  by  exposing  the 
anhydrous  salt  to  the  vapour  of  hydrochloric  acid,  which  appears  to  be  the  second 
term  in  this  series ;  and  Mitscherlich  still  maintains  the  existence  of  a  peculiar  sul- 
phate of  magnesia  containing  six  equivalents  of  water  of  crystallization,  which  will 
constitute  the  third  term.     It  is  evident  that  the  cause  of  such  double  classes  of 
salts  is  as  deeply  seated  as  that  of  dimorphism,  and  hence,  possibly,  the  magnesian 
sulphate  itself,  which  exists  in  the  two  classes,  is  not  the  same  in  its  constitution 
with  reference  to  heat. 

2.  Bibasic  salts. — That  class  of  phosphates  which  received  the  name  of  pyro- 
phosphates,  was  the  first  in  which  one  equivalent  of  acid  was  found  to  neutralize  two 
equivalents  of  base ;  their  formulae  being  2RO,  P05.     The  classes  of  tartrates  and 
racemates  which  have  long  been  known  to  chemists,  are  also  bibasic  salts.     It  is  the 
character  of  a  bibasic  acid  to  unite  at  once  with  two  different  bases  of  the  same 
natural  family,  which  accounts  for  the  formation  of  Rochelle  salt,  the  tartrate  of 
potassa  and  soda,  of  which  the  formula  is  KO,  NaO  +  C8H4Oi0.     It  has  also  been 
shown   that   gallic   acid   is   bibasic,   the   gallate   of   lead   being   thus   composed : 
2PbO  -f  C7H03.     Now  if  we  attempt  to  make  this  a  monobasic  salt  by  dividing  the 
equivalents  both  in  base  and  acid  by  two,  an  equivalent  of  gallic  acid  would  come 
to  contain  half  an  equivalent  of  hydrogen,  which  Liebig  considers  as  conclusive 
against  the  division  of  its  atomic  weight.     Itaconic,  comenic,  euchronic,  fulminic, 
and  several  other  organic  bibasic  acids,  might  be  named.     The  compound  acids 
formed  by  the  union  of  two  others,  and  called  copulated  acids,  such  as  hyposulpho- 
benzoic  acid,  are  usually  of  this  class. 

3.  Tribasic  salts.  —  The  tribasic  phosphates  of  the  formula  3RO,  P05,  have 
likewise  proved  to  be  the  type  of  a  class  of  salts.     One  equivalent  of  arsenic  acid 
neutralizes  three  equivalents  of  base ;  so,  it  is  probable,  does  one  atom  of  phospho- 
rous acid.    Tannic  acid  also  saturates  three  atoms  of  base,  the  formula  of  the  tannate 
of  lead  being  3PbO  +  C18H509  (Liebig).     There  is  the  same  necessity  to  admit  that 
citric  acid  is  tribasic,  and  the  formula  of  a  citrate  3RO-f-C,aH60,,,  as  there  is  to 
allow  that  gallic  acid  is  bibasic.     Most  of  the  citrates  contain  two  equivalents  of 
fixed  base  and  one  of  water,  but  the  citrate  of  silver  contains  three  equivalents  of 
oxide  of  silver.     Cyanuric,  meconic,  camphoric,  and  several  other  organic  acids,  are 
tribasic. 

Two  of  the  three  atoms  of  base  in  this  class  of  salts  may  be  different,  as  is  ob- 
served in  certain  citrates,  cyanurates,  and  phosphates,  or  the  whole  three  may  be 
different,  as  in  the  phosphate  called  microcosmic  salt,  which  contains  at  once  soda. 
11 


162     ARRANGEMENT   OF   THE   ELEMENTS  IN   COMPOUNDS. 

oxide  of  ammonium,  and  water  as  bases.1  Two  or  more  of  the  bases  may  likewise 
be  isomorphous,  or  at  least  belong  to  the  same  natural  family  as  soda  and  oxide  of 
ammonium,  water,  and  magnesia. 

Salts  usually  denominated  Subsalts. —  The  preceding  classes  of  salts,  and  many 
other  bodies  also,  are  capable  of  combining  with  a  certain  proportion  of  water, 
generally  vaguely  spoken  of  as  water  of  crystallization.  The  compounds  of  the 
present  class  appear  to  be  salts  which  have  assumed  a  fixed  metallic  oxide  in  the 
place  of  this  water.  They  may,  therefore,  be  truly  neutral  in  composition,  the  excess 
of  oxide  not  standing  in  the  relation  of  base  to  the  acid.  It  appears  that  the  for- 
mulae of  the  nitrates  named  are  as  follows : — 

Nitrate  of  water  (acid  of  sp.  gr.  1.42) HO,  N05+3HO. 

Nitrate  of  copper  (prismatic) ...CuO,  N05  +  3HO. 

Nitrate  of  copper  (rhomboidal) CuO,  N05  +  6HO. 

Subnitrate  of  copper CuO,  N05-f  3(CuO,  HO). 

I  have  distinguished  as  constitutional  the  three  atoms  of  water  which  exist  in  these 
and  all  the  magnesian  nitrates,  and  which  are  replaced  by  three  atoms  of  hydrated 
oxide  of  copper  in  the  subnitrate  of  copper,  which  is  therefore  a  nitrate  of  copper, 
with  the  addition  of  constitutional  (not  basic)  oxide  of  copper ;  a  view  which  is  ex- 
pressed by  the  arrangement  of  the  symbols  in  its  formula. 

The  subnitrates  of  zinc  and  lead,  and  probably  also  those  of  nickel  and  cobalt, 
have  a  similar  composition  (Gerhardt).  A  similar  correspondence  is  observed  be- 
tween the  crystallized  neutral  sulphate  of  copper,  and  the  subsulphate  of  copper, 
containing  four  equivalents  of  oxide  of  copper,  and  five  of  water  to  one  of  acid  : — 

Sulphate  of  copper,  CuO,  S03,  HO  +  4HO. 

Subsulphate  of  copper,  CuO,  S03,  (CuO,  HO) +  2  (CuO,  HO)  +  2HO. 

Three  equivalents  of  water  in  the  neutral  salt  appear  to  be  replaced  by  three  equi- 
valents of  hydrated  oxide  of  copper  in  the  subsalt.  The  remaining  2 HO  of  the 
latter  salt  are  expelled  by  a  moderate  heat,  while  the  other  4HO  in  combination 
with  oxide  of  copper,  are  extricated  by  a  much  higher  temperature,  and  their  sepa- 
ration attended  by  a  palpable  decomposition  of  the  salt,  as  it  affords  a  portion  of 
soluble  neutral  salt  afterwards  to  water.  The  remark  is  made  by  M.  Gerhardt,  that 
the  number  of  such  subsalts  is  greatly  exaggerated,  which  is  quite  in  accordance 
with  my  own  observations ;  few  salts  combining  with  an  excess  of  oxide  in  more 
than  one  or  two  proportions.  Most  subsalts  are  entirely  insoluble  in  water,  but 
when  they  possess  a  certain  degree  of  solubility,  they  may  afford  other  analogous 
subsalts  by  double  decomposition.  Thus  a  solution  of  bisubnitrate  of  lead,  PbO, 
NOg  +  PbO,  HO,  on  the  addition  of  neutral  chromate  of  potassa  allows  the  red 
bisubchromate  of  lead,  PbO,  Cr03-fPbO,  to  precipitate.  M.  Gerhardt,  who  ob- 
served this  fact,  considers  that  it  assimilates  the  nitrates  and  pyrophosphates,  and 
indicates  that  the  latter  are  ordinary  subsalts.  But  this  is  really  a  coincidence  of 
small  importance,  while  nitric  acid  affords  no  bibasic  hydrate,  nor  a  bibasic  salt  of 
soda,  as  phosphoric  acid  does. 

Water,  oxide  of  copper,  oxide  of  lead,  and  the  hydrates  of  these  metallic  oxides, 
appear  to  be  the  bodies  most  disposed  to  attach  themselves  to  salts  in  this  manner. 
The  strong  alkalies,  potassa  and  soda,  are  never  found  in  such  a  relation,  or  dis- 
charging any  other  function  than  that  of  base  to  the  acid  of  the  salt.  These  views 
of  subsalts,  in  which  their  constitutional  neutrality  is  preserved,  have  been  extended 
to  organic  compounds.  Many  neutral  organic  bodies  appear  to  be  capable  of  com- 
bining with  metallic  oxides,  particularly  with  oxide  of  lead  —  such  as  sugar,  amidin, 
dextrin,  orcin,  and  they  generally  combine  with  several  atoms  of  the  oxide.  Thus 
in  the  compound  of  orcia  and  oxide  of  lead,  C18H703  +  5PbO,  the  orcin  is  combined 

•Inquiries  respecting  the  Constitution  of  Salts;  of  oxalates,  nitrates,  phosphates,  sul- 
phates, and  chlori  les.  Phil.  Trans.  1837,  page  47. 


CONSTITUTION   OF   SALTS.  163 

with  five  atoms  of  constitutional  oxide  of  lead,  which  actually  replace  five  atoms  of 
constitutional  water,  which  orcin  in  its  ordinary  state  contains. 

Constitutional  water  is  sometimes  replaced  by  a  salt,  which  never  happens  with 
basic  water.  Thus  cane  sugar  may  be  represented  as  CraH,^Dn,  or  rather  C^H^O^; 
of  which  one  atom  of  water  may  be  replaced  by  chloride  of  sodium,  and  the  com- 
pound formed,  C^H^C^,  +  NaCl.  It  is  to  be  observed  that  constitutional  water  is 
superadded  to  a  salt,  and  such  an  element  is  removed  and  replaced  without  affecting 
the  structure  of  the  body  to  which  it  is  attached.  The  replacing  substance  may 
also  be  a  compound  of  a  very  different  character  from  water ;  for  besides  metallic 
oxides  and  salts,  ammonia  and  certain  anhydrous  acids  appear  to  be  capable  of  at- 
taching themselves  to  salts,  in  the  same  manner  as  constitutional  water. 

A  different  view  of  the  constitution  of  subsalts  is  advocated  by  M.  Millon,  who 
assumes  the  existence  of  poly-atomic  bases,  or  that  two,  three,  four,  and  even  six 
equivalents  of  water  or  a  metallic  oxide,  may  together  constitute  a  single  equivalent 
of  base,  and  unite  as  such  with  a  single  equivalent  of  acid  to  form  a  neutral  salt 
(Annales  de  Chim.  et  de  Phys.,  xviii.  333). 

Salts  of  the  type  of  red  chromate  of  potassa. — Several  salts  unite  with  anhydrous 
acids.  Thus  both  chloride  of  sodium  and  chloride  of  potassium  absorb  and  combine 
with  two  atoms  of  anhydrous  sulphuric  acid  without  decomposition,  when  exposed 
to  the  vapour  of  that  substance.  Sulphate  of  potassa  also  combines  with  one  atom 
of  anhydrous  sulphuric  acid.  All  these  compounds  are  destroyed  by  water.  But 
the  red  chromate  of  potassa,  generally  called  bichromate  of  potassa,  which  consists 
of  chromate  of  potassa  together  with  one  atom  of  chromic  acid,  is  possessed  of  greater 
stability,  as  is  likewise  the  compound  of  chloride  of  sodium  or  potassium  with  two 
atoms  of  chromic  acid.  Another  compound  containing  one  atom  of  potassium  and 
three  atoms  of  chromic  acid,  known  as  the  terchromate  of  potassa,  may  be  viewed  as 
a  combination  of  chromate  of  potassa  with  two  atoms  of  chromic  acid,  and  repre- 
sented by  KO,  O03-f  2O03.  The  bichromate  of  potassa  will  then  be  KO,  O03-f 
Cr03,  and  the  chromate  containing  chloride  of  potassium,  KCl-f2Cr03.  The  binio- 
date  of  potassa  (iodate  of  water  and  potassa)  may  be  rendered  anhydrous,  and,  when 
so,  is  a  salt  of  the  same  class. 

Double  salts. — Salts  combine  with  each  other,  but  by  no  means  indiscriminately. 
With  a  few  exceptions,  which  may  be  placed  out  of  consideration  for  the  present, 
the  combining  salts  have  always  the  same  acid — sulphates  combining  with  sulphates, 
chlorides  with  chlorides.  Their  bases  or  their  metals,  however,  must  belong  to  dif- 
ferent natural  families.  Thus  it  may  be  questioned  whether  a  salt  of  potassa  ever 
combines  with  a  salt  of  soda,  certainly  never  with  a  salt  of  ammonia.  Salts  of  the 
numerous  metals  including  hydrogen,  belonging  to  the  magnesian  family,  do  not 
combine  together.  Thus  sulphate  of  magnesia  does  not  form  a  double  salt  with  sul- 
phate of  lime,  with  sulphate  of  zinc,  or  with  sulphate  of  water ;  while  on  the  other 
hand  salts  of  this  family  are  much  disposed  to  combine  with  salts  of  the  potassium 
family  —  sulphate  of  soda,  for  instance,  forming  double  salts  with  sulphate  of  lime, 
sulphate  of  zinc,  and  sulphate  of  water.  We  have  thus  the  means  of  distinguishing 
between  a  double  salt,  and  the  salt  of  a  bibasic  or  tribasic  acid.  The  bisulphate  and 
binoxalate  of  potassa  saturated  with  soda,  form  sulphates  and  oxalates  of  potassa  and 
soda,  which  separate  from  each  other  by  crystallization,  although  the  acid  salts  are 
themselves  double  salts  of  water  and  potassa.  But  the  acid  fulminate  of  silver,  or 
the  acid  tartrate  of  potassa  (bitartrate),  affords  only  one  salt  when  saturated  with 
soda,  in  which  isomorphdus  bases  exist,  and  which,  therefore,  is  a  salt  of  one  acid, 
and  not  a  compound  of  two  salts.  The  great  proportion  of  the  salts  which  are 
named  super,  acid  and  fei-salts,  contain  a  salt  of  water,  and  are  double  salts  —  such 
as  the  supercarbonate  of  soda  (HO,  C02-f-NaO,C02),  the  bisulphate  of  potassa  (HO, 
S03-f  KO,  S03),  and  the  binacetate  of  soda:  but  a  few  of  them  are  bibasic  or  tri- 
basic salts,  containing  one  or  two  atoms  of  water  as  base  —  such  as  the  salt  called 
bitartrate  of  potassa,  or  biphosphate  of  potassa  (2HO,  K0  +  P06). 

From  these  observations  must  be  excepted  double  salts  formed  by  fusion,  and 


164      ARRANGEMENT  OF  ELEMENTS  IN  COMPOUNDS. 

many  salts  formed  in  highly  acid  solutions,  which  are  scarcely  limited  in  variety  of 
composition ;  carbonate  of  potassa  fusing  with  the  carbonate  or  sulphate  of  soda,  and 
sulphate  of  baryta  crystallizing  in  combination  with  sulphate  of  water,  from  solution 
in  sulphuric  acid.  Such  salts  are  decomposed  by  water,  and  are  otherwise  deficient 
in  stability,  compared  with  the  soluble  double  salts,  to  which  alone  the  preceding 
remarks  apply. 

There  is  no  parallelism  between  the  constitution  of  a  double  salt  and  that  of  a 
simple  salt  itself,  or  foundation  for  the  statements  which  are  sometimes  made,  that 
one  of  the  salts  which  compose  a  double  salt  has  the  relation  to  the  other  of  an  acid 
to  a  base,  and  that  one  salt  is  electro-negative  to  the  other.  The  resolution  of  a 
double  salt  into  its  constituent  salts  by  electricity,  has  never  been  exhibited,  and  is 
not  to  be  expected,  from  what  is  known  of  electrolytic  action ;  while  no  analogy 
whatever  subsists  between  a  double  salt  and  a  simple  salt  on  the  binary  view  of  the 
constitution  of  the  latter.  Besides,  the  supposed  analogy  is  destroyed  by  what  is 
known  of  the  derivation  of  double  salts.  Sulphate  of  magnesia  acquires  an  atom  of 
sulphate  of  potassa  in  the  place  of  an  atom  of  water,  which  is  strongly  attached  to  it, 
in  becoming  the  double  sulphate  of  magnesia  and  potassa.  In  the  same  way,  the 
sulphate  of  water  has  an  atom  of  water  also  replaced  by  sulphate  of  potassa,  in  be- 
coming the  bisulphate  of  potassa ;  relations  which  appear  in  the  rational  formulae 
of  these  salts : 

Sulphate  of  magnesia MgS(H)  -f  6H 

Sulphate  of  magnesia  and  potassa MgS(KS)  +  6H 

Sulphate  of  water  (acid  of  sp.  gr.  1.78) ?§($).. 

Bisulphate  of  potassa HS(KS) 

It  thus  appears  that  a  provision  exists  in  sulphate  of  magnesia  itself  for  the  forma- 
tion of  a  double  salt,  and  that  the  molecular  structure  4s  unaltered,  notwithstanding 
the  assumption  of  the  sulphate  of  potassa  as  a  constituent.  The  derivation  of  the 
acid  oxalates  likewise  throws  much  light  on  the  nature  of  double  salts.  The  oxalate 
of  potassa  contains  an  atom  of  constitutional  water,  which  is  replaced  by  hydrated 
oxalic  acid  (the  crystallized  oxalate  of  water),  in  the  formation  of  the  binoxalate  of 
potassa  (double  oxalate  of  potassa  and  water),  or  by  the  oxalate  of  copper  in  the 
formation  of  the  double  oxalate  of  potassa  and  copper,  as  exhibited  in  the  following 
formulae,  in  which  the  replacing  substances  are  enclosed  in  brackets  to  mark  them 
as  before : 

Oxalate  of  potassa KCC,  (H) 

Binoxalate  of  potassa KCC,  (HOC H2) 

Oxalate  of  potassa  and  copper KCC,  (CuCCH2) 

Now  the  anomalous  salt,  quadroxalate  of  potassa,  is  derived  in  the  same  way  from 
the  binoxalate,  as  the  binoxalate  itself  is  derived  from  the  neutral  oxalate,  two  atoms 
of  water  being  displaced  by  two  atoms  of  hydrated  oxalic  acid,  thus : 

Binoxalate  of  potassa KCC,  HCC,  (2H) 

Quadroxalate  of  potassa KCC,  HCC,  (2HCCH2) 

These  examples  illustrate  the  derivation  of  double  salts  by  substitution.  The 
structure  of  the  salts,  too,  exemplifies  what  may  be  called  consecutive  combination. 
The  basis  of  the  last  mentioned  salt,  for  instance,  is  oxalate  of  potassa,  which  is  in 
direct  combination  with  oxalate  of  water.  A  compound  body  is  thus  produced 
which  seems  to  unite  as  a  whole,  with  two  atoms  of  hydrated  oxalic  acid.  This  is 
very  different  from  the  direct  combination  of  all  the  elements  which  compose  the 
salt. 

In  the  formation  of  many  other  classes  of  double  salts,  no  substitution  is  observed, 
but  simply  the  attachment  of  two  salts  together,  often  of  an  anhydrous  with  a  hy- 


CONSTITUTION   OF   SALTS.  165 

drated  salt,  in  which  case  the  last  often  carries  its  combined  water  along  with  it, 
and  sometimes  acquires  an  additional  proportion.  Thus  in  the  formula  of  the  double 
chloride  of  potassium  and  copper,  KCl-fCuCl,  2HO,  the  formulas  of  its  constituent 
salts  reappear  without  alteration  j  and  in  that  of  alum,  sulphate  of  potassa  is  found 
with  the  hydrated  sulphate  of  alumina  annexed,  of  which  the  water  is  increased 
from  eighteen  to  twenty-four  atoms.  In  these  and  all  other  double  salts,  the  cha- 
racters of  the  constituent  salts  are  very  little  affected  by  their  state  of  union.  If 
one  of  them  has  an  acid  reaction,  like  sulphate  of  alumina  or  chloride  of  copper,  it 
retains  the  same  character  in  combination ;  and  nothing  resembling  a  mutual  neu- 
tralization of  the  salts  by  each  other  is  ever  observed.  No  heat  is  evolved  in  their 
formation.  (Memoirs  of  the  Chemical  Society,  ii.  51). 

The  compounds  of  chlorides  with  chlorides,  and  of  iodides  with  iodides,  are  nume- 
rous, and  were  viewed  by  Bonsdorf  as  simple  salts,  in  which  one  of  the  chlorides  is 
the  acid,  and  the  other  the  base.  But  such  an  opinion  can  no  longer  be  entertained, 
the  chlorides  themselves  being  unquestionably  salts,  and  their  compounds,  therefore, 
double  salts. 

The  combinations  of  such  salts  with  each  other  as  contain  different  acids  are  not 
so  well  understood,  the  theory  of  their  formation  having  hitherto  been  little  attended 
to.  They  are  in  general  decomposed  by  water,  and  easily,  if  the  solubility  of  one 
of  their  constituents  is  considerable,  as  is  observed  of  the  compounds  of  iodate  of 
soda  with  one  and  with  two  proportions  of  chloride  of  sodium,  of  the  biniodate  of 
potassa  with  the  sulphate  of  potassa,  of  the  oxalate  of  lime  with  the  chloride  of 
calcium. 

The  compound  cyanides,  which  form  a  considerable  class  of  salts,  must  be  excepted 
from  all  the  preceding  general  statements  in  regard  to  double  salts.  Cyanides  of 
the  same  family  combine  together,  as  cyanide  of  iron  with  cyanide  of  hydrogen ;  the 
compound  cyanide  also  generally  consists  of  three  and  not  of  two  simple  cyanides ; 
and  lastly,  the  properties  of  compound  cyanides  are  very  different  from  those  of  the 
simple  cyanides  which  are  supposed  to  compose  them.  The  simple  cyanide  of  po- 
tassium, for  instance,  is  highly  poisonous,  while  the  double  cyanide  of  potassium 
and  iron  is  as  mild  in  its  action  upon  the  animal  economy  as  sulphate  of  soda.  But 
the  compound  cyanides  may  be  removed  from  the  class  of  double  salts,  on  a  specu- 
lative view  of  their  constitution  which  their  anomalous  character  led  me  to  propose. 
It  is  to  be  premised  that  the  supposed  double  proto-cyanide  of  iron  and  potassium 
(yellow  prussiate  of  potassa)  affords  no  hydrocyanic  acid  whatever  when  distilled 
with  an  excess  of  sulphuric  acid  at  a  temperature  not  exceeding  100° ;  which  sug- 
gests the  idea  that  it  does  not  contain  cyanides  or  cyanogen.  Assuming  the  exist- 
ence of  a  new  compound  radical,  N3C6,  which  has  three  times  the  atomic  weight  of 
cyanogen,  and  may  be  called  prussine,  and  which  is  also  tribasylous  or  capable  of  com- 
bining with  three  atoms  of  hydrogen  or  metal,  like  the  radical  of  the  tribasic  class 
of  phosphates,  then  the  compound  cyanides  assume  a  constitution  of  extreme  sim- 
plicity. We  have  one  atom  of  prussine  combined  always  with  three  atoms  of  hydro- 
gen or  metal  in  the  following  salts :  in  the  proto-cyanide  of  iron  and  potassium  with 
one  of  iron  and  two  of  potassium  ]  in  the  compound  called  ferro-cyanic  acid,  with 
one  of  iron  and  two  of  hydrogen ;  in  Mosander's  salts,  with  one  of  iron,  one  of  po- 
tassium and  one  of  barium,  calcium,  &c. ;  with  two  of  iron  and  one  of  potassium  in 
the  salt  which  precipitates  on  distilling  the  yellow  prussiate  of  potassa  with  sulphuric 
acid  at  212°.  To  many  of  these,  parallel  combinations  might  be  adduced  from  the 
tribasic  phosphates.  Prussides  likewise  combine  together,  producing  double  prus- 
sides,  such  as 

Percyanide  of  iron  and  potassium 

(red  prussiate  of  potassa) Fe2,  N3C6  -f  K3,  N3C6 

Prussian  blue Fe2,  N3C6+Fe3,  N3C6 

Basic  prussian  blue Fe2,  N3C6  -f  Fe3,  N3C6  -f  FeA 


166   ARRANGEMENT  OF  ELEMENTS  IN  COMPOUNDS. 

Formation  of  salts  by  substitution.  —  Chemists  have  come  to  pronounce  less 
decidedly  on  theories  of  the  constitution  of  salts  and  the  arrangement  of  elements 
in  these  and  other  compounds,  since  their  attention  has  been  fixed  upon  the  forma- 
tion of  compounds,  by  the  subtitution  of  one  element  for  another,  without  injury  to 
the  original  form  or  type,  and  often  to  give  a  preference  to  empirical  over  rational 
formulae,  while  their  opinions  on  chemical  constitution  were  suspended.  The  ele- 
mentary composition  of  oil  of  vitriol,  or  the  hydric  sulphate,  is  expressed  by  S04H ; 
the  sulphate  type,  and  other  neutral  sulphates,  are  formed  by  replacing  the  hydro- 
gen by  a  metal;  the  zinc  sulphate,  S04Zn  •  the  soda  sulphate,  S04Na.  M.  Ger- 
hardt,  assuming  as  a  law  that  the  equivalent  of  all  compound  bodies  gives  two 
volumes  of  vapour,  divides  the  equivalents  of  the  following  elements  by  two  — 
nitrogen,  phosphorus,  chlorine,  hydrogen,  and  all  the  metals ;  and  is  thereby  enabled 
to  construct  substitution  formulae,  which  are  often  remarkable  for  their  simplicity. 
This  will  appear  in  the  following  selected  formulae :  — 

FORMULAE  BY  M.  GERHARDT. 
(0=8,  S=16;  the  other  symbols  =  half  the  usual  equivalents.) 

I.    NITRATES. 

Hydric  nitrate N03H         ~) 

Magnesia  nitrate N03Mg        v  Monobasylous  salts. 

Potassa  nitrate N03K          J 

II.    SULPHATES. 

Hydric  sulphate S04H2 

Magnesia  sulphate...  .  SOJMffo        i -O-L      i 

Potassa  sulphate SO^f        ^ibasylous  nlta. 

Potassa  bisulphate S04KH 

III.    TRIBASIC   PHOSPHATES. 

Hydric  phosphate P04H3 


Subphosphate  of  soda P04Na3 

Phosphate  of  soda P04Na2H 

Biphosphate  of  soda P04NaH2 


Tribasylous  salts. 


The  preceding  groups  are  symbolized  without  any  division  of  the  equivalents 
used ;  but  M.  Gerhardt  departs  from  this  practice,  when  necessary,  in  the  unitary 
system  of  notation  which  he  recommends :  — 

Anhydrous  alum S04  (K,  A13) 

2^       IF 

Pyrophosphate  of  soda PC^  (Na2) 

Subphosphate  of  soda-f-HO PO*  (Na3H) 

"2 

Although  a  rational  formula,  strictly  speaking,  expresses  no  more  than  a  decom- 
position,—  and  the  rational  formulae  of  a  compound  may  truly,  therefore,  be  as 
numerous  as  the  modes  of  decomposition  of  which  it  is  susceptible,  —  still  much 
would  undoubtedly  be  lost  by  abandoning  such  formulae  for  formulae  which  are 
entirely  empirical ;  unless,  indeed,  it  is  found  that  the  uniform  practice  of  exhibiting 
the  leading  constituent,  in  the  proportion  of  a  single  equivalent,  should  bring  to- 
gether different  bodies  under  common  formulae,  which  are  types  of  useful  classifica- 
tion, as  M.  Gerhardt  maintains. 

Salts  of  Jlmmonia.  —  Ammonia  is  a  gaseous  compound  of  one  equivalent  of  ni- 
trogen and  three  of  hydrogen,  of  which  the  solution  in  water  is  caustic  and  alkaline, 
and  which  neutralizies  acids  perfectly,  as  potassa  and  soda  do.  But  all  its  oxygen- 
acid  salts  contain,  besides  ammonia,  an  equivalent  of  water  which  is  essential  to 
them,  and  inseparable  without  the  destruction  of  the  salt;  and  with  this  additional 


CONSTITUTION    OF    SALTS.  167 

constituent  they  are  isomorphous  with  the  salts  of  potassa.  Hydrochloric  acid  also 
unites  with  ammonia  without  losing  its  hydrogen,  and  the  compound  or  hydrochlo- 
rate  of  ammonia,  which  is  isomorphous  with  the  chloride  of  potassium,  contains, 
therefore,  an  equivalent  of  hydrogen,  besides  chlorine  and  ammonia.  On  the  now 
generally  received  theory  of  these  salts,  the  ammonia  with  this  hydrogen,  or  that  of 
the  water  in  the  oxygen-acid  salts,  constitutes  a  hypothetical  basyl,  ammonium 
(NH4),  to  which  allusion  has  already  been  made  as  being  isomorphous  with  potas- 
sium. This  view  of  the  constitution  of  the  salts  of  ammonia  will  be  made  obvious 
by  a  few  examples  :  — 


i 

ON    THE    AMMONIUM    THEORY. 


Hydrochlorate  of  ammonia,  HN8,  HC1  ....  Chloride  of  ammonium,  NH4,  Cl 

Sulphate  of  ammonia,  NH3,  HO,  S03    ...  Sulphate  of  oxide  of  ammonium,  NH40,  S03 

Nitrate  of  ammonia,  NH3  HO,  N05         ...  Nitrate  of  oxide  of  ammonium,  NH40,  N05 

The  application  of  this  theory  to  the  compounds  of  ammonia  with  hydrosulphuric 
acid  and  sulphur  is  particularly  felicitous.  These  compounds  may  be  thus  repre- 
sented, and  placed  in  comparison  with  their  potassium  analogues,  NH4  being  equi- 
valent to  K :  — 

Sulphide  of  ammonium NH4S  ...  KS 

Sulphide  of  ammonium  and  hydrogen  (bihy- 

drosulphate  of  ammonia NH4S,  HS  ...  KS,  HS 

Tritosulphide  of  ammonium NH4S3          ...  KS3 

Pentasulphide  of  ammonium NH4S5          ...  KS5 

Ammonium  is  supposed  to  present  itself  in  a  tangible  form,  and  in  possession  of 
metallic  characters,  in  the  formation  of  what  is  called  the  ammoniacal  amalgam. 
When  mercury  alloyed  with  one  per  cent,  of  sodium  is  poured  into  a  saturated  cold 
solution  of  sal  ammoniac  (chloride  of  ammonium),  it  undergoes  a  prodigious  increase 
of  bulk,  expanding  sometimes  from  one  volume  to  two  hundred  volumes,  without 
becoming  in  the  least  degree  vesicular,  and  acquiring  a  butyraceous  consistence, 
while  its  metallic  lustre  is  not  impaired.  A  small  addition  is  at  the  same  time  made 
to  its  wejght,  estimated  at  from  1  part  in  2000  to  1  in  10,000,  which  certainly  con- 
sists of  ammonia  and  hydrogen  in  the  proportions  of  ammonium.  The  sodium,  it  is 
supposed,  combines  with  the  chlorine  of  chloride  of  ammonium,  and  the  liberated 
ammonium  with  mercury,  so  that  the  metallic  product  is  an  amalgam  of  ammonium. 
It  speedily  resolves  itself  again  spontaneously  into  running  mercury,  ammonia,  and 
hydrogen,  unless  the  temperature  be  reduced  so  far  as  to  freeze  it.  After  all,  how- 
ever, neither  isolation  nor  the  metallic  character  is  essential  to  ammonium  as  an 
alkaline  radical,  other  basyls  being  now  admitted,  such  as  ethyl  and  benzoyl,  which 
have  no  claim  to  such  characters. 

Other  classes  of  ammoniacal  salts  may  be  formed  in  which  the  fourth  equivalent 
of  hydrogen  in  ammonium  is  replaced  by  a  metal  of  the  magnesian  family, — by 
copper  in  particular,  which  most  resembles  hydrogen.  Thus  anhydrous  chloride 
of  copper  absorbs  a  single  equivalent  of  ammonia  with  great  avidity  and  the  evolu- 
tion of  much  heat,  which  cannot  afterwards  be  separated  from  it  by  the  agency  of 
heat.  The  compound  appears  to  be  strictly  analogous  to  chloride  of  ammonium,  but 
contains  an  equivalent  of  copper  in  the  place  of  hydrogen.  Its  formula  is  NH3Cu, 
Cl,  and  it  may  be  named  the  chloride  of  cupr ammonium.  This  salt  and  many 
others  are  likewise  capable  of  combining  with  more  ammonia,  which  is  retained  less 
strongly,  and  has  the  relation  of  constitutional  water  to  the  salt.  The  constitution 
of  these  combinations  will  be  more  minutely  considered  in  other  parts  of  the  work. 

Amidogen  and  amides.  —  The  existence  of  another  compound  of  nitrogen  and 
hydrogen  (NH2),  containing  an  equivalent  less  of  hydrogen  than  ammonia,  is  recog- 
nized in  an  important  series  of  saline  compounds,  although  it  has  not  been  isolated. 
These  compounds  are  called  amides,  and  hence  the  name  amidogen  applied  to  their 
radical.  When  potassium  is  heated  in  ammoniacal  gas,  the  metal  is  converted  into 


168         ARRANGEMENT   OF    ELEMENTS   IN    COMPOUNDS. 

a  fusible  green  matter,  which  is  the  amide  of  potassium,  while  an  equivalent  of 
hydrogen  is  disengaged.  Amidogen  exists  also  in  the  white  precipitate  of  mercury 
formed  on  adding  ammonia  to  corrosive  sublimate,  the  product  being  a  double  chlo- 
ride and  amide  of  mercury  (HgCl  +  HgNH2). 

Amides  are  produced  in  an  interesting  way,  by  the  abstraction  of  the  elements 
of  water  from  compounds  of  ammonia  with  oxygen  acids.  Thus,  on  decomposing 
oxalate  of  ammonia  by  heat,  the  acid  losing  a  proportion  of  oxygen,  and  the  am- 
monia a  proportion  of  hydrogen,  oxamide  sublimes,  which  consists  of  NH2  +  2CO. 
When  ammoniacal  gas  and  anhydrous  sulphuric  acid  vapour  are  mixed  together,  a 
saline  substance  is  produced  which  dissolves  in  water,  but  is  not  sulphate  of  ammo- 
nia, the  solution"  affording  no  indications  of  sulphuric  acid.  It  is  believed  to  be  a 
hydrated  sulphamide,  or  to  be  constituted  thus,  NH2,  S02  +  HO  ;  a  compound  which 
it  will,  be  observed  contains  neither  ammonia  nor  sulphuric  acid.  Similar  products 
result  from  the  action  of  ammonia  on  dry  carbonic  acid  and  all  the  other  anhydrous 
oxygen  salts.  The  difference  between  these  compounds  and  the  true  salts  of  am- 
monia affords  an  argument  in  favour  of  the  ammonium  theory  of  the  latter. 

ANTITHETIC   OR   POLAR   FORMULAE. 

Formulae  for  compounds  may  be  constructed  to  exhibit  the  attraction  of  the  ulti- 
mate elements  for  each  other  without  involving  any  contested  theory  of  the  consti- 
tution of  compounds,  and  which  indeed  might  supersede  the  consideration  of  such 
views,  were  ifc  not  that  the  nomenclature,  which  it  would  be  inconvenient  to  alter 
greatly,  is  founded  upon  the  latter.  A  certain  amount  of  information  is  given  in 
the  ordinary  formulas  by  the  arrangement  of  the  symbols,  the  symbol  of  the  basyl- 
ous  or  positive  constituent  being  placed  before  the  symbol  of  the  halogenous  or 
negative  constituent,  as  in  HO  for  water,  S03  for  sulphuric  acid.  To  carry  out 
this  principle  farther,  and  make  its  application  more  perspicuous,  I  have  suggested 
the  writing  of  a  formula  in  two  lines,  placing  all  the  negative  constituents  in  the 
upper,  and  the  positive  in  the  lower  line  :  — 

~ 


Potassa  .......  -==  Water  .......  -=   Sulphuric  acid....  ~  Ammonia 

K. 


Cyanogen....  -^-   Olefiant  gas  -^-4  Carbonic  oxide...    -^  Hydric  oxalate  =~ 


From  their  construction  these  formulas  are  named  antithetic,  the  two  orders  of 
constituents  being  placed  opposite  or  against  each  other  ;  or  polar,  from  exhibiting 
the  opposite  attractive  forces  of  the  elements.  Several  decompositions  already 
referred  to,  and  others,  may  be  made  more  intelligible  by  their  aid. 

Decomposition  of  ammoniacal  salts.  —  In  the  decomposition  of  oxalate  of  ammo- 
nia and  formation  of  oxamide,  the  change  consists  in  the  abstraction  of  two  equiva- 
lents of  water  from  the  constituents  of  the  salt  :  the  formulae  being  — 

N003       02     N02 
Oxalate  or  ammonia  ....................       ~        —    r=:r       oxamic>e. 


The  interesting  observation  has  lately  been  made  by  M.  Dumas,  that  by  distillation 
with  anhydrous  phosphoric  acid,  four  equivalents  of  water  are  separated  from  oxalate 
of  ammonia,  and  cyanogen  formed.  Supposing  that  the  formation  of  oxamide  pre- 
cedes this  last  decomposition,  we  have  — 

N02       02       N 
Oxamide  ...................................  H~C~~~H2==  C~2  c}TanoSen< 

It  is  seen,  that  although  we  cannot  say  that  water  exists  either  in  oxalate  of  ammonia 
or  in  oxamide,  still  40  is  negative  and  4H  positive  in  the  first  of  these  substances, 
and  20  negative  with  2H  positive  in  the  second,  the  relation  which  these  elements 


ANTITHETIC   OR   POLAR   FORMULAE.  169 

bear  to  each  other  in  water.  The  polar  relation  of  these  elements,  therefore,  docs 
not  require  to  be  subverted,  when  they  are  led  to  unite  and  take  the  form  of  water, 
under  the  influence  of  the  attraction  of  phosphoric  acid  for  that  oxide.  It  is  mani- 
festly a  law  of  decomposition  that  those  decompositions  take  place  most  readily  which 
permit  the  elements  to  continue  in  their  original  polar  condition  and  position  in  the 
formulae;  the  explanation  being,  that  such  decompositions  are  promoted  by  the 
peculiar  attractions  of  the  ultimate  elements  for  each  other  as  they  exist  in  the  ori- 
ginal compound ;  or  the  compound  molecule  is  broken  up  in  the  direction  in  which 
it  naturally  divides. 

The  decomposition  by  phosphoric  acid  of  other  salts  of  ammonia  containing  acids 
related  to  the  alcohols,  illustrates  the  same  constancy  of  polar  relation  in  the  ele- 
ments before  and  after  the  change.  Thus,  formiate  of  ammonia  gives  hydrocyanic 
acid  by  the  abstraction  of  four  equivalents  of  water :  — 

N  0  H03       04      NH  , 

Formiate  of  ammonia — ^ =-  =  -^-  hydrocyanic  acid. 

H3JuL     \j%  Jbi4         C2 

Here  the  hydrogen  of  hydrocyanic  acid  is  represented  as  negative,  and  it  can  cer- 
tainly be  replaced  by  chlorine,  a  negative  element,  and  the  chloride  of  cyanogen 
formed :  — 

NH  _, .    .,     ,  NCI 

Hydrocyanic  acid -^—  Chloride  of  cyanogen -^- 

\Jn  ^2 

With  a  metallic  oxide,  however,  hydrocyanic  acid  gives  a  cyanide,  and  then  the 
hydrogen  appears  positive  — 

N  N 

Hydrocyanic  acid -^-^  Cyanide  of  silver 

(j2ti  t2Ag 

But  hydrocyanic  acid  is  in  the  lowest  degree  feeble  in  its  powers  as  an  acid,  or  as 
cyanide  of  hydrogen,  and  its  hydrogen  appears  to  be  just  on  the  limit  between  the 
basylous  and  halogenous  character  and  position. 

Acetate  of  ammonia  distilled  with  phosphoric  acid  also  loses  four  equivalents  of 
water,  like  all  the  ammoniacal  salts  in  question,  and  gives  the  cyanide  of  methyl : — 

.    ,,     ,                 N003H3       04      H2HN 
Acetate  of  ammonia          — ~ =-  =  — — — —  cyanide  of  methyl. 

The  chloracetate  of  ammonia  in  losing  4HO  gives  a  liquid  body  of  the  composi- 
tion C4C13N:— 

N  0  03C13        04       C12  C1N 

Chloracetate  of  ammonia — =-  =  -^ — — 

jLX3Jti     \_/4  Jti4         \j%     \j% 

Here  the  single  negative  H  of  hydrocyanic  acid  is  also  under  the  positive  attraction 
of  the  C2  of  the  hydrocarbon,  C2H2,  a  cross  attraction,  which  forms  a  bond  of  union 
between  the  hydrocyanic  acid  and  hydrocarbon,  and  supports  the  equilibrium. 

Why  is  ammonia  a  base  ? — Of  ammonia  and  hydrochloric  acid  the  antithetic  for- 
mulae are —  • 

N  01 

H~3          H 

There  can  be  little  doubt  but  that  when  these  bodies  are  united,  the  highly  nega- 
tive chlorine  shares,  or  assumes  entirely,  the  positive  attraction  of  the  third  equiva- 
lent of  hydrogen  in  ammonia,  which  there  is  reason  to  believe  is  less  powerfully 
attracted  or  neutralized  by  the  negative  nitrogen  than  the  other  two  equivalents  of 
hydrogen.  We  thus  obtain  the  following  formula : — 

Hydrochlorate  of  ammonia 

jU2  U2 


170        ARRANGEMENT   OF   ELEMENTS   IN    COMPOUNDS. 

Now  the  acid  character  of  hydrochloric  acid,  which  is  neutralized  in  the  salt,  de- 
pends upon  the  former  substance  being  a  compound  in  which  a  powerful  salt-radical, 
chlorine,  is  united  with  a  weak  basyl,  hydrogen.  With  a  powerful  basyl,  such  as 
potassium,  chlorine  gives  a  neutral  salt,  the  chloride  of  potassium.  But  it  is  proba- 
ble that  the  subchloride  of  hydrogen,  H2G1,  if  it  could  exist  in  a  separate  state, 
would  be  an  equally  neutral  salt,  for  hydrogen  belongs  to  the  magnesian  class  of  ele- 
ments, two  atoms  of  which  appear  to  be  equivalent  to  one  atom  of  the  potassium 
class,  or  H2C1  to  be  equivalent  to  KC1,  and  possibly  isomorphous  with  it.  One 
atom  of  nitrogen  there  are  also  grounds  for  believing  to  be  equivalent  in  composition 

to  two  atoms  of  oxygen,  or  N=20.     Hence  the  compound  ^  has  a  character  of 

-ti2 

saturation,  or  polar  neutralization,  like  ^  or  two  equivalents  of  water.     In  ammo- 

H2 

nia,  therefore,  the  third  basylous  atom  of  hydrogen  may  well  be  considered  as  un- 
saturated,  and  to  be  what  imparts  a  basylous  or  positive  character  and  activity  to  the 
compound.  In  metallic  oxides  which  are  bases,  we  have  also  the  positive  property 
of  the  metal  imperfectly  saturated  by  the  weak  negative  body  oxygen,  and  the  posi- 
tive attraction  therefore  in  excess. 

In  the  oxygen  acids,  on  the  contrary,  there  is  an  excess  of  negative  attraction  from 
the  predominance  of  the  oxygen  element,  and  it  is  remarkable  that  in  the  more 
powerful  acids,  such  as  sulphuric,  nitric,  and  chloric,  one  equivalent  of  this  oxygen 
is  but  feebly  united,  and  its  negative  attraction  free  to  act,  like  the  positive  attraction 
of  the  third  equivalent  of  hydrogen  in  ammonia!  Hence  ammonia  and  anhydrous 
sulphuric  acid  readily  combine  : — 

N         00_a  =  N  002 
H2H         S         H2  H  S 

From  the  action  of  the  affinities  exhibited  in  the  last  formula,  a  stable  equilibrium 
results ;  but  it  is  not  intended  to  express  that  amidogen,  water,  and  sulphurous  acid, 
exist  ready  formed  in  the  compound.  Indeed,  in  no  case  do  the  formulas  express 
actual  formation  of  subordinate  compounds,  or  anything  more  than  what  are  consi- 
dered to  be  the  predominating  set  of  attractions  among  all  the  possible  attractions 
which  the  elements  have  for  each  other,  and  all  of  which  they  continue  to  exert  in 
some  degree. 

In  sulphate  of  oxide  of  ammonium,  the  affinities  of  equilibrium  are  those  of  the 
elements  of  amidogen,  suboxide  of  hydrogen,  and  sulphuric  acid : — 

Constitution  of  Sulphate  of  Ammonia.     Sulphate  of  Ammonia. 

*L  4.  2.    2?        =        N  °  °3 

HI       H        S  H2  H2  b 

In  this  and  all  the  other  oxygep-acid  salts  of  ammonia,  the  highly  alkaline  oxide 
H20  appears,  and  constitutes  the  point  of  attachment  for  the  acid.  Other  sources 
of  stability  in  the  sulphate  of  ammonia  are  —  first,  the  attraction  of  N  for  its  third 
atom  of  hydrogen,  which  is  never  entirely  relinquished,  although  the  latter  is  more 
under  the  influence  of  the  0  of  the  water;  and,  secondly,  the  attraction  of  the  03 
of  the  sulphuric  acid  for  the  basylous  H2 :  for  these  cross  attractions  prevent  the 
division  of  the  compound  into  subordinate  compounds  under  the  influence  of  the 
predominating  affinities  first  enumerated.  This  salt  may  be  taken  as  a  fair  example 
of  the  assumed  mode  of  formation  of  compounds,  in  which  the  affinities  of  the  ele- 
mentary atoms  only  are  operative,  to  the  entire  exclusion  of  the  affinities  usually 
assigned  to  subordinate  groups  of  elements  acting  as  compound  radicals  01  quasi- 
elements. 

Why  are  arsenic  and  phosphoric  acids  tribasic? — Phosphoric  acid,  P05,  maybe 
'Considered,  from  its  properties  and  mode  of  formation,  as  phosphorous  acid,  P03  -{- 
two  equivalents  of 'oxygen  less  strongly  combined;  and  in  the  same  way  arsenic 


ATOMIC   VOLUME   OF   BODIES.  171 

acid,  As05,  as  arsenious  acid,  As03  -f  two  equivalents  of  oxygen.  Now,  when 
united  with  a  base,  which  we  shall  suppose  a  metallic  protoxide,  RO,  these  two 
surplus  equivalents  of  oxygen  in  the  phosphoric  acid,  added  to  the  single  equivalent 
of  oxygen  in  the  base,  convert  an  equivalent  of  the  latter  into  an  acid  of  the  formula 
R03.  Two  more  equivalents  of  base  are  required  —  one  to  neutralize  this  R03,  and 
the  other  to  neutralize  the  phosphorous  acid,  P03;  making  three  equivalents  of  base 
to  every  single  equivalent  of  phosphoric  acid.  The  general  formula  for  a  so-called 
tribasic  phosphate  is,  therefore  — 

0  03  0  03 


and  resembles  a  double  sulphate,  RO,  S03+R0,  S03. 

Tribasic  subphosphate  of  lime  (3CaO,  P05)  ................  /T-7T3-fT-5 

Oa  Oa  \jQi  Jr 

Phosphoric  acid  appears  farther  to  have  the  power,  when  heated  strongly,  of  as- 
suming the  two  equivalents  of  oxygen  referred  to  into  a  more  intimate  state  of  com- 
bination, possibly  with  the  loss  of  a  portion  of  combined  heat,  and  gives  the  class 
of  monobasic  metaphosphates.  The  general  formula  of  a  metaphosphate  is  — 

Metaphosphate  .........................................  ffl? 

A  pyrophosphate,  or  so-called  bibasic  phosphate,  is,  on  this  view,  a  compound  of 
a  common  phosphate  and  metaphosphate  :  — 

,>  0  03  0  03          O  03 

Pyrophosphate...,  ................................  R^OTF     +     RP 

Hence  the  equivalent  of  a  pyrophospate  contains  four  equivalents  of  base  and  two 
of  phosphoric  acid  —  the  reason  why  so  many  double  pyrophosphates  appear  to  exist. 
Phosphoric  acid  is  thus  supposed  to  resemble  those  conjugate  organic  acids  which 
combine  with  two  equivalents  of  base,  because  they  possess  the  elements  of  two  dif- 
ferent acids. 

ATOMIC   VOLUME   OF   SOLID  BODIES. 

Since  the  existence  of  simple  relations  between  the  combining  volumes  of  gaseous 
bodies  was  ascertained  by  Gay-Lussac,  various  attempts  have  been  made  to  establish 
similar  relations  between  the  measures,  as  well  as  the  weights,  in  which  bodies,  in 
the  liquid  and  solid  form,  enter  into  combination.  If  the  atoms  of  all  elements  had, 
in  the  solid  form,  the  same  bulk,  their  specific  gravities  would  be  regulated  by  their 
atomic  weights,  and  be  in  the  same  proportion.  It  was  early  observed  by  M.  Dumas, 
that  a  close  approximation  to  this  simple  ratio  holds  among  the  specific  gravities  of 
a  considerable  number  of  isomorphous  bodies  j  but  it  is  by  no  means  general.  The 
subject  has  received  its  fullest  investigation  from  Professor  Schroeder  of  Mannheim1, 
Dr.  Hermann  Kopp2  of  Giessen,  and  Messrs.  Playfair  and  Joule.3  Much  informa- 
tion has  been  collected,  and  many  curious  relations  in  the  specific  gravities  of  parti 
cular  bodies  pointed  out;  but  the  general  deductions  drawn  can,  in  general,  claim 
only  a  certain  degree  of  probability.  Much  of  the  uncertainty  arises  from  the  spe- 
cific gravity  of  a  body  in  the  solid  form  being  often  variable  between  rather  wide 

1  Die  Molecularvolume  der  chemischen  Verbindungen  im  festen  und  flussigen  Zustande 
Mannheim,  1843. 

2  Bemerkungen  zur  Volumtheorie,  Braunschweig,  1844;  Annales  de  Chimie  et  de  Phy- 
sique, 2e  Se>.  T.  Ixxv.  and  3e  Se>.  T.  iv.  p.  462. 

3  Memoirs  of  the  Chemical  Society  of  London,  vol.  ii.  p.  401;  vol.  iii.  pp.  57  and  199. 
Also,  a  paper  on  the  Constitution  of  Aqueous  Solutions  of  Acids  and  Alkalies,  by  Mr.  J.  J 
Griffin  ;  ibid.  p.  155. 


172 


ATOMIC    VOLUME    OF    SOLID   BODIES. 


limits.  Thus  platinum,  in  a  pulverulent  state,  reduced  from  its  oxide  and  from  the 
double  chloride  of  platinum  and  ammonium  respectively,  is  found  to  have  the  spe- 
cific gravity  17-766  in  the  first  case,  and  21-206  in  the  second  (Playfair  and  Joule) ; 
and  the  effect  of  compression  upon  the  malleable  metals  is  generally  very  sensible. 
As  the  rate  of  dilatation  of  different  solids  and  liquids  by  heat  is  very  dissimilar,  it  is 
obvious  their  relations  in  density  may  also  be  disturbed  or  disguised  by  temperature. 
At  present,  I  shall  confine  myself  to  a  summary  of  the  results  of  M.  Kopp  on 
this  subject,  which  partake  least  of  a  speculative  character.  The  atomic  volume, 
which  I  substitute  for  the  specific  volume  of  Dr.  Kopp,  in  the  following  tables,  is 
the  volume  or  measure  of  an  equivalent  or  atomic  proportion  of  the  different  sub- 
stances enumerated.  The  calculated  density  is  obtained  by  dividing  the  atomic 
weight  by  this  volume.  Thus  an  equivalent  of  mercury,  1266  parts  by  weight,  has 
the  volume  93  assigned  to  it.  ISow  1266,  divided  by  93,  gives  13-6  as  the  "calcu- 
lated" specific  gravity,  wbich  coincides  with  the  specific  gravity  of  mercury  actually 
observed  by  Kupffer  and  others.  The  atomic  volume  -for  oxygen  will  afterwards 
appear  to  be  16,  or  a  multiple  of  that  number,  and  is  the  modulus  of  the  scale. 

TABLE  I. 

Atomic  Volume  and  Specific  Gravity  of  Elements. 


Substances 

O    -4-> 

§•§> 

°  °5 

1|1 

HI 
|^> 

Calculated 
Sp.  Grav. 

Observed  Specific  Gravity. 

Antimony  
Arsenic  

Sb 
As 

806 
470 

120 
80 

6-72 

5-87 

6-70  Karsten;  6-6  Breithaupt;  6-85  Mus- 
chenbroeck. 
5-70,  5-96  Guibourt;  5-62  Karsten;  5-67 

Bismuth  

Bi 

1330 

135 

9-85 

Herapath. 
9-88  Thenard;  9-83  Herapath;  9-65  Karsten. 

Bromine  

Br 

489 

160 

3-06 

2-99  Loewig;  2-97  Balard. 

Cadmium  
Chlorine 

Cd 
Cl 

697 
221 

81 
160 

8-60 
1-38 

8-66  Herapath;  8-63  Karsten,  Kopp;  8-60 
Stromeyer. 
1-33  Faraday 

Chromium  .... 
Cobalt  

Cr 
Co 

352 
369 

69 
44 

5-10 
8-39 

5-10  Thomson. 
8-49  Brunner;  8-51  Berz.;  8-71  Lampadius. 

Copper 

Cu 

396 

44 

9-00 

8-96    Berzelius-    9-00   Muschenb  •    8-72 

Cyanogen  
Gold 

Cy 
Au 

165 
1243 

160 

65 

1-03 
19-1 

Karsten. 
About  0-9  Faraday. 
19-26  Brisson. 

Iridium  
Iodine  

Ir 
I 

1233 
789 

57 
160 

21-6 
4-93 

19-5  Mohs;  23-5  Breithaupt;  21-8  Hare. 
4-95  Gay-Lussac. 

Iron 

Fe 

339 

44 

7-70 

7-6   7-8Broling;  7-79  Karsten. 

Lead  

Pb 

1294 

114 

11-35 

11  -33  Kupffer;  11-39  Karsten;  11-35  Hera- 

Manganese... 
Mercury  
Molybdenum 
Nickel  
Osmium  
Palladium.... 
Phosphorus  .. 
Platinum  
Potassium.... 
Rhodium  
Selenium  
Silver  

Mn 

Hg 
Mo 
Ni 
Os 
Pd 
P 
Pt 
K 
R 
Se 
As 

346 
1266 
599 
370 
1244 
666 
196 
1233 
490 
651 
495 
1352 

44 

93 
69 
44 
57 
57 
111 
57 
583 
57 
115 
130 

7-86 
13-6 
8-68 
8-41 
21-8 
11-7 
1-77 
21-6 
0-84 
11-4 
4-30 
10-4 

path. 
8-03  Bachmann;  8-01  John. 
13-6  Kupffer,  Karsten,  Cavallo. 
8-62,  8-64  Bucholz. 
8-40Tourte;  8-38Tupputi;  8-60  Brunner. 
Native  ;   19-5  (?)  Thenard. 
11-3  Wollaston;  12-1  Lowry. 
1-77  Berzelius. 
21-0  Borda;  21-5  Berzelius;  23-5  (?)  Cloud. 
0-86  Gay-Lussac,  Thenard;  0-87  Sementini. 
11-0  Wollaston;  11-2  Cloud. 
4-30,  4-32  Berzelius:  4-31  Boullay. 
10-4  Karsten. 

Sodium 

Na 

291 

292 

0-99 

0*97  Gay-Lussac  and  Thenard. 

Sulphur  

3 

201 

101 

1-99 

1-99,  2-05  Karsten;  1-99  Breithaupt. 

Tin 

St 

735 

101 

7-28 

7-28  Herapath  ;  7-29  Kupffer,  Karsten. 

Titanium  
Tungsten  
Zinc  

T 
W 

Zn 

304 
1183 
403 

57 

69 
58 

5-33 
17-1 

6-95 

5-3  Wollaston  ;  5-28  Karsten. 
17-2  Allan  and  Aiken;   17-4  Bucholz. 
6-92  Karsten  ;  6-86,  7-21  Berzelius. 

ATOMIC  VOLUME  OP  SOLID  BODIES. 


173 


It  will  be  observed  that  certain  analogous  substances  possess  the  same  atomic 
volume: — bromine,  chlorine,  cyanogen,  and  iodine;  chromium,  molybdenum,  and 
tungsten ;  cobalt,  copper,  iron,  manganese,  and  nickel ;  iridium,  osmium,  palladium, 
platinum,  and  rhodium. 

There  are  also  analogous  substances  of  which  the  atomic  volume  of  one  is  double 
that  of  the  other.  The  volume  of  an  equivalent  of  silver  is  double  that  of  gold, 
and  the  volume  of  potassium  double  that  of  sodium. 

When  a  substance  enters  into  combination,  it  either  occupies  its  own  volume,  or 
assumes  a  new  volume,  which  last  may  remain  constant  through  a  class  of  com- 
pounds. Hence  the  volumes  in  the  preceding  table  are  described  as  the  primitive 
atomic  volumes.  The  metals  enumerated  possess  the  following  atomic  volumes  in 
their  salts  :  —  Atomic  volume  in  Salts. 

Ammonium 218 

Barium  143 

Calcium  60 

Magnesium  40 

Potassium  234 

Sodium  130 

Strontium  108 

The  other  metals  are  supposed  to  retain  their  primitive  volumes  in  combination. 

In  explaining  the  atomic  volume  of  carbonates,  it  is  supposed  by  Dr.  Kopp  that 
the  salt-radical  C03  enters  into  its  combinations  with  the  atomic  volume  151. 
In  the  nitrates,  the  salt-radical  N06  is  supposed  to  have  the  atomic  volume  358. 
In  one  class  of  sulphates,  S04  is  supposed  to  have"  the  atomic  volume  236;  in 
another,  the  atomic  volume  186. 

In  the  chromates,  the  atomic  volume  of  Cr04  is  228 ;  and,  in  the  tungstates, 
that  of  W04  is  244. 

The  atomic  volume  of  chlorine  is  196  in  one  class  of  chlorides,  and  245  in  another. 
On  combining  the  atomic  volumes  of  the  metals  contained  in  the  salts  with  these 
suppositions  for  their  salt-radicals,  the  atomic  volume  of  the  compound  is  obtained, 
and  the  following  calculated  specific  gravities  : — 

TABLE  II. — Atomic  Volume  and  Specific  Gravity  of  Salts. 
CARBONATES. 


CARBONATES. 

Atomic 
Weight. 

Formula. 

Calculated 
Atomic  Volume. 

Calcu- 
lated 
Sp.  Gr. 

Observed 
Specific  Gravity. 

Cadmium    .     .    . 

1073 

Cd4-C03 

81-J-151  —  232 

4-63 

4-42  Herapath-  4-49  K 

Xron    

715 

Fe-4-CO, 

144-f-lSl  —  195 

3-67 

3-33  Mohs-  3-87  Naum 

Lead  

1670 

Pb-j-CO, 

114-J-151  —  265 

6-30 

6-43    Karsten  •     6-47 

Manganese    

722 

Mn-fC03 

44-J-151  —  195 

3-70 

Breithaupt. 
3-55   3-59  Mohs 

Silver  

1728 

Aff-J-CO, 

130-J-151  —  281 

6-15 

6-08  Karsten 

Zinc 

779 

Zn-j-CO 

ftft_f_1?>1  —  ?OQ 

3-73 

4-44   Mohs  •    4-4    4-5 

Baryta  

1233 

Ba-l-CO,, 

143  -f  151  —  294 

4-19 

Naumann. 
4-30    Karsten  •     4-24 

632 

•*  T  ^W3 

Ca-f  C03 

60-f-151  —  211 

3-00 

Breit.;  4-30  Mohs. 
fArragonite          3-00 
Breit  ;  2-93  Mohs. 

Magnesia  

534 

Ms-4-CO 

40-|-151  —  191 

2-80 

]  Calc.     spar        2-70 
[      Kar.;2-72Beudanl. 
2-31  Breithaupt' 

Potassa  

866 

K-I-CO 

234-1-151  —  385 

2-25 

3-00,  3-11  Mohs; 
2-88,  2-97  Naum. 
2-26  Karsten 

Soda  

667 

Na-fC03 

130-fl51  —  281 

2-37 

2-47  Karsten 

Strontia 

923 

Sr-f-CO 

10fi_j_lf>l  —  2^Q 

3-56 

3-60  Mohs-  3-62  K 

Dolomite  

1166 

Mg+CO, 

40+151>402 

2-90 

2-88  Mohs 

Mesiline  

1250 

Ca-|-C03 
Mg+C03 

60-J-151  $ 
40+151?       3g 

3-94 

3.35  Mohs 

Fe-fC03 

44-J-151  £  ~ 

174 


ATOMIC    VOLUME   OF    SOLID   BODIES 
NITRATES. 


NITRATES. 

Atomic 
Weight. 

Formula. 

Calculated 
Atomic  Volume. 

Calcu- 
lated 
Sp.  Gr. 

Observed 
Specific  Gravity. 

Lead  

2071 

Pb-}-N06 

114-|-358  —  472 

4-40 

4-40  Karsten  •  4-77  Breit- 

Silver  

2129 

Ae4-N0* 

180-J-358  —  488 

4-36 

haupt;  4-34  Kopp. 
4-36  Karsten 

1004 

Am+NO 

2184-358  —  576 

1-74 

Baryta          . 

1634 

Ba-f-NOs 

143+358  —  501 

3-20 

3-19  Karsten 

Potassa  

1267 

K4-NO* 

234+  358^=592 

2-14 

2-10  Karst  •  2-06  Kopp 

Soda 

1068 

Na+NO 

130_j_2fi8  —  488 

2-19 

2-19  Marx  •    2-20  Kopp 

Stroii  tia  

1324 

Sr+N0« 

108+358  —  466 

2-84 

2-26  Karsten. 
2-89  Karsten. 

SULPHATES:  FIRST  CLASS. 


SULPHATES. 

Atomic 
Weight. 

Formula. 

Calculated 
Atomic  Volume. 

Calcu- 
lated 
Sp.  Gr. 

Observed 
Specific  Gravity. 

Copper  .. 

997 

Cu-f-S04 

444-236—280 

3-56 

3-53  Karsten. 

Silver 

1953 

Air-l-SO, 

1304-236  —  366 

5-34 

5-34  Karsten. 

Zinc  

1004 

*»e  1  kJW4 
Zn-i-SO, 

58+236—  294 

?-42 

3-40  Karsten. 

Lime  

857 

Ca+SO. 

60+236—296 

2-90 

2-96     Naumann;       2-93 

Magnesia  
Soda 

759 
892 

Mg-fS04 
Na+SO 

40+236=276 
1304-236  —  366 

2-75 
2-44 

Karsten. 
2-61  Karsten. 
2-46  Mohs-  2-63  K 

SULPHATES  :  SECOND  CLASS. 


SULPHATES. 

Atomic 
Weight. 

Formula. 

Calculated 
Atomic  Volume. 

Calcu- 
lated 
Sp.  Gr. 

Observed 
Specific  Gravity. 

Lead  
Baryta  

1895 
1458 

Pb4-S04 
Ba4-S0, 

114+186=300 
143+186—  329 

6-32 
4-43 

6-30  Mohs;  6-17  Karst. 
4-45  Mohs  ;  4-20  Karst. 

Potassa 

1091 

K4-SO 

234+186  —  420 

2-60 

2-62  Karst.;  2-66  Kopp. 

Strontia  

1148 

Sr4-S04 

108+186=294 

3-90 

3-95  Breit;  3-59  Karsten. 

CIIROMATES  AND  TUNGSTATES. 


CHROMATES 
and 
TUNGSTATES. 

Atomic 
Weight. 

Formula. 

Calculated 
Atomic  Volume. 

Calcu- 
lated 
Sp.  Gr. 

Observed 
Specific  Gravity. 

Lead  

2046 

Pb+Cr04 

114+228—342 

5-98 

5-95  Breith.;  6-00  Mohs. 

1241 

K+Cr04 

234+228—462 

2-69 

2-64  Karst.;  2-70  Kopp. 

Lead         .   . 

2877 

Pb+W04 

114+244—358 

8-04 

8-0  Gmel.;  8-1  Leonh. 

Lime  

1839 

Ca+W04 

60+244—304 

6-05 

6-04  Kars.;  6-03  Meiss. 

CHLORIDES:  FIRST  CLASS. 


CHLORIDES. 

Atomic 
Weight. 

Formula. 

Calculated 
Atomic  Volume. 

Calcu- 
lated 
Sp.  Gr. 

Observed 
Specific  Gravity. 

Lead  

1736 

Pb+Cl 

114+196  —  310 

5-60 

5-68,  5-80  Karsten;  5-24, 

Silver  

1794 

Aff4-Cl 

130+196—326 

5-50 

5-34  Monro. 
5-50,5-57  Karsten;  5-55 

Barium  

1299 
733 

Ba+Cl 
Na+Cl 

143+196=339 
130+196  —  326 

3-83 
2-25 

Boul.  ;  5-13  Herap. 
3-86  Boul.  ;  3-70  Karst. 
2-26  Mohs;   2-15  Kopp; 

2-08  Karsten. 

ATOMIC  VOLUME   OF   SOLID  BODIES. 
CHLORIDES:    SECOND  CLASS. 


175 


CHLORIDES. 

Atomic 
Weight. 

Formula. 

Calculated 
Atomic  Volume. 

Calcu- 
lated 
Sp.  Gr. 

Observed  Specific  Gravity. 

Copper  .  .. 

1234 

2Cu-f-Cl 

884-245=333 

3-70 

3-68  Karsten. 

Mercury  -I 

Ammonium  .... 
Calcium  ......... 

1708 
2974 
669 
698 

Hg+Cl 
2Hg4-Cl 
Am-j-Cl 
Ca-fCl 

93-f-245=338 
1864-245=431 
2184-245=463 
604-245—305 

5-05 
6-90 
1-44 
2-29 

5-14  Gmel.  ;   5-43  Boul.  ; 
5-40  Karsten. 
6-99  Karsten  ;  6-71  Hera- 
path;  7-14  Boullay. 
1-45  Watson;  1-50  Kopp; 
1-53  Mohs. 
2-21,  2-27  Boullay;  1-92 

Potassium  
Strontium  

932 
989 

R4-C1 
Sn+Cl 

2344-245=479 
108+245=353 

1-94 

2-80 

Karsten. 
1-94  Kopp  ;  1-92  Karsten. 
2-80  Karsten. 

In  explaining  the  specific  gravity  of  oxides,  it  is  necessary  to  make  three  assump- 
tions for  the  specific  volume  of  oxygen.  In  the  first  small  class  of  oxides,  the  oxy- 
gen is  contained  with  the  atomic  volume  16 ;  in  the  second  and  large  class,  with  the 
atomic  volume  32 ;  and,  in  the  third  class,  with  the  atomic  volume  64.  The  metals 
are  supposed  to  retain  their  primitive  atomic  volumes. 

TABLE  III.  —  Jltomic  Volume  and  Specific  Gravity  of  Oxides. 
FIRST    CLASS. 


OXIDES. 

Atomic 
Weight. 

Formula. 

Calculated 
Atomic  Volume. 

Calcu- 
lated 
Sp.  Gr. 

Observed  Specific  Gravity. 

Antimony 

1006 

Sb-j-20 

1204-32  —  154 

6-53 

6-58  Boullay  •  6-70  Karat 

Chromium  
Tin  

1003 
935 

2Cr-f30 
Sn-j-20 

1384-48=186 
101  +  32  —  133 

5-39 
7-03 

5-21  Wohler. 
6-96  Mohs;  6-90  Boullay  • 

6-64  Herapath. 

SECOND  CLASS. 


OXIDES. 

Atomic 
Weight. 

Formula. 

Calculated 
Atomic  Volume. 

Calcu- 
lated 
Sp.  Gr. 

Observed  Specific  Gravity. 

Antimony  
Bismuth     . 

1913 
2960 

2Sb+30 
2Bi+30 

240+96=336 
270+96  —  366 

5-69 
8-09 

5-78  Boullay;  5-57  Mohs. 
8-17  Karst  •  8-21  Herap  • 

Cadmium  
Cobalt 

797 
1038 

Cd+0 
2Co4-30 

81  +  32=113 

88  +  96  —  184 

7-05 

5-64 

8-45  Koyer  and  Dum. 
6-95  Karsten. 
5-60  Boullay'  5  '32  Herap 

Copper  

496 

978 

Cu+0 
2Fe+30 

44+32=  76 
88+96  —  184 

6-53 
5-31 

6-43  Karst.  ;  6-13  Boul.  ; 
6-40  Herapath. 
5-23  Boullay  5-25  Mohs 

Lead  

,    1394 
1494 

Pb  +  0 
Pb+20 

114+32=146 
114+64  —  178 

9-55 
8-40 

9-50  Boullay;  9-28  Herap.; 
9-21  Karsten. 
8-90  Herap  •  8-92  Karst 

Manganese  
Mercury  

2889 

446 
1366 

2Pb+30 

Mn+0 
He4-0 

228+96=324 

44+32—  76 
93  +  32  —  125 

8-91 

5-87 
10-9 

8-94  Muschenbroek  ;  8-60 
Karst,;  9-20  Boullay. 
4-73  Herapath. 
11-0  Boullay  11-1  Hera 

Molybdenum... 
Tin  

799 
835 

Mo+20 
Sn  I  0 

69+64=133 
101  +  32  —  133 

6-01 

6-28 

path;   11-2  Karsten. 
5-67  Bucholz. 
6*67  Herapath 

Titanium  
Zinc  

504 
503 

Ti+20 
Zn  1  O 

67+64—121 
58+3°  —  90 

4-16 
5-48 

4-18Klaproth;  4-20,  4-25 
Breithaupt. 
5-43  Mohs  •  5'60  Boullay 

Ilmemte  

942  J 

f      1  4-96  —  197 

4.70 

5-73  Karsten. 
4-73,   4-79   Breithaupt; 

Ti   /    ' 

v  &7  /    ' 

4-75,  4-78  Kupffer. 

176 


CHEMICAL   AFFINITY 
THIRD  CLASS. 


OXIDES. 

Atomic 
Weight. 

Formula. 

Calculated 
Atomic  Volume. 

Calcu- 
lated 
Sp.  Gr. 

Observed  Specific  Gravity 

Copper  .          . 

892 

2Cu-j-0 

gg_j_  64  —  152 

5-87 

5  '75  Karsten    Boyer  and 

Mercury 

2632 

2Hff-l-0 

186-f-  64  —  950 

10-05 

Dumas  ;  6-05  Herapach. 
10-69  Herap  •  8*95Xknit 

Molybdenum... 
Silver 

899 
1452 

Mo+30 
Aff-4-O 

69  -f  192=261 
1304-   64  —  194 

3-44 

7-48 

3-46  Bergman,  Thomson  ; 
3-49  Berzelius. 
7'14Herapatlr  7-25  Boul- 

Tungsten  

1483 

Ag-J-V7 

W+30 

69+192=261 

5-68 

lon;  8-26  Karsten. 
5-27  Herapath;  6-12  Ber- 
zelius ;  7-14  Karsten. 

Dr.  Kopp  has  endeavoured  to  determine  the  atomic  volume  of  the  constituents 
3f  many  other  classes  of  compounds.  The  specific  gravity  of  the  compounds  of  sul- 
phur and  arsenic  with  the  metals,  of  water  with  oxides  and  salts,  of  chlorine  with 
the  non-metallic  elements,  are  explained  in  a  similar  manner  on  a  small  number  of 
suppositions.  He  also  shows  with  considerable  success  that  in  those  isomorphous 
substances,  of  which  the  crystalline  form  is  only  similar,  and  not  absolutely  identi- 
cal, as  the  carbonates  (p.  140),  the  observed  difference  between  the  atomic  volumes 
corresponds  with  the  difference  between  the  crystalline  forms.  The  variation  in  the 
atomic  volume  is  thus  manifested  by  a  variation  in  the  crystalline  form. 

[See  Supplement,  p.  685.] 


CHAPTER  IV. 

CHEMICAL   AFFINITY. 

IN  the  preceding  section,  compound  bodies  have  been  viewed  as  already  formed, 
and  existing  in  a  state  of  rest.  The  arrangement,  weights,  and  other  properties  of 
their  atoms,  have  also  been  examined  with  the  relations  and  classification  of  the  com- 
pounds themselves.  But  chemistry  is  more  than  a  descriptive  science ;  for  it  em- 
braces, in  addition  to  views  of  composition,  the  consideration  of  the  action  of  bodies 
upon  each  other,  which  leads  to  the  formation  and  destruction  of  compounds.  Cer- 
tain bodies,  when  placed  in  contact,  exhibit  a  proneness  to  combine  with  each  other, 
or  to  undergo  decomposition,  while  others  may  be  mixed  most  intimately  without 
change.  The  actual  phenomena  of  combination  suggest  the  idea  of  peculiar  attach- 
ments and  aversions  subsisting  between  different  bodies,  and  it  was  in  this  figurative 
sense  that  the  term  affinity  was  first  applied  by  Boerhaave  to  a  property  of  matter. 
A  specific  attraction  between  different  kinds  of  matter  must  be  admitted  as  the 
cause  of  combination,  and  this  attraction  may  be  conveniently  distinguished  as  che- 
mical affinity. 

The  particles  of  a  body  in  the  solid  or  liquid  state  exhibit  an  attraction  for  each 
other,  which  is  the  force  of  cohesion,  and  even  different  kinds  of  matter  nave  often 
an  attraction  for  each  other,  which  is  probably  of  the  same  nature,  although  distin- 
guished as  adhesion.  This  force  retains  bodies  in  contact  which  are  once  placed  in 
sufficient  proximity  to  each  other.  It  is  exhibited  in  the  adhesion  of  two  smooth 
pieces  of  lead  pressed  together,  or  perfectly  flat  pieces  of  plate-glass,  which  some- 
times cannot  again  be  separated.  The  action  of  glue,  wax,  mortar,  and  other 
cements,  in  attaching  bodies  together,  depends  entirely  upon  the  same  force.  In 
detaching  glue  from  the  surface  of  glass,  the  latter  is  sometimes  injured,  and  por- 
tions of  it  are  torn  off  by  the  glue,  the  adhesive  attraction  of  the  two  bodies  being 


CHEMICAL   AFFINITY.  177 

greater  than  the  cohesion  of  the  glass.  The  property  of  water  to  adhere  to  solid 
surfaces  and  wet  them,  its  imbibition  by  a  sponge,  the  ascent  of  liquids  in  narrow 
tubes,  and  other  phenomena  of  capillary  attraction,  and  the  rapid  diffusion  of  a  drop 
of  oil  over  the  surface  of  water,  are  illustrations  of  the  same  attraction  between  a 
liquid  and  a  solid,  and  between  different  liquids.  But  this  kind  of  attraction  is  de- 
ficient in  a  character  which  is  never  absent  in  true  chemical  affinity  —  it  effects  no 
change  in  the  properties  of  bodies.  It  may  bind  different  kinds  of  matter  together, 
but  if  does  not  alter  their  nature. 

The  tendency  of  different  gases  to  diffuse  through  each  other  till  a  uniform  mix- 
ture is  formed,  is  another  property  of  matter,  —  the  effect  of  a  force  wholly  indepen- 
dent of  chemical  affinity.  It  is  certain  that  this  physical  property  is  not  lost  in 
liquids,  and  that  it  contributes  to  that  equable  diffusion  of  a  salt  through  a  menstru- 
um, which  occurs  spontaneously,  and  \ntfthout  agitation  to  promote  it.  (Jerichau, 
in  Pogo-endorff's  Annalen,  xxxiv.  613;  or  Dove  and  Moser's  Repertorium  der  Phy- 
sik,  i.  96,  1837.) 

Solution.  —  The  attraction  between  salt  and  water,  which  occasions  the  solution 
of  the  former,  differs  in  several  circumstances  from  the  affinity  which  leads  to  the 
production  of  definite  chemical  compounds.  In  solution,  combination  takes  place  in 
indefinite  proportions,  a  certain  quantity  of  common  salt  dissolving  in,  or  combining 
with  any  quantity  of  water  however  large ;  while  a  certain  quantity  of  water,  such 
as  100  parts,  can  dissolve  any  quantity  of  that  salt  less  than  37  parts,  the  proportion 
which  saturates  it.  Water  has  a  constant  solvent  power  for  every  other  soluble  salt; 
but  the  maximum  proportion  of  salt  dissolved,  or  the  saturating  quantity,  has  no 
relation  to  the  atomic  weight  of  the  salt,  and  indeed  varies  exceedingly  with  the 
temperature  of  the  solvent.  The  limit  to  the  solubility  of  a  salt  seems  to  be  imme- 
diately occasioned  by  its  cohesion.  Water,  in  proportion  as  it  takes  up  salt,  has  its 
power  to  disintegrate  and  dissolve  more  of  the  soluble  body  gradually  diminished ; 
it  dissolves  the  last  portions  slowly  and  with  difficulty,  and  at  last,  when  saturated, 
is  incapable  of  overcoming  the  cohesion  of  more  salt  that  may  be  added  to  it.  The 
solubility  in  water  of  another  body  in  the  liquid  state  is  not  restrained  by  cohesion, 
and  is  in  general  unlimited.  Thus  alcohol,  and  also  soluble  salts  above  the  tempe- 
rature at  which  they  liquefy  in  their  water  of  crystallization,  dissolve  in  water  in 
any  proportion.  Generally  speaking,  also,  those  salts  dissolve  in  largest  quantity 
which  are  most  fusible,  or  of  which  the  cohesion  is  most  easily  overcome  by  heat,  as 
the  hydrated  salts ;  and  among  anhydrous  salts,  the  nitrates,  chlorates,  chlorides,  and 
iodides,  which  are  all  remarkable  for  their  fusibility.  In  this  species  of  combination, 
bodies  are  not  materially  altered  in  properties;  indeed,  are  little  affected  except 
in  their  cohesion. 

The  union  also  between  a  body  and  its  solvent  differs  in  a  marked  manner  from 
proper  chemical  combination  in  the  relation  of  the  bodies  to  each  other  which  exhibit 
it.  Bodies  combine  chemically  with  so  much  the  more  force  as  their  properties  are 
more  opposed,  but  they  dissolve  the  more  readily  in  each  other,  the  more  similar 
their  properties.  Thus,  metals  combine  with  non-metallic  bodies,  acids  with  alka- 
lies ;  but  to  dissolve  a  metal,  another  metal  must  be  used,  such  as  mercury ;  oxi- 
dated bodies  dissolve  in  oxidated  solvents,  as  the  salts  and  acids  in  water;  while 
liquids  which  contain  much  hydrogen  are  the  best  solvents  of  hydrogenated  bodies 
— an  oil,  for  instance,  of  a  fat  or  a  resin;  alcohol  and  ether  dissolving  the  essential 
oils  and  most  organic  principles,  but  few  salts  of  oxygen  acids.  The  force  which 
produces  solution  differs,  therefore,  essen-tially  from  chemical  affinity  in  being  exerted 
between  analogous  particles,  in  preference  to  particles  which  aie  very  unlike;  and 
resembles  more,  in  this  respect,  the  attraction  of  cohesion. 

A  more  accurate  idea  of  the  varying  solubility  of  a  salt  at  different  temperatures 
may  be  conveyed  by  a  curve  constructed  to  represent  it,  than  by  any  other  means 
The  perpendicular  lines  in  the  following  diagram,  indicate  the  degrees  of  tempera- 
ture which  are  marked  below  them,  and  the  horizontal  lines,  quantities  of  salt  dis- 
solved by  100  parts  by  weight, of  water.  The  proportion  of  any  salt  dissolved  at  a 

1  O 


178 


CHEMICAL    AFFINITY. 


particular  temperature  may  be  learned  by  carrying  the  eye  along  the  perpendicular 
line  expressing  that  temperature,  till  it  cuts  the  curve  of  the  salt,  and  then  horizon- 
tally to  the  column  of  parts  dissolved.1 


SOLUBILITY   OP    SALTS    IN    ONE   HUNDRED   PARTS    OF   WATER, 

80 


32°   50°   68°   86°   104°  122°  140°  158°   176°  194°  212°  230° 

It  will  be  observed  that  the  perpendicular  lines  advance  by  9°,  the  first  being 
32°,  and  the  last  230°.  The  solubility  of  nitrate  of  potassa  increases  from  13  parts 
in  100  water  at  32°,  to  80  parts  at  118°,  or  very  rapidly  with  the  temperature. 
Sulphate  of  soda  is  seen  by  the  form  of  its  curve  to  increase  in  solubility  from  5 
parts  at  32°  to  52  parts  at  92°,  but  then  to  diminish  in  solubility  with  farther  ele- 
vation of  temperature.  In  this  salt,  sulphate  of  magnesia  and  chloride  of  barium, 
the  solubility  is  expressed  in  parts  of  the  anhydrous,  and  not  the  hydrated  salt. 
The  lines  of  chloride  of  barium  and  chloride  of  potassium  are  parallel,  showing  a 
remarkable  relation  between  the  solubilities  of  these  two  salts,  which  does  not  appear 
in  any  others.  The  line  of  chloride  of  sodium  is  observed  to  cut  all  the  lines  of 
temperature  at  the  same  height,  100  parts  of  water  dissolving  37  parts  of  that  salt 
at  all  temperatures. 

Chemical  affinity  acts  only  at  insensible  distances,  and  has  no  effect  in  causing 
bodies  to  approach  each  other  which  are  not  in  contact,  differing  in  this  respect  from 
the  attraction  of  gravitation,  which  acts  at  all  distances,  however  great,  although 
with  a  diminishing  force.  Hence,  the  closest  approximation  of  unlike  particles  is 
necessary  to  develope  their  affinities,  and  produce  combination.  Sulphur  and  copper 
in  mass  have  no  effect  upon  each  other,  but  if  both  be  in  a  state  of  great  division, 
and  rubbed  together  in  a  mortar,  a  powerful  affinity  is  brought  into  play,  the  bodies 
themselves  disappear,  and  sulphuret  of  copper  is  produced  by  their  union,  with  the 
evolution  of  much  heat.  The  affinity  of  bodies  is,  therefore,  promoted  by  every 
thing  which  tends  to  their  close  approximation ;  in  solids,  by  their  pulverization  and 
intermixture,  this  attraction  residing  in  the  ultimate  particles  of  bodies ;  in  gases, 
by  their  spontaneous  diffusion  through  each  other,  which  occasions  a  more  complete 
intermixture  than  is  attainable  by  mechanical  means;  and  between  liquids,  or 
between  a  liquid  and  solid,  by  the  adhesive  attraction  which  liquids  possess,  which 
must  lead  to  perfect  contact,  and  also  by  a  disposition  of  liquid  bodies  to  intermix, 
of  the  same  physical  character  as  gaseous  diffusion.  Elevation  of  temperature  has 

1  An  extensive  and  very  careful  series  of  experiments  on  the  solubility  of  salts  in  water 
*t  different  temperatures  has  been  made  by  M.  Poggiale,  Ann.  de  Chim.  et  de  Phys.  3e  Sor, 
T.  fill.  p.  463 ;  and  the  Rapport  Annud  of  Berzelius,  Paris,  1846,  p.  18. 


SOLUBILITY    OF    SALTS.  179 

certainly  often  a  specific  action  in  increasing  the  affinity  of  two  bodies,  but  it  also  oftea 
acts  by  producing  a  perfect  contact  between  them,  from  the  fusion  or  vaporization  of 
one  or  both  bodies.  Hence,  no  practice  is  more  general  to  promote  the  combination 
of  bodies  than  to  heat  them  together. 

If  the  affinity  between  two  gases  is  sufficiently  great  to  begin  combination,  the 
process  is  never  interrupted,  but  is  continued  from  the  diffusion  of  the  gases  through 
each  other  till  complete,  or  at  least  till  one  of  the  gases  is  entirely  consumed.  Thus, 
when  hydrochloric  acid  and  arnmomacal  gases,  in  equal  measures,  are  introduced  into 
a  jar  containing  at  the  same  time  a  large  quantity  of  air,  the  formation  of  hydrochlo- 
rate  of  ammonia  proceeds,  the  gases  appearing  to  search  out  each  other,  till  no  por- 
tion of  uncombined  gas  remains.  The  combination  of  two  liquids,  or  of  a  liquid  and 
a  solid,  is  also  facilitated  in  the  same  manner  by  the  mobility  of  the  fluid,  and  pro- 
ceeds without  interruption,  unless,  perhaps,  the  product  of  the  combination  be  solid, 
and  by  its  formation  interpose  an  obstacle  to  the  contact  of  the  combining  bodies. 
But  the  affinities  of  two  solids  which  are  not  volatile  are  rarely  developed  at  all, 
owing  to  the  imperfection  of  contact.  Even  the  action  of  very  powerful  affinities 
between  a  solid  and  a  liquid  or  a  gas,  is  often  arrested  in  the  outset  from  the  phy- 
sical condition  of  the  former.  Thus,  the  affinity  between  oxygen  and  lead  is  cer- 
tainly considerable,  for  the  metal  is  rapidly  converted  into  a  white  oxide  when 
ground  to  powder  and  agitated  with  water  in  its  usual  aerated  condition  j  and  in  the 
state  of  extreme  division  in  which  lead  is  obtained  by  calcining  its  tartrate  in  a  glass 
tube,  the  metal  is  a  pyrophorus,  and  combines  with  oxygen  when  cold  with  so  much 
avidity  as  to  take  fire  and  burn  the  moment  it  is  exposed  to  the  air.  Iron  also,  in 
the  spongy  and  divided  state  in  which  it  is  procured,  by  reducing  the  peroxide  by 
means  of  hydrogen  gas  at  a  low  red  heat,  absorbs  oxygen  with  equal  avidity  at  the 
temperature  of  the  air,  and  takes  fire  and  burns.  But  notwithstanding  an  affinity 
for  oxygen  of  such  intensity,  these  metals  in  mass  oxidate  very  slowly  in  air,  parti- 
cularly lead,  which  is  quickly  tarnished  indeed,  but  the  thin  coating  of  oxide  formed 
does  not  penetrate  to  a  sensible  depth  in  the  course  of  several  years.  The  suspen- 
sion of  the  oxidation  may  be  partly  due  to  the  comparatively  small  surface  which  a 
compact  body  exposes  to  air,  and  which  becomes  covered  by  a  coat  of  oxide,  and 
protected  from  farther  change ;  but  partly  also  to  the  effect  of  the  conducting  power 
of  a  considerable  mass  of  metal  in  preventing  the  elevation  of  temperature  consequent 
upon  the  oxidation  of  its  surface.  For  metals  oxidate  with  increased  facility  at  a 
high  temperature,  such  as  the  lead  pyrophorus  quickly  attains  from  the  oxidation  of 
the  great  surface  which  it  exposes,  compared  with  its  weight.  The  heat  from  the 
oxidation  of  the  superficial  particles  of  the  compact  metal,  however,  is  not  accumu- 
lated, but  carried  off  and  dissipated  by  the  conducting  power  of  the  contiguous  par- 
ticles, so  that  elevation  of  temperature  is  effectually  repressed.  It  thus  appears  that 
the  state  of  aggregation  of  a  solid  may  oppose  an  insuperable  bar  to  the  action  of  a 
very  powerful  affinity. 

The  affinity  of  two  bodies,  one  or  both  of  which  are  in  the  state  of  gas,  is  often 
promoted  in  an  extraordinary  manner  by  the  contact  of  certain  solid  bodies.  Thus, 
oxygen  and  hydrogen  gases  may  be  mixed  and  retained  for  any  length  of  time  in 
that  state  without  exhibiting  any  affinity  for  each  other,  and  the  gaseous  mixture 
may,  indeed,  be  heated  in  a  glass  vessel  to  any  temperature  short  of  redness  without 
showing  any  disposition  to  combine.  But  if  a  clean  plate  of  platinum  be  introduced 
into  the  cold  mixture,  the  gases  in  contact  with  the  metallic  surface  instantly  unite 
and  form  water ;  other  portions  of  the  mixture  come  then  in  contact  with  the  plati- 
num, and  combine  successively  under  its  influence,  so  that  a  large  quantity  of  the 
gaseous  mixture  may  be  quickly  united.  The  temperature  of  the  platinum  also 
rises,  from  the  heat  evolved  by  the  combination  occurring  at  its  surface,  and  the 
influence  of  the  metal  increasing  with  its  temperature,  combination  proceeds  at  an 
accelerated  rate,  till  the  platinum  becoming  red  hot,  may  cause  the  combination  to 
extend  to  a  distance  from  it,  by  kindling,  the  gaseous  mixture.  Platinum  acts  in 
this  manner  with  greatest  energy  when  in  a  highly  divided  state,  as  in  the  form  of 


180  CHEMICAL    AFFINITY. 

spongy  platinum,  owing  to  the  greater  surface  exposed,  and  the  rapidity  with  which 
it  is  heated.  The  metal  itself  contributes  no  element  to  the  water  formed,  and  is  in 
no  respect  altered.  It  is  an  action  of  the  metallic  surface,  which  must  be  perfectly 
clean,  and  is  retarded  or  altogether  prevented  by  the  presence  of  oily  vapours  and 
many  other  combustible  gases,  which  soil  the  metallic  surface.  Mr.  Faraday  is  dis- 
posed to  refer  the  action  to  an  adhesive  attraction  of  the  gases  for  the  metal,  under 
the  influence  of  which  they  are  condensed  and  their  particles  approximated  within 
the  sphere  of  their  mutual  attraction,  so  as  to  combine.  This  opinion  is  favoured 
by  the  circumstance  that  the  property  is  not  peculiar  to  platinum,  but  appears  also 
in  other  metals,  in  charcoal,  pounded  glass,  and  all  other  solid  bodies ;  although  all 
of  them,  except  the  metals,  act  only  when  their  temperature  is  above  the  boiling 
point  of  mercury.  But,  on  the  other  hand,  at  low  temperatures,  the  property 
appears  to  be  confined  to  a  few  metals  only  which  resemble  platinum  in  their  che- 
mical characters  ;  namely,  in  having  little  or  no  disposition  to  combine  with  oxygen 
gas,  and  in  not  undergoing  oxidation  in  the  air.  The  action  of  platinum  may,  there- 
fore, be  connected  with  its  chemical  properties,  although  in  a  way  which  is  quite 
unknown  to  us.  The  same  metal  disposes  carbonic  oxide  gas  to  combine  with  oxy- 
gen, but  much  more  slowly  than  hydrogen ;  and  it  is  remarkable  that  if  the  most 
minute  quantity  of  carbonic  oxide  be  mixed  with  hydrogen,  the  oxidation  of  the 
latter  under  the  influence  of  the  platinum  is  arrested,  and  not  resumed  till  after  the 
carbonic  oxide  has  been  slowly  oxidated  and  consumed,  which  thus  takes  the  prece- 
dence of  the  hydrogen  in  combining  with  oxygen.  This  extraordinary  interference 
of  a  minute  quantity  of  carbonic  oxide  gas,  which  cannot  from  its  nature  be  supposed 
to  soil  the  surface  of  the  platinum  like  a  liquefiable  vapour,  seems  to  point  to  a  che- 
mical, perhaps  to  an  electrical  explanation  of  the  action  of  the  platinum,  rather  than 
to  the  adhesive  attraction  of  the  metal.  The  oxidation  of  alcohol  at  the  temperature 
of  the  air,  and  also  at  a  low  red  heat,  is  promoted  in  the  same  manner  by  contact 
with  platinum. 

Order  of  affinity.  —  The  affinity  between  bodies  appears  to  be  of  different  de- 
grees of  intensity.  Lead,  for  instance,  has  certainly  a  greater  affinity  than  silver  for 
oxygen,  the  oxide  of  the  latter  being  easily  decomposed  when  heated  to  redness, 
while  the  oxide  of  the  former  may  be  exposed  to  the  most  intense  heat  without  losing 
a  particle  of  oxygen.  Again,  it  may  be  inferred  that  potassium  has  a  still  greater 
affinity  for  oxygen  than  lead  possesses,  as  we  find  the  oxide  of  lead  easily  reduced 
to  the  metallic  state  when  heated  in  contact  with  charcoal,  while  potassa  is  decom- 
posed in  the  same  manner  with  great  difficulty.  But  the  order  of  affinity  is  often 
more  strikingly  exhibited  in  the  decomposition  of  a  compound  by  another  body. 
Thus,  sulphuretted  hydrogen  gas  is  decomposed  by  iodine,  which  combines  with  the 
hydrogen,  forming  hydriodic  acid,  and  liberates  sulphur.  The  affinity  of  iodine  for 
hydrogen  is,  therefore,  greater  than  that  of  sulphur  for  the  same  body.  But  hydri- 
odic acid  is  deprived  of  its  hydrogen  by  bromine,  and  hydrobromic  acid  is  formed ; 
and  this  last  is  decomposed  in  its  turn  by  chlorine,  and  hydrochloric  acid  produced. 
It  thus  appears  that  the  order  of  the  affinity  of  the  elements  mentioned  for  hydrogen 
is,  chlorine,  bromine,  iodine,  sulphur.  The  order  of  decompositions,  in  the  precipi- 
tation of  metals  by  each  other  from  their  saline  solutions,  also  indicates  the  degree 
of  affinity.  Thus,  from  the  decomposition  of  the  nitrates  of  the  following  metals, 
the  order  of  their  affinity  for  nitric  acid  and  oxygen  may  be  inferred  to  be  as  fol- 
lows:—  zinc,  lead,  copper,  mercury,  silver;  zinc  throwing  down  lead  from  the 
nitrate  of  lead,  and  all  the  other  metals  which  follow  it;  lead  throwing  down  cop- 
per ;  copper,  mercury ;  and  mercury,  silver ;  while  nitrate  of  zinc  itself  is  not  affected 
by  any  other  metal,  and  nitrate  of  silver  is  decomposed  by  all  the  metals  enumerated. 
Bodies  were  first  thus  arranged  according  to  the  degree  of  their  affinity  for  a  parti- 
cular substance,  inferred  from  the  order  of  their  decompositions,  by  Geoffroy  and 
Bergman,  and  tables  of  affinity  constructed,  of  which  the  following  is  an 
example :  — 


ORDER   OF   DECOMPOSITION.  181 

Order  of  Affinity  of  the  Alkalies  and  Earths  for  Sulphuric  Acid. 

Baryta. 

Strontia. 

Potassa. 

Soda. 

Lime. 

Ammonia. 

Magnesia. 

Baryta  is  capable  of  taking  sulphuric  acid  from  strontia,  potassa,  and  every  other 
base  which  follows  it  in  the  table,  —  the  experiment  being  made  upon  sulphates  of 
these  bases  dissolved  in  water;  while  sulphate  of  baryta  is  not  decomposed  by  any 
other  base.  Lime  separates  ammonia  and  magnesia  from  sulphuric  acid,  but  has  no 
effect  upon  the  sulphates  of  soda,  potassa,  strontia,  and  baryta;  and  in  the  same 
manner  any  other  base  decomposes  the  sulphates  of  the  bases  below  it  in  the  column, 
but  has  no  effect  upon  those  above  it.  Tables  of  this  kind,  when  accurately  con- 
structed, may  convey  much  valuable  information  of  a  practical  kind,  but  it  is  never 
to  be  forgotten  that  they  are  strictly  tables  of  the  order  of  decomposition  and  of  the 
comparative  force  or  order  of  affinity  in  one  set  of  conditions  only.  This  will  appear 
by  examining  how  far  decomposition  is  affected  by  accessory  circumstances  in  a  few 
cases. 

Circumstances  which  affect  the  order  of  decomposition.  —  Volatility  in  a  body 
promotes  its  separation  from  others  which  are  more  fixed,  and  consequently  facilitates 
the  decomposition  of  compounds  into  which  the  volatile  body  enters.  Hence,  by 
the  agency  of  heat,  water  is  separated  from  hydrated  salts ;  ammonia,  from  its  com- 
binations with  a  fixed  acid,  such  as  the  phosphoric ;  and  a  volatile  acid  from  many 
of  its  salts  :  as  sulphuric  acid  from  the  sulphate  of  iron,  carbonic  acid  from  the  car- 
bonate of  lime,  &c.  Ammonia  decomposes  hydrochlorate  of  morphia  at  a  low  tem- 
perature, but,  on  the  other  hand,  morphia  decomposes  the  hydrochlorate  of  ammonia 
at  the  boiling  point  of  water,  and  liberates  ammonia,  owing  to  the  volatility  of  that 
body.  The  fixed  acids,  such  as  the  silicic  and  phosphoric,  disengage  in  the  same 
way  at  a  high  temperature  those  acids  which  are  generally  reputed  most  powerful, 
and  by  which  silicates  and  phosphates  are  decomposed  with  facility  at  a  low  tempe- 
rature. Many  such  cases  might  be  adduced  in  which  the  order  of  decomposition  is 
reversed  by  a  change  of  temperature.  The  volatility  of  one  of  its  constituents  must, 
therefore,  be  considered  an  element  of  instability  in  a  compound. 

Decomposition  from  unequal  volatility  is,  of  course,  checked  by  pressure,  and 
promoted  by  its  removal  and  by  every  thing  which  favours  the  escape  of  vapour; 
such  as  the  presence  of  an  atmosphere  of  a  different  sort  into  which  the  volatile 
constituent  may  evaporate.  Carbonate  of  lime  is  decomposed  easily  at  a  red  heat, 
provided  a  current  of  air  or  of  steam  is  passing  over  it  which  may  carry  off  the 
carbonic  acid  gas,  but  the  decomposition  ceases  when  the  carbonate  is  surrounded 
by  an  atmosphere  of  its  own  gas ;  and  the  carbonate  may  even  be  heated  to  fusion, 
in  the  lower  part  of  a  crucible,  without  decomposition.  Here  the  occurrence  of 
decomposition  depends  entirely  upon  the  existence  of  a  foreign  atmosphere  into 
which  carbonic  acid  can  diffuse.  Nitrates  of  alumina,  and  peroxide  of  iron  in  solu- 
tion, are  decomposed  by  the  spontaneous  evaporation  of  their  acid,  even  at  the 
temperature  of  the  air;  and  so  is  an  alkaline  bicarbonate  when  in  solution,  but  not 
when  dry.  A  change  in  the  composition  of  the  gaseous  atmosphere  may  affect  the 
order  of  decomposition,  as  in  the  following  cases :  — 

When  steam  is  passed  over  iron  at  a  red  heat,  a  portion  of  it  is  decomposed,  oxide 
of  iron  being  formed  and  hydrogen  gas  evolved.  From  this  experiment  it  might  be 
inferred  that  the  affinity  of  iron  for  oxygen  is  greater  than  that  of  hydrogen.  But, 
let  a  stream  of  hydrogen  gas  be  conducted  over  oxide  of  iron  at  the  very  same  tem- 
perature, and  water  is  formed,  while  the  oxide  of  iron  is  reduced  to  the  metallic 
state.  Here  the  hydrogen  appears  to  have  the  greater  affinity  for  oxygen.  But  the 
result  is  obviously  connected  with  the  relative  proportion  between  the  hydrogen  and 


182  CHEMICAL   AFFINITY. 

steam  which  are  at  once  in  contact  with  the  metal  and  its  oxide  at  a  red  heat. 
When  steam  is  in  excess,  water  is  decomposed,  but  when  hydrogen  is  in  excess, 
oxide  of  iron  is  decomposed ;  and  why  ?  because  the  excess  of  steam  in  the  first 
case  is  an  atmosphere  into  which  hydrogen  can  diffuse,  and  the  disengagement  of 
that  gas  is  therefore  favoured;  but  in  the  second  case  the  atmosphere  is  principally 
hydrogen,  and  represses  the  evolution  of  more  hydrogen,  but  facilitates  that  of 
steam.  The  affinity  of  iron  and  hydrogen  for  oxygen  at  the  temperature  of  the 
experiment  is  so  nearly  balanced,  that  the  one  affinity  prevails  over  the  other,  accord- 
ing as  there  is  a  proper  atmosphere  into  which  the  gaseous  product  of  its  action  may 
diffuse.  This  affords  an  intelligible  instance  of  the  influence  of  mass  or  quantity  of 
material,  in  promoting  a  chemical  change ;  the  steam  or  the  hydrogen,  as  it  prepon- 
derates, exerting  a  specific  influence,  in  the  capacity  of  a  gaseous  atmosphere. 

The  remarkable  decomposition  of  alcohol  by  sulphuric  acid,  which  affords  ether, 
is  another  similar  illustration  of  decomposition  depending  upon  volatility,  and  affected 
by  changes  in  the  nature  of  the  atmosphere  into  which  evaporation  takes  place. 
Alcohol  or  the  hydrate  of  ether  is  added  in  a  gradual  manner  to  sulphuric  acid 
somewhat  diluted,  and  heated  to  280°.  In  these  circumstances,  the  double  sulphate 
of  ether  and  water  is  formed ;  water,  which  was  previously  combined  as  a  base  to 
the  acid,  being  displaced  by  ether,  and  set  free  together  with  the  water  of  the 
alcohol.  The  first  effect  of  the  reaction,  therefore,  is  the  disengagement  of  watery 
vapour,  and  the  creation  of  an  atmosphere  of  that  substance  which  tends  to  check 
its  farther  evolution.  But  the  existence  of  such  an  atmosphere  offers  a  facility  for 
the  evaporation  of  ether,  which  accordingly  escapes  from  combination  with  the  acid 
and  continues  to  be  replaced  by  the  water,  the  affinity  of  sulphuric  acid  for  water 
and  for  ether  being  nearly  equal,  till  ether  forms  such  a  proportion  of  the  gaseous 
atmosphere  as  to  check  its  own  evolution,  and  to  favour  the  evolution  of  watery 
vapour.  Then  the  sulphate  of  ether  conies  in  its  turn  to  be  decomposed  as  before, 
and  ether  evolved.  Hence,  both  ether  and  water  distil  over  in  this  process,  the 
evolution  of  one  of  these  bodies  favouring  the  separation  and  disengagement  of  the 
other.  In  this  description,  the  evolution  of  water  and  ether  are  for  the  sake  of 
perspicuity  supposed  to  alternate,  but  it  is  evident  that  the  result  of  such  an  action 
will  be  the  simultaneous  evolution  of  the  two  vapours  in  a  certain  constant  relation 
to  each  other. 

Influence  of  insolubility.  —  The  great  proportion  of  chemical  reactions  which  we 
witness  are  exhibited  by  bodies  dissolved  in  water  or 'some  other  menstruum,  and 
are  affected  to  a  great  extent  by  the  relations  of  themselves  and  their  products  to 
their  solvent.  Thus  carbonate  of  potassa  dissolved  in  water  is  decomposed  by  acetic 
acid,  and  carbonic  acid  evolved,  the  affinity  of  the  acetic  acid  prevailing  over  that 
of  the  carbonic  acid  for  potassa.  But  if  a  stream  of  carbonic  acid  gas  be  sent  through 
acetate  of  potassa  dissolved  in  alcohol,  acetic  acid  is  displaced,  or  the  carbonic  acid 
prevails,  apparently  from  the  insolubility  of  the  carbonate  of  potassa  in  alcohol. 
The  insolubility  of  a  body  appears  to  depend  upon  the  cohesive  attraction  of  its 
particles,  and  such  decompositions  may  therefore  be  ascribed  to  the  prevalence  of 
that  force. 

Formation  of  compounds  by  substitution.  —  It  is  remarkable  that  compounds  are 
in  general  more  easily  formed  by  substitution,  than  by  the  direct  union  of  their  con- 
stituents ;  indeed,  many  compounds  can  be  formed  only  in  that  manner.  Carbonic 
acid  is  not  absorbed  by  anhydrous  lime,  but  readily  by  the  hydrate  of  lime,  the 
water  of  which  is  displaced  in  the  formation  of  the  carbonate.  In  the  same  manner, 
ether,  although  a  strong  base,  does  not  combine  directly  with  acids,  but  the  salts  of 
ether  are  derived  from  its  hydrate  or  alcohol,  by  the  substitution  of  an  acid  for  the 
water  of  the  alcohol.  In  all  the  cases,  likewise,  in  which  hydrogen  is  evolved  during 
the  solution  of  a  metal  in  a  hydrated  acid,  a  simple  substitution  of  the^  metal  for 
hydrogen  occurs. 

Combination  takes  place  with  the  greatest  facility  of  all  when  double  decomposi- 
tion can  occur.  Thus  carbonate  of  lime  is  instantly  formed  and  precipitated,  when 


DOUBLE   DECOMPOSITION   OF  SALTS.  183 

carbo9?te  of  soda  is  added  to  nitrate  of  lime,  nitrate  of  soda  being  formed  at  the 
same  time  and  remaining  in  solution. 

Before  Decomposition.  After  Decomposition. 


Carbonate  of  soda  {  ^         ~        ~-  Citrate  of  soda. 


vr-,  f>  •,.  f  Nitric  acid 

Nitrate  of  lime...  j  Lime ^  Carbonate  of  lime. 

Here  a  double  substitution  occurs,  lime  being  substituted  for  soda  in  the  carbonate, 
and  soda  for  lime  in  the  nitrate.  Such  reactions  may  therefore  be  truly  described 
as  double  substitutions  as  well  as  double  decompositions.  They  are  most  commonly 
observed  on  mixing  two  binary  compounds  or  two  salts.  But  reactions  of  the  same 
nature  may  occur  between  compounds  of  a  higher  order,  such  as  double  salts,  and 
new  compounds  be  thus  produced,  which  cannot  be  formed  by  the  direct  union  of 
their  constituents.  Thus  the  two  salts,  sulphate  of  zinc  and  sulphate  of  soda,  when 
simply  dissolved  together,  at  the  ordinary  temperature,  always  crystallize  apart,  and 
do  not  combine.  But  the  double  sulphate  of  zinc  and  soda  is  formed  on  mixing 
strong  solutions  of  sulphate  of  zinc  and  bisulphate  of  soda,  and  separates  by  crystal- 
lization ;  the  sulphate  of  water  with  constitutional  water  (hydrated  acid  of  sp.  gr. 
1-78)  being  produced  at  the  same  time,  and  remaining  in  solution.  The  reaction 
which  occurs  may  be  thus  expressed  : 

Before  Decomposition.  After  Decomposition. 

HO,  SOs+(NaO,  S03)  )  (  HO,  S03-f-HO 

ZnO,  S03+ (HO)  }  I  ZnO,  S03  +  NaO,  S03 

in  which  the  constituents  of  both  salts  before  decomposition  inclosed  in  brackets,  are 
found  to  have  exchanged  places  after  decomposition,  without  any  other  change  in 
the  original  salts.1  The  double  sulphate  of  lime  and  soda  can  be  formed  artificially 
only  in  circumstances  which  are  somewhat  similar.  It  is  produced  on  adding  sul- 
phate of  soda  to  acetate  of  lime,  the  sulphate  of  lime,  as  it  then  precipitates,  carrying 
down  sulphate  of  soda  in  the  place  of  constitutional  water  (Liebig). 

Different  hydrates  of  the  same  body,  such  as  peroxide  of  tin,  differ  sensibly  in 
properties,  and  afford  different  compounds  with  acids,  unquestionably  because  these 
compounds  are  formed  by  substitution.  The  constant  formation  of  phosphates  con- 
taining one,  two,  or  three  atoms  of  base,  on  neutralising  the  corresponding  hydrates 
of  phosphoric  acid  with  a  fixed  base,  likewise  illustrates  in  a  striking  manner  the 
derivation  of  compounds,  on  this  principle.  Many  insoluble  substances,  such  as  the 
earth  silica,  possess  a  larger  proportion  of  water,  when  newly  precipitated,  than  they. 
retain  afterwards,  and  in  that  high  state  of  hydration  they  may  exhibit  affinities  for 
certain  bodies  which  do  not  appear  in  other  circumstances.  Hydrated  silica  dissolves 
in  water  at  the  moment  of  its  separation  from  a  caustic  alkali ;  and  alumina  dissolves 
readily  in  ammonia,  when  produced  in  contact  with  that  substance  by  the  oxidation 
of  aluminum.  The  usual  disposition  to  enter  into  combination,  which  silica  and 
alumina  then  exhibit,  is  generally  ascribed  to  their  being  in  the  nascent  state ;  a 
body  at  the  nioment  of  its  formation  and  liberation,  in  consequence  of  a  decomposi- 
tion, being,  it  is  supposed,  in  a  favourable  condition  to  enter  anew  into  combination. 
But  their  degree  of  hydration  in  the  nascent  state  may  be  the  real  cause  of  their 
superior  aptitude  to  combine. 

Double  decompositions  take  place  without  the  great  evolution  of  heat  which  often 
accompanies  the  direct  combination  of  two  bodies,  and  with  an  apparent  facility  or 
absence  of  effort,  as  if  the  combinations  were  just  balanced  by  tne  decompositions 
which  occur  at  the  same  time.  It  is,  perhaps,  from  this  cause  that  the  result  of 
double  decomposition  is  so  much  affected  by  circumstances,  particularly  by  the  insolu- 
bility of  one  of  the  compounds.  For  it  is  a  general  law,  to  which  there  is  no  excep- 

1  On  Water  as  a  Constituent  of  Sulphates,  Phil.  Mag.  3d  series,  vol.  vi.  p.  417. 


184  CHEMICAL   AFFINITY. 

tion,  that  two  soluble  salts  cannot  be  mixed  without  the  occurrence  of  decomposition, 
if  one  of  the  products  that  may  be  formed  is  an  insoluble  salt.  On  mixing  carbonate 
of  soda  and  nitrate  of  lime,  the  decomposition  seems  to  be  determined  entirely  by 
the  insolubility  of  the  carbonate  of  lime,  which  precipitates.  When  sulphate  of 
soda  and  nitrate  of  potassa  are  mixed,  no  visible  change  occurs,  and  it  is  doubtful 
whether  the  salts  act  upon  each  other,  but  if  the  mixed  solution  be  concentrated, 
decomposition  occurs,  and  sulphate  of  potassa  separates  by  crystallization  owing  to 
its  inferior  solubility. 

It  may  sometimes  be  proved  that  double  decomposition  occurs  on  mixing  soluble 
salts,  although  no  precipitation  supervenes.  Thus,  on  mixing  strong  solutions  of 
sulphate  of  copper  and  chloride  of  sodium,  the  colour  of  the  solution  changes  from 
blue  to  green,  which  indicates  the  formation  of  chloride  of  copper  and  consequently 
that  of  sulphate  of  soda  also.  Now  it  is  known  that  hydrochloric  acid  will  displace 
sulphuric  acid  from  the  sulphate  of  copper  at  the  temperature  of  the  experiment, 
while  sulphuric  acid  will,  on  the  other  hand,  displace  hydrochloric  from  chloride  of 
sodium.  It  hence  appears  that  in  the  preceding  double  decomposition,  those  acids 
and  bases  unite  which  have  the  strongest  affinity  for  each  other,  and  the  same  thing 
may  happen  on  mixing  other  salts.  But  where  the  order  of  the  affinities  for  each 
other  of  the  acids  and  bases  is  unknown,  the  occurrence  of  any  change  upon  mixing 
salts,  or  the  extent  to  which  the  change  proceeds,  is  entirely  matter  of  conjecture. 

It  was  the  opinion  of  Berthollet,  founded  principally  upon  the  phenomena  of  the 
double  decompositions  of  salts,  that  decompositions  are  at  all  times  dependent  upon 
accidental  circumstances,  such  as  the  volatility  or  insolubility  of  the  product,  and 
never  result  from  the  prevalence  of  certain  affinities  over  others ;  and  consequently 
that  in  accounting  for  such  changes,  the  consideration  of  affinity  may  be  neglected. 
He  supposed  that  when  a  portion  of  base  is  presented  at  once  to  two  acids,  it  is 
divided  equally  between  them,  or  in  the  proportion  of  the  quantities  of  the  two  acids, 
and  that  one  acid  can  come  to  possess  the  base  exclusively,  only  when  it  forms  a 
volatile  or  an  insoluble  compound  with  that  body,  and  thereby  withdraws  it  from 
the  solution,  and  from  the  influence  of  the  other  acid.  His  doctrine  will  be  most 
easily  explained  by  applying  it  to  a  particular  case,  and  expressing  it  in  the  language 
of  the  atomic  theory.  The  reaction  between  sulphuric  acid  and  nitrate  of  potassa 
is  supposed  to  be  as  follows.  On  mixing  eight  atoms  of  the  acid  with  the  same 
number  of  atoms  of  the  salt,  the  latter  immediately  undergoes  partial  decomposition, 
its  base  being  equally  shared  between  the  two  acids  which  are  present  in  equal 
quantities ;  and  a  state  of  statical  equilibrium  is  attained  in  which  the  bodies  in 
contact  are  — 

(a)  Four  atoms  sulphate  of  potassa. 
Four  atoms  nitrate  of  potassa. 
Four  atoms  sulphuric  acid. 
Four  atoms  nitric  acid. 

The  nitrate  of  potassa,  it  is  supposed,  is  decomposed  to  the  extent  stated,  and  no 
farther,  however  long  the  contact  is  protracted.  But  let  the  whole  of  the  free  nitric 
acid  now  be  distilled  off  by  the  application  of  heat  to  the  mixture,  and  a  second 
partition  of  the  potassa  of  the  remaining  nitrate  of  potassa  is  the  consequence ;  the 
free  sulphuric  acid  decomposing  the  salt  till  the  proportion  of  the  two  acids  uncom- 
bined  in  the  mixture  is  again  equal,  when  a  state  of  equilibrium  is  attained.  The 
mixture  then  consists  of — 

(5)  Six  atoms  sulphate  of  potassa. 
Two  atoms  nitrate  of  potassa. 
Two  atoms  sulphuric  acid. 
Two  atoms  nitric  acid. 

On  removing  the  free  nitric  acid  as  before,  a  third  partition  of  the  potassa  of  the 


DOUBLE    DECOMPOSITION    OF    SALTS.  185 

remaining  nitrate  of  potassa  between  the  two  acids  on  the  same  principle  takes 
place,  of  which  the  result  is  — 

(c)  Seven  atoms  sulphate  of  potassa. 
One  atom  nitrate  of  potassa. 
One  atom  sulphuric  acid. 

One  atom  nitric  acid. 

The  proportion  of  the  two  acids  free  being  always  the  same.  The  repeated  applica- 
tion of  heat,  by  removing  the  free  nitric  acid,  will  cause  the  sulphuric  to  be  again 
in  excess,  which  will  necessitate  a  new  partition  of  the  potassa  of  the  remaining 
nitrate  of  potassa,  till  at  last  the  entire  separation  of  the  nitric  acid  will  be  effected, 
and  the  fixed  product  of  the  decomposition  be — 

(d)  Eight  atoms  sulphate  of  potassa. 

Here  the  affinity  of  the  sulphuric  and  nitric  acids  for  potassa  is  supposed  to  be  equal ; 
and  the  complete  decomposition  of  the  nitrate  of  potassa  by  the  former  acid,  which 
takes  place,  is  ascribed  to  the  volatility  of  the  latter  acid,  which,  by  occasioning  its 
removal  in  proportion  as  it  is  liberated,  causes  the  fixed  sulphuric  acid  to  be  ever  in 
excess. 

Complete  decompositions  in  which  the  precipitation  of  an  insoluble  substance 
occurs,  were  explained  by  Berthollet  in  the  same  manner.  On  adding  a  portion  of 
baryta  to  sulphate  of  soda,  the  baryta  decomposes  the  salt,  and  acquires  sulphuric 
acid,  till  that  acid  is  divided  between  the  two  bases  in  the  proportion  in  which  they 
are  present,  and  at  this  point  decomposition  would  cease,  were  it  not  that  the  whole 
sulphate  of  baryta  formed  is  removed  by  precipitation.  But  a  new  formation  of  that 
salt  is  the  necessary  consequence  of  that  equable  partition  of  the  acid  between  the 
two  bases  in  contact  with  it,  which  is  the  condition  of  equilibrium  •  and  the  new 
product  precipitating,  more  and  more  of  it  is  formed,  till  the  sulphate  of  soda  is 
entirely  decomposed,  and  its  sulphuric  acid  removed  by  an  equivalent  of  baryta. 

According  to  these  views  of  Berthollet,  no  decomposition  should  be  complete 
unless  the  product  be  volatile  or  insoluble,  as  in  the  cases  instanced.  But  such  a 
conclusion  is  not  consistent  with  observation,  as  it  can  be  shown  that  a  body  may 
be  separated  completely  from  a  compound,  and  supplanted  by  another  body,  although 
none  of  the  products  is  removed  by  the  operation  of  either  of  the  causes  specified, 
but  all  continue  in  solution  and  in  contact  with  each  other.  Thus  the  salt  borax, 
which  is  a  biborate  of  soda,  is  entirely  decomposed  by  the  addition  to  its  solution  of  a 
quantity  of  sulphuric  acid  not  more  than  equivalent  to  its  soda,  although  the  libe- 
rated boracic  acid  remains  in  solution ;  for  the  liquid  imparts  to  blue  litmus  paper 
a  purple  or  wine-red  tint,  which  indicates  free  boracic  acid,  and  not  that  character- 
istic red  tint,  resembling  the  red  of  the  skin  of  the  onion,  which  would  inevitably  be 
produced  by  the  most  minute  quantity  of  the  stronger  acid,  if  free.  But  if  the 
borax  were  only  decomposed  in  part  in  these  circumstances,  and  its  soda  equally 
divided  between  the  two  acids,  then  free  sulphuric,  as  well  as  boracic  acid,  should 
be  found  in  the  solution.  The  complete  decomposition  of  the  salt  can  be  accounted 
for  in  no  way  but  by  ascribing  it  to  the  higher  affinity  of  sulphuric  acid  for  soda, 
than  that  of  boracic  acid  for  the  same  base. 

According  to  the  same  views,  on  mixing  together  two  neutral  salts  containing  dif- 
ferent acids  and  bases,  and  which  do  not  precipitate  each  other,  each  acid  should 
combine  with  both  bases,  so  as  to  occasion  the  formation  of  four  salts.  Again,  four 
salts,  of  which  the  acids  and  bases  are  all  dissimilar,  should  react  upon  each  other  in 
such  a  way  as  to  produce  sixteen  salts,  each  acid  acquiring  a  portion  of  the  four 
bases ;  and  certain  acids  and  bases,  dissolved  together  in  certain  proportions,  could 
have  but  one  arrangement  in  which  they  would  remain  in  equilibrio.  Hence  the 
salts  in  a  mineral  water  would  be  ascertained  by  determining  the  acids  and  bases 
present,  and  supposing  all  the  bases  proportionally  divided  among  the  acids.  But 
this  conclusion  is  inconsistent  with  a  fact  observed  in  the  preparation  of  factitious 


186  CHEMICAL    AFFINITY. 

mineral  waters,  namely,  that  their  taste  depends  not  only  on  the  nature  of  the  salts, 
but  also  upon  the  order  in  which  they  are  added.  (Dr.  Struve,  of  Dresden.)  Before 
we  can  determine  how  the  acids  and  bases  are  arranged  in  a  mineral  water,  or  what 
salts  it  contains,  it  may  therefore  be  necessary  to  know  the  history  of  its  formation. 
Instead  of  supposing  the  bases  equally  distributed  among  the  acids  in  mixed  saline 
solutions,  it  is  now  more  generally  assumed  that  the  strongest  base  may  be  exclu- 
sively in  possession  of  the  strongest  acid,  and  the  weaker  bases  be  united  with  the 
weaker  acids ;  a  mode  of  viewing  their  composition  which  agrees  best  with  the  medi- 
cal qualities  of  mineral  waters.  It  thus  appears  that  the  doctrines  of  Berthollet,  by 
which  the  resulting  actions  between  bodies  in  contact  are  made  to  depend  upon 
their  relative  quantities  or  masses,  and  the  physical  properties  of  the  products  of 
their  combination,  to  the  entire  exclusion  of  the  agency  of  proper  affinities  between 
the  bodies,  cannot  be  admitted  as  a  true  representation  of  the  actual  phenomena  of 
combination.  [See  Supplement,  p.  730.] 

CATALYSIS,    OR  DECOMPOSITION   BY   CONTACT. 

An  interesting  class  of  decompositions  has  of  late  attracted  considerable  attention, 
which,  as  they  cannot  be  accounted  for  on  the  ordinary  laws  of  chemical  affinity, 
have  been  referred  by  Berzelius  to  a  new  power,  or  rather  new  form  of  the  force  of 
chemical  affinity,  which  he  has  distinguished  as  the  Catalytic  force,  and  the  effect 
of  its  action  as  Catalysis  (from  xata,  downwards,  and  kuc^  I  unloosen).  A  body 
in  which  this  power  resides,  resolves  others  into  new  compounds,  merely  by  contact 
with  them,  or  by  an  action  of  presence,  as  it  has  been  termed,  without  gaining  or 
losing  anything  itself.  Thus  an  acid  converts  a  solution  of  starch  (at  a  certain  tem- 
perature), first  into  gum  and  then  into  sugar  of  grapes,  although  no  combination 
takes  place  between  the  elements  of  the  acid  and  those  of  the  starch,  the  acid  being 
found  free,  and  undiminished  in  quantity,  after  effecting  the  change.  The  same 
mutations  are  produced  in  a  more  remarkable  manner  by  the  presence  of  a  minute 
quantity  of  a  vegetable  principle,  diastase,  allied  in  its  general  properties  to  gluten, 
which  appears  in  the  germination  of  barley  and  other  seeds,  and  converts  their 
starch  into  sugar  and  gum,  which,  being  soluble,  form  the  sap  that  rises  into  the 
germ,  and  nourishes  the  plant.  This  example  of  the  action  of  a  catalytic  power  in 
an  organic  secretion  is  probably  not  the  only  one  in  the  animal  and  vegetable  king- 
doms, for  it  is  not  unlikely  that  it  is  by  the  action  of  such  a  force  that  very  different 
substances  are  obtained  from  the  same  crude  material  by  different  organs.  In  ani- 
mals, this  crude  material,  which  is  the  blood,  flows  in  the  uninterrupted  vessels,  and 
gives  rise  to  all  the  different  secretions ;  such  as  milk,  bile,  urine,  &c.,  without  the 
presence  of  any  foreign  body  which  could  form  new  combinations.  A  beautiful 
instance  of  an  action  of  catalysis  was  traced  by  Liebig  and  Wohler  in  the  chemical 
changes  which  the  bitter  almond  exhibits.  The  application  of  heat  and  water  to 
the  almond,  by  giving  solubility  to  its  emulsin  or  albuminous  principle,  enables  it  to 
act  upon  an  associated  principle,  amygdalin,  of  a  neutral  character,  which  then  fur- 
nishes bodies  so  unlike  itself  as  the  volatile  oil  of  almonds,  hydrocyanic  and  formic 
acids.  The  action  of  yeast  in  fermentation  is  a  more  familiar  illustration  of  a  simi- 
lar power.  The  presence  of  that  substance,  although  insoluble,  is  sufficient  to  cause 
the  resolution  of  sugar  into  carbonic  acid  gas  and  alcohol,  a  decomposition  which  can 
be  effected  by  no  other  known  means.  Changes  of  this  kind,  although  most  frequent 
in  organic  compounds,  are  not  confined  to  them.  The  binoxide  of  hydrogen  is  a  body 
of  which'  the  elements  are  held  together  by  a  very  slight  affinity.  It  is  not  decom-< 
posed  by  acids,  but  alkalies  give  its  elements  a  tendency  to  separate,  slow  effer- 
vescence occurring  with  the  disengagement  of  oxygen,  and  water  being  formed. 
Nor  do  soluble  substances  alone  produce  this  effect;  other  organic  and  inorganic 
bodies,  also  —  such  as  manganese,  silver,  platinum,  gold,  fibrin,  £c.,  which  are  per- 
fectly insoluble —  exert  a  similar  power.  The  decomposition,  in  these  instances, 
takes  place  by  the  mere  presence  of  the  foreign  body,  and  without  the  smallest 


DECOMPOSITION    BY    CONTACT.  18/ 

quantity  of  it  entering  into  the  new  compound ;  for  the  most  minute  researcher 
have  failed  in  discovering  the  slightest  alteration  in  the  foreign  body  itself.  The 
liquid  persulphide  of  hydrogen,  and  a  solution  of  the  'nitrosulphate  of  ammonia  of 
Pelouze,  are  decomposed  in  the  same  way,  and  by  contact  of  nearly  all  the  substances 
which  act  upon  peroxide  of  hydrogen.  One  remarkable  difference,  indeed,  is  observa- 
ble, namely,  that  alkalies  impart  stability  to  nitrosulphate  of  ammonia,  while  acids 
decompose  it,  or  the  reverse  of  what  happens  with  both  the  binoxide  and  bisulphide 
of  hydrogen  (Phil.  Mag.  3d  Series,  vol.  x.  p.  489). 

The  phenomena  referred  to  catalysis  are  of  a  recondite  nature,  and  much  in  need 
of  elucidation.  The  influence  of  platinum,  formerly  noticed,  in  disposing  hydrogen 
and  oxygen  to  unite,  is  probably  connected  with  the  catalytic  power  of  the  same 
metal,  but  is  at  present  equally  inexplicable.  It  would  be  unphilosophical  to  rest 
satisfied  by  referring  such  phenomena  to  a  force  of  the  existence  of  which  we  have 
no  evidence.  The  doctrine  of  catalysis  must  be  viewed  in  no  other  light  than  as  a 
convenient  fiction,  by  which  we  are  enabled  to  class  together  a  number  of  decompo- 
sitions not  provided  for  in  the  theory  of  chemical  affinity,  as  at  present  understood, 
but  which,  it  is  to  be  expected,  will  receive  their  explanation  from  new  investiga- 
tions. It  is  a  provisional  hypothesis,  like  the  doctrine  of  isomeri. m  for  which  the 
occasion  will  cease  as  the  science  advances. 


SECTION    II. CHEMICAL   POLARITY. 

Illustrations  from  magnctical  polarity.  —  The  ideas  of  induction  .^nd  polarity, 
which  now  play  so  important  a  part  in  physical  theories,  were  originally  suggested 
by  the  phenomena  of  magnetism,  which  still  afford  the  best  experimental  illustra- 
tions of  them.  A  bar  magnet  exhibits  attractive  power  which  is  not  possessed  in 
an  equal  degree  by  every  particle  composing  the  bar,  but  is  chiefly  localized  in  two 
points  at  or  near  its  extremities.  The  powers,  too,  residing  at  these  points  are  not 
one  and  the  same,  or  similar,  but  different,  indeed  contrary,  in  their  nature ;  and 
are  distinguished  by  the  different  names  of  Austral  magnetism  and  Boreal  magnet- 
ism. The  opposition  in  the  mode  of  action  of  these  powers  is  so  perfect,  that  they 
completely  negative  or  neutralize  each  other  when  residing  in  the  same  particle  of 
matter  in  equal  quantity  or  degree,  as  they  are  supposed  really  to  exist  in  iron  before 
it  is  magnetized ;  and  they  only  signalize  their  presence  when  displaced  and  sepa- 
rated to  a  distance  from  each  other,  as  they  are  in  a  magnet.  A  body  possessing 
any  such  powers  residing  in  it,  which  are  not  general  but  local,  and  not  the  same 
but  opposite,  is  said  (in  the  most  general  sense)  to  possess  polarity. 

In  the  theory  of  magnetism,  it  is  found  necessary  to  consider  a  magnet  as  com- 
posed of  minute  indivisible  particles  or  filaments  of  iron,  each  of  which  has  indivi- 
dually the  properties  of  a  separate  magnet.  The  displacement  or  separation  of  the 
two  attractive  powers  takes  place  only  within  these  small  particles,  which  are  called 
the  magnetic  elements,  and  must  be  supposed  so  minute  that  they  may  be  the  ulti- 
mate particles  or  atoms  themselves  of  the  iron.  A  magnetic  bar  may,  therefore,  be 
represented  as  composed  of  minute 

portions,  a  b  in  fig.  60  representing  Fl°-  6^- 

one  such  portion ;  the  right  hand  ex-  | 
tremities  of  each  of  which  possess  one  % 
species  of  magnetism,  and  the  left  -g 
hand  extremities  the  other.  The  un-  •< 
shaded  ends  being  supposed  to  possess  austral,  and  the  shaded  ends  boreal  magnet- 
ism, then  the  ends  of  the  bar  itself,  of  which  these  sides  of  the  elementary  magnets 
form  the  faces,  possess  respectively  austral  and  boreal  magnetism,  and  are  the  austral 
and  boreal  poles  of  the  magnet.  Such,  then,  is  the  polar  condition  of  a  bar  of  iron 
possessing  magnetism,  of  which,  the  attractive  and  repulsive  powers  residing  at  the 
extremities  are  the  results.  Of  the  existence  of  such  a  structure  the  breaking  of  a 
maguet  into  two  or  more  parts  affords  a  proof,  for  it  forms  as  many  complete  mag- 


Oli 


188 


CHEMICAL   POLARITY. 


Fia.  61. 


FIG.  62. 


FIG.  63. 


nets  as  there  are  parts,  new  poles  appearing  at  all  the  fractured  extremities.  A 
magnetic  element,  it  is  to  b~e  remembered,  is  itself  insecable,  like  a  chemical  atom, 
so  that  the  division  must  take  place  between  magnetic  elements. 

When  to  the  boreal  pole  B  of  a  magnet  (fig.  61),  which  may  be 
of  the  horse-shoe  form,  a  piece  of  soft  iron,  a  b,  wholly  destitute  of 
magnetic  powers,  is  presented,  a  similar  displacement  of  the  mag- 
netic forces  of  its  elements  occurs  as  in  the  magnet  itself;  or  a  b 
becomes  a  magnet  by  induction,  and  may  attract  and  induce  mag- 
netism in  a  second  bar  a'  b'  ;  both  of  which  continue  magnetic  so 
long  as  the  first  remains  in  the  same  position,  and  under  the  influ- 
ence of  A  B.  These  induced  magnets  must  have  the  same  polar 
molecular  structure  as  the  original  magnet,  but  their  magnetism  is 
only  temporary,  and  is  immediately  lost  when  they  are  removed 
from  the  permanent  magnet.  The  displacement  of  the  magnetisms 
in  these  induced  magnets  commences  at  the  extremity  a  of  a  b,  in 
contact  with  B,  which  extremity  has  the  opposite  magnetism  of  B, 
(the  different  kinds  of  magnetism  being  mutually  attractive,)  and  is 
the  austral  pole  of  a  b  ;  and  b  is  its  boreal  pole.  Of  a'  b',  again, 
the  upper  extremity  a'  in  contact  with  b'  is  the  austral,  and  the  lower  extremity  b' 
the  boreal  pole,  or  b  and  b'  have  the  same  kind  of  magnetic  power  as  the  pole  B  of 
the  original  magnet,  from  which  they  are  dependent.  A  third  bar  of  soft  iron 
placed  at  V  is  likewise  polarized,  and  the  series  of  induced  magnets  may  be  still 
farther  extended,  but  the  attractive  powers  developed  in  the  different  members  of 
the  series  become  less  and  less  with  their  distance  from  the  pole  B  of  the  original 
magnet. 

A  similar  set  of  bars  may  be  connected  with  A  (fig. 
62),  which  become  temporary  magnets  also  according  to 
the  same  law,  the  lower  extremities  of  this  set  being 
austral.  On  now  uniting  the  lower  extremities  of  both 
sets  by  another  bar  of  soft  iron  a"  b",  (fig.  63),  either 
set  renders  a"  b"  a  magnet,  having  its  austral  pole  at  a" 
and  its  boreal  pole  at  b"  ;  and  acting  together,  they  com- 
municate a  degree  of  magnetism  to  the  uniting  bar  greater 
than  either  set  possessed  before  they  were  united.  By 
this  connexion,  also,  the  inductive  actions  of  each  set  of 
bars  are  brought  to  bear  upon  the  other,  and  the  attrac- 
tive  forces  at  all  their  poles  are  thereby  greatly  increased. 
In  the  most  favourable  conditions  as  to  the  size  and  con- 
nexion of  the  temporary  magnets  with  relation  to  the 
primary  magnet,  each  of  the  former,  however  numerous, 
acquires  powers  equal  to  those  of  the  original  magnet. 
This  general  enhancement  of  power  in  the  induced  magnets  has  been  acquired, 
therefore,  by  completing  the  circle  of  them  between  A  and  B. 

It  is  also  important  to  observe,  with  a  view  to  the  future  applica- 
tion of  the  remark,  that  a  single  bar  of  soft  iron,  or  lifter,  as  b  a, 
"  ;.  64),  connecting  the  poles  of  a  magnet  A  B,  not  only  acquires 
at  b  and  a  equal  though  opposite  powers  to  the  contiguous  poles  of 
the  magnet,  but  also  reacts  by  induction  on  these  poles  themselves 
in  a  gradual  manner,  and  increases  their  magnetism.  The  original 
magnetic  forces  of  A  and  B  are  therefore  increased,  by  the  opportu- 
nity to  act  inductively,  which  the  connecting  bar  affords  them.  The 
threads  of  steel  filings  which  are  taken  up  by  a  magnet,  (see  figure 
65)  illustrate  the  inductive  action  of  magnetism,  for  each  grain  of 
steel  is  a  complete  magnet,  and  the  threads  a  series  of  connected 


IB 


A 

/    \ 

B 

6 

d 

V 

a' 

tt 

V 

V              tf 

Fm.  64. 


IB 


magnets.     It  will  be  observed  also  that  these  threads  diverge  from  each  other; 
because,  while  unlike  poles  are  in  contact  in  each  thread,  which  attract,  like  poles 


REPRESENTATION  OF   A   DOUBLE   DECOMPOSITION.   189 


Fio.  65 


are  in  contact  of  adjoining  threads  which  repel.     This  repulsion  of  polar  chains  by 
each  other,  there  will  be  occasion  again  to  refer  to. 

Atomic  representation  of  a  double  decomposition.  —  Chemical  polarity,  although 
less  adapted  for  exhibition,  is  still  more  simple  than  magnetic  polarity  in  its  nature, 
while  it  is  of  a  more  fundamental  character,  and  appears  to  be  the  basis  of  all  other 
polarities  whatever.  In  a  binary  compound,  —  such  as  chloride  of  potassium,  — 
there  reside  two  attractive  powers,  opposite  in  their  nature ;  namely,  the  halogenous 
affinity  of  the  salt-radical  chlorine,  and  the  basylous  affinity  of  the  metal  potassium. 
The  atomic  theory  gives  form  to  the  molecule  of  chloride  of  potassium :  one  atom, 
Cl,  being  the  seat  of  the  halogenous,  chlorous,  or  negative  affinity  (as  we  shall  also 
call  it) ;  and  the  other  atom,  K,  the  seat  of  the  basylous  or  positive  affinity.  A 
binary  saline  molecule  is  thus  entirely  similar  to  a  magnetic  element.  We  have  to 
deal  with  two  affinities  only,  —  the  chlorous  and  basylous.  Atoms  possessing  differ- 
ent affinities  attract  each  other ;  while  atoms  possessing  the  same  affinity  repel  each 
other. 

The  two  binary  compounds,  hydrochloric  acid  (chloride  of  hydrogen)  and  oxide 
of  lead,  when  brought  into  contact,  mutually  decompose  each  other,  forming  chloride 
of  lead  and  water:  HOI  and  PbO=PbCl  and  HO. 
At  the  instant  of  acting  upon  each  other,  the  two 
compound  molecules  must  have  a  certain  relative 
position.  Under  (1),  the  basylous  hydrogen  of  the 
hydrochloric  acid  is  presented  to  the  basylous  lead  of 
the  oxide  of  lead,  atoms  which  repel  each  other. 
In  (2)  and  (3),  on  the  contrary,  a  basylous  atom  of 
one  molecule  is  presented  to  a  halogenous  atom  in 
the  other,  H  to  O  in  (2),  and  Cl  to  Pb  in  (3).  These 
are  attractive  pairs ;  but,  before  they  can  enter  into 
new  combinations,  they  must  be  released  from  the 
atoms  with  which  they  are  already  combined ;  which 
can  be  effected  in  (4),  the  only  disposition  of  the  polar  molecules  in 
which  both  attractive  poles  are  together,  and  the  actual  decompositions 
and  combinations  possible :  Cl  is  in  contact  with  Pb  at  the  same  time 
that  H  is  in  contact  with  0,  allowing  the  simultaneous  formation  of 
Pb  Cl  and  H  0.  This  is  no  more  than  the  expression  of  a  double 
decomposition  in  the  language  of  the  atomic  theory. 

It  is  further  to  be  observed,  that,  in  the  original  polar  molecules  (4), 
although  approximation  and  combination  are  promoted  by  the  attraction  of  the  con- 
tiguous unlike  poles,  they  are  opposed  by  the  mutual  repulsion  of  the  like  poles  ; 
Cl  repelling  0,  and  Pb  repelling  H.  This  unfavourable  influence  of  the  repulsions 
is  reduced  to  a  minimum  in  the  arrangement  of  several  pairs  of  the  hydrochloric 
acid  and  oxide  of  lead  molecules  to  form  one  circle.  In  (5),  four  pairs  of  the  polarfc 
molecules  are  symmetrically  placed ;  HC1  alternately  with  PbO,  and  the  attractive 
poles  of  the  different  molecules  together.  Affinities  tending  to  a  simultaneous 
formation  of  chloride  of  lead  and  water  are  equally  favoured  in  this  arrangement^  as 
in  (4) ;  while  the  mutual  repulsion  of  the  like  atoms,  —  such  as  the  H  and  Pb,  or 
the  Cl  and  0  of  the  adjoining  molecules  A  and  B  —  is  less,  as  these  like  atoms  arc 
more  distant  from  each  other  in  the  circular  arrangement.  It  is  obvious  that  the 


190 


CHEMICAL   POLARITY. 


FIG.  66. 


repelling  atoms  will  be  more  distant  the  larger 
the  circle,  or  the  more  nearly  a  segment  of  it 
approaches  to  a  straight  line.  This  arrange- 
ment of  many  pairs  in  a  circle,  being  a  condi- 
tion of  equilibrium,  is  a  necessary  one,  and 
must  take  place  in  all  double  decompositions 
occurring  in  a  liquid  where  the  binary  mole~ 
cules  are  free  to  move.  The  formation  of  such 
polar  circuits  explains  the  ready  occurrence  of 
double  decompositions ;  but  it  is  of  still  more 
importance,  as  being  the  simplest  and  most  in- 
telligible exhibition  of  a  voltaic  circle. 

Action  of  an  acid  upon  two  metals  in  con- 
tact. —  When  a  plate  of  zinc  is  plunged  into 
hydrochloric  acid,  a  chemical  change  of  a  simple 
nature  ensues  j  the  metal  dissolves,  combining 
with  the  chlorine  of  the  acid  and  displacing  its 
hydrogen,  the  gas-bubbles  of  which  form  upon  the  zinc  plate,  increase  in  size,  detach 
themselves,  and  rise  through  the  liquor  to  its  surface.  The  solution  of  zinc,  when 
effected  by  its  substitution  for  hydrogen,  as  in  this  experiment,  is  attended  by  a  train 
of  extraordinary  phenomena,  which  become  apparent  when  a  second  metal,  such  as 
copper,  silver,  or  platinum,  is  placed  in  the  same  acid  fluid,  and  allowed  to  touch 
the  zinc,  the  second  metal  being  one  upon  which  the  fluid  exerts  no  solvent  actiou, 
or  a  less  action  than  upon  zinc. 

The  zinc  plate  being  connected  by  a  metallic  wire  with  a 
copper  plate,  as  represented  in  fig.  66,  and  both  dipped 
together  in  the  hydrochloric  acid,  the  zinc  only  is  acted  upon, 
.  and  dissolves  as  rapidly  as  before  ;  but  much  of  the  hydrogen 
gas  now  appears  upon,  and  is  discharged  from  the  surface  of 
copper  the  copper  plate,  and  not  fron  the  zinc.  The  hydrogen, 
being  produced  by  the  solution  of  the  zinc,  thus  appears  to 
travel  through  the  liquid  from  that  metal  to  the  copper.  But 
no  current  or  movement  in  the  liquid  is  perceptible,  nor  any 
phenomenon  whatever  to  indicate  the  actual  passage  of  matter 
through  the  liquid  in  that  direction.  The  transference  of 
the  hydrogen  must  take  place  by  the  propagation  of  a  decom- 
position through  a  chain  of  particles  of  hydrochloric  acid 
extending  from  the  zinc  to  the  copper,  and  may  be  conceived  by  the  diagram  on  the 
margin,  in  which  each  pair  of  associated  circles  marked  cl  and  h  represents  a  particle 

of  hydrochloric  acid.  The  chlorine  cl  of  par- 
ticle 1  in  contact  with  the  zinc  combining 
with  that  metal,  its  hydrogen  h  combines,  the 
moment  it  is  set  free,  with  the  chlorine  of 
particle  2,  as  indicated  by  the  connecting 
bracket  below,  and  liberates  the  hydrogen  of 
copper  that  particle,  which  hydrogen  forthwith  com- 
bines with  the  chlorine  of  particle  8,  and  so 
on  through  a  series  of  particles  of  any  extent 
till  the  decomposition  reaches  the  copper  plate, 
when  the  last  liberated  atom  of  hydrogen  (that 
of  particle  3,  in  the  diagram)  not  having  hy- 
drochloric acid  to  act  upon,  is  evolved  and  rises  as  gas  in  contact  with  the  copper 
plate. 

It  is  to  be  observed  that  this  succession  of  decompositions  and  recombinations 
leading  to  the  discharge  of  the  hydrogen  at  the  copper,  does  not  occur  at  all  unless 
that  plate  be  in  metallic  connexion  with  the  zinc,  by  means  of  a  wire,  as  in  the 


zinc 


Fia.  67. 


ACTION  OF   ACID   ON   METALS   IN   CONTACT 


101 


FIQ.  68. 


ZlTU 


figure,  or  by  the  plates  themselves  touching  without  or  within  the  acid  fluid.  This 
would  seem  to  indicate  that  while  the  decomposition  travels  from  the  zinc  to  the 
copper  through  the  acid,  some  force  or  influence  is  propagated  at  the  same  time 
through  the  wire,  from  the  copper  back  again  to  the  zinc.  That  something  does  pass 
through  the  wire  in  these  circumstances  is  proved  by  its  being  heated,  and  .by  its 
temporary  assumption  of  certain  electrical  and  magnetic  properties.  Whether  any- 
thing material  does  pass,  or  it  is  merely  a  vibration  or  vibratory  impulse,  or  a  cer- 
tain induced  condition  that  is  propagated  through  the  molecules  of  the  wire,  of 
which  the  electrical  appearances  are  the  effects,  cannot  be  determined  with  certainty. 
But  a  power  to  effect  decomposition,  the  same  in  kind  as  that  occurring  in  the  acid 
jar,  and  which  acts  in  the  same  sense  or  direction,  is  propagated  through  the  wire, 
and  appears  to  be  fundamental  to  all  the  other  phenomena. 

Let  the  wire,  supposed  to  be  of  platinum,  con- 
necting the  zinc  and  copper  plates,  be  divided  in 
the  middle,  and  the  extremities  A  and  B  of  the 
portions  attached  to  the  copper  and  zinc  plates 
respectively  be  flattened  into  small  plates,  and 
then  dipped  at  a  little  distance  from  each  other 
in  a  second  vessel  containing  hydriodic  acid. 
Iodine  will  soon  appear  at  A,  although  that  ele- 
ment is  incapable  of  combining  with  the  sub- 
stance of  the  platinum,  and  hydrogen  gas  will 
appear  at  B.  If  the  connecting  wire  and  the 
small  plates  A  and  B  were  of  zinc  or  of  copper, 
the  hydriodic  acid  would  be  decomposed  precisely 
in  the  same  manner,  but  the  iodine  as  it  reached 
A  would  unite  with  the  metal  and  form  an  iodide. 
Supposing  a  decomposing  force  to  have  originated  in  the  zinc  plate,  a»d  to  have 
circulated  through  the  hydrochloric  acid  in  the  jar  to  the  copper  plate,  and  onwards 
through  the  wires  and  the  hydriodic  acid  back  to  the  zinc,  as  indicated  by  the 
direction  of  the  arrows,  then  the  hydrogen  of  the  hydriodic  acid  has  followed  the 
same  course,  and  been  discharged  against  the  metallic  surface  to  which  the  arrow 
points. 

The  solution  of  the  zinc  in  hydrochloric  acid  which  developes  these  powers,  acting 
at  a  distance,  is  not  itself  impeded,  but  on  the  contrary  is  promoted  by  exerting 
such  an  influence :  for,  placed  alone  in  the  acid,  that  metal  scarcely  dissolves  at  all, 
if  pure  and  uncontaminated  with  other  metals,  or  if  its  surface  has  been  silvered 
with  mercury ;  but  it  dissolves  with  rapidity  when  a  copper  plate  is  associated  with 
it  in  the  same  jar,  in  the  manner  described.  Hence  the  decomposing  power  which 
appears  between  A  and  B  cannot  be  viewed  as  actually  a  portion  of  that  which 
causes  the  solution  of  the  zinc  in  the  hydrochloric  acid,  for  that  force  has  suffered 
no  diminution  in  its  own  proper  sphere  of  action. 

This  combination  of  metals  and  fluids  is  known  as  the  simple  voltaic  circle. 

To  explain  the  phenomena  of  the  voltaic  circle,  the  existence  of  a  substantial 
principle,  the  electric  fluid,  has  been  assumed,  of  such  a  nature  that  it  is  readily 
communicable  to  matter,  and  capable  of  circulating  through  the  voltaic  arrangement, 
carrying  with  it  peculiar  attractive  and  repulsive  forces  which  occasion  the  decom- 
positions observed.  A  vehicle  was  thus  created  for  the  chemical  affinity  which  is 
found  to  circulate.  But  it  is  generally  allowed  that  this  form  of  the  electrical 
hypothesis  ha.«  not  received  support  from  observations  of  a  decent  date,  particularly 
from  the  great  discoveries  of  Mr.  Faraday,  which  have  completely  altered  the  aspect 
of  this  department  of  science,  and  suggest  a  very  different  interpretation  of  the  phe- 
nomena. All  electrical  phenomena  whatever  are  found  to  involve  the  presence  of 
matter,  or  there  is  no  evidence  of  the  independent  existence  of  electricity  apart  from 
matter;  so  that  these  phenomena  may  really  be  exhibitions  of  the  inherent  proper- 
ties of  matter.  The  idea  of  anything  like  a  circulation  of  electricity  through  the 


192  CHEMICAL   POLARITY. 

voltaic  circle  appears  to  be  abandoned.  Electrical  induction,  by  which  certain 
forces  are  propagated  to  a  distance,  is  found  to  be  always  an  action  of  contiguous 
particles  upon  each  other,  in  which  it  is  unnecessary  to  suppose  that  any  thing 
passes  from  particle  to  particle,  or  is  taken  from  one  particle  and  added  to  another. 
The  change  which  a  particle  undergoes  takes  place  within  itself,  and  it  is  looked 
upon  as  a  temporary  development  of  diiferent  powers  in  different  points  of  the  same 
particle.  The  doctrine  of  polarity  has  thus  come  to  be  introduced  into  the  discus- 
sion of  electrical  phenomena.1 

One  reason  for  retaining  the  theory  of  an  electric  fluid  or  fluids  is,  that  it  affords 
the  means  of  expressing  in  distinct  terms  those  strictly  physical  laws  which  are 
reputed  electrical  ]  and  for  many  purposes  such  an  hypothesis  is  unquestionably 
useful,  if  not  absolutely  necessary;  but  it  has  nothing  to  recommend  it  in  the 
description  of  the  chemical  phenomena  of  the  voltaic  circle.  These  admit  of  a 
perfectly  intelligible  statement,  when  viewed  as  an  exhibition  of  ordinary  chemical 
affinity,  acting  in  particular  circumstances,  without  any  electrical  hypothesis. 

Polarity  of  the  arrangement.  —  It  is  to  be  assumed  that  the  zinc  and  hydro- 
chloric acid  are  both  composed  of  particles,  or  molecules,  which  are  susceptible  of  a 
polar  condition.  Of  hydrochloric  acid,  the  chemical  atom  is  the  polar  molecule,  and 
it  therefore  consists  of  an  atom  of  chlorine  and  an  atom  of  hydrogen  associated 
together.  The  polar  molecule  of  zinc  may  be  supposed,  for  a  reason  which  will 
afterwards  appear,  to  consist  of  a  pair  likewise  of  associated  atoms,  which,  however, 
are  in  this  body  both  of  the  same  element.  The  powers  appearing  in  a  polar  mole- 
cule of  zinc  and  of  hydrochloric  acid  are  the  same.  One  pole  of  each  molecule  has 
the  basylous  attraction,  or  affinity,  which  is  characteristic  of  zinc,  or  zincous  attrac- 
tion, and  may  be  called  the  zincous  pole ;  while  the  other  has  the  halogenous  attrac- 
tion, or  affinity,  which  is  characteristic  of  chlorine,  or  chlorous  attraction,  and  may 
be  called  the  chlorous  pole. 

Zinc  and  acid  in  contact  may  therefore  be  represented  (fig.  69)  by  trains  of  asso- 
ciated pairs  of  atoms.  In  the  molecule 

Zinc  Fia-  69-  of  hydrochloric  acid  B,  which  is  next 

'  'the  zinc,  the  chlorine  atom  forms  the 

chlorous  pole,  and  is  turned  towards 


ing  its  molecule  to  take  that  position, 

which  may  be  indicated  by  inscribing  cl  in  the  circle  which  represents  the  chlorine 
atom.  The  other  atom  of  the  molecule  B,  or  the  hydrogen,  is  the  opposite,  or 
zincous  pole,  and  is  marked  z.  Of  the  two  atoms  forming  the  polar  molecule  A  of 
the  zinc,  the  exterior  atom  which  is  in  contact  with  the  acid  has  thereby  zincous 
attraction  developed  in  it,  and  becomes  the  zincous  pole,  while  the  interior  becomes 
the  chlorous  pole,  as  indicated  in  both  by  the  inscribed  letters.  This  polar  condition 
of  the  zinc  must  be  supposed  the  necessary  and  immediate  consequence  of  its  contact 
with  the  polar  acid. 

But  each  of  these  particles  throws  a  train  of  particles  of  its  own  kind  into  a 
similar  state  of  polarity :  A,  the  contiguous  particles  E  and  I  of  the  zinc,  and  B, 
the  contiguous  particles  C  and  D  of  the  acid.  For  cl  of  A  becoming  a  chlorous 
pole,  developes  near  it  in  an  opposite,  or  zincous  pole  in  z  of  E,  and  a  chlorous  pole 
in  cl,  the  more  remote  extremity  of  E ;  in  the  same  manner  as  the  austral  pole  of  a 
magnet  developes,  by  induction,  a  boreal  and  austral  pole  in  a  piece  of  soft  iron 
applied  to  it.  And  as  the  induced  magnet,  thus  formed,  will  react  upon  a  second 
piece  of  iron,  and  render  it  also  magnetic,  so  the  polarized  particle  E  renders  I 

1  For  Mr.  Faraday's  views,  the  eleventh  and  subsequent  series  of  his  Researches,  in  the 
Philosophical  Transactions  for  1886,  and  the  following  years,  may  be  referred  to.  He  haa 
'avoured  the  scientific  world  with  a  reprint  of  the  whole  series :  Faraday's  Experimental 
Researches  in  Electricity:  R.  and  J.  E.  Taylor,  London,  1839.  The  subject  is  also  syste- 
matically treated  in  the  work  of  the  late  Professor  Daniell,  entitled  an  Introduction  to  the 
'tudy  of  Chemical  Philosophy,  which  may  be  consulted  with  advantage. 


SIMPLE   VOLTAIC   CIRCLE.  193 

similarly  polar.  The  polar  arrangement  of  the  particles  C  and  D  of  the  acid  is 
produced  by  B  in  the  same  manner.  But  as  in  a  series  of  induced  magnets  (fig.  61, 
page  188),  the  magnetism  acquired  diminishes  with  the  distance  from  the  pole  of  the 
original  magnet,  so  in  trains  of  chemically  polarized  molecules,  such  as  A,  E,  I  and 
B,  C,  D,  the  amount  of  polarity  developed  in  each  molecule  will  diminish  with  the 
distance  from  the  sources  of  induction  A  and  B ;  I  being  polarized  to  a  less  degree 
than  E,  and  D  than  C. 

In  the  electrical  theory  of  the  voltaic  circle  as  modified  by  Mr.  Faraday,  the  zinc 
and  hydrochloric  acid  are  equally  supposed  to  have  a  polarizable  molecule.  The 
polarity  is  also  developed  in  these  molecules  by  their  approximation  or  contact. 
The  molecule  of  hydrochloric  acid  is  supposed  to  contain  the  positive  and  negative 
electricities,  which  possess  contrary  powers,  like  the  two  magnetisms,  and  are  in 
combination  and  neutralize  each  other,  in  the  non-polar  condition  of  the  molecule. 
But  the  contact  of  zinc  causes  the  separation  of  the  two  electricities  in  the  acid 
molecule,  its  atom  of  chlorine  next  the  zinc  becoming  negative,  and  its  atom  of 
hydrogen  positive.  The  electricities  of  the  zinc  molecule  are  separated  at  the  same 
time,  the  side  of  the  molecule  next  the  acid  becoming  positive,  and  the  distant  side 
negative.  The  positive  and  negative  sides  of  the  two  different  molecules  are  thus 
in  contact, -the  different  electricities,  like  the  different  magnetisms,  attracting  each 
other.  Hence,  one  side  of  each  molecule  is  said  to  be  positive  instead  of  zincous, 
and  the  other  side  to  be  negative  instead  of  chlorous.  Polarity  of  the  molecule  is 
supposed  in  both  views,  but  on  one  view  the  polar  forces  are  the  two  electricities, 
on  the  other  two  chemical  affinities.  The  difference  between  the  two  views  is  little 
more  than  nominal,  for  in  both  the  same  powers  and  properties  are  ascribed  to  the 
acting  forces.  The  electricities  are  supposed  to  be  the  cause  of  the  chemical  affini- 
ties, but  it  may  with  equal  justice  be  assumed  that  chemical  affinities  are  the  cause 
of  the  phenomena  reputed  electrical.  One  set  of  forces  only  is  necessary  for  the 
explanation  of  the  phenomena  of  combination,  and  the  question  is,  whether  are 
these  forces  electrical  or  chemical  ?  Shall  electricity  supersede  chemical  affinity,  or 
chemical  affinity  supersede  electricity  ?  If  the  electricities  should  be  retained,  in 
discussing  the  voltaic  circle,  their  names  might  well  be  changed,  the  positive  called 
zincous  electricity,  and  the  negative  chlorous  electricity,  which  express  (as  will 
appear  more  clearly  afterwards),  the  nature  of  the  chemical  affinities  with  which 
these  electricities  are  invested,  and  of  which  they  are  indeed  constituted  the  sole 
depositories.  The  propagation  of  the  effects  to  a  distance  is  supposed  to  take  place 
by  the  polarization  of  chains  of  molecules,  on  the  electrical  as  well  as  chemical 
theory  of  the  voltaic  circle ;  so  that  the  explanations  which  follow,  although  expressed 
in  the  language  of  the  chemical  theory,  are  the  same  in  substance  as  those  which  are 
given  on  the  electrical  theory  as  now  understood. 

If  the  attractions  of  the  respective  zincous  and  chlorous  poles  of  A  and  B  which 
are  in  contact,  rise  to  a  certain  point,  the  atom  z  of  A  is  detached  from  the  mass  of 
metal,  and  combines  with  the  atom  cl  of  B,  which  last  atom  is  disengaged  at  the 
same  time  from  its  hydrogen.  Chloride  of  zinc  is  produced  and  dissolves  in  the 
liquid,  while  hydrogen  is  disengaged  and  rises  from  the  surface  of  the  metal ;  or  we 
have  the  ordinary  circumstances  of  the  solution  of  an  isolated  mass  of  zinc  in 
hydrochloric  acid. 

SIMPLE   VOLTAIC   CIRCLE. 

Circle  with  the  connecting  wire  unbroken.  —  When  the  zinc  is  pure,  or  its  surface 
amalgamated  with  mercury,  the  zincous  •  and  chlorous  attractions  of  the  touching 
poles  of  A  and  B  are  not  sufficiently  intense  to  produce  these  effects,  and  combina- 
tion does  not  occur.  Let  a  copper  plate  F  G  H  (fig.  70),  be  then  introduced  into 
the  acid,  and  connected  by  a  metallic  wire  H  K  I  with  the  zinc.  The  particles  of 
the  acid  assume  chlorous  and  zincous  poles  as  before ;  so  also  do  those  of  the  zinc, 
and  the  chain  of  polar  molecules  is  now  continued  through  the  zinc  and  wire  to  the 
13 


194  CHEMICAL    POLARITY. 

FIG.  70. 
Connecting  wire. 


copper,  the  exterior  particle  F  of  which,  it  will  be  observed,  comes  tnereby  to  pre- 
sent a  chlorous  pole  to  the  acid.  The  contiguous  particle  D  of  acid  is  thus  exposed 
to  a  second  induction  from  the  chlorous  polarity  of  the  copper,  which  increases  the 
zincous  polarity  of  the  side  of  D  next  F,  and,  therefore,  co-operates  in  enhancing 
the  polar  conditions  already  assumed  by  the  chain  of  acid  particles  extending  be- 
tween the  two  metals.  An  endless  chain  or  circle  of  polar  molecules  symmetrically 
arranged  is  thus  formed,  such  as  exists  in  a  magnet  of  which  the  poles  are  united 
by  a  lifter,  in  which  every  particle  in  the  chain  has  its  own  polar  condition  elevated 
by  induction,  and  at  the  same  time  does  itself  react  upon  and  elevate  the  polar  con- 
dition of  every  other  particle  in  the  chain.  The  result  of  this  is  that  the  primary 
attraction  of  the  zinc  atom  z  of  A,  for  .the  chlorine,  cl  of  the  hydrochloric  acid  B, 
is  increased,  and  attains  that  degree  of  intensity  at  which  the  resistance  to  the  im- 
pending combination  is  overcome,  and  the  z  and  cl  of  A  and  B  unite.  But  in  a 
circle  of  polar  molecules,  in  which  the  condition  of  any  one  molecule  determines 
and  is  determined  by  that  of  every  other,  the  intensity  of  the  polar  condition  is 
necessarily  the  same  in  every  element  of  the  circle.  The  chemical  polarity,  there- 
fore, of  the  other  particles  forming  the  chain,  must  increase  to  an  equal  degree  as 
with  A  and  B,  when  the  circle  is  completed,  and  the  same  change  must  now  occur 
in  all  of  them  that  has  occurred  in  A  and  B.  The  pole  of  B  next  C  is  intensely 
zincous,  while  that  of  C  next  B  is  intensely  chlorous,  whence  the  chlorine  and 
hydrogen  cl  and  z  of  these  two  particles  combine  together.  At  the  same  time,  and 
for  the  same  reason,  the  hydrogen  z  of  C  unites  with  the  chlorine  cl  of  D ;  and  so 
on,  through  a  chain  of  particles  of  hydrochloric  acid  of  any  length,  till  the  copper 
is  reached,  when  the  last  acid  particle,  D  in  the  figure,  yields  its  hydrogen  z  to  the 
chlorous  pole  of  the  copper  cl.  But  the  hydrogen  not  being  capable  of  combining 
permanently  with  the  copper,  is  liberated  as  gas  upon  the  surface  of  that  metal. 

Some  internal  change  of  a  similar  character  appears  to  take  place  in  the  chain  of 
polarized  molecules  extending  through  the  metals  themselves — a  series  of  molecular 
detachments  and  re-attachments,  among  the  atoms  of  their  polar  molecules,  like  the 
decompositions  and  recorn positions  in  the  acid,  causing  evolution  of  heat  and  other 
phenomena,  generally  reputed  electrical,  which  the  zinc  and  copper  plates  and  the 
connecting  wire  exhibit. 

Amalgamation  of  the  zinc  plate. — The  polar  molecule  of  the  metals  has  been 
assumed  to  contain  two  atoms  (like  that  of  the  acid),  with  the  view  of  assimilating 
these  intestine  changes  in  the  solid  to  those  occurring  in  the  fluid  portion  of  the 
voltaic  circuit,  and  also  because  it  appears  to  account  for  the  advantage  of  amalga- 
mating the  zinc  surface.  In  the  amalgamated  plate,  it  is  not  zinc  itself,  but  a 
chemical  combination  of  mercury  and  zinc,  which  is  presented  to  the  acid,  in  which 
mercury  is  the  negative  element,  and  which  might,  therefore,  be  called  a  hydrargyrido 
of  zinc.  That  combination  likewise  is  fluid.  It  must  constitute  the  polar  molecule, 
which  will  then  consist  of  an  atom  of  mercury  as  chlorous  pole,  and  an  atom  of  zinc 
as  zincous  pole,  and  not  of  two  atoms  of  zinc.  Such  metallic  molecules  being  capable 
of  movement  from  their  fluidity  will  place  themselves,  in  forming  a  polar  chain,  with 
Htieir  unlike  poles  together,  as  the  fluid  acid  particles  arrange  themselves.  So  that 


SIMPLE   VOLTAIC   CIRCLE.  195 

in  an  amalgam  of  zinc,  of  which  A,  E,  and  I,  are  polar  molecules  (fig.  70),  all  the 
atoms  marked  cl  are  mercury,  and  those  marked  z  are  zinc.  It  thus  follows  that, 
when  by  contact  with  an  acid  the  amalgam  is  polarized,  it  presents  a  face  of  zinc 
only  to  the  acid.  If  the  mercury  were  exposed  to  the  acid,  that  metal  would  com- 
pletely derange  the  result,  acting  locally  like  a  copper  plate,  as  will  afterwards  be 
explained.  The  previous  combination  of  the  zinc  (with  mercury)  likewise  prevents 
that  metal  from  yielding  easily  to  the  chlorine  of  hydrochloric  acid ;  and  the  zinc 
of  the  amalgam  is,  therefore,  not  dissolved,  till  the  affinities  are  enhanced  by  the 
introduction  of  a  copper  plate  into  the  acid,  and  the  formation  of  a  voltaic  circle. 

It  would  thus  appear  that  zinc,  associated  with  copper,  dissolves  more  readily  in 
the  acid  than  when  alone,  because  the  attraction  or  affinity  of  the  zinc  for  chlorine 
is  increased  by  the  completion  of  a  circle  of  similarly  polar  molecules,  in  the  same 
manner  as  the  magnetic  intensity  at  one  of  the  poles  of  a  magnet  is  increased  on 
completing  the  circle  of  similarly  polarized  elements,  by  connecting  that  pole  by 
means  of  soft  iron  with  the  other  pole  (Fig.  64,  page  188). 

Although  the  terms  of  the  electrical  hypothesis  are  at  present  avoided,  still  it 
will  be  convenient  to  denominate  the  zinc,  being  the  metal  which  dissolves  in  the 
acid,  the  active  or  positive  metal,  and  the  copper,  which  does  not  dissolve,  the  inac- 
tive or  negative  metal  of  the  voltaic  circle. 

Looking  to  the  condition  of  the  two  connected  metals  in  the  acid,  it  will  be  ob- 
served that  the  surface  of  the  zinc  presented  to  the  acid  has  zincous  affinity,  or  is 
zinco-polar,  but  the  surface  of  the  copper  presented  to  the  acid  has,  on  the  contrary, 
chlorous  affinity,  or  is  chloro-polar.  Such  a  condition  of  the  copper  is  necessary  to 
the  propagation  of  the  induction ;  and  the  advantage  of  copper  or  platinum  as  the 
negative  metal  in  a  voltaic  arrangement  depends  upon  there  being  little  or  no  impe- 
diment to  either  of  these  metals  assuming  the  chlorous  condition,  that  can  arise 
from  the  peculiar  affinity  of  the  metals  named  for  the  chlorine  of  the  acid ;  an 
affinity  which  tends  to  cause  them  to  be  superficially  zincous  instead  of  chlorous. 
If  the  second  metal  were  zinc,  the  surface  of  it  would  be  disposed  to  dissolve  in 
the  acid,  and  becoming  on  that  account  zincous,  would  induce  a  polarization  in  the 
intermediate  acid  in  an  opposite  sense  from  that  induced  by  the  first  plate  of  zinc ; 
which  counter  polarizing  actions  would  mutually  neutralize  each  other.  The  acid 
between  the  two  zinc  plates  would  be  like  a  piece  of  iron  connecting  two  like  mag- 
netic poles,  which  itself  is  not  then  polarized. 

But  if  one  of  the  two  zinc  plates  were  less  disposed  to  dissolve  in  the  acid  than 
the  other,  from  the  physical  condition  of  its  surface,  from  the  acid  being  weaker 
there,  or  from  any  other  cause,  then  the  plate  so  situated  might  become  negative  to 
the  other,  and  a  voltaic  circle  of  weak  power  be  established,  in  which  both  metals 
were  zinc. 

Impurity  of  the  zinc. — If  zinc  is  alone  in  the  acid,  and  every  superficial  particle 
of  the  metal  equally  disposed  dissolve,  then  the  zinc  everywhere  exposes  a  surface 
in  a  state  of  zincous  polarity;  and  a  polar  circle  in  the 
FIG.  71.  liquid,  starting  from  one  particle  of  the  zinc  and  returning 

upon  another,  cannot  be  established,  as  this  requires  that  a 
part  of  the  zinc  surface  be  chlorous.  But  if  the  zinc  contains 
on  its  surface  a  single  particle  of  copper,  a  chlorous  pole  is 
created,  upon  which  an  inductive  circle  starting  from  an 
adjoining  particle  of  zinc,  A,  (fig.  71),  and  passing  through 
Acid.  tne  liquid,  may  return  as  shown  in  the  figure.  It  is  the 
formation  of  such  circles  that  causes  impure  zinc,  which 
is  contaminated  by  other  metals,  to  dissolve  so  much  more 
quickly  in  an  acid  than  the  pure  metal.  Why  such  circles 
are  not  formed  when  the  positive  metal  in  combination 
with  the  zinc  is  mercury,  which  forms  a  fluid  alloy,  has 
already  been  accounted  for;  and  the  nature  of  the  evil 
which  might  otherwise  attend  the  amalgamation  of  the 
zinc  is  now  evident. 


196 


CHEMICAL   POLARITY. 


The  whole  chain  of  polar  molecules  in  the  voltaic  circle  admits  of  a  natural 
division  into  two  segments,  the  acid  or  liquid  segment  BCD  (fig.  70),  and  th*e 
metallic  segment,  A  K  F,  each  of  which  has  a  pair  of  poles,  the  unlike  poles  of 
the  two  segments  being  opposed"  te  each  other.  The  pole  at  B  of  the  acid  portion 
is  chlorous,  and  is  opposed  to  the  zincous  pole  at  A  of  the  metallic  segment;  while 
the  pole  of  the  liquid  segment  at  D  is  zincous,  and  is  opposed  to  the  chlorous  pole 
or  the  metallic  segment  at  F.  The  distribution  of  polarity  in  these  two  segments 
is,  therefore,  the  same  as  in  two  magnets  with  their  unlike  or  attracting  poles  in 
contact. 

Such,  then,  is  the  action  of  affinity  by  induction,  which  the  mere  introduction  of 
zinc  and  copper  in  contact  into  the  same  acid  liquid  is  sufficient  to  develope,  and 
which  accounts  for  the  discharge  of  the  hydrogen  upon  the  surface  of  the  copper  in 
such  an  arrangement,  the  remarkable  phenomenon  by  a  description  of  which  this 
subject  was  introduced. 

Circle  with  the  connecting  wire  broken.  —  It  remains  for  us  to  apply  the  same 
principles  to  explain  thje  additional  phenomena  of  the  second  case  described,  in 
which  the  connecting  wire,  supposed  to  be  of  platinum,  between  the  zinc  and  copper 
plates,  is  divided,  and  the  broken  extremities  introduced  into  hydriodic  acid  (fig.  70, 
page  194). 

Broken  at  any  point,  as  at  K,  (Fig.  70),  it  is  evident  that  if  the  polarized  condi- 
tion be  still  sustained,  the  portion  of  the  metallic  segment  connected  with  the  copper 
plate  will  terminate  with  a  zincous  pole  at  K,  and  that  connected  with  the  zinc  with 
a  chlorous  pole  ;  which  may  be  indicated  respectively  by  K  and  L,  in  fig.  72.  When 

FIG.  72. 


Zinc. 


F      Copper. 


hydriodic  acid  is  interposed  between  K  and  L,  the  breach  is  repaired  by  the  polari- 
zatioja  of  a  chain  of  particles  of  that  acid.  The  extremity  K,  being  zincous,  induces 
chlorous  polarity  in  the  side  of  the  hydriodic  acid  particle  which  it  touches  ;  in  con- 
sequence of  which  the  iodine  atom  (the  analogue  of  chlorine)  of  the  hydriodic  acid 
molecule  is  presented  to  that  pole,  and  liberated  there  when  decomposition  occurs. 
The  extremity  L  of  the  zinc  or  positive  metal  element  is  chlorous,  and  therefore  in- 
duces zincous  polarity  in  the  particle  of  hydriodic  acid  which  it  touches,  and  hydro- 
gen (the  analogue  of  zinc)  is  liberated  there.  The  polarity  in  an  induced  circle 
must  necessarily  be  of  equal  intensity  at  every  point  in  it,  and  being  sufficient  at  A 
to  cause  the  decomposition  of  the  hydrochloric  acid,  must  also  decompose  the  hydrio- 
dic acid  between  K  and  L  ;  otherwise  it  is  never  established  at  A,  nor  anywhere 
else. 

In  the  present  arrangement,  the  voltaic  circle  is  broken  into  four  segments,  or 
has  four  polar  elements,  every  terminal  pole  of  which  is  in  contact  with  a  pole  of  a 
different  name  ;  and  the  whole  arrangement  may  be  compared  to  a  circle  of  four 
magnets  with  the  attractive  poles  in  contact. 

These  elements  are  :  —  First,  the  zinc  plate  or  positive  metal,  A  L,  of  which  the 
end  at  A,  in  the  hydrochloric  acid  (fig.  73),  has  zincous  affinity,  and  the  end  faced 
with  platinum  at  L,  in  the  hydriodic  acid,  chlorous  affinity. 


COMPOUND    VOLTAIC   CIRCLE. 


197 


Zinc  or 
positive 
metal. 


Copper  or 
negative 
metal. 


FIG.  73.  Secondly,  the  body  of  hydrochloric  acid, 

Fluid.  A  F,  between  the  zinc  and  copper  plates, 

of  which  the  surface  at  A,  in  contact  with 
the  positive  metal,  has  chlorous,  and  that 
at  F,  in  contact  with  the  negative  metal, 
zincous  affinity. 

Thirdly,  the  copper  or  negative  metal 
F  K,  of  which  the  end  at  F  in  the  hydro- 
chloric acid  has  chlorous  affinity,  and  that 
faced  with  platinum  at  K  in  the  hydriodic 
acid,  zincous  affinity. 
Fluid.  And  fourthly,  the  body  of  hydriodic 

acid,    K  L,    between   the    zincous   and 

chlorous  poles  of  the  negative  and  positive  metals,  of  which  the  surface  K,  in  con- 
tact with  the  negative  metal,  is  chlorous,  and  the  surface  L,  in  contact  with  the 
positive  metal,  zincous. 

In  every  voltaic  circle  employed  to  produce  decomposition  these  four  elements  are 
to  be  looked  for.  Hereafter,  in  adverting  to  any  one  of  these  elements,  it  will  be 
sufficient  to  confine  our  notice  to  its  terminal  polarities  or  affinities,  without  recurring 
to  the  polarized  condition  of  the  element  itself,  upon  which  its  terminal  affinities 
depend. 

COMPOUND    VOLTAIC    CIRCLE. 

In  both  the  arrangements  described  there  is  only  one  source  of  polarizing  force, 
namely,  the  action  between  the  zinc  and  acid  at  A.  But  a  circle  of  a  similar  nature 
may  be  constructed  embracing  within  itself  two  or  more  of  such  primary  sources  of 
polarizing  power,  and  the  intensity  of  the  polar  condition  of  the  whole  circle  be 
Jhereby  greatly  increased. 

•    Figure  74  represents  such  a  circle,  in  which  there  are  two  zinc  plates,  both 

supposed  to  be  in  contact  with  hydrochloric  acid, 
namely  at  A  and  at  C,  and  a  copper  plate  attached 
to  each  of  these  zincs.  The  polar  condition  of  such 
a  circle  will  easily  be  observed.  By  the  contact  of 
the  acid  and  zinc  at  A,  a  zincous  pole  is  established 
there  in  the  first  zinc  plate,  and  a  chlorous  pole  in 
the  acid,  which  are  so  inscribed  in  the  diagram. 
These  occasion  the  formation  of  a  chlorous  pole  a.t 
D  in  the  first  copper,  the  united  zinc  and  copper 
A  D  forming  together  one  polar  element ;  and  a 
zincous  pole  at  B  in  the  acid,  the  column  A  B  of 
acid  being  the  second  polar  element.  The  further  effect  of  the  induction  is  to  pro- 
duce a  chlorous  pole  at  B  in  the  second  copper,  of  which  the  corresponding  zincous 
pole  is  at  C,  in  the  second  zinc ;  the  united  zinc  and  copper  B  C  forming  together  a 
third  polar  element.  And,  as  a  last  consequence  of  the  inducing  force  originating 
at  A,  the  column  of  acid  between  C  and  D  becomes  a  fourth  polar  element  of  the 
circle,  having  a  chlorous  pole  at  C  and  a  zincous  pole  at  D.  Now  it  will  be  observed 
that  the  chemical  affinity  between  the  acid  and  zinc  at  C  tends  to  produce  the  same 
polar  conditions  at  that  point  as  are  already  established  there  from  the  effect  of  in- 
duction. The  extremity  of  the  zinc  plate  at  C  is"  in  fact  zincous,  'both  primarily  and 
by  induction ;  and  the  acid  in  contact  with  it  chlorous,  likewise  both  primarily  and 
by  induction ;  and  generally,  throughout  the  whole  circle,  the  polar  conditions  de- 
termined by  the  second  chemical  action  at  C  are  the  same  as  those  determined  by 
the  first  action  at  A. 

In  the  last  arrangement,  the  inductive  actions  are  in  the  same  direction,  and 
favour  each  other ;  but  a  circle  may  be  constructed  in  which  the  inductions,  being 


Fia.  74. 


198 


CHEMICAL   POLARITY. 


FIG.  75. 

Fluid. 


Zinc. 


Copper. 


Fluid. 


polar  elements  F  A, 
FIG.  76. 


cM 


Zincl 


in  opposite  directions,  oppose  and  neutralize 
each  other.  Thus  if  A  D  (fig.  75)  be  entirely 
zinc,  both  its  extremities  being  exposed  to 
acid,  will  tend  equally  to  be  zincous.  In  the 
same  way,  if  B  C  be  entirely  copper,  the  con- 
dition of  both  its  extremities  will  be  chlorous, 
from  the  action  of  the  acid  on  the  two  ends 
of  the  zinc;  and,  consequently,  the  elements 
of  such  a  circle  could  have  no  polarity. 

A  circle  is  represented  in  fig.  76,  contain- 
ing three  sources  of  polarizing  force.  It  con- 
sists of  three  alternations  of  copper  and  zinc 
symmetrically  arranged,  and  forming  three 
C,  and  D  E,  with  three  acid  columns  between  these  alterna- 
tions, which  form  three  additional  polar  elements, 
A  B,  C  D,  and  E  F.  The  number  of  alternations 
of  copper  and  zinc  with  acid  may  obviously  be  in- 
creased to  any  extent,  and  the  chemical  action  of 
the  acid  on  the  zinc  in  each  alternation  is  found  to 
increase  in  a  marked  manner  up  to  the  number  of 
10  or  12  alternations.  This  increase  of  the  affinity 
is  undoubtedly  owing  to  the  favouring  inductive 
action  which  the  chemical  actions  at  the  different 
points  have  upon  each  other.  Such  a  compound 
circle  may  be  compared  to  a  number  of  magnets 
disposed  in  a  circle  with  their  attracting  poles  toge- 
ther, of  which  each  would  have  its  magnetic  intensity  exalted  by  induction  from  all 
the  rest.  When  such  a  circle  is  broken  at  any  point,  all  chemical  action  and  polari- 
zation cease  till  contact  is  again  made,  and  the  circuit  completed.  The  polarization, 
too,  being  the  result  of  a  circular  induction  involving  so  many  lines  or  chains  of 
particles,  cannot,  when  once  established,  be  more  or  less  at  any  one  point  in  the 
circuit  than  at  others.  The  resulting  chemical  action  must,  therefore,  be  every 
where  equal  in  the  circle,  and  consequently  the  same  quantity  of  zinc  be  dissolved, 
and  hydrogen  evolved  in  each  acid. 

If  any  metallic  element  of  this  compound  circle  be  broken,  and  a  polarizable 
liquid  be  interposed  between  the  metallic  extremities  so  as  to  complete  the  circuit, 
decomposition  occurs  in  that  liquid  as  in  the  simple  interrupted  circle  (fig.  72).  But 
the  polarizing  influence  of  the  compound  circle  being  of  high  intensity,  more 
numerous  and  difficult  decompositions  are  effected  by  means  of  it  than  by  the  simple 
circle.  The  compound  voltaic  circle  is  indeed  a  decomposing  instrument  of  great 
efficiency. 

If,  in  this  arrangement,  the  position  of  one  of  the  metals  in  the  series  be  reversed, 
so  that  a  zinc  is  where  a  copper  should  be,  then,  by  the  action  of  the  acid  on  that 
zinc,  polarization  in  the  wrong  direction  is  occasioned,  which  greatly  diminishes  the 
general  polarity  of  the  circle,  reducing  it  in  an  arrangement  of  ten  alternations  to 
one-fourth,  according  to  Mr.  Daniell. 

Voltaic  battery.  —  In  the  first  of  the  two  annexed  diagrams  (see  fig.  77)  is  repre- 
sented a  compound  circle,  such  as  is  employed  to  produce  decomposition,  and  called 
a  voltaic  battery,  consisting  of  three  acid  jars,  each  of  which  contains  a  zinc  and 
copper  plate,  and  which  are  termed  active  cells,  as  they  are  sources  of  polarizing 
power,  from  the  action  of  acid  upon  zinc  which  takes  place  in  them. 

In  the  second  diagram  (see  fig.  78),  the  same  arrangement  is  repeated,  with  the 
addition  of  a  third  jar,  termed  the  decomposing  cell,  which  contains  any  binary  polar 
liquid,  with  two  platinum  plates  immersed  in  it.  Each  copper,  it  will  be  seen,  is 
connected  by  a  wire  with  the  following  zinc ;  and,  in  the  first  diagram,  the  copper  in 
the  third  cell  C"  is  immediately  connected  with  the  zinc  in  the  first  cell  Z  by  a  wire, 


VOLTAIC   BATTERY. 
FIG.  77. 


199 


FIG.  78. 


and  the  circuit  thus  completed.  The  polar  elements  in  the  circle  of  the  first  diagram 
it  will  be  found,  are  six  in  number ;  namely,  the  three  acid  columns  between  the 
metals  in  the  cells  a  b,  c  d,  and  ef;  and  the  three  pairs  of  zinc  and  copper  plates, 
each  of  which  pairs  forms  a  single  polar  element,  of  which  the  surface  of  the  zinc 
is  the  zincous,  and  the  surface  of  the  copper  the  chlorous  pole.  In  the  second 
diagram,  one  of  these  metallic  elements  Z  C"  is  divided,  and  a  polar  liquid  g  7i,  in 
the  cell  of  decomposition,  interposed  between  the  broken  extremities  PI  and  PP. 
To  ascertain  the  polar  condition  of  the  extremities,  or  the  terminal  platinum  plates 
in  the  decomposing  cell,  it  is  to  be  observed  that  PI'  with  Z  forms  one  polar  element, 
of  which  Z  being  a  zincous  pole,  PI'  must  be  a  chlorous  pole.  Again,  PI  with  C" 
forms  one  polar  element,  of  which  C"  being  a  chlorous  pole,  PI  must  be  a  zincous 
pole.  Now,  the  platinum  plates  PI  and  PI',  which  are  thus  zincous  and  chlorous, 
are  disposed  in  the  decomposing  cell,  in  regard  to  one  another, — the  first  to  the  left, 
and  the  second  to  the  right,  as  the  zincous  and  chlorous  plates  (the  zinc  and  copper) 
also  are  arranged  .in  the  active  cells.  It  will  be  convenient  to  distinguish  by  names 
the  poles  which  these  terminal  platinum  plates  constitute,  as  they  are  much  more 
frequently  referred  to,  and  of  greater  consequence  than  any  other  poles  in  the  voltaic 
battery,  when  used  as  an  instrument  of  decomposition,  as  it  constantly  is.  The 
chlorous  plate  PF,  which  is  in  connexion  with  a  zinc  plate  Z,  may  be  called  the 
chloroid  (like  chlorine),  and  the  zincous  plate  PI,  which  is  connected  with  a  copper 
plate  C",  may  be  called  the  zincoid  (like  zinc), — names  which  express  the  virtual 
properties  of  each  plate,  or  the  particular  attractive  power  and  affinity  which  each 
of  them  acquires  from  its  place  in  the  circle. 

When  hydrochloric  acid  is  the  polar  liquid  interposed  between  these  plates,  chlo- 
rine is  of  course  attracted  by  the  surface  of  the  zincoid,  and  discharged  there ;  and 
hydrogen  by  the  face  of  the  chloroid,  and  discharged  upon  that  plate.  On  the  elec- 
trical hypothesis,  the  same  plates  are  variously  denominated : — 


200  CHEMICAL   POLARITY. 

The  zincoid  as  the  positive  pole,  the  positive  electrode,  the  anode,  and  the  zin- 
code. 

The  chloroid  as  the  negative  pole,  the  negative  electrode,  the  cathode,  and  the 
platinode. 

The  cell  of  decomposition  thus  interpolated  in  the  voltaic  circle  is  an  obstacle  to 
induction,  and  reacts  on  the  whole  series,  reducing  the  chemical  action  and  evolution 
of  hydrogen  in  each  of  the  active  cells  by  at  least  one-third.  In  that  retarding  cell 
itself,  the  amount  of  decomposition  is  necessarily  the  same  as  in  the  other  cells. 
Mr.  Daniell  found  the  chemical  action  reduced  to  one-tenth  in  a  series  of  eight  active 
and  two  such  retarding  cells ;  and  entirely  stopped  by  three  retarding  to  seven  active 
cells. 

•  OP   THE    SOLID    ELEMENTS   OF   THE   VOLTAIC   CIRCLE. 

The  elements  of  a  Voltaic  Circle  are  obviously  of  two  different  kinds — the  metals 
or  solid  portions,  through  the  substance  of  which  chemical  induction  is  propagated 
without  decomposition ;  and  the  liquids  in  the  cells,  which  yield  to  the  induction 
and  suffer  decomposition.  In  reference  to  the  first,  it  is  to  be  observed  that,  as  only 
iron  and  one  or  two  other  metals  of  the  same  natural  family  are  susceptible  of  mag- 
netic polarity,  so  the  susceptibility  of  chemical  polarity  which  appears  in  the  voltaic 
battery  is  not  possessed  by  solids  in  general,  but  is  confined  to  the  class  of  bodies  to 
which  zinc  belongs, — the  metals,  all  of  which  possess  it,  with  the  addition  of  carbon 
in  the  form  of  charcoal,  and  certain  metallic  sulphides,  more  particularly  the  sul- 
phide of  silver  when  heated.  Weak  solutions  of  the  alkaline  sulphides,  containing 
an  excess  of  sulphur,  also  admit  of  a  feeble  polarity  without  undergoing  decomposi- 
tion. The  non-metallic  elements,  with  their  compounds,  the  oxides  and  salts  of  the 
metals,  are  destitute  of  this  power,  and  cannot,  therefore,  be  used  as  solid  elements 
of  the  circle.  A  body  available  for  this  purpose  is  termed  a  conductor  on  the  elec- 
trical hypothesis,  a  name  which  may  be  retained  as  it  is  not  at  variance  with  the 
function  assigned  to  the  metals  in  the  circle  viewed  as  a  chemico-polar  arrangement. 
Two  different  metals  are  combined  in  a  circle,  one  of  which  is  acted  on  by  the  liquid, 
and,  therefore,  called  the  active  or  the  positive  metal ;  while  the  other  is  not  acted 
upon,  and  is,  therefore,  called  the  inactive  or  the  negative  metal ;  and  it  has  already 
been  stated,  that  the  more  easily  acted  on  by  the  liquid,  or  the  more  highly  positive 
the  one  metal,  and  the  less  easily  acted  upon,  or  more  negative  the  other  metal,  the 
more  proper  and  efficacious  is  the  combination.  In  the  following  table  several  of  the 
metals  are  arranged  in  the  order  in  which  they  appear  positive  or  negative  to  each 
other,  when  acted  on  by  the  acid  fluids  commonly  employed  in  the  voltaic  battery. 
Each  metal  is  positive  to  any  one  below  it  in  the  table,  and  negative  to  any  one 
above  it. 

Most  positive. 
Potassium. 
Sodium. 
Manganese. 
Zinc. 

Cadmium. 
Iron. 
Nickel. 
Cobalt. 
Lead. 
Tin. 

Bismuth. 
Copper. 
Silver. 
Mercury. 
Palladium. 


VOLTAIC  PROTECTION  OF  METALS.  201 

Carbon. 
Platinum. 
Rhodium. 
Iridium. 
Gold. 
Most  negative. 

Zinc,  which  stands  high  in  the  list,  is  the  only  metal  which  can  he  used  with 
advantage  in  the  voltaic  battery,  as  the  positive  metal.  Although  closely  approach- 
ing zinc  in  the  strength  of  its  affinities,  iron  is  ill  adapted  for  the  purpose,  from  the 
impossibility  of  amalgamating  its  surface,  the  irregularity  of  its  structure,  and  cer- 
tain peculiarities  of  this  metal  in  reference  to  chemico-polarity.  Platinum  forms  an 
excellent  negative  metal,  from  the  weakness  of  its  affinities,  and  is  generally  used 
for  the  plates  in  the  cell  of  decomposition.  Silver  also  is  highly  negative,  but  copper 
is  the  only  negative  metal  which  from  its  cheapness  can  be  used  in  the  construction 
of  active  cells  of  considerable  magnitude. 

Voltaic  protection  of  metals.  —  But  although  the  difference  between  two  metals 
in  point  of  affinity  be  very  small,  yet  their  association  in  the  same  acid  always  gives 
a  decided  .predominance  to  the  affinity  of  the  more  positive,  by  causing  the  surface 
of  the  other  to  become  chlorous,  and  therefore  wholly  inactive  in  an  acid  fluid.  A 
negative  metal  may  thus  be  protected  from  the  solvent  action  of  saline  and  acid 
liquids,  by  association  with  a  more  positive  metal ;  iron,  for  instance,  by  zinc,  as  in 
articles  of  galvanized  iron,  which  are  coated  with  the  former  metal.  The  process 
is  analogous  to  the  making  of  tin-plate.  The  surface  of  the  iron  (generally  sheet 
iron)  is -first  cleaned  from  all  adhering  oxide  by  a  dilute  acid;  then  immersed  in  a 
weak  solution  of  tin,  with  fragments  of  metallic  tin,  according  to  the  improved 
practice  of  Messrs.  Morewood  and  Rogers,  by  which  the  iron  is  covered  by  a  film 
of  tin,  to  which  zinc  is  capable  of  adhering  more  uniformly  than  to  an  iron  surface. 
The  article  so  prepared  is  then  passed  once  through  a  bath  of  melted  zinc,  of  which 
the  surface  is  covered  by  the  fused  chloride  of  zinc  and  ammonium,  to  protect  the 
metal  from  oxidation.  It  thus  acquires  a  smooth  and  beautifully  crystallized  coating 
of  zinc.  Copper  is  protected  by  either  zinc  or  iron,  as  was  remarkably  illustrated 
in  the  attempt  made  by  Sir  H.  Davy  to  defend  the  copper  sheathing  of  ships  from 
corrosion  in  sea- water,  by  means  of  his  protectors.  These  were  small  masses  of 
iron  or  zinc  fixed  upon  the  ship's  copper,  at  different  points  under  the  water  line. 
They  completely  answered  the- purpose  of  protecting  the  copper,  but  unfortunately 
gave  rise  to  a  deposition  of  earthy  matter  upon  that  metal  to  which  barnacles  and 
sea-weeds  attached  themselves,  and  thereby  diminished  the  facility  of  the  ship's 
motion  through  the  water.  The  more  recent  substitution,  by  Mr.  Muntz,  of  an 
alloy  of  60  parts  of  copper  and  40  of  zinc,  for  pure  copper,  has  proved  more  suc- 
cessful. In  actisg  as  a  protecting  positive  metal,  zinc  necessarily  undergoes  corro- 
sion, but  more  slowly  than  might  be  expected.  On  zinced  articles  which  are  exposed 
to  the  air  only,  and  not  immersed  in  water,  a  film  of  suboxide  of  zinc  soon  appears, 
which  forms  a  hard  covering,  and  protects  the  metal  below  from  further  change. 

On  the  other  hand,  the  injurious  effect  of  association  with  a  negative  metal  ia 
often  accidentally  illustrated,  as  in  the  corrosion  of  the  ends  of  iron  railings,  which 
are  fixed  in  their  sockets  by  lead,  a  more  negative  metal.  In  dye-coppers,  an  iron 
steam-pipe  with  a  rose  of  lead  or  copper  is  quickly  destroyed.  Some  kinds  of  cast 
iron  undergo  a  rapid  corrosion,  when  exposed  to  sea-water,  the  carbon  acting  as  a 
negative  body  and  ultimately  remaining  in  the  form  of  plumbago  after  all  the  metal 
has  disappeared. 

A  weak  voltaic  circle  may  even  be  formed  of  a  single  positive  metal  in  an  acid, 
as  the  zinc  A  B  (fig.  79),  provided  the  surfaces  of  the  metal  exposed  to  the  acid  at 
A  and  B  are  in  different  conditions  as  to  purity  or  mechanical  structure,  and  there- 
fore unequally  acted  upon  by  the  acid ;  whereupon  the  part  least  disposed  to  dissolve 
becomes  negative  to  the  other.  A  zinc  plate  may  also  be  unequally  acted  on  and 


202 


CHEMICAL   POLARITY. 


FIG.  80. 


thrown  into  a  polar  state,  from  the  liquid  in  which  it  is  im- 
mersed varying  in  composition  and  activity  at  different  points 
of  the  metallic  surface.  A  circle  may  thus  be  formed  of  one 
metal  A  Z  B,  with  two  liquids  A  E  and  E  B,  which  merge 
into  each  other,  and  form  together  one  polar  element  A  B. 

The  two  metals  in  a  circle  have  generally  been  exhibited 
in  metallic  contact,  and  forming  together  one  polar  element, 
but  they  may  be  separated,  as  are  the  zinc  and  copper  plates 
A  D  and  C  B  in  the  diagram  (fig.  80),  by  two  fluids,  pro- 
vided these  fluids  are  such  as  a  strong  acid  at  A  B,  and  as 
iodide  of  potassium  at  D  C,   the  first  of  which  acts  very 
powerfully  on  zinc,  while  the  other  acts  very  feebly  upon 
that  metal  (unless  associated  with  copper);   so  that  of  the  consequent  opposing 
inductions,  that   originating   at   A  greatly  exceeds  and 
overpowers  that  of  D.     It  is  likewise  necessary  that  the 
fluid  D  C  be  of  easy  decomposition,  so  as  to  yield  to  the 
polar  power  of  the  single  circle.     In  this  arrangement, 
however,  it  is  obvious  that  the  zinc  itself  forms  a  complete 
polar  segment,  of  which  A  is  the  zincous,  and  I)  the  chlo- 
rous pole ;  and  the  copper  also  an  entire  polar  segment 
of  which  B  is  the  chlorous,  and  C  the  zincous  pole. 

The  preceding  table  exhibits  the  relation  which  the 
metals  enumerated  assume  to  each  other,  in  the  acid  and 
saline  solutions  usually  employed  as  exciting  fluids.  But 
the  relation  of  any  one  metal  to  another  is  not  the  same  in  all  exciting  fluids.  Thus 
when  tin  and  copper  are  placed  in  acid  solutions,  the  former  is  most  rapidly  corroded 
and  becomes  the  positive  metal,  according  to  its  position  in  the  series,  but  if  they 
are  put  into  a  solution  of  ammonia  which  acts  most  upon  the  copper,  then  the  latter 
becomes  the  positive  metal.  Copper  is  positive  to  lead  in  strong  nitric  acid,  which 
oxidizes  the  former  most  freely,  whereas  in  dilute  nitric  acid,  by  which  the  lead  is 
most  rapidly  dissolved,  the  lead  is  positive. 


LIQUID    ELEMENTS    OF    THE   VOLTAIC    CIRCLE. 

With  the  view  of  simplifying  the  statement  of  the  circular  decompositions  which 
occur  in  the  voltaic  circle,  the  exciting  fluid  has  hitherto  always  been  supposed  to 
be  hydrochloric  acid  (chloride  of  hydrogen),  and  this  compound  is  a  fair  type  of  the 
class  of  bodies  which  possess  a  polar  molecule,  and  are  available  for  the  purpose  of 
bringing  these  changes  into  play.  The  exciting  fluid  is  always  a  saline  body  in  the 
general  sense ;  that  is,  a  binary  compound  of  a  salt-radical  or  halogen,  such  as  chlo- 
rine, with  a  basyl,  such  as  hydrogen  or  a  metal.  The  chloride  or  copper,  chloride 
of  sodium,  chloride  of  ammonium,  or  the  chloride  of  any  other  basyl,  may  be  sub- 
stituted for  hydrochloric  acid,  although  not  all  with  the  same  advantage ;  and  the 
chlorides  of  basyls  may  be  replaced  by  their  iodides,  sulphionides  (sulphates),  nitra- 
tionides  (nitrates),  and  salts  of  other  acids,  as  exciting  fluids,  provided  they  have 
the  condition  of  liquidity,  which  gives  mobility  to  their  particles,  and  permits  that 
disposition  of  them  which  is  assumed  in  a  polar  chain.  The  liquids  which  yield  in 
the  cell  of  decomposition  are  of  the  same  nature,  possessing  always  a  binary  polar 
molecule,  although  the  liquid  which  forms  the  best  exciting  fluid  is  not  always  the 
most  easily  decomposed  in  the  decomposing  cell. 

The  positive  metal  which  is  exposed  to  the  exciting  fluid  always  acts  in  one  way, 
displacing  the  basyl  and  combining  with  the  halogen  of  that  body;  in  the  manner 
the  zinc  has  been  seen  to  liberate  hydrogen  and  combine  with  chlorine,  when  hydro- 
chloric acid  is  the  excitiag  fluid.  The  positive  metal  is  thus  substituted  for  a  similar 
basyl  in  a  pre-existing  saline  compound.  That  metal  may  dissolve  in  another  man- 
ner, by  uniting  directly,  for  instance,  with  free  chlorine  or  iodine  in  solution,  but 


LIQUID   ELEMENTS   OF   THE   VOLTAIC   CIRCLE.         203 

then  no  polar  chain  is  formed.  Particles  of  chlorine  may  extend  from  the  zinc  to 
the  associated  negative  metal,  but  not  possessing  a  binary  molecule  they  have  no 
occasion  to  throw  themselves  into  a  polar  chain  in  order  to  act  upon  the  zinc,  as  the 
molecules  of  hydrochloric  acid  require  to  do  in  the  same  circumstances.  The  par- 
ticles of  these  free  elements  appear  to  be  incapable  of  that  polar  condition,  having 
chlorous  affinity  on  one  side  and  zincous  on  the  other,  of  which  both  the  solid  and 
liquid  constituents  of  the  voltaic  circle  must  be  susceptible.  Judging  from  the  uni- 
formity in  composition  of  exciting  liquids,  their  capacity  to  form  polar  chains  depends 
on  their  consisting  of  an  atom  of  basyl  and  an  atom  of  salt-radical,  which  are  respec- 
tively the  locus  of  zincous  and  chlorous  affinity  or  polarity.  Such  molecules  may  be 
looked  upon  as  in  a  state  of  tension  when  forming  a  part  of  a  polar  chain,  each  about 
to  divide  into  its  chlorous  and  zincous  atoms.  Mr.  Faraday  had  established  that  all 
exciting  liquids  are  binary  compounds  of  single  equivalents  of  salt-radical  and  basyl, 
or  prolo-compounds,  such  as  hydrochloric  acid  itself,  proto-chloride  of  tin,  &c.  Other 
saline  bodies  which  are  per-compounds,  such  as  bichloride  of  tin,  are  not  exciting  or 
polar,  because,  as  may  be  supposed,  they  are  not  naturally  resolvable  into  a  chlorous 
and  zincous  atom,  but  into  a  chlorous  atom  and  another  salt;  the  "bichloride  of  tin, 
for  instance,  into  chlorine  and  proto-chloride  of  tin.  Certain  compounds,  which  are 
deficient  in  the  saline  character  and  not  polarizable,  such  as  chloride  of  sulphur,  and 
the  liquid  chlorides  of  phosphorus  arid  carbon,  have  been  enumerated  as  exceptions 
to  this  rule.  None  of  these  bodies,  however,  is  really  a  proto-compound. 

The  zinc  or  positive  metal,  too,  always  forms  a  proto-compound  in  dissolving, 
which  is  a  saline  body.  The  order  of  the  chemical  changes  in  the  exciting  fluid 
therefore  is  as  follows :  —  The  zinc  in  decomposing  a  binary  compound  and  forming 
a  binary  compound  liberates  an  atom  of  its  own  class ;  which  atom  repeats  the  same 
actions ;  supplying  at  the  same  time  another  atom  of  the  same  kind  to  act  in  the 
same  manner,  and  that  another,  from  the  zinc  to  the  copper  plate.  The  combining 
bodies  are  always  a  basyl  and  a  salt-radical,  and  therefore  only  two  kinds  of  attrac- 
tion or  affinity  are  at  work  throughout  the  chain,  those  of  a  basyl  and  a  salt-radical, 
the  zincous  and  chlorous  affinities.  Hence,  in  the  present  subject  of  chemical 
polarity,  we  have  to  deal  with  but  two  attractive  forces,  the  zincous  and  the  chlorous, 
as  in  magnetism  with  but  two  magnetic  forces,  the  austral  and  the  boreal. 

On  the  electrical  hypothesis,  a  body  which  is  thus  decomposed  in  the  active  cells, 
or  in  the  cell  of  decomposition,  is  called  an  electrolyte  (decomposable  by  electricity), 
and  this  kind  of  decomposition  is  distinguished  as  electrolysis.  The  two  elements 
of  an  electrolyte,  which  travel  or  are  transferred  in  opposite  directions,  in  its  decom- 
position have  been  named  ions  (from  'uov,  going) ;  the  halogen  which  travels  to  the 
positive  metal  or  terminal,  the  anion  (going  upwards),  and  the  basyl,  which  is  trans- 
ferred to  the  negative  metal,  or  terminal,  the  cation  (going  downwards).  Strictly 
chemical  expressions  equivalent  to  the  former  would  be  zincolyte  and  zincolysis,  the 
decompositions  throughout  the  circle  being  referred  to  the  affinity  of  zinc  or  the 
positive  metal. 

The  characters  of  the  two  constituents  of  an  electrolyte  may  be  shortly  noticed. 
The  class  of  basyl  constituents  is  composed  of  the  metals  in  their  order  as  positive 
metals,  beginning  with  potassium,  and  terminating  with  mercury,  platinum,  and  the 
less  oxidable  metals.  Ammonium  has  a  claim  to  be  introduced  high  in  this  list,  and 
should  probably  be  accompanied  by  the  analogous  basyl  of  the  aniline  class  of  bases 
and  of  the  vegeto-alkalies,  although  in  respect  to  the  decomposition  of  their  salts  in 
the  voltaic  circle,  we  have  little  precise  information.  Hydrogen  likewise  finds  a 
place  near  copper  in  this  class. 

At  the  head  of  the  halogen  constituents  of  electrolytes  may  be  placed  iodine  and 
the  other  members  of  the  chlorine  family.  These  are  followed  by  the  halogens  of 
the  sulphates,  nitrates,  carbonates,  acetates,  and  other  oxygen-acid  salts.  Sulphur 
must  be  allowed  to  follow  the  last,  as  the  salt-radical  of  the  sohible  sulphides,  and 
the  lowest  place  be  assigned  to  oxygen,  as  the  salt-radical  of  the  soluble  metallic 
oxides ;  of  oxide  of  potassium,  for  instance,  and  of  water.  It  is  unusual  to  speak 


204  CHEMICAL    POLARITY. 

of  oxygen  as  a  salt-radical,  and  of  caustic  potassa  and  water  as  salts,  but  the  binary 
theory  of  salts  recognizes  no  essential  difference  between  the  chloride,  sulphionide, 
and  oxide  of  a  basyl,  the  oxide  being  connected  with  the  more  highly  saline  com- 
pounds through  the  sulphide,  and  the  list  of  salt-radicals  forming  a  continuous 
descending  series  from  iodine  to  oxygen. 

The  facility  of  decomposition  of  different  electrolytes  appears  to  depend  more  upon 
the  high  place  of  their  salt-radical,  than  upon  the  nature  of  their  other  constituent. 
The  iodides,  for  instance,  as  iodide  of  potassium  and  hydriodic  acid,  are  the  most 
easily  decomposed  of  all  salts,  yielding  to  the  polar  influence  of  the  single  circle. 
Then  follow  the  chlorides,  —  chloride  of  lea<J,  fused  by  heat,  yielding  to  a  very 
moderate  power.  After  these  the  salts  of  strong  oxygen  acids,  such  as  sulphates 
and  nitrates  either  of  strong  bases,  such  as  potassa  and  soda,  or  of  weak  bases,  such 
as  oxide  of  copper  and  water  (the  hydrated  acids  are  such  salts).  The  carbonates 
and  acetates,  which  have  much  weaker  salt-radicals,  are  still  less  easily  decomposed, 
and  finally  oxides  are  decomposed  with  great  difficulty.  Water  itself  is  polarized 
with  such  extreme  difficulty,  and  decomposed  when  alone  to  so  minute  a  degree, 
even  by  a  powerful  battery,  as  long  to  have  left  its  claim  uncertain  to  be  considered 
an  electrolyte,  when  in  a  state  of  purity. 

Widely  as  the  more  characteristic  halogens  and  basyls  differ,  still  the  classes  pass 
by  imperceptible  gradations  into  each  other,  and  form  portions  of  one  great  circular 
series.  Mercury  and  the  more  negative  metals,  although  clearly  basyls,  appear  at 
times  to  assume  the  salt-radical  relation  to  the  highly  positive  metals;  such  a  cha- 
racter is  evinced  in  mercury,  by  the  energy  with  which  it  unites  with  sodium  and 
potassium,  and  by  its  function  in  the  amalgamated  zinc  plate  of  the  voltaic  circle. 
So  that  the  salt-radical  or  basyl  character  of  a  body  is  not  absolute,  but  always  rela- 
tive to  certain  other  bodies. 

The  addition  of  a  salt  or  acid,  even  in  minute  quantity,  to  water  in  the  cell  of 
decomposition,  causes  the  copious  evolution  of  oxygen  and  hydrogen  gases  at  the 
zincoid  and  chloroid,  and  is  therefore  often  spoken  of  as  facilitating,  by  its  presence, 
the  decomposition  of  the  water,  in  some  way  which  cannot  be  explained.  But  the 
phenomena  are  unattended  with  difficulty  on  the  binary  theory  of  saline  bodies. 
When  sulphate  of  soda  exists  in  the  water  of  the  decomposing  cell,  it  may  be  sul- 
phionide of  sodium  which  is  decomposed,  S04,  the  sulphate  radical  being  evolved  at 
the  zincoid,  and  sodium  at  the  chloroid.  But  the  sodium  having  a  strong  affinity 
for  oxygen  reacts  upon  the  water  at  the  pole,  forming  soda  and  liberating  hydrogen, 
which  therefore  appear  together ;  while  S04  having,  as  a  high  salt-radical,  a  power- 
ful affinity  for  hydrogen,  likewise  decomposes  water,  and  thus  evolves  oxygen,  which, 
with  a  free  acid,  appears  at  the  zincoid.  A  solution  of  chloride  of  sodium  is  decom- 
posed in  the  same  manner,  its  elements  chlorine  and  sodium  being  attracted  to  the 
zincoid  and  chloroid  respectively,  but  neither  of  these  elements  appearing  as  such. 
Both  decompose  water,  and  thus  produce  oxygen  with  hydrochloric  acid  at  the 
zincoid,  and  soda  with  hydrogen  at  the  chloroid.  It  has  indeed  been  ascertained 
that  the  polar  influence  which  apparently  effects  two  decompositions  in  these  circum- 
stances, namely,  that  of  water  into  oxygen  and  hydrogen,  and  of  a  salt  into  its  acid 
and  alkali,  is  no  more  in  quantity  than  is  necessary  to  decompose  one  of  these  bodies, 
the  circulating  power  being  measured  by  the  quantity  of  fused  chloride  of  lead 
decomposed  in  another  part  of  the  circuit  (Daniell).  There  can  be  little  doubt, 
then,  that  only  one  binary  compound  is  immediately  decomposed,  and  that  the  two 
sets  of  products  which  appear  at  the  terminals  are  the  results  of  secondary  decom- 
position. Indeed,  the  decomposition  of  salts  in  the  voltaic  circle  is  supposed  to 
afford  considerable  support  to  the  salt-radical  theory  of  these  bodies  (page  156.) 

Certain  salts  form  a  polar  chain,  or  conduct,  without  undergoing  decomposition, 
in  a  way  which  cannot  at  present  be  explained,  particularly  the  iodide  of  mercury 
and  fluoride  of  lead,  both  fused  by  heat.  According  to  recent  observations  of  M. 
Matteucci  many  other  fused  salts  conduct  to  a  greater  extent  than  is  indicated  by 
their  decomposition. 


TWO   POLAK   LIQUIDS. 


205 


Secondary  decompositions.  —  The  products  of  voltaic  action  are  frequently  of  the 
secondary  character  just  described,  the  original  products  being  lost  from  their  reac- 
tion upon  the  liquid  in  which  they  are  produced,  or  upon  the  substance  of  the 
metallic  terminals.  Thus,  salts  of  the  vegetable  acids  often  afford  carbonic  acid, 
and  salts  of  ammonia  nitrogen,  instead  of  oxygen,  at  the  positive  terminal  or  zincoid ; 
the  oxygen  liberated  having  reacted  upon  the  combustible  constituents  of  these 
bodies/  "Nitrates,  again,  may  afford  nitrogen,  or  nitric  oxide,  at  the  negative  termi- 
nal or  chloroid,  in  consequence  of  the  oxidation  of  the  hydrogen  evolved  there.  The 
nascent  condition  of  the  liberated  elements  favours  such  secondary  actions.  When 
the  zincoid  is  composed  of  a  positive  metal,  such  as  zinc  itself  or  copper,  the  chlorous 
element  is  absorbed  there,  combining  with  the  metal.  The  decomposition  of  a  salt 
is  also  then  much  easier,  the  action  of  the  circle  being  greatly  assisted  by  the  proper 
affinity  of  the  matter  of  the  zincoid  for  a  chlorous  body.  Indeed,  when  two  pieces 
of  the  same  metal  communicate  by  means  of  one  of  its  salts,  the  phenomena  are  the 
same  as  if  the  metallic  circuit  were  complete  (Faraday).  Insoluble  sulphides, 
chlorides,  and  other  compounds  of  a  positive  metal  acting  as  the  zincoid,  have  thus 
been  slowly  produced  in  a  single  circle  with  a  weak  exciting  fluid ;  which  products 
have  exhibited  distinct  crystalline  forms,  resembling  natural  minerals,  not  otherwise 
producible  by  art.  The  hydrogen  evolved  upon  a  platinum  chloroid,  immersed  in 
the  solution  of  a  copper  or  iron  salt,  may  also  reduce  these  metals  upon  the  surface 
of  the  platinum,  in  the  form  of  brilliant  octahedral  crystals.  In  the  active  cells 
themselves  a  secondary  decomposition  is  apt  to  occur,  the  hydrogen  evolved  decom- 
posing the  salt  of  zinc  which  accumulates  in  the  liquid,  and  occasioning  a  deposition 
of  that  metal  upon  the  copper  plate ;  an  occurrence  which  may  determine  an  oppo- 
site polarity,  and  cause  the  action  of  the  circle  to  decline.  But  on  disconnecting  the 
zinc  and  copper  plates,  the  foreign  deposit  upon  the  latter  is  quickly  dissolved  off  by 
the  acid.  The  inconvenience  of  this  secondary  decomposition  in  the  exciting  cells 
is  avoided  by  dividing  the  cell  into  two  compartments,  by  a  porous  plate  of  earthen- 
ware interposed  between  the  zinc  and  copper  plates.  The  salt  of  zinc  formed  about 
that  metal  is  prevented  from  diffusing  to  the  copper,  by  the  diaphragm,  although  it 
allows,  from  its  porosity,  a  continuity  of  liquid  polar  molecules  between  the  metals. 

Two  polar  liquids  separated  by  a  porous  diaphragm.  —  The  liquids  on  either 
side  of  the  porous  division  may  also  be  different,  provided  they  have  both  a  polar 
molecule.  Thus,  in  fig.  81,  the  polar  chain  is  composed  of  molecules  of  hydrochloric 
acid,  extending  from  the  zinc  to  the  porous  division  at  a;  and  of  molecules  of  chlo- 
ride of  copper,  from  a  to  the  copper  plate.  When  the  01  of  molecule  1  unites  with 
zinc,  the  H  of  that  molecule  unites  with  the  Cl  of  molecule  2  (as  indicated  by  the 
connecting  bracket  below),  the  H  of  molecule  2  with  the  Cl  of  molecule  3,  the  Cu 
of  molecule  3  with  the  Cl  of  molecule  4,  and  the  Cu  of  this  molecule,  being  the  last 

Fio.  81. 


Copper 


206  CHEMICAL   POLARITY. 

in  the  chain,  is  deposited  upon  the  copper,  plate.  Dilute  sulphuric  acid,  in  contait 
with  an  amalgamated  zinc  plate,  and  the  same  acid  fluid  saturated  with  sulphate  of 
copper,  in  contact  with  the  copper  plate,  are  a  combination  of  fluids  of  most  frequent 
application.  In  such  an  arrangement,  the  formation  of  small  gas  bubbles  upon  the 
negative  plate,  which  makes  its  contact  with  the  acid  fluid  imperfect,  is  avoided ;  and 
the  surface  of  that  plate  is  kept  clean  and  entirely  metallic  by  the  constant  deposi- 
tion of  fresh  copper  upon  it.  The  copper  is  deposited  in  a  coherent  state,  and  forms 
a  plate,  which  may  be  stripped  off  from  the  original  copper  after  attaining  any 
desired  degree  of  thickness,  —  and  presents  an  exact  impression  of  the  surface  of  the 
latter.  In  the  operation  of  electrotyping,  the  article  to  be  copied  is  so  placed  in  a 
copper  solution  as  the  negative  plate  of  a  voltaic  pair,  being  first  made  conducting,  if 
not  metallic  and  already  so,  by  rubbing  its  surface  over  with  fine  plumbago.  With 
a  negative  plate  of  platinum,  undiluted  nitric  acid  may  be  used  in  the  place  of  the 
acid  solution  of  copper  in  the  last  arrangement,  with  oil  of  vitriol,  diluted  with  four 
or  five  times  its  bulk  of  water,  about  a  positive  plate  of  amalgamated  zinc.  The 
polar  molecules  will  be,  on  the  binary  theory  of  salts,  N06  +  Hj  in  the  former,  and 
S04  +  H,  in  the  latter  fluid.  The  hydrogen  is  also  here  entirely  suppressed  at  the 
negative  plate,  uniting  with  the  fifth  equivalent  of  oxygen  in  nitric  acid  to  form 
water,  which  is  attended  with  the  evolution  of  peroxide  of  nitrogen,  N04.  The 
solution  of  the  zinc,  with  such  an  arrangement  of  fluids,  appears  to  give  the  most 
intense  polarization  that  can  be  attained. 

Application  of  the  voltaic  circle  to  chemical  synthesis.  —  The  liquid  in  the 
decomposition  cell  may  be  divided  by  a  porous  diaphragm  placed  between  the  plati- 
num plates,  which  form  the  zincoid  and  the  chloroid  in  a  similar  manner,  and  the 
synthetical  results  of  the  voltaic  action  be  had  more  readily  apart  from  each  other. 
With  a  solution  of  chlorate  of  potassa  between  the  plates,  it  is  found  that  the  oxy- 
gen, instead  of  being  evolved  at  the  positive  pole  as  gas,  is  communicated  to  the 
chlorate  of  potassa  there,  and  converts  it  into  perchlorate  (Berzelius).  In  a  solution 
of  chloride  of  potassium,  even  when  rendered  acid  by  sulphuric  acid,  chlorate,  and 
afterwards  perchlorate  of  potassa  were  found  at  the  positive  pole  (Kolbe).  A  con- 
centrated solution  of  chloride  of  ammonium  evolves  hydrogen  at  the  negative  pole ; 
but  neither  oxygen  nor  chlorine  at  the  positive  pole.  But  the  surface  of  the  plati- 
num plate  representing  the  latter  pole  is  covered  with  small,  yellow,  oily  drops  of 
chloride  of  nitrogen,  which,  as  soon  as  the  two  poles  are  brought  into  contact, 
decompose  with  explosion  (Kolbe).  A  solution  of  the  yellow  prussiate  of  potassa 
is  converted  into  the  red  prussiate  by  the  action  of  the  oxygen  at  the  positive  pole 
(Smee).  Dr.  Kolbe  oxidized  the  cyanide  of  potassium  in  the  same  manner,  and 
converted  it  into  cyanate  of  potassa,  but  did  not  succeed  in  obtaining  a  percyanate  : 
nor  did  he  succeed  in  forming  a  fluorate  of  potassa  from  the  fluoride  of  potassium  by 
the  same  means  (Mem.  of  the  Chem.  Soc.,  vol.  iii.  p.  287).  The  decomposition  of 
a  concentrated  neutral  solution  of  valerianate  of  potassa  in  the  cold  gave  a  gaseous 
carbo-hydrogen,  C8H8,  of  double  the  density  of  olefiant  gas,  and  what  appeared  to 
be  a  new  ether,  containing  C2H2  less  than  amylic  ether.  Such  transformations  from 
the  series  of  one  alcohol  to  that  of  another  are  of  great  importance,  and  the  attaining 
them  by  voltaic  action  highly  interesting.  Six  pairs  of  Bunsen's  carbo-zinc  battery 
were  employed  in  these  decompositions,  and  the  action  continued  for  several  days 
(Kolbe,  Memoirs  of  the  Chemical  Society,  vol.  iii.  p.  378). 

Transference  of  the  ions.  —  With  a  double  diaphragm  cell,  in  which  the  liquid 
between  the  poles  was  divided  into  three  portions,  Messrs.  Daniell  and  Miller  were 
enabled  to  make  some  singular  observations  on  the  transfer  of  the  ions  and  their 
accumulation  at  the  poles.  With  a  neutral  salt  of  the  potassium  family  (such  as 
sulphate  of  soda),  for  one  equivalent  of  salt  decomposed,  half  an  equivalent  of  free 
acid  is  added  to  the  division  of  the  cell  containing  the  positive  pole,  and  half  an 
equivalent  of  free  alkali  to  the  division  containing  the  negative  pole  —  the  amount 
of  transference  which  the  polar  decomposition  requires  :  but,  with  a  salt  of  the  mag- 
nesian  family  (such  as  sulphate  of  zinc),  while  the  acid  travels  as  usual  to  the  posi- 


VOLTAIC   ENDOSMOSE.  207 

tive  pole  and  accumulates  there,  no  corresponding  transference  of  oxide  of  zinc 
takes  place  in  the  opposite  direction.  This  seems  to  imply  that  water  travels,  as 
base,  instead  of  oxide  of  zinc.  All  the  magnesian  salts  retain  one  equivalent  of 
water  very  strongly  j  and,  in  the  polar  chain,  probably  assume  this  water  as  their 
base,  so  as  to  become  equivalent  to  hydrated  acids  in  solution.  In  the  decomposi- 
tion of  salts  of  oxide  of  ammonium,  the  ammonia  also  appears  passive,  and  does  not 
move  towards  the  negative  pole,  although  the  acid  of  the  salt  travels  as  usual 
towards  the  positive  pole.  The  water,  which  is  essential  to  the  salts  of  oxide  of 
ammonium,  appears  to  be  here  again,  the  base  which  travels ;  and  in  a  polar  chain 
extending  through  a  salt  of  ammonia,  such  as  the  sulphate  of  ammonia,  we  have 
probably  sulphate  of  water  as  the  polar  molecule ;  the  ions  being  S04  and  H ;  cot 
S04  and  NH^1 

Voltaic  endosmose.  —  It  was  first  observed  by  Mr.  Porrett,  that  in  the  decompo- 
sition cell,  divided  into  two  chambers  by  a  permeable  diaphragm  of  wet  bladder  or 
porous  earthenware,  the  liquid  tends  to  pass  from  the  chamber  containing  the  positive 
terminal  plate  into  that  containing  the  negative  terminal,  so  as  to  rise  at  times  seve- 
ral inches  in  the  latter  above  its  level  in  the  former  (Annals  of  Philosophy,  1816). 
This  accumulation  of  liquid  at  the  negative  pole  is  only  considerable  with  liquids 
of  an  inferior  conducting  power,  that  is,  of  difficult  decomposition,  and  is  greatest  in 
pure  water. 

The  transfer  takes  place  of  a  large  quantity  of  water  with  the  hydrogen  of  the 
negative  pole,  as  if  the  ions  were  0  on  the  one  side,  and  H  +  Water  on  the  other. 
In  a  polar  molecule,  such  as  this  implies,  we  must  have  an  aggregation  of  many 
atoms  of  water  forming  one  compound  polar  atom.  Let  us  suppose  six  atoms  of 
water  associated  H606 ;  the  polar  molecule  will  be  H605  +  0,  in  which  H605  is  the 
basyl,  and  0  the  salt-radical.  Taking  advantage  of  the  graphical  representation  of 
such  a  compound  molecule  by  a  polar  formula  (page  168),  in  which  the  letters 
exhibit  the  relative  position  of  the  constituent  atoms,  we  have  — 


Positive  Pole. 


123456 
000000 

H  H  H  H  H  H 


Negative  Pole. 


The  oxygen  1  is  alone  attracted  by  the  positive  metal  or  pole  with  which  it  is  in 
contact,  while  hydrogen  (1)  being  so  far  relieved  from  the  attraction  of  its  own 
oxygen,  comes  under  the  influence  of  oxygen  2,  3,  4,  5,  and  6.  As  the  salt-radical 
0  (1)  separates,  we  have  thus  the  temporary  formation  of  the  basylous  atom  — 

0   0   0   0   0  ?  or  05. 
H  H  H  H  H  H'       H6 

But  instead  of  involving  six  atoms  of  water,  as  in  this  illustration,  the  compound 
polar  molecule  may  embrace  hundreds  or  thousands.  It  will  always  be  represented 
by  HnOn_j  -f-  0  j  HnOn_,  being  the  basylous  atom  which  is  transferred  to  the  nega- 
tive pole,  and  0  the  salt-radical  atom  which  is  transferred  to  the  positive  pole.  It 
appears  to  be  by  a  polarization  of  this  sort  that,  in  bad  conductors,  mass  compensates 
for  conducting  power;  as  in  the  return  current  of  the  electric  telegraph  through  the 
earth,  where  the  resistance  is  found  to  be  even  less  than  in  the  metallic  wires ; 
indeed,  quite  inappreciable. 

It  is  found  by  Mr.  J.  Napier  that  the  passage  of  a  salt  without  decomposition, 
such  as  sulphate  of  copper,  from  the  positive  to  the  negative  division  of  the  decom- 
position cell,  may  take  place  independently  of  the  water  in  which  it  is  dissolved,  and 
to  a  greater  proportional  amount  (Mem.  Chem.  Soc.  ii.  28).  This  unequal  move- 
ment of  the  salt  and  water  proves  that  the  phenomenon  is  not  simply  a  flowing  of 

1  Professors  Daniell  and  Miller,  "  On  the  Electrolysis  of  Secondary  Compounds,"  in  the 
Philosophical  Transactions,  1844. 


208  CHEMICAL   POLARITY. 

the  liquid  towards  the  negative  pole ;  and  it  allows  us  to  suppose  that  an  aggregate 
polar  molecule  may  be  formed  of  many  atoms  of  a  salt,  as  well  as  of  water.  It  is 
only  in  dilute  saline  solutions  that  the  voltaic  endosmose  is  perceptible. 

VOLTAIC    CIRCLES    WITHOUT   A   POSITIVE  METAL. 

If  we  dip  together  into  an  acid  fluid  two  platinum  plates,  one  clean,  and  the  other 
coated  with  a  film  of  zinc  or  highly  positive  metal,  we  have  the  speedy  solution  of 
the  positive  inetal  by  the  usual  polar  decomposition,  and  hydrogen  transferred  to  the 
opposite  platinum  plate.  It  appears  that  hydrogen,  sulphur,  phosphorus,  and  various 
other  oxidable  substances,  will  originate  a  polar  decomposition  in  water  or  a  saline 
fluid,  when  associated  with  platinum,  in  the  same  manner  as  the  zinc  is  in  the  last 
experiment;  and  circles  may  thus  be  formed  without  a  positive  metal.  The  non- 
metallic  but  oxidable  elements  enumerated  cannot  be  substituted  m  mass  for  zinc  or 
the  positive  metal,  because  they  are  non-conductors ;  but  in  the  thinnest  films  they 
are  not  so,  if  we  may  judge  from  experiments  of  this  kind,  and  become  quite  equi- 
valent to  metals.  Farther,  with  chlorine  or  any  other  strongly  halogenous  element 
dissolved  in  water,  and  placed  in  contact  with  one  of  the  platinum  plates,  while  the 
other  is  clean,  we  may  have  a  polarization  originating  with  the  chlorine,  and  causing 
the  transfer  of  the  oxygen  or  salt-radical  of  the  interposed  water,  or  saline  fluid,  to 
the  clean  platinum.  Nothing  like  this  is  witnessed  in  the  voltaic  combination  of 
two  metals ;  it  is  equivalent  to  an  action  in  which  the  copper  or  negative  metal 
originated  the  polarization  by  its  aflinity  for  the  hydrogen  or  basylous  constituent  of 
the  polar  liquid. 

1.  With  hydrogen  gas  dissolved  in  the  acid  fluid  of  one  chamber  of  the  divided 
cell,  and  air  or  oxygen  in  the  other,  polarization  occurs  on  uniting  the  platinum 
plates,  attended  with  the  oxidation  of  the  hydrogen  and  disappearance  of  both  gases 
(Schonbein).  Viewing  this  arrangement  as  a  simple  circle,  consisting  of  a  liquid 
and  metallic  segment  (page  194),  we  have  to  consider  particularly  the  composition 
flf  the  terminal  polar  molecules  at  either  end  of  the  metallic  segment  —  platinum 
with  hydrogen  must  form  the  one  at  the  positive  pole,  and  platinum  with  oxygen 
the  other  at  the  negative  pole :  — 

(1)  Pt  H  0  Pt 

h  acid  }- 

These  are  equivalent  to  the  external  molecules  of  the  two  metals,  zinc  and  copper, 
in  the  usual  voltaic  arrangement,  which  are  composed  in  that  case  of  two  atoms  of 
zinc  on  the  one  side,  and  two  atoms  of  copper  on  the  other  (fig.  70,  page  194) :  — 

(2)  Zn  Zn  Cu  Cn 

—    -f-  acid  —    + 

The  peculiar  superiority  of  platinum,  as  the  single  metal,  in  arrangements  of  the 
present  class,  depends  upon  its  strictly  intermediate  character  between  basyls  and 
halogens,  so  that  it  lends  itself  to  form  a  polar  binary  molecule  equally  with  hydro- 
gen or  oxygen  in  (1),  —  with  both  basyl  and  salt-radical. 

The  intermediate  liquid  (the  acid)  must  be  a  binary  compound  as  usual.  Here 
the  positive  hydrogen  combines  with  the  salt-radical  of  that  binary  compound,  and 
sends  its  hydrogen  or  basyl  to  the  second  or  opposite  plate ;  while  the  oxygen  at 
that  plate  decomposes  the  binary  liquid  also,  sending  back  oxygen  or  salt-radical  to 
the  hydrogen  of  the  first  plate.  There  are,  therefore,  two  concurring  polarizations 
in  every  polar  chain,  tending  to  bring  about  simultaneously  the  same  combinations 
and  decompositions  throughout  the  circle  :  hydrogen  enters  into  combination  on  the 
one  side,  and  oxygen  on  the  other,  in  one  and  the  same  polar  chain.  The  union 
of  concurring  primary  zincous  and  chlorous  polarizations,  exhibited  in  such  an 
arrangement,  offers  a  new  means  of  increasing  polar  intensity,  entirely  different  from 
the  multiplication  of  couples  in  the  compound  circle,  of  which  the  application  will 


GAS-BATTERY. 


209 


be  fully  observed  afterwards  in  the  nitric  acid  battery  of  Mr.  Grove.  The  tempo- 
rary combination  of  hydrogen  with  copper,  the  former  as  the  basylous  and  the  latter 
as  the  halogenous  element  of  one  polar  molecule,  which  it  is  necessary  to  assume  in 
explaining  the  circular  polarity  of  the  ordinary  voltaic  circle  (page  194),  is  quite  in 
accordance  with  the  relation  of  hydrogen  to  platinum  in  the  present  circles. 

2.  A  circle  of  still  higher  power  is  formed  with  chlorine  gas,  dissolved  in  the 
negative  chamber,  against  hydrogen  in  the  positive  chamber  of  the  divided  cell. 
Here  the  terminal  polar  molecules  of  the  metallic  segment  are  :  — 

(3)  Pt  H  ..........................................  Cl  Pt 


FIG.  82. 


3.  Inflammation  of  mixed  hydrogen  and  oxygen  by  platinum.  —  There  is  every 
reason  to  believe  that  the  remarkable  action  of  clean  platinum,  both  in  the  form  of 
a  plate  and  of  platinum  sponge,  in  disposing  a  mixture  of  oxygen  and  hydrogen  in 
the  gaseous  state  to  unite,  is  the  same  in  nature  as  its  action  upon  these  elements 
liquefied  and  in  solution  in  water.    In  the  former,  as  in  the  latter  case,  a  polar  chain 
must  arrange  itself  in  the  platinum  mass,  of  which  one  terminal  molecule  is  platinide 
of  hydrogen,  and  the  other  oxide  of  platinum  (3).     A  less  certain  point  is,  whether 
the  chain  is  completed  by  the  interposition  of  a  binary  molecule  of  water  already 
formed,  between  the  polar  H  and  0  ;  or  these  atoms  come  immediately  into  contact, 
and  close  the  circle,  without  the  intervention  of  any  compound  polar  molecule. 

4.  Gas-battery.  —  The  gas-battery  of  Mr.  Grove  belongs  to  this  class  of  voltaic 
arrangements.     It  is  essentially  an  apparatus  in  which  a  supply  of  both  negative 
and  positive  gas  is  kept  over  the  liquid  at  each  plate,  to  supply  loss  by  absorption. 
A  simple  circle  consists  of  a  bottle  (fig.  82),  containing  a  dilute  acid,  with  two  tubes 
filled  with  oxygen  and  hydrogen  respectively,  and  placed  in  two  openings  in  the 
bottle.     The  platinum  plates  contained  in  these  tubes 

are  made  rough  by  adhering  reduced  spongy  platinum, 
which  enables  them  also  to  retain  the  better  on  their 
surface  a  portion  of  the  acid  fluid  into  which  they  dip. 
The  two  plates  are  connected  by  a  wire  above  the  tubes, 
which  is  represented  in  the  figure  .as  carried  round  a 
magnetic  needle,  to  obtain  evidence  of  polarization  in 
the  wire.  Here,  as  in  (2),  the  gases  only  act  when  in 
contact  with  the  platinum  surface  and  taking  a  part  in 
the  terminal  polar  molecule,  and  also  when  covered  by 
liquid,  which  is  necessary  to  complete  the  polar  chain 
between  the  terminal  polar  molecules  on  each  side.  The 
-gases  in  the  tubes  are  supplementary,  and  do  not  take  a 
part  in  the  polar  chain.  The  modifications  of  this  bat- 
tery, where,  instead  of  hydrogen  gas,  sulphur  or  phos- 
phorus, vaporized  in  nitrogen  gas,  or  a  gaseous  hydro- 
carbon,  is  placed  at  the  positive  pole,  are  of  the  same 
character,  and  only  act  by  supplying  a  film  of  an  oxida- 
ble  body,  such  as  sulphur,  or  phosphorus,  to  the  surface 
of  the  platinum,  capable  of  forming  the  positive  element 
of  a  polar  molecule  with  that  metal.  This,  again,  must 
be  covered  by  the  binary  acid  fluid,  in  order  to  commu- 
nicate by  a  polar  chain  with  the  oxygen  of  the  terminal 
molecule  of  platinum  and  oxygen  in  the  negative 
chamber  of  the  divided  cell.  (Grove,  on  the  Gas 
Yoltaic  Battery  :  Philosophical  Transactions,  1843  and 
1845). 

5.  Closely  resembling  these  circles  is  that  in  which  one  of  the  platinum  plates  is 
covered  by  a  film  of  peroxide  of  lead  or  peroxide  of  manganese.     The  platinum 
plate  may  be  so  prepared  by  making  it  the  negative  terminal  for  a  short  time  in  a 

14 


210  CHEMICAL   POLARITY. 

solution  of  acetate  of  lead  or  of  protosulphate  of  manganese.  In  an  acid  fluid, 
which  is  capable  of  dissolving  the  protoxide  of  lead  or  manganese,  polarization 
occurs,  the  excess  of  oxygen  of  the  attached  peroxide  forming  with  platinum  a  polar 
molecule,  in  which  the  oxygen  is  the  chlorous  element.  This  decomposes  the  saline 
molecule  of  the  acid,  or  water,  causing  the  transference  of  the  salt-radical  or  oxygen 
to  the  clean  platinum  plate,  where  it  may  be  evolved  as  gas.  This  most  nearly  re- 
sembles the  case  with  chlorine  —  water  at  one  platinum  plate,  which  causes  the 
evolution  of  oxygen  at  the  other  platinum  plate ;  the  only  source  of  polarizing  power 
in  the  circle  being  a  chlorous  affinity. 

6.  By  much  the  most  powerful  voltaic  arrangement  of  this  class  is  that  in  which 
one  chamber  of  the  divided  cell  is  charged  with  a  solution  of  sulphide  of  potassium, 
and  the  other  chamber  with  strong  nitric  acid.1  Here  we  have  two  concurring 
sources  of  polarization  in  one  polar  chain,  namely,  the  affinity  of  sulphur  for  oxygen, 
tending  to  transmit  hydrogen  in  one  direction,  and  the  easy  decomposition  of  nitric 
acid  into  N  04  and  0,  supplying  oxygen  to  the  surface  of  the  platinum,  which  sends 
a  chlorous  element  in  the  opposite  direction.  The  terminal  polar  molecules  of  the 
metallic  segment  of  the  circle  are  — 

(4)  Pt  S  0  Pt 

—  +  —  + 

With  a  single  pair  of  plates  so  charged,  water  may  be  decomposed.  The  action 
is  equally  powerful  with  chlorine  substituted  for  the  nitric  acid.  Such  combinations 
of  fluids  may  be  greatly  varied  :  all  that  is  necessary  is  an  oxidable  substance  at  one 
plate,  and  an  oxidizing  substance  at  the  other.  In  the  first  class  are  protosalts  of 
iron,  tin  and  manganese,  sulphides,  sulphites,  hyposulphites;  in  the  second,  chlo- 
rine, nitric,  chromic  and  manganic  acids,  and  persalts  of  iron  and  tin.  Taking  pro- 
toxide of  iron  against  peroxide  as  an  example  of  these  cases,  the  terminal  molecules 
of  the  metallic  segment  may  be  represented  as  — 

(5)  Pt  Fe  0  Pt 

— .+  —  + 

It  is  true  we  have  no  evidence  of  the  actual  separation  of  the  iron  or  of  the 
oxygen  upon  the  platinum  surface  j  still  there  is  reason  to  believe  such  a  polarity  to 
be  established,  assisted  by  secondary  affinities ;  the  oxygen  of  the  protoxide  of  iron 
passing  over  to  an  adjoining  double  molecule  of  protoxide,  and  converting  it  into 
peroxide,  to  allow  the  metal  to  join  in  a  polar  molecule  with  the  platinum.  At  the 
same  time,  the  peroxide  of  iron  at  the  negative  plate  may  become  protoxide,  while 
its  oxygen  is  engaged  in  forming  a  polar  molecule  with  the  platinum.  But  the  in- 
tensity of  polarization  with  the  salts  of  iron  against  each  other  is  feeble  compared 
with  that  of  chlorine  or  nitric  acid  against  an  alkaline  sulphide.  In  all  these  cases 
the  polar  circle  must  be  completed  by  a  saline  compound  in  the  liquid  or  liquids, 
which  may  serve  as  the  means  of  connecting  the  terminal  molecules  described  of 
the  platinum  plates,  and  by  metallic  polar  molecules  through  the  wire  connecting 
the  platinum  plates. 

It  was  supposed  by  M.  Becquerel  that  a  circle  of  the  present  description  may  be 
formed  in  which  the  affinities  are  those  of  an  acid  for  an  alkali :  the  acid  and  alka- 
line solutions  being  separated  by  porous  baked  clay,  which  leaves  them  in  free  liquid 
contact,  although  their  actual  mixture  proceeds  with  extreme  slowness.  Sulphuric 
acid  and  potassa,  however,  are  generally  admitted  to  be  nearly  or  altogether  incapable 
of  producing  this  effect,  while  acids  which  part  readily  with  oxygen,  such  as  iodic, 
chloric,  chromic,  or  nitric  acid,  with  an  alkali,  produce  a  powerful  effect.  The 
polarization  may  be  referred  to  the  oxygen  of  the  acids,  in  these  last  cases,  at  the 
negative  terminal,  and  is  a  chlorous  affinity.  It  may  possibly  be  often  assisted  by 

1  Mr.  A.  R.  Arnott,  on.  "Some  New  Cases  of  Voltaic  Action;"  Memoirs  of  the  Chem. 
Soc.  i.  142. 


THEORETICAL    CON SIDER ATIONS.  211 

minute  quantities  of  ammonia,  organic  or  other  oxidizable  matter,  at  the  positive 
terminal  in  the  alkaline  solution.     (Becquerel,  Elements  cTElectro-Chimie,  1843). 

Theoretical  considerations.  —  The  focility  with  which  circular  decompositions 
take  place,  and  the  necessity  of  their  occurrence  in  the  action  of  binary  compounds, 
which  was  explained  under  the  atomic  exhibition  of  a  double  decomposition  at  page 
189,  are  undoubtedly  the  key  to  the  great  stimulus  to  chemical  activity,  which  the 
voltaic  arrangement  affords.  Reverting  to  the  original  illustration  of  the  action  of 
hydrochloric  acid  upon  zinc,  it  may  be  observed  that  zinc  has  a  strong  attraction  for 
chlorine,  and  would  combine  at  once  with  that  element  if  the  latter  were  free,  with- 
out foreign  aid  of  any  kind.  But  with  the  chlorine  of  hydrochloric  acid  the  case  is 
different.  That  chlorine  is  already  combined  and  strongly  retained  by  its  own 
hydrogen  :  to  enable  the  chlorine  to  enter  into  a  new  combination  we  must  relieve 
it  from  this  attraction,  by  engaging  otherwise  the  affinity  of  the  hydrogen.  The 
contrivance  of  the  voltaic  circle  is  to  present  another  halogen  to  the  hydrogen,  and 
thus  divert  its  affinity  from  the  chlorine — the  latter  being  thereby  left  free  to  com- 
bine with  the  zine.  This  requires  a  train  of  similar  decompositions  passing  round  a 
circle  to  the  zinc,  illustrated  in  diagram  70  of  page  194;  and  which  ends  in  re- 
lieving the  external  combining  atom  of  zinc  from  the  attraction  of  even  the  conti- 
guous atom  of  the  same  kind ;  thus  dissolving  the  attraction  of  aggregation  in  the 
metal,  and  resigning  the  external  atom  of  zinc  entirely  to  the  attraction  of  the 
equally  relieved  chlorine.  It  is  entirely,  therefore,  because  the  agent  applied  to  the 
zinc  is  a  binary  compound,  and  not  a  free  element,  that  this  circular  mode  of  action 
is  necessary. 

It  is  to  be  remarked  in  explanation  of  the  facility  with  which  the  mutual  combi- 
nations and  decompositions  in  a  circular  chain  occur,  that  they  do  not  necessarily 
consume  any  power  or  occasion  waste  of  force.  They  may  be  compared  to  the 
movement  of  a  nicely  balanced  beam  on  its  pivot,  or  the  oscillation  of  a  pendulum, 
in  which  the  motion  is  equal  in  two  opposite  directions,  and  requires  only  the  mini- 
mum of  effort  to  produce  it. 

Farther,  it  is  not  to  be  supposed  that  zinc  dissolves  by  a  circular  action  of  affinity, 
only  when  a  negative  metal  is  attached  to  it,  and  a  voltaic  circle  purposely  con- 
structed. For  this  positive  metal  never  appears  to  dissolve  in  hydrochloric  acid  in 
any  other  manner ;  the  formation  of  little  polar  circles  in  the  fluid,  starting  from  one 
point  of  the  metallic  mass  and  returning  upon  another,  being  always  required  for  its 
solution  (page  195).  In  the  solution  of  zinc,  therefore,  by  a  binary  saline  body, 
such  as  hydrochloric  acid,  the  circular  or  voltaic  polarization  is  the  necessary,  as  well 
as  the  most  effective  mode  of  action  of  chemical  affinity. 

The  molecular  condition  of  conductors,  such  as  carbon  and  the  metals,  in  a  voltaic 
circle,  appears  to  be  that  of  polymeric  combination.  Their  atoms  must  be  feebly 
basylous  and  chlorous  to  each  other ;  the  distinction  possibly  depending  upon  ine- 
quality in  their  proportions  of  combined  heat,  and  maintain  the  relation  of  combina- 
tion. Again,  many  of  these  binary  molecules  are  associated  together  like  the  many 
similar  atoms  of  carbon,  or  of  hydrogen,  which  we  find  associated  in  the  polymeric 
hydrocarbons.  The  whole  must  be  held  together  by  their  chemical  affinities,  and 
the  aggregation  of  the  mass  be  the  final  resultant  of  the  same  attractions.  The 
determination  of  the  polar  condition  in  two  metals,  by  the  mere  application  of  heat 
or  cold  to  their  junction,  requires  the  assumption  of  the  sali-molecular  structure  of 
metals;  and- the  other  proposition,  that  affinity  passes  into  aggregation,  is  equally 
necessary  to  account  for  the  polar  (or  electrical)  effects  which  are  produced  by  fric- 
tion or  abrasion,  as  they  appear  to  extend  to  the  division  of  chemical  molecules. 

The  cumulative  nature  of  chemical  combination  is  well  illustrated  in  such  com- 
pounds as  the  acid  hydrates  —  in  dilute  sulphuric  acid,  for  instance,  where  we  find 
an  atom  of  acid  uniting  with  more  and  more  atoms  of  water,  with  a  decreasing 
affinity,  but  without  any  assignable  limit  to  their  number.  It  is  worthy  of  remark 
that  the  acids  are  bodies  with  chlorous  or  negative  atoms,  and  their  peculiar  affinity 


212  CHEMICAL   POLARITY. 

in  excess.     The  polar  formula  for  sulphuric  acid  (page  168)  is  — 3;  or  three  nega- 

S 
tive  to  one  positive  atom.     By  the  apposition  of  a  single  binary  molecule  of  water, 

sulphate  of  water  is  produced,  — - — ,  in  which  the  excessive  proportion  of  chlorous 

S  H 

atoms  and  affinity  in  the  compound  is  in  some  degree  diminished,  the  formula  of  the 
latter  presenting  four  negative  to  two  positive  atoms.  The  apposition  of  more  and 
more  molecules  of  water  is  determined  by  this  excess  of  chlorous  affinity,  which  it 
tends  to  neutralize;  the  constant  difference,  or  excess  of  two  chlorous  over  the 
number  of  basylous  atoms,  becoming  proportionally  less  with  large  numbers  of  added 
molecules  of  water.  All  the  magnesian  bases  appear  to  assume  water  to  assist  in 
neutralizing  their  acid  in  the  same  manner,  and  retain  one  equivalent  of  this  water 
in  general  very  strongly.  In  the  formation  of  a  polar  chain  through  a  solution  of  a 
sulphate  of  this  class,  we  have  had  reason  to  suppose  that  the  sulphuric  acid  applies 
itself,  for  the  time,  to  the  water  rather  than  the  metallic  oxide  as  its  base  (page  206). 
The  phenomena  of  voltaic  endosmose  were  also  found  to  favour  the  idea  of  the 
polarization  of  highly  aggregated  molecules,  in  which  the  binary  molecule  was  repre- 
sented by  a  single  atom  of  chlorine  or  salt-radical,  against  a  single  atom  of  hydrogen 
or  metal  associated  with  a  large'number  of  atoms  of  water,  which  constituted  together 
the  basylous  atom.  The  application  of  polar  formulae  to  the  explanation  of  voltaic 
decompositions  of  all  kinds  would,  I  believe,  more  correctly  express  the  molecular 
changes  that  occur,  than  the  usual  assumption  of  the  binary  division  of  the  com- 
pound body,  in  an  absolute  manner,  into  a  basylous  atom  and  a  fictitious  group 
forming  a  halogen  body. 

GENERAL    SUMMARY. 

1.  In  a  closed  voltaic  circle,  a  certain  number  of  lines  or  chains  of  polarized  mole- 
cules is  established,  each  chain  being  continuous  round  the  circle.  Hence  the  polar 
condition  of  the  circle  must  be  every  where  the  same.  The  same  number  of  par- 
ticles of  exciting  fluid  are  simultaneously  polar  upon  the  surface  of  every  zinc  plate 
in  the  active  cells,  and  also  upon  the  surface  of  the  zincoid  in  the  cell  of  decomposi- 
tion, and  the  consequent  chemical  change,  or  decomposition  occurring,  is  of  the  same 
amount  in  all  the  cells  in  the  same  time.  This  equality  in  condition  and  restilts  is 
essential  to  a  circular  polarization,  such  as  exists  in  the  voltaic  circle. 

The  number  of  polar  chains  that  can  be  established  at  the  same  time  in  a  parti- 
cular voltaic  arrangement,  is  obviously  affected  by  several  circumstances  :  — 

(1)  By  the  size  of  the  zinc  plate :  the  number  of  particles  of  zinc  that  may  be 
simultaneously  acted  upon  by  the  exciting  fluid  being  directly  proportional  to  the 
extent  of  metallic  surface  exposed. 

(2)  By  the  nature  and  accidental  state  of  the  exciting  liquid,  some  electrolytes 
being  more  easily  acted  on  by  the  positive  metal  than  others ;  while  the  state  of 
dilution,  temperature,  and  other  circumstances,  may  affect  the  facility  of  decomposi- 
tion of  any  particular  electrolyte. 

(3)  The  adhesion  of  the  gas  bubbles  of  hydrogen  to  the  copper  plate,  at  which 
they  are  evolved,  interferes  much  with  the  action  of  a  battery ;  partly  by  reducing 
the  surface  of  copper  in  contact  with  acid,  and  partly  by  acting  as  a  zincous  ele- 
ment, and  originating  an  opposite  polarization  in  the  battery  (page  209).    By  taking 
up  the  hydrogen,  by  means  of  a  solution  of  sulphate  of  copper  in  contact  with  ths 
copper  plate,  Mr.  Daniell  increased  the  amount  of.  circulating  force  six  times. 

(4)  The  chemical  action  in  a  cell  is  also  diminished  by  increasing  the  distance 
from  each  other  in  the  exciting  fluid  of  the  positive  and  negative  metals. 

(5)  The  lines  of  chemico-polar  molecules  in  the  exciting  fluid  should  be  repulsive 
of  each  other,  like  lines  of  magneto-polar  elements,  as  illustrated  in  the  mutual 
repulsion  and  divergence  of  the  threads  of  steel  filings  which  attach  themselves  to 


GENERAL   SUMMARY.  213 

the  pole  of  a  magnet  (fig.  65,  page  189).  That  the  lines  of  induction  do  diverge 
greatly  in  the  acid,  starting  from  the  zinc  as  a  centre,  is  placed  beyond  doubt  by 
many 'experiments  of  Mr.  Darnell,  A  small  ball  of  zinc  suspended  in  a  hollow 
copper  globe  filled  with  acid,  is  the  arrangement  in  which  this  divergence  is  least 
restrained,  and  was  found  to  be  the  most  effective  form  of  the  voltaic  circle.  When 
the  copper,  too,  is  a  flat  plate,  and  wholly  immersed  in  the  acid,  the  back  is  found 
to  act  as  a  negative  surface,  as  well  as  the  face  directly  exposed  to  the  zinc,  showing 
that  the  lines  of  induction  in  the  acid  expand,  and  open  out  from  each  other,  some 
bonding  round  the  edge  of  the  copper  plate  and  terminating  their  action,  after  a 
second  flexure,  on  its  opposite  side.  To  collect  these  diverging  lines,  the  surface  of 
the  copper  may  be  increased  with  advantage  to  at  least  four  times  that  of  the  zinc. 

(6)  The  polar  chains  of  molecules,  in  the  connecting  wires  and  other  metallic 
portions  of  the  circle  must  be  equally  repulsive  of  each  other.  Hence  the  small 
size  of  the  negative  plates  in  the  active  cells,  and  of  the  platinum  plates  in  the  cell 
of  decomposition,  and  the  thinness  of  the  connecting  wires,  are  among  the  circum- 
stances which  diminish  the  number  of  polar  chains  that  can  be  established,  and 
impair  the  general  efficiency  of  a  battery. 

2.  The  effect  of  multiplying  the  active  cells  in  a  battery  is  not  to  increase  the 
number  of  polar  chains,  or  quantity  of  decomposition,  but  to  increase  the  intensity 
of  the  induction  in  each  chain ;  although  this  increase  in  intensity  generally  aug- 
ments the  quantity  also,  in  an  indirect  manner,  by  overcoming  more  or  less  com- 
pletely such  obstacles  to  induction  as  have  been  enumerated. ' 

3.  The  intensity  of  the  induction,  also,  is  much  greater  with  some  electrolytes 
than  others.     Thus  a  single  pair  of  zinc  and  platinum  plates  excited  by  dilute  sul- 
phuric acid,  decomposes  iodide  of  potassium,  proto-chloride  of  tin,  and  fused  chloride 
of  silver,  but  not  fused  nitre,  chloride  or  iodide  of  lead,  or  solution  of  sulphate  of 
soda.     With  the  addition,  however,  of  a  little  nitric  acid  to  the  sulphuric,  the  same 
single  circle  decomposes  all  these  bodies,  and  even  water  itself.     Here  we  have  a 
primary  chlorous  induction  from  the  oxygen  of  the  nitrous  acid,  in  addition  to  the 
basylous  induction  of  the  zinc  (page  208).     The  former  action  also  is  attended 
by  the  suppression  of  the  hydrogen,  so  that  the  evolution  of  that  gas  upon  the 
negative  plate  is  avoided. 

4.  The  division  of  the  connecting  wire,  and  the  separation  of  its  extremities  to 
the  most  minute  distance  from  each  other,  is  sufficient  to  stop  all  induction  and  the 
propagation  of  the  polar  condition  in  an  arrangement  with  the  usual  good  conducting 
fluids.     In  a  powerful  voltaic  battery  consisting  of  seventy  large  Daniell  cells,  no 
induction  was  observed  to  pass  when  the  terminal  wires  were  separated  not  more 
than  the  one-thousandth  of  an  inch,  even  with  the  flame  of  a  spirit-lamp  or  rarefied 
air  between  them.     Absolute  contact  of  the  wires  was  necessary  to  establish  the  cir- 
culation.    But  after  contact  was  made,  and  the  wires  were  heated  to  whiteness,  they 
might  be  separated  to  a  small  distance  without  the  induction  being  interrupted  :  the 
space  between  them  was  then  filled  with  an  arch  of  dazzling  light,  containing 
detached  particles  of  the  wire  in  a  state  of  intense  ignition,  which  were  found  to 
proceed  from  the  zincoid  to  the  chloroid,  —  the  former  losing  matter,  and  the  other 
acquiring  it.     So  highly  fixed  a  substance  as  platinum  is  carried  from  the  one 
terminal  to  the  other  in  this  manner;    but  the  transference  of  matter  is  most 
remarkable  between  charcoal  points,  which  may  be  separated  to  the  greatest  distance, 
and  afford  the  largest  and  most  brilliant  arch  of  flame.     A  similar,  although  it  may 
be  an  excessively  minute  detachment  of  matter,  is  found  to  accompany  the  electric 
spark  in  all  circumstances.     Hence,  the  electric  spark  always  contains  matter.     In 
a  powerful  water  battery,  however,  of  a  thousand  couples,  where  the  conducting  power 
of  the  liquid  is  low,  good  sparks  are  obtained  on  approaching  the  terminals  (Gassiot). 

5.  When  terminal  wires  of  a  voltaic  circle  are  grasped  in  the  hands,  the  circuit 
may  be  completed  by  the  fluids  of  the  body,  provided  the  battery  contains  a  consi- 
derable number  of  cells,  and  the  induction  is  of  high  intensity :  the  nervous  system 
is  then  affected,  the  sensation  of  the  electric  shock  being  experienced. 


214  CHEMICAL   POLARITY. 

6.  The  conducting  wire  becomes  heated  precisely  in  proportion  to  the  number  of 
polar  chains  established  in  it,  and  consequently  in  proportion  to  the  size  of  the  zinc 
plate ;  and  this  to  the  same  degree  from  the  induction  of  a  single  cell  as  from  any 
number  of  similar  cells.  Wires  of  different  metals  are  unequally  heated,  according  to 
the  resistance  which  they  offer  to  induction.     The  following  numbers  express  the 
heat  evolved  by  the  same  circulation  in  different  metals,  as  observed  by  Mr.  Snow 
Harris : — 

Heat  evolved.  Resistance. 

Silver 6  1 

Copper 6  1 

Gold 9  H 

Zinc 18 3 

Platinum  30 5 

Iron  30  5 

Tin  36  6 

Lead 72  12 

Brass  10  3 

The  conducting  powers  of  the  metals  are  inversely  as  these  numbers ;  silver  being 
a  better  conductor  than  platinum  in  the  proportion  of  5  to  1.  The  conducting  power 
of  all  of  them  is  found  to  be  diminished  by  heat. 

7.  As  a  portion  of  the  voltaic  circle,  the  conducting  wire  acquires  extraordinary 
powers  of  another  kind,  which  can  only  be  very  shortly  referred  to  here,  belonging 
as  they  properly  do  to  physics. 

(1)  Another  wire  placed  near  and  parallel  to  the  conducting  wire,  has  the  polar 
condition  of  its  molecules  disturbed,  and  an  induction  propagated  through  it  in  an 
opposite  direction  to  that  in  the  conducting  wire. 

(2)  If  the  conducting  wire  be  twisted  in  the  manner  of  a  corkscrew  so  as  to  form 
a  hollow  spiral  or  helix,  it  will  be  found  in  that  form  to  represent  a  magnet,  one  end 
of  the  helix  being  a  north,  and  the  other  a  south  pole ;  andj  if  moveable,  will  arrange 
itself  in  the  magnetic  meridian,  under  the  influence  of  the  earth's  magnetism.     Its 
poles  are  attracted  by  the  unlike  poles  of  an  ordinary  magnet,  and  it  imparts  mag- 
netism to  soft  iron  or  steel  by  induction.     Two  such  helices  attract  and  repel  each 
other  by  their  different  poles,  like  two  magnets.     Indeed,  an  ordinary  magnet  may 
be  viewed  as  a  body  having  a  helical  chain  of  its  molecules  in  a  state  of  permanent 
chemico-polarity. 

(3)  If  a  bar  of  soft  iron  bent  into  the  form  of  a  horse-shoe,  with  a  copper  wire 
twisted  spirally  round  it,  be  applied  like  a  lifter  to  the  poles  of  a  permanent  magnet, 
at  the  instant  of  the  soft  iron  becoming  a  magnet  by  induction,  the  molecules  of  the 
spiral  become  chemico-polar ;  and  when  contact  is  broken  with  the  permanent. mag- 
net, and  the  soft  iron  ceases  to  be  a  magnet,  the  wire  exhibits  a  polarity  the  reverse 
of  the  former.    By  a  proper  arrangement,  electric  sparks  and  shocks  may  be  obtained 
from  the  wire,  while  the  soft  iron  included  within  it  is  being  made  and  unmade  a 
magnet.     The  magneto-electric  machine  is  a  contrivance  for  this  purpose,  and  is 
now  coming  to  supersede  the  old  electric  machine,  as  a  source  of  what  is  termed 
electricity  of  tension.     Magnetic  and  electric  effects  are  thus  reciprocally  produced 
from  each  other. 

(4)  When  the  pole  of  a  magnetic  needle  is  placed  near  the  conducting  wire,  the 
former  neither  approaches  nor  recedes  from  the  latter,  but  exhibits  a  disposition  to 
revolve  round  it.     The  extraordinary  and  beautiful  phenomena  of  electrical  rotation 
are  exhibited  in  an  endless  variety  of  contrivances  and  experiments.     As  the  mag- 
netic needle  is  generally  supported  .upon  a  pivot,  it  is  free  to  move  only  in  a  horizon- 
tal plane,  and  consequently  when  the  conducting  wire  is  held  over  or  under  it  (the 
needle  being  supposed  in  the  magnetic  meridian),  the  poles  in  beginning  to  describe 
circles  in  opposite  directions  round  the  wire,  proceed  to  move  to  the  right  and  left 
of  it,  and  thus  deviate  from  the  true  meridian.     The  amount  of  deviation  in  degrees 


GENERAL    SUMMARY.  215 

is  proportional  to  the  quantity  of  circulating  induction,  and  may  be  taken  to  repre- 
sent it,  as  is  done  in  a  useful  instrument,  the  galvanometer,  to  be  afterwards  de- 
scribed. It  was  in  the  form  of  these  deflections,  that  the  phenomena  exhibited  by  a 
magnet,  under  the  influence  of  a  conducting  wire,  first  presented  themselves  to 
Oersted  in  1819. 

8.  Thermo-electrical  phenomena  are  produced  from  the  effect  of  unequal  tempera 
ture  upon  metals  in  contact.     If  heat  be  applied  to  the  point  c 

(fig.  83),  at  which  two  bars  of  bismuth  and  antimony  b  and  a  are  ^'G-  83* 
soldered  together,  on  connecting  the  free  extremities  by  a  wire,  the 
whole  is  found  to  form  a  weak  voltaic  circle,  with  the  induction 
from  6  through  the  wire  to  a.  Hence  in  this  thermo-polar  arrange- 
ment the  bismuth  is  the  negative  metal,  and  may  be  compared  to 
the  copper  in  the  voltaic  cell.  If  cold  instead  of  heat  be  applied 
to  c,  a  current  also  is  established,  but  in  an  opposite  direction  to 
the  former.  Similar  circuits  may  be  formed  of  other  metals,  which 
may  be  arranged  in  the  following  order,  the  most  powerful  combi- 
nation being  formed  of  those  metals  which  are  most  distant  from 
each  other  in  the  following  enumeration  :  bismuth,  platinum,  lead, 
tin,  copper  or  silver,  zinc,  iron,  antimony.  When  heated  at  their  points  of  contact, 
the  current  proceeds  through  the  wire  from  those  which  stand  first  to  the  last.  Ac- 
cording to  Nobili,  similar  circuits  may  be  formed  with  substances  of  which  the 
conducting  power  is  lower  than  that  of  the  metals. 

Several  pairs  of  bismuth  and  antimony  bars  may  be  associated  as  in  fig.  84,  and 
the  extreme  bars  being  connected  by  a  wire,  form 
an  arrangement  resembling  a  compound  voltaic  FlG-  84- 

circle.  Upon  heating  the  upper  junctions,  and 
keeping  the  lower  ones  cool,  or  on  heating  the 
lower  ones  and  keeping  the  others  cool,  an  induc- 
tion is  established  in  the  wire,  more  intense  than 
in  the  single  pair  of  metals,  but  still  very  weak. 
The  conducting  wire  strongly  affects  a  needle, 
causing  a  deflection  proportional  to  the  inequality 
of  temperature  between  the  ends  of  the  bars. 
Melloni's  thermo-multiplier  is  a  delicate  instru- 
ment of  this  kind,  which  is  even  more  sensitive  to  changes  of  temperature  than  the 
air-thermometer,  and  has  afforded  great  assistance  in  exploring  the  phenomena  of 
radiant  heat  (page  55). 

In  such  a  compound  bar,  also,  unequal  temperature  may  be  produced,  by  making 
it  the  connecting  wire  of  a  single  and  weak  voltaic  circle  j  whereupon  the  metals 
become  cold  at  their  junction,  if  the  induction  is  from  the  bismuth  to  the  antimony, 
and  hot  at  the  same  point  if  the  induction  is  in  the  opposite  direction.  These  are 
the  converse  of  the  preceding  phenomena,  in  which  electrical  effects  were  produced 
by  inequality  of  temperature. 

9.  The  friction  of  different  bodies  is  another  source  of  electrical  phenomena. 
One,  at  least,  of  the  bodies  rubbed  together  must  not  be  a  conductor,  and  in  general 
two  non-conductors  are  used.     When  a  silk  handkerchief  or  a  piece  of  resin  is 
rubbed  upon  glass,  both  are  found,  after  separation,  in  a  polar  condition,  and  con- 
tinue in  it.     The  rubbing  surface  of  the  glass  becomes  and  remains  zincous,  and 
that  of  the  resin  or  silk  is  chlorous ;  and  a  molecular  polarization  is  at  the  same 
time  established  through  the  whole  mass  of  both  the  glass  and  resin,  reaching  to 
their  opposite  surfaces,  which  exhibit  the  other  polarity.     The  powers  thus  appear- 
ing on  the  two  rubbing  surfaces,  being  manifestly  different,  were  distinguished  by 
the  names  of  the  bodies  on  which  they  are  developed;  that  upon  the  glass  as  vitreous 
electricity  (basylous  affinity),  and  that  upon  the  resin  as  resinous  electricity  (halo- 
genous  affinity). 

In  comparing  the  chemico-polarity  excited  by  friction  with  that  of  the  voltaic 


216  CHEMICAL    POLARITY. 

circle,  we  observe  that  the  former  is  of  high  intensity  but  small  in  quantity,  or 
affecting  only  a  small  number  of  trains  of  molecules.  Also  that  the  polar  condition 
is  more  or  less  permanent,  depending  upon  the  insulation,  and  attended  with  a  dis- 
turbance of  the  polar  condition  of  surrounding  bodies  to  a  considerable  distance, 
giving  rise  to  electrical  attractions  and  repulsions,  or  statical  phenomena.  If  both 
the  excited  vitreous  and  resinous  surfaces  have  a  conducting  metal,  such  as  a  sheet 
of  tin-foil,  applied  to  them,  and  each  sheet  have  a  wire  proceeding  from  it,  the 
wires  and  tin-foil  are  polarized  similarly  to  the  glass  and  the  resin  which  they  cover; 
and  a  saline  body  placed  between  the  extremities  of  the  wires,  which  are  respectively 
a  zincoid  and  chloroid,  is  polarized  also,  and  decomposed.  But  the  amount  of  de- 
composition, which  is  a  true  measure  of  the  quantity  of  polar  chains,  is  extremely 
minute  compared  with  the  amount  of  polarization  in  the  voltaic  circle.  Thus,  Mr. 
Faraday  has  calculated  that  the  decomposition  of  one  grain  of  water  by  zinc,  in  the 
active  cell  of  the  voltaic  circle,  produces  as  great  an  amount  of  polarization  and 
decomposition  in  the  cell  of  decomposition,  as  950,000  charges  of  a  large  Leyden 
battery,  of  several  square  feet  of  coated  surface ;  an  enormous  quantity  of  power, 
equal  to  a  most  destructive  thunder-storm.  The  polarization  from  friction  is  there- 
fore singularly  intense,  although  remarkably  deficient  in  quantity,  or  in  the  number 
of  chains  of  polar  molecules. 

The  kinds  of  matter  susceptible  of  this  intense  polarization  are  so  many  and  so 
various,  such  as  glass,  minerals,  wood,  resins,  sulphur,  oils,  air,  &c.,"as  to  make  it 
difficult  !to  suppose  that  the  polar  molecule  is  of  the  same  chemical  constitution  in 
all  of  them,  as  it  is  in  the  electrolytes  of  the  voltaic  circle.  Indeed,  it  must  be 
admitted  that  all  matter  whatever  may  be  forced  into  a  polar  condition  by  a  most 
intense  induction. 

Electrical  induction  at  a  distance,  Mr.  Faraday  has  shown  to  be  always  an  action 
of  contiguous  particles,  chains  of  particles  of  air,  or  some  other  "dielectric,"  extend- 
ing between  the  excited  body  which  is  inducing,  and  the  induced  body.  His  inves- 
tigations of  this  subject  led  to  the  remarkable  discovery  that  the  intensity  of  electric 
induction  at  a  constant  distance  from  the  inducing  body  is  not  always  the  same,  but 
varies  in  different  media,  the  induction  through  a  certain  thickness  of  shell-lac,  for 
instance,  being  twice  as  great  as  through  the  same  thickness  of  air.  Numbers  may 
be  attached  to  different  bodies  which  express  their  relative  inductive  capacities :  — 

Specific  inductive  capacity  of  air 1 

"  «  glass 1.76 

«  «  shell-lac '. 2 

"  «  sulphur. 2.24 

The  inductive  capacity  of  all  gases  is  the  same  as  that  of  air,  and  this  property,  it  is 
remarkable,  does  not  alter  in  these  bodies  with  variations  in  their  density. 

10.  Mr.  Faraday  has  lately  made  the  important  discovery  that  a  ray  of  polarized 
light  passing  through  a  transparent  liquid  or  solid,  is  deflected,  and  takes  a  spiral 
direction,  or  has  a  motion  of  rotation  communicated  to  it  by  the  approximation  of 
the  pole  of  a  powerful  electro  or' natural  magnet;  the  pole  of  the  latter  being  so 
placed  that  the  ray  is  in  the  direction  of  the  lines  of  attraction  of  the  magnet.     The 
amount  of  the  deflection  of  the  ray  varies  in  different  transparent  bodies,  and  is 
approximative^  expressed  for  oil  of  turpentine  by  11.8,  heavy  borate  of  lead  glass 
6.0,  flint-glass  2.8,  rock-salt  2.2,  water  1,  alcohol  and  ether  less  than  water  (Phil. 
Trans.  1846). 

11.  Operating  with   electro-magnets  of  the  highest   power,  Mr.   Faraday  has 
obtained  results  of  a  fundamental  nature  respecting  the  magnetic  capacity  of  differ- 
ent kinds  of  matter.     The  magnetic  field  being  represented  as  in  fig.  85,  where 
N  and  S  are  the  two  poles,  the  dotted  line  N  S  connecting  these  poles,  or  line 
of  magnetic  force,  is  conveniently  termed  the  axial  direction,  and  the  line  e  r,  per- 
pendicular to  the  former,  the  equatorial  direction.     When  a  bar  of  bismuth,  two 
inches  long,  0.33  inch  wide,  and  0.2  thick,  was  delicately  suspended  by  a  thread  of 


DIAMAGNETIC   METALS.  217 

qf 

untwisted  silk,  and  placed  between. the  magnets,  it  Fia.  85. 

arranged  itself  in  the  direction  of  e  r,  or  equatorially.  # 

All  kinds  of  solid,  liquid,  and  even  gaseous  matter 

have  a  certain  amount  of  tendency  to  place  them- -mn 

selves,  like  the  bismuth  bar,  across   the  axial  or    --||||| 
proper  magnetic  direction.     This  equatorial  tendency  "" 
is,  however,  overcome  and  negatived  by  the  smallest  j. 

proper  magnetic  property  which  bodies  may  possess, 

as  this  is  the  axial  polarity,  and  causes  the  substance  to  set  with  its  greatest  length 
in  the  direction  N  3.  Besides  iron,  nickel  and  cobalt,  the  usual  magnetic  metals, 
platinum,  palladium  and  titanium,  proved  to  be  axial  bodies.  So  are  all  the  salts 
containing  iron,  nickel,  or  cobalt,  as  base.  Even  bottle  glass  is  comparatively  very 
magnetic,  from  the  iron  it  contains ;  so  is  crown  (window)  glass,  but  not  flint  glass. 
The  solutions  of  these  salts  are  also  magnetic.  Crystals  of  the  yellow  ferrocyanide 
and  red  ferricyanide  of  potassium  are  not  magnetic,  but  set  equatorially.  The  iron, 
it  will  be  remembered,  belongs  to  the  acid  in  these  last  salts.  The  salts  of  the 
oxides  of  the  following  metals  proved  magnetic,  and  Mr.  Faraday  is  disposed  to 
infer  that  the  metals  themselves  are  so  —  manganese,  cerium,  chromium.  Paper 
and  many  other  organic  and  mineral  substances  often  contain  enough  of  iron  to 
make  them  fall  into  the  same  class. 

The  bodies  which  place  themselves  equatorially  are  named  diamagnetic.  The 
endless  list  of  them  is  also  headed  by  metals,  which  appear  to  possess  this  power  in 
different  degrees  of  intensity  according  to  the  following  order  :  — 


DIAMAGNETIC   METALS. 


Bismuth 
Antimony 
Zinc 
Tin 


Cadmium 
Mercury 
Silver 
Copper 


The  other  non-magnetic  metals  are  diamagnetic  in  a  less  degree.  This  property 
is  not  sensibly  impaired  by  heating  the  metals  up  to  their  fusing  points.  The  pro- 
perty may  be  experimentally  illustrated  by  pointed  pieces  of  rock  crystal,  glass, 
phosphorus,  sealing-wax,  caoutchouc,  wood,  beef,  bread,  &c.  (Phil.  Trans.  1846). 

Hot  air  and  flame  are  more  diamagnetic  than  cold  or  cooler  air,  so  that  a  stream 
of  the  former  spreads  itself  equatorially  in  ascending  between  magnetic  poles.  Of 
many  gases  and  vapours  tried  by  Mr.  Faraday,  oxygen  was  found  to  be  the  least 
diamagnetic ;  and  this  element  appears  to  lower  the  equatorial  tendency  of  the  gases 
into  which  it  enters  as  a  constituent.  Nitrogen  is  more  highly  diamagnetic  than 
carbonic  acid  or  hydrogen.  In  an  atmosphere  of  carbonic  acid  gas  (instead  of  air) 
between  the  magnetic  poles,  streams  of  hydrogen  gas,  coal  gas,  olefiant  gas,  muriatic 
acid,  and  ammonia,  passed  equatorially,  and  are  therefore  more  diamagnetic.  A 
stream  of  oxygen,  which  is  so  little  diamagnetic,  had,  consequently,  "  the  appearance 
of  being  strongly  magnetic  in  coal  gas,  passing  with  great  impetuosity  to  the  mag- 
netic axis,  and  clinging  about  it ;  and  if  much  muriate  of  ammonia  fume  were  pur- 
posely formed  at  the  time,  it  was  carried  by  the  oxygen  to  the  magnetic  field  with 
such  force  as  to  hide  the  ends  of  the  magnetic  poles.  If,  then,  the  magnetic  action 
were  suspended  for  a  moment,  this  cloud  descended  by  its  gravity ;  but  being  quite 
below  the  poles,  if  the  magnet  were  again  rendered  active,  the  oxygen  cloud  imme- 
diately started  up  and  took  its  former  place.  The  attraction  of  iron  filings  to  a 
magnetic  pole  is  not  more  striking  than  the  appearance  presented  by  the  oxygen 
under  these  circumstances"  (Faraday,  Phil.  Mag.  xxxi.  415). 


218 


CHEMICAL   POLAEITY. 


FIG.  86. 


VOLTAIC   INSTRUMENTS. 

DanielVs  constant  battery.  -s-  A  cell  of  this  battery  consists  of  a  cylinder  of  cop- 
per 3 1  inches  in  diameter,  which  experience  has  proved  to  the  inventor  to  afford  the 
most  advantageous  distance  between  the  metallic  surfaces,  but  which  may  vary  in 
height  from  6  to  20  inches,  according  to  the  power  which  it  is  wished  to  obtain.  A 
membranous  bag,  formed  of  the  gullet  of  an  ox,  is  hung  in  the  centre  by  a  collar 
and  circular  copper  plate,  resting  upon  a  rim  within  and  near  the  top  of  the  cylin- 
der ;  and  in  this  is  suspended  by  a  wooden  cross-bar,  a  cylindrical  rod  of  amalgamated 
zinc  half  an  inch  in  diameter.  Or  a  tube  of  porous  earthenware,  shut  at  the  bottom, 
is  substituted  for  the  membrane  with  great  convenience.  The  outer  cell  is  charged 
with  a  mixture  of  8  measures  of  water  and  1  of  oil  of 
vitriol,  which  has  been  saturated  with  sulphate  of  copper, 
and  portions  of  the  solid  salt  are  placed  upon  the  circular 
copper  plate,  which  is  perforated  like  a  colander,  for  the 
purpose  of  keeping  the  solution  always  in  a  state  of  satu- 
ration. The  internal  tube  is  filled  with  the  same  acid 
mixture  without  the  salt  of  copper.  A  section  of  the 
upper  part  of  one  of  these  cells  is  here  represented :  a  b 
c  d  (fig.  86)  is  the  external  copper  cylinder;  efg  h,  the 
internal  cylinder  of  earthenware,  and  /  m  the  rod  of  amal- 
gamated zinc.  Upon  a  ledge  c  d,  within  an  inch  or  two 
of  the  top  of  the  cylinder,  rests  the  cylindrical  colander 
i  k}  which  contains  the  copper  salt,  and  both  the  sides 
and  bottom  of  which  are  perforated  with  holes.  A  num- 
ber of  such  cells  may  be  connected  into  a  compound  cir- 
cuit, with  wires  soldered  to  the  copper  cylinders,  and  fastened 
to  the  zinc  by  clamps  and  screws  as  shown  below,  in  fig.  87 
(Daniell's  Int.  to  Ch.  Phil.)  Instead  of  the  zinc  cylinder  a 
thick  plate  of  laminated  zinc  is 

Fia  ^7-  now  generally  used,  which   is 

more     regularly    amalgamated 
than  the  cast  cylinder. 

In  this  instrument  the  sul- 
phate of  zinc,  formed  by  the 
solution  of  the  zinc  rod,  is 
retained  in  the  stoneware  cylin- 
der, and  prevented  from  diffus- 
ing to  the  copper  surface ;  while 
the  hydrogen,  instead  of  being 
evolved  as  gas  on  the  surface  of 
the  latter  metal,  decomposes  the 
oxide  of  copper  of  the  salt  there, 
and  occasions  a  deposition  of 
metallic  copper  on  the  copper 
plate.  Such  a  circle  will  not 
vary  in  its  action  for  hours  together,  which  makes  it  invaluable  in  the  investigation 
of  voltaic  laws.  It  owes  its  superiority  principally  to  three  circumstances :  —  to  the 
amalgamation  of  the  zinc,  which  prevents  the  waste  of  that  metal  by  solution  when 
the  circuit  is  not  completed ;  to  the  non-occurrence  of  the  precipitation  of  zinc  upon^ 
the  copper  surface ;  and  to  the  complete  absorption  of  the  hydrogen  at  the  copper 
surface,  the  adhesion  of  globules  of  gas  to  the  metallic  plates  greatly  diminishing, 
and  introducing  much  irregularity  into  the  action  of  a  circle. 

Grove's  nitric  acid  battery.  —  In  this  battery  the  positive  metal  is  amalgamated 
zinc,  and  the  negative  metal  platinum,  while  the  intermediate  liquid  is  of  two  kinds, 
dilute  sulphuric  acid  of  sp.  gr.  1.125  in  contact  with  the  zinc,  and  strong  nitric  acid 


d 


GROVE   S  NITRIC   ACID   BATTERY. 
FIG.  88. 
e 


219 


in  contact  with  the  platinum.  In  fig.  88,  a  represents  a  flat 
cell  of  porous  earthenware,  to  contain  the  nitric  acid  and 
platinum  plate ;  I,  the  platinum  plate ;  d,  the  zinc  plate, 
which  is  doubled  up  to  include  the  porous  cell ;  e,  a  cell 
of  glazed  earthenware  to  contain  the  sulphuric  acid  and 
zinc  plate ;  /,  a  wooden  frame  to  support  the  last  cell,  termi- 
nated above  by  copper  plates  provided  with  clamps,  by  which 
the  terminal  wires  are  attached.  Two  wooden  wedges,  such 
as  c,  are  required  to  fix  the  upper  end  of  the  zinc  plate  on 
the  one  side,  and  the  platinum  plate  on  the  other,  as  in  fig. 
89.  Convenient  dimensions  for  the  principal  parts  are,  the 
the  external  cell  e,  4£  inches  by  2f  and  l|  \  porous  cell  a, 
4%  by  2§  and  f  inch;  platinum  plate  5  inches  by  2^,  and 
weighing  about  10  grains  in  the  square  inch. 

Fia.  90. 


220 


CHEMICAL   POLARITY. 


FIG.  91. 


In  fig.  90,  six  of  these  cells  are  placed  together  in  a  wooden  frame,  with  the  upper 
part  of  each  end  of  the  frame  of  stout  sheet  copper,  to  which  the  plates  and  wires 
can  be  clamped.  The  wires  from  the  platinum  and  zinc  ends  of  the  battery,  have 
platinum  plates,  a  and  b,  attached  to  them  as  terminals.  A  battery  of  this  size  will 
evolve  8  or  10  cubic  inches  of  mixed  oxygen  and  hydrogen  gases  in  the  voltameter 
per  minute.  It  is  equal  to  several  times  as  many  cells  of  the  preceding  battery. 
The  polarizing  power  is  very  intense,  and  little  more  decomposing  power  is  gained 
by  increasing  the  number  of  cells  beyond  five  or  six. 

T/ie  carbo-zinc  battery  of  Bunsen,  which  is  much  used  on  the  continent,  is  a 
modification  of  the  last  construction,  in  which  charcoal  in  contact  with  the  nitric  acid 
is  substituted  for  platinum.  The  carbon  is  in  the  form  of  a  hollow  cylinder,  and  is 
made  by  coking  pounded  coal  in  a  proper  iron  mould.  By 
soaking  the  coke  in  sugar,  and  calcining  a  second  time,  great 
compactness  is  given  to  the  cylinder.  The  latter  is  so  large 
as  to  include  the  porous  cell  containing  the  zinc  and  acid,  and 
is  itself  placed  in  a  stout  glass  cylinder,  of  which  the  neck  is 
I  contracted  so  as  to  support  the  coke  cylinder  (fig.  91).  The 
zinc  cylinder  c  is  connected  by  a  slip  b  and  ring  a  of  the 
same  metal  with  the  coke  cylinder,  of  which  the  upper  end 
is  made  a  little  conical  to  hold  the  ring.  This  battery  has 
the  advantage  of  enlarged  negative  surface,  and  provides 
ample  space  for  the  nitric  acid. 

For  other  useful  forms  of  the  battery,  such  as  that  intro- 
duced by  Mr.  Since,  in  which  a  thin  sheet  of  silver  covered 
by  a  deposit  of  platinum  (platinized  silver)  is  the  negative  metal,  I  must  refer  to 
works  upon  Electricity. 

Bird's  battery  and  decomposing  cell.  —  To  M.  Becquerel  we  are  particularly 
indebted  for  the  investigation  of  the  decomposing  powers  of  feeble  currents,  sustained 
for  a  long  time,  the  results  of  which  are  of  great  interest,  both  from  the  nature  of 
the  substances  that  can  be  thus  decomposed,  and  from  the  form  in  which  the  ele- 
ments of  the  body  decomposed  are  presented,  the  slow  formation  of  these  bodies 
permitting  their  deposition  in  regular  crystals  (Traite  Experimental  de  1'Electricite 
at  du  Magnetisme,  par  M.  Becquerel).  Dr.  Golding  Bird  has  also  added  to  the 
number  of  bodies  decomposed  by  such  means,  and  contrived  a  simple  form  of  the 
battery,  which,  with  BecquerePs  decomposing  cell,  renders  such  decompositions 
certain  and  easy  (Phil.  Trans.  1887,  p.  37).  The  decomposing  cell  consists  of  a 

glass  cylinder  a  (fig.  92)  within  another 
glass  cylinder  b.  The  inner  cylinder  a  is 
4  inches  long,  and  1£  inch  in  diameter,  and 
is  closed  at  the  lower  end  by  a  plug  of 
plaster  of  Paris  0.7  inch  in  thickness  :  this 
cylinder  is  fixed  by  means  of  wedges  of 
cork  within  the  other,  which  is  a  plain  jar, 
about  8  inches  deep  by  2  inches  in  diameter. 
A  piece  of  sheet  copper  c,  4  inches  long  and 
3  inches  wide,  having  a  copper  conducting 
wire  soldered  to  it,  is  loosely  coiled  up  and 
placed  in  the  inner  cylinder  with  the  plaster 
bottom :  a  piece  of  sheet  zinc  z,  of  equal 
size,  is  also  loosely  coiled,  and  placed  in  tho 
outer  cylinder;  this  zinc  likewise  being 
furnished  with  a  conducting  wire.  The  outer  cylinder  is  then  nearly  filled  with  a 
weak  solution  of  common  salt,  and  the  inner  with  a  saturated  solution  of  sulphate 
of  copper.  The  two  fluids  are  prevented  from  mixing  by  the  plaster  diaphragm, 
and  care  being  taken  that  they  are  at  the  same  level  in  both  the  cylinders,  the  circle 
will  afford,  on  joining  the  wires,  a  continuous  current  for  weeks,  the  chloride  of 


FIG.  92. 


VOLTAIC   INSTRUMENTS.  221 

sodium  and  the  sulphate  of  copper  being  very  slowly  decomposed.  After  it  has 
been  in  action  for  some  weeks,  chloride  of  zinc  is  found  in  the  outer  cylinder :  and 
beautiful  crystals  of  metallic  copper,  frequently  mixed  with  the  ruby  suboxide  (closely 
resembling  the  native  copper  ruby  ore  in  appearance),  with  large  crystals  of  sulphate 
of  soda,  are  found  adhering  to  the  copper  plate  in  the  smaller  cylinder,  especially  on 
that  part  where  it  touches  the  plaster  diaphragm. 

The  decomposing  cell  is  the  counterpart  of  the  battery  itself,  consisting,  like  it, 
of  two  glass  cylinders,  one  within  the  other,  the  smaller  one  e  having  a  bottom  of 
plaster  of  Paris  fixed  into  it:-  this  smaller  tube  may  be  about  \  inch  wide  and  3 
inches  in  length,  and  is  intended  to  hold  the  metallic  or  other  solution  to  be  decom- 
posed, the  external  tube  d,  in  which  the  other  is  immersed,  being  filled  with  a  weak 
solution  of  common  salt.  In  the  latter  solution  a  slip  of  amalgamated  zinc-plate  z7, 
soldered  to  the  wire  coming  from  the  copper  plate  c  of  the  battery,  is  immersed ; 
and  a  slip  of  platinum  foil  pi,  connected  with  the  wire  from  the  zinc  plate  z  of  the 
battery,  is  immersed  in  the  liquor  of  the  smaller  tube,  being  held  in  its  place  by  a 
cork,  through  which  its  wire  passes.  The  whole  arrangement  is  now  obviously  a 
pair  of  active  cells,  of  which  c  d  is  one  metallic  element,  and  z  pi  the  other ;  and 
the  fluid  between  z  and  c  divided  by  the  porous  plaster  diaphragm,  one  fluid  ele- 
ment, and  the  fluid  between  z  and  pi,  divided  by  a  porous  plaster  diaphragm, 
another  fluid  element ;  although  it  will  be  convenient  to  speak  of  the  last  as  the  cell 
of  decomposition.  With  a  solution  of  chlorides  or  nitrates  of  iron,  copper,  tin,  zinc, 
bismuth,  antimony,  lead  or  silver,  in  the  smaller  tube,  Dr.  Bird  finds  the  metals  to 
be  reduced  upon  the  surface  of  the  platinum,  generally  but  not  invariably  in  posses- 
sion of  a  perfect  metallic  lustre,  always  more  or  less  crystalline,  and  often  very 
beautifully  so.  The  crystals  of  copper  rival  in  hardness  and  malleability  the  finest 
specimens  of  native  copper,  and  those  of  silver,  which  are  needles,  are  white  and 
very  brilliant.  The  solution  of  fluoride  of  silicon  in  alcohol  being  introduced  into 
the  small  tube  by  Dr.  Bird,  a  deposition  of  silicon  upon  the  platinum  was  found  to 
take  place  in  24  hours,  which  was  nearly  black  and  granular,  and  is  described  as 
exhibiting  a  tendency  to  a  crystalline  form.  From  an  aqueous  solution  of  the  same 
fluoride,  a  deposition  of  gelatinous  silica  was  observed  to  take  place  around  the 
reduced  silicon,  mixed  with  which,  or  precipitated  in  a  zone  on  the  sides  of  the  tube, 
especially  if  of  small  diameter,  frequently  appear  minute  crystalline  grains  of  silica 
or  quartz,  of  sufficient  hardness  to  scratch  glass,  and  appearing  translucent  under  the 
microscope.  With  a  modification  of  the  decomposing  cell  described,  Dr.  Bird  suc- 
ceeded in  decomposing  a  solution  of  chloride  of  potassium,  and  obtained  an  amalgam 
of  potassium.  The  inner  tube  e  was  replaced  by  a  small  glass  funnel,  the  lower 
opening  of  which  was  stopped  with  stucco,  and  which  thus  closed  retained  a  weak 
solution  of  the  alkaline  chloride  poured  into  it.  Every  thing  external  to  this  funnel 
remaining  as  usual,  mercury,  contained  in  a  short  glass  tube,  like  a  thimble,  was 
placed  in  the  funnel,  and  covered  by  the  liquid,  and  instead  of  the  platinum  plate,  a 
platinum  wire,  coiled  .into  a  spiral  at  the  extremity,  was  plunged  into  the  mercury, 
the  other  end  of  this  wire  being  connected  with  the  zinc  plate  z  of  the  battery.  The 
circuit  having  been  thus  completed,  the  mercury  had  swollen  in  eight  or  ten  hours 
to  double  its  former  bulk,  and  when  afterwards  thrown  into  distilled  water,  evolved 
hydrogen,  and  produced  an  alkaline  solution.  A  solution  of  hydrochlorate  of  am- 
monia being  substituted  for  that  of  chloride  of  potassium,  in  this  experiment,  the 
metal  swells  to  five  or  six  times  its  bulk  in  a  few  hours,  and  the  semi-fluid  amalgam 
of  ammonium  is  formed.  These  feeble  currents  thus  effect  decompositions  in  the 
lapse  of  time,  which  batteries  of  the  ordinary  form,  and  considerable  magnitude, 
may  effect  very  imperfectly,  or  fail  entirely  in  producing. 

Volta-meter.  —  The  decomposing  power  of  a  battery  is  represented  by  the 
quantity  of  oxygen  and  hydrogen  gases  evolved  in  a  cell  of  decomposition  con- 
taining dilute  sulphuric  acid.  The  volta-meter  (figure  93)  is  simply  a  cell  so 
charged,  and  of  a  proper  form  to  allow  of  the  gases  evolved  being  collected  and 
measured. 


i 


222 


CHEMICAL   POLARITY 
Fio.  93. 


FIG.  94. 


Galvanometer.  — The  sensibility  of  the  magnetic  needle  to  the  influence  of  the 
conducting  wire  of  a  voltaic  circle  brought  near  it,  has  been  applied  to  the  construc- 
tion of  an  instrument  which  will  indicate  the  feeblest  polarization  or  slightest  cur- 
rent in  the  connecting  wire.  It  con- 
sists of  a  pair  of  magnetic  needles  (fig. 
94),  fixed  on  one  axis  with  their 
attracting  poles  opposite  each  other, 
so  as  to  leave  them  little  or  no  direc- 
tive power,  and  render  them  astatic, 
which  is  delicately  suspended  by  a 
single  fibre  of  unspun  silk.  The  lower 
needle  is  enclosed  within  a  circle 
formed  by  a  hank  of  covered  wire  B, 
of  which  p  and  n  are  the  extremities. 
When  the  terminal  wires  of  a  battery 
are  connected  with  the  wires,  the  hank 
of  wire  of  the  galvanometer  becomes 
part  of  the  connecting  wire,  and  the 
needle  is  deflected.  The  inductions 
proceeding  in  one  direction  above  the 
needle  and  returning  in  the  opposite 
direction  below  the*  needle,  conspire  to 
produce  the  same  deflection ;  and  the 
upper  needle  having  its  poles  reversed, 
is  deflected  in  the  same  direction,  by 
the  wire  below  it,  as  the  lower  needle 
is  by  the  wire  above  that  needle. 

Every  turn  of  the  wire  also  repeats  the  influence  upon  the  needle,  so  that  the 
deflection  is  increased  in  proportion  to  the  number  of  turns  or  coils  in  the  hank 
of  wire.  [See  Supplement,  p.  679.] 


OXYGEN. 


228 


CHAPTER  V. 

NON-METALLIC    ELEMENTS. 


SECTION  I. — OXYGEN. 

Equivalent  8  (hydrogen  =  1,  or  100  as  the  basis  of  the  Oxygen  Scale;  density 
1105-6  (air  =  1000);  combining  measure   f    ]    (one  volume.} 

THE  following  thirteen  of  the  sixty-two  elementary  bodies  known,1  are  included 
in  the  class  of  non-metallic  elements: — oxygen,  hydrogen,  nitrogen,  carbon,  boron, 
silicon  or  silicium,  sulphur,  selenium,  phosphorus,  chlorine,  bromine,  iodine,  and 
fluorine.  Of  these,  oxygen,  from  certain  relations  which  it  bears  to  all  the  others, 
and  from  its  general  importance,  demands  the  earliest  consideration. 

The  name  oxygen  is  compounded  of  o(fo,  acid,  and  yswuo,  I  give  rise  to,  and  was 
given  to  this  element  by  Lavoisier,  with  reference  to  its  property  of  forming  acids 
in  uniting  with  other  elementary  bodies.  Oxygen  is  a  permanent  gas,  when  uncom- 
bined,  and  forms  one-fifth  part  of  the  air  of  the  atmosphere.*  In  a  state  of  combi- 
nation, this  element  is  the  most  extensively  diffused  body  in  nature,  entering  as  a 
constituent  into  water,  into  nearly  all  the  earths  and  rocks  of  which  the  crust  of  the 
globe  is  composed,  and  into  all  organic  products,  with  a  few  exceptions.  It  was  first 
recognised  as  a  distinct  substance  by  Dr.  Priestley  in  England,  in  1774,  and  about 
a  year  afterwards  by  Scheele  in  Sweden,  without  any  knowledge  of  Priestley's  ex-' 
perirnents.  From  this  discovery  may  be  dated  the  origin  of  true  chemical  theory. 

Preparation.  —  Oxygen  gas  is  generally  disengaged  from  some  compound  contain- 
ing it,  by  the  action  of  heat. 

1.  It  was  first  procured  by  Priestley,  by  heating  Red  Precipitate  (oxide  of  mer- 
cury), which  is  thereby  resolved  into  fluid  mercury  and  oxygen  gas.  To  illustrate 
the  formation  of  oxygen  in  this  way,  200  grains  of  red  precipitate  may  be  introduced 
into  the  body  of  a  small  retort  a  of  hard  or  difficultly  fusible  glass,  and  the  retort 

FIG.  95. 


united  in  an  air-tight  manner  with  a  small  globular  flask  6,  having  two  openings, 
both  closed  by  perforated  corks,  one  of  which  admits  the  beak  of  the  retort,  and  the 

1  This  number  includes  three  elements  —  erbium,  terbium,  and  ilmenium,  of  which  the 
existence  is  doubtful. 


[See  Supplement,  p.  759.] 


224  OXYGEN. 

other  an  exit  tube  c,  of  glass,  bent  as  in  the  figure.  The  extremity  of  the  exit 
tube  is  introduced  into  a  graduated  jar  capable  of  holding  50  or  60  cubic  inches, 
and  placed  in  an  inverted  position,  full  of  water,  upon  the  shelf  of  a  pneumatic 
water-trough.  Heat  is  then  applied  to  the  retort  by  means  of  an  Argand  spirit 
lamp  powerful  enough  to  raise  it  to  a  red  heat,  and  maintain  it  at  that  temperature 
for  a  considerable  time.  The  first  effect  of  the  heat  is  to  expand  the  air  in  the  re- 
tort, bubbles  of  which  issue  from  the  tube  c,  and  rise  to  the  top  of  the  jar  displacing 
water  ;  but  more  gas  follows,  which  is  oxygen,  and  at  the  same  time  metallic  mer- 
cury condenses  in  the  neck  of  the  retort  and  runs  down  into  the  intermediate  flask  6. 
When  the  red  precipitate  in  the  retort  has  entirely  disappeared,  the  lamp  may  be 
extinguished,  and  the  retort  allowed  to  cool  completely.  The  end  of  the  exit  tube  c 
being  now  above  the  level  of  the  water  in  the  jar,  which  is  nearly  full  of  gas,  a 
portion  of  the  latter,  equal  in  bulk  to  the  air  which  first  left  the  retort,  will  return 
to  it,  from  the  contraction  of  the  gas  within  the  retort.  The  jar  will  be  found  in. 
the  end  to  contain  44  cubic  inches  of  gas,  which  is  therefore  the  measure  of  oxygen 
produced  in  the  experiment,  and  the  flask  to  contain  185  grains  of  mercury.  Now 
44  cubic  inches  of  oxygen  weigh  15  grains;  and  a  true  analysis  of  the  red  precipi- 
tate has  been  effected,  of  which  the  result  is,  that  200  grains  of  that  substance 
consist  of  — 

185  grains  mercury. 
15      ({      oxygen,  (44  cubic  inches). 

200 

But  oxygen  gas  is  more  generally  derived  from  two  other  substances  —  oxide  of 
manganese  and  chlorate  of  potassa. 

2.  When  the  gas  is  required  in  large  quantity,  and  exact  purity  is  immaterial, 
the  oxide  of  manganese  is  preferred  from  its  cheapness.  This  is  a  black,  heavy 
mineral,  found  in  Devonshire,  in  Hesse  Darmstadt,  and  other  localities,  of  which 
upwards  of  40,000  tons  are  consumed  annually  in  the  manufactures  of  the  country. 
it  is  called  an  oxide  of  manganese,  because  it  is  a  compound  of  the  metal  manga- 
nese with  oxygen.  In  explanation  of  what  takes  place  when  this  substance  is  heated, 
it  is  necessary  to  state  that  manganese  is  capable  of  uniting  with  oxygen  in  several 
proportions,  namely,  one  equivalent,  or  27.67  parts  of  manganese,  with  8,  and  with 
16  parts  of  oxygen  ;  and  two  equivalents  of  manganese  with  24  parts  of  oxygen. 
These  compounds  are:  — 

Protoxide  of  manganese  ................................    Mn-f-   0. 

Sesquioxide  ...........  ....................................  2Mn  +  30. 

Binoxide,  or  native  black  oxide  ........................    Mn  +  20. 

Now  the  binoxide,  however  strongly  heated,  never  loses  more  than  one-third  of  its 
oxygen,  being  converted  into  a  compound  of  the  first  two  oxides:  that  is,  three 
equivalents  of  binoxide  (131.01  parts)  lose  two  equivalents  of  oxygen  (16  parts), 
ind  leave  a  compound  of  one  efy.  of  sesquioxide  and  one  eq.  of  protoxide  ;  a  change 
which  may  be  thus  expressed:  — 


One  of  the  malleable  iron  bottles  in  which  mercury  is  imported  is  readily  con- 
verted into  a  retort,  in  which  the  black  oxide  may  be  heated,  by  removing  its 
screwed  iron  stopper,  and  replacing  this  by  an  iron  pipe  of  three  feet  in  length,  one 
end  of  which  has  been  cut  to  the  screw  of  the  bottle.  This  pipe  may  be  bent,  like  a, 
figure  96,  if  the  bottle  is  to  be  heated  in  an  open  fire,  or  in  a  furnace  open  at  the 
top.  From  3  to  9  pounds  of  the  oxide  may  be  introduced  as  a  charge,  accoidiug  to 
the  quantity  of  gas  to  be  prepared,  each  pound  of  good  German  manganese  yielding 
aj^out  1400  cubic  inches,  or  5.05  gallons  of  gas.  Upon  the  first  application  of  heat, 


OXYGEN. 


225 


water  comes  off,  as  steam,  mixed  occasionally  with  a  gas  which  extinguishes  flame ; 
this  is  owing  to  the  impurity  of  the  oxide.  The  products  may  be  allowed  to  escape, 
till  the  point  of  a  wood-match,  red  without  flame,  applied  to  the  orifice,  is  rekindled 
and  made  to  burn  with  brilliancy ;  the  gas  is  then  sufficiently  pure,  and  means  must 
be  taken  for  collecting  it.  A  small  flexible  tin  tube  b,  of  any  convenient  length,  is 


FIG.  96. 


adapted  to  the  iron  pipe,  by  means  of  a  perforated  cork,  by  which  the  gas  is  coi 
veyed  to  a  pneumatic  trough,  and. collected  in  glass  jars  filled  with  wate%  as  in  th* 
former  experiment;  or,  as  this  process  affords  considerable  quantities  of  oxygon,  thf 
gas  is  more  generally  conducted  into  the  inferior  cylinder  or  drum  of  a  copper  ga 
holder  c,  full  of  water.  The  water  dofes  not  flow  out  by  the  recurved  tube  whic 
forms  the  lower  opening,  but  is  retained  in  the  vessel  by  the  pressure  of  the  atmc- 
sphere  on  the  surface  of  the  water  in  that  tube,  as  water  is  retained  in  a  bird'j 
drinking-glass.  But  when  the  tin  tube  is  introduced  into  the  gas-holder  by  thh 
opening,  water  escapes  by  it,  in  proportion  as  gas  is  thrown  into  the  cylinder  and 
rises  in  bubbles  to  the  top.  The  progress  of  filling  the  gas-holder  may  be  observed 
by  the  glass  gauge-tube  g,  which  is  open  at  both  ends,  and  connected  with  the  top 
and  bottom  of  the  cylinder,  so  that  the  water  stands  at  the  same  height  in  the  tube 
as  in  the  cylinder.  Convenient  dimensions  for  the  cylinder  itself  are  16  inches  in 
height  by  12  in  diameter;  to  fill  which  a  charge  of  three  pounds  of  manganese  may 
be  used.  The  gauge-tube  is  so  aj)t  to  be  broken,  or  to  occasion  leakage  at  its  junc- 
tions with  the  cylinder,  when  the  latter  is  large  and  unwieldy,  that  it  is  generally 
better  to  forego  the  advantage  it  offers,  and  dispense  with  this  addition  to  the  gas- 
holder. When  applied  to  a  small  gas-holder,  the  ends  of  the  tube  are  conveniently 
adapted  to  the  openings  of  the  cylinder,  by  means  of  perforated  corks, 
which  are  afterwards  covered  by  a  mixture  of  white  and  red  lead  with 
a  drying  oil.  * 

After  the  cylinder  is  filled,  the  lower  opening  by  which  the  gas 
was  admitted  is  closed  by  a  good  cork,  or  by  a  brass  cap  made  to  screw 
over  it.  The  superior  cylinder  is  an  open  water  trough,  connected 
with  the  inferior  cylinder  by  two  tubes  provided  with  stop-cocks,  m 
and  n,  one  of  which,  m,  is  continued  to  the  bottom  of  that  vessel,  and 
conveys  water  from  the  superior  cylinder,  while  the  other  tube,  n,  ter- 
minates at  the  top  of  the  inferior  cylinder,  and  affords  a  passage  by 
which  the  gas  can  escape  from  it,  when  water  is  allowed  to  descend  by 
the  other  tube.  The  tube  and  perforation  of  the  stopcock  of  m  should 


Fia.  97. 


226 


OXYGEN. 


FIG.  98. 


be  considerably  wider  than  n.  A  jar  a  is  filled  with  gas  by  inverting  it  full  of  water 
in  the  superior  cylinder,  over  the  opening  of  n,  as  exhibited  in  the  figure,  and  allow- 
ing the  gas  to  ascend  from  the  inferior  cylinder.  Gas  may  likewise  be  obtained  by 
the  stopcock  /  (fig.  96),  water  being  allowed  to  enter  by  m  at  the  same  time- 

Oxygen  may  likewise  be  disengaged  from  oxide  of  manganese  in  a  flask  or  retort, 
by  means  of  sulphuric  acid  diluted  with  an  equal  bulk  of  water,  but  this  is  not  a 
process  to  be  recommended.  When  the  quantity  of  oxygen  required  is  not  very 
large,  it  is  better  to  have  recourse  to  chlorate  of  potassa,  which  has  also  the  advan- 
tage of  giving  a  perfectly  pure  gas. 

3.  A  well-cleansed  Florence  oil  flask,  the  edges  of  the  mouth  of  which  have  been 

heated  and  turned  over  so  as  to  form. 
a  lip,  with  a  bent  glass  tube  and  per- 
forated cork  fitted  to  it  (fig.  98),  forms 
a  convenient  retort  in  which  about 
half  an  ounce  of  chlorate  of  potassa 
may  be  heated  by  means  of  a  gas 
flame  or  Argand  spirit  lamp.  The 
salt  melts,  although  it  contains  no 
water,  and  when  nearly  red-hot  emits 
abundance  of  oxygen  gas.  At  one 
point  of  the  decomposition,  the  effer- 
vescence may  become  so  violent  as 
to  burst  the  flask,  especially  if  th« 
exit  tube  be  narrow,  unless  the  heat 
be  moderated.  The  chlorate  of  pot- 
assa parts  with  all  the  oxygen  it  pos- 

sesses, which  amounts  to  39-2  per  cent,  of  its  weight,  and  leaves  a  white  hard  salt, 
the  chloride  of  potassium. 

The  otfly  inconvenience  attending  the  preceding  process  is  the  high  temperature 
required,  which  would  soften  a  retort  or  flask  of  flint  glass.  It  was  discovered, 
however,  by  M.  Mitscherlich,  that  chlorate  of1  potassa  is  decomposed  at  a  much 
lower  temperature  when  mixed  with  dry  powders,  upon  which  it  exercises  no  chemi- 
cal action,  particularly  metallic  peroxides,  such  as  the  binoxide  of  manganese  and 
the  black  oxide  of  copper.  Nothing  can  answer  better  than  the  binoxide  of  man- 
ganese, after  being  made  anhydrous  by  a  short  exposure  to  a  red  heat.  Two  parts 
of  chlorate  of  potassa  in  powder,  mixed  with  one  part  of  the  dried  oxide,  forms  a 
useful  "  oxygen  mixture,"  which  may  be  made  in  quantity  and  preserved  for  occa- 
sional use. 

From  an  atomic  statement  of  the  composition  of  chlorate  of  potassa,  it  appears 
that  one  equivalent  of  it  (122-5  parts)  contains  six  equivalents  of  oxygen  (48  parts), 
namely  five  eq.  in  the  chloric  acid  and  one  eq.  in  the  potassa,  the  whole  of  which 
come  off,  leaving  one  equivalent  of  chloride  of  potassium  (74-5  parts)  :  — 


Half  an  ounce  of  chlorate  of  potassa  should  yield  270  cubic  inches,  or  nearly  a 
gallon  of  pure  oxygen  gas. 

4.  Another  process  for  oxygen  gas,  proposed  by  Mr.  Bahnain,  consists  in  heating 
in  a  retort  3  parts  of  the  bichromate  of  potassa  in  powder,  with  4  parts  of  undiluted 
sulphuric  acid  :  the  gas  comes  off  in  a  continuous  stream,  and  a  mixture  of  sulphate 
of  potassa  and  sulphate  of  sesquioxide  of  chromium  remains  behind  in  the  retort. 
The  decomposition  which  takes  place  is  explained  in  the  following  formula  :  — 
KO,  O206  with  4  S03,  give  KO,  S03  with  O203  3S08  and  30. 

The  bichromate  of  potassa  loses  one-half  of  the  oxygen  contained  in  the  chromic 
acid,  or  about  16  per  cent,  of  its  weight;  one  ounce  of  salt  yielding  about  200 
cubic  inches  of  gas. 


OXYGEN.  227 

[5.  When  a  perfectly  pure  gas  is  not  required,  oxygen  may  be  obtained  in  large 
quantity  from  nitrate  of  potassa.  The  same  apparatus  is  used  as  in  the  decomposi- 
tion of  black  oxide  of  manganese :  the  nitre,  of  which  8  or  10  pounds  may  be  used 
at  once,  is  to  be  exposed  to  a  well-regulated  heat  of  a  charcoal  fire,  the  draught 
being  urged  or  diminished  in  proportion  to  the  rapidity  of  the  flow  of  gas.  A  red  heat 
is  about  the  best  temperature  for  the  operation.  The  gas  which  comes  over  at  this 
temperature  contains  about  96  per  cent,  of  oxygen,  and  when  after  some  time  it  is 
found  necessary  to  urge  the  fire  that  the  flow  of  gas  may  be  kept  up,  the  per  centage 
diminishes,  and  may  fall  as  low  as  66.  Two  of  the  five  equivalents  of  oxygen  in 
the  nitric  acid  are  given  off  in  the  first  part  of  the  operation,  and  in  the  latter  part 
the  remaining  oxygen  with  the  nitrogen.  —  R.  B.] 

Properties.  —  Oxygen  gas  is  colourless,  and  destitute  of  odour  and  taste.  It  is 
heavier  than  air  in  the  ratio  of  1105-6  to  1000,  according  to  the  latest  careful  de- 
termination, that  of  M.  Regnault.1 

At  the  temperature  of  60°,  and  with  the  barometer  at  30  inches,  100  cubic  inches 
of  oxygen  gas  weigh  34-19  grains  (Regnault).  One  cubic  inch,  therefore,  weighs 
0-3419  gr.,  or  about  one-third  of  a  grain.  It  has  never  been  liquefied  by  cold  or 
pressure. 

Oxygen  is  so  sparingly  soluble  in  water,  that  when  agitated  in  contact  with  that 
fluid  no  perceptible  diminution  of  its  volume  takes  place.  But  when  water  is  pre- 
viously deprived  of  air  by  boiling,  and  allowed  to  cool  in  a  close  vessel,  100  cubic 
inches  of  it  dissolve  3|  cubic  inches  of  this  gas. 

If  a  lighted  wax  taper  attached  to  a  copper  wire  be  blown  out,  and  dipped  into 
a  vessel  of  oxygen  gas,  while  the  wick  remains  red-hot,  it  instantly  rekindles  with 
a  slight  explosion,  and  burns  with  great  brilliancy.     If  soon  withdrawn  and  blowr 
out,  it  may  be  revived  again  in  the  same  manner,  and  the 
experiment   be   repeated    several   times   in   the   same   gas.  ^IG<  "• 

Lighted  tinder  burns  with  flame  in  oxygen,  and  red-hot 
charcoal  with  brilliant  scintillations.  Burning  sulphur  in- 
troduced into  this  gas  in  a  little  hemispherical  cup  of  iron-plate 
with  a  wire  attached  to  it,  burns  with  an  azure  blue  flame  of 
considerable  intensity.  Phosphorus  introduced  into  oxygen 
in  the  same  manner,  burns  with  a  dazzling  light  of  the 
greatest  splendour,  particularly  after  the  phosphorus  boils 
and  rises  through  the  gas  in  vapour.  Indeed,  all  bodies 
which  burn  in  air,  burn  with  increased  vivacity  in  oxygen 
gas.  Even  iron  wire  may  be  burned  in  this  gas.  For  this 
purpose  thin  harpsichord  wire  should  be  coiled  about  a 
cylindrical  rod  into  a  spiral  form.  The  rod  being  withdrawn, 
a  piece  of  thread  must  be  twisted  about  one  end  of  the  wire, 
and  dipped  into  melted  sulphur ;  the  other  end  of  the  wire  is 
to  be  fixed  into  a  cork,  so  that  the  spiral  may  hang  vertically. 
The  sulphured  end  is  then  to  be  lighted,  and  the  wire  suspended  in  a  jar  of 
oxygen,  open  at  the  bottom,  such  as  that  represented  in  fig.  97,  page  225,  supported 

]  Annales  de  Chimie,  &c.,  1845,  3e.  ser.  t.  xiv.  p.  211.  The  mean  of  three  weighings 
previously  made  by  MM.  Dumas  and  Boussingault,  was  1105-7  (ibid.  t.  viii.  p.  201).  Baron 
Wrede  found  1105-2.  At  a  much  earlier  period  T.  de  Saussure  obtained  Rcgnault's  number, 
1105-6.  These  coincidences  in  the  results  of  independent  observers  appear  to  prove  that  a 
close  approximation  has  been  made  to  the  true  density  of  this  gas :  an  important  datum. 
The  earlier  determination  of  MM.  Dulong  and  Berzelius  was  1102-6  (ibid.  1820,  2e.  ser.  t. 
xv.  p.  386).  According  to  M.  Regnault,  the  weight  of  1000  cubic  centimeters  (1  liter)  of 
oxygen  gas,  at  32°  F.,  barometer  29-92  inches  (760  millimeters),  is  1-4298  gramme.  Hence, 
000  c.  c.  being  equal  to  61-028  English  c.  inches,  and  1  gramme  to  15-4440  English  grains, 
100  cubic  inches  of  oxygen,  at  the  specified  temperature  and  pressure,  weigh  36-1390  grains. 
Calculating  with  Regnault's  coefficient  for  the  expansion  of  air  (page  40),  1  volume  of  oxy- 
gen will  become  1-05701  volume,  at  60°,  and  100  cubic  inches  of  oxygen  will  weigh  34-1898 
grains  at  that  temperature. 


228  OXYGEN. 

upon  an  earthenware  plate.  The  wire  is  kindled  by  the  sulphur,  and  burns  with 
an  intense  white  light,  throwing  out  a  number  of  sparks,  or  occasionally  allowing  a 
globule  of  fused  oxide  to  fall ;  while  the  wire  itself  continues  to  fuse  and  burn  till 
it  is  entirely  consumed,  or  the  oxygen  is  exhausted.  The  experiment  forms  one  of 
the  most  beautiful  and  brilliant  in  chemistry.  The  globules  of  fused  oxide  are  of  so 
elevated  a  temperature,  that  they  remain  red-hot  for  some  time  under  the  surface 
of  water,  and  fuse  deeply  into  the  substance  of  the  stoneware  plate  upon  which 
they  fall. 

[A  portion  of  cast  iron  placed  upon  ignited  charcoal  and  subjected  to  a  stream 
of  oxygen,  soon  melts  and  burns  brilliantly,  throwing  off  showers  of  bright  sparks 
on  all  sides.  —  R.  B.] 

Oxygen  gas  is  respirable,  and  indeed  is  constantly  taken  into  the  lungs  from  the 
atmosphere  in  ordinary  respiration.  When  a  portion  of  dark  blood  drawn  from  a 
vein  is  agitated  with  this  gas,  the  colour  becomes  of  a  fine  vermilion  red.  The  same 
change  occurs  in  the  blood  of  living  animals,  during  respiration,  from  the  absorp- 
tion of  oxygen  gas,  which  is  required  to  maintain  the  animal  heat.  A  small  animal, 
also,  such  as  a  mouse  or  bird,  lives  four  or  five  times  longer  in  a  vessel  of  oxygen 
than  it  will  in  an  equal  bulk  of  air.  But  the  continued  respiration  of  this  gas  in  a 
state  of  purity  is  injurious  to  animal  life.  A  rabbit  is  found  to  breathe  it  without 
inconvenience  for  some  time,  but  after  an  interval  of  an  hour  or  more  the  circulation 
and  respiration  are  much  quickened,  and  a  state  of  great  excitement  of  the  general 
system  supervenes;  this  is  by  and  by  followed  by  debility,  and  death  occurs  in  from 
six  to  ten  hours.  The  blood  is  found  to  be  highly  florid  in  the  veins  as  well  as  the. 
arteries,  and,  according  to  Broughton,  the  heart  continues  to  act  strongly  after  the 
breathing  has  ceased. 

Oxygen  may  be  made  to  unite  with  all  the  other  elements  except  fluorine,  and 
forms  oxides,  while  the  process  of  uniting  with  oxygen  is  termed  oxidation.  With 
the  same  element  oxygen  often  unites  in  several  proportions,  forming  a  series  of 
oxides,  which  are  then  distinguished  from  each  other  by  the  different  prefixes  enu- 
merated under  Chemical  nomenclature  (page  106).  Many  of  its  compounds  are 
acids,  particularly  those  which  contain  more  than  one  equivalent  of  oxygen  to  one 
of  the  other  element,  and  compounds  of  this  nature  are  those  which  it  most  readily 
forms  with  the  non-metallic  elements  :  such  as  carbonic  acid  with  carbon,  sulphurous 
acid  with  sulphur,  phosphoric  acid  with  phosphorus.  But  oxygen  unites  in  prefer- 
ence with  single  equivalents  of  a  large  proportion  of  the  metallic  class  of  elements, 
and  forms  bodies  which  are  alkaline  or  have  the  character  of  bases :  such  as  potassa, 
lime,  magnesia,  protoxide  of  iron,  &c.  A  certain  number  of  its  compounds  are 
neither  acid  nor  alkaline,  and  are  therefore  called  neutral  bodies :  such  as  the  oxide 
of  hydrogen  or  water,  carbonic  oxide,  and  nitrous  oxide.  The  greater  number  of 
these  neutral  oxides  are  also  protoxides. 

It  has  already  been  stated  that  in  a  classification  of  the  elements  oxygen  does  not 
stand  alone,  but  forms  one  of  a  small  natural  family  along  with  sulphur,  selenium, 
and  tellurium.  These  elements  also  form  acid,  basic,  and  neutral  classes  of  com- 
pounds, with  the  same  bodies  as  oxygen  does,  of  which  the  sulphur  compounds  are 
well  known,  and  always  exhibit  a  well-marked  analogy  to  the  corresponding  oxides. 
Oxygen-acids  unite  with  oxygen  bases,  and  form  neutral  salts :  so  do  sulphur-acids 
with  sulphur-bases,  selenium-acids  with  selenium-bases,  and  tellurium-acids  wfth 
tellurium-bases. 

The  combinations  of  oxygen,  like  those  of  all  other  bodies,  are  attended  with  the 
evolution  of  heat.  This  result,  which  is  often  overlooked  in  other  combinations,  in 
which  the  proportions  of  the  bodies  uniting  and  the  properties  of  their  compound 
receive  most  attention,  assumes  an  unusual  degree  of  importance  in  the  combinations 
of  oxygen.  The  economical  applications  of  the  light  and  heat  evolved  in  these  com- 
binations are  of  the  highest  consequence  and  value,  and  oxidation  alone,  of  all  che- 
mical actions,  is  practised,  not  for  the  value  of  the  products  which  it  affords,  and 
indeed  without  reference  to  them,  but  for  the  sake  of  the  incidental  phenomena 


OXYGEN.  229 

attending  it.  Of  the  chemical  combinations,  too,  which  we  habitually  witness,  those 
of  oxygen  are  infinitely  the  most  frequent,  which  arises  from  its  constant  presence 
and  interference  as  a  constituent  of  the  atmosphere.  Hence,  when  a  body  combines 
with  oxygen,  it  is  said  to  be  burned  ;  and  instead  of  undergoing  oxidation  it  is  said 
to  suffer  combustion  ;  and  a  body  which  can  combine  with  oxygen  and  emit  heat  is 
termed  a  combustible.  Oxygen,  in  which  the  body  burns,  is  then  said  to  support 
combustion,  and  called  a  supporter  of  combustion. 

The  heat  evolved  in  combustion  is  definite,  and  can  be  measured.  With  this 
view  it  is  employed  to  melt  ice,  to  raise  the  temperature  of  water  from  32°  to  212°, 
or  to  convert  water  into  steam,  and  its  quantity  is  estimated  by  the  extent  to  which 
it  produces  these  effects.  The  heat  from  the  oxidation  of  a  combustible  body  is  thus 
found  to  be  as  constant  as  any  other  of  its  properties.  Despretz  obtained,  by  such 
experiments,  the  results  contained  in  the  following  table  :  — 

HEAT   FROM    COMBUSTION. 

1  pound  of  pure  charcoal heats  from  32°  to  212°,  78  pounds  of  water. 

—  charcoal  from  wood —  75  — 

—  baked  wood —  36  — 

—  wood  containing  20  per  cent,  of  water  —  27  — 

—  bituminous  coal —  60  — 

_  turf —  25  to  30  — 

—  alcohol —  67-5  — 

—  olive  oil,  wax,  &c —  90  to  95  — 

_  ether —  80  — 

—  hydrogen —  236-4  — 

The  quantity  of  heat  evolved  appears  to  be  connected  with  the  proportion  of 
oxygen  consumed,  for  the  greater  the  weight  of  oxygen  with  which  a  pound  of  any 
combustible  unites,  the  more  heat  is  produced.  The  following  results  indicate  that 
the  heat  depends  exclusively  upon  the  oxygen  consumed,  four  different  combustibles 
in  consuming  a  pound  of  oxygen  affording  nearly  the  same  quantity  of  heat :  — 

HEAT    OF   COMBUSTION. 

1  pound  of  oxygen  with  hydrogen  heats  from  32°  to  212°,  29J  pounds  of  water. 

—  with  charcoal  —  29  — 

—  with  alcohol  —  28  — 

—  with  ether  —  28£  — 

The  quantity  of  combustible  consumed  in  these  experiments  varied  considerably, 
but  the  oxygen  being  the  same,  the  heat  evolved  was  nearly  the  same  also.  But 
when  the  same  quantity  of  oxygen  converted  phosphorus  into  phosphoric  acid, 
exactly  twice  as  much  heat  was  evolved,  according  to  Despretz,  as  in  the  former 
experiments.  The  superior  vivacity  of  the  combustion  of  these  and  other  bodies  in 
pure  oxygen,  compared  with  air,  depends  entirely  upon  the  rapidity  of  the  process, 
and  the  larger  quantity  of  combustible  oxidated  in  a  given  time.  A  candle 
burns  with  more  light  and  heat  in  oxygen  than  in  air,  but  it  consumes  proportion- 
ally faster.  [/See  Supplement,  p.  751.] 

Oxidation  is  often  a  very  slow  process,  and  imperceptible  in  its  progress  —  as  in 
the  rusting  of  iron  and  tarnishing  of  lead  exposed  to  the  atmosphere.  The  heat 
being  then  evolved  in  a  gradual  manner  is  instantly  dissipated,  and  never  accumu- 
lates. But  when  the  oxide  formed  is  the  same,  the  nature  of  the  change  effected  is 
in  no  way  altered  by  its  slowness.  Iron  oxidates  rapidly  when  introduced  in  a  state 
of  ignition  into  oxygen  gas,  and  lead,  in  the  form  of  the  lead  pyrophorus,  which 
contains  that  metal  in  a  high  state  of  division,  takes  fire  spontaneously  and  burns 
in  the  air;  circumstances  then  favouring  the  rapid  progress  of  oxidation. 

Oxidation  may  also  go  on  with  a  degree  of  rapidity  sufficient  to  occasion  a  sensible 
evolution  of  heat,  but  without  flame  and  open  combustion.  The  absorption  of 
oxygen  by  spirituous  liquors  in  becoming  acetic  acid,  and  by  many  other  organic 


230  OXYGEN. 

substances,  is  always  attended  with  the  production  of  heat.  The  smouldering  com- 
bustion of  iron  pyrites  and  some  other  metallic  ores  in  the  atmosphere,  is  a  pheno- 
menon of  the  same  nature.  Most  bodies  which  burn  with  flame  also  admit  of  being 
oxidated  at  a  temperature  short  of  redness,  and  exhibit  the  phenomenon  of  low  com- 
bustion. Thus,  tallow  thrown  upon  an  iron  plate  not  visibly  red-hot,  melts  and 
undergoes  oxidation,  diffusing  a  pale  lambent  flame  visible  only  in  the  dark  (Dr.  C. 
J.  B.  Williams).  If  the  tallow  be  heated  in  a  little  cup  with  a  wire  attached,  till 
it  boils  and  catches  fire,  and  the  flame  then  be  blown  out,  the  hot  tallow  will  still 
continue  in  a  state  of  low  combustion,  of  which  the  flame  may  not  be  visible,  but 
which  is  sufficient  to  cause  the  renewal  of  the  high  combustion,  if  the  cup  is  imme- 
diately introduced  into  a  jar  of  oxygen  gas.  A  candle  newly  blown  out  is  sometimes 
rekindled  in  oxygen,  although  no  point  of  the  wick  remains  visibly  red,  owing  to  the 
continuance  of  this  low  combustion.  When  a  coil  of  thin  platinum  wire,  or  a  piece 
of  platinum  foil,  is  first  heated  to  redness,  and  then  held  over  a  vessel  containing 
ether  or  hot  alcohol,  the  vapours  of  these  substances,  mixed  with  the  air,  oxidate 
upon  the  hot  metallic  surface,  and  may  sustain  the  metal  at  a  red  heat  for  a  long 
time,  without  the  occurrence  of  combustion  with  flame.  The  product,  however,  of 
the  low  combustion  of  these  bodies  is  peculiar,  as  is  obvious  from  its  pungent 
odour. 

Combustion  in  air.  —  The  affinity  for  oxygen  of  all  ordinary  combustibles  is 
greatly  promoted  by  heating  them,  and  is  indeed  rarely  developed  at  all  except  at  a 
high  temperature.  Hence,  to  determine  the  commencement  of  combustion,  it  is 
commonly  necessary  that  the  combustible  be  heated  to  a  certain  point.  But  the 
degree  of  heat  necessary  to  inflame  the  combustible  is  in  general  greatly  inferior  to 
what  is  evolved  during  the  progress  of  the  combustion,  so  that  a  combustible,  once 
inflamed,  maintains  itself  sufficiently  hot  to  continue  burning  till  it  is  entirely  con- 
sumed. Here  the  difference  may  be  observed  between  combustion  and  simple  igni- 
tion. A  brick  heated  till  it  be  red-hot  in  a  furnace,  and  taken  out,  exhibits  ignition, 
but  has  no  means  within  itself  of  sustaining  a  high  temperature,  and  soon  loses  the 
heat  which  it  had  acquired  in  the  fire,  and  on  cooling  is  found  unchanged. 

The  oxidable  constituents  of  wood,  coal,  oils,  tallow,  wax,  and  all  the  ordinary 
combustibles,  are  the  same,  namely,  carbon  and  hydrogen,  which  in  combining  with 
oxygen,  at  a  high  temperature,  always  produce  carbonic  acid  and  water;  volatile 
bodies,  which  disappear,  forming  part  of  the  aerial  column  that  rises  from  the  burn- 
ing body.  The  constant  removal  of  the  product  of  oxidation,  thus  effected  by  its 
volatility,  greatly  favours  the  progress  of  combustion  in  such  bodies,  by  permitting 
the  free  access  of  air  to  the  unconsumed  combustible.  The  influence  of  air  in  com- 
bustion is  obvious  from  the  facility  with  which  a  fire  is  checked  or  extinguished 
when  the  •  supply  of  air  is  lessened  or  withheld,  and,  on  the  contrary,  revived  and 
animated  when  the  supply  of  air  is  increased  by  blowing  up  the  fire.  For  the 
oxygen  of  the  air  being  consumed  in  combining  with  the  combustible,  a  constant 
renewal  of  it  is  necessary.  Hence,  if  a  lighted  taper,  floated  by  a  cork  upon  water, 
be  covered  with  a  bell  jar  having  an  opening  at  top,  such  as  that  in  which  the  iron- 
wire  was  burned,  the  taper  will  burn  for  a  short  time  without  change,  then  more  and 
more  feebly,  in  proportion  as  the  oxygen  is  exhausted,  and  at  last  will  expire.  The 
air  remaining  in  the  jar  is  no  longer  suitable  to  support  combustion,  and  a  second 
lighted  taper  introduced  into  it  by  the  opening  at  top  is  immediately  extinguished. 

In  combustion,  no  loss  whatever  of  ponderable  matter  occurs ;  nothing  is  annihi- 
lated. The  matter  formed  may  always  be  collected  without  difficulty,  and  is  found 
to  have  exactly  the  weight  of  the  oxygen  and  combustible  together  which  have  dis- 
appeared. The  most  simple  illustrations  of  this  fact  are  obtained  in  the  combustion 
of  those  bodies  which  afford  a  solid  product.  *  Thus  when  two  grains  of  phosphorus 
are  kindled  in  a  measured  volume  of  oxygen  gas,  they  are  found  converted  after 
Combustion  into  a  quantity  of  white  powder  (phosphoric  acid),  which  weighs  4$ 
grains,  or  the  phosphorus  acquires  2£  grains;  at  the  same  time  7-}  cubic  inches 
of  oxygen  disappear,  which  weigh  exactly  2£  grains.  In  the  same  way,  when  iron- 


OXYGEN. 


231 


FIG.  100. 


wire  is  burned  in  oxygen,  the  weight  of  solid  oxide  produced  is  found  to  be  equal 
to  that  of  the  wire  originally  employed  added  to  that  of  the  oxygen  gas  which  has 
disappeared.  But  the  oxidation  of  mercury  affords  a  more  complete  illustration  of 
what  occurs  in  combustion.  Exposed  to  a  moderate  degree  of  heat  for  a  considerable 
time  in  a  vessel  filled  with  oxygen,  that  metal  is  converted  into  red  scales  of  oxide, 
possessing  the  additional  weight  of  a  certain  volume  of  oxygen  which  has  disappeared. 
But  if  the  oxide  of  mercury  so  produced  be  then  put  into  a  small  retort,  and  recon- 
verted by  a  red  heat  into  oxygen  and  fluid  mercury,  the  quantity  of  oxygen  emitted 
is  found  to  be  the  same  as  had  combined  with  the  mercury  in  the  first  part  of  the 
operation;  thus  proving  that  oxygen  is  really  present  in  the  oxidized  body. 

The  evolution  of  heat,  which  is  the  most  striking  phenomenon  of  combustion,  still 
remains  to  be  accounted  for.  It  has  been  referred  to  the  loss  of  latent  heat  by  the 
combustible  and  oxygen,  when,  from  the  condition  of  gas  or  liquid,  one  or  both 
become  solid  after  combustion }  to  a  reduction  of  capacity  for  heat,  the  specific  heat 
of  the  product  being  supposed  to  be  less  than 
that  of  the  bodies  burned ;  and  to  a  discharge 
of  the  electricities  belonging  to  the  different 
bodies,  occurring  in  the  act  of  combination. 
But  the  first  two  hypotheses  are  manifestly 
insufficient,  and  the  last  is  purely  speculative. 
The  evolution  of  heat  during  intense  chemical 
combination,  such  as  oxidation,  may  be  received 
at  present  as  an  ultimate  fact ;  but  if  we  choose 
to  go  beyond  it,  we  must  suppose  that  the  heat 
exists  in  a  combined  and  latent  state  in  either 
the  oxygen  or  combustible,  or  in  both  j  that 
each  of  these  bodies  is  a  compound  of  its  ma- 
terial basis  with  heat,  the  whole  or  a  definite 
quantity  of  which  they  throw  off  on  combining 
with  each  other.  Heat,  like  other  material 
substances,  is  here  supposed  not  to  evince  its 
peculiar  properties  while  in  a  state  of  combina- 
tion with  other  matter,  but  only  when  isolated 
and  free.  This  view  gives  a  literal  character 
to  the  expressions  —  liberation,  disengagement, 
and  evolution  of  heat  during  combus- 
tion. The  phenomenon,  it  is  to  be 
remembered,  is  not  confined  to  oxida- 
tion, but  occurs  in  an  equal  degree  in 
combinations  without  oxygen,  and  in- 
deed to  a  greater  or  less  extent  in  all 
chemical  combinations  whatever. 

Pure  oxygen  has  not  as  yet  found 
any  considerable  application  in  the  arts. 
But  by  the  chemist  it  is  applied  to  sup- 
port combustion  with  the  view  of  pro- 
ducing intense  heat.  A  jet  of  this  gas 
from  a  gas-holder  (fig.  100),  thrown 
upon  the  flame  of  a  spirit-lamp,  pro- 
duces a  blow-pipe  flame  of  great  inten- 
sity, adequate  to  fuse  platinum.  Or, 
if  coal-gas  be  conducted  to  the  oxygen 
jet  (fig.  101),  and  the  gases  kindled 
as  they  issue  together,  a  flame  is  pro- 
ducod  of  equally  high  temperature. 
Where  a  large  quantity  of  oxygen  is 


FIG.  101. 


232  HYDROGEN. 

required,  as  in  this  application  of  it,  the  gas  may  be  obtained  by  heating  oxide  of 
manganese  in  a  cylinder  of  cast  iron  supported  over  a  furnace,  like  the  retort  for 
coal  gas.  The  calcined  oxide  does  not  regain  its  oxygen  when  afterwards  exposed  to 
the  air,  as  was  once  supposed,  but  would  still  be  of  some  value  in  the  preparation 
of  chlorine. 

Ozone.  —  When  electric  sparks  are  taken  through  perfectly  dry  oxygen,  a  small 
portion  of  the  gas  acquires  new  properties,  according  to  A.  de  la  Rive,  and  is  sup- 
posed by  Berzelius  to  pass  into  an  allatropic  condition,  in  which  it  is  named  ozone 
from  the  peculiar  odour  it  possesses,  and  which  is  somewhat  metallic  in  character. 
The  oxygen  evolved  from  the  decomposition  of  water  in  the  voltameter  (page  221) 
has  the  same  odour.  But  the  most  ready  mode  of  producing  it  is  to  place  a  few 
sticks  of  phosphorus  in  a  quart  bottle  containing  a  little  water  at  the  bottom  of  it- 
While  the  sticks  of  phosphorus  undergo  the  low  combustion  and  are  luminous,  pro- 
ducing fumes  of  phosphorus  acid  and  absorbing  much  oxygen,  they  give  rise  to  the 
appearance  of  ozone  in  the  air  of  the  bottle  in  a  manner  not  at  present  understood. 

This  substance  has  never  been  obtained  in  a  separate  state,  but  air  impregnated 
with  it  acts  very  much  as  if  a  trace  of  chlorine  gas  were  present,  which  ozone  appears 
to  resemble.  In  ozonized  air,  paper  impregnated  with  a  solution  of  iodide  of  potas- 
sium immediately  becomes  brown  from  the  liberation  of  iodine ;  also  paper  contain- 
ing a  solution  of  sulphate  of  manganese  soon  becomes  brown  or  black,  from  the 
formation  of  binoxide  of  manganese.  The  same  air  made  to  stream  through  a  solu- 
tion of  the  yellow-ferrocyanide  of  potassium  converts  it  into  the  red  ferricyanide. 
Ozone  appears  to  be  a  gas  not  sensibly  dissolved  by  water.  It  is  destroyed  by  a 
heat  of  140°,  by  contact  with  olefiant  gas,  and  such  other  hydrocarbons  as  combine 
with  chlorine,  by  phosphorus,  or  reduced  silver.  In  the  latter  case  nothing  appears 
except  oxide  of  silver.  It  passes,  I  find,  through  dry  and  porous  stoneware,  and  is 
therefore  not  likely  to  be  merely  an  electrical  grouping  of  gaseous  molecules.  Pro- 
fessor Schqnbein,  who  named  this  substance,  and  has  made  it  the  object  of  many 
investigations,  considers  it  to  be  a  volatile  peroxide  of  hydrogen.  [See  Supple- 
ment, p.  759.] 


SECTION   II. 


HYDROGEN. 

Equivalent  1,  as  the  basis  of  the  Hydrogen  Scale,  or  12-5  (00^0^71= 100);  symbol 
H;  density  69-26  (air  1000);  cpmbining  measure  \    \    \  (two  volumes'). 

Hydrogen  gas,  which  was  long  confounded  with  other  inflammable  airs,  was  first 
correctly  described  by  Cavendish,  in  1766.  It  does  not  exist  uncombined  in  nature ; 
at  least  the  atmosphere  does  not  contain  any  appreciable  proportion  of  hydrogen. 
But  it  is  one  of  the  elements  of  water,  and  enters  into  nearly  every  organic  sub- 
stance. Its  name  is  derived  from  i>Swp,  water,  and  yswow,  I  give  rise  to,  and  refers 
to  its  forming  water  when  oxidated. 

Preparation.  —  This  element,  although  resembling  oxygen  in  being  a  gas,  appears 
to  be  more  analogous  to  a  metal  in  its  relations  to  other  elements.  By  heating  oxide 
of  mercury,  it  is  resolved  into  oxygen  and  mercury ;  and  several  other  metallic 
oxides,  such  as  those  of  silver  and  gold,  are  susceptible  of  a  similar  decomposition. 
But  some  others  are  deprived  of  only  a  portion  of  their  oxygen  by  the  most  intense 
heat,  such  as  binoxide  of  manganese ;  and  many,  such  as  the  protoxide  of  lead,  are 
not  decomposed  at  all  by  simple  calcination.  By  igniting  the  latter  oxide,  however, 
mixed  with  charcoal,  its  oxygen  goes  off  in  combination  with  carbon,  as  carbonic 
oxide,  and  the  lead  is  left.  The  oxide  of  hydrogen -or  water  is  similarly  affected. 
Potassium  and  sodium  brought  into  contact  with  it,  at  the  temperature  of  the  air, 


HYDROGEN.  233 

combine  with  its  oxygen,  and  are  converted  into  the  oxides,  potassa  and  soda;  and 
hydrogen  is  consequently  liberated. 

Iron  and  many  other  metals  decompose  water,  and  become  oxides,  at  a  red  heat. 
Hence,  hydrogen  gas  is  sometimes  procured  by  transmitting  steam  through  an  iron 
tube  filled  with  iron  turnings,  placed  across  a  furnace  and  heated  red-hot  (fig.  102). 

Fia.  102. 


The  vapour  is  obtained  by  boiling  water  in  the  small  retort  a,  and  the  gas  pro- 
duced by  its  decomposition  collected  in  the  usual  manner  at  the  pneumatic  trough. 
But  it  is  necessary  to  have  a  flask  b  between  the  iron  tube  and  the  trough,  to  pre- 
vent an  accident  from  the  water  of  the  trough  finding  access  to  the  red-hot  tube,  in 
the  event  of  condensation  of  the  vapour  in  a. 

Some  other  compounds  of  hydrogen  are  decomposed  more  easily  than  water,  by 
iron  and  zinc.  The  chloride  of  hydrogen  or  hydrochloric  acid  is  decomposed  by 
these  metals,  and  evolves  hydrogen  at  the  ordinary  temperature  of  the  air.  But 
this  gas  is  more  generally  obtained  by  putting  pieces  of  zinc  or  iron  into  oil  of 
vitriol  or  the  concentrated  sulphuric  acid,  diluted  with  six  or  eight  times  its  bulk 
of  water.  The  hydrogen  is  then  derived  from  the  decomposition  of  the  proportion 
of  water  intimately  united  with  the  acid,  as  illustrated  in  the  following  diagram, 
zinc  being  used",  and  the  quantities  expressed : — 

Before  decomposition.  After  decomposition. 

49  oil  of  vitriol,  or  C  Hydrogen  1 1     Hydrogen. 

sulphate    of  -j  Oxygen  8 

water  (_  Sulphuric  acid    40 

32.52  zinc  Zinc 32.52 — 1^80.52    Sulphate    of 

oxide  of  zinc. 

81.52  81.52  81.52 

Or  by  symbols  : — 

H0  +  S03  and  Zn=ZnO  +  S03  and  H. 

The  zinc  dissolves  in  the  acid  with  effervescence,  from  the  escape  of  hydrogen  gas. 
It  will  be  observed  that  the  products  after  decomposition,  mentioned  in  the  last 
column,  hydrogen  and  sulphate  of  oxide  of  zinc,  are  similar  to  those  before  decom- 
position, in  the  first  column,  zinc  and  sulphate  of  water;  and  that  the  change  oc- 
curring is  simply  the  substitution  of  zinc  for  hydrogen  in  the  sulphate  of  water. 
The  large  quantity  of  water  used  with  the  acid  is  useful  to  dissolve  the  sulphate  of 
zinc  formed. 

Zinc  is  generally  preferred  to  iron,  in  the  preparation  of  hydrogen,  and  is  pre- 
viously granulated,  by  being  fused  in  a  stone-ware  crucible,  and  poured  into  water ; 
if  sheet  zinc  be  used,  which  is  better,  it  is  cut  into  small  pieces.  The  common  glass 
retort  may  be  used  in  the  experiment,  or  a  gas-bottle,  such  as  the  half-pound  phial 
'see  fig.  103),  with  a  cork  having  two  perforations  fitted  with  glass  tubes,  one  of 
which  descends  to  the  bottom  of  the  bottle,  and  is  terminated  externally  by  a  funnel 
for  introducing  the  acid,  whilst  the  other  is  the  exit  tube,  by  which  the  hydrogen 


234  HYDROGEN. 

escapes.     With  an  ounce  or  two  of  zinc  in  it,  tht 
Fm.  103  bottle  is  two-thirds  filled  with  water,  and  the  undi- 

luted acid  added  from  time  to  time  by  the  funnel, 
so  as  to  sustain  a  continued  effervescence.  No  gas 
escapes  by  the  funnel  tube,  as  its  extremity  within 
the  bottle  is  always  covered  by  the  fluid.  To  pro- 
duce large  quantities,  a  half-gallon  stone-ware  jar 
may  be  mounted  as  a  gas-bottle,  with  a  flexible  me- 
tallic pipe  fitted  to  the  cork  as  the  exit  tube.  This 
gas  may  be  collected,  like  oxygen,  either  in  jars 
over  the  pneumatic  trough,  or  in  the  gas-holder. 
The  first  jar  or  two  filled  will  contain  the  air  of  the 
gas-bottle,  and  therefore  must  not  be  considered  as 
pure  hydrogen.  One  ounce  of  zinc  is  found  to 
cause  the  evolution  of  615  cubic  inches  of  hydrogen 
gas. 

Properties.  —  Hydrogen  gas  thus  prepared  is 
not  absolutely  pure,  but  '  contains  traces  of  sul- 
phuretted hydrogen  and  carbonic  acid,  which  may  be  removed  by  agitating 
the  gas  with  lime-water  or  caustic  alkali.  It  has  also  a  particular  odour,  which 
is  not  essential  to  hydrogen,  as  the  gas  evolved  from  the  amalgam  of  sodium, 
acted  on  by  pure  water  without  acid,  is  perfectly  inodorous.  An  oily  compound  of 
carbon  and  hydrogen,  which  appears  to  be  the  cause  of  this  odour,  may  be  separated 
in  a  sensible  quantity  from  the  gas  prepared  by  iron,  by  transmitting  it  through 
alcohol.  Of  the  pure  gas,  water  does  not  dissolve  more  than  1J  per  cent,  of  its 
bulk.  Hydrogen  has  never  been  liquefied  by  cold  or  pressure. 

Hydrogen  is  the  lightest  substance  in  nature,  being  sixteen  times  lighter  than 
oxygen,  and  14.4  times  lighter  than  air;  100  cubic  inches  of  it  weigh  only  2.14 
grains.  Soap-bubbles  blown  with  this  gas  ascend  in  the  atmosphere;  and  it  is  used, 
as  is  well  known,  to  inflate  balloons,  which  begin  to  rise  when  the  weight  of  the 
stuff  of  which  they  are  made  and  the  hydrogen  together,  are  less  than  the  weight 
of  an  equal  bulk  of  air.  A  light  bag  is  prepared  for  making  this  experiment  in  the 
chamber,  by  distending  the  lining  membrane  of  the  crop  of  the  turkey,  which  may 
weigh  35  or  36  grains,  and  when  filled  with  hydrogen,  about  5  grains  more,  or  41 
grains;  the  same  bulk  of  air,  however,  would  weigh  50  or  51  grains;  so  that  the 
little  balloon  when  filled  with  hydrogen  has  a  buoyant  power  of  9  or  10  grains. 
Larger  bags  are  prepared  for  the  same  purpose,  of  gold-beaters'  skin.  Sounds  pro- 
duced in  this  gas  were  found  by  Leslie  to  be  extremely  feeble ;  much  more  feeble, 
indeed,  than  its  rarity  compared  with  air  could  account  for.  Hydrogen  may  be 
taken  into  the  lungs  without  inconvenience,  when  mixed  with  a  large  quantity  of 
air,  being  in  no  way  deleterious ;  but  it  does  not,  like  oxygen,  support  respiration, 
and  therefore  an  animal  placed  in  pure  hydrogen  soon  dies  of  suffocation.  A  lighted 
taper  is  extinguished  in  the  same  gas. 

Hydrogen  is  eminently  combustible,  and  burns  when  kindled  in  the  air  with  a 
yellow  flame  of  little  intensity,  which  moistens  a  dry  glass  jar  held  over  it;  the  gas 
combining  with  the  oxygen  of  the  air  in  burning,  and  producing  water.  If  before 
being  kindled  the  gas  is  first  mixed  with  enough  of  air  to  burn  it  completely,  or 
with  between  two  and  three  times  its  volume,  and  then  kindled,  the  combustion  of 
the  whole  hydrogen  is  instantaneous  and  attended  with  explosion.  With  pure  oxygen, 
instead  of  air,  the  explosion  is  much  more  violent,  particularly  when  the  gases  are 
mixed  in  the  proportions  of  two  volumes  of  hydrogen  to  one  of  oxygen,  which  are 
the  proper  quantities  lor  combination.  The  combustion  is  not  thus  propagated 
through  a  mixture  of  these  gases,  when  either  of  them  is  in  great  excess.  The 
sound  in  such  detonations  is  occasioned  by  the  concussion  which  the  atmosphere  re- 
ceives from  the  sudden  dilatation  of  gaseous  matter,  in  this  case  of  steam,  which  is 
prodigiously  expanded  from  the  heat  evolved  in  its  formation.  ' 


HYDROGEN. 


235 


FIG.  104. 


A  musical  note  may  be  produced  by  means  of  these  detonations, 
when  they  are  made  to  succeed  each  other  very  rapidly.  If  hydro- 
gen be  generated  in  a  gas-bottle  (fig.  104),  and  kindled  as  it 
escapes  from  an  upright  glass  jet  having  a  small  aperture,  the  gas 
will  be  found  to  burn  tranquilly;  but  on  holding  an  open  glass 
tube  of  about  two  feet  in  length  over  the  jet,  like  a  chimney,  the 
flame  will  be  elongated  and  become  flickering.  A  succession  or 
little  detonations  is  produced,  from  the  gas  being  carried  up  and 
mixing  with  the  air  of  the  tube,  which  follow  each  other  so 
quickly  as  to  produce  a  continuous  sound  or  musical  note. 

Several  circumstances  affect  the  combination  of  hydrogen  with 
oxygen,  which  are  important.  These  gases  may  be  mixed  togethei 
iri  a  glass  vessel,  and  preserved  for  any  length  of  time  without 
combining.  But  combination  is  instantly  determined  by  name,  by 
passing  the  electric  spark  through  the  mixture,  or  even  by  intro- 
ducing into  it  a  glass  rod,  not  more  than  just  visibly  red-hoi. 
Hydrogen,  indeed,  is  one  of  the  more  easily  inflammable  gases. 
If  the  mixed  gases  be  heated  in  a  vessel  containing  a  quandcy  of  pulverized 
glass,  or  any  sharp  powder,  they  begin  to  unite  in  contact  with  the  foreign  body 
in  a  gradual  manner  without  explosion,  at  a  temperature  not  exceeding  660°. 
The  presence  of  metals  disposes  them  to  unite  at  a  stiil  lower  temperature ; 
and  of  the  metals,  those  which  have  no  disposition  of  themselves  to  oxidate,  such 
as  gold  and  platinum,  occasion  this  slow  combustion  at  the  lowest  temperature. 
In  1824,  Dobereiner  made  the  remarkable  discovery  thac  newly  prepared  spongy 
platinum  has  an  action  upon  hydrogen  mixed  with  oxygen,  independently  of.  its 
temperature,  and  quickly  becomes  red-hot  when  a  jet  of  hydrogen  is'  thrown 
upon  it  in  air,  combination  of  the  gases  being  effected  by  their  contact  with  the 
metal.  In  consequence  of  this  ignition  of  the  platinum  the  hydrogen  itself  is  soon 
inflamed,  as  it  issues  from  the  jet.  An  instrument  depending  upon  this  action  of 
platinum  has  been  constructed  for  producing  an  instantaneous  light.  Afterwards, 
Mr.  Faraday  observed,  that  the  divided  state  of  the  platinum,  although  favourable, 
is  not  essential  to  this  action ;  and  that  a  plate  of  that  metal,  if  its  surface  be  scru- 
pulously clean,  will  cause  a  combination  of  the  gases,  accompanied  with  the  same 
phenomena  as  the  spongy  platinum.  This  action  of  •platinum  is  manifested  at  tem- 
peratures considerably  below  the  freezing  point  of  water,  and  in  an  explosive  mixture 
largely  diluted  with  air  or  hydrogen.  Spongy  platinum,  made  into  pellets  with  a 
little  pipe-clay,  and  dried,  when  intro- 
duced into  mixtures  of  oxygen  and  hy- 
drogen will  be  found  to  cause  a  gradual 
and  silent  combination  of  the  gases,  in 
whatever  proportions  they  are  mingled, 
which  will  not  cease  till  one  of  them  is 
completely  exhausted.  The  theory  of  this 
effect  of  platinum  is  very  obscure.  It 
belongs  to  a  class  of  actions  depending 
upon  surface,  not  confined  to  that  metal, 
and  by  which  other  combustible  vapor- 
ous bodies  are  affected  besides  hydrogen. 

The  flame  of  hydrogen,  although  so 
slightly  luminous,  is  intensely  hot;  few 
combinations  producing  so  high  a  tem- 
perature as  the  combustion  of  hydro- 
gen. In  the  oxi-hydrogen  blow-pipe, 
oxygen  and  hydrogen  gases  are  brought 
by  tubes  o  and  h  (fig.  105),  from  dif- 
ferent gas-holders,  and  allowed  to 


FIG  105. 


236 


HYDROGEN. 


mix  immediately  before  they  escape  by  the  same  orifice,  at  which  they  are  inflamed. 
This  is  most  safely  effected  by  fixing  a  jet  for  the  oxygen  within  the  jet  of  hydrogen 
(fig.  106),  so  that  the  oxygen  is  introduced  into  the  middle  of  the  flame  of  hydrogen 


FIG.  106. 


— a  construction  first  proposed  by  Mr.  Maugham,  [first  made  and  used  by  Professor 
Hare.  —  R.  B.]  and  adapted  to  the  use  of  coal-gas  instead  of  hydrogen  by  Mr. 
Daniell.  (Phil.  Mag.  3d  ser.,  vol.  ii.  p.  57.)  Each  of  the  gases  may  be  more  con- 
veniently contained  in  a  separate  air-tight  bag  of  Macintosh  cloth  capable  of  holding 
from  4  to  6  cubic  feet  of  gas,  and  provided  with  press-boards.  These  require  to  be 
loaded  with  two  or  three  561bs.,  when  in  use,  to  send  out  the  gas  with  sufficient 

pressure.     At  this  flame  the  most 

Fia.  107.  refractory  substances,  such  as  pipe- 

clay, silica  and  platinum,  are  fused 
with  facility,  and  the  latter  even 
dissipated  in  the  state  of  vapour. 
The  flame  itself,  owing  to  the  ab- 
sence of  solid  matter,  is  scarcely 
luminous,  but  any  of  the  less  fusi- 
ble earths,  upon  which  it  is  thrown, 
— a  mass  of  quick-lime,  for  instance 
(a,  fig.  105) — is  heated  most  in- 
tensely, and  diffuses  a  light,  which, 
for  whiteness  and  brilliancy,  may  be  compared  to  that  of  the  sun.  With  the  requi- 
site supply  of  the  gases,  this  light  may  be  sustained  for  hours,  care  being  taken  to 
move  the  mass  of  lime  slowly  before  the  flame,  so  that  the  same  surface  may  not  be 
long  acted  upon  ]  for  the  high  irradiating  power  of  the  lime  is  soon  impaired,  it  is 
supposed  from  a  slight  agglutination  of  its  particles  occasioned  by  the  heat.  This 
light,  placed  in  the  focus  of  a  parabolic  reflector,  was  found  to  be  visible,  in  the 
direction  in  which  it  was  thrown,  at  a  distance  of  69  miles,  in  one  experiment  made 
by  Mr.  Drummond,  when  using  it  as  a  signal  light.  The  heating  effects  are  even 
more  intense  when  the  gases  are  forced  into  a  common  receptacle,  and  allowed  to 
escape  from  under  pressure,  but  there  is  the  greatest  risk  of  the  flame  passing  back 
through  the  exit  tube  and  exploding  the  mixed  gases ;  an  accident  which  would 
expose  the  operator  to  the  greatest  danger.  Mr.  Hemming' s  apparatus,  however, 
may  be  used  without  the  least  apprehensioTi.  A  common  bladder  is  used  to  hold 
the  mixture,  and  the  gas  before  reaching  the  jet,  at  which  it  is  burned,  is  made  to 
pass  through  his  safety  tube.  This  consists  of  a  brass  cylinder  about  six  inches 
long  and  three-fourths  of  an  inch  wide,  filled  with  fine  brass  wire  of  the  same 
length,  which  is  tightly  wedged  by  forcibly  inserting  a  pointed  rod  of  metal  into  the 
centre  of  the  bundle.  The  conducting  power  of  the  metallic  channels  through 
which  the  gas  has  then  to  pass  is  so  great  as  completely  to  intercept  the  passage  of 
flame.  A  similar  safety  tube  of  smaller  size  is  interposed  at  />,  in  fig.  105,  of  the 
first  arrangement. 

Hydrogen  is  capable  of  forming  two  compounds  with  oxygen,  namely,  water, 
which  is  the  protoxide,  and  the  binoxide  of  hydrogen. 

The  most  important  of  the  present  applications  of  hydrogen  gas  is  in  the  oxi- 
hydrogeu  blow-pipe.  It  has  been  superseded,  as  a  material  for  inflating  balloons, 
by  coal  gas,  the  balloon  being  proportionally  enlarged  to  compensate  for  the  less 
buoyancy  of  the  latter  gas.  [See  Supplement,  p.  7.62.] 


WATER. 


237 


PROTOXIDE   OF   HYDROGEN. — WATER. 

Equivalent  9,  or  112.5  on  the  oxygen  scale;  formula  H  +  0,  or  HO;  density  1; 
as  steam  622  (air  1000);  combining  measure  of  steam  \    \    \  . 

Mr.  Cavendish  first  demonstrated,  in  1781,  that  the  product  of  the  combustion 
of  hydrogen  and  oxygen  is  water.  He  burned  known  quantities  of  these  gases  in  a 
dry  glass  vessel,  and  found  that  water  was  formed  in  quantity  exactly  equal  to  the 
weights  of  the  gases  which  disappeared.  It  was  afterwards  established  by  Hum- 
boldt  and  Gay-Lussac,  that  the  gases  unite  rigorously  in  the  proportion  of  two 
volumes  of  hydrogen  to  one  volume  of  oxygen,  and  that  the  water  produced  by 
their  union  occupies,  while  it  remains  in  the  state  of  vapour,  exactly  two  volumes 
(page  126).  The  proportion  of  the  constituents  of  water  by  weight  was  determined 
with  great  care  by  Berzelius  and  Dulong.  Their  method  was  to  transmit  dry  hydro- 
gen gas  over  a  known  weight  of  the  black  oxide  of  copper,  contained  in  a  glass  tube, 
and  heated  to  redness  by  a  lamp.  The  gas  was  afterwards  conveyed  through  another 
weighed  tube  containing  the  hygrometric  salt,  chloride  of  calcium.  The  hydrogen 
gas  in  passing  over  the  oxide  of  copper,  combines  with  its  oxygen  and  forms  water, 
which  is  carried  forward  by  the  excess  of  hydrogen  gas,  and  absorbed  in  the  chloride 
of  calcium  tube.  The  weight  of  this  water  being  ascertained,  the  proportion  of 
oxygen  it  contains  is  determined  by  ascertaining  the  loss  which  the  oxide  of  copper 
has  sustained  :  the  difference  is  the  hydrogen. 

The  apparatus  for  such  an  experiment  is  illustrated  in  the  following  diagram 
(fig.  108).  The  oxide  of  copper  to  be  reduced  is  contained  in  F,  a  small  flask  of 

FIG.  108. 


hard  glass,  having  two  openings,  and  heated  by  a  spirit  lamp.  This  flask  communi- 
cates with  another,  G,  intended  to  receive  the  greater  part  of  the  water  produced  in 
the  experiment,  which  is  followed  by  a  bent  tube  H,  containing  fragments  of  pumice 
soaked  in  oil  of  vitriol,  intended  to  receive  the  last  portions.  The  hydrogen  gas  for 
this  purpose  must  be  very  pure,  and  thoroughly  dry.  It  is  evolved  slowly  from  a 
gas-bottle  A,  and  passes  through  a  second  bottle  B,  and  the  bent  tube  C,  both  con- 
taining a  concentrated  solution  of  caustic  potassa ;  and  afterwards  the  bent  tube  D, 
containing  a  solution  of  chloride  of  mercury  in  pumice :  and  lastly  through  the  bent 
tube  F,  containing  oil  of  vitriol  in  pumice,  proceeding  thence  entirely  purified  into 
F,  and  the  excess  of  hydrogen  gas  escaping  byjf.  Numerous  most  careful  experi- 


238  HYDROGEN. 

ments,  lately  executed  in  this  manner  by  M.  Dumas,  prove  that  water  consists 
exactly  by  weight  of  — 

Oxygen  ..............................  88-91  ........................  8 

Hydrogen  ...........................  11-09  ........................  1 


The  oxygen  and  hydrogen  are  therefore  combined  exactly  in  the  proportion  of  8 
to  1,  as  appears  by  the  proportions  of  the  last  column.  This  experiment  serves  not 
only  to  determine  rigorously  the  composition  of  water,  but  it  offers  also  the  best 
method  of  ascertaining  the  composition  of  such  metallic  oxides  as  are  de-oxidized 
by  hydrogen. 

Properties.  —  When  cooled  down  to  32°,  water  freezes,  if  in  a  state  of  agitation, 
but  may  retain  the  liquid  condition  at  a  lower  temperature,  if  at  rest  (page  60)  ;  the 
ice,  however,  into  which  it  is  converted  cannot  be  heated  above  32°  without  melting. 
Ice  is  lighter  than  water,  its  specific  gravity  being  0-916  ;  and  one  of  the  forms 
(fig.  109)  of  its  crystal  is  a  rhomboid,  very  nearly  resembling  Iceland  spar. 

FIG.  109. 


Water  is  elastic  and  compressible,  yielding,  according  to  Oersted,  53  millionths 
of  its  bulk  to  the  pressure  of  the  atmosphere,  and,  like  air,  in  proportion  to  the 
compressing  force  for  different  pressures.  The  peculiarities  of  its  expansion  by  heat, 
while  liquid,  have  already  been  fully  described  (page  38).  Under  a  barometric 
pressure  of  30  inches,  it  boils  at  212°,  but  evaporates  at  all  inferior  temperatures 
Its  boiling  point  is  elevated  by  the  solution  of  salts  in  it,  and  the  temperature  of 
the  steam  from  these  solutions  is  not  constantly  212°,  as  has  been  alleged,  but  that 
of  the  last  strata  of  liquid  through  which  the  steam  has  passed.  When  mixed  with 
air,  the  vapour  of  water  has  a  tendency  to  condense,  it  is  said,  in  vesicles,  which 
inclose  air ;  forming  in  this  condition  the  masses  of  clouds,  which  remain  suspended 
in  the  atmosphere  from  the  lightness  of  the  vesicles,  the  substance  of  mists  and  fogs, 
and  "  vapour"  generally,  in  its  popular  meaning.  The  vesicles  may  be  observed  by 
a  lens  of  an  inch  in  focal  length,  over  the  dark  surface  of  hot  tea  or  coffee,  mixed 
with  an  occasional  solid  drop  which  contrasts  with  them.  According  to  the  experi- 
ments of  Saussure,  made  upon  the  mists  of  high  mountains,  these  vesicles  generally 
vary  in  size  from  the  l-4500th  to  the  1-2 780th  of  an  inch,  but  are  occasionally 
observed  as  large  as  a  pea.  They  are  generally  condensed  by  their  collision  into 
solid  drops,  and  fall  as  rain ',  but  their  precipitation  in  that  form  is  much  retarded 
in  some  conditions  of  the  atmosphere.  It  is  proper  to  add,  however,  that  Prof.  J. 
Forbes  and  several  other  eminent  meteorologists  disbelieve  entirely  the  existence  of 
vesicular  vapour. 

It  was  lately  discovered  by  Mr.  Grove  that  the  vapour  of  water  is  decomposed  to 
a  small  but  sensible  extent  by  an  exceedingly  high  temperature,  and  resolved  into 
its  constituent  gases.  If  a  small  ball  of  platinum,  of  the  size  of  a  large  pea,  with  a 
wire  attached  to  it,  be  heated  in  the  flame  of  the  oxi-hydrogen  blow-pipe  to  bright 
whiteness,  and  till  it  begins  to  show  symptoms  of  fusion,  and  then  plunged  into  hot 
water,  minute  bubbles  of  gas  rise  with  the  steam,  which  consist  of  a  mixture  of 
oxygen  and  hydrogen.  Only  a  small  portion  of  the  steam,  not  amounting  to  even 


WATER.  239 

one-thousandth  part  of  the  whole  produced  (it  is  supposed)  suffers  decomposition. 
The  occurrence  of  a  decomposition  in  such  circumstances,  which  is  unquestionable, 
appears  singular,  seeing  that  oxygen  and  hydrogen  certainly  combine  at  the  same, 
or  even  a  higher,  temperature  in  the  flame  of  the  blow-pipe,  which  is  employed  to 
heat  the  platinum  ball.  The  combustion  in  the  blow-pipe  may,  indeed,  be  incom- 
plete, but  this  is  unlikely,  for  I  find  that  when  the  mixed  gases  are  exploded  in  a 
glass  tube,  the  combustion  is  so  complete  that  certainly  not  one  part  in  four  thousand, 
if  any  portion  whatever,  escapes  combustion.  It  is  a  question  whether  the  decom- 
position  of  the  steam  by  ignited  platinum  is  not  an  exhibition  of  the  deoxidizing 
action  of  light  rather  than  the  effect  of  heat  j  the  blow-pipe  flame  itself  being  scarcely 
visible,  while  the  decomposing  platinum,  although  necessarily  of  a  lower  tempera- 
ture, is  highly  incandescent. 

A  cubic  inch  of  water  at  62°,  Bar.  30  inches,  weighs  in  air  252.458  grains.  The 
imperial  gallon  has  been  defined  to  contain  10  pounds  avoirdupois  (70,000  grains) 
of  distilled  water  at  that  temperature  and'  pressure.  Its  capacity  is  therefore  277.19 
cubic  inches.  The  specific  gravity  of  water  at  60°  is  1,  being  the  unit  to  which  the 
densities  of  all  other  liquids  and  solids  are  conveniently  referred  j  it  is  815  times 
heavier  than  air  at  that  temperature. 

In  its  chemical  relations  water  is  eminently  a  neutral  body.  Its  range  of  affinity 
is  exceedingly  extensive,  water  forming  definite  compounds,  to  all  of  which  the  name 
hydrate  is  applied,  with  both  acids  and  alkalies,  with  a  large  proportion  of  the  salts, 
and  indeed  with  most  bodies  containing  oxygen.  It  is  also  the  most  general  of  all 
solvents.  Gay»Lussac  has  observed  that  the  solution  of  a  salt  is  uniformly  attended 
with  the  production  of  cold,  whether  the  salt  be  anhydrous  or  hydrated,  and  that, 
on  the  contrary,  the  formation  of  a  definite  hydrate  is  always  attended  with  heat ;  a 
circumstance  which  indicates  an  essential  difference  between  solution  and  chemical 
combination  (Ann.  de  Ch.  et  de  Phys.  t.  Ixx.  p.  407).  Even  the  dilution  of  strong 
solutions  of  some  salts,  such  as  those  of  ammonia,  occasions  a  fall  of  temperature. 
The  solvent  power  of  water  for  most  bodies  increases  with  its  temperature.  Thus 
at  57°  water  dissolves  one-fourth  of  its  weight  of  nitre,  at  92°  one-half,  at  131°  an 
equal  weight,  and  at  212°  twice  its  weight  of  that  salt.  Solutions  of  such  salts,  satu- 
~ated  at  a  high  temperature,  deposit  crystals  on  cooling.  But  the  crystallization  of 
some  saturated  solutions  is  often  suspended  for  a  time,  in  a  remarkable  manner,  and 
afterwards  determined  by  slight  causes.  Thus,  if  two  pounds  of  crystallized  sulphate 
of  soda  be  dissolved  in  one  pound  of  water,  with  the  assistance  of  heat,  and  the  solu- 
tion be  filtered  while  hot  through  paper,  to  remove  foreign  solid  particles,  and  then 
set  aside  in  a  glass  matrass,  with  a  few  drops  of  oil  on  its  surface,  it  may  become 
perfectly  cold  without  crystallization  occurring.  Violent  agitation  even  may  not 
cause  it  to  crystallize.  But  when  any  solid  body,  such  as  the  point  of  a  glass  rod, 
or  a  grain  of  salt,  is  introduced  into  the  solution,  crystals  immediately  begin  to  form 
about  the  solid  nucleus,  and  shoot  out  in  all  directions  through  the  liquid.  The 
solubility  of  many  salts  of  soda  and  lime  does  not  increase  with  the  temperature, 
like  that  of  other  salts. 

Water  is  also  capable  of  dissolving  a  certain  quantity  of  air  and  other  gases,  which 
may  again  be  expelled  from  it  by  boiling  the  water,  or  by  placing  it  in  vacuo.  Rain- 
water generally  affords  2£  per  cent,  of  its  bulk  of  air,  in  which  the  proportion  of 
oxygen  gas  is  so  high  as  32  per  cent.,  and  in  water  from  freshly  melted  snow  34.8 
per  cent.,  according  to  the  observations  of  G-ay-Lussac  and  Humboldt,  while  the 
oxygen  in  atmospheric  air  does  not  exceed  21  per  cent.  Boussingault  finds  that  the 
quantity  of  air  retained  by  water,  at  an  altitude  of  6  or  8000  feet,  is  reduced  to 
one-third  of  its  usual  proportion.  Hence  it  is  that  fishes  cannot  live  in  Alpine  lakes, 
the  air  contained  in  the  water  not  being  in  adequate  quantity  for  their  respiration 
The  following  table  exhibits  the  absorbability  of  different  gases  by  water  deprived 
of  all  its  air  by  ebullition  :  — 


240 


HYDROGEN. 


100  cubic  inches  of  water  at  60°  and  30  Bar.,  absorb  of 

Henry. 

106 
100 


Dalton. 

Hydrosulphuric  acid 100  C.  I. 

Carbonic  acid...  .  100 


Saussure. 
253 
106 
76 
15.5 
65 
6.2 
4.2 
4.6 


Nitrous  oxide 100  77.6 

Olefiant  gas 12.5  14 

Oxygen 3.7  3.55 

Carbonic  oxide 1.56  2.01 

Nitrogen , 1.56  1.47 

Hydrogen 1.64                   1.53 

The  results  of  Saussure  are  probably  nearest  the  truth  for  hydrosulphuric  acid  and 
nitrous  oxide,  but  for  the  other  gases  those  of  Dalton  (Manchester  Memoirs,  2d  ser. 
p.  287)  and  Henry  (Phil.  Trans.  1843,  pp.  29,  274)  are  most  to  be  depended  on.* 

Uses.  —  Rain  received  after  it  has  continued  to  fall  for  some  time  may  be  taken 
as  pure*  water,  excepting  for  the  air  it  contains.  But  after  once  touching  the  soil, 
it  becomes  impregnated  with  various  earthy  and  organic  matters,  from  which  it  can 
only  be  completely  purified  by  distillation.  A  copper  still  should  be  used  for  that 
purpose,  provided  with  a  copper  or  block-tin  worm,  which  is  not  used  for  the  distil 
lation  of  spirits,  as  traces  of  alcohol  remaining  in  the  worm  and  becoming  acetic  acid, 
cause  the  formation  of  acetate  of  copper,  which  would  be  washed  out  and  contami- 
nate the  distilled  water.  The  use  of  white  lead  cement  about  the  joinings  of  the 
worm  is  also  to  be  avoided,  as  the  oxide  of  lead  is  readily  dissolved  by  distilled 
water.  The  first  portions  of  the  distilled  water  should  be  rejected,  as  they  often 
contain  ammonia,  and  the  distillation  should  not  be  carried  to  dryness. 

Water  employed  for  economical  purposes  is  generally  submitted  to  a  more  simple 
process,  that  of  filtration,  by  which  it  is  rendered  clear  and  transparent  by  the 
removal  of  matter  mechanically  suspended  in  it.  Such  foreign  matter  may  often  be 
removed  in  a  considerable  degree  by  subsidence,  on  which  account  it  is  desirable  that- 
the  water  should  stand  at  rest  for  a  time,  before  being  filtered.  The  filtration  of 
liquids  generally  is  effected,  on  the  small  scale,  by  allowing  them  to  flow  through 
unsized  or  filter  paper,  and  that  of  water,  on-  the  large  scale,  by  passing  it  through 
beds  of  sand.  The  sand  preferred  for  that  purpose  is  not  fine,  but  gravelly,  and 
crushed  cinders  or  furnace  clinkers  may  be  substituted  for  it.  Its  function,  as  that 
also  of  the  paper  in  the  chemist's  filter,  is  to  act  as  a  support,  for  the  finer  particles 
of  mud  or  precipitate  which  are  first  deposited  on  its  surface,  and  form  the  bed  that 
really  filters  the  water.  When  the  mud  accumulates  so  as  to  impede  the  action  of 
the  sand  filter,  the  surface  of  the  sand  is  scraped,  and  an  inch  or  two  of  it  removed. 

Fig.  110  is  a  section  of  the  water-filter,  as  it  is  usually  constructed  for  public 

FIG.  110. 


*  [See  Supplement,  p.  763.] 


WATER.  241 

works  in  Lancashire.  An  excavation  of  about  six  feet  in  depth,  and  of  sufficient 
extent,  is  lined  to  a  considerable  thickness  with  well  puddled  clay,  to  make  it  water- 
tight. Upon  the  clay  floor  is  laid  first  a  stratum  of  large  stones,  then  a  stratum  of 
smaller  stones,  and,  finally,  a  bed  of  coarse  sand  or  gravel,  L  L.  To  allow  the  air 
to  escape  from  the  lower  beds,  small  upright  tubes,  open  at  both  ends,  B  and  C,  are 
inserted  in  these  beds,  and  rising  above  the  surface  of  the  water  W  W.  The  filtered 
water  enters,  from  the  lowest  bed,  into  a  large  open  iron  cylinder  A,  the  lower  part 
of  which  is  perforated  for  that  purpose.  The  filtered  water  stands  at  the  same  height 
in  the  gauge  tube  D  as  in  A ;  this  height  is  observed  by  means  of  a  float  balanced 
by  a  weight  which  traverses  a  scale  of  feet  and  inches  at  D. 

Upward  filtration  through  a  bed  of  sand  is  sometimes  practised,  but  it  has  the 
disadvantage  that  the  filter  cannot  be  cleaned  in  the  manner  indicated.  Filtering 
under  high  pressure,  and  with  great  rapidity,  has  been  practised  in  a  very  compact 
apparatus,  consisting  of  a  box,  not  above  three  feet  square,  filled  with  sand.  This 
filter,  which  becomes  speedily  choked  with  the  mud  it  detains,  is  cleansed  by  sud- 
denly reversing  the  direction  in  which  the  water  is  passing  through  the  box,  which 
occasions  a  shock  that  has  the  effect  of  loosening  the  sand,  and  allowing  the  water 
to  bring  away  the  mud.  The  action  of  such  a  filter,  erected  at  the  Hotel-Dieu  of 
Paris,  was  favourably  reported  on  by  M.  Arago  ( Annal.  de  Chirn.  et  de  Phys.  t.  Ixv. 
p.  428). 

Matter  actually  dissolved  in  water  is  not  affected  by  filtration.  No  repetition  of 
the  process  would  withdraw  the  salt  from  sea-water  and  make  it  fresh.  Hence  the 
impregnation  of  peaty  matter,  which  river  water  generally  contains,  and  to  the 
greatest  extent  in  summer,  when  the  water  is  concentrated  by  evaporation,  is  not 
removed  by  filtering.  Animal  charcoal  is  the  proper  substance  for  discolouring 
liquids,  as  it  withdraws  organic  colouring  matter,  even  when  in  a  state  of  solution. 

In  the  process  of  clarifying  liquors  by  dissolving  in  them  the  white  of  egg  and 
other  albuminous  fluids,  the  temperature  is  raised  so  as  to  coagulate  the  albumen, 
which  thus  forms  a  delicate  net-work  throughout  the  liquid,  and  is  afterwards  thrown 
up  as  scum  in  the  boiling,  carrying  all  the  foreign  matter  suspended  in  the  liquid 
along  with  it. 

Gelatine,  isinglass,  or  other  "  finings,"  added  to  wine  in  a  turbid  state,  produce 
a  precipitate  with  its  tannin,  which  carries  down  all  suspended  matter;  and  on 
the  settling  of  this  precipitate,  or  its  separation  by  filtering,  the  wine  is  found 
transparent. 

The  most  usual  earthy  impurities  in  water,  occasioning  its  hardness,  are  sulphate 
of  lirne,  and  the  carbonate  of  lime  dissolved  in  carbonic  acid,  both  of  which  are 
precipitated  on  boiling  the  water,  and  occasion  an  earthy  incrustation  of  the  boiler. 

So  far  as  this  precipitation  is  due  to  carbonate  of  lime  it  may  be  avoided  by 
adding  hydrochlorate  of  ammonia  to  the  water,  by  which  the  lime  is  converted  into 
chloride  of  calcium  and  becomes  soluble.  Water  containing  carbonate  of  lime  may 
be  also  softened  by  the  addition  of  lime-water,  as  recommended  by  Professor  Clark. 
Thames  water  requires  for  this  purpose  the  addition  of  about  one-fourteenth  of  its 
bulk  of  lime-water.  This  action  of  lime-water  will  be  explained  under  carbonic  acid. 

When  waters  contain  iron,  they  are  termed  chalybeate :  this  metal  is  most  fre- 
quently in  the  state  of  carbonate  dissolved  in  carbonic  acid,  and  rarely  in  a  propor 
tion  exceeding  one  grain  in  a  pound  of  water.  The  sulphurous  waters,  which  are 
recognised  by  their  peculiar  odour,  and  by  blackening  silver  and  salts  of  lead,  con- 
tain hydrosulphuric  acid  in  a  proportion  not  exceeding  the  usual  proportion  of  air 
in  spring  water,  and  generally  no  oxygen.  Saline  waters  for  the  most  part  contain 
various  salts  of  lime  and  magnesia,  and  generally  common  salt.  Their  density  is 
always  considerably  higher  than  that  of  pure  water.  Sea-water  contains  3£  per 
cent,  of  saline  matter,  and  has  a  density  1.0274.  Its  composition  is  interesting,  as 
the  sea  comes  to  be  the  grand  depository  of  all  the  soluble  matter  of  the  globe.  A 
minute  analysis  of  the  water  of  the  English  Channel,  executed  by  Mr.  Schweitzer, 
is  subjoined:  — 
16 


242  HYDROGEN. 

Sea-water  of  the  English  Channel.  Grains. 

Water 964.74372 

Chloride  of  sodium 27.05948 

Chloride  of  potassium 0.76552 

Chloride  of  magnesium 3.66658 

Bromide  of  magnesium 0.02929 

Sulphate  of  magnesia 2.29578 

Sulphate  of  lime.... 1.40662 

Carbonate  of  lime 0.03301 

1000.0000 

In  addition  to  those  constituents,  distinct  traces  of  iodine  and  of  ammonia  were 
detected  (Phil.  Mag.  3d  ser.  vol.  xv.  p.  58).  According  to  Professor  Forchammer, 
the  whole  quantity  of  saline  matter  in  water  from  different  parts  of  the  Atlantic 
varied  from  35.7  parts  (German  sea)  to  36.6  parts  (tropics)  in  1000  parts  of  the 
water.  The  relative  proportion  of  the  salts  in  the  water  of  different  seas  varied  very 
little  (Reports  of  the  British  Association,  1846,  p.  90). 


BINOXIDE   OF    HYDROGEN. 

Equivalent,  17,  or  212.5  on  Oxygen  Scale;  formula  H  +  20  or  H02. 

The  second  compound  of  hydrogen  and  oxygen  is  a  liquid,  containing  twice  as 
much  oxygen  as  water,  and  is  a  body  possessed  of  very  extraordinary  properties. 
It  was  discovered  by  Thenard,  in  1818,  who  prepared  it  by  a  long  and  intricate 
process. 

Preparation.  —  The  formation  of  the  binoxide  of  hydrogen  depends  upon  the 
existenc#of  a  corresponding  binoxide  of  barium.  The  latter  is  obtained  by  calcining 
pure  nitrate  of  baryta  at  a  high  temperature  in  a  porcelain  retort,  and  afterwards 
exposing  the  earth  baryta  or  protoxide  of  barium,  which  is  left,  in  a  porcelain  tube 
heated  to  redness,  to  a  stream  of  oxygen  gas,  which  the  protoxide  rapidly  absorbs, 
becoming  binoxide.  Treated  with  a  little  water,  the  binoxide  of  barium  slakes  and 
falls  to  powder,  forming  a  hydrate,  of  which  the  formula  is  Ba02  +  HO.  Dilute 
acids  have  a  peculiar  action  upon  this  hydrate,  which  will  be  easily  understood,  if 
the  binoxide  of  barium  is  represented  as  the  protoxide  united  with  an  additional 
equivalent  of  oxygen,  or  as  BaO  +  0.  They  combine  with  the  protoxide  of  barium, 
forming  salts  of  baryta,  and  the  second  equivalent  of  oxygen,  instead  of.  being  libe- 
rated in  consequence,  unites  with  the  water  of  the  hydrate,  the  HO  of  the  preceding 
formula  giving  rise  to  HO-fO  or  the  binoxide  of  hydrogen,  which  dissolves  in  the 
water.  Although  it  would  be  inconvenient  to  abandon  the  systematic  ryime  binoxide 
of  hydrogen  for  this  compound,  still  it  must  be  allowed  that  ^the  properties  of  the 
body,  as  well  as  its  mode  of  preparation,  are  more  favourable  to  the  idea  of  its 
being  a  combination  of  water  with  oxygen,  or  oxygenated  water,  as  it  was  first 
named  by  its  discoverer,  than  a  direct  combination  of  its  elements.  It  is  recom- 
mended by  Thenard  to  dissolve  the  binoxide  of  barium  in  hydrochloric  acid  consi- 
derably diluted  with  water,  and  to  remove  the  baryta  by  sulphuric  acid,  which  forms 
an  insoluble  sulphate  of  baryta.  The  hydrochloric  acid,  again  free  in  the  liquor,  is 
saturated  a  second  time  with  binoxide  of  barium,  and  precipitated  ',  and  after  several 
repetitions  of  these  two  operations,  the  hydrochloric  acid  itself  is  removed  by  the 
cautious  addition  of  sulphate  of  silver,  and  the  sulphuric  acid  of  the  last  salt  by  solid 
baryta.  Such  is  an  outline  of  the  process,  but  its  success  requires  attention  to  a 
number  of  minute  precautions,  which  are  fully  detailed  in  the  Traite  de  Chemie  of 
the  author  quoted  (vol.  i.  p.  479,  6th  ed.)  The  weak  solution  of  binoxide  of 
hydrogen,  which  this  process  affords,  may  be  concentrated  by  placing  it  with  a  vessel 
f»f  strong  sulphuric  acid  under  the  receiver  of  an  air-pump,  until  the  solution  attains 


NITROGEN.  243 

a  density  of  1.452,  when  the  binoxide  itself  begins  to  rise  in  vapour  without  change. 
It  then  contains  475  times  its  volume  of  oxygen. 

M.  Pelouze  abridges  this  process  considerably  by  employing  hydro-fiuoric  acid  or 
fluosilicic  acid,  in  place  of  hydrochloric  acid,  to  decompose  the  binoxide  of  barium. 
By  this  operation,  the  baryta  separates  at  once  with  the  acid,  in  the  state  of  the  in- 
soluble fluoride  of  barium,  and  nothing  remains  in  solution  but  the  binoxide  of 
hydrogen.  After  thus  decomposing  several  portions  of  binoxide  of  barium  succes- 
sively in  the  same  liquor,  the  fluoride  of  barium  may  be  separated  by  filtration,  and 
the  binoxide  of  hydrogen,  which  is  still  dilute,  be  concentrated  by  means  of  the 
air-pump. 

Properties.  —  Binoxide  of  hydrogen  is  a  colourless  liquid  resembling  water,  but 
less  volatile,  having  a  metallic  taste,  and  instantly  bleaching  litmus  and  other  or- 
ganic colouring  matters.  It  is  decomposed  with  extreme  facility,  effervescing  from 
escape  of  oxygen  at  a  temperature  of  59°,  and  when  suddenly  exposed  to  a  greater 
heat,  such  as  212°,  actually  exploding  from  the  rapid  evolution  of  that  gas.  It  is 
rendered  more  permanent  by  dilution  with  water,  and  still  more  so  by  the  addition 
of  the  stronger  acids,  while  alkalies  have  the  opposite  effect. 

The  circumstances  attending  the  decomposition  of  this  body  are  the  most  curious 
facts  in  its  history.  Many  pure  metals  and  metallic  oxides  occasion  its  instantaneous 
resolution  into  water  and  oxygen  gas,  by  simple  contact,  without  undergoing  any 
change  themselves,  affording  a  striking  illustration  of  catalysis  (page  186);  and  this 
decomposition  may  excite  an  intense  temperature,  the  glass  tube  in  which  the  expe- 
riment is  made  sometimes  becoming  red  hot.  Some  protoxides  absorb  at  the  same 
time  a  portion  of  the  oxygen  evolved,  and  are  raised  to  a  higher  degree  of  oxidation, 
but  most  of  them  do  not;  and  certain  oxides,  such  as  the  oxides  of  silver  and  gold, 
are  reduced  to  the  metallic  state,  their  own  oxygen  going  off  along  with  that  of  the 
binoxide  of  hydrogen.  The  decomposition  of  these  metallic  oxides  cannot  be 
ascribed  to  the  heat  evolved,  for  oxide  of  silver  is  reduced  in  a  very  dilute  solution 
of  the  binoxide  of  hydrogen,  although  the  decomposition  is  not  then  attended  with 
a  sensible  elevation  of  temperature.  The  metallic  oxides  which  are  decomposed  in 
this  remarkable  manner  are  originally  formed  by  the  decomposition  of  other  com- 
pounds, and  not  by  the  direct  union  of  their  elements,  which,  in  fact,  exhibit  little 
affinity  for  each  other.  In  this  general  character  they  agree  with  binoxide  of  hydro- 
gen itself. 

Uses.  —  The  binoxide  of  hydrogen  is  a  substance  which  it  is  exceedingly  desirable 
to  possess,  with  the  view  of  employing  it  in  bleaching,  and  for  other  purposes,  as  a 
powerful  oxidating  agent.  But  the  expense  and  uncertainty  of  the  process  for  pre- 
paring this  compound  have  hitherto  prevented  any  application  of  it  in  the  arts,  or 
even  its  occasional  use  as  a  chemical  re-agent. 


SECTION  III. 

NITROGEN. 

Synonyme,  AZOTE.     Equiv.  14,  or  175  (0=100);  symbol  N;  density  971.37; 
combining  measure    |    |    |  • 

Dr.  Rutherford,  of  Edinburgh,  examined  the  air  which  remains  after  the  respira- 
tion of  an  animal,  and  found  that  after  being  washed  with  lime-water,  which  removes 
carbonic  acid,  it  was  incapable  of  supporting  either  combustion  or  respiration.  He 
concluded  that  it  was  a  peculiar  gas.  Lavoisier  afterwards  discovered  that  this  gas 
exists  in  the  air  of  the  atmosphere,  forming  indeed  4-5ths  of  that  mixture,  and  gave 
it  the  name  azote,  (from  a,  privative,  and  £w»7,  life),  from  its  inability  to  support  re- 
spiration. It  was  afterwards  named  nitrogen  by  Chaptal,  because  it  is  an  element 
of  nitric  acid.  Besides  existing  in  air,  nitrogen  forms  a  constituent  of  most  animal 


244  NITROGEN. 

and  of  many  vegetable  substances.    In  a  natural  arrangement  of  the  elements,  nitro- 
gen appears  to  have  its  place  between  oxygen  and  phosphorus  (page  147). 

Preparation* — Nitrogen  is  generally  procured  by  allowing  a  combustible  body  to 
combine  with  the  oxygen  of  a  certain  quantity  of  air  confined 
FIG.  111.  in  a  vessel.     For  that  purpose  a  little  metallic  or  porcelain 

cup  may  be  floated,  by  means  of  a  cork,  on  the  surface  of  the 
water-trough.  A  few  drops  of  alcohol  are  then  introduced 
into  the  cup,  or  a  small  piece  of  phosphorus  is  placed  in  it, 
and  being  kindled,  a  tall  bell  jar  is  held  over  the  cup,  with 
its  lip  in  the  water.  The  combustion  soon  terminates,  and 
the  water  of  the  trough  rises  in  the  jar.  Alcohol  does  not 
consume  the  oxygen  entirely,  a  small  portion  of  it  still  re- 
maining mingled  with  the  nitrogen ;  a  certain  quantity  of 
carbonic  acid  gas  is  also  produced  by  its  combustion.  But 
the  combustion  of  phosphorus  exhausts  the  oxygen  com- 
pletely, and  leaves  nitrogen  unmixed  with  any  other  gas. 

Nitrogen  may  be  likewise  conveniently  obtained  by  con- 
ducting chlorine  gas  into  diluted  ammonia.  For  delicate  purposes  of  research  this 
gas  is  best  prepared  by  carrying  air  through  a  tube  filled  with  reduced  metallic 
copper  in  a  pulverulent  form,  and  heated  to  redness,  by  which  the  oxygen  is  en- 
tirely absorbed. 

Properties. — Nitrogen  gas  is  tasteless  and  inodorous;  has  never  been  liquefied, 
and  is  less  soluble  in  water  than  oxygen.  It  is  a  little  lighter  than  air,  (specific 
gravity  .9714),  which  possesses  the  mean  density  of  79.1  volumes  of  nitrogen  and 
20.9  volumes  of  oxygen.  Nitrogen  is  a  singularly  inert  substance,  and  does  not 
unite  directly  with  any  other  single  element,  so  far  as  I  am  aware,  under  the  influ- 
ence of  light  or  of  a  high  temperature,  unless,  perhaps,  oxygen  and  carbon.  A 
burning  taper  is  instantly  extinguished  in  this  gas,  and  an  animal  soon  dies  in  it, 
not  because  the  gas  is  injurious,  but  from  the  privation  of  oxygen,  which  is  required 
in  the  respiration  of  animals.  Nitrogen  appears  to  be  chiefly  useful  in  the  atmo- 
sphere, as  a  diluent  of  the  oxygen,  thereby  repressing  to  a  certain  degree  the  activity 
of  combustion  and  other  oxidating  processes.  Of  the  fixation  of  free  nitrogen  of 
plants,  there  is  no  evidence.  When  heated  with  oxygen,  nitrogen  does  not  burn 
like  hydrogen,  nor  undergo  oxidation.  But  nitrogen  may  be  made  to  unite  with 
oxygen  by  transmitting  several  hundred  electric  sparks  through  a  mixture  of  these 
gases  in  a  tube,  with  water  or  an  alkali  present,  and  nitric  acid  is  produced.  The 
water  formed  by  the  combustion  of  hydrogen  in  air,  or  of  a  mixture  of  hydrogen 
and  nitrogen  in  oxygen,  has  often  an  acid  reaction,  which  is  due  to  a  trace  of  nitric 
acid.  But  when  the  hydrogen  is  mixed  with  air  in  excess,  so  as  to  prevent  great 
elevation  of  temperature  during  the  combustion,  the  oxidation  of  the  nitrogen  does 
not  take  place  (Kolbe).  Nitric  acid  is  also  a  product  of  the  oxidation  of  a  variety 
of  compounds  containing  nitrogen.  Ammonia  mixed  with  air,  on  passing  over 
spongy  platinum  at  a  temperature  of  about  572°,  is  decomposed,  and  the  nitrogen 
it  contains  is  completely  converted  into  nitric  acid,  by  combining  with  the  oxygen 
of  the  air.  Cyanogen  and  air,  under  similar  circumstances,  occasion  the  formation 
of  nitric  and  carbonic  acids.  (Kuhlman,  Phil.  Mag.  3d  ser.,  vol.  xiv.  p.  157). 
Nitric  acid  is  also  largely  produced  by  the  oxidation  of  organic  matters  during 
putrefaction  in  air,  when  an  alkali  or  lime  is  present,  as  in  the  natural  nitre  soils 
and  artificial  nitre  beds. 

A  suspicion  has  always  existed  that  nitrogen  may  be  a  compound  body,  but  it  has 

'  resisted  all  attempts  to  decompose  it,  and  the  evidence  of  its  elementary  character 

is  equally  good  with  that  of  most  other  bodies  reputed  simple.     Before  considering 

the  compounds  of  nitrogen  with  oxygen,  we  may  notice  the  properties  of  atmospheric 

air,  which^  is  regarded  as  a  mechanical  mixture  of  these  gases. 

*  ISee  Supplement,  p.  765.] 


THE    ATMOSPHEKE.  245 


THE    ATMOSPHERE. 

According  to  the  new  and  most  careful  determination  of  the  "weight  of  air  by  M. 
Regnault,  100  cubic  inches  of  atmospheric  air,  deprived  of  aqueous  vapour  and  the 
small  quantity  of  carbonic  acid  it  usually  contains,  weigh  30.82926  grains,  at  60° 
and  30  Bar.  Its  density  at  the  same  temperature  and  pressure  is  estimated  at  1C)00, 
and  is  conveniently  assumed  as  the  standard  of  comparison  for  the  densities  of 
gaseous  bodies,  as  water  is  for  solids  and  liquids.  Hence,  at  62°,  air  is  810  times 
lighter  than  water,  and  11,000  times  lighter  than  mercury.  The  bulk  of  air  varies 
with  its  temperature  and  the  pressure  affecting  it,  according  to  the  same  laws  as 
other  gases  (pages  40  and  8 1).1 

The  mean  pressure  of  the  atmosphere  at  the  surface  of  the  sea  is  generally  esti- 
mated as  equal  to  the  weight  of  a  column  of  mercury  of  30  inches  in  height,  which 
is  about  15  pounds  on  the  square  inch  of  surface,  and  is  equivalent  to  a  column  of 
water  of  nearly  34  feet  in  height.  The  oxygen  alone  is  equal  to  a  column  of  7.8 
feet  of  water  over  the  whole  earth's  surface,  from  which  an  idea  may  be  formed  of 
the  immense  quantity  of  that  element,  and  how  small  the  effect  must  be  of  the 
oxidating  processes  observed  at  the  earth's  surface  in  diminishing  it.  If  the  atmo- 
sphere were  of  uniform  density,  its  height,  as  inferred  from  the  barometer,  would 
be  11,000  times  30  inches,  or  5.208  miles,  but  the  density  of  air  being  proportional 
to  the  pressure  upon  it,  diminishes  with  its  elevation,  the  superior  strata  being  always 
more  rare  and  expanded  than  the  inferior  strata  upon  which  they  press. 

DENSITY   OF   THE    ATMOSPHERE. 

Height  above  the  sea  in  miles.  Volume. 

0  1 

2-705  2 

5-41  4 

8-115  8 

1082  16 

13-424  32 

16-23  64 

At  a  height  of  2.705  miles  (11,556  feet)  the  atmosphere  is  of  half  density,  by 
calculation,  or  one  volume  is  expanded  into  2,  and  the  barometer  would  stand  at  15 
inches ;  the  density  is  again  halved  for  every  2.7  miles  additional  elevation.  From 
calculations  founded  on  the  phenomena  of  refraction,  the  atmosphere  is  supposed  to 

1 1.  WEIGHT  OF  1  LITRE  OF  GASES,  at  0°  C.,  Bar.  0.76  metre  (Regnault). 

In  Grammes. 

Atmospheric  Air  1.293187 

Nitrogen ." 1.256167 

Oxygen  1.429802 

Hydrogen  0.089578 

Carbonic  Acid  1.977414 

II.  WEIGHT  or  100  CUBIC  INCHES  OF  GASES  ;  Bar.  29.92  inches. 

At  32°  F.  At  60°  F. 

In  Grains.  In  Grains. 

Atmospheric  Air 32.58684 30.82926 

Nitrogen 31.66020 29.95260 

Oxygen  36.13896 34.18979 

Hydrogen 2.16216 2.04554 

Carbonic  Acid  50.03856  47.33972 

Here  the  French  litre  is  taken  at  61.028  English  cubic  inches;  the  gramme  at  15.444f 
grains ;  and  the  volume  of  air  and  the  other  gases,  at  60°,  1.05701,  their  volume  at  32° 
being  1.  (Regnault,  Compt.  Rend.  t.  20,  p.  975). 


246  NITROGEN. 

extend,  in  a  state  of  sensible  density,  to  a  height  of  nearly  45  miles.  It  is  certainly 
limited,  probably  from  the  expansibility  of  the  aerial  particles  having  a  natural  limit 
(page  81).  The  atmospheric  pressure  also  varies  at  the  same  place,  from  the  effect 
of  winds  and  other  Causes,  which  are  not  fully  understood.  Hence  the  use  of  the 
barometer  as  a  weather  glass  j  for  wet  and  stormy  weather  is  generally  preceded  by 
a  fall  of  the  mercury  in  the  barometer,  and  fair  and  calm  weather  by  its  rise. 

The  temperature  of  the  atmosphere  is  greatest  at  the  earth's  surface,  and  has  been 
observed  to  diminish  one  degree  for  every  352  feet  of  ascent,  in  the  lower  strata. 
It  is  believed,  however,  that  the  progressive  diminution  is  less  rapid  at  great  distances 
from  the  earth.  But  at  a  certain  height,  the  region  of  perpetual  congelation  is 
attained  even  in  the  warmest  climates ;  the  summits  of  the  Andes,  which  rise  21,000 
feet,  being  perpetually  covered  with  snow  under  the  equator.  The  line  of  perpetual 
congelation,  which  has  been  fixed  at  15,207  feet  at  0°  latitude,  descends  progres- 
sively in  higher  latitudes,  being  3,818  feet  at  60°,  and  only  1,016  feet  at  75°.  The 
decrease  of  temperature  with  elevation  in  the  atmosphere  is  ascribed  to  two  causes. 
1.  To  the  property  which  air  has  of  becoming  cold  by  expansion,  which  arises  from 
an  increase  of  its  latent  heat  with  rarefaction.  The  actual  temperature  of  the  differ- 
ent strata  of  the  atmosphere  is  indeed  believed  to  be  that  due  to  their  dilatation, 
supposing  that  they  had  all  the  same  original  temperature  and  density  as  the  lowest 
stratum.  2.  To  the  circumstance  that  the  atmosphere  derives  its  heat  principally 
from  contact  with  the  earth's  surface.  The  sun's  rays  appear  to  suffer  little  absorp- 
tion in  passing  through  the  atmosphere;  but  there  are  some  observations  on  the 
force  of  solar  radiation  which  are  not  easily  reconciled  with  that  circumstance.  A 
thermometer  of  which  the  bulb  is  blackened,  rises  a  certain  number  of  degrees  above 
the  temperature  of  the  air,  when  exposed  to  the  sun,  but  the  rise  is  decidedly  greater 
on  high  mountains  than  near  the  level  of  the  sea,  and  in  temperate,  or  even  arctic 
climates,  which  is  more  remarkable,  than  within  the  tropics.  It  is  a  question  how 
solar  radiation  is  obstructed  in  the  hotter  climates  (Darnell's  Meteorological  Essays, 
2d  edit.) 

The  blue  colour  of  the  sky  has  been  found  by  Brewster  to  be  due  to  light  that 
has  suffered  polarization,  which  is  therefore  reflected  light,  like  the  white  light  of 
clouds.  The  air  of  the  atmosphere  must  therefore  have  a  disposition  to  absorb  the 
red  and  yellow  solar  rays,  and  to  reflect  the  blue  rays.  At  great  heights,  the  blue 
colour  of  the  sky  was  observed  by  Theodore  de  Saussure  to  become  deeper  and 
deeper,  being  mixed  with  black,  owing  to  the  absence  of  white  reflecting  vapour  or 
clouds.  The  red  and  golden  tints  of  clouds  appear  to  be  connected  with  a  remark- 
able property  of  steam  observed  by  Professor  J.  Forbes.  A  light  seen  at  night 
through  steam  issuing  into  the  atmosphere  from  under  a  pressure  of  from  5  to  30 
pounds  on  the  inch,  is  found  to  appear  of  a  deep  orange  red  colour,  exactly  as  if 
observed  through  a  bottle  containing  nitrous  acid  vapour.  The  steam,  when  it  pos- 
sesses this  colour,  is  mixed  with  air,  and  on  the  verge  of  condensation ;  and  it  is 
known  that  the  golden  hues  of  sunset  depend  upon  a  large  proportion  of  vapour  in 
the  air,  and  are  indeed  a  popular  prognostic  of  rain  (Phil.  Mag.  3d  ser.  vol.  xiv.  pp. 
121,  425,  and  vol.  xv.  pp.  25,  419.) 

Winds.  —  The  movement  of  masses  of  air,  or  wind,  is  always  produced  by  ine- 
quality of  temperature  of  the  atmosphere  at  different  points  of  the  earth's  surface, 
or  in  different  regions  of  the  atmosphere  of  equal  elevation.  The  primary  move- 
ment is  always  an  ascending  current,  the  heated  and  expanded  air  over  some  spot 
rising  in  a  vertical  column.  Dense  and  colder  air  flows  towards  that  point,  pro- 
ducing the  horizontal  current  which  is  remarked  by  an  observer  on  the  earth's  sur- 
face. Some  winds  are  of  a  very  limited  range,  and  depend  upon  local  circum- 
stances; such  are  the  sea  and  land  breeze  experienced  upon  the  coasts  of  tropical 
countries.  From  its  low  conducting  power,  the  surface  of  the  land  is  more  quickly 
heated  than  the  sea,  so  that  soon  after  sunrise  the  expanded  air  over  the  former 
begins  to  ascend,  and  is  replaced  by  colder  air  from  the  sea,  forming  the  sea-breeze. 
But  after  sunset,  the  earth's  heat,  being  less  in  quantity,  is  more  quickly  dissipated 


THE   ATMOSPHERE.  247 

by  radiation  than  that  of  the  sea,  and  the  air  over  the  land  becomes  dense  and  flows 
outwards,  displacing  the  air  over  the  sea,  and  producing  the  land-breeze.  It  is 
obvious  that  these  inferior  currents  must  be  attended  by  a  superior  current  in  an 
opposite  direction,  or  that  the  air  in  these  winds  is  carried  in  a  perpendicular  vortex 
of  no  great  extent,  of  which  the  motion  is  reversed  twice  every  twenty-four  hours. 
A  grand  movement  of  a  similar  nature  is  produced  in  the  atmosphere,  from  the 
high  temperature  of  the  equatorial  compared  with  the  polar  regions  of  the  globe ; 
the  air  over  the  former  constantly  ascending,  and  having  its  place  supplied  by  hori- 
zontal currents  from  the  latter,  within  the  lower  region  of  the  atmosphere.  Hence, 
if  the  earth  were  at  rest,  the  wind  would  constantly  blow  at  its  surface,  from  the 
poles  to  the  equator,  and  in  the  opposite  direction  in  the  upper  strata  of  the  atmo- 
sphere. But  the  earth,  accompanied  by  its  atmosphere,  makes  a  diurnal  revolution 
upon  its  axis,  in  which  any  point  on  its  surface  is  always  passing  to  a  point  in  space 
previously  to  the  east  of  it,  and  with  a  velocity  proportional  to  its  circle  of  latitude 
on  the  globe ;  a  velocity  which  is  consequently  nothing  at  the  poles,  and  attains  its 
maximum  at  the  equator.  The  result  of  this  is,  that  the  lower  current  or  polar 
stream,  in  tending  to  the  equator,  is  constantly  passing  over  parallels  of  latitude 
which  have  a  greater  degree  of  velocity  of  rotation  to  the  east,  than  the  stream  itself, 
which  comes  thus  to  be  felt  as  a  resistance  from  the  east;  and  instead  of  appearing 
as  a  wind  directly  from  the  north,  as  it  really  is,  this  stream  appears  as  a  wind  from 
the  east,  with  a  certain  northerly  declination,  which  diminishes  as  the  stream, 
approaches  the  equator,  where  it  flows  directly  from  the  east,  constituting  the  great 
trade-wind  which  constantly  blows  across  the  Atlantic  and  Pacific  Oceans  from  east 
to  west  within  the  tropics.  Our  keen  east  winds  in  spring  have  a  low  temperature, 
which  attests  their  arctic  origin.  The  upper  or  equatorial  current  has  its  course 
deflected  by  similar  causes;  starting  from  the  equator  it  has  a  greater  projectile 
force  to  the  east  than  the  parallels  of  latitude  over  which  it  has  to  pass,  and  retaining 
this  motion  towards  the  east  it  appears,  as  it  passes  over  them,  a  west  wind  or  wind 
from  the  west.  The  upper  current,  flowing  in  the  opposite  direction  from  the  trade- 
wind  below,  was  actually,  experienced  by  Humboldt  and  Bonpland  on  the  summit 
of  the  Peak  of  Teneriffe,  and  has  been  indicated  at  various  times  by  the  transport 
of  volcanic  ashes  by  its  means. 

These  currents,  instead  of  flowing  in  a  uniform  manner  over  and  under  each  other; 
appear  often  to  descend,  and  to  flow  side  by  side,  giving  rise  to  hot  and  cold  seasons 
in  their  different  courses,  and  the  great  variability  of  climate  of  the  temperate  zone. 
On  the  great  oceans,  within  the  temperate  zone,  westerly  winds  prevail  greatly  over 
easterly,  which  are  supposed  by  some  to  be  the  upper  current  descending  to  the 
surface  of  the  earth.  These  westerly  winds  temper  the  climate  of  the  western  sea- 
board both  of  Europe  and  America,  which  is  much  milder  than  the  climate  of  their 
eastern  coasts. 

The  nature  of  the  movement  of  the  atmosphere  in  hurricanes  has  lately  received 
considerable  elucidation.  It  appears  that  they  move  in  circles,  and  are  great  hori- 
zontal vortices,  which  are  probably  produced  by  currents  of  air  meeting  obliquely, 
like  the  little  eddies  or  whirlwinds  formed  at  the  corner  of  streets.  The  whole 
vortex  also  travels,  but  its  movement  of  translation  is  slow  compared  with  its  velocity 
of  rotation  (Colonel  Reid  on  the  Law  of  Storms ;  also  the  work  of  Mr.  Espy). 

Some  hurricanes  in  the  United  States  have  a  path  of  only  a  few  hundred  yards 
in  width,  but  extending  for  many  miles.  An  interesting  theory  of  the  origin  of 
these,  and  many  other  local  winds,  has  been  proposed  by  Mr.  Espy,  and  favourably 
reported  upon  by  M.  Babinet,  to  the  French  Institute.  When  a  column  of  air, 
saturated  with  vapour  at  a  high  temperature,  ascends  in  the  atmosphere,  it  expands 
by  the  removal  of  pressure  and  becomes  colder,  as  happens  with  dry  air  of  the  same 
temperature.  But  on  being  cooled  to  a  certain  point  of  temperature  by  its  ascent, 
vapour  condenses  in  the  former,  and  raising  the  temperature  of  the  column  makes  it 
specifically  lighter  and  more  buoyant.  The  ascent  of  damp  air  has  thus  a  tendency 
to  perpetuate  itself,  and  may  give  rise  to  a  most  powerful  upward  aspiration,  as  is 


248  NITROGEN. 

shown  by  calculation,  quite  adequate  to  prostrate  trees,  and  produce  the  mechanical 
effects  observed ;  the  whole  funnel  being  carried  over  the  surface  of  the  earth  by  a 
more  general  movement  of  the  atmosphere. 

Vapour.  —  The  properties  of  the  atmosphere  are  much  affected  by  the  presence 
of  watery  vapour  in  it,  which  it  acquires  from  contact  with  the  surface  of  the  sea, 
lakes,  rivers,  and  humid  soil.  The  quantity  which  can  rise  into  the  air  is  limited 
by  its  temperature  (page  90),  and  comes  to  be  deposited  again  from  various  causes. 
The  surface  of  the  earth  is  cooled  by  radiation,  and  occasions  the  precipitation  of 
dew  from  the  air  in  contact  with  it.  Vapour  is  also  condensed  into  drops,  from 
various  agencies  within  the  atmosphere  itself.  The  following  are  the  principal 
causes  of  clouds  and  rain.  1.  The  ascent  of  air  in  the  atmosphere,  and  its  conse- 
quent rarefaction,  which  is  attended  with  cold.  A  cloud  will  be  observed  within  the 
receiver  of  an  air-pump,  on  the  plate  of  which  a  little  water  has  been  spilt,  on  making 
two  or  three  rapid  strokes  of  the  pump,  which  is  due  to  this  cause.  It  is  observed 
in  operation  in  the  formation  of  the  clouds  and  mists  which  settle  on  the  summits 
of  mountains.  The  wind  passing  over  the  surface  of  a  level  country  is  impeded  by 
a  mountain  ;  rising  in  the  atmosphere  the  stream  overcomes  the  obstacle,  and  pro- 
duces a  cloud  as  it  passes  over  the  mountain,  which  appears  stationary  on  its  sum- 
mit. 2.  The  mixing  of  opposite  currents  of  hot  and  cold  air,  both  saturated  with 
humidity,  may  occasion  rain,  from  the  circumstance,  first  conjectured  by  Dr.  Hutton, 
that  the  currents  of  air  on  mixing  and  attaining  a  mean  temperature  are  incapable 
of  sustaining  the  mean  quantity  of  vapour.  Thus,  supposing  equal  volumes  of  air 
at  60°  and  40°,  both  saturated  with  vapour,  to  be  mixed,  the  tension  of  vapour  at 
the  former  temperature  being  the  0.524th  of  an  inch  of  mercury,  and  at  the  latter 
the  0.263d  of  an  inch,  the  mean  tension  is  0.393d  of  an  inch.  But  the  tension  of 
vapour  at  50°,  the  intermediate  temperature  is  only  the  0.375th  of  an-  inch;  and 
consequently  the  excess  of  the  former  tension,  or  vapour  of  the  0.018th  of  an  inch 
of  tension,  must  condense  as  rain.  But  this  is  an  inconsiderable  cause  of  rain  com- 
pared with  the  next.  3.  Contact  of  air  in  motion  with  the  cold  surface  of  earth,  or 
mere  proximity,  appears  to  be  the  most  usual  cause  of  its  refrigeration,  and  of  the 
precipitation  of  rain  from  it.  The  mean  temperature  of  January  in  this  country 
is  about  34°,  but  with  a  south-west  wind  the  thermometer  may  be  observed  gradu- 
ally to  rise  in  the  course  of  48  hours  to  54°.  Now  supposing  this  wind  to  be  satu- 
rated with  vapour  at  54°,  and  to  be  cooled  to  34°,  as  it  is  on  its  first  arrival,  the 
moisture  which  it  must  deposit  is  very  considerable,  as  will  appear  by  the  following 
calculation :  — 

Tension  of  vapour  at  54° 0.429  inch. 

«  «       at  34° 0.214     « 

Condensed 0.215     « 

The  mean  annual  fall  of  rain  in  London  amounts  to  a  column  of  23  inches. 
The  quantity  collected  by  a  rain-gauge  is  found  to  be  affected  to  an  extraordinary 
extent  by  very  moderate  differences  of  elevation.  Thus  the  annual  fall  of  rain  in 
three  situations  was  found,  by  Professor  J.  Phillips,  to  be  as  follows :  — 

Inches.  Height. 

Top  of  York  Minster 15-910  242  feet. 

Roof  of  Museum 20.461  73     « 

Surface  of  ground... 24.401  0     " 

The  last  stated  cause  of  rain  throws  some  light  on  this  inequality :  the  air  is  more 
cooled  near  the  ground,  and  therefore  deposits  most  humidity. 

The  annual  fall  is  greater  near  the  equator,  and  diminishes  in  high  latitudes.  At 
Granada  (lat.  12°  N.),  it  is  126  inches;  at  Calcutta  (lat.  19°  46'),  81  inches; 
Rome,  39  inches;  average  of  England,  31  inches;  St.  Petersburgh,  16  inches; 


THE    ATMOSPHERE. 


249 


Fia.  112. 


Uleaborg,  13£  inches.     The  number  of  rainy  days  follows  a  different  proportion, 
the  average  during  the  year  being  about  as  follows :  — 

In  Northern  Europe 180 

In  Central  Europe 146 

In  Southern  Europe 1201 

When  clouds  form  at  temperatures  below  32°,  the  aqueous  vapour  is  converted 
into  an  infinity  of  little  needle-like  crystals,  which  often  diverge  from  each  other  at 
angles  of  60°  and  120°,  as  do  also  the  thin  crys- 
tals in  freezing  water.  Snow  differs  very  much 
in  the  arrangement  of  these  spiculse  (fig.  112),  but 
the  flakes  are  all  of  the  same  configuration  in  the 
same  storm.  The  figures  are  essentially  referable 
to  a  hexagonal  star  or  prism,  one  of  the  crystal- 
line forms  of  ice.  Hail  is  also  produced  by  cold, 
but  in  circumstances  which  are  entirely  different. 
It  occurs  only  in  summer  or  in  warm  climates, 
and  when  the  sun  is  above  the  horizon.  It  seems 
to  be  produced  in  a  humid  ascending  current  of 
air,  greatly  cooled  by  rarefaction,  which  has  an 
upward  velocity  sufficient  to  sustain  the  falling 
hailstones  at  the  same  place  till  they  attain  consi- 
derable magnitude.  The  formation  of  hail  is 
always  attended  with  thunder  or  signs  of  electri- 
city ;  and  it  has  been  found  that  small  districts 
may  be  protected  from  its  devastations  by  the  ele- 
vation of  many  thunder  rods. 

Analysis  of  air.  —  A  knowledge  of  the  com- 
position of  the  atmosphere  followed  that  of  its 
constituent  gases.  Various  modes  of  analysis  are 
practised:  —  1.  A  stick  of  phosphorus  introduced 
into  a  known  measure  of  air  in  a  graduated  tube, 
effects  a  complete  absorption  of  the  oxygen  in  24  hours.  On  afterwards  withdraw- 
ing the  phosphorus  the  diminution  of  volume  may  be  observed,  which  always  indi- 
cates 20  or  21  per  cent,  of  oxygen.  2.  A  known  measure  of  air  may  be  mixed 
with  a  slight  excess  of  hydrogen  more  than  sufficient  to  combine  with  its  oxygen, 
100  volumes  of  air,  for  example,  with  50  volumes  of  hydrogen,  and  the  mixture 
exploded  in  a  strong  glass  tube  of  proper  construction,  by  means  of  the  electric  spark. 
The  diminution  in  volume  of  the  gases  after  combustion  is  observed ;  and  as  oxygen 
and  hydrogen  unite  in  the  exact  ratio  of  one  volume  of  the  first  to  two  volumes  of 
the  second,  one-third  of  the  diminution  represents  the  volume  of  oxygen  in  the 
measure  of  air  employed.  The  tube  used  for  this  purpose  is  called  the  voltaic 
eudiometer.  The  syphon  eudiometer  is  a  convenient  instru- 
ment of  this  kind.  It  is  formed  of  a  straight  tube  moderately 
stout,  of  about  l-4th  or  3-8ths  of  an  inch  internal  diameter, 
sealed  at  one  end,  and  about  22  inches  long.  The  closed  end 
of  this  tube  being  softened  by  heat,  two  stout  platinum  wires 
are  thrust  through  the  glass  from  opposite  sides  of  the  tubes, 
so  that  their  extremities  in  the  tube  approach  within  one-tenth 
of  an  inch  of  each  other.  These  are  intended  for  the  trans- 
mission of  the  electric  spark,  and  are  retained,  as  if  cemented, 
in  the  apertures  of  the  glass  when  the  latter  cools.  One-half 
the  tube  next  the  closed  end  is  afterwards  graduated  into 
hundredths  of  a  cubic  inch,  and  the  tube  is  bent  in  the  middle, 
like  a  syphon,  as  represented  by  a  in  the  figure.  By  a  little 
dexterity,  a  portion  of  the  gaseous  mixture  to  be  exploded  is 

See  Miiller's  Physics  and  Meteorology,  and  Kiimtz's  Meteorology,  by  Walker. 


FIG.  113. 


250  NITROGEN. 

transferred  to  the  sealed  limb  of  the  instrument,  at  the  water  or  mercurial  trough, 
and  the  measure  noted  with  the  liquid  at  the  same  height  in  both  limbs.  The 
mouth  of  the  open  limb  may  then  be  closed  by  a  cork,  which  can  be  fixed  down  by 
soft  copper  wire.  A  chain  being  now  hung  to  one  platinum  wire,  the  other  is  pre- 
sented to  the  prime  conductor  of  an  electric  machine,  or  the  knob  of  a  charged  Ley- 
den  phial  b,  so  as  to  take  a  spark  through  the  mixture,  which  is  thereby  exploded. 
The  risk  of  the  tube  being  broken  by  the  explosion,  which  is  considerable  in  the 
ordinary  form  of  the  eudiometer,  is  completely  avoided  in  this  instrument  by  the 
compression  of  the  air  retained  by  the  cork  in  the  open  limb,  this  air  acting  as  a 
recoil  spring  upon  the  occurrence  of  the  explosion  in  the  other  limb.  3.  The  com- 
bustion of  the  mixed  gases  may  be  determined  without  explosion  by  means  of  a  little 
pellet  of  spongy  platinum,  and  the  experiment  can  then  be  conducted  over  mercury 
in  an  ordinary  graduated  tube.  4.  Another  exact  method  of  removing  oxygen  from 
air,  recommended  by  G-ay-Lussac,  is  the  introduction  into  the  air  of  slips  of  copper 
moistened  with  hydrochloric  acid,  which  absorb  oxygen  with  great  avidity. 

5.  A  solution  in  ammonia  of  the  subchloride  of  copper,  or  of  any  salt  of  the  sub- 
oxide  of  that  metal,  such  as  the  sulphite,  absorbs  oxygen  with  great  avidity,  and 
may  be  used  in  the  analysis  of  air. 

6.  In  the  recent  careful  analyses  of  air  by  MM.  Dumas  and  Boussingault  (Compt. 
Rend.  12,  1005)  the  oxygen  was  withdrawn,  by  passing  air  over  reduced  metallic 
copper  at  a  red  heat.     To  obtain  the  necessary  precision  in  the  results,  the  experi- 
ment was  conducted  in  the  following  manner.     In  fig.  114,  a  b  is  a  tube  of  the 

FIG.  114. 


difficultly  fusible  or  hard  glass  used  in  organic  analysis,  which  is  filled  with 
metallic  copper  (reduced  from  the  black  oxide  of  copper  by  hydrogen),  and  placed 
in  a  long  trough -furnace  of  sheet  iron,  in  which  it  can  be  heated  to  redness  through- 
out its  whole  length.  The  tube  is  provided  with  stopcocks  at  both  ends,  and 
attached  by  caoutchouc  tubes  to  small  glass  tubes.  By  one  of  these  small  tubes 
it  communicates  with  a  glass  balloon  Y,  of  about  1200  cubic  inches  in  capacity, 
having  a^stopcock  u;  and  by  the  other  r,  with  a  series  of  tubes  A,  B,  and  C.  Of 
these  A  is  a  series  of  bulbs  containing  a  concentrated  solution  of  caustic  potassa, 
and  is  intended  for  the  absorption  of  the  small  portion  of  carbonic  acid  present  in 
air;  the  U-shaped  tube  B  contains  fragments  of  pumice  impregnated  with  the 
same  alkaline  solution;  and  the  similar  tube  C  is  filled  with  pumice  impregnated 
with  oil  of  vitriol,  in  order  to  dry  the  air. 

The  balloon  V  is  weighed  and  applied  to  the  other  apparatus  in  a  vacuous  state. 
The  tube  a  b  containing  the  metallic  copper  is  also  weighed  beforehand.     The  tube 


THE    ATMOSPHERE.  251 

and  copper  being  heated  to  low  redness,  the  stopcocks  are  partially  opened,  and  air 
allowed  to  flow  in  a  gradual  manner  into  V.  The  oxygen  is  entirely  absorbed  by 
the  copper,  and  the  weight  of  that  constituent  ascertained  by  weighing  the  tube  a  b 
after  the  experiment.  The  nitrogen  passes  on  alone  into  V,  and  its  weight  is  found 
by  again  weighing  that  balloon.  A  great  many  analyses  made  in  this  way  gave  the 
following  mean  results  :  — 

Air  by  weight.  Air  by  volume. 

Oxygen  ...........................  23.10  ......................  20-90 

Nitrogen  ..........................  76.90  ......................  79.10 


Air  from  distant  localities  and  different  elevations  has  not  exhibited  any  sensible 
variation  in  composition.  [See  Supplement,  p.  762.] 

The  theory  of  the  constitution  of  mixed  gases  of  Dalton  supposes  that  the  oxygen 
and  nitrogen  of  air  form  independent  atmospheres,  the  one  gas  not  pressing  upon  or 
interfering  with  the  other.  If  each  of  these  atmospheres  were  of  uniform  density, 
their  heights  would  obviously  be  inversely  as  the  densities  of  the  two  gases,  the 
height  of  the  nitrogen  column  8,  and  that  of  the  oxygen  7  ;  and  the  proportion  of 
the  one  gas  to  the  other  would  vary  with  the  elevation.  The  same  variation  should 
occur  in  the  atmosphere  in  its  actual  state  :  the  proportion  being  supposed  21  per 
cent,  at  the  level  of  the  sea,  by  a  calculation  on  this  principle  it  should  be  20.070 
per  cent,  at  a  height  of  10,000  Parisian  feet,  and  19.140  per  cent,  at  a  height  of 
20,000  feet.  But  as  the  influence  of  the  great  polar  and  equatorial  currents  is 
allowed  to  extend  to  a  greater  height  in  the  atmosphere  than  the  last,  and  than  has 
ever  been  reached  by  man,  it  is  not  to  be  wondered  at  that  no  diminution  in  the 
proportion  of  oxygen  is  observable  in  the  accurate  analyses  of  air  from  the  summit 
of  the  Faulhorn  (8000  feet)  which  were  lately  made  by  Brunner,  with  the  view  of 
testing  this  hypothesis.  (Poggendorff,  Handworterbuch  der  Chemie,  Bd.  i.  S.  570). 

Besides  these  constituents,  the  atmosphere  always  contains  a  variable  quantity  of 
watery  vapour  and  carbonic  acid  gas.  The  presence  of  the  latter  is  observed  by 
exposing  to  the  air  a  bason  of  lime-water,  which  is  soon  covered  "by  a  pellicle  of 
carbonate  of  lime.  Its  proportion  is  ascertained  by  adding  baryta-water  of  a  known 
strength,  from  a  graduated  pipette,  to  a  large  bottle  of  the  air  to  be  examined  j 
agitating  after  each  addition,  till  a  slip  of  yellow  turmeric  paper  is  made  perma- 
nently brown  by  the  baryta-water  after  agitation,  which  proves  that  more  of  the 
latter  has  been  added  than  is  neutralized  by  the  carbonic  acid  of  the  air.  The  car- 
bonic acid  is  in  the  equivalent  proportion  (by  weight)  of  the  quantity  of  baryta 
which  has  been  neutralized. 

Another  and  perhaps  more  exact  method  is  to  draw  a  large  but  known  volume  of 
dry  air  through  a  U  tube,  containing  pumice  impregnated  with  caustic  potassa,  and 
to  pass  it  afterwards  through  a  second  U  tube,  containing  oil  of  vitriol.  The  in- 
crease of  weight  on  both  tubes  weighed  together  is  the  proportion  of  carbonic  acid. 

Like  every  subject  connected  with  the  atmosphere,  the  proportion  of  carbonic 
acid  which  it  contains  was  ably  investigated  by  the  Saussures.  The  elder  philoso- 
pher of  that  name  detected  the  presence  of  this  gas  in  the  atmosphere  resting  upon 
the  perpetual  snows  of  the  summit  of  Mont  Blanc,  so  that  there  can  be  no  doubt 
that  carbonic  acid  is  diffused  through  the  whole  mass  of  the  atmosphere.  The 
younger  Saussure  has  ascertained,  by  a  series  of  several  hundred  analyses  of  air, 
that  the  mean  proportion  of  carbonic  acid  is  4.9  volumes  in  10,000  volumes  of  air, 
or  almost  exactly  1  in  2000  volumes;  but  it  varies  from  6.2  as  a  maximum  to  3.7, 
as  a  minimum  in  10,000  volumes.  Its  proportion  near  the  surface  of  the  earth  is 
greater  in  summer  than  in  winter,  and  during  night  than  during  day  upon  an  ave- 
rage of  many  observations.  It  is  also  rather  more  abundant  in  elevated  situations, 
as  on  the  summits  of  high  mountains,  than  in  the  plains  ;  a  distribution  of  this  gas 
which  proves  that  the  action  of  vegetation  at  the  surface  of  the  earth  is  sufficient  to 
keep  down  the  proportion  of  it  in  the  atmosphere,  within  a  certain  limit.  (Saussure, 


252  NITROGEN. 

Ann.  de  China,  et  de  Phys.  t.  xxxviii.  p.  411 ;  and  t.  xliv.  p.  5).  An  enormous 
quantity  of  carbonic  acid  is  discharged  from  the  elevated  cones  of  the  active  volca- 
noes of  America,  according  to  the  observations  of  Boussingault,  which  may  partly 
account  for  the  high  proportion  of  that  gas  in  the  upper  regions  of  the  atmosphere. 
The  gas  emitted  from  the  volcanoes  of  the  old  world,  according  to  Davy  and  others, 
is  principally  nitrogen. 

Carbonic  acid  is  a  constituent  of  the  atmosphere  which  is  essential  to  vegetable 
life,  plants  absorbing  that  gas,  and  deriving  from  it  the  whole  of  their  carbon.  Ex- 
tensive forests,  such  as  those  of  the  Landes  in  France,  which  grow  upon  sands  abso- 
lutely destitute  of  carbonaceous  matter,  can  obtain  their  carbon  in  no  other  manner. 
But  the  oxygen  of  the  carbonic  acid  is  not  retained  by  the  plant,  for  the  lignin  and 
other  constituent  principles  of  vegetables,  contain,  it  is  well  known,  no  more  oxygen 
than  is  sufficient  to  form  water  with  their  hydrogen,  and  which,  indeed,  has  entered 
the  plant  as  water.  The  oxygen  of  the  carbonic  acid  must  therefore  be  returned  in 
some  form  to  the  atmosphere.  The  discharge  of  pure  oxygen  gas  from  the  leaves 
of  plants  was  first  observed  by  Priestley,  and  the  general  action  of  plants  upon  the 
atmosphere  has  subsequently  been  minutely  studied  by  Sir  H.  Davy  and  Dr.  Dau- 
beny.  The  decomposition  of  carbonic  acid  requires  the  concurrence  of  light  ]  and 
is  not  therefore  sensible  during  the  night.  That  plants  fully  compensate  for  the 
loss  of  oxygen  occasioned  by  the  respiration  of  animals  and  other  natural  processes 
is  not  improbable ;  but  the  mass  of  the  atmosphere  is  so  vast  that  any  change  in  its 
composition  must  be  very  slowly  effected.  It  has,  indeed,  been  estimated  that  the 
proportion  of  oxygen  consumed  by  animated  beings  in  a  century  does  not  exceed 
l-7200th  of  the  whole  quantity. 

Other  gases  and  vaporous  bodies  are  observed  to  enter  the  atmosphere,  but  none 
of  them  can  afterwards  be  detected  in  it,  with  the  exception  of  hydrogen  in  some 
form,  probably  as  the  light  carburetted  hydrogen  of  marshes,  of  which  Boussingault 
believes  that  he  has  been  able  to  detect  the  presence  of  a  minute  but  appreciable 
proportion.  (Ann.  de  Chim.  et  de  Phys.  Ivii.  148).  He  also  observed  concentrated 
sulphuric  acid  to  be  blackened  when  exposed  in  a  glass  capsule  to  the  air,  protected 
from  dust,  and  "at  a  distance  from  vegetation,  which  he  ascribes  to  the  occasional 
presence  in  the  air  of  some  volatile  carbonaceous  compound  which  is  absorbed  and 
decomposed  by  the  acid. 

Ammonia  (N  H3)  also  is  a  minute  but  essential  constituent  of  air,  probably  in 
the  form  of  carbonate.  It  is  brought  down  by  rain,  and  is  the  principal  source  of 
the  nitrogen  of  plants. 

Omitting  the  aqueous  vapour  always  present  in  air,  but  of  which  the  proportion 
is  constantly  fluctuating,  it  may  be  represented  as  follows,  in  10,000  volumes : — 

COMPOSITION   OF   DRY  AIR  BY   VOLUME. 

Nitrogen 7912 

Oxygen  2080 

Carbonic  acid  4 

Carburetted  hydrogen  (C  H2) 4 

Ammonia Trace 

To,"ooo" 

Of  the  odoriferous  principles  of  plants,  the  miasmata  of  marshes  and  other  mat- 
ters of  contagion,  the  presence,  although  sufficiently  obvious  to  the  sense  of  smell, 
or  by  their  effects  upon  the  human  constitution,  cannot  be  detected  by  chemical 
tests.  But  it' may  be  remarked  in  regard  to  them,  that  few  or  none  of  the  com- 
pound volatile  bodies  we  perceive  entering  the  atmosphere,  could  long  escape  de- 
struction from  oxidation.  The  atmosphere  contains,  indeed,  within  itself,  the  means 
of  its  own  purification,  and  slowly  but  certainly  converts  all  organic  substances  ex- 
posed to  it  into  simpler  forms  of  matter,  such  as  water,  carbonic  acid,  nitric  acid, 


THE    ATMOSPHERE.  253 

and  ammonia.  Although  the  occasional  presence  of  matters  of  contagion  in  the 
atmosphere  is  not  to  be  disputed,  still  it  is  an  assumption,  without  evidence,  that 
these  substances  are  volatile  or  truly  vaporous.  Other  matters  of  infection  with 
which  we  can  compare  them,  such  as  the  matter  of  cow-pox,  may  be  dried  in  the 
air,  and  are  not  in  the  least  degree  volatile.  Indeed,  volatility  of  a  body  implies  a 
certain  simplicity  of  constitution  and  limit  to  the  number  of  atoms  in  its  integrant 
particle,  which  true  organic  bodies  appear  not  to  possess.  Again,  the  source  of  such 
bodies  being  at  all  times  inconsiderable,  they  would,  if  vapours,  be  liable  to  a  speedy 
attenuation  by  diffusion  so  great  as  to  render  their  action  wholly  inconceivable.  It 
is  more  probable  that  matters  of  contagion  are  highly  organized  particles  of  fixed 
matter,  which  may  find  its  way  into  the  atmosphere,  notwithstanding,  like  the  pollen 
of  flowers,  and  remain  for  a  time  suspended  in  it ;  a  condition  which  is  consistent 
with  the  admitted  difficulty  of  reaching  and  destroying  those  bodies  by  gaseous 
chlorine,  and  with  the  washing  of  walls  and  floors  as  an  ordinary  disinfecting  prac- 
tice. On  this  obscure  subject,  I  may  refer  to  a  valuable  paper  by  the  late  Dr. 
Henry  upon  the  application  of  heat  to  disinfection,  in  which  it  is  proved  that  a  tem- 
perature of  212°  is  destructive  to  such  contagious  matters  as  could  be  made  the 
subject  of  experiment.  (Phil.  Mag.  2d  ser.,  vols.  x.  p.  363 ;  xi.  pp.  22,  207  (1832). 
With  reference  to  gaseous  disinfectants,  it  may  be  remarked  that  sulphurous  acid 
gas  (obtained  by  burning  sulphur)  is  preferable,  on  speculative  grounds,  to  chlorine. 
No  agent  checks  more  effectually  the  first  development  of  animal  or  vegetable  life. 
This  it  does  by  preventing  oxidation.  In  the  same  manner  it  renders  impossible  the 
first  step  in  putrefactive  decomposition  and  fermentation.  All  animal  odours  and 
emanations  are  most  immediately  and  effectively  destroyed  by  it.  The  fetid  odour 
from  the  boiling  solution  of  cochineal  (for  instance),  which  is  so  persistent  in  dye- 
houses,  is  most  completely  removed  by  the  admission  of  sulphurous  acid  vapour  (J . 
Graham). 

The  compounds  of  nitrogen  or  oxygen  are  the  following :  — 

Protoxide  of  nitrogen  or  nitrous  oxide NO 

Binoxide  of  nitrogen  or  nitric  oxide N02 

Nitrous  acid N03 

Peroxide  of  nitrogen  (hyponitric  acid  of  Thenard) N04 

Nitric  acid N05 


PROTOXIDE   OP   NITROGEN. 

Syn.  PROTOXIDE  OF  AZOTE,  NITROUS  OXIDE;  Eq.  22  or  275;  NO;  density 

15204; 


This  gas  was  discovered  by  Dr.  Priestley  about  1776,  and  studied  by  Davy, 
whose  "  Researches,  Chemical  and  Philosophical,"  published  in  1809,  contain  an 
elaborate  investigation  of  its  properties  and  composition.  Davy  first  observed  the 
stimulating  power  of  nitrous  oxide  when  taken  into  the  lungs,  a  property  which  has 
since  attracted  a  considerable  degree  of  popular  attention  to  this  gas. 

Preparation*  —  Protoxide  of  nitrogen  is  always  prepared  from  the  nitrate  of 
ammonia.  Some  attention  must  be  paid  to  the  purity  of  that  salt,  which  should 
contain  no  hydrochlorate  of  ammonia.  It  is  formed  by  adding  pounded  carbonate 
of  ammonia  to  pure  nitric  acid,  which,  if  concentrated,  may  be  previously  diluted 
with  half  its  bulk  of  water,  so  long  as  there  is  effervescence;  and  a  small  excess  of 
the  carbonate  may  be  left  at  the  end  in  the  liquor.  The  solution  should  be  filtered, 
and  concentrated  till  its  boiling  point  begins  to  rise  above  250°,  and  a  drop  of  it 
becomes  solid  on  a  cool  glass  plate.  On  cooling,  it  forms  a  solid  cake,  which  may 
be  broken  into  fragments.  To  obtain  nitrous  oxide,  a  quantity  of  this  salt,  which 
should  never  be  less  than  6  or  8  ounces,  is  introduced  into  a  retort,  or  a  globular 

*  [See  Supplement,  p.  766.] 


254 


NITROGEN. 


FIG.  115.  flask,  called  a  bolt-head  cr,  and  heated  by  a 

charcoal  choffer  b,  the  diffused  heat  of 
which  is  more  suitable  than  the  heat  of  a 
lamp.  Paper  may  be  pasted  over  the  cork 
of  the  bolt-head  to  keep  it  air-tight.  At  a 
temperature  not  under  340°  the  salt  boils 
and  begins  to  undergo  decomposition,  being 
resolved  into  nitrous  oxide  and  water.  As 
heat  is  evolved  in  this  decomposition,  which 
is  a  kind  of  combustion  or  deflagration,  the 
choffer  must  be  withdrawn  to  such  a  dis- 
tance from  the  flask  as  to  sustain  only  a 
moderate  ebullition.  If  the  temperature  is 
allowed  to  rise  too  high,  the  ebullition  be- 
comes tumultuous,  and  the  flask  is  filled 

with  white  fumes,  which  have  an  irritating  odour ;  and  the  gas  which  then  comes 
off  is  little  more  than  nitrogen.  Nitrous  oxide  should  be  collected  in  a  gasometer 
or  in  a  gas-holder  filled  with  water  of  a  temperature  about  90°,  as  cold  water  absorbs 
much  of  this  gas.  The  whole  salt  undergoes  the  same  decomposition,  and  nothing 
whatever  is  left  in  the  retort.1 

Nitrous  oxide  is  likewise  produced  when  the  salt  called  nitro-sulphate  of  ammonia 
is  thrown  into  an  acid;  and  also  when  zinc  and  tin  are  dissolved  in  dilute  nitric 
acid,  but  the  latter  processes  do  not  afford  the  gas  in  a  state  of  purity. 

The  nature  of  the  decomposition  of  the  nitrate  of  ammonia  will  be  best  explained 
by  the  following  diagram,  in  which  an  equivalent  of  the  salt,  or  80  parts,  is  sup- 
posed to  be  used.  It  will  be  observed  that  the  three  equivalents  of  hydrogen  in 
the  ammonia  are  burned,  or  combine  with  three  equivalents  of  the  oxygen  of  the 
nitric  acid,  and  form  water,  while  the  two  equivalents  of  nitrogen  in  the  ammonia 
and  nitric  acid  combine  with  the  two  remaining  equivalents  of  the  oxygen  of  the 
latter :  — 


Before  decomposition. 


80  Nitrate  of  ammonia. 


Oxygen 

8- 

Oxygen 

8  - 

(54  Nitric  acid 

Oxygen 
Oxygen 

fc 

Oxygen 

8  ^ 

Nitrogen 

14    . 

Nitrogen 

14"' 

17  Ammonia 

Hydrogen 
Hydrogen 

1  - 
1  - 

Hydrogen 

1 

9  Water            "Water" 

9 

After  decomposition. 

-.-.-22  Nitrous  oxide. 

— — :^;;--22  Nitrous  oxide. 


9  Water. 
9  Water. 
9  Water. 
9  Water. 


Or  in  symbols :  — 


NH3,  HO-f  N05=2NO  and  4HO. 


From  the  diagram  it  appears  that  80  grains  of  the  salt  yield  44  grains  of  nitrous 
oxide  and  35  grains  of  water.  One  grain  of  salt  yields  rather  more  than  one  cubic 
inch  of  gas. 

Properties.  —  Nitrous  oxide  possesses  the  usual  mechanical  properties  of  gases, 
and  has  a  faint  agreeable  smell.  It  has  been  liquefied  by  evolving  it  from  the 
decomposition  of  the  nitrate  of  ammonia  in  a  sealed  tube,  and  possessed  in  the  liquid 
state  an  elastic  force  of  above  50  atmospheres  at  45°.  [It  has  also  been  liquefied 
by  mechanical  compression  (Natterrer,  Ann.  de  Phar.  54,  254).  Liquid  nitrous 
oxide  is  colourless,  very  volatile,  boils  under  the  pressure  of  one  atmosphere  at 


1  For  the  preparation  and  properties  of  this  and  other  gases,  the  Elements  of  Chemistry 
;J829)  of  the  late  Dr.  Henry  may  still  be  consulted  with  advantage. 


THE   ATMOSPHERE.  255 

— 125°  (Regnault,  Corupt.  Rend.  t.  28,  383)  :  a  drop  falling  on  the  hand  produces 
effects  similar  to  a  burn ;  potassium,  charcoal,  sulphur,  and  phosphorus  float  on  its 
surface  unaltered,  but  ignited  charcoal  bums  with  brilliancy.  Water  poured  on  it, 
freezes  instantly,  and  the  liquid  is  converted  into  gas  with  almost  explosive  rapidity. 
Issuing  from  a  jet  pipe,  part  is  reduced  to  a  solid  state  by  the  sudden  evaporation 
of  the  rest.  The  solid  is  snowlike,  and  placed  on  the  hand  produces  the  same  effects 
as  the  liquid  (Dumas,  Compt.  Rend.  t.  27,  463).  When  the  liquid  is  exposed  to 
the  cold  produced  by  the  vaporization  of  solid  carbonic  acid  and  ether,  it  freezes  at 
the  temperature  of  — 150°  (Faraday). — 'R.  B.]  The  gas  is  formed  by  the  union 
of  a  combining  measure,  or  2  volumes  of  nitrogen,  with  a  combining  measure,  or  1 
volume  of  oxygen,  which  are  condensed  into  2  volumes,  the  combining  measure  of 
this  gas.  The  weight  of  a  single  volume,  or  the  density  of  the  gas,  is  therefore  by 
calculation  — 

971.4+971.4  +  1105.6 
2 

Cold  water  agitated  with  this  gas  dissolves  about  three-fourths  of  its  volume  of  the 
gas,  and  acquires  a  sweetish  taste,  but,  I  believe,  no  stimulating  properties.  Bodies 
which  burn  in  air,  burn  with  increased  brilliancy  in  this  gas,  if  introduced  in  a  state 
of  ignition.  A  newly  blown  out  taper  with  a  red  wick  may  be  rekindled  in  it,  as  in 
oxygen.  Mixed  with  an  equal  bulk  of  hydrogen,  and  ignited  by  flame  and  the 
electric  spark,  it  detonates  violently.  In  all  these  cases  of  combustion,  the  nitrous 
oxide  is  decomposed,  its  oxygen  uniting  with  the  combustible  and  its  nitrogen  being 
set  free.  When  transmitted  through  a  red-hot  porcelain  tube,  nitrous  oxide  is 
likewise  decomposed  and  resolved  into  oxygen,  nitrogen,  and  the  peroxide  of 
nitrogen. 

Nitrous  oxide  was  supposed  by  Davy  to  combine  with  alkalies,  when  generated 
in  contact  with  them,  but  these  compounds  have  since  been  found  to  contain  nitro- 
sulphuric  acid. 

This  gas  may  be  respired  for  two  or  three  minutes  without  inconvenience,  and 
\vk  n  the  gas  is  unmixed  with  air,  and  the  lungs  have  been  well  emptied  of  air 
lu  fore  respiring,  it  induces  an  agreeable  state  of  reverie  or  intoxication,  often  accom- 
panied with  considerable  excitement,  which  lasts  for  a  minute  or  two,  and  disappears 
without  any  unpleasant  consequences.  The  gas  from  an  ounce  and  a  half  or  two 
ounces  of  nitrate  of  ammonia  is  sufficient  for  a  dose,  and  it  s,hould  be  respired  from, 
a  bag  of  the  size  of  a  large  ox-bladder,  and  provided  with  a  wooden  tube  of  an  inch 
internal  diameter.  The  volume  of  the  gas  diminishes  rapidly  during  the  inspiration, 
and  finally  only  a  few  cubic  inches  remain.  An  animal  entirely  confined  in  this 
gas  soon  dies  from  the  prolonged  effects  of  the  intoxication. 


BINOXIDE   OP   NITROGEN. 

Syn.  BINOXIDE,  OR  DEUTOXIDE  OP  AZOTE,  NITRIC  OXIDE;  Eg.  30  or  375; 
N02;  density  1038-8; 

This  gas,  which  comes  off  during  the  action  of  nitric  acid  upon  most  metals, 
appears  to  have  been  collected  by  Dr.  Hales,  the  father  of  pneumatic  chemistry,  but 
its  properties  were  first  minutely  studied  by  Dr.  Priestley. 

Prrparation* — Binoxide  of  nitrogen  is  easily  procured  by  the  action  of  nitric 
acid  diluted  to  the  specific  gravity  1.2,  upon  sheet  copper  clipped  into  small  pieces. 
As  no  heat  is  required,  this  gas  may  be  evolved  like  hydrogen  from  a  gas  bottle 
(page  234).  Mercury  may  be  substituted  for  copper,  but  it  is  then  necessary  to 
apply  a  gentle  heat  to  the  materials.  This  gas  may  be  collected  and  retained  over 
water  without  loss. 

*  [See  Supplement,  p.  766.] 


256 


NITROGEN. 


In  dissolving  in  nitric  acid,  the  copper  takes  oxygen  from  one  portion  of  acid  and 
becomes  oxide  of  copper,  which  combines  with  another  portion  of  acid,  and  forms 
the  nitrate  of  copper,  the  solution  of  which  is  of  a  blue  colour.  The  portion  of 
nitric  acid  which  is  decomposed  losing  three  equivalents  of  oxygen  and  retaining 
two,  appears  as  nitric  oxide  gas.  This  is  more  clearly  shown  in  the  following 
diagram  :  — 

ACTION    OF    NITRIC   ACID    UPON    COPPER. 


Before  decomposition. 


54  Nitric  acid 


32  Copper 

54  Nitric  acid 
32  Copper  .... 
54  Nitric  acid 
32  Copper  .... 
54  Nitric  acid 


Nitrogen  14 

Oxygen  

Oxygen  

1  Oxygen  

!  Oxygen  

L  Oxygen  

...  Copper 32 

...  Nitric  acid 54 

...  Copper 32 

...  Nitric  acid 54 

...  Copper 32 

...  Nitric  acid ,       ..54 


After  decomposition. 
'30  Binoxide  of  nitrogen. 


312 

Or  in  symbols : — 


312 


94  Nitrate  of  copper. 
94  Nitrate  of  copper. 

94  Nitrate  of  copper. 
312 


4N05  and  3Cu=3(Cu  0,  N05)  and  N02 


Properties.  —  This  gas  is  colourless,  but  when  mixed  with  air  it  produces  ruddy 
fumes  of  the  peroxide  of  nitrogen.  It  is  irritating,  and  causes  the  glottis  to  contract 
spasmodically  when  an  attempt  is  made  to  respire  it.  Nitric  oxide  has  never  been 
liquefied  :  water  at  60°,  according  to  Dr.  Henry,  takes  up  only  5  or  6  per  cent,  of 
this  gas.  It  is  formed  of  one  combining  measure  of  nitrogen  or  2  volumes,  and  two 
combining  measures  of  oxygen  or  2  volumes,  united  without  condensation,  so  that 
the  combining  measure  of  nitric  oxide  contains  4  volumes.  The  weight  of  one  vo- 
lume, or  the  density  of  the  gas,  is  therefore 

971.4-f971.4-f  1105. 


This  gas  is  not  decomposed  by  a  low  red  heat. 

Many  combustibles  do  not  burn  in  nitric  oxide,  although  it  contains  half  its  vo- 
lume of  oxygen.  A  lighted  candle  and  burning  sulphur  are  extinguished  by  it; 
mixed  with  hydrogen,  it  is  not  exploded  by  the  electric  spark  or  by  flame,  but  it 
imparts  a  green  colour  to  the  flame  of  hydrogen  burning  in  air.  Phosphorus  and 
charcoal,  however,  introduced  in  a  state  of  ignition  into  this  gas,  continue  to  burn 
with  increased  vehemence.  The  state  of  combination  of  the  oxygen  in  this  gas 
appears  to  prevent  that  substance  from  uniting  with  combustibles,  unless,  like  the 
two  last  mentioned,  they  evolve  so  much  heat  as  to  decompose  the  nitric  oxide. 
Several  of  the  more  oxidable  metals,  such  as  iron,  withdraw  the  half  of  the  oxygen 
from  this  gas,  when  left  in  contact  with  it,  and  convert  it  into  nitrous  oxide. 

No  property  of  nitric  oxide  is  more  remarkable  than  its  attraction  for  oxygen, 
and  it  may  be  employed  to  separate  this  from  all  other  gases.  Nitric  oxide  indicates 
the  presence  of  free  oxygen  in  a  gaseous  mixture,  by  the  appearance  of  fumes  which 
are  pale  and  yellow  with  a  small,  and  reddish  brown  and  dense  with  a  large  propor- 
tion of  the  latter  gas  ,  and  also  by  a  subsequent  contraction  of  the  gaseous  volume, 
arising  from  the  absorption  of  these  fumes  by  water.  Added  in  sufficient  quantity, 
nitric  oxide  will  thus  withdraw  oxygen  most  completely  from  any  mixture.  But 


NITROUS    ACID.  257 

notwithstanding  this  property,  nitric  oxide  cannot  be  employed  with  advantage  in 
the  analysis  of  air  or  similar  mixtures,  for  the  contraction  which  it  occasions  does 
not  afford  certain  data  for  determining  the  proportion  of  oxygen  which  has  disap- 
peared. Nitric  oxide  is  capable  of  combining  with  different  proportions  of  oxygen, 
a  combining  measure  or  4  volumes  of  the  gas  uniting,  in  such  experiments,  with  1, 
'2  or  3  volumes  of  oxygen,  and  forming  nitrous  acid,  peroxide  of  nitrogen  or  nitric 
acid,  or  several  of  these  compounds  at  the  same  time. 

This  oxide  of  nitrogen,  like  the  preceding,  is  a  neutral  body,  and  has  a  very 
limited  range  of  affinity.  A  substance  is  left  on  igniting  the  nitrate  of  potassa  'or 
baryta,  which  was  supposed  to  be  a  compound  of  nitric  oxide  with  potassium,  or 
barium,  but  Mitscherlich  finds  it  to  be  either  the  caustic  protoxide  itself  or  the 
peroxide  of  the  metal. '  But  nitric  oxide  is  absorbed  by  a  solution  of  the  sulphate 
of  iron,  which  it  causes  to  become  black ;  the  greater  part  of  the  gas  may  be  ex- 
pelled again  by  boiling  the  solution.  All  the  soluble  proto-salts  of  iron  have  the 
same  property,  and  the  nitric  oxide  remains  attached  to  the  oxide  of  iron  when  pre- 
cipitated in  the  insoluble  salts  of  that  metal.  The  proportion  of  nitric  oxide  in 
these  combinations  is  found  by  Peligot  to  be  definite;  one  eq.  of  the  nitric  oxide  to 
four  of  the  protoxide  of  iron ;  or,  the  nitric  oxide  contains  the  proportion  of  oxygen 
required  to  convert  the  protoxide  into  sesquioxide  of  iron.  (Ann.  de  Chim.  et  de 
Phys.  t.  liv.  p.  17).  Nitric  oxide  is  also  absorbed  by  nitric  acid.  With  sulphurous 
acid  nitric  oxide  forms  a  compound  which  will  be  more  particularly  noticed  under 
that  acid. 

NITROUS   ACID. 

Syn.  AZOTOTJS  ACID  ( T/ienard).     Eq.  38  or  475 ;  N03. 

The  direct  mode  of  forming  this  compound  is  by  mixing  4  volumes  of  binoxide 
of  nitrogen  with  1  volume  of  oxygen,  both  perfectly  dry,  and  exposing  the  mixture 
to  a  great  degree  of  cold.  The  gases  unite,  and  condense  into  a  liquid  of  a  green 
colour,  which  is  very  volatile,  and  forms  a  deep  reddish  yellow  coloured  vapour. 
Nitrous  acid  prepared  in  this  way  is  decomposed  at  once  when  thrown  into  water; 
an  effervescence  occurring,  from  the  escape  of  nitric  oxide,  and  nitric  acid  being 
produced,  which  gives  stability  to  a  portion  of  the  nitrous  acid.  Nitrous  acid  cannot 
be  made  to  unite  directly  with  alkalies  and  earths,  probably  owing  to  the  action  of 
water  first  described.  But  when  oxygen  gas  is  mixed  with  a  large  excess  of  nitric 
oxide,  in  contact  with  a  solution  of  caustic  potassa,  the  gases  were  found  by  Gay- 
Lussac  always  to  disappear  in  the  proportions  of  nitrous  acid,  which  was  produced 
and  entered  into  combination  with  the  potassa,  forming  a  nitrite  of  potassa.  Similar 
nitrites  may  also  be  produced  by  calcining  the  nitrate  of  soda  till  the  fused  salt  be- 
comes alkaline ;  or  by  boiling  the  nitrate  of  lead  with  metallic  lead.  The  nitrite 
of  soda  may  be  dissolved  and  filtered,  and  the  solution  precipitated  by  nitrate  of 
silver;  a  process  which  gives  the  nitrite  of  silver,  a  salt  possessing  a  sparing  degree 
of  solubility,  like  that  of  cream  of  tartar,  but  which  may  be  purified  by  solution 
and  crystallization,  and  then  affords  ready  means  of  obtaining  the  other  nitrites  by 
double  decomposition  (Mitscherlich).  Nitrous  acid  is  liberated  from  the  nitrites  by 
acetic  acid.  When  free  sulphuric  acid  is  added  to  a  solution  of  nitrite  of  silver,  the 
disengaged  nitrous  acid  is  immediately  resolved  into  nitric  acid  and  nitric  oxide. 
The  subnitrite  of  lead,  on  the  other  hand,  may  be  decomposed  by  the  bisulphate  of 
potassa  or  soda  to  obtain  a  neutral  nitrite  of  one  of  these  bases  (Berzelius).  The 
nitrites  of  potassa  and  soda  are  soluble  in  alcohol,  while  the  nitrates  are  not  so. 

Nitrous  acid  is  also  capable  of  combining  with  several  acids,  in  particular  with 
iodic,  nitric,  and  sulphuric  acids.  Its  combination  with  the  last  is  obtained  by  seal- 
ing up  together  liquid  sulphurous  acid  and  peroxide  of  nitrogen  (N04)  in  a  glass 
tube.  In  the  course  of  a  few  days  the  tube  may  be  opened :  the  substances  are 
combined,  and  form  a  solid  mass,  which  may  be  heated  up  to  (200°  C.)  its  point  of 
fusion.  At  a  higher  temperature  it  distils  without  alteration.  In  this  experiment, 
sulphurous  acid  acquires  an  equivalent  of  oxygen,  and  becomes  sulphuric  acid. 


258  NITROGEN. 

while  peroxide  of  nitrogen  loses  an  equivalent  of  oxygen,  and  becomes  nitrous  acid, 
"but  one  half  only  of  the  latter  acid  formed  unites  with  sulphuric  acid,  the  composi- 
tion of  the  body  formed  being  N03  +  2S03.  The  reaction  is  expressed  as  follows: — 

2S03  and  2N04=N03+2S03  and  N03. 

This  compound  is  soluble  in  strong  oil  of  vitriol  without  decomposition ;  but  from 
sulphuric  acid  somewhat  diluted  it  takes  water,  and  forms  a  crystalline  substance, 
which  often  appears  in  the  manufacture  of  sulphuric  acid,  as  we  shall  afterwards 
find.  The  original  solid  compound  is  decomposed  by  pure  water  or  highly  diluted 
sulphuric  acid,  and  the  sulphuric  and  nitrous  acids  become  free.  The  tendency  of 
nitrous  acid  to  combine  with  other  acids  has  already  been  noticed,  as  assimilating 
this  compound  of  nitrogen  to  arsenious  acid  and  the  oxide  of  antimony  (page  147). 

PEROXIDE   OF   NITROGEN. 

Syn.  HYPONITRIC  ACID,  NITROUS  GAS  (Berzelius).     Eq.  46  or  575;  N04;  theo- 
retical density,  1591.3 ;     |     j     | 

This  compound  forms  the  principal  part  of  the  ruddy  fumes  which  always  appear 
on  mixing  nitric  oxide  with  air.  As  it  cannot  be  made  to  unite  either  directly  or 
indirectly  with  bases,  and  has  no  acid  properties,  any  designation  for  this  oxide  of 
nitrogen  which  implies  acidity  should  be  avoided,  and  the  name  nitrous  acid  in  par- 
ticular, which  is  applied  on  the  continent  to  the  preceding  compound.  The  name 
peroxide  of  nitrogen  is  more  in  accordance  with  the  rules  generally  followed  in 
naming  such  compounds. 

Preparation.  —  When  4  volumes  of  nitric  oxide  and  2  of  oxygen,  both  perfectly 
dry,  are  mixed,  this  compound  is  alone  produced,  and  the  six  volumes  of  mixed 
"  gases  are  condensed  into  4  volumes,  which  may  be  considered  the  combining  mea- 
sure of  peroxide  of  nitrogen.     The  weight  of  1  volume,  or  the  density  of  ^this  gas, 
must  therefore  be 

1038.5X4-f-1105.6X2__1591  g 
4 

The  peroxide  of  nitrogen  is  also  contained  in  the  coloured  and  fuming  nitric  acid 
of  commerce,  and  may  be  obtained  in  the  liquid  condition  by  gently  warming  that 
acid,  and  condensing  the  vapour  which  comes  over,  by  transmitting  it  through  a 
glass  tube  surrounded  by  ice  and  salt.  But  it  is  prepared  with  most  advantage  from 
the  nitrate  of  lead,  the  crystals  of  which,  after  being  pounded  and  well  dried,  to 
deprive  the  salt  of  hygrometric  water,  are  distilled  in  a  retort  of  hard  glass,  or 
porcelain,  at  a  red  heat,  and  the  red  vapours  condensed  in  a  receiver  kept  very  cold 
by  a  freezing  mixture.  Oxygen  gas  escapes  during  the  whole  process,  the  nitric 
acid  of  the  nitrate  of  lead  being  resolved  into  oxygen  and  peroxide  of  nitrogen;  or 
N06=N04  and  0.  As  obtained  by  the  last  process,  which  was  proposed  by  Du- 
long,  peroxide  of  nitrogen  is  a  highly  volatile  liquid,  boiling  at  82°,  of  a  red  colour 
at  the  usual  temperature,  orange  yellow  at  a  lower  temperature,  and  nearly  colour- 
less below  zero,  of  density  1451,  and  a  white  solid  mass  at  — 40°.  It  is  exceed- 
ingly corrosive,  and,  like  nitric  acid,  stains  the  skin  yellow.  The  red  colour  of  its 
vapour  becomes  paler  at  a  low  temperature,  but  with  heat  increases  greatly  in  inten- 
sity, so  as  to  appear  quite  opaque  when  in  a  considerable  body  at  a  high  tempera- 
ture. It  is  the  vapour  which  Brewster  observed  to  produce  so  many  dark  lines  in 
the  spectrum  of  a  ray  of  light  which  passes  through  it  (page  100).  The  peroxide 
is  not  decomposed  by  a  low  red  heat,  and  appears  to  be  the  most  stable  of  the  oxides 
of  nitrogen.  No  compound  of  it  is  known,  unless  peroxide  of  nitrogen  be  the 
radical,  as  some  suppose,  of  nitric  acid.  But  Berzelius  is  inclined  to  consider  this 
oxide  as  itself  a  compound  of  nitric  and  nitrous  acids,  for 


NITRIC   ACID.  259 

N06  +  N08=2N<V 

The  liquid  peroxide  of  nitrogen  is  partially  decomposed  by  water,  nitric  oxide 
coming  off  with  effervescence,  and  more  and  more  nitric  acid  being  produced,  in 
proportion  to  the  quantity  of  water  added ;  but  a  portion  of  the  peroxide  always 
escapes  this  action,  being  protected  by  the  nitric  acid  formed.  In  the  progress  of 
this  dilution  the  liquid  undergoes  several  changes  of  colour,  passing  from  red  to 
yellow,  from  that  to  green,  then  to  blue,  and  becoming  at  last  colourless.  The 
peroxide  of  nitrogen  is  readily  decomposed  by  the  more  oxidable  metals,  and  is  a 
powerful  oxidizing  agent. 

NITRIC    ACID. 

Syn.  AZOTIC  ACID  ( Thenard).     Eq.  54  or  675 ;  N06. 

A  knowledge  of  this  highly  important  acid  has  descended  from  the  earliest  ages 
of  chemistry,  but  its  composition  was  first  ascertained  by  Cavendish,  in  1785.  He 
succeeded  in  forming  nitric  acid  from  its  elements,  by  transmitting  a  succession  of 
electric  sparks  during  several  days  through  a  small  quantity  of  air,  or  through  a 
mixture  of  1  volume  of  nitrogen  and  2£  volumes  of  oxygen,  confined  in  a  small  tube 
over  water,  or  over  solution  of  potassa ;  in  the  last  case,  the  absorption  of  the  gases 
was  complete,  and  nitrate  of  potassa  was  obtained.  A  trace  of  this  acid  in  combina- 
tion with  ammonia  has  been  detected  in  the  rain  of  thunder-storms,  produced  pro- 
bably in  the  same  manner.  It  was  also  observed  by  Gay-Lussac  to  be  the  sole 
product  when  nitric  oxide  is  added,  in  a  gradual  manner,  to  oxygen  in  excess  over 
water;  the  gases-  then  unite,  and  disappear  in  the  proportion, of  4  volumes  of  the 
former  to  3  of  the  latter.  It  is  also  a  constituent  of  the  salt,  nitre  or  salpetre,  found 
in  the  soil  of  India  and  Spain,  which  is  a  nitrate  of  potassa,  and  also  of  nitrate  of 
soda,  which  occurs  in  large  quantities  in  South  America. 

[Anhydrous  nitric  acid  was  first  prepared  in  1849,  by  M.  Deville  (Compt.  Rend, 
t.  z8,  p.  257),  by  treating  dry  nitrate  of  silver  with  dry  chlorine.  The  nitrate  of 
silver  is  placed  in  a  U-tube,  to  which  a  second,  having  a  spherical  reservoir  at  the 
curved  part,  is  attached.  The  first  tube  is  immersed  in  a  vessel  of  water,  which  can 
be  heated  by  a  spirit-lamp,  and  the  second  in  a  freezing  mixture.  Chlorine  gas  is 
evolved  and  passed  first  through  a  tube  containing  chloride  of  calcium,  then  another 
filled  with  pumice  moistened  with  sulphuric  acid,  that  it  may  be  perfectly  dried 
before  it  reaches  the  nitrate  of  silver.  All  the  joints  are  united  by  the  blow-pipe. 
The  nitrate  of  silver  is  heated  to  356°  F.,  and  a  stream  of.  carbonic  acid  passed 
through  the  apparatus  to  dry  the  salt,  after  which  it  is  allowed  to  cool  and  the 
chlorine  is  transmitted.  At  common  temperatures  there  is  no  appearance  of  action, 
but  when  the  heat  is  raised  to  203  and  then  lowered  to  between  135  and  155°, 
decomposition  takes  place,  chloride  of  silver  is  produced,  and  crystals  of  nitric  acid 
begin  to  appear  in  the  second  U-tube  at  the  part  not  immersed  in  the  freezing  mix- 
ture, and  a  small  quantity  of  liquid  condenses  in  the  spherical  reservoir,  while 
oxygen  and  chlorine  gases  escape.  To  transfer  the  nitric  acid,  the  stream  of  chlo- 
rine is  replaced  by  carbonic  acid,  and  the  freezing  mixture  taken  away ;  the  liquid  is 
now  removed  from  the  reservoir  and  a  bulb  attached  to  receive  the  anhydrous  acid. 
This  bulb  is  immersed  in  the  freezing  mixture,  and  the  acid  evaporating  at  ordinary 
temperature  condenses  in  the  bulb,  which  when  filled  is  to  be  sealed  by  the  blow- 
pipe. 

Properties.  —  Anhydrous  nitric  acid  forms  transparent  colourless  crystals,  belong- 
ing to  the  right  rhombic  system.  It  fuses  at  a  little  above  85°,  and  boils  about 

1  Trait4  de  Chimie,  par  J.  J.  Berzelius,  traduite  par  MM.  Esslinger  et  Hoeffer,  Didot, 
Paris,  1845.  An  excellent  edition  of  this  most  valuable  system  of  chemistry. 


260  NITROGEN. 

113°,  decomposing  slightly  at  that  temperature.  In  contact  witli  water,  it  dissolves 
with  the  evolution  of  much  heat. 

At  ordinary  temperatures  it  is  liable  to  spontaneous  decomposition,  and  bursts  the 
bulb  by  the  increased  tension  of  the  confined  gases  (Dumas,  Compt.  Rend.  t.  28, 
p.  323):  —  B.  B.]  [See  Supplement,  p.  766.] 

Preparation.  —  This  acid  has  not  until  recently  been  obtained  in  an  insulated 
state,  but  in  combination  with  water,  as  in  aqua  fortis  or  the  hydrate  of  nitric  acid, 
or  with  a  fixed  base,  as  in  the  ordinary  nitrates.  The  hydrate,  (which  is  popularly 
termed  nitric  acid,)  is  eliminated  from  nitrate  of  potassa  by  means  of  oil  of  vitriol, 
which  is  itself  a  hydrate  of  sulphuric  acid.  That  acid  unites  with  potassa,  in  this 
decomposition,  and  forms  sulphate  of  potassa,  displacing  nitric  acid,  which  last 
brings  off  in  combination  with  itself  the  water  of  the  oil  of  vitriol.  There  is  a  great 
advantage,  first  pointed  out  by  Mr.  Phillips,  in  using  two  equivalents  of  oil  of  vitriol 
to  one  of  nitrate  of  potassa,  which  is  98  of  the  former  to  101  of  the  latter,  or  nearly 
equal  weights.  The  acid  and  salt,  in  these  proportions,  are  introduced  into  a  capa- 
cious plain  retort,  provided  with  a  flask  as  a  receiver.  Upon  the  application  of  heat, 
a  little  of  the  nitric  acid  first  evolved  undergoes  decomposition,  and  red  fumes 
appear,  but  soon  the  vapours  become  nearly  colourless,  and  are  easily  condensed  in 
the  receiver.  During  the  whole  distillation,  the  temperature  need  not  exceed  260°. 
The  mass  remains  pasty  till  all  the  nitric  acid  is  disengaged,  and  then  enters  into 
fusion }  red  vapours  again  appearing  towards  the  end  of  the  process.  The  residuary 
salt  is  the  bisulphate  of  potassa,  or  double  sulphate  of  water  and  potassa,  HO.S03-f- 
KO.S03.  The  rationale  of  this  important  process  is  exhibited  in  the  following 
diagram :  — 

PROCESS   FOR   NITRIC   ACID. 

Before  decomposition.  After  decomposition. 

(Nitric  acid 54 ,-  63  Nitric  acid  and  water. 

101  Nitrate  of  potassa...  \ 

(Potassa 47 


(Water 

49  Oil  of  vitriol J 

I  Sulphuric  acid    40 ^  87  Sulphate  of  potar- 

49  Oil  of  vitriol Vl  of  vitriol....    49  49  Sulphate  of  water 


In  this  operation  twice  as  much  sulphuric  acid  is  employed  as  is  required  to  neutra- 
lize the  potassa  of  the  nitre,  by  which  means  the  whole  nitric  acid  is  eliminated 
without  loss  at  a  moderate  temperature,  and  a  residuary  salt  is  left  which  is  easily 
removed  from  the  retort. 

With  half  the  preceding  quantity,  or  a  single  equivalent  of  oil  of  vitriol,  the 
materials  in  the  retort  are  apt  to  undergo  a  vesicular  swelling,  upon  the  application 
of  heat,  and  to  pass  into  the  receiver.  Abundance  of  ruddy  fumes  are  also  evolved, 
that  are  not  easily  condensed,  and  prove  that  the  nitric  acid  is  decomposed.  The 
temperature  in  this  process  must  also  be  raised  inconveniently  high  towards  the  end 
of  the  operation,  in  order  to  decompose  the  whole  nitre.  The  peculiarities  of  the 
decomposition  here  arise  from  the  formation  of  bisulphate  of  potassa  in  the  operation, 
the  whole  sulphuric  acid  uniting  in  the  first  instance  with  half  the  potassa  of  the 
nitre.  Now,  it  is  only  at  an  elevated  temperature  that  the  acid  salt  thus  formed 
can  decompose  the  remaining  nitre  ]  —  a  temperature  which  is  sufficient  to  decom- 
pose nitric  acid,  as  may  be  proved  by  transmitting  the  vapour  of  the  concentrated 
acid  through  a  tube  heated  to  the  same  degree. 

Ordinary  nitric  acid  for  manufacturing  purposes  is  generally  prepared  by  dis- 
tilling nitrate  of  soda  with  an  equivalent  of  sulphuric  acid  not  at  its  highest  degree 
of  concentration  in  a  large  cylinder  of  cast  iron  (fig.  116,  page  261),  supported  in 
brickwork  over  a  fire.  Both  ends  of  the  cylinder  are  moveable,  and  generally  con- 
sist of  circular  discs  of  stone.  The  nitric  acid  which  distils  over  is  condensed  in  a 


CITRIC   ACID. 


261 


Fia.  117. 


IPOjQOipQ 


series  of  large  vessels  of  salt-glaze  ware,  of  FIG.  116. 

the  form  of  Woulf  bottles,  of  which  two, 
A,  B,  are  shown  in  the  figure. 

The  iron  cylinders  are  generally  so  sup- 
ported that  two  of  them  are  heated  by  one 
fire,  as  in  fig.  117,  which  is  a  sectional  view 
of  three  pairs  of  such  retort  cylinders.  The 
iron  of  the  vault  or  roof  of  the  cylinder  is 
most  apt  to  be  corroded  by  the  acid  vapours, 
and  is  therefore  protected  by  a  coating  of  fire- 
clay or  of  tiles  of  the  same  material  cemented 
together. 

Properties.  —  The  acid  prepared  by  the 
first  process  is  colourless,  or  has  only  a  straw 
yellow  tint.  If  the  oil  of  vitriol  has  been  in 
its  most  concentrated  condition,  which  is 
seldom  the  case,  the  nitric  acid  is  in  its 
state  of  highest  concentration  also,  and  con- 
tains no  more  than  a  single  equivalent  of 
water.  The  density  of  this  acid  is  1.522  at 
58°;  but  a  slight  heat  disengages  a  little 

peroxide  of  nitrogen  from  it,  and  its  density  becomes  1.521  (Mitscherlich).  The 
density  of  the  strongest  colourless  nitric  acid  which  Mr.  Arthur  Smith  could  pre- 
pare was  1.517  at  60°  ;  it  boiled  at  184°,  and  came  within  1  per  cent,  of  the 
protohydrate  in  composition  (Chem.  Mem.  iii.  402).  When  distilled,  it  is  partially 
decomposed  by  the  heat,  and  affords  a  product  of  a  strong  yellow  colour.  Its  vapour 
transmitted  through  a  porcelain  tube,  heated  to  dull  redness,  is  decomposed  in  a 
great  measure  into  oxygen  and  peroxide  of  nitrogen ;  and  into  oxygen  and  nitrogen 
gases,  when  the  tube  is  heated  to  whiteness.  The  colourless  liquid  acid  becomes 
yellow,  when  exposed  to  the  rays  of  the  sun,  and  on  loosening  the  stopper  of  the 
bottle  it  is  sometimes  projected  with  force,  from  the  state  of  compression  of  the  dis- 
engaged oxygen.  Hence  to  preserve  this  acid  colourless  it  must  be  kept  in  a 
covered  bottle.  It  congeals  at  about  — 40°,  but  diluted  with  half  its  weight  of 
water,  it  becomes  solid  at  1J°,  and  with  a  little  more  water  its  freezing  point  is 
again  lowered  to  — 45°.  Exposed  to  the  air,  the  concentrated  acid  fumes,  from  the 
condensation  by  its  vapour  of  the  moisture  in  the  atmosphere.  It  also  attracts 
moisture  from  damp  air,  and  increases  in  weight ;  and  when  suddenly  mixed  with 
3-4ths  of  its  weight  of  water,  may  rise  in  temperature  from  60°  to  140°. 

Nitric  acid  has  a  great  affinity  for  water,  and  diminishes  in  density  with  the  pro- 
portion of  water  added  to  it.  A  table  has  been  constructed  in  which  the  per 
eentage  of  absolute  acid  is  expressed  in  mixtures  of  various  densities,  which  is  useful 
for  reference  and  will  be  given  in  an  appendix.  There  appears  to  be  no  definite 
hydrate  of  this  acid  between  the  first  (the  nitrate  of  water),  and  that  containing 
3  eq.  of  water  additional  (A.  Smith).  The  first  has  no  action  upon  tin  or  iron 
The  second  is  acid  of  density  1.424,  which  therefore  contains  4  eq.  of  water.  This 
last  hydrate  was  found  by  Dr.  Dalton  to  have  the  highest  boiling  point  of  any 
hydrate  of  nitric  acid :  it  is  250°,  and  both  weaker  and  stronger  acids  are  brought 
to  this  strength  by  continued  ebullition,  the  former  losing  water  and  the  latter  acid. 
The  density  of  the  vapour  of  this  hydrate  is  found  to  be  1243  by  A.  Bineau,  and 
it  contains  2  volumes  of  nitrogen,  5  volumes  of  oxygen,  and  8  volumes  of  steam 
condensed  into  10  volumes,  which  are  therefore  the  combining  measure  of  this 
vapour  (Ann.  de  Chim  et  de  Phys.  Ixviii.  p.  418). 

Nitric  acid  is  exceedingly  corrosive,  and  one  of  the  strongest  acids,  yielding  only 
in  that  respect  to-  sulphuric  acid.  The  facility  with  which  it  parts  with  its  oxygen 
renders  it  very  proper  for  oxidating  bodies  in  the  humid  way,  a  purpose  for  which  it 
is  constantly  employed.  Nearly  all  the  metals  are  oxidized  by  means  of  it;  some 


262  NITROGEN. 

of  them  with  extreme  violence,  such  as  copper,  mercury,  and  zinc,  when  the  con- 
centrated acid  is  used;  and  tin  and  iron  by  the  acid  very  slightly  diluted.  Poured 
upon  red-hot  charcoal,  it  causes  a  brilliant  combustion.  When  mixed  with  a  fourth 
of  its  bulk  of  sulphuric  acid,  and  thrown  upon  a  few  drops  of  oil  of  turpentine,  it 
occasions  an  explosive  combustion  of  the  oil.  Sulphur  digested  in  nitric  acid  at 
the  boiling  point  is  raised  to  its  highest  degree  of  oxidation  and  becomes  sulphuric 
acid ;  iodine  is  also  converted  by  it  into  iodic  acid.  Most  vegetable  and  animal 
substances  are  converted  by  nitric  acid  into  oxalic  and  carbonic  acids.  It  stains  the 
cuticle  and  nails  of  a  yellow  colour,  and  has  the  same  effect  upon  wool ;  the  orange 
patterns  upon  woollen  table-covers  are  produced  by  means  of  it.  In  the  undiluted 
state  it  forms  a  powerful  cautery. 

In  acting  upon  the  less  oxidable  metals,  such  as  copper  and  mercury,  nitric  acid 
is  itself  decomposed,  and  nitric  oxide  gas  produced,  which  comes  off  with  efferves- 
cence. Palladium  and  silver,  when  they  are  dissolved  by  the  acid  in  the  cold,  pro- 
duce nitrous  acid  in  the  liquor  and  evolve  no  gas,  but  this  is  very  unusual  in  the 
solution  of  metals  by  nitric  acid.  Those  metals,  such  as  zinc,  which"  are  dissolved 
in  diluted  acids  with  the  evolution  of  hydrogen,  act  in  two  ways  upon  nitric  acid ; 
sometimes  they  decompose  it,  so  as  to  disengage  a  mixture  of  peroxide  of  nitrogen 
and  nitric  oxide,  and  at  other  times  they  decompose  both  water  and  nitric  acid  at  once, 
in  such  proportions  that  the  hydrogen  of  the  water  combines  with  the  nitrogen  of 
the  acid  to  form  ammonia,  which  last  combines  with  another  portion  of  acid,  and  is 
retained  in  the  liquor  as  nitrate  of  ammonia.  The  protoxide  of  nitrogen  is  also 
evolved  when  zinc  is  dissolved  in  very  feeble  nitric  acid,  which  may  arise  from  the 
action  of  hydrogen  upon  nitric  oxide.  Nitric  acid,  in  its  highest  state  of  concentra- 
tion, exerts  no  violent  action  upon  certain  organic  substances,  such  as  lignin  01 
woody  fibre  and  starch,  for  a  short  time,  but  unites  with  them  and  forms  singular 
compounds.  A  proper  acid  for  such  experiments  is  procured  with  most  certainty 
by  distilling  100  parts  of  nitre,  with  no  more  than  60  parts  of  the  strongest  oil  of 
vitriol.  If  paper  is  soaked  for  one  minute  in  such  an  acid,  and  afterwards  washed 
with  water,  it  is  found  to  shrivel  up  a  little  and  become  nearly  as  tough  as  parch- 
ment, and  when  dried  to  be  remarkably  inflammable,  catching  fire  at  so  low  a  tem- 
perature as  356°,  and  burning  without  any  nitrous  odour  (Pelouze).  Or  if  tho 
strong  undiluted  nitric  acid  of  commerce  be  mixed  with  an  equal  weight  of  oil  of 
vitriol,  and  cotton-wool  be  immersed  in  the  mixture  for  a  minute  or  two  and  after- 
wards washed  with  water,  it  is  converted  into  gun-cotton,  without  injury  to  the 
cotton  fibre  (Schonbein). 

Nitric  acid  forms  an  important  class  of  salts,  the  nitrates,  which  occasion  defla- 
gration when  fused  with  a  combustible  at  a  high  temperature,  from  the  oxygen  in 
their  acid,  and  are  remarkable  as  a  class  for  their  general  solubility,  no  nitrate  being 
insoluble  in  water.  The  nitrate  of  the  black  oxide  of  mercury  is  perhaps  the  least 
soluble  of  these  salts.  The  nitrates  of  potassa,  soda,  ammonia,  baryta,  and  strontia, 
are  anhydrous ;  but  the  nitrates  of  the  extensive  magnesian  class  of  oxides  all  con- 
tain water  in  a  state  of  intimate  combination,  and  have  a  formula  analogous  to  that 
of  hydrated  nitric  acid,  or  the  nitrate  of  water  itself.  Of  the  four  atoms  of  water 
contained  in  hydrated  nitric  acid  of  sp.  gr.  1.42,  one  is  combined  with  the  acid  as 
base,  and  may  be  named  basic  water,  while  the  other  three  are  in  combination  with 
the  nitrate  of  water,  and  may  be  termed  the  constitutional  water  of  that  salt.  The 
same  three  atoms  of  constitutional  water  are  found  in  all  the  magnesian  nitrates, 
with  the  addition  often  of  another  three  atoms  of  water,  as  appears  from  the  follow- 
ing formulae :  — 

Nitric  acid,  1.42 HO.N05  +  3HO 

Prismatic  nitrate  of  copper CuO.N05  +  3HO 

Rhomboidal  nitrate  of  copper CuO.N05-f  3HO  +  3HO 

Nitrate  of  magnesia MgO.N05  +  3HO  + 3HO 


NITRIC   ACID.  263 

It  is  doubtful  whether  the  proportion  of  constitutional  water  in  any  of  these 
nitrates  can  be  reduced  below  3  atoms  by  heat  without  the  loss  of  a  portion  of  nitric 
acid  at  the  same  time,  and  the  partial  decomposition  of  the  salt.  The  nitrates  of 
the  potassa  and  magnesian  classes  do  not  combine  together,  and  no  double  nitrates 
are  known,  nor  nitrates  with  excess  of  acid.  The  nitrates  with  excess  of  metallic 
oxide,  which  are  called  subnitrates,  appear  to  be  formed  on  the  type  of  the  magne- 
sian class:  the  subnitrate  of  copper,  being  CuO.N05  +  3Cu0.3HO  (Gerhardt),  or 
nitrate  of  copper  with  3  atoms  hydrated  oxide  of  copper.  The  water  is  strongly 
retained,  and  requires  a  temperature  of  300°  to  expel  it.  The  nitrate  of  red  oxide 
of  mercury  is  HgO.NOj-f  HgO  (Kane). 

Nitric  acid  in  a  solution  cannot  be  detected  by  precipitating  that  acid  in  combi- 
nation with  any  base,  as  the  nitrates  are  all  soluble,  so  that  tests  of  another  nature 
must  be  had  recourse  to,  to  ascertain  its  presence.  A  highly  diluted  solution  of  sulphate 
of  indigo  may  be  boiled  without  change,  but  on  adding  to  it  at  the  boiling  temperature 
a  liquid  containing  free  nitric  acid,  the  blue  colour  of  the  indigo  is  soon  destroyed. 
If  it  is  a  neutral  nitrate  which  is  tested,  a  little  sulphuric  acid  should  be  added  to 
the  solution,  to  liberate  the  nitric  acid,  before  mixing  it  with  the  sulphate  of  indigo. 
It  is  also  necessary  to  guard  against  the  presence  of  a  trace  of  nitric  acid  in  the  sul- 
phuric acid.  Another  test  of  the  presence  of  nitric  acid  has  been  proposed  by  De 
Richemont.  The  liquid  containing  the  nitrate  is  mixed  with  rather  more  than  an 
equal  bulk  of  oil  of  vitriol,  and  when  the  mixture  has  become  cool,  a  few  drops  of  a 
strong  solution  of  protosulphate  of  iron  are  added  to  it.  Nitric  oxide  is  evolved, 
and  combines  with  the  protosulphate  of  iron,  producing  a  rose  or  purple  tint  even 
when  the  quantity  of  nitric  acid  is  very  small.  One  part  of  nitric  acid  in  24,000 
of  water  has  been  detected  in  this  manner.  Free  nitric  acid  also  is  incapable  of  dis- 
solving gold-leaf,  although  heated  upon  it,  but  acquires  that  property  when  a  drop 
of  hydrochloric  acid  is  added  to  it.  But  in  testing  the  presence  of  this  acid,  it  is 
always  advisable  to  neutralize  a  portion  of  the  liquor  with  potassa,  and  to  evaporate 
so  as  to  obtain  the  thin  prismatic  crystals  of  nitre,  which  may  be  recognised  by  their 
form,  by  their  cooling  nitrous  taste,  their  power  to  deflagrate  combustibles  at  a  red 
heat,  and  by  the  characteristic  action  of  the  acid  they  contain,  when  liberated  by 
sulphuric  acid,  upon  copper  and  other  metals,  in  which  ruddy  nitrous  fumes  are 
produced. 

SWhen  obtained  from  nitrate  of  soda,  it  may  contain  iodine.     This  impure  acid 
ds,  on  distillation,  a  sublimate  of  iodine  after  all  the  nitric  acid  has  come  over. 
Neutralized  with  potassa,  mixed  with  a  solution  of  starch,  and  sulphuric  acid  added 
dn>p  by  drop,  the  liquid  assumes  a  blue  colour  (Grmelin's  Handbook,  vol.  ii.  p.  393). 
—  R.  B.] 

If  nitric  acid  be  rigidly  pure,  it  may  be  diluted  with  distilled  water,  and  is  not 
disturbed  by  nitrate  of  silver,  nor  by  chloride  of  barium,  the  first  of  which  discovers 
the  presence  of  hydrochloric  acid  by  producing  a  white  precipitate  of  chloride  of 
silver ;  the  last  discovers  sulphuric  acid  by  forming  the  white  insoluble  sulphate  of 
baryta.  The  fuming  nitric  acid  may  be  freed  from  hydrochloric  acid,  by  retaining 
it  warm  on  a  sand-bath  for  a  day  or  two,  when  the  chlorine  of  the  hydrochloric  acid 
goes  off  as  gas.  To  free  it  from  sulphuric,  it  should  be  diluted  with  a  little  water, 
and  distilled  from  nitrate  of  baryta;  but  the  process  for  nitric  acid  which  has  been 
described  gives  it  without  a  trace  of  sulphuric  acid,  when  carefully  conducted. 

Uses.  —  Nitric  acid  is  sometimes  used  in  the  fumigations  required  for  contagious 
diseases,  particularly  in  wards  of  hospitals  from  which  the  patients  are  not  removed, 
the  fumes  of  this  acid  being  greatly  less  irritating  than  those  of  chlorine.  For  the 
purpose  of  fumigation,  pounded  nitre  and  concentrated  sulphuric  acid  are  used, 
being  heated  together  in  a  cup.  Nitric  acid  is  par  excellence  the  solvent  of  metals, 
and  has  other  most  numerous  and  varied  applications  not  only  in  chemistry,  but 
likewise  in  the  arts  and  manufactures. 


264 


NITROGEN. 


NITROGEN    AND    HYDROGEN AMMONIA. 

Eq.  17  or  212.5;  H3N;  density  596.7; 

With  hydrogen,  nitrogen  forms  a  remarkable  gaseous  compound  —  ammonia, 
which  derives  its  name  from  sal  ammoniac,  a  salt  from  which  it  is  generally 
extracted,  and  which  again  was  so  named  from  being  first  prepared  in  the  district 
of  Ammonia,  in  Libya.  Ammonia  is  produced  in  the  destructive  distillation  of  all 
organic  matters  containing  nitrogen,  which  has  given  rise  to  one  of  its  popular 
names,  the  Spirits  of  Hartshorn.  It  is  also  produced  during  the  putrefaction  of  the 
same  matters,  and  finds  its  way  into  the  atmosphere  (page  252).  A  trace  of  it  is 
always  found  in  the  native  oxides  of  iron,  in  the  varieties  of  clay,  and  in  some  other 
minerals. 

Nitrogen  and  hydrogen  mixed  together  do  not  exhibit  any  disposition  to  combine, 
even  when  heated ;  but  if  electric  sparks  be  taken  through  a  mixture  of  those  gases, 
particularly  with  the  presence  of  any  acid  vapour,  a  sensible  trace  of  a  salt  of  am- 
monia is  produced.  Hydrogen,  however,  if  evolved  in  contact  with  nitrogen,  will 
in  cer.tain  circumstances  form  ammonia.  Thus  in  the  rusting  of  iron  in  water  con- 
taining air  or  nitrogen  and  carbonic  acid,  the  hydrogen  which  is  then  evolved  from 
the  decomposition  of  the  water,  appears  to  combine  in  its  nascent  state  with  nitrogen. 
If,  while  zinc  is  dissolving  in  dilute  sulphuric  acid,  nitric  acid  be  added  drop  by 
drop  till  the  evolution  of  hydrogen  gas  ceases,  the  latter  will  be  found  to  have  united 
with  the  nitrogen  of  the  nitric  acid,  and  much  ammonia  to  be  formed ;  the  oxygen 
of  the  nitric  acid  combining  with  hydrogen  also,  to  form  water,  at  the  same  time. 
If  the  proportion  of  nitric  acid  be  relatively  small,  Mr.  Nesbitt  finds  that  it  may  be 
entirely  converted  into  ammonia  in  this  manner.  When  zinc  is  dissolved  in  nitric 
acid  alone,  which  is  neither  much  diluted  nor  very  strong,  but  in  an  intermediate 
condition,  the  same  suppression  of  hydrogen  and  formation  of  ammonia  is  observed. 

Preparation.  — In  a  state  of  purity,  ammonia  is  a  gas,  of  which  the  well-known 
liquor  or  aqua  ammonia  is  a  solution  in  water.  This  solution,  which  is  of  constant 
use  as  a  reagent,  is  prepared  by  mixing  intimately  sal  ammoniac  (hydrochlorate  of 
ammonia)  with  an  equal  weight  of  slaked  lime,  introducing  the  mixture  into  a  glass 
retort  or  bolt-head,  which  is  afterwards  filled  up  with  slaked  lime  (A,  fig.  118),  and 

FIG.  118. 


PROCESS  FOR   AMMONIA. 


265 


distilling  by  the  diffused  heat  of  a  chauffer  or  sand-pot.  If  recourse  is  had  to 
the  gas-flame,  the  heat  may  be  conveniently  diffused  by  placing  the  burner  within 
a  cylinder  of  sheet  iron  about  14  inches  in  height,  as  represented  in  the  figure,  with 
a  perforated  stage  B,  covered  with  small  fragments  of  pumice-stone,  on  which  the 
flask  A  is  supported.  Ammoniacal  gas  comes  off,  which  should  be  conducted  into 
a  quantity  of  distilled  water  in  the  bottle  C,  to  condense  it,  equal  to  the  weight  of 
the  salt  employed.  Chloride  of  calcium  and  the  excess  of  lime  remain  in  the  retort, 
and  a  considerable  quantity  of  water  is  liberated  in  the  process,  and  distils  over 
with  the  ammonia.  This  reaction  is  explained  in  the  following  diagram  :  — 


PROCESS   FOR   AMMONIA. 


Before  decomposition. 

C  Ammonia  17 
53.5  Hydrochlorate  of  ammonia  •!  Hydrogen    1 

(Chlorine    35.5 

Oxygen       8 
28      Lime -I  Calcium    20 


After  decomposition. 
17     Ammonia. 


81.5 


81.5 


9     Water,      [cium. 
55.5  Chloride  of  cal- 

81.5 


Or  in  symbols : 


NH4C1  and  CaO=NH3  with  HO  and  CaCl. 


FIG.  119. 


To  obtain  ammoniacal  gas,  a  portion  of  the  solution  prepared  by  the  preceding 
process  may  be  introduced  into  a  small  plain  retort,  A  (fig.  119),  by  means  of  the 
long  funnel  B ;  and  the  short  bent  tube  C  being  adapted  by  a 
perforated  cork  to  the  mouth  of  the  retort,  the  liquid  is  boiled 
by  a  gentle  heat,  when  the  gas  is  first  expelled  from  its  superior 
volatility,  and  collected  in  a  jar  filled  with  mercury,  and  inverted 
over  the  mercurial  trough  (fig.  120,  page  266).  Or  the  gas  may 
be  derived  at  once  from  sal  ammoniac,  mixed  with  twice  its 
weight  of  quicklime  in  a  small  retort,  and  collected  over  mer- 
cury. 

Properties.  —  Ammonia  is  a  colourless  gas,  of  a  strong  and 
pungent  odour,  familiar  in  spirits  of  hartshorn.  It  is  composed 
of  2  volumes  of  nitrogen  and  6  of  hydrogen,  condensed  into  4 
volumes,  which  form  the  combining  measure  of  this  gas.  Am- 
monia is  resolved  into  its  constituent  gases,  in  these  proportions, 
when  transmitted  through  an  ignited  porcelain  tube  containing 
platinum,  iron,  or  copper  wire.  The  two  latter  metals  absorb  a 
little  nitrogen  (Despretz),  and  become  brittle,  but  the  platinum 
remains  unaltered.  By  a  pressure  of  6.5  atmospheres,  at  50°, 
it  is  condensed  into  a  transparent  colourless  liquid,  of  which  the 
sp.  gr.  is  0.731  at  60°.  Ammoniacal  gas  is  inflammable  in  air 
in  a  low  degree,  burning  in  contact  with  the  flame  of  a  taper. 
A  small  jet  of  this  gas  will  also  burn  in  oxygen.  A  mixture 
of  ammoniacal  gas  with  an  equal  volume  of  nitrous  oxide  may  be 
detonated  by  the  electric  spark,  and  affords  water  and  nitrogen. 
Water  is  capable  of  dissolving  about  500  times  its  volume  of 
ammoniacal  gas  in  the  cold,  and  the  solution  is  always  specifi- 
cally lighter,  and  has  a  lower  boiling  point  than  pure  water. 
According  to  the1  observations  of  Davy,  solutions  of  sp.  gr. 
0.872;  0.9054,  and  0.9692,  contain  respectively  32.5,  25.37, 


NITROGEN. 
FIG.  120. 


and  9.5  per  cent,  of  ammonia.  Mr.  Griffin,  who  has  constructed  a  table  of  the 
densities  of  solutions  of  ammonia  from  experiment,  finds  that  no  sensible  condensa- 
tion of  volume  occurs  in  these  mixtures,  and  that  their  densities  are  the  mean  of 
those  of  water  1  and  anhydrous  liquid  ammonia,  supposing  the  latter  to  be 
0.7083  at  62°  (Mem.  Chem.  Soc.  iii.  189).  Ammoniacal  gas  is  also  largely  soluble 
in  alcohol. 

Solution  of  ammonia  has  an  acrid  alkaline  taste,  and  produces  blisters  on  the 
tongue  and  skin.  When  cooled  slowly  to  — 40°,  it  crystallizes  in  long  needles  of  a 
silky  lustre.  The  solution  has  a  temporary  action  upon  turmeric  paper,  which  it 
causes  to  be  brown  while  humid ;  it  also  restores  the  blue  colour  of  litmus  reddened 
by  an  acid,  changes  the  blue  colour  of  the  infusion  of  red  cabbage  into  green,  and 
neutralizes  the  strongest  acids,  properties  which  it  possesses  in  common  with  the 
fixed  alkalies.  Tt  is  distinguished  as  the  volatile  alkali.  When  ammonia  is  free, 
it  may  always  be  discovered,  by  its  odour,  by  forming  dense  white  fumes  with  hydro- 
chloric acid,  and  by  producing  a  deep  blue  solution  with  salts  of  copper. 

Ammonia,  in  solution,  is  decomposed  by  chlorine,  with  the  evolution  of  nitrogen 
gas  and  formation  of  hydrochlorate  of  ammonia :  when  ammonia  and  chlorine,  both 
in  the  state  of  gas,  are  mixed  together,  the  action  that  ensues  is  attended  with  flame. 
Dry  iodine  absorbs  ammoniacal  gas,  and  forms  a  brown  viscous  liquid,  which  water 
decomposes,  dissolving  out  hydriodate  of  ammonia,  and  leaving  a  black  powder, 
which  is  the  explosive  iodide  of  nitrogen. 

Ammonia  forms  several  classes  of  compounds  with  acids  and  salts  (page  166), 
and  exhibits  highly  curious  reactions  with  many  other  substances,  which  do  not 
admit  of  being  discussed  so  early,  but  which  I  shall  return  to  later  in  the  work. 
[See  Supplement,  p.  766.] 

SECTION  IV. 

CARBON. 

Eq.  6  or  75;  C;  density  of  vapour  (hypothetical]  416   — 

Carbon  is  found  in  great  abundance  in  the  mineral  kingdom  united  with  other 
substances,  as  in  coal,  of  which  it  is  the  basis,  and  in  the  acid  of  carbonates :  it  is 
also  the  most  considerable  clement  of  the  solid  parts  of  both  animals  and  vegetables. 


GRAPHITE.  267 

It  exists  in  nature,  or  may  be  obtained  by  art,  under  a  variety  of  appearances,  and 
possessed  of  very  different  physical  properties.  Carbon  is  a  dimorphous  body, 
occurring  crystallized  in  the  diamond  and  graphite  in  wholly  different  forms,  and 
when  artificially  produced  forming  several  amorphous  varieties  of  charcoal  which  are 
very  unlike  each  other.  [See  Supplement,  p.  769.] 

Diamond.  —  This  valuable  gem  is  found  throughout  the  range  of  the  Ghauts  in 
India,  but  chiefly  at  Golconda,  in  Borneo,  and  also  in  Brazil.  It  is  always  associated 
with  transported  materials,  such  as  rolled  gravel,  or  found  in  a  sort  of  breccia  or 
pudding-stone,  composed  of  fragments  of  jasper,  quartz,  and  calcedony,  so  that  it  is 
still  a  question  whether  the  diamond  is  of  mineral  or  vegetable  origin.  On  removing 
the  crust  with  which  the  crystals  are  covered,  they  are  exceedingly  brilliant,  refract 
light  powerfully,  and  are  generally  perfectly  transparent,  although  diamonds  are 
sometimes  black,  blue,  and  of  a  beautiful  rose-colour.  The  primitive  form  of  diamond 
is  the  regular  octohedron,  or  two  four-sided  pyramids,  of  which  the  faces  are  equi- 
lateral triangles,  applied  base  to  base  (fig.  55,  page  143).  It  is  more  frequently 
found  in  the  pyramidal  octohedron, — a  figure  bounded  by  24  sides,  which  presents 
the  general  aspect  of  a  regular  octohedron,  on  every  facet  of  which  has  been  placed 
a  low  pyramid  of  three  facets ;  or,  each  facet  of  the  octohedron  is  replaced  by  6 
secondary  triangles,  and  the  crystal  becomes  almost  spherical,  and  presents  48  facets. 
These  facets  often  appear  curved  from  the  effect  of  attrition.  The  diamond  can 
always  be  cleaved  in  the  direction  of  the  faces  of  the  octohedron,  which  possess  that 
particular  brilliancy  characteristic  of  the  diamond.  It  is  the  hardest  of  the  genis. 
An  edge  of  its  crystal  formed  by  flat  planes  only  scratches  glass,  but  if  the  edge  is 
formed  of  curved  faces,  like  the  edge  of  a  convex  lens,  it  then,  besides  abrading  the 
surface,  produces  a  fissure  to  a  small  depth,  and  in  the  form  of  the  glazier's  diamond 
is  used  to  cut  glass.  The  weight  of  diamonds  is  generally  estimated  by  the  carat, 
which  is  about  3.2  grains.  The  diamond  is  remarkably  indestructible,  and  may  be 
heated  to  whiteness  in  a  covered  crucible  without  injury,  but  it  begins  to  burn  in 
the  open  air,  at  about  the  melting  point  of  silver,  charcoal  sometimes  appearing  on 
its  surface,  and  is  entirely  converted  into  carbonic  acid  gas.  When  heated  to  the 
highest  degree  between  the  charcoal  points  of  a  strong  voltaic  battery,  the  diamond 
swells  up  considerably,  and  divides  into  portions.  After  cooling,  it  is  found  entirely 
altered  in  appearance,  having  become  of  a  metallic  gray,  friable,  and  resembling  in 
every  respect  the  coke  from  bituminous  coal.  This  experiment  appears  to  show  that 
a  high  temperature  is  unfavourable  to  the  existence  of  diamonds,  and  that  they  can- 
not therefore  be  originally  formed  at  a  very  elevated  temperature.  The  diamond  is 
quickly  consumed  in  fused  nitre,  when  the  carbonic  acid  is  retained  by  the  potash  j 
this  is  a  simple  mode  of  analyzing  the  diamond,  by  which  it  has  been  proved  to  be 
pure  carbon.  The  diamond  is  a  non-conductor  of  electricity.  Its  density  varies 
from  3.5  to  3.55. 

Graphite. — This  mineral,  which  is  also  known  as  Black  Lead  and  Plumbago, 
occurs  in  rounded  masses  deposited  in  beds  in  the  primitive  formations,  particularly 
in  granite,  mica-schist,  and  primitive  limestone.  Borrowdale  in  Cumberland  is  a 
celebrated  locality  of  graphite,  and  affords  the  only  specimens  which  are  sufficiently 
hard  for  making  pencils.  It  is  occasionally  found  crystallized  in  plates  which  are 
six-sided  tables.  Graphite  may  also  be  produced  artificially,  by  putting  an  excess 
of  charcoal  in  contact  with  fused  cast  iron,  when  a  portion  of  the  carbon  dissolves, 
and  separates  again  on  cooling,  in  the  form  of  large,  and  beautiful  leaflets.  In  the 
condition  of  graphite,  carbon  is  perfectly  opaque,  soft  to  the  touch,  possessed  of  the 
metallic  lustre,  and  of  a  specific  gravity  from  1.9  to  2.3.  It  always  contains  iron 
and  manganese,  apparently  in  the  state  of  oxides,  and  in  combination  with  silicic  and 
titanic  acids,  sometimes  to  the  extent  of  28  per  cent.,  but  in  some  specimens,  as  in 
those  from  Barreros  in  Brazil,  not  more  than  a  trace  of  those  metals  is  found,  which 
is  to  be  considered  an  accidental  constituent,  and  not  essential  to  the  mineral. 
Neither  in  the  form  of  diamond  nor  graphite  does  carbon  exhibit  any  indication  of 
fusion  or  volatility  under  the  most  intense  heat.  Anthracite  is  often  nearly  pure 


208  CARBON. 

carbon,  but  always  contains  a  portion  of  hydrogen,  and  is  related  to  bituminous  coal, 
and  not  to  graphite.     [Sre  $HjDp7eitte»t?,  p.  770.] 

Charcoal.  —  Owing  to  its  infusibility  carbon  presents  itself  under  a  variety  of 
aspects,  according  to  the  structure  of  the  substance  from  which  it  is  derived,  and*  the 
accidental  circumstances  of  its  preparation.  The  following  are  the  principal  varieties : 
gas  carbon,  lamp-black,  wood  charcoal,  coke,  and  ivory  black. 

1.  Gas  carbon  has  the  metallic  lustre,  and  a  density  of  1.76;   it  is  compact, 
generally  of  a  mammillated  structure,  but  sometimes  in  fine  fibres,  and  considerably 
resembles  graphite,  but  is  too  hard  to  give  a  streak  upon  paper.     It  is  the  product 
of  a  slow  deposition  of  carbon  from  coal  gas  at  a  high  temperature,  and  is  frequently 
found  to  line  the  gas  retorts  to  a  considerable  thickness,  and  to  fill  up  accidental 
fissures  in  them  (Dr.  Colquhoun,  Ann.  of  Philos.,  New  Ser.,  vol.  xii.  p.  1). 

2.  Lamp-black  is  the  soot  of  imperfectly  burned  combustibles,  such  as  tar  or  resin. 
Carbon  is  deposited  in  a  powder  of  the  same  nature,  and  of  the  purest  form,  when 
alcohol  vapour  or  a  volatile  oil  is  transmitted  through  a  porcelain  tube  at  a  red  heat; 
and  the  lustrous  charcoal,  which  is  obtained  on  calcining,  in  close  vessels,  starch, 
sugar,  and  many  other  organic  substances,  which  fuse  and  afford  a  bright  vesicular 
carbon  of  a  metallic  lustre,  is  possessed  of  the  same  characters.     The  charcoal  of  the 
latter  sources,  however,  always  retains  traces  of  oxygen  and  hydrogen.     Lamp-black 
is  deficient  in  an  attraction  for  organic  matters  in  solution,  which  ordinary  charcoal 


3.  Wood  charcoal.     Wood  was  found  by  Karsten  to  lose  57  per  cent,  of  its 
weight  when  thoroughly  dried  at  212°,  and  10  per  cent,   more  at  304°.     The 
remaining  33  parts  of  baked  wood  afforded,  when  calcined,  25  of  charcoal,  while 
100  parts  of  the  same  wood  calcined,  without  being  previously  dried,  left  only  14 
per  cent,  of  carbon.     It  is  the  absence  of  this  large  quantity  of  water  which  causes 
the  heat  of  burning  charcoal  to  be  so  much  more  intense  than  that  of  wood.     When 
calcined  at  a  high  temperature,  charcoal  becomes  dense,  hard,  and  less  inflammable. 
The  knots  in  wood  sometimes  afford  a  charcoal  which  is  particularly  hard,  and  is 
used  in  polishing  metals,  but  it  contains  silica.     From  the  minuteness  of  its  pores, 
the  charcoal  of  wood  absorbs  many  times  its  volume  of  the  more  liquefiable  gases ; 
Such  as  ammoniacal  gas,  hydrochloric  acid,  hydrosulphuric  acid,  and  carbonic  acid, 
condensing  90  times  its  volume  of  the  first,  and  35  of  the  last :  of  oxygen,  it  con- 
denses 9.25  volumes;  of  nitrogen,  7.5  volumes;  and  of  hydrogen,  1.75  volumes.    It 
also  absorbs  moisture  with  avidity  from  the  atmosphere,  and  other  condensible  vapours, 
such  as  odoriferous  effluvia.     From  this  last  property  freshly  calcined  charcoal,  when 
wrapt  up  in  clothes  which  have  contracted  a  disagreeable  odour,  destroys  it,  and  has  a 
considerable  effect  in  retarding  the  putrefaction  of  organic  matter  with  which  it  is 
placed  in  contact.    Water  is  also  found  to  remain  sweet,  and  wine  to  be  improved  in 
quality,  if  kept  in  casks  of  which  the  inside  has  been  charred.    In  the  state  of  a  coarse 
powder,  wood  charcoal  is  particularly  applicable  as  a  filter  for  spirits,  which  it  de- 
prives of  the  essential  oil  which  they  contain.    It  is  much  less  destructible  by  atmos- 
pheric agencies  than  wood,  and  hence  the  points  of  stakes  are  often  charred,  before 
being  driven  into  the  ground,  in  order  to  preserve  them.     Charcoal  decomposes  the 
vapour  of  water  at  a  red  heat,  giving  rise  to  a  gaseous  mixture,  which  was  found  by 
Bunsen  to  consist,  in  100  volumes,  of  hydrogen  56,  carbonic  oxide  29,  carbonic 
acid  14.8,  and  light  carburetted  hydrogen  0.2  volume.    • 

4.  The  coke  of  those  species  of  coal  which  do  not  fuse  when  heated  is  a  remark- 
ably dense  charcoal,  considerably  resembling  that  of  wood,  and  of  great  value  as  fuel, 
from  the  high  temperature  which  can  be  produced  by  its  combustion.     When 
burned  it  generally  leaves  2  or  3  per  cent,  of  earthy  ashes,  while  the  ashes  from 
wood  charcoal  seldom  exceed  1  per  cent.     The  density  of  pulverised  coke  varies 
from  1.6  to  2.0.     Coke  and  wood  charcoal,  after  being  strongly  heated,  are  good 
conductors  of  electricity. 

5.  Ivory  black,  Bone  black,  and  Animal  charcoal,  are  names  applied  to  bones 
calcined  or  converted  into  charcoal  in  a  close  vessel.     The  charcoal  thus  produced 


ANIMAL  CHARCOAL. 


269 


la  mixed  with  not  less  than  10  times  its  weight  of  phosphate  of  lime,  and  being  in 
a  state  of  extreme  division,  exposes  a  great  deal  of  surface.  It  possesses  a  remark- 
able attraction  for  organic  colouring  matters,  and  is  extensively  used  in  withdrawing 
the  colouring  matter  from  syrup  in  the  refining  of  sugar,  from  the  solution  of  tartaric 
acid,  and  in  the  purification  of  many  other  organic  liquids.  The  usual  practice, 
which  was  introduced  by  Dumont,  is  to  filter  the  liquid  hot  through  a  bed  of  this 
charcoal  in  grains  of  the  size  of  those  of  gunpowder,  and  of  two  or  three  feet  in 
thickness.  It  is  found  that  the  discolouring  power  is  greatly  reduced  by  dissolving 
out  the  phosphate  of  lime  from  ivory  black  by  an  acid,  although  this  must  be  done 
in  certain  applications  of  it,  as  when  it  is  used  to  discolour  the  vegetable  acids.  A 
charcoal  possessed  of  the  same  valuable  property  even  in  a  higher  degree  for  its 
weight,  is  produced  by  calcining  dried  blood,  horns,  hoofs,  clippings  of  hides,  in 
contact  with  carbonate  of  potash,  and  washing  the  calcined  mass  afterwards  with 
water.  Even  vegetable  matters  afford  a  charcoal  possessed  of  considerable  discolour- 
ing power,  if  mixed  with  chalk,  calcined  flint,  or  any  other  earthy  powder,  before 
being  carbonized.  One  hundred  parts  of  pipe  clay  made  into  a  thin  paste  with 
water,  and  well  mixed  with  20  parts  of  tar  and  500  of  coal  finely  pulverized,  have 
been  found  to  afford,  after  the  mass  was  dried  and  ignited  out  of  contact  with  air,  a 
charcoal  which  was  little  inferior  to  bone  black  in  quality.  When  charcoal  which 
has  been  once  used  in  such  a  filter  is  calcined  again,  it  is  found  to  have  lost  much 
of  its  discolouring  power.  This  is  owing  to  the  deposition  upon  its  surface  of  a 
lustrous  charcoal,  of  the  lamp-black  variety,  produced  by  the  decomposition  of  the 
organic  colouring  matters,  which  has  little  or  no  discolouring  power.  But  if  the 
charcoal  of  the  sugar  filters  be  allowed  to  ferment,  the  foreign  matter  in  it  is 
destroyed ;  and  if  afterwards  well  washed  with  water  and  dried,  before  being  cal- 
cined, it  will  be  found  to  recover  a  considerable  portion  of  its  original  power. 

Bussy  has  constructed,  from  observation,  the  following  table  of  the  efficiency  of 
the  different  charcoals.  (Journ.  de  Pharm.  t.  viii.  p.  257).  These  substances  are 
compared  with  ivory  black,  as  being  the  most  feeble  species,  although  this  is  superior 
by  several  degrees  to  the  best  wood  charcoal.  The  relative  efficiency,  it  will  be  ob- 
served, is  not  the  same  for  two  different  kinds  of  colouring  matter : — 


Species  of  charcoal 
same  weight. 

Relative  decolou- 
ration of  sulphate 
of  indigo. 

Relative  De- 
colouration of 
Syrup. 

Blood  charred  with  carbonate  of  potassa  

50 

20 

Blood  charred  with  chalk    .              . 

18 

H 

Blood  charred  with  phosphate  of  lime  

12 

10 

Glue  charred  with  carbonate  of  potassa  

36 

15  5 

White  of  egff  charred  with  the  same 

34 

15  5 

Gluten  charred  with  the  same    

10  6 

8  8 

Charcoal  from  acetate  of  potassa  

5  6 

4  4 

12 

8  8 

Lamp-black   not  calcined         

4 

o  o 

Lamp-black  calcined  with  carbonate  of  potassa     

15  2 

10  6 

Bone  charcoal,  after  the  extraction   of  the  earth  of 
bones  by  an,  acid,  and  calcination  with  potassa  
Bone  charcoal  treated  with  an  acid  

45 
1  87 

20 
1  6 

Oil  charred  with  the  phosphate  of  lime  

2 

1  9 

Bone  charcoal,  in  its  ordinary  state  

1 

1 

This  remarkable  action  of  charcoal  in  withdrawing  matters  from  solution  is  cer-' 
tainly  an  attraction  of  surface,  but  it  is  capable,  notwithstanding,  of  overcoming 
chemical  affinities  of  some  intensity.  The  matters  remain  attached  to  the  surface 
of  the  charcoal,  without  being  decomposed  or  altered  in  nature.  For  if  the  blue 
sulphate  of  indigo  be  neutralized  and  then  filtered  through  charcoal,  the  whole 
colouring  matter  is  retained  by  the  latter,  and  the  filtered  liquid  is  colourless.  But 


270  CARBON. 

a  solution  of  caustic  alkali  will  divest  the  chnrcoal  of  the  blue  colouring  matter,  and 
carry  it  away  in  solution.  The  salts  of  quinine,  morphine,  and  other  organic  bases 
and  bitter  principles,  are  carried  down  by  animal  charcoal  used  in  excess  (Waring- 
ton,  Mem.  Chein.  Soc.  iii.  326).  Hence  this  substance  is  a  very  general  antidote 
to  vegetable  poisons,  as  was  proved  by  Dr.  Garrod.  Other  substances  also  are  carried 
down  by  animal  charcoal,  besides  organic  matters.  Lime  from  lime  water,  iodine 
from  solution  in  iodide  of  potassium,  hydrosulphuric  acid  from  solution  in  water, 
soluble  subsalts  of  lead,  and  metallic  oxides  dissolved  in  ammonia  or  caustic  potassa; 
but  it  has  little  or  no  action  upon  most  neutral  salts.  The  charcoal  is  apt  with  time 
to  react  upon  the  substance  it  carries  down,  probably  from  their  closeness  of  contact, 
reducing  the  oxides  of  silver,  lead,  and  copper,  for  instance,  to  the  metallic  state  in. 
a  short  time.  Animal  charcoal  soon  disappears  when  heated  in  chlorine  water,  and 
is  converted  into  carbonic  acid  ;  and  the  affinities  of  carbon  generally  are  more  active 
in  this  than  in  its  other  forms.  \_See  Supplement,  p.  769.] 

Carbon  is  chemically  the  same  under  all  these  forms.  This  element  cannot  be 
crystallized  artificially  by  the  usual  methods  of  fusion,  solution  or  sublimation,  if  we 
except  its  solution,  in  cast  iron,  which  gives  it  in  the  form  of  graphite  and  not  of 
the  diamond.  It  is  chemically  indifferent  to  most  bodies  at  a  low  temperature,  but 
combines  directly  with  some  metals  by  fusion,  and  forms  compounds  named  carburets 
or  carbides:  in  these  compounds,  however,  the  metal  is  most  probably  the  negative 
constituent.  When  heated  to  low  redness  it  burns  readily  in  air  or  oxygen,  forming 
a  gaseous  compound  carbonic  acid,  which,  when  cool,  has  sensibly  the  same  volume 
as  the  original  oxygen.  With  half  the  proportion  of  oxygen  in  carbonic  acid,  carbon 
forms  a  protoxide,  carbonic  oxide  gas.  The  last  gas  being  supposed  similar  to  steam 
or  to  nitrous  oxide  in  its  constitution,  will  be  composed  of  2  volumes  of  carbon  va- 
pour and  1  volume  of  oxygen  gas  condensed  into  2  volumes,  an  assumption  upon 
which  the  density  of  carbon  vapour,  which  there  are  no  means  of  determining  ex- 
perimentally, is  usually  calculated,  and  made  about  420 ;  the  combining  measure  of 
this  vapour  containing  2  volumes  (page  129).  The  density  deduced  from  the  equi- 
valent of  carbon  is  more  nearly  416.1  That  the  equivalent  of  carbon  is  exactly  6, 
as  originally  maintained  by  Dr.  Prout,  has  been  established  beyond  doubt  by  M. 
Dumas,  by  the  combustion  of  the  diamond  in  a  stream  of  oxygen  gas.  Pure  carbon 
then  unites  with  oxygen  in  the  proportion  of  3  to  8  exactly,  or  6  to  16,  to  form 
carbonic  acid  (p.  272). 

Uses.  —  Several  valuable  applications  of  this  substance  have  already  been  inci- 
dentally described.  Carbon  may  be  said  to  surpass  all  other  bodies  whatever  in  its 
affinity  for  oxygen  at  a  high  temperature ;  and  being  infusible,  easily  got  rid  of  by 
combustion,  and  forming  compounds  with  oxygen  which  escape  as  gas,  this  body  is 
more  suitable  than  any  other  substance  to  effect  the  reduction  of  metallic  oxides ; 
that  is,  to  deprive  them  of  their  oxygen,  and  to  produce  from  them  the  rnetal  with 
the  properties  which  characterize  it. 

CARBONIC   ACID. 

Eq.  22  or  275;  C02;  density  1529.0;  [_Q 

This  gas  was  first  discovered  to  exist  in  lime-stone  and  the  mild  alkalies,  and  to 
be  expelled  from  the  first  by  heat,  and  from  both  by  the  action  of  acids,  by  Dr. 
Black,  and  was  named  by  him  Fixed  Air.  He  also  remarked  that  the  same  gas  is 
formed  in  respiration,  fermentation,  and  combustion ;  it  was  afterwards  proved  to 
contain  carbon  by  Lavoisier. 

1  The  number  for  carbon  vapour  deduced  from  the  density  of  oxygen  gas,  that  is,  six- 
Bixteeriths  of  that  density,  is  414.61  (page  130) ;  while  six-fourteenths  of  the  density  of 
nitrogen  is  416.304,  and  six  times  the  density  of  hydrogen,  415.56.  The  density  of  nitro- 
gen is  probably  the  least  objectionable,  and  the  number  deduced  from  it  for  carbon  (4 1C) 
therefore  the  safest. 


CARBONIC    ACID. 
FIG.  121. 


271 


Preparation.  —  Carbonic  acid  is  readily  procured  by  pouring  hydrochloric  acid  of 
sp.  gr.  1.1,  upon  fragments  of  marble  contained  in  a  gas-bottle  (fig.  121),  or  by  the 
action  of  diluted  sulphuric  acid  upon  chalk.  A  gas  comes  off  with  effervescence, 
which  may  be  collected  at  the  water  trough,  but  cannot  be  retained  long  over  water 
without  considerable  loss,  owing  to  its  solubility. 

From  the  great  weight  of  carbonic  acid  a  bottle  may  be  filled  with  this  gas  by 
displacing  air.  The  gas  being  evolved  in  the  gas-bottle  A  (fig.  122),  is  first  con- 
veyed into  a  wash-bottle  B,  containing*  water,  to  condense  any  hydrochloric  acid 
vapour  with  which  the  gas  may  be  accompanied ;  then  passing  through  a  U-shaped 
drying  tube  C,  containing  fragments  of  chloride  of  calcium,  to  absorb  aqueous  va- 
pour, and  then  conveyed  to  the  lower  part  of  the  bottle  D.  When  generated  in  the 
close  apparatus  of  Thilorier  for  the  purpose  of  liquefying  it  (page "7 7),  this  gas  is 
evolved  from  bicarbonate  of  soda  and  sulphuric  acid. 

Fia.  122. 


:a 


Properties.  —  This  gas  extinguishes  flame,  does  not  support  animal  life,  and  ren- 
ders lime  water  turbid.  Its  density  is  considerable,  being  1529  (Regnault),  or  a 
half  more  than  that  of  air,  the  gas  containing  2  volumes  of  the  hypothetical  carbon 
vapour  and  2  volumes  of  oxygen,  condensed  into  2  volumes,  which  form  the  com- 
bining measure.  Cold  water  dissolves  rather  more  than  an  equal  volume  of  this 
gas;  the  solution  has  an  agreeable  acidulous  taste,  and  sparkles  when  poured  from 
one  vessel  into  another.  It  communicates  a  wine-red  tint  to  litmus  paper,  whick 


272  CARBON. 

disappears  again  when  the  paper  dries ;  when  poured  into  lime  water,  it  first  throws 
down  a  white  flaky  precipitate  of  carbonate  of  lime  or  chalk,  which  it  afterwards 
redissolves  if  the  solution  of  the  gas  be  added  in  excess.  The  quantity  of  this  gas 
which  water  takes  up  is  found  to  be  sensibly  proportional  to  the  pressure ;  a  very 
large  volume  of  the  gas  is  forced  into  soda,  magnesia,  and  other  aerated  waters, 
much  of  which  escapes  on  removing  the  pressure  from  these  liquids. 

Liquefied  by  pressure,  carbonic  acid  has  an  elastic  force  of  38-5  atmospheres  at 
32°  (Faraday).  The  specific  gravity  of  liquid  carbonic  acid,  at  the  same  tempera- 
ture, is  0'83  :  it  dilates  remarkably  from  heat,  its  expansion  being  four  times  greater 
than  that  of  air,  20  volumes  of  the  liquid  at  32°  becoming  29  at  86°,  and  its  den- 
sity varying  from  0.9  to  0.6  as  its  temperature  rises  from  — 4°  to  86°.  (Thilorier, 
Annal.  de  Chim.  et  de  Phys.  Ix.  p.  427).  It  is  a  colourless  liquid,  which  mixes  in 
all  proportions  with  ether,  alcohol,  naphtha,  oil  of  turpentine,  and  bisulphide  of 
carbon,  but  is  insoluble  in  water  and  fat  oils.  At  temperatures  below  — 72°  it  is 
solid  (page  80). 

Potassium  heated  in  a  small  glass  bulb  blown  upon  a  tube,  through  which  gaseous 
carbonic  acid  is  transmitted,  undergoes  oxidation,  and  liberates  carbon,  the  existence 
of  which  in  the  gas  may  thus  be  shown ;  or,  for  this  experiment,  a  cleansed  and  dry 
Florence  oil-flask  may  be  filled,  by  displacement,  with  the  dried  gas  (fig.  122),  and 
a  pellet  of  potassium  being  introduced,  combustion  may  be  determined  by  applying 
the  flame  of  an  Argand  spirit-lamp  for  a  few  seconds  to  the  bottom  of  the  flask. 
But  burning  phosphorus,  sulphur,  and  other  combustibles,  are  immediately  extin- 
guished by  carbonic  acid,  and  the  combustion  does  not  cease  from  the  absence  of 
oxygen  only,  but  from  a  positive  influence  in  checking  combustion  which  this  gas 
exerts,  for  a  lighted  candle  is  extinguished  in  air  containing  no  more  than  one-fourth 
of  its  volume  of.  carbonic  acid.  It  is  generally  believed  that  any  mixture  of  carbonic 
acid  and  air  will  support  the  respiration  of  man,  which  will  maintain  the  flame  of  a 
candle,  and  therefore  a  lighted  candle  is  often  let  down  into  wells  or  pits  suspected 
to  contain  this  gas,  to  ascertain  whether  they  are  safe  or  not.  But  although  air  in 
which  a  candle  can  burn  may  not  occasion  immediate  insensibility,  still  the  continued 
respiration  for  several  hours  of  air  containing  not  more  than  1  or  2  per  cent,  of  car- 
bonic acid,  has  been  found  to  produce  alarming  effects  (Broughton).  The  accidents 
from  burning  a  pan  of  charcoal  in  close  rooms  are  occasioned  by  this  gas.  It  acts 
as  a  narcotic  poison  upon  the  system.  A  small  animal  thrown  into  convulsions 
from  the  respiration  of  this  gas,  may  be  recovered  by  sudden  immersion  in  cold 
water. 

Carbonic  acid  is  thrown  off  from  the  lungs  in  respiration,  as  may  be  proved  by 
directing  a  few  expirations  through  lime-water.  The  air  of  an  ordinary  expiration 
contains,  on  an  average,  as  observed  by  Dr.  Prout,  3-45  per  cent,  of  its  volume  of 
this  gas,  and  the  proportion  varies  from  3.3  to  4.1  per  cent., — being  greatest  at  noon, 
and  least  during  the  night.  Carbonic  acid  is  also  a  product' of  the  vinous  fermenta- 
tion, and  is  the  cause  of  the  agreeable  pungency  of  beer,  ale,  and  other  fermented 
liquors,  which  become  stale  when  exposed  to  the  air  from  the  loss  of  this  gas.  It 
also  exists  in  all  kinds  of  well  and  spring  water,  and  contributes  to  their  pleasant 
flavour,  for  water  which  has  been  deprived  of  its  gases  by  boiling  is  insipid  and  dis- 
agreeable. Carbonic  acid  is  also  largely  produced  by  the  combustion  of  carbonaceous 
fuel,  and  appears  to  exist  in  considerable  quantity  in  the  earth,  being  discharged  by 
active  volcanoes,  and  from  fissures  in  their  neighbourhood,  long  after  the  volcanoes 
are  extinct.  The  Grotto  del  Cane  in  Italy  owes  its  mysterious  properties  to  this 
gas,  and  many  mineral  springs,  such  as  those  of  Tunbridge,  Pyrmont,  and  Carlsbad, 
are  highly  charged  with  it.  It  comes  thus  to  be  always  present  in  the  atmosphere 
in  a  sensible,  although  by  no  means  considerable  proportion  (page  251). 

Composition  of  carbonic  acid.  —  The  composition  of  this  substance,  which,  like 
that  of  water,  in  one  of  the  fundamental  data  of  chemical  analysis,  is  determined 
with  extreme  exactness  in  the  following  manner : — A  known  weight  of  a  very  pure 
form  of  carbon,  such  as  the  diamond,  its  placed  in  a  little  trough  or  cradle  of  plati 


COMPOSITION   OF   CARBONIC   ACID.  273 

num,  which  is  introduced  into  a  porcelain  tube  a  b  (fig.123),  placed  across  a  furnace. 
To  effect  the  combustion  of  the  carbon,  the  end  a  of  this  tube  is  made  to  communi- 
cate by  means  of  a  glass  tube  with  an  apparatus  supplying  a  stream  of  oxygen  gas, 
perfectly  dried  by  passing  through  the  U  tube  E,  which  contains  fragments  of  pumice 
impregnated  with  concentrated  sulphuric  acid.  The  second  and  fourth  U  tubes,  A 
and  D,  are  charged  in  the  same  manner.  The  bulb  apparatus  B  contains  a  concen- 
trated solution  of  caustic  potassa,  and  the  pumice  in  the  adjoining  U  tube  c  is  im- 
pregnated with  the  same  fluid.  These  tubes,  B  and  c,  containing  the  alkali,  witl 
the  tube  following  them,  D,  are  accurately  weighed  together  in  a  good  balance. 

FIG.  123. 


The  different  parts  being  connected  by  short  tubes  of  caoutchouc,  as  represented 
in  the  figure,  the  apparatus  is  then  filled  with  oxygen  gas,  which  ought  to  be  slowly 
disengaged.  The  tube  a  b,  which  contains  the  carbon,  is  heated  to  redness,  and  the 
latter  soon  enters  into  combustion,  and  is  changed  into  carbonic  acid.  The  gases 
pass  through  the  series  of  tubes,  A,  B,  c,  D.  In  A,  any  trace  of  moisture  is  absorbed 
by  the  sulphuric  acid,  which  may  escape  from  the  inner  surface  of  the  tube  a  b  when 
heated,  and  in  B  and  c  the  carbonic  acid  produced  is  absorbed  by  the  caustic  alkali. 
The  excess  of  oxygen,  which  passes  on  uncondensed,  takes  up  a  little  aqueous  va- 
pour in  B  and  c,  which  tends  to  diminish  the  weight  of  the  potassa  apparatus;  for, 
although  the  tension  of  the  vapour  of  the  alkaline  solution  is  small,  the  latter  cannot 
be  used  so  concentrated  as  to  make  the  tension  insensible.  The  last  U  tube  D  re- 
medies this  inconvenience  by  drying  the  gases  perfectly  again  before  they  escape 
into  the  atmosphere. 

In  such  a  combustion  the  formation  of  a  little  carbonic  oxide  gas  is  to  be  appre- 
hended. This  is  provided  against  by  filling  the  part  of  the  tube  a  6,  next  b,  with 
very  porous  oxide  of  copper,  which  is  heated  to  redness  during  the  experiment.  In 
passing  through  this  oxide,  any  small  quantity  of  carbonic  oxide  which  may  exist  is 
necessarily  converted  into  carbonic  acid.  The  oxide  of  copper  is  separated  by  a  pad 
of  asbestos  from  that  part  of  the  tube  containing  the  little  cradle  with  the  carbon. 
The  evolution  of  the  oxygen  is  also  continued  for  some  time  after  the  combustion 
of  the  carbon  is  complete,  in  order  to  sweep  the  tubes  by  means  of  that  gas,  and 
carry  forward  the  whole  carbonic  acid  formed  into  the  potassa  bulbs  where  it  is  ab- 
sorbed. 

On  disconnecting  the  apparatus  afterwards,  and  examining  the  cradle  in  which 
the  carbon  was  placed,  to  ascertain  whether  its  combustion  is  complete,  a  little  in- 
combustible earthy  matter,  not  exceeding  a  few  hundredths  of  a  grain,  will  generally 
be  found  remaining,  which  had  existed  mechanically  diffused  through  the  carbon. 
The  weight  of  the  cradle  and  residue,  deducted  from  the  original  weight  of  the 
cradle  and  carbon,  gives  obviously  the  exact  weight  of  the  carbon  consumed ;  while 
the  original  weight  of  the  system  of  tubes  B,  c,  and  D,  deducted  from  their  final 
18 


274  CARBON. 

weight,  gives  the  exact  weight    of  carbonic  acid  formed.     (Cours  Elementaire  do 
Chimie,  par  M.  V.  Regnault). 

It  is  found  in  this  way  that  6  parts  of  carbon  produce  exactly  ^22  parts  of  carbonic 
acid,  or  carbonic  acid  contains — 

1  eq.  carbon  6 27.27 

2  eq.  oxygen  16 72.73 

22  "100."00 

Carbonates.  —  Carbonic  acid  combines  with  bases,  and  forms  the  class  of  car- 
bonates. The  hydrate  of  this  acid  seems  incapable  of  existing  in  an  uncombined 
state,  but  it  exists  in  the  alkaline  bicarbonates,  which  are  double  carbonates  of  water 
and  the  alkali.  If  this  hydrate  were  formed,  we  may  presume  that  it  would  be 
analogous  to  the  crystallized  carbonate  of  magnesia,  of  which  the  formula  is 
MgO,C02-f  HO  +  2HO,  and  also  the  same  with  another  2HO;  the  salt  of  magnesia 
of  most  acids  resembling  the  salt  of  water.  Carbonate  of  lime,  in  the  hydrated 
condition,  has  a  similar  formula.  Carbonates  of  potassa,  soda,  and  ammonia,  retain 
a  strong  alkaline  reaction,  owing  to  the  weakness  of  this  acid,  and  the  carbonates 
generally  are  decomposed  with  effervescence  by  all  other  acids,  except  the  hydro- 
cyanic. 

Uses.  —  Carbonic  acid  is  used  in  the  preparation  of  aerated  waters.  The  strong 
vessels  in  which  the  impregnation  is  effected,  should  be  of  copper,  well  tinned,  and 
not  of  iron,  as  with  the  concurrence  of  water  carbonic  acid  acts  strongly  upon  that 
metal.  It  is  sometimes  desirable  to  remove  carbonic  acid  from  air  or  other  gaseous 
mixtures,  and  this  is  generally  done  by  means  of  caustic  alkali  or  lime-water.  When 
very  dry,  or  so  humid  as  to  be  actually  wet,  the  hydrate  of  lime  absorbs  this  gas 
with  much  less  avidity  than  when  of  a  certain  degree  of  dryness,  in  which  it  is  not 
so  dry  as  to  be  dusty,  but  at  the  same  time  not  sensibly  damp.  The  dry  hydrate 
§  may  be  brought  at  once  to  this  condition,  by  mixing  it  intimately  with  an  equal 
weight  of  crystallized  sulphate  of  soda  in  fine  powder ;  and  this  mixture,  in  a  stratum 
of  not  more  than  an  inch  in  thickness,  intercepts  carbonic  acid  most  completely,  and 
may  rise  in  temperature  to  above  200°,  from  the  rapid  absorption  of  the  gas.  It  is 
quite  possible  to  respire  through  a  cushion  of  that  thickness,  filled  with  the  mixture, 
and  such  an  article  might  be  found  useful  by  parties  entering  an  atmosphere  over- 
charged with  carbonic  acid,  like  that  of  a  coal-mine  after  the  occurrence  of  an  ex- 
plosion of  fire-damp. 

Carbonic  acid  is  the  highest  degree  of  oxidation  of  which  carbon  is  susceptible ; 
but  another  oxide  of  carbon  exists  containing  less  oxygen.  [See  Supplement,  p.  771.] 

CARBONIC   OXIDE. 

Eg.  14  or  175;  CO;  density  967-8;   fTI 

Priestley  is  the  discoverer  of  this  gas,  but  its  true  nature  was  first  pointed  out  by 
Cruikshanks,  and  about  the  same  time  by  Clement  and  Desormes. 

Preparation.  —  Carbonic  acid  is  readily  deprived  of  half  its  oxygen,  at  a  red  heat, 
by  a  variety  of  substances,  and  so  reduced  to  the  state  of  carbonic  oxide.  The  latter 
gas  may  therefore  be  obtained  by  transmitting  carbonic  acid  over  red-hot  fragments 
of  charcoal  contained  in  an  iron  or  porcelain  tube ;  or  by  calcining  chalk  mixed  with 
l-4th  of  its  weight  of  charcoal  in  an  iron  retort.  It  is  likewise  prepared  by  gently 
heating  crystallized  oxalic  acid  with  five  or  six  times  its  weight  of  strong  oil  of 
vitriol  in  a  glass  retort.  The  latter  process  affords  a  mixture  of  equal  volumes  of 
carbonic  acid  and  carbonic  oxide,  the  elements  of  oxalic  acid  being  carbon  and 
oxygen  in  the  proportion  to  form  these  gases,  and  this  acid  being  incapable  of  exist- 
ing except  in  combination  with  water  or  some  other  base.  Now  the  sulphuric  acid 
unites  with  the  water  of  the  crystallized  oxalic  acid,  and  the  latter  acid  being  set  free  is 


CARBONIC   OXIDE. 


275 


instantly  decomposed.  The  gas  of  all  these  processes  contains  much  carbonic  acid, 
of  which  it  may  be  deprived  by  washing  it  with  milk  of  lime,  or  a  strong  solution 
of  potassa. 

Another  process  suggested  by  Mr.  Fownes  affords  a  perfectly  pure  gas.  It  con- 
sists in  heating  the  crystallized  ferrocyanide  of  potassium  in  a  glass  retort  or  flask  A 
(fig.  124),  with  four  or  five  times  its  weight  of  oil  of  vitriol.  The  gas  may  be 

FIG.  124. 


passed  through  a  wash-bottle  B,  containing  a  little  water,  and  be  collected  in  the 
bottle  C  over  the  water-trough  in  the  usual  manner.  One  equivalent  of  ferrocyanide 
of  potassium  and  9  equivalents  of  water  are  then  resolved  into  6  equivalents  of 
carbonic  oxide,  2  equivalents  of  potassa,  1  equivalent  of  protoxide  of  iron,  and  3 
equivalents  of  ammonia :  — 

2K.FeC6Ns+9HO=6CO  +  2KO  +  FeO  +  3H8N. 

Half  an  ounce  of  the  salt  yields  300  cubic  inches  of  carbonic  oxide. 

Properties* — This  gas,  as  has  already  been  stated,  is  presumed  to  contain  2 
volumes  of  carbon  vapour,  and  1  volume  of  oxygen,  condensed  into  2  volumes,  so 
that  its  combining  measure  is  2  volumes  :  its  density  is  967.79  (Wrede).  Carbonic 
oxide  is  14  times  heavier  than  hydrogen,  like  nitrogen,  and  coincides  remarkably  in 
its  rate  of  transpiration  (page  86)  and  other  physical  properties  with  the  latter  gas. 
It  is  very  fatal  to  animals,  and  when  inspired  in  a  pure  state  almost  immediately 
produces  coma.  Carbonic  oxide  is  not  more  soluble  in  water  than  atmospheric  air, 
and  has  never  been  liquefied.  It  is  easily  kindled,  and  burns  with  a  pale  blue  flame, 
like  that  of  sulphur,  combining  with  half  its  volume  of  oxygen,  and  forming  carbonic 
acid,  which  retains  the  original  volume  of  the  carbonic  oxide.  This  combustion  is 
often  witnessed  in  a  coke  or  charcoal  fire.  The  carbonic  acid,  produced  in  the  lower 
part  of  the  fire,  is  converted  into  carbonic  oxide,  as  it  passes  up  through  the  red-hot 
embers,  and  afterwards  burns  above  them  with  a  blue  flame,  where  it  meets 
with  air. 

Carbonic  oxide  is  a  neutral  body,  like  water,  and  combines  directly  with  only  a 
very  few  substances.  It  unites  with  an  equal  volume  of  chlorine  under  the  influence 
of  the  sun's  rays,  and  forms  phosgene  gas  or  Chloroxicarbonic  Gas.  As  the  gases 
contract  to  half  their  volume  on  combining,  the  density  of  this  gas  is  the  sum  of 

*  [See  Supplement,  pp.  771,  772.] 


276  CARBON. 

carbonic  oxide  968,  and  chlorine  2440,  or  3408  j  its  formula  is  CO.C1.  Chloroxi- 
carbonic  gas  is  colourless,  and  has  a  peculiar  suffocating  odour.  In  contact  with 
water  it  is  decomposed  at  the  same  time  with  an  equivalent  of  water;  hydrochloric 
and  carbonic  acids  are  produced  —  that  is  — 

CO.C1  and  HO=C02  and  HC1. 

Carbonic  oxide  is  also  absorbed  by  potassium  gently  heated,  and  that  metal  is 
employed  to  separate  this  gas  from  a  mixture  of  hydrogen  and  gaseous  carbohydro- 
gens,  as  in  the  analysis  of  coal  gas.  But  carbonic  oxide  has  been  supposed  to  exist 
in  a  greater  number  of  compounds,  and  to  be  the  radical  of  a  series,  of  which  the 
following  substances  are  members :  — 

CARBONIC   OXIDE    SERIES. 

Carbonic  oxide CO 

Carbonic  acid CO-f  0 

Chloroxicarbonic  gas CO  +  C1 

Oxalic  acid 2CO  + 0 

Oxamide 2CO  +  NH. 

Carbonoxide  of  potassium 7CO  +  3K 

Rhodizonic  acid .* 7CO  +  3HO 

Croconic  acid 5CO  +  H 

Melliticacid 4CO  +  H 

In  these  compounds  carbonic  oxide  is  represented  as  playing  the  part  of  a  simple 
substance,  and  forming  a  variety  of  products  by  uniting  with  oxygen,  chlorine, 
hydrogen,  and  other  elements. 

Mellitic,  croconic,  and  rhodizonic  acids  are  sometimes  enumerated  as  oxides  of 
carbon,  along  with  carbonic  acid,  carbonic  oxide,  and  oxalic  acid,  but  the  former 
bodies  have  not  an  equal  claim  to  the  same  early  consideration  as  the  latter  com- 
pounds. 

• 

OXALIC   ACID. 

Eq.  36  or  450 ;  C203.     Oxalate  of  water,  HO,C203  +  2HO. 

This  acid,  discovered  by  Scheele  in  1776,  exists  in  the  form  of  an  acid  salt  of 
potassa,  in  a  great  number  of  plants,  particularly  in  the  species  of  Oxalis  and 
Rumex :  combined  with  lime  it  also  forms  a  part  of  several  lichens.  Oxalate  of 
lime  occurs  likewise  as  a  mineral,  humboldite,  and  forms  the  basis  of  a  species  of 
urinary  calculus.  This  acid  is  also  produced  by  the  oxidation  of  carbon  in  combi- 
nation, in  a  variety  of  circumstances,  being  the  general  product  of  the  oxidation  of 
organic  substances  by  nitric  acid,  hypermanganate  of  potassa,  and  by  fused  potassa. 
Those  matters  which  contain  oxygen  and  hydrogen  in  the  proportion  of  water  fur- 
nish the  largest  quantity  of  oxalic  acid. 

This  acid  has  been  derived  in  quantity  from  lichens,  but  it  is  usually  prepared  by 
acting  upon  1  part  of  sugar  by  5  parts  of  nitric  acid,  of  1.42,  diluted  with  10  parts 
of  water  at  a  gentle  heat  till  no  gas  is  evolved,  and  evaporating  to  crystallize.  The 
crystals  must  be  drained,  and  crystallized  a  second  time,  as  they  are  apt  to  retain  a 
portion  of  nitric  acid.  Acting  upon  1  part  of  sugar,  with  6.6  parts  of  nitric  acid, 
of  density  1.245,  Mr.  L.  Thompson  obtained  1.1  parts  of  crystallized  oxalic  acid. 
One  half  of  the  carbon  of  the  sugar  appeared  to  be  converted  into  oxalic  acid,  and 
the  other  half  into  carbonic  acid;  the  nitric  acid  being  entirely  converted  into 
binoxide  of  nitrogen,  by  loss  of  oxygen. 

Oxalic  acid  forms  long,  four-sided,  oblique  prisms,  with  dihedral  summits,  or 
terminated  by  a  single  face.  These  crystals  contain  three  equivalents  of  water,  one 
of  which  is  basic,  and  the  other  two  constitutional,  or  water  of  crystallization.  The 


OXALIC   ACID.  277 

latter  two  may  be  expelled  at  a  temperature  above  212°,  and  the  protohydrate  rises 
at  the  same  time  in  vapour,  and  condenses  as  a  woolly  sublimate.  Heated  in  a 
retort,  the  hydrated  acid  undergoes  decomposition  about  311°,  and  is  converted  into 
carbonic  oxide,  carbonic  acid,  and  formic  acid,  without  leaving  any  fixed  residue. 
Concentrated  nitric  acid,  with  heat,  converts  oxalic  acid  into  water  and  carbonic 
acid.  When  heated  with  sulphuric  acid,  oxalic  acid  yields  equal  volumes  of  carbonic 
oxide  and  carbonic  acid;  C203  being  equivalent  to  C0  +  C02  (page  274).  No 
charring,  nor  evolution  of  any  other  gas,  occurs,  so  that  the  action  of  concentrated 
sulphuric  acid  affords  the  means  of  recognising  oxalic  acid  or  any  oxalate.  Crystal- 
lized oxalic  acid  is  soluble  in  8  parts  of  water,  at  59°,  in  its  own  weight  of  boiling 
water,  and  in  4  parts  of  alcohol,  at  59°. 

Oxalic  acid  is  a  powerful  acid,  which  combines  with  bases,  and  forms  a  well- 
defined  class  of  salts,  —  the  oxalates  :  it  disengages  carbonic  acid  easily  from  all  its 
combinations.  Added  to  lime-water,  or  any  soluble  salt  of  lime,  oxalic  acid  forms 
a  white  precipitate — the  oxalate  of  lime,  which  is  a  highly  insoluble  salt.  Absolute 
oxalic  acid,  C203,  has  not  been  isolated,  and  appears  incapable  of  existing  except  in 
combination  with  water,  or^sorae  other  base. 

Composition  of  oxalic  acid.  —  The  analysis  of  oxalic  acid  is  effected  in  the  fol- 
lowing manner : — Ten  grains  of  the  crystals,  reduced  to  powder,  are  exactly  weighed 
and  mixed  with  200  or  300  grains  of  oxide  of  copper,  recently  calcined,  and  per- 
fectly dry.  This  mixture  is  introduced  into  a  tube  of  white  Bohemian  glass,  which 
is  not  easily  fused,  open  at  one  end,  about  0.4  inch  jn  internal  diameter,  and  14  or 
15  inches  long,  the  other  end  being  drawn  out,  bent  upward,  and  sealed  (a,  fig.  125). 

FIG.  125. 


This  is  placed  in  a  furnace,  of  a  trough  form,  as  represented  in  the  figure,  constructed 
of  sheet  iron,  and  heated  to  low  redness  by  burning  charcoal.  Immediately  con- 
nected with  the  combustion  tube,  by  means  of  a  perforated  cork,  is  a  tube  of  the 
form  ft,  containing  fragments  of  strongly  dried  chloride  of  calcium.  In  this  tube 
the  water  of  the  oxalic  acid  is  condensed,  and  the  weight  of  that  constituent  is 
ascertained  by  weighing  the  tube,  before  and  after  the  combustion.  Beyond  the 
chloride  of  calcium  tube,  and  connected  with  it  fcy  a  short  caoutchouc  tube,  c,  is  a 
glass  instrument,  p  m  r,  containing  a  strong  solution  of  caustic  potassa,  of  density 
1.25  to  1.27,  for  the  absorption  of  the  carbonic  acid  produced  by  the  combustion 
of  the  carbon  of  the  oxalic  acid  by  the  oxygen  of  the  oxide  of  copper.  This  instru- 
ment consists  of  five  balls,  of  which  m  is  larger  than  the  others;  no  more  of  the 
potassa  ley  is  put  into  it  than  fills  the  three  central  balls,  leaving  a  bubble  of  air  in 
each.  One  corner  is  elevated  a  little  by  a  cork  placed  under  it,  and  the  whole  sup- 
ported on  a  folded  towel :  the  potassa  balls,  when  filled  with  ley,  commonly  weigh 
from  760  to  900  grains.  This  apparatus  is  also  weighed  before  and  after  the  com- 
bustion, and  the  increase  ascertained. 

The  experiment,  when  properly  conducted,  gives  4.29  grains  water  condensed  in 
the  chloride  of  calcium  tube,  and  6.98  grains  of  carbonic  acid  absorbed  in  the  potassa 
bulbs.  But  4.29  grains  of  water  contain  0.47  grain  of  hydrogen,  and  6.98  grains 
of  carbonic  acid  ^contain  1.905  grains  of  carbon.  Now,  as  oxalic  acid  contains  nothing 
but  carbon,  hydrogen,  and  oxygen,  we  obtain  thus,  for  the  composition  of  10  grains 
of  oxalic  acid  : — 


278 


CARBON. 


Hydrogen 0.476 

Carbon 1.905 

Oxygen 7.619 

10.000 

To  learn  the  relation  between  the  number  of  equivalents  of  these  constituents  of 
oxalic  acid,  it  •  is  necessary  to  divide  the  weight  of  each  of  them  by  its  chemical 
equivalent : — 

0.476  1.905 

=  0.4760.  =  0.3175. 

1  6 

7.619 


=  0.9524. 


8 


These  fractions  are  in  the  proportion  of  2,  3,  and  6 ;  from  which  it  follows,  that  the 
formula  of  the  crystallized  oxalic  acid  is  C2  H3  06  or  a*  multiple  of  it.  Allowing 
the  3H  to  be  in  combination  with  3O,  as  water,  we  finally  obtain  the  formula  Ca 
03  -f  3HO,  for  the  crystallized  acid.  [See  Supplement,  p.  772.] 

CARBON  AND  HYDROGEN  —  HYDRIDES  OP  CARBON. 

A  large  number  of  compounds  of  carbon  and  hydrogen  are  known ;  many  of  them 
found  in  the  organic  kingdom,  and  others  derived  from  the  decomposition  of  organic 
compounds.  Some  of  these  are  liquid  bodies,  some  solid,  and  others  gaseous.  At 
present  we  shall  confine  ourselves  to  the  three  gaseous  compounds  which  in  simplicity 
of  composition  resemble  inorganic  compounds. 

PROTOCARBURETTED   HYDROGEN. 

Syn.1  Light  carburetted  hydrogen,  Gas  of  the  Acetates,  Marsh-gas,  Fire-damp. 
Eq.  16,  or  200;  C2  H4;  density  559.6;  combining  measure 


FIG.  126. 


This  gas  is  a  constant  product  of  the 
putrefactive  decomposition  of  wood  and 
other  compounds  of  carbon,  under  water, 
and  is  most  readily  obtained  by  stirring 
the  mud  at  the  bottom  of  stagnant  pools, 
and  collecting  the  gas  as  it  rises  in  an  in- 
verted bottle  and  funnel  (fig.  126).  It 
always  contains  10  or  20  per  cent,  of  car- 
bonic acid,  which  may  be  separated  from  it 
by  lime-water,  and  a  small  proportion  of 
nitrogen.  This  gas  also  issues,  in  some 
places,  in  considerable  quantities  from  fis- 
sures in  the  earth,  coming  often  from  sub- 
terraneous deposits  of  coal;  and  in  the 
working  of  coal-mines  it  is  found  pent  up 
in  cavities,  and  would  appear  sometimes  to 
be  discharged  from  the  fresh  surface  of  the 
coal  in  sensible  quantity.  Hence,  this  gas 
is  sometimes  described  as  the  inflammable 


'Such  systematic  designations  as  have  hitherto  been  applied  to  this 'and  a  few  other 
hydrides  of  carbon  have  not  in  general  been  clear,  and  involve  the  serious  error  of  repre- 
senting the  carbon  as  the  negative  element. 


PROTOCARBURETTED    HYDROGEN. 


279 


air  of  marshes,  and  the  fire-damp  of  mines.  It  is  also  the  most  considerable  consti- 
tuent of  coal  gas,  ^ind  of  the  gaseous  mixture  obtained  on  passing  the  vapour  of 
alcohol  through  an  ignited  porcelain  tube. 

Preparation.  —  This  gas  is  obtained  by  distilling  a  mixture  of  dried  acetate  of 
soda,  hydrate  of  potassa  and  quicklime,  in  a  coated  glass  retort.  Four  ounces  of  cr. 
acetate  of  soda  may  be  dried  on  a  sand-bath  till  anhydrous ;  the  salt  is  then  reduced 
to  powder,  and  intimately  mixed  with  four  ounces  of  sticks  of  caustic  potassa  and 
six  ounces  of  quicklime,  both  well  pounded.  A  Florence  oil  flask,  or  other  flask  of 
hard  glass,  is  coated  with  a  mortar  composed  of  a  mixture  of  Paris-plaster,  and  half 
its  weight  of  sand  and  coal-ashes,  A  (fig.  127);  and  provided  with  a  perforated  cork 

FIG.  127. 


and  bent  tube  B,  one  extremity  of  which  should  descend  three  or  four  inches  in  the 
neck  of  the  flask.  The  materials  above  being  introduced  into  the  flask,  the  latter 
is  placed  in  an  open  charcoal  furnace  C,  and  strongly  heated.  The  gas  comes  off, 
and  may  be  collected  in  jars  over  the  pneumatic  trough,  or  received  in  a  gas-holder 
D  filled  with  water. 

Properties.  —  The  observed  density  of  protocarburetted  hydrogen  is  559.6;  it  is 
composed  of  4  volumes  carbon  vapour,  and  8  volumes  hydrogen,  condensed  into  4 
volumes,  which  are  the  combining  measure  of  this  gas.  Hence  its  specific  gravity 
is  by  calculation  — 

416X4  +  69.26X8        __  .   _ 

=  554.5. 

4 

It  is  inodorous,  neutral,  respirable  when  mixed  with  air,  not  more  soluble  in 
water  than  pure  hydrogen,  and  has  never  been  liquefied.  This  carburetted  hydrogen 
requires  twice  its  bulk  of  oxygen  to  burn  it  completely,  and  affords  water  and  an 
equal  bulk  of  carbonic  acid.  The  oxidation  of  this  gas  mixed  with  oxygen  is  not 
determined,  at  the  temperature  of  the  air,  by  spongy  platinum  or  platinum  black. 
In  air  it  burns,  when  lighted,  with  a  strong  yellow  flame.  It  is  a  compound  of 
considerable  stability,  but  is  decomposed  in  part  when  sent  through  a  tube  heated 
to  whiteness,  and  resolved  into  carbon  and  hydrogen.  This  gas  is  not  affected  in 


280. 


CARBON. 


the  dark  by  chlorine,  but  when  the  mixture  of  these  gases,  in  a  moist  state,  is 
exposed  to  light,  carbonic  and  hydrochloric  acid  gases  are  produced. 

Although  instantly  kindled  by  flame,  protocarburetted  hydrogen  requires  a  high 
temperature  to  ignite  it.  Hydrogen,  hydrosulphuric  acid  gas,  and  olefiant  gas,  and 
carbonic  oxide,  are  all  ignited  by  a  glass  rod  heated  to  low  redness,  but  glass  must 
be  heated  to  bright  redness  or  to  whiteness,  to  inflame  this  gas.  Sir  H.  Davy  dis- 
covered that  flame  could  not  be  communicated  to  an  explosive  mixture  of  the  gas  of 
mines  and  air,  through  a  narrow  tube,  because  the  cooling  influence  of  the  sides  of 
the  tube  prevented  the  gaseous  mixture  contained  in  it  from  ever  rising  to  the  high 
temperature  of  ignition.  A  metallic  tube  had  a  greater  cooling  property,  from  its 
high  conducting  power,  and  consequently  obstructed  to  a  greater  degree  the  passage 
of  flame,  than  a  similar  tube  of  glass;  and  even  the  meshes  of  metallic  wire-gauze, 
when  they  did  not  exceed  a  certain  magnitude,  were  found  to  be  impermeable  by 
flame.  Experiments  of  this  kind  may  be  made  upon  coal-gas,  the  flame  of  which 
will  be  found  incapable  of  passing  through  a  sheet  of  iron-wire  trellis,  containing 
not  less  than  400  holes  in  the  square  inch.  If  the  gas  be  allowed  to  pass  through 
the  trellis,  and  kindled  above  it,  the  flame,  it  will  be  found,-  does  not  return  through 
the  apertures  to  the  jet  whence  the  gas  issues.  Upon  these  observations,  Sir  H. 
Davy  founded  his  invaluable  invention  of  the  Safety-lamp,  —  an  instrument  now 
indispensable  to  the  safe  working  of  the  most  extensive  and  valuable  of  our  coal- 
fields. 

Safety-lamp.  —  As  left  by  Davy,  this  is  simply  an  oil  lamp,  enclosed  in  a  cage 
of  wire-gauze,  the  upper  part  of  which  is  double  (fig.  128).  Mr.  Buddie  used  iron- 
wire  gauze  for  the  lamp,  containing  from  784  to  800  holes  in  the 
FIG.  128.  square  inch.  A  crooked  wire,  which  works  tightly  in  a  narrow  tube 
passing  upwards  through  the  body  of  the  lamp,  affords  the  means  of 
trimming  the  wick,  without  undoing  the  wire-gauze  cover  of  the  lamp. 
When  the  lamp  is  carried  into  an  atmosphere  charged  with  firu-damp, 
a  blue  flame  is  observed  within  the  gauze  cylinder,  from  the  combus- 
tion of  the  gas,  and  the  flame  in  the  centre  of  the  lamp  may  be  extin- 
guished. The  miner  should  then  withdraw,  for  although  the  gauze 
has  often  been  observed  to  become  red-hot,  without  inflaming  the 
external  explosive  atmosphere,  yet  the  texture  of  the  gauze  may  be 
destroyed,  if  retained  long  at  so  high  a  temperature.  It  has  always 
been  known,  since  this  lamp  was  first  proposed,  that  when  it  is  exposed 
to  a  strong  current  of  the  explosive  mixture,  the  flame  may  pass  too 
quickly  through  the  apertures  of  the  gauze  to  be  cooled  below  the 
point  of  ignition,  and,  therefore,  communicate  with  the  external 
atmosphere.  But  this  is  easily  prevented  by  protecting  the  lamp 
from  the  draught,  and  an  accident  from  this  cause  is  not  likely  to 
occur  in  a  coal-mine.1 

The  carburetted  hydrogen  does  not  explode  when  mixed  with  air 
in  a  proportion  much  above  or  below  the  quantity  necessary  for  its 
complete  combustion.  With  3  or  4  times  its  volume  of  air  it  does 
not  explode  at  all,  with  5£  or  6  volumes  of  air  it  detonates  feebly, 
and  with  7  to  8  most  powerfully.  With  14  volumes  of  air,  the 
mixture  is  still  explosive,  but  with  larger  proportions  of  air,  the  gas  only  burns 
about  the  flame  of  the  taper.  The  large  quantity  of  air  which  is  then  mixed  with 
the  gas  absorbs  so  much  heat  as  to  prevent  the  temperature  of  the  gaseous  atmo- 
sphere from  rising  to  the  point  of  ignition. 

Coal-gas.  —  The  products  of  the  distillation  of  coal  in  an  iron  retort  are  of  three 
kinds:  a  black  oily  liquid,  of  a  heterogeneous  nature,  known  as  coal-tar;  a  watery 


1  For  additional  information  respecting  the  safety-lamp,  the  reader  is  referred  to  Davy's 
Essay  on  Flame,  to  Dr.  Paris's  Life,  and  Dr.  J.  Davy's  Life  of  Sir  H.  Davy,  and  to  the  Re- 
port of  the  Parliamentary  Committee  on  Accidents  in  Mines,  1835. 


PROTOCARBURETTED   HYDROGEN. 


281 


fluid,  known  as  the  ammoniacal  liquor,  and  the  elastic  fluids  which  form  coal-gas. 
To  purify  the  gas,  it  is  cooled  by  transmitting  it  through  iron  tubes  or  shallow  boxes, 
in  which  it  deposits  some  condensible  matter ;  and  it  is  afterwards  exposed  to  milk 
of  lime,  to  absorb  hydrosulphuric  acid  gas,  which  it  invariably  contains,  and  fre- 
quently afterwards  to  dilute  sulphuric  acid  or  a  solution  of  sulphate  of  iron,  which 
arrests  a  little  hydrosulphate  of  ammonia  and  a  trace  of  hydrocyanic  acid.  The 
hydrate  of  lime  is  often  applied  in  the  state  of  a  damp  powder,  and  not  diffused 
through  water. 

The  process  may  be  illustrated  by  the  arrangement  represented  in  fig.  129.     The 
coal  to  be  distilled  is  contained  in  an  iron  or  stoneware  retort  A,  which  should  not  be 

FIQ.  129. 


more  than  half  filled  if  the  coal  is  of  a  bituminous  quality,  and  is  heated  by  a  small 
charcoal  furnace.  Tar  and  a  watery  fluid  containing  ammonia  condense  in  B,  which 
represents  the'  condenser.  The  gas  passes  on  to  C,  a  glass  jar,  with  stages  of  wire- 
gauze  supporting  slaked  lime,  and  forming  a  lime-purifier.  The  gas  is  then  con- 
veyed by  the  tube  F  into  the  bell-jar  E,  filled  with  water,  and  inverted  over  another 
glass  jar  D,  serving  as  a  water-tank.  The  jar  E,  which  represents  the  gasometer, 
is  connected  by  a  string  passing  over  two  pulleys  above,  with  an  iron  weight  which 
balances  it.  When  the  gasometer  rises  and  is  full,  the  gas  may  be  allowed  to  escape 
by  the  tube  F  and  the  jet  and  stopcock  at  the  side,  by  removing  or  diminishing  the 
counterpoise  to  the  jar  E. 

Dr.  Henry  obtained  the  following  results  from  an  examination  of  the  gas  from 
the  best  cannel  coal,  at  different  periods  of  the  distillation  :  — 


282 


CARBON. 


COAL   GAS   IN    100   VOLUMES. 


Density. 

Olefiant 
gas. 

Carburetted 
hydrogen. 

Carbonic 
oxide. 

Hydrogen 

Nitrogen 

At  beginning  of  process... 
After  five  hours 

650 
500 
345 

13 

7 
0 

82.5 
56 
20 

3.2 
11 
10 

0 
21.3 
60 

1.3 
4.7 
10 

After  ten  hours   .    ... 

Besides  the  constituents  mentioned,  coal-gas,  when  first  made,  contains  small 
quantities  of 

Ammonia  Hydrocyanic  acid 

Hydrosulphuric  acid  Bisulphide  of  carbon 

Carbonic  acid  Naphtha  vapour.1 

All  of  these  bodies  are  separated  from  it  in  the  process  of  purification,  except  the 
two  last,  namely,  naphtha  vapour,  which  is  the  chief  cause  of  the  odour  of  coal-gas, 
and  bisulphide  of  carbon,  which  affords  a  little  sulphurous  acid  when  the  gas  is 
burned.  The  heterogeneous  nature  of  the  gaseous  mixture  is  well  shown  upon 
introducing  a  quantity  of  dry  iodine  into  a  bottle  of  coal-gas,  when  several  liquid 
and  solid  compounds  of  iodine  are  formed  with  the  different  carbohydrogens  present. 
Iodine,  on  the  other  hand,  is  not  affected  in  the  slightest  degree  by  fire-damp,  but 
remains  with  its  metallic  lustre  unchanged  in  that  gas.  Indeed,  in  the  ordinary 
fire-damp  no  other  combustible  gas  whatever  can  be  found,  besides  protocarburetted 
hydrogen  (Mem.  of  Chem.  Soc.  iii.  7). 

The  superiority  of  coal-gas,  in  illuminating  power,  depends  principally  upon  the 
high  proportion  of  olefiant  gas  and  the  denser  carbohydrogens  which  it  contains. 
The  free  hydrogen  and  carbonic  oxide  present  give  no  light,  and  are  positively  inju- 
rious. As  the  highly  illuminating  constituents  are  dense,  and  contain  much  carbon, 
the  value  of  coal-gas  is  to  a  certain  extent  proportional  to  its  density,  and  to  the 
quantity  of  oxygen  which  it  requires  for  complete  combustion.  In  the  analysis  of 
coal-gas,  the  different  gases  may  thus  be  separated :  1st.  Olefiant  gas,  naphtha 
vapour,  and  similar  carbohydrogens,  by  mixing  the  gas  over  water,  in  a  dark  place, 
with  half  its  bulk  of  chlorine,  and  afterwards  washing  with  caustic  potassa;  or,  by 
introducing  a  small  pellet  of  coke  charged  with  fuming  sulphuric  acid  and  attached 
to  a  platinum  wire,  into  the  gaseous  mixture,  over  mercury,  and  afterwards  absorb- 
ing the  acid  vapour  by  a  fragment  of  hydrate  of  potassa :  2dly,  carbonic  oxide,  by 
potassium  gently  heated  in  the  gas ;  3dly,  the  proportion  of  protocarburetted  hydro- 
gen gas  may  be  determined  by  detonating  the  mixture  over  mercury,  in  an  eudio- 
meter (fig.  113,  page  249),  with  a  measured  quantity  of  oxygen,  and  ascertaining 
the  quantity  of  carbonic  acid  formed,  which  retains  the  volume  of  this  carburetted 
hydrogen ;  4thly,  the  free  hydrogen,  by  observing  the  quantity  of  oxygen  remain- 
ing, by  means  of  a  stick  of  phosphorus  introduced  into  the  gas,  and  thereby  ascer- 
taining the  quantity  of  oxygen  consumed  in  the  last  combustion ;  from  this  quantity 
deduct  twice  the  measure  of  the  carburetted  hydrogen  found,  and  half  the  remaining 
measure  of  consumed  oxygen  represents  the  hydrogen;  5th,  the  residuary  gas  after 
these  processes  is  the  nitrogen  of  the  coal-gas.2 

1  Dr.  Henry's  Papers  on  Coal-Gas  are  contained  in  the  Philosophical  Transactions  for 
1808,  1820,  and  1824. 

2  The  tubes  and  eudiometers  for  measuring  gases  require  to  be  very  minutely  graduated : 
this  is  attained  with  peculiar  accuracy  and  facility  by  the  method  recommended  by  Professor 
Bunsen.     His  instrument  for  graduating  glass  tubes  (fig.  ]  30)  consists  of  a  mahogany  board 
A,  5ij-  feet  long,  7  inches  wide,  and  f  of  an  inch  thick.     In  the  middle  of  this  board  is  a 
groove  extending  its  whole  length,  1  inch  wide,  £  inch  deep,  and  rounded  at  bottom  as  a 
bed  for  the  reception  of  the  tube.     At  one  part,  5  inches  from  the  end,  is  placed  a  brasa 
plate  B,  1£  foot  long  and  2  inches  wide,  in  such  a  position  that  when  screwed  down  its  edge 
comes  one-half  over  the  groove.     It  is  furnished  with  four  screw-nuts,  passing  through  slits 


PROTOCARBURETTED  HYDROGEN.          283 

Structure  of  flame.  —  The  quantit}r  of  light  obtained  from  the  combustion  of 
coal-gas  depends  entirely  upon  the  manner  in  which  it  is  burned,  which  will  appear 

in  the  plate,  a  quarter  of  an  inch  long,  so  as  to  allow  a  certain  advancement  or  withdrawal 
of  the  plate  at  pleasure. 

FIG.  130. 


C  and  D  are  two  similar  plates,  placed  at  the  other  end  of  the  wooden  board,  C  having 
the  same  amount  of  motion  as  B,  and  being  precisely  similar  in  every  respect.  D  is  a  brass 
plate  of  the  same  dimensions  as  B  and  C,  which  is  cut,  at  intervals  of  five  millimeters,  into 
notches,  every  alternate  one  being  one-twentieth  and  one-tenth  of  an  inch  deep.  There  is 
also  a  wooden  rod  E,  3  feet  long,  1  inch  broad,  and  half  an  inch  thick.  This  is  provided 
with  two  steel  points,  placed  by  screws  at  half  an  inch  from  either  end.  One  of  these,  F,  is 
in  the  form  of  a  knife,  the  other,  G,  of  a  bradawl ;  a  screw-driver  is  also  provided,  that 
these  points  may  be  attached  or  removed  at  pleasure. 

When  a  tube  is  to  be  graduated,  it  is  covered  with  a  thin  layer  of  melted  wax  and  turpen- 
tine, by  means  of  a  camel's  hair  pencil,  and  is  laid  in  the  groove  between  C  and  D,  which 
are  then  screwed  down  in  their  places,  so  as  to  retain  the  tube  firmly  in  its  position.     A 
standard  tube,  previously  mathematically  divided  into  millimeters, 
(the  most  convenient  division,)  is  now  placed  in  the  groove  under  FIG.  131. 

B,  (fig.  131)  which  is  then  screwed  upon  it.  The  rod,  E,  is  now 
used,  the  pointed  steel,  G,  being  put  into  one  of  the  millimeter 
marks  on  the  standard  tube;  the  knife  point,  F,  falls  upon  the 
waxed  tube,  and  is  made  to  produce  a  line  upon  it,  the  length  of  which  is  regulated  by  the 
distance  between  the  edges  of  the  brass  plates  C  and  D.  The -pointed  steel  is  now  removed 
back  one  millimeter  on  the  standard  tube,  and  the  corresponding  mark  made  on  the  waxed 
one ;  and  thus  we  proceed  until  the  whole  of  the  waxed  tube  is  divided  into  millimeters. 
The  object  of  the  notches  is,  that  a  longer  mark  may  be  made  at  every  five  millimeters,  and 
a  still  longer  one  at  every  ten,  in  order  to  aid  the  eye  in  reading.  The  waxed  tube  is  now 
removed  to  a  leaden  trough  containing  pounded  fluor  spar  and  sulphuric  acid,  slightly 
heated,  which  etches  it  more  successfully  than  a  solution  of  hydrofluoric  acid.  Previously, 
however,  to  being  etched,  it  is  desirable  to  figure  the  number  of  millimeters  at  the  space 
of  every  ten ;  and  this  is  conveniently  done  by  the  steel  pointer  G,  after  being  removed 
from  the  rod  E.  The  tube  is  rubbed  with  vermilion  .powder  when  in  use,  to  make  the  gra- 
duation more  legible. 

We  have  thus  an  accurate  measure  of  length  etched  upon  the  tube,  which  should  be  one 
of  pretty  uniform  calibre.  The  next  point  is  to  determine  the  true  value  of  each  of  the 
divisional  marks :  this  is  done  by  calibrating  it  throughout  all  its  length  by  small  portions 
of  mercury,  —  say  equal  in  bulk  to  five  'grains  of  water.  By,  this  means  the  relative  value 
of  each  mark  is  determined,  and  the  proportion  which  it  bears  to  any  given  standard.  The 
only  possible  error  is  in  the  assumption  that  the  tube  is  of  even  calibre  within  the  space 
occupied  by  one  measure  of  mercury ;  but  the  quantity  of  this  added  is  so  small,  that  any 
such  error  becomes  quite  inappreciable.  The  convenience  of  this  graduator  is  so  great, 
that  a  lung  tube  may  be  beautifully  divided  in  the  course  of  an  hour.  The  standard  tube 
should  be  made  of  glass,  but  the  original  divisions  from  which  this  standard  is  taken  may 
be  those  of  wood  or  any  other  material. 

The  tubes  recommended  by  Bunsen  are  18  or  19  inches  in  length,  about  0.6  inch  in  inter- 
nal, and  0.8  inch  in  external  diameter.  One  of  these  is  converted  into  a  eudiometer,  in 
which  the  gases  are  exploded,  by  inserting  near  the  closed  end,  by  fusion,  two  platinum 
wires  of  the  thickness  of  horse-hair,  for  the  purpose  of  passing  the  electric  spark.  During 
the  explosion  the  open  end  of  the  tube  is  pressed  firmly  upon  a  smooth  pad  of  caoutchouc, 
placed  under  the  mercury  at  the  bottom  of  the  pneumatic  trough.  The  graduation  of  these 
tubes  being  linear,  enables  the  observer  to  read  off  the  difference  in  height  between  the 
mercury  in  the  tube  and  trough,  and  to  make  the  necessary  correction  on  the  volume 
measured  ;  all  exact  experiments  on  gaseous  volumes  must  be  made  over  mercury.  This 
department  of  chemical  analysis  has  been  brought  to  a  high  degree  of  accuracy  and  perfec- 
tion by  Professor  Bunsen.  (See  Reports  of  the  British  Association,  1845,  page  148  ;  and 
Liebig  and  Poggendorff's  Handworterbuch  der  Cheniie,  ii.  1053.) 


284  CARBON. 

from  the  consideration  of  the  structure  of  luminous  flames.     The  flame  of  a  spirit- 

lamp,  candle,  or  gas-jet,  is  hollow,  as  may  be  observed  by  depressing  a  sheet  of 

wire-trellis  upon  it,  which  gives  a  section  of  the  flame ;  the  seat  of  the  combustion 

being  the  margin  of  the  flame,  where  alone  the  combustible  vapour  is  in  contact 

with  the  air.     Of  volatile  carbonaceous  combustibles,  the  flame  consists 

Fia.  132.    0£  three  parts,  which  are  represented  in  section  (fig.  132)  :  — 

A,  cone  of  vapourized  combustible. 

B,  sphere  of  partial  combustion, 
c,  sphere  of  complete  combustion. 

In  B,  where  the  supply  of  air  is  insufficient  for  complete  combustion,  it 
is  the  hydrogen  principally  which  burns,  the  carbon  being  liberated  in 
solid  particles,  which  are  heated  white-hot  from  the  combustion  of  that 
gas.  The  sphere  B,  indeed,  is  the  luminous  portion  of  the  flame,  for 
the  light  depends  entirely  upon  the  deposition  of  carbon  arising  from 
the  consecutive  combustion  of  the  two  elements  of  the  vapour.  Gaseous 
bodies,  however  strongly  heated,  emityno  light,  or  at  most  not  more  than  a  sensible 
glow,  and  luminous  flame  has  justly  been  described  by  Davy  as  always  containing  solid 
matter  heated  to  whiteness.  The  same  sphere  of  the  flame,  possessing  an  excess  of 
combustible  matter  at  a  high  temperature,  takes  oxygen  from  metallic  oxides,  such 
as  arsenious  acid,  placed  in  it,  and  developes  their  metals.  It  is,  therefore,  often 
referred  to  as  the  deoxidizing  or  reducing  flame.  In  the  external  hollow  cone,  c, 
the  deposited  carbon  meets  with  oxygen,  and  is  entirely  consumed.  The  hottest 
point  in  the  whole  flame  is  within  this  sphere,  near  the  summit  of  B.  This  part  of 
the  flame,  possessing  an  excess  of  oxygen  at  a  high  temperature,  is  the  proper  place 
for  kindling  a  combustible,  and  is  called  the  oxidizing  flame  :  its  properties  are  the 
opposite  of  those  of  B. 

When  coal-gas  is  mingled  with  an  equal  bulk  of  air  before  being  burned,  it  is 
found  to  lose  half  its  illuminating  power.  It  may  be  conveniently  mixed  with  a 
quantity  of  air  sufficient  for  its  complete  combustion,  by  placing  over  an  argand 
burner,  a  brass  chimney  of  5  inches  in  height  provided  with  a  cap  of  wire-gauze ; 
when  kindled  above  the  wire-gauze,  the  gas  burns  with  a  blue  flame,  not  more 
luminous  than  that  of  sulphur.  The  flame  is  so  feebly  luminous  because  no  depo- 
sition of  carbon  occurs  in  it.  The  quantity  of  heat  is  the  same,  whether  the  gas 
is  burned  so  as  to  produce  much  or  little  light ;  and  where  the  gas  is  burned  for 
heat,  this  mode  of  combustion  has  the  advantage  of  giving  a  flame  without  smoke. 
The  heat  derived  from  coal-gas  burned  in  this  manner  is  not,  however,  so  intense  as 
that  of  an  argand  spirit-lamp. 

A  result  of  the  circumstances  which  determine  the  quantity  of  light  from  different 
flames  is,  that  the  larger  the  flame  till  it  begins  to  be  smoky,  the  greater  the  pro- 
portion of  light  obtained  from  the  consumption  of  the  same  quantity  of  gas.  It 
was  observed  that  an  argand  burner,  supplied  with  l£  cubic  feet  of  gas  per  hour, 
gave  as  much  light  as  a  single  candle ;  with  2  cubic  feet  per  hour  the  light  was 
equal  to  4  candles,  and  with  3  cubic  feet  to  10  candles.  Hence  argands,  bat-wings, 
and  other  burners,  in  which  a  considerable  quantity  of  gas  is  burned  together,  are 
more  economical  than  plain  jets.  The  brightness  of  ordinary  flame,  which  depends 
essentially  upon  the  consecutive  combustion  of  hydrogen  and  carbon,  is  increased  by 
everything  which  promotes  the  rapidity  and  intensity  of  the  combustion,  without 
deranging  the  order  of  oxidation,  such  as  a  rapid  supply  of  air,  and  the  substitution 
of  pure  oxygen  for  air,  as  in  Gurney's  Bude  Light.  Not  only  is  there  then  more 
light,  because  there  is  more  combustion  in  the  same  time,  but  the  temperature  of 
the  flame  being  greater,  the  luminous  carbon  is  also  heated  to  a  higher  degree  of 
whiteness. 

[See  Supplement,  p.  772.J 


BICARBURETTED   HYDROGEN. 


285 


BICARBURETTED   HYDROGEN. 

Syn.  Olefiant  gas,  Elayk ;  Eq.ZS  or  350;  C4H4;  density  985.2;    |     |     | 

This  gas  was  discovered  in  1796,  by  certain  associated  Dutch  chemists,  who  gave 
it  the  name  of  olefiant  gas,  because  it  forms  with  chlorine  a  compound  having  the 
appearance  of  oil.  It  is  usually  prepared  by  heating  together  1  measure  of  spirits 
of  wine  with  3  measures  of  oil  of  vitriol,  in  a  capacious  retort,  till  the  liquid  becomes 
black  and  effervescence  begins,  and  maintaining  it  at  that  particular  temperature.  It 
is  collected  over  water,  which  deprives  it  of  a  portion  of  ether  vapour  and  sulphurous 
acid,  with  which  it  is  accompanied.  [See  Supplement,  p.  771.] 

A  process  which  yields  a  purer  gas,  and  in  larger  volume,  is  the  following. 
Twenty-eight  ounces  of  water  are  added  to  twice  their  volume  of  oil  of  vitriol,  in  a 
large  globular  flask  A  (fig.  131),  which  gives  an  acid  of  about  1.6  density  when 

Fio.  133. 


cool.  Without  waiting  to  cool,  however,  24  ounce  measures  of  spirits  of  wine  are 
added,  and  the  whole  allowed  to  stand  for  a  night.  The  flask  is  supported  on  a  bed 
of  pumice  over  the  gas-flame  as  already  described  (page  264),  and  the  latter  regu- 
lated so  as  to  keep  the  liquid  in  a  state  of  moderate  ebullition.  The  gas  evolved  is 
passed  through  two  two-pound  bottles,  B  and  C,  the  first  of  which,  B,  is  empty,  or 
contains  only  a  little  water  at  the  beginning,  and  is  intended  for  the  condensation 
of  a  considerable  portion  of  alcohol  and  ether  which  distil  over,  while  C  is  half  filled 
with  a  strong  solution  of  caustic  potassa,  to  absorb  the  sulphurous  and  carbonic  acids 
produced.  These  two  wash-bottles  are  immersed  in  jars  containing  cold  water.  The 
third  wash-bottle,  D,  contains  oil  of  vitriol,  and  the  U-tube  E,  pumice  soaked  in  the 
same  fluid  to  absorb  ether- vapour ;  while  the  gas  is  collected  at  last  in  bottles,  F, 
over  water  made  sensibly  alkaline  by  caustic  potassa. 

This  gas  is  formed  by  a  peculiar  decomposition  of  alcohol,  in  contact  with  sul- 
phuric acid  boiling  at  325°,  or  a  little  higher,  in  which  the  alcohol  is  resolved  into 
olefiant  gas  and  water,  C4H502=:C4H4  and  2HO.  This  decomposition  will  be  re- 
ferred to  again  more  particularly  under  the  head  of  alcohol. 

Bicarburetted  hydrogen  gas  contains  2  volumes  of  carbon  vapour  and  2  volumes 
of  hydrogen  condensed  into  1  volume,  and  is  theoretically  of  the  same  density  as 
nitrogen  and  carbonic  oxide,  or  fourteen  times  heavier  than  hydrogen.  It  was  con 
densed  by  cold  and  pressure  into  a  transparent  liquid,  which  is  not  solidifiable  (page 
79).  This  gas,  when  carefully  deprived  of  ether,  has  a  sweet  odour,  which  is  pecu- 
liar but  not  strong.  Water  absorbs  about  one-eighth  of  its  volume  of  this 


286  CARBON. 

alcohol  takes  up  2  volumes,  oil  of  turpentine  2.5,  and  olive  oil  1  volume.  It  is 
absorbed  by  fuming  sulphuric  acid,  and  by  the  perchloride  of  antimony,  forming 
peculiar  compounds.  The  substances  named  leave  certain  gaseous  impurities  uncon- 
densed,  which  often  amount  to  15  or  20  per  cent.,  and  appear  to  be  principally  pro- 
tocarburetted  hydrogen.  The  gas  of  the  process  described  above  is  entirely  absorbed 
by  the  perchloride  of  antimony,  except  about  4  per  cent. ;  but  it  appears  to  contain 
the  vapour  of  some  denser  carbohydrogen,  not  absorbed  by  oil  of  vitriol,  as  the 
specific  gravity  of  the  gas  so  prepared  is  often  as  high  as  that  of  air,  or  1000,  in- 
stead of  985.2  as  observed  by  Saussure. 

This  gas  burns  with  a  white  flame,  which  is  much  more  brilliant  than  that  of 
protocarburetted  hydrogen.  It  requires  three  times  its  volume  of  oxygen  to  burn 
it  completely,  and  yields  twice  its  volume  of  carbonic  acid  gas  and  twice  its  volume 
of  aqueous  vapour;  for  one  volume  of  bicarburetted  hydrogen  contains  2  volumes 
of  carbon  vapour,  each  of  which  requires  1  volume  oxygen  and  becomes  1  volume 
carbonic  acid,  and  2  volumes  hydrogen,  each  of  which  requires  J  volume  oxygen 
and  forms  1  volume  steam.  This  gas  is  entirely  decomposed,  when  passed  through 
a  porcelain  tube  at  a  white  heat,  into  carbon,  which  is  deposited,  and  twice  its  vo- 
lume of  hydrogen  gas. 

Bicarburetted  hydrogen  mixed  with  twice  its  volume  of  chlorine  gas  is  condensed, 
and  forms  a  liquid  compound  of  an  oily  consistence,  C4H4C12,  from  which  it  was 
named  olefiant  gas,  or  the  oil-making  gas,  and  Elayle  (from  « tae-w  and  vty,  the  source 
of  an  oil),  by  Berzelius.  This  substance,  which  is  also  known  as  Dutch  liquid,  will 
be  described  under  the  derivatives  of  alcohol.  [See  Supplement,  p.  772.] 

GAS   OF   OIL. 

Bicarburetted  hydrogen  of  Faraday;  Eq.  56  or  700;  C8H8;  density 
1926.4;  Q^j 

This  gas,  which  is  twice  as  condensed  as  olefiant  gas,  is  one  of  the  products  of  the 
decomposition  of  the  fixed  oils  by  heat,  and  exists,  therefore,  in  the  gas  prepared 
from  oil.  It  is  liquefied  when  oil  gas  is  greatly  compressed,  and  also  by  a  cold  of 
0°  F.  The  flame  of  this  gas  is  very  brilliant;  it  is  only  sparingly  soluble  in  water, 
but  pretty  soluble  in  alcohol  and  the  fat  oils ;  sulphuric  acid  dissolves  a  hundred 
times  its  volume.  It  combines  with  an  equal  volume  of  chlorine,  and  forms  a  liquid 
compound  having  some  analogy  to  Dutch  liquid. 

This  gas  requires  6  volumes  of  oxygen  to  burn  it,  and  gives  rise  to  water  and  4 
volumes  of  carbonic  acid. 

CARBON   AND    NITROGEN  —  CYANOGEN. 

Eq.  26  or  325;  NC2;  density  1819;  |     |     | 

This  compound  is  a  gas,  which  was  first  obtained  by  Gay-Lussac  in  1815.  It  is 
prepared  by  heating  the  cyanide  of  mercury  in  a  small  glass  retort,  and  is  collected 
at  the  mercurial  trough.  The  cyanide  is  resolved  into  running  mercury  and  cyano- 
gen gas,  and  frequently  leaves  a  black  coaly  mass  in  the  retort,  which  Professor 
Johnston  has  shown  to  consist  of  carbon  and  nitrogen,  in  the  same  proportions  as 
the  gas  itself. 

Cyanogen  gas  contains  4  volumes  of  carbon  vapour  and  2  volumes  of  nitrogen, 
condensed  into  2  volumes;  its  density  is  1819.  When  this  gas  is  exploded  with 
twice  its  volume  of  oxygen,  it  affords  2  volumes  of  carbonic  acid  gas,  and  1  volume 
of  nitrogen ;  an  experiment  from  which  its  composition  may  be  deduced.  Water  at 
60°  absorbs  4.5  times  its  volume  of  this  gas,  and  alcohol  23  volumes.  By  a  pressure 
of  3.6  atmospheres  at  45°,  cyanogen  is  condensed  into  a  limpid  liquid,  which  eva- 
p'orates  again  on  removal  of  the  pressure.  Cyanogen  burns  with  a  beautiful  purple 


BORON. 


287 


FIG.  134. 


flame  in  air  or  oxygen.  The  solution  of  cyanogen  in  water  undergoes  spontaneous 
decomposition.  By  alkalies  the  gas  is  absorbed,  and  a  cyanide  and  cyanate  formed. 

Carbon  does  not  burn  when  heated  in  nitrogen  gas,  and  appears  to  be  incapable 
of  uniting  with  that  element  when  alone,  or  unless  when  assisted  by  the  presence 
of  a  third  body,  such  as  potassium,  which  unites  with  and  gives  stability  to  the 
compound.  Cyanogen  is  thus  produced  when  nitrogen  is  sent  over  fragments  of 
charcoal  saturated  with  potassa,  heated  white-hot  in  a  porcelain  tube  placed  across  a 
furnace,  and  obtained  as  cyanide  of  potassium.  A 
peculiar  form  of  furnace,  in  which  this  remarkable 
process  is  conducted  on  a  large  scale  at  Newcastle, 
with  considerable  success,  is  described  by  Mr. 
Bramwell  (Repertory  of  Inventions,  3  ser.  ix.  280). 
It  consists  essentially  of  a  vertical  flue  in  brickwork 
A  B  D,  (fig.  134),  containing  charcoal  charged 
with  a  solution  of  carbonate  of  potassa,  the  middle 
portion  of  which,  B,  is  placed  within  the  flue  of 
the  adjoining  furnace  2  2,  by  which  it  is  "heated  in- 
tensely, and  also  obtains  a  supply  of  nitrogen, 
which  enters  A  B  D  by  a  number  of  small  open- 
ings into  the  external  flue.  The  passage  of  gases 
upwards  through  the  potassa-charcoal  is  further 
promoted  by  the  action  of  air-pumps  connected 
with  the  tubes  Gr  and  H.  The  materials  are  intro- 
duced at  the  top  on  removing  a  lid  C,  and  after 
descending  through  the  tube  are  allowed  to  fall 
into  a  cistern  of  water  F,  in  which  the  cyanide  of 
potassium  is  found  dissolved.  The  pipes  I  and  J 
dip  into  water,  to  intercept  ammonia  or  any  other 
volatile  product. 

Cyanogen  is  a  salt-radical,  and  unites  with  all 
the  metals,  as  chlorine  and  iodine  do,  forming  a 

class  of  cyanides.  It  also  combines  with  hydrogen  and  forms  a  hydrogen-acid,  namely, 
hydrocyanic  or  prussic  acid.  Cyanogen  properly  belongs  to  organic  chemistry,  in 
which  department  its  numerous  combinations  will  be  considered. 

Mellon,  N4C6.  —  This  is  another  salt-radical,  and  was  formed  by  Liebigby  heating 
the  bisulphide  of  cyanogen  in  a  glass  flask  to  redness,  when  it  is  resolved  into  sul- 
phur, bisulphide  of  carbon,  and  mellon.  It  is  a  lemon  yellow  powder,  insoluble  in 
water  and  alcohol ;  it  unites  directly  with  hydrogen  and  with  potassium,  forming 
hydro-mellonic  acid,  a  hydrogen-acid,  and  mellonide  of  potassium,  a  saline  body. 


SECTION   V. 


BORON. 

Eq.  10.9  or  136.2;  B;  density  of  vapour  (hypothetical)  751;  |     |~~|  . 

Boron  is  an  element  having  some  analogy  to  carbon,  but  sparingly  diffused  in 
nature.  It  is  never  found,  except  in  combination  with  oxygen  as  boracic  acid,  of 
which  the  salt  of  soda  has  long  been  brought  to  Europe  from  India  in  a  crude  state, 
under  the  name  of  tinkal,  and  termed  borax  when  purified.  The  impure  borax  or 
tinkal  forms  a  saline  incrustation  in  the  beds  of  certain  small  lakes  in  an  upper 
province  of  Thibet,  which  dry  up  during  summer.  But  the  most  considerable  of 
the  present  sources  of  boracic  acid  are  the  hot  lagoons  of  a  district  in  Tuscan}, 
which  are  charged  with  the  free  acid,  from  the  condensation  in  them  of  vapours  of  a 
volcanic  origin.  Boracic  acid  is  likewise  found  in  the  hot  springs  of  Lipari.  It  is  a 
constituent  also  of  several  minerals,  of  which  datolite  and  boracite  are  the  most  re- 


288  BORON. 

markable.  Boron  was  first  discovered  by  Sir  H.  Davy  in  1807,  by  exposing  boracic 
acid  to  the  action  of  a  powerful  voltaic  battery,  and  was  afterwards  obtained  by 
Gay-Lussac  and  Thenard  in  greater  quantity,  by  heating  boracic  acid  with  potas- 
sium. [/See  Supplement,  p.  773.] 

Preparation.  —  Boron  is  prepared  with  greatest  advantage  from  a  combination  of 
fluoride  of  boron  and  fluoride  of  potassium,  which  is  obtained  on  saturating  hydro- 
fluoric acid  with  boracic  acid,  and  afterwards  adding  to  it,  drop  by  drop,  the  fluoride 
of  potassium.  This  compound,  which  is  of  slight  solubility,  is  collected  on  a  filter, 
and  dried  at  an  elevated  temperature,  but  which  should  not  reach  a  red  heat.  Equal 
weights  of  the  compound  and  of  potassium  are  mixed  together  in  a  cylinder  or  tube 
of  iron,  closed  at  one  end,  which  is  gently  heated,  and  the  mixture  stirred  with  an 
iron  rod,  till  the  potassium  is  melted.  Heated  afterwards  more  strongly  by  a  spirit- 
lamp,  the  mass  evolves  heat,  and  becomes  red-hot ;  the  potassium  combines  with  the 
fluorine,  and  a  mixture  is  obtained  of  boron  and  the  fluoride  of  potassium.  On 
treating  this  with  water,  the  fluoride  of  potassium  dissolves,  and  the  boron  remains 
alone.  In  washing  it  farther,  instead  of  pure  water,  which  causes  the  oxidation  of 
boron,  a  solution  of  sal  ammoniac  should  be  employed,  which  does  not  act  upon  that 
body,  and  the  sal  ammoniac  remaining  in  the  boron  may  be  taken  up  by  alcohol. 

Properties.  —  Thus  prepared,  boron  is  obtained  in  the  form  of  a  greenish-brown 
powder,  without  the  metallic  lustre,  which  becomes  hard  and  assumes  a  deeper 
colour,  when  ignited  in  vacuo,  or  in  gases  which  do  not  combine  with  it,  but  under- 
goes no  farther  change.  Heated  in  atmospheric  air  or  oxygen  it  burns  with  a  vivid 
light,  scintillating  powerfully,  and  forms  boracic  acid.  Nitric  acid  and  many  other 
substances  also  oxidate  it  easily,  and  always  produce  that  compound.  Fused  with 
carbonate  of  potassa,  it  decomposes  the  carbonic  acid,  and  gives  borate  of  potassa, 
carbon  being  liberated.  Boron  is  not  known  to  possess  any  other  degree  of  oxidation. 
Boron  combines  with  sulphur,  with  the  disengagement  of  light,  when  heated  in  the 
vapour  of  that  substance ;  and  it  takes  fire  spontaneously  in  chlorine,  and  forms  a 
gaseous  chloride  of  boron,  of  which  the  formula  is  BC13,  and  the  density  3942  by* 
observation  and  4035  by  calculation.  This  gas  is  composed  of  2  vols.  of  boron 
vapour  and  6  of  chlorine,  condensed  into  4  vols.,  which  are  its  combining  measure. 
It  may  likewise  be  formed  by  transmitting  chlorine  gas  over  a  mixture  of  boracic 
acid  and  charcoal,  ignited  in  a  porcelain  tube.  *A  corresponding  fluoride  of  boron  is 
evolved  from  boracic  acid,  ignited  with  the  fluoride  of  calcium  or  fluor-spar,  with  the 
formation  of  borate  of  lime.  The  density  of  this  fluoride  is  2312.4.  Both  of  these 
gases  are  decomposed  by  water,  boracic  acid  being  formed  with  hydrochloric  or 
hydrofluoric  acid. 

Boracic  or  Boric  acid.  —  This  acid  is  prepared  by  dissolving  the  salt  borax  at 
212°  in  two  and  a  half  times  its  weight  of  water,  and  adding  enough  of  hydrochloric 
acid  to  make  the  liquid  strongly  acid  to  test  paper.  Chloride  of  sodium  is  formed, 
which  continues  in  solution,  while  the  boracic  acid  separates  in  thin  shining  crystal- 
line plates,  on  cooling.  These  plates  are  drained,  and  being  sparingly  soluble,  may 
be  washed  with  a  little  cold  water,  and  afterwards  redissolved  in  boiling  water,  and 
made  to  crystallize  anew.  Fused  at  a  red  heat  in  a  platinum  crucible,  these  plates 
give  the  vitrified  acid,  of  which  the  density  is  1-83.  Boracic  acid  has  a  weak  taste, 
which  is  scarcely  acid,  and  it  affects  blue  litmus  like  carbonic  acid,  imparting  to  it  a 
wine-red  tint,  and  not  that  clear  red,  free  from  purple,  which  the  stronger  acids  pro- 
duce. It  renders  yellow  turmeric  paper  brown,  like  the  alkalies.  The  acid  of  the 
carbonates,  however,  is  displaced  by  boracic  acid  in  the  cold,  and  at  a  red  heat  this 
acid  decomposes  even  the  sulphates,  from  its  comparative  fixity.  The  crystals  of 
boracic  acid  are  a  hydrate,  and  contain  3  equivalents  of  water,  of  which  the  formula 
is  HO.B03  +  2HO.  At  60°  it  requires  25.66  times  its  weight  of  water  to  dissolve 
it,  but  only  2.97  times  at  212°.  With  the  assistance  of  the  vapour  of  water,  it  is 
slightly  volatile,  but  alone  it  is  more  fixed,  and  fuses,  under  a  red  heat,  into  a  trans- 
parent glass.  At  the  white  heat  of  our  furnaces  boracic  acid  does  not  boil ;  but  the 
tension  of  its  vapour  is  so  considerable  at  that  temperature  that  it  evaporates  entirely 


SILICON   OR   SILICIUM.  289 

away  in  the  end.  The  hydrated  acid  dissolves  in  alcohol,  and  the  solution  burns 
with  a  fine  green  flame.  It  communicates  fusibility  to  many  substances  in  uniting 
with  them,  and  generally  forms  a  glass.  On  this  account  borax  is  much  used  as  a 
flux. 

Borates.  —  Boracic  acid  is  remarkable  for  the  variety  of  proportions  in  which  it 
unites  with  alkalies;  all  these  borates  have  an  alkaline  reaction  like  the  carbonates. 
The  relative  proportions  of  oxygen  and  boron  in  boracic  acid  are  known,  but  the 
number  of  equivalents  of  these  elements  in  this  acid  is  not  so  certain.  Dumas 
inferred  from  the  density  of  the  chloride  that  it  is  a  terchloride,  and  boracic  acid, 
which  corresponds,  will  therefore  consist  of  3  eq.  of  oxygen  to  1  eq.  of  boron,  and 
its  formula  be  B03.  This  makes  borax  the  biborate  of  soda.  [See  Supplement, 
p.  774.] 

% 

SECTION  VI. 

SILICON    OB    SILICIUM. 

Eq.  21.35  or  266.82;  Si;  density  of  vapour  (hypothetical)  1475;  |     |    | 

Silica  or  siliceous  earth,  the  oxide  of  the  present  element,  is  the  most  abundant 
of  all  the  matters  which  compose  the  crust  of  the  globe.  It  constitutes  sand,  the 
varieties  of  sand-stone  and  quartz  rock,  and  enters  into  felspar,  mica,  and  a  great 
variety  of  minerals,  which  form  the  basis  of  other  rocks.  [See  Supplement,  p.  776.] 

Preparation.  —  Silica  may  be  decomposed  by  heating  it  with  potassium,  which 
deprives  it  of  oxygen  ;  but  a  better  process  for  obtaining  silicon  is  to  heat  the  double 
fluoride  of  silicon  and  potassium,  with  8  or  9-10ths  of  its  weight  of  potassium,  with 
the  same  precautions  as  in  the  preparation  of  boron.  The  materials,  however,  in 
this  case  may  be  heated  in  a  glass  tube,  as  well  as  in  an  iron  cylinder.  The  double 
fluoride  employed  is  prepared  by  neutralizing  fluosilicic  acid  with  potassa.  A  di£. 
ferent  process  is  suggested  by  Berzelius,  which  consists  in  heating  potassium  in  a 
tube  of  hard  glass  with  a  small  bulb  blown  upon  it,  which  is  filled  with  the  vapour 
of  the  fluoride  of  silicon,  supplied  from  the  ebullition  of  that  liquid  contained  in  a 
small  retort  connected  with  the  glass  tube.  The  potassium  burns  in  this  vapour, 
and  at  the  end,  silicon  is  found,  with  fluoride  of  potassium,  in  the  place  of  the  metal- 
(Traite,  t.  1,  p.  307).  But  the  silicon  from  all  these  processes  is  always  in  combi- 
nation with  a  little  potassium,  and  mixed  with  a  little  fluoride  of  silicon  and  potas- 
sium unreduced.  Hence,  on  applying  cold  water  to  the  mass,  hydrogen  gas  is 
disengaged,  and  potassa  formed,  and  the  silicon  separates.  The  potassa  thus  produced 
can,  with  the  aid  of  hot  water,  dissolve  the  silicon,  which  then  oxidates  and  becomes 
silica,  so  that  cold  water  only  must  be  employed  to  wash  the  silicon,  which  may  be 
thrown  upon  a  filter.  After  a  time,  the  liquid  which  passes  has  an  acid  reaction, 
which  arises  from  its  dissolving  an  acid  double  fluoride  of  silicon  and  potassium,  of 
sparing  solubility,  which  has  escaped  decomposition,  and  is  mixed  with  the  silicon. 
The  washing  is  continued  so  long  as  the  water  dissolves  anything. 

Properties.  —  The  silicon  which  is  thus  obtained  is,  in  its  pure  state,  a  dull  brown 
powder,  which  soils  the  fingers,  and  when  heated  in  air  or  oxygen,  inflames  and 
burns,  but  is  never  more  than  partially  converted  into  silica.  It  may  be  ignited 
strongly  in  a  covered  crucible  without  loss,  and  then  shrinks  in  dimensions,  acquires 
a  deep  chocolate  colour,  and  becomes  so  dense  as  to  sink  in  oil  of  vitriol.  By  this 
ignition  the  properties  of  silicon  are  altered  to  a  degree  which  is  very  remarkable  in 
a  simple  substance.  It  was  previously  readily  soluble  in  hydrofluoric  acid,  with 
evolution  of  hydrogen,  and  in  caustic  potassa,  but  it  is  now  no  longer  acted  upon  by 
that  or  any  other  acid,  nor  by  alkalies.  The  ignited  silicon  also  refuses  to  burn  in 
air  or  oxygen,  even  when  intensely  heated  by  the  blowpipe  flame.  Charcoal,  it  will 
be  remembered,  is  more  dense  and  less  combustible  after  being  strongly  heated ;  but 
that  substance  is  not  altered  by  heat  to  the  same  extent  as  silicon.  Mixed  and 
19 


290  SILICON   OR    SILICIUM. 

heated  with  dry  carbonate  of  potassa,  silicon  in  any  condition  is  oxidated  completely, 
its  action  upon  the  carbonic  acid  of  the  salt  being  attended  with  ignition,  and  carbon 
liberated.  Silicon  burns  when  heated  in  sulphur  vapour,  and  forms  a  sulphide, 
which  water  dissolves,  but  decomposes  at  the  same  time,  hydrosulphuric  acid  and 
silica  being  produced,  and  the  last,  notwithstanding  its  usual  insolubility,  retained 
in  solution.  Silicon  likewise  burns  in  chlorine ;  and  the  chloride  of  silicon  may  be 
otherwise  formed  by  transmitting  chlorine  over  a  mixture  of  charcoal  and  silica 
ignited  in  a  porcelain  tube.  The  silica  is  decomposed  by  neither  charcoal  nor  chlo- 
rine singly,  but  acting  together  upon  the  silica,  these  bodies  produce  carbonic  oxide 
and  chloride  of  silicon.  This  compound  is  a  volatile  liquid,  of  which  the  formula  is 
Si  C13 ;  that  of  the  sulphide  of  silicon  Si  S3. 

Silica  or  Silicic  Jlcid,  Si  03.  —  This  earth,  which  is  the  only  oxide  of  silicon, 
constitutes  a  number  of  minerals,  nearly  in  a  state  of  purity,  such  as  rock-crystal, 
quartz,  flint,  sandstone,  the  amethyst,  calcedony,  cornelian,  agate,  opal,  &c.  The 
first  chemical  examination  of  its  properties  and  compounds  is  due  to  Bergman. 

Preparation.  —  Silica  may  be  had  very  nearly,  if  not  absolutely  pure,  by  heating 
a  colourless  specimen  of  rock-crystal  to  redness  and  throwing  it  into  water,  after 
which  treatment  the  mineral  may  be  easily  pulverized.  It  is  obtained  in  a  state  of 
more  minute  division,  by  transmitting  the  gaseous  fluoride  of  silicon  (fluosilicic  acid) 
into  water ;  or  by  the  action  of  acids  upon  some  of  the  alkaline  compounds  of  silica. 
Equal  parts  of  carbonate  of  potassa  and  carbonate  of  soda  may  be  fused  in  a  platinum 
crucible,  at  a  temperature  which  is  not  high ;  and  pounded  flint  or  any  other  siliceous 
mineral,  thrown  by  little  and  little  into  the  fused  mass,  dissolves  in  it  with  an  effer- 
vescence due  to  the  escape  of  carbonic  acid  gas.  The  addition  of  the  mineral  is 
continued  so  long  as  it  determines  this  effervescence.  The  mass  being  allowed  "to 
cool,  is  afterwards  dissolved  in  water  acidulated  with  hydrochloric  acid,  which  takes 
up  the  silica  as  well  as  the  alkalies ;  the  liquor  is  filtered  and  then  evaporated  to 
dryness.  The  silica  may  contain  a  little  peroxide  of  iron  or  alumina,  to  dissolve 
which  the  saline  mass,  when  perfectly  dry,  is  moistened  with  concentrated  hydro- 
chloric acid,  and  after  two  hours  the  acid  mass  is  washed  with  hot  water.  The  silica 
remains  undissolved ;  it  may  be  dried  well  and  ignited. 

Properties.  —  Silica  so  prepared  is  a  white,  tasteless  powder,  which  is  rough  to 
the  touch,  and  feels  gritty  between  the  teeth.  It  is  extremely  mobile  when  heated, 
and  is  thrown  out  of  a  crucible,  at  a  high  temperature,  by  the  slightest  breath  of 
wind.  It  is  absolutely  insoluble  in  water,  acids,  and  most  liquids.  Finely  divided 
silica,  however,  decomposes  an  alkaline  carbonate  at  the  boiling  point,  and  is  dis- 
solved. Its  density  is  2.66.  The  heat  of  the  strongest  wind-furnace  is  not  sufficient 
to  fuse  silica,  but  it  melts  into  a  limpid  colourless  glass  in  the  flame  of  the  oxihy- 
drogen  blowpipe,  and  may  be  drawn  out  into  threads  (Grirardin).  Silica  is  found 
frequently  crystallized,  its  ordinary  form  being  a  six-sided  prism  terminated  by  a 
six-sided  pyramid,  as  in  rock-crystal.  Sometimes  the  prism  is  very  short  or  disap- 
pears entirely,  and  the  pyramid  only  is  seen,  as  in  ordinary  quartz. 

Silicic  acid  dissolved  by  acids.  —  The  conditions  of  the  solubility  of  silicic  acid 
in  other  acids  are  peculiar.  Once  precipitated,  whether  gelatinous,  like  boiled 
starch,  or  pulverulent,  it  is  no  longer  in  the  least  degree  soluble  either  in  water  or 
acids.  If  to  a  dilute  solution  of  an  alkaline  silicate,  hydrochloric  acid  be  added 
slowly  and  drop  by  drop,  the  silicic  acid  is  precipitated  in  proportion  as  the  alkali  is 
neutralized.  But,  on  the  contrary,  no  silicic  acid  is  precipitated,  if  strong  hydro- 
chloric acid  in  considerable  excess  be  added  all  at  once  to  the  solution  of  alkaline 
silicate,  or  if  the  latter  be  poured  in  a  gradual  manner  into  hydrochloric  acid  whethe-r 
strong  or  greatly  diluted  with  water.  It  thus  appears  that  silicic  acid  only  dissolves 
in  the  stronger  acids,  when  presented  to  them  in  the  nascent  state,  or  at  the  moment 
of  leaving  another  combination.  It  appears  to  enter  into  combination  with  the  acid 
which  dissolves  it ;  for  if  the  latter  is  exactly  neutralized  by  adding  a  strong  solution 
of  potassa,  drop  by  drop,  the  whole  of  the  silica  is  precipitated. 

A  pure  solution  of  silicic  acid  in  hydrochloric  acid,  free  from  saline  matter,  is  best 


SILICATES. .  291 

obtained  from  the  silicate  of  copper.  The  latter  is  prepared  by  precipitating  chlo- 
ride of  copper  by  the  solution  of  an  alkaline  silicate ',  washing  the  insoluble  silicate 
of  copper  which  falls,  by  several  times  mixing  it  with  water  and  allowing  it  to 
subside,  so  as  to  get  rid  of  the  chloride  of  potassium  present.  The  silicate  of  copper 
is  then  dissolved  in  hydrochloric  acid,  filtered,  and  hydrosulphuric  acid  gas  made  to 
stream  through  the  liquid,  to  precipitate  the  copper.  The  black  insoluble  sulphide 
of  copper  is  removed  by  filtration,  and  a  perfectly  colourless  solution  of  silicic  acid 
is  obtained,  which  may  be  boiled,  to  expel  the  excess  of  hydrosulphuric  acid,  without 
injury.  This  solution  is  very  acid,  and  when  neutralized  by  ammonia  or  potassa  it 
allows  gelatinous  silica  to  precipitate. 

Hydrates  of  silicic  acid.  —  When  the  last  solution  of  silica  in  hydrochloric  acid 
is  evaporated  in  vacuo  over  fragments  of  quicklime,  it  deposits  the  protohydrate  of 
silica,  Si03-fHO,  in  very  thin  crystalline  filaments,  grouped  in  stars,  which  are 
colourless,  transparent,  and  possessed  of  considerable  lustre.  This  is  also  the  com- 
position of  the  gelatinous  silica,  precipitated  from  an  alkaline  silicate,  when  allowed 
to  dry  in  air.  The  silica  has  first  the  appearance  of  a  transparent  jelly,  which  is 
tenacious,  and  cracks  on  drying,  forming  a  mass  like  gum.  When  this  hydrate  is 
dried  at  212°,  one  half  of  the  water  escapes,  and  another  definite  hydrate,  2Si03  + 
HO,  remains  (Doveri).  Another  hydrate  was  obtained,  by  M.  Ebelmen,  by  the 
spontaneous  decomposition  of  silicic  ether,  of  which  the  composition  is2Si03  +  3HO. 
At  370°  C.  (698°  F.),  silicic  acid  does  not  retain  more  than  a  trace  of  water. 
(Doveri :  Observations  on  the  Properties  of  Silica,  Annales  de  Chim.  et  de  Phys. 
xxi.  p.  40,  1847.) 

Hydrofluoric  acid  has  an  affinity  quite  peculiar  for  silica,  decomposing  it,  and  car- 
rying off  the  silicon,  in  the  form  of  the  volatile  fluoride  of  silicon  :  — 

3HF  and  Si03=SiF3  and  3HO. 

The  water  of  springs  and  wells  always  contains  a  little  soluble  silica,  which  can 
only  be  separated  by  evaporating  the  water  to  dryness.  In  some  mineral  waters 
the  proportion  of  silica  is  very  considerable,  and  it  is  often  associated  with  an  alkaline 
carbonate,  which  silica  is  capable  of  decomposing  at  the  boiling  point;  as  in  the  hot 
alkaline  spring  of  Reikum  in  Iceland,  and  in  the  boiling  jets  of  the  Geyser,  which 
deposit  about  their  crater  an  incrustation  of  silica.  There  can  be  no  doubt  likewise 
that  much  of  the  crystalline  quartz  in  nature,  besides  all  the  agates,  calcedonies,  and 
silicious  petrifactions,  have  been  formed  from  an  aqueous  solution. 

Silicates.  —  Although  silica  has  no  acid  reaction,  it  is  certainly  an  acid,  and  is 
indeed  capable  of  displacing  the  most  powerful  of  the  volatile  acids  at  a  high  tempe- 
rature. It  is  capable  of  uniting  with  metallic  oxides,  by  way  of  fusion,  in  a  great 
variety  of  proportions.  Its  compounds  with  excess  of  alkali  are  caustic  and  soluble, 
but  those  with  an  excess  of  silica  are  insoluble,  and  form  the  varieties  of  glass, 
which  will  be  described  under  the  silicate  of  soda.  With  alumina  it  forms  the  less 
fusible  compounds  of  porcelain  and  stoneware,  which  will  be  noticed  under  that 
earth.  A  large  number  of  mineral  species  also  are  earthy  silicates.  It  seems 
probable  that  silicic,  like  phosphoric  acid,  forms  several  classes  of  salts,  of  which 
those  containing  the  largest  number  of  atoms  of  base  are  the  most  easily  decomposed 
by  acids.  At  the  same  time,  some  allatropic  difference  may  be  suspected  between 
the  silicic  acid  itself,  as  it  exists  in  these  different  classes  of  salts,  such  as  there  is 
between  ignited  and  unignited  silicon.  [See  Supplement,  pp.  777,  778.] 

The  formula  for  silicic  acid  is  not  very  certainly  established.  Most  chemists 
admit  it  to  be  Si03,  or  analogous  to  sulphuric  acid,  S03,  and  then  the  equivalent 
of  silicon  is  266.7.  But  others  adopt  the  formula  Si02,  considering  silicic  acid 
analogous  to  carbonic  acid,  C02;  the  equivalent  of  silicon  then  becomes  177.8. 
The  last  view  is  most  in  accordance  with  the  density  of  silicic  ether  vapour.  On 
the  other  hand,  the  composition  of  two  intermediate  compounds  between  the  chloride 
of  silicon,  SiCl3,  and  the  sulphide  of  silicon,  SiS3,  namely,  SiS012  and  SiS2Cl,  is 
most  simply  represented  on  the  first  view.  (Is.  Pierre.) 


292  s 

SECTION   VII. 

SULPHUR. 

Eq.  16  or  200;  S;  at  600°,  density  of  vapour  6634,  and  combining  measure  l-3d 
volume;  at  1800°,  density  about  one-third  of  above,  and  combining  measure 
1  volume  I  I  . 

This  element  is  exhaled  in  large  quantity  from  volcanoes,  either  in  a  pure  state 
or  in  combination  with  hydrogen,  and  by  condensing  in  fissures  forms  sulphur 
veins,  from  which  the  greater  part  of  the  sulphur  of  commerce  is  derived.  (See 
Reeherches  sur  les  furnerolles,  par  MM.  Melloni  and  Piria :  Annales  de  Chim.  et 
de  Phys.  2de  se>.  Ixxiv.  331.)  It  exists  also  in  combination  with  many  metals,  as 
iron,  lead,  copper,  zinc,  &c.  ;  and  is  sometimes  extracted  from  iron  pyrites  or  bisul- 
phide of  iron.  Sulphur  is  classed  with  oxygen  ;  and  the  higher  sulphides  resemble 
peroxides  in  losing  a  portion  of  their  sulphur,  as  some  of  the  latter  lose  a  portion  of 
their  oxygen,  when  strongly  heated.  Sulphur  is  likewise  extensively  diffused,  as  a 
( onstituent  of  the  sulphuric  acid,  in  gypsum  and  other  native  sulphates.  This  ele- 
ment also  enters  into  the  organic  kingdom,  being  invariably  associated  in  minute 
quantity  with  albuminous  or  protein  compounds. 

Properties* — Sulphur  is  found  in  commerce  in  rolls,  which  are  formed  by  pour- 
ing melted  sulphur  into  cylindrical  moulds,  and  also  in  the  form  of  a  fine  crystalline 
powder,  the  flowers  of  sulphur,  which  are  obtained  by  throwing  the  vapour  of  sul- 
phur into  a  close  apartment,  of  which  the  temperature  is  below  the  point  of  fusion 
of  that  substance,  and  in  which  the  sulphur  therefore  condenses  in  the  solid  form 
and  in  minute  crystals,  just  as  watery  vapour  does  in  the  atmosphere  below  32°,  in 
the  form  of  snow.  The  purity  of  the  flowers  is  more  to  be  depended  upon  than 
that  of  roll-sulphur.  Sulphur  is  insipid  and  generally  inodorous,  but  acquires  an 
odour  when  rubbed ;  it  is  very  friable,  a  roll  of  it  generally  emitting  a  crackling 
sound,  and  sometimes  breaking,  when  held  in  the  warm  hand.  Its  specific  gravity 
is  1.98.  It  fuses  at  234°,  forming  a  transparent  and  nearly  colourless  liquid,  which 
is  lighter  than  the  solid  sulphur.  As  the  temperature  is  elevated,  the  liquid  becomes 
more  yellow,  and  passes  abruptly  into  a  dark  brown  at  482°.  These  allatropic  con- 
ditions are  distinguished  by  Frarikenheim  as  Sa  and  S|3.  In  the  last  state  it  is  so 
thick  and  viscous  as  to  flow  with  difficulty.  This  change  in  its  degree  of  fluidity  is 
not  occasioned  by  an  increase  of  density,  for  fluid  sulphur  continues  to  expand  with 
the  temperature.  Thrown  into  water,  while  in  this  condition,  sulphur  forms  a  mass 
which  remains  soft  and  transparent  for  some  time  after  it  is  perfectly  cool,  and  may 
be  drawn  into  threads  which  have  considerable  elasticity.  From  500°  to  its  boiling 
point,  788°,  when  it  is  distinguished  as  Sy,  it  becomes  again  more  fluid,  and  if 
allowed  to  cool  returns  through  the  same  conditions,  becoming  again  very  fluid, 
before  freezing.  Sulphur  has  considerable  volatility,  beginning  to  rise  in  vapour 
before  it  is  completely  fused.  At  its  boiling  point  it  forms  a  transparent  vapour  of 
an  orange  colour,  and  distils  over  unchanged.  The  density  of  this  vapour,  taken  a 
little  above  its  boiling  point,  is  vtery  considerable,  being  observed  to  lie  between 
6510  and  6617  by  Dumas,  to  be  6900  by  Mitscherlich.  These  results  indicate  the 
unusual  combining  measure  of  l-3d  of  a  volume  for  this  vapour,  which  gives  the 
theoretical  density  6634.  But  sulphur-vapour  has  lately  been  shown  by  M.  Bineau 
to  be  one  of  those  bodies  of  which  the  density  changes  with  the  temperature  (page 
132),  and  to  fall  at  1000°  C.  under  ordinary  pressure  to  about  one-third  of  what  it 
is  about  450°  or  500°  C.  The  anomaly  of  its  density  is  thus  removed,  and  the 
combining  measure  of  sulphur-vapour  made  to  be  1  volume,  or  the  same  as  oxygen. 
Sulphur  and  many  other  substances  may  be  obtained  in  distinct  crystals,  on  pass- 
ing from  a  state  of  fusion,  by  operating  in  a  particular  manner.  A  considerable 
quantity  of  sulphur  is  fused  in  a  stoneware  crucible,  and  allowed  to  cool  till  it  begins 
to  solidify;  the  solid  crust  which  covers  its  surface  is  then  broken,  and  the  portion 

*  {See  Supplement,  p.  775.] 


PROPERTIES    OF    SULPHUR.  293 

remaining  fluid  poured  out.  On  afterwards  breaking  the  crucible,  when  it  has  be- 
come quite  cold,  the  sulphur  is  found  to  have  a  considerable  cavity,  which  is  lined 
with  fine  crystals,  like  a  geode  in  quartz.  Sulphur  is  dimorphous ;  the  form  which 
it  assumes  at  a  high  temperature,  and  consequently  in  its  passage  from  a  state  of 
fusion,  is  a  secondary  modification  of 
an  oblique  prism  with  a  rhomboidal 
base  (fig.  135),  belonging  to  the 
Fifth  System  of  crystallization 
(page  144).  Sulphur  is  soluble  in 
the  sulphide  of  carbon,  the  chloride 
of  sulphur  and  oil  of  turpentine,  and  is  deposited  from  solution  in  these  menstrua 

at  a  lower  temperature,  and  of  its  sec-:  t.d 

FIG.  136.  form,  which  is  an  elongated  octohedron 

with  a  rhomboidal  base  (fig.  136),  be- 
longing to  the  Third  System.  Such  is 
likewise  the  form  of  the  grains  of  flowers 
of  sulphur,  and  of  the  fine  transparent 
crystals  of  native  sulphur;  which  last 
appear  also  to  be  formed  by  sublimation. 
Sulphur  is  not  soluble  in  water  nor  in 
alcohol.  It  combines  readily  with  most 
metals ;  some  of  tnem,  such  as  copper  and  silver  in  very  thin  plates,  burning  in  its 
vapour,  as  iron  does  in  oxygen  gas.  When  iron  and  some  other  metals  are  mixed 
in  a  state  of  division  with  flowers  of  sulphur,  and  heat  applied,  the  sulphur  first 
melts,  and  after  a  few  seconds  combination  ensues  with  turgescence  of  the  mass, 
which  becomes  red-hot.  Sulphur  unites  with  bodies  generally  in  the  same  multiple 
proportions  as  oxygen,  and  sometimes  in  additional  proportions,  particularly  with 
potassium,  and  the  metals  of  the  alkalies  and  alkaline  earths.  When  boiled  with 
caustic  potassa  or  lime,  red  solutions  are  formed  which  contain  a  large  quantity  of 
sulphur,  a  considerable  proportion  of  which  is  deposited  as  a  white  hydrate  of  sul- 
phur, upon  the  addition  of  an  acid.  With  hydrogen,  sulphur  unites  in  single  equi- 
valents, and  forms .  hydrosulphuric  acid  gas,  which  is  the  analogue  of  water  in  the 
sulphur  series  of  compounds;  and  also  another  compound,  the  bisulphide  of  hydro- 
gen, which  is  deficient  in  stability,  like  the  binoxide  of  hydrogen,  and  is  decomposed 
or  preserved  by  similar  agencies. 

Sulphur  is  readily  inflamed,  taking  fire  below  its  boiling  point,  and  burning  with 
a  pale  blue  flarne  and  the  formation  of  suffocating  fumes,  which  are  sulphurous  acid 
gas.  It  exhausts  the  oxygen  of  a  confined  portion  of  air  by  its  combustion  more 
completely  than  carbonaceous  combustibles,  and  on  that  account,  and  partly  also 
from  a  negative  influence  which  sulphurous  acid  has  upon  the  combustion  of  other 
bodies,  it  may  be  employed  in  particular  circumstances  to  extinguish  combustion ;  a 
handful  of  lump  sulphur  being  dropped  into  a  burning  chimney  as  the  most  effectual 
means  of  extinguishing  it.  Sulphur  unites  directly  with  oxygen  only  in  the  propor- 
tion of  sulphurous  acid,  but  several  compounds  of  the  same  elements  may  be  formed, 
which  are  all  acids ;  namely — 

1.  Sulphurous  acid S   02 

'2.  Hyposulphurous  acid S2  02 

3.  Sulphuric  acid S    03 

4.  Hyposulphuric  acid S2  05 

5.  Monosul-hyposulphuric  acid  S3  O5 

6.  Bisul-hyposulphuric  acid  S4  05 

7.  Trisul-hyposulphuric  acid  S6  05 

Uses.  —  From  its  ready  inflammability  sulphur  has  long  been  applied  to  wood 
matches.  But  its  most  considerable  applications  are  in  the  composition  of  gun- 
powder and  other  deflagrating  mixtures,  and  in  the  manufacture  of  sulphuric  acid, 
which  there  will  again  be  occasion  to  notice  in  a  more  particular  manner. 


294 


SULPHUR. 


SULPHUROUS    ACID. 

Eg.  32  or  400 ;  S02 ;  density  of  gas  2247 ;  combining  measure  I     I     I 

Sulphurous  acid  was  distinguished  as  a  particular  substance  by  Stahl,  and  first 
recognised  as  a  gas  by  Dr.  Priestley.     It  was  subsequently  analyzed  with  accuracy^ 
by  Gay-Lussac  and  by  Berzelius. 

Preparation.  —  When  sulphur  is  burned  in  dry  air  or  oxygen  gas,  sulphurous 
acid  is  the  sole  product,  and  the  gas  is  found  to  have  undergone  no  change  in  vo- 
lume. But  sulphurous  acid  is  more  conveniently  prepared  in  laboratories  by  several 
other  processes. 

(1.)  An  intimate  mixture  of  6  parts  of 

FIG.  137.  binoxide  of  manganese  and  1  part  of  flowers 

of  sulphur  is  heated  in  a  small  retort  of  hard 
glass  (fig.  137 ;)  the  gas  is  carried  through  a 
wash-bottle  to  arrest  a  little  vapour  of  sul- 
phur which  is  carried  over.  Here  the  sul- 
phur is  burnt  at  the  expense  of  a  portion  of 
the  oxygen  of  the  binoxide  of  manganese. 
Sulphurous  acid,  which  is  the  product  of  the 
combustion,  escapes,  and  protoxide  of  man- 
ganese remains  in  the  retort.  (Regnault). 

S  and  2  Mn02=S02  and  2  MnO.        * 

(2.)  By  heating  oil  of  vitriol  upon  mercury  or  copper,  either  of  which  becomes 
an  oxide  at  the  expense  of  one  portion  of  the  sulphuric  acid,  and  thereby  causes  the 
formation  of  sulphurous  acid.  Sheet  copper  cut  into  small  pieces  is  put  into  a  flask 
to  which  undiluted  oil  of  vitriol  is  added,  and  a  moderate  heat  applied.  The  gas  is 
carried  through  a  bottle,  containing  a  little  water  to  condense  the  vapour  of  sulphuric 
acid,  of  which  a  little  is  carried  over,  and  afterwards  through  a  tube  containing  chlo- 
ride of  calcium,  if  it  is  desired  to  dry  the  gas. 

(3.)  Charcoal,  chips  of  wood,  straw,  and  such  bodies,  occasion  a  similar  decom- 
position of  sulphuric  acid,  when  heated  with  it,  but  the  gas  is  then  mixed  with  a 
large  quantity  of  carbonic  acid.  If  the  sulphurous  acid,  however,  is  to  be  used  to 
impregnate  water,  or  in  making  alkaline  sulphites,  the  presence  of  that  gas  is  imma- 
terial. With  that  object,  a  quantity  of  oil  of  vitriol,  equal  in  volume  to  4  ounce 
measures  of  water,  which  for  brevity  may  be  spoken  of  as  4  ounce  measures  of  oil 
of  vitriol,  is  introduced  into  a  flask  with  half  an  ounce  of  pounded  wood-charcoal, 
and  the  two  substances  well  mixed  with  agitation  (fig.  138).  Effervescence  takes 
place  upon  applying  heat  to  the  flask,  from  the  evolution 
of  gas,  which  may  be  conducted  in  the  first  instance  into 
an  intermediate  phial,  through  the  cork  of  which  a  stout 
tube  passes,  open  at  both  ends,  and  about  3-8ths  of  an 
inch  in  internal  diameter.  This  phial  contains  about  an 
ounce  of  water,  into  which  the  wider  tube  dips,  and  the 
tube  from  the  flask  descends  still  lower.  The  phial  serves 
the  purpose  of  a  wash-bottle  in  condensing  any  sulphuric 
acid  vapour  that  may  be  carried  over  by  the  gas,  or  of 
intercepting  the  liquid  material  in  the  flask,  if  thrown  out 
by  ebullition,  and  also  of  preventing  the  liquid  in  the* 
second  bottle  from  passing  back,  by  the  glass  tube,  into 
the  generating  flask,  on  the  occurrence  of  a  contraction 
of  the  air  in  that  flask,  by  cooling  or  any  other  cause. 
When  that  contraction  happens  in  this  arrangement,  the 
external  air  enters  the  intermediate  phial  by  its  open 
tube.  The  second  bottle  is  nearly  filled  with  water  to  be 
impregnated  by  the  gas. 


SULPHUROUS    ACID.  295 

Properties.  —  Water  at  60°  is  capable  of  dissolving  nearly  50  times  its  volume 
of  sulphurous  acid,  which  makes  it  necessary  to  collect  this  gas  for  examination  by 
displacement  of  air,  or  in  jars  filled  with  mercury  in  the  mercurial  trough.  Its 
density  is  2247,  and  it  contains  2  volumes  of  oxygen  with  1  volume  of  sulphur 
vapour  (density  2211),  condensed  into  2  volumes,  which  form  its  combining  mea- 
sure. It  may  easily  be  obtained  in  the  liquid  state  by  transmitting  the  dry  gas 
obtained  by  the  first  or  second  process  through  a  U-shaped  tube,  surrounded  by  a 
freezing  mixture  of  ice  and  salt,  or  better,  of  ice  and  chloride  of  calcium.  It  forms 
a  colourless  and  very  mobile  liquid,  of  sp.  gr.  1.45,  which  boils  at  14°.  The  vola- 
tility of  this  liquid  is  small  at  considerably  lower  temperatures,  and  it  is  not  appli- 
cable with  advantage  to  produce  intense  cold  by  its  evaporation  (Kemp).  Sulphurous 
acid  crystallizes  from  a  saturated  solution  in  water,  at  a  temperature  of  4  or  5  de- 
grees above  32°,  in  combination  with  72  per  cent,  of  water  or  9  equivalents, 
S02  +  9HO  (Pierre,  Ann.  de  Chim.  et  Phys.  3  ser.  23.416). 

Sulphurous  acid  is  not  decomposed  by  a  high  temperature;  but  several  substances, 
such  as  carbon,  hydrogen,  and  potassium,  which  have  a  strong  affinity  for  oxygen, 
decompose  it  at  a  red  heat.  This  acid  blanches  many  vegetable  and  animal  colours, 
—  thus  violets  plunged  for  a  short  time  into  a  solution  of  sulphurous  acid  become 
completely  white ;  and  the  vapours  of  burning  sulphur  are  "therefore  employed  to 
whiten  straw  and  to  bleach  silk,  to  which  they  also  impart  a  peculiar  gloss.  The 
colours  are  not  destroyed,  and  may  in  general  be  restored  by  the  application  of  a 
stronger  acid  or  an  alkali.  Dry  sulphurous  acid  exhibits  no  affinity  for  oxygen,  but 
in  contact  with  a  litUe  water  these  gases  slowly  combine,  and  sulphuric  acid  is  formed. 
From  the  same  affinity  for  oxygen,  sulphurous  acid  deprives  the  solution  of  perman- 
ganate of  potassa  of  its  red  colour,  and  throws  down  iodine  from  iodic  acid.  It 
decomposes  the  solutions  of  those  metals  which  have  a  weak  affinity  for  oxygen,  such 
as  gold,  silver,  mercury  (with  heat),  and  throws  down  these  bodies  in  the  metallic 
state.  Sulphurous  acid  is  conveniently  withdrawn  from  a  gaseous  mixture  by  means 
of  peroxide  of  lead,  which  is  converted  by  absorbing  this  gas  into  the  white  sulphate 
of  lead.  By  nitric  acid,  sulphurous  acid  is  immediately  converted  into  sulphuric 
acid. 

Sulphites.  —  The  alkaline  sulphites  have  a  considerable  resemblance  to  the  cor- 
responding sulphates.  Their  acid  is  precipitated  by  the  chloride  of  barium,  but  the 
sulphite  of  baryta  is  dissolved  by  hydrochloric  acid.  When  in  solution  the  sulphites 
gradually  absorb  oxygen  from  the  air,  and  pass  into  sulphates.  Sulphurous  acid  is 
a  weak  acid,  and  its  salts  are  decomposed  by  most  other  acids. 

Uses. — Besides  the  application  of  which  sulphurous  acid  is  susceptible  in  bleaching, 
it  is  likewise  employed  in  French  hospitals,  in  the  treatment  of  diseases  of  the  skin. 
The  gas  is  then  applied  in  the  form  of  a  bath.  (Dumas,  Traite  de  Chimie  appliquee 
aux  Arts,  i.  151). 

This  oxide  of  sulphur,  besides  acting  as  an  acid,  has  been  supposed  to  play  the 
part  of  a  radical,  like  carbonic  oxide,  and  to  pervade  a  class  of  compounds,  in  which 
hyposulphurous  acid  and  sulphuric  acid  are  included :  — 

SULPHUROUS  ACID    SERIES. 

Sulphurous  acid S02 

Sulphuric  acid S02  +  0 

Hyposulphurous  acid S02-f  S 

Chlorosulphurjc  acid S02-fCl 

Nitrosulphuric  acid S02  +  N02 

Azotosulphuric  acid 2S02  +  N05 

SULPHURIC  ACID. 

Eq.  40  or  500;  S03;  density  of  vapour  27G2;   j    |    | 

Chemists  have  been  in  possession  of  processes  for  preparing  this  acid  since  the 
id  of  the  fifteenth  century.     It  is  of  all  reagents  the  one  in  most  frequent  use, 


296  SULPHUR. 

being  the  key  to  the  preparation  of  most  other  acids;  which,  in  consequence  of  its 
superior  affinities,  it  separates  from  their  combinations ;  and  being  the  acid  preferred 
to  others,  from  its  cheapness,  for  various  useful  and  important  purposes  in  the  arts. 
Preparation. — Sulphuric  acid  was  first  obtained  by  the  distillation  of  green  vitriol 
or  copperas,  a  native  sulphate  of  iron,  and  this  process  is  still  followed  in  Bohemia, 
for  the  preparation  of  a  highly  concentrated  acid,  known  as  the  Nordhausen  acid, 
from  being  long  produced  at  Nordhausen  in  Saxony.  The  sulphate  of  iron  contains 
seven  equivalents  of  water,  and  is  first  dried,  by  which  its  water  is  reduced  consider- 
ably below  a  single  equivalent,  and  then  distilled  in  a  retort  of  stoneware  at  a  red 
heat.  When  the  experiment  is  performed  on  a  small  scale,  the  heat  of  an  argand 
spirit-lamp  is  sufficient;  and  in  the  place  of  copperas,  the  sulphate  of  iron  previously 
peroxidized,  the  sulphate  of  bismuth,  of  antimony,  or  of  mercury,  may  be  employed. 
The  first  effect  of  heat  upon  the  dried  sulphate  of  iron  is  to  cause  an  evolution  of 
sulphurous  acid  gas,  a  portion  of  sulphuric  acid  being  decomposed  in  converting  the 
protoxide  of  iron  of  that  salt  into  sesquioxide, 

2  (FeO.S03)  =  S02  and  S03  and  Fe203; 

but  the  salt  used  in  Bohemia,  it  appears,  is  a  native  sulphate,  in  which  the  greater 
part  of  the  iron  is  already  in  the  state  of  sesquioxide,  so  that  little  sulphurous  acid 
is  lost.  Vapours  afterwards  come  over,  which  condense  into  a  fuming  liquid,  gene- 
rally of  a  black  colour,  and  of  a  density  about  1.9,  which  is  the  Nordhausen  acid, 
and  contains  less  than  one  equivalent  of  water  to  two  of  sulphuric  acid.  This  acid 
is  preferred  for  dissolving  indigo,  and  for  some  other  purposes  in  the  arts,  and  is  the 
best  source  of  anhydrous  sulphuric  acid. 

But  sulphuric  acid  is  prepared,  in  vastly  greater  quantity,  by  the  oxidation  of 
sulphur.  When  burned  in  air  or  oxygen,  sulphur  does  not  attain  a  higher  degree 
of  oxidation  than  sulphurous  acid,  but  an  additional  proportion  of  oxygen  may  be 
communicated  to  it  by  two  methods,  and  sulphuric  acid  formed. 

1.  When  a  mixture  of  sulphurous  acid  and  air,  which  must  be  previously  dried, 
is  made  to  pass  over  spongy  platinum,  or  a  ball  of  clean  platinum  wire,  at  a  high 
temperature,  the  sulphurous  acid  is  converted  into  sulphuric  acid  at  the  expense  of 
the  oxygen  of  the  air.     After  a  time,  however,  the  platinum  loses  this  property,  and 
the  process,  although  interesting  in  a  scientific  point  of  view,  does  not  answer,  on 
account  of  that  change,  as  a  manufacturing  method. 

2.  Sulphurous  acid  mixed  with  air  may  be  converted  into  sulphuric  acid,  by  the 
agency  of  nitric  oxide,  which  is  the  process  generally  pursued  in  the  manufacture 
of  this  acid.     The  theory  of  this  latter  method,  which  is  by  no  means  obvious,  has 
been  illustrated  by  the  researches  of  Clement-Desormes,  Davy,  De  la  Provostaye, 
and  others.     It  is  generally  considered  as  depending  upon  the  following  reactions : — 

1.  When  binoxide  of  nitrogen  N02  mixes  with  air  in  excess,  it  is  instantly  con- 
verted into  peroxide  of  nitrogen  N04. 

2.  Peroxide  of  nitrogen  is  converted  by  co-ntact  with  a  small  quantity  of  water 
into  the  nitrate  of  water  and  nitrous  acid. 

2N04  and  HO  =  HO.N05  and  N03. 

3.  Nitrous  acid  in  contact  with  a  large  quantity  of  water  is  converted  into  nitrate 
of  water  and  binoxide  of  nitrogen. 

3N03  and  water  in  excess =HO.N05  +  Water  and  2N02. 

Consequently,  uniting  the  last  two  operations,  peroxide  of  nitrogen  is  converted  by 
a  large  quantity  of  water  into  nitric  acid  and  binoxide  of  nitrogen. 

4.  Sulphurous  acid  takes  oxygen  from  hydrated  nitric  acid,  and  becomes  sulphuric 
acid,  disengaging  peroxide  of  nitrogen. 

As  the  peroxide  of  nitrogen  gives  nitric  acid  and  binoxide  of  nitrogen  (3),  and 
the  last  gas  is  converted  by  air  into  peroxide  of  nitrogen  (1),  the  production  of  nitric 
acid  may  be  repeated  without  end,  and  more  and  more  sulphurous  acid  is  converted 


SULPHUKIC    ACID.  297 

by  the  latter  into  sulphuric  acid.  It  thus  appears  that  with  a  sufficient  supply  of 
air  or  oxygen,  a  small  quantity  of  nitric  acid  (or  of  binoxide  of  nitrogen)  may  con- 
vert a  large  quantity  of  sulphurous  acid  into  sulphuric  acid.  The  binoxide  of  nitrogen, 
only  acting  as  a  purveyor  of  oxygen,  is  re-obtained  entire,  without  loss,  at  the  end 
of  the  process.  The  sulphurous  has  derived  the  oxygen  necessary  to  convert  it  into 
sulphuric  acid,  really  from  the  air,  but  in  an  indirect  manner. 

In  the  manufacture  upon  the  large  scale,  the  sulphurous  acid  is  converted  into 
sulphuric  acid,  in  oblong  chambers  of  sheet-lead,  supported  by  an  external  framework 
of  wood.  Sulphurous  acid  from  burning  sulphur,  nitric  acid  vapour,  and  steam,  are 
simultaneously  admitted  into  the  leaden  chamber ;  and  the  sulphuric  acid  formed 
accumulates  in  the  liquid  state  upon  the  floor  of  the  chamber.  The  diagram  below 
represents  one  of  the  forms  of  the  chamber,  with  its  appendages. 

FIG.  139. 


a  represents  the  water  boiler  with  its  furnace,  for  supplying  the  chamber  with 
steam  ;  b,  the  section  of  a  small  chamber  in  brickwork,  or  furnace,  called  the  burner, 
upon  the  floor  of  which  the  sulphur  burns,  and  in  which  there  is  a  tripod  supporting 
an  iron  capsule,  which  contains  the  materials  for  nitric  acid,  namely,  oil  of  vitriol, 
and  either  nitre  or  nitrate  of  soda.  The  heat  of  the  burning  sulphur  evolves  the 
nitric  acid  from  these  materials,  and  consequently  the  sulphurous  acid  becomes 
mixed  with  nitric  acid  vapour,  which  it  carries  forward  with  it,  by  a  tube  represented 
in  the  figure,  into  the  chamber,  where  these  acid  vapours  meet  with  the  steam 
admitted  near  the  same  point,  and  the  formation  of  sulphuric  acid  takes  place.  The 
nitric  acid  vapour  is  equivalent  to  binoxide  or  to  peroxide  of  nitrogen,  as  the  first 
effect  of  the  sulphurous  acid  is  to  reduce  the  nitric  acid  to  a  lower  state  of  oxidation. 
From  8  to  19  parts  of  sulphur  are  consumed  in  the  burner  for  1  part  of  nitrate  of 
soda  decomposed  there,  so  that  the  quantity  of  nitrous  fumes  is  small  compared  with 
the  quantity  of  sulphurous  acid  thrown  into  the  chamber.  The  chamber  represented 
is  72  feet  in  length  by  14  in  breadth,  and  10  in  height,  and  is  divided  into  three 
compartments,  by  leaden  curtains  placed  across  it,  two  of  which,  d  and  /,  are  sus- 
pended from  the  roof,  and  reach  to  within  six  inches  of  the  floor,  and  one,  e,  rises 
from  the  floor  to  within  six  inches  of  the  roof :  g  is  a  leaden  conduit  tube,  for  the 
discharge  of  the  uncondensible  gases,  which  should  communicate  with  a  tall  chimney, 
to  carry  off  these  gases  and  to  occasion  a  slight  draught  through  the  chamber.  The 
curtains  serve  to  detain  the  vapours,  and  cause  them  to  advance  in  a  gradual  manner 
through  the  chamber,  so  that  the  sulphuric  acid  is  deposited  as  completely  as  pos- 
sible, before  the  vapours  reach  the  discharge  tube.  When  the  oxygen  of  the  chamber 
is  exhausted,  the  admission  of  acid  vapours  is  discontinued,  till  the  air  in  it  is 
renewed.  But  the  admission  of  air  to  the  chamber  is  generally  so  regulated,  that  a 
continuous  current  is  maintained  through  the  chamber,  and  the  combustion  proceeds 
without  interruption.  When  steam  is  admitted  in  proper  quantity,  as  in  this  method, 
it  is  not  necessary  to  begin  by  covering  the  floor  with  water. 

The  acid  may  be  drawn  off  from  the  floor  of  the  chamber  of  a  sp.  gr.  as  high  as 
1.6.  It  is  further  concentrated  in  open  leaden  pans,  till  it  begins  to  act  upon  the 
metal,  and  afterwards  in  retorts  of  platinum  or  glass.  It  still  retains  small  quantities 
of  nitrous  acid  and  sulphate  of  lead,  from  which  it  can  be  completely  purified  by 
dilution  with  water  and  a  second  distillation.  The  acid  thus  obtained,  in  its  most 
concentrated  state,  is  a  definite  compound  of  one  eq.  acid  and  one  eq.  of  water, 
HO.S03,  which  last  cannot  be  separated  by  heat,  the  hydrate  distillirfg  over  un- 
changed. It  is  the  Oil  of  Vitriol  of  commerce. 


298 


SULPHUR. 


Fia.  140. 


The  construction  of  the  leaden  chamber  is  greatly  varied ;  one  chamber  of  great 
dimensions  is  often  used  without  any  division  by  curtains;  or  the  vapour  is  carried 
successively  through  a  series  of  three,  four,  or  five  connected  chambers.  The  sul- 
phurous acid,  also,  is  often  derived  from  the  combustion  of  bisulphide  of  iron  (iron 
pyrites),  instead  of  sulphur;  a  peculiar  kiln  or  flue  being  employed  for  burning  the 
former.  At  the  suggestion  of  Gray-Lussac,  the  nitrous  vapour,  as  it  ultimately 
leaves  the  chamber  with  the  air  exhausted  of  oxygen,  is  absorbed  by  being  made  to 
pass  through  a  column  of  coke,  over  which  a  stream  of  the  concentrated  sulphuric 
acid  is  flowing.  The  sulphuric  acid,  after  being  charged  with  nitrous  vapours  or 
nitric  acid,  is  transported  back  to  the  anterior  part  of  the  chamber,  and  there  ex- 
posed to  the  sulphurous  acid,  as  the  latter  leaves  the  sulphur  burner.  This  exposure 
denitrates  the  sulphuric  acid,  much  sulphurous  acid  becoming  sulphuric  acid,  and 
peroxide  of  nitrogen  being  liberated  in  the  state  of  vapour.  (See  Kiiapp's  Chemical 
Technology,  edited  by  Drs.  Ronalds  and  Richardson,  i.  234,  Am.  ed.). 

When  the  supply  of  aqueous  vapour  in  the  chamber  is  insufficient,  a  white  crys- 
talline compound  appears,  known  as  the  crystalline  substance  of  the  leaden  chambers : 
it  is  deposited  most  frequently  in  the  tube  by  which  two  chambers  communicate.  It 
contains  the  elements  of  2  eq.  sulphuric  acid,  and  1  eq.  nitric  acid,  2S02-f  N05; 
but  several  other  views  of  the  arrangement  of  its  elements  may  be  entertained  with 
equal  probability.  This  substance,  which  is  also  termed  azoto-sulphuric  acid  (S2N09), 
is  decomposed  by  water,  and  gives  sulphuric  acid,  nitric  acid,  and  binoxide  of 
nitrogen : 

3(S2N09)  and  7HO=6(HO.S03)  and  HO.N05,  and  2N02. 

The  formation  of  the  crys- 
talline substance,  and  the  ge- 
neral operation  of  the  leaden 
chamber,  may  be  illustrated 
by  the  arrangement  in  fig.  140. 
Binoxide  of  nitrogen  evolved 
by  the  action  of  dilute  nitric 
acid  on  copper  in  the  gas-bot- 
tle C,  and  sulphurous  acid 
evolved  by  the  action  of  cop- 
per clippings  on  concentrated 
sulphuric  acid  in  the  flask  B, 
are  conveyed  into  a  large  glass 
globe,  A,  containing  air. 
Ruddy  fumes  of  peroxide  of 
nitrogen  first  appear,  but  soon 
the  inner  surface  of  the  globe 
is  frosted  over  with  the  crys- 
talline compound.  If  steam  or  water  be  now  introduced,  by  one  of  the  free  tubes, 
the  crystals  disappear  with  effervescence,  from  escape  of  gas,  sulphuric  acid  is  pro- 
duced, and  the  changes  are  repeated  till  the  air  in  A  is  exhausted. 

Properties.  —  Anhydrous  sulphuric  acid  is  obtained  by  gently  heating  the  fuming 
acid  of  Nordhausen  in  a  retort,  and  receiving  its  vapour  in  a  bottle  artificially  cooled, 
which  can  afterwards  be  closed  by  a  glass  stopper.  It  condenses  in  solid  fibres,  like 
asbestos,  which  are  tenacious,  and  may  be  moulded  by  the  fingers  like  wax.  The 
density  of  the  solid  at  68°  is  1.97  :  at  77°  it  is  liquid;  and  a  little  above  that  tem- 
perature it  enters  into  ebullition,  affording  a  colourless  vapour,  which  produces  dense 
white  fumes  on  mixing  with  air,  by  condensing  moisture.  The  dry  acid  does  not 
redden  litmus,  an  effect  which  requires  the  presence  of  moisture.  It  combines  with 
sulphur,  and  produces  liquid  compounds,  which  are  of  a  brown,  green,  and  blue 
colour,  and,  with  one-tenth  of  its  weight  of  iodine,  forms  a  compound  of  a  fine  green 
colour,  which  assumes  the  crystalline  form.  Heated  in  the  acid  vapour,  caustic  lime 


SULPHURIC     ACID.  299 

or  baryta  inflames  and  burns  for  a  few  seconds ;  the  vapour  is  absorbed,  and  sulphate 
of  lime  or  baryta  formed.  The  anhydrous  acid  has  a  great  affinity  for  water,  and 
when  dropped  into  that  liquid,  occasions  a  burst  of  vapour  from  the  heat  evolved. 
The  density  of  its  vapour  was  found  to  be  3000  by  Mitscherlich,  but  it  is  probably 
2762,  and  formed  of  3  volumes  of  oxygen  and  1  volume  of  sulphur  vapour  con- 
densed into  2  volumes,  which  constitute  its  combining  measure.  This  vapour  is 
resolved  by  a  strong  red  heat  into  sulphurous  acid  and  oxygen.* 

When  the  Nordhausen  acid  is  retained  below  32°,  well-formed  crystals  appear  in 
it,  which  Mitscherlich  finds  to  be  a  compound  of  two  equivalents  of  acid  and  one 
of  water,  or  2S03  +  HO.  (Eleiuens  de  Chimie,  par  E.  Mitscherlich,  t.  ii.  p.  57). 
This  compound  is  resolved  by  heat  into  the  anhydrous  acid,  which  sublimes,  and 
the  first  hydrate,  or  oil  of  vitriol. 

The  most  concentrated  oil  of  vitriol  of  the  leaden  chambers  (HO-f  S03)  is  a 
dense,  colourless  fluid  of  an  oily  consistence,  which  boils  at  620°,  and  freezes  at 
— 29°,  yielding  often  regular  six-sided  prisms  of  a  tabular  form.  It  has  a  specific 
gravity  at  60°  of  1.845.  It  is  a  most  powerful  acid,  supplanting  all  others  from 
their  combinations,  with  a  few  exceptions,  and  when  undiluted  is  highly  corrosive. 
It  chars  and  destroys  most  organic  substances.  It  has  a  strong  sour  taste,  and  red- 
dens litmus  even  though  greatly  diluted.  Sulphur  is  soluble  to  a  small  extent  in 
the  concentrated  acid,  and  communicates  a  blue,  green,  or  brown  tint  to  it ;  so  are 
selenium  and  tellurium.  Charcoal  also  appears  to  be  slightly  soluble  in  this  acid, 
imparting  to  it  a  pink  tint,  which  afterwards  becomes  reddish-brown.  The  concen- 
trated acid  has  a  great  affinity  for  water,  which  it  absorbs  from  the  atmosphere,  and 
is  usefully  employed  to  dry  substances  placed  near  it  in  vacuo.  Considerable  heat 
is  evolved  in  its  combination  with  water  :  when  4  parts  by  weight  of  the  concentrated 
acid  are  suddenly  mixed  with  1  part  of  water,  the  temperature  rises  to  300°.  When 
diluted  with  about  thirty  times  its  weight  of  water,  sulphate  of  water  HO.S03, 
evolves  heat,  which  may  be  represented  by  23  degrees;  while  HO.S03+HO, 
similarly  diluted,  evolves  14  degrees,  or  9  degrees  less,  and  HO.S03+5HO,  5 
degrees  only,  or  18  degrees  less.  Hence  the  first  equivalent  of  water  which  com- 
bines with  oil  of  vitriol  appears  to  evolve  as  much  heat  as  the  following  four  equiva- 
lents (Mem.  Chem.  Soc.,  i.  107).  In  a  series  of  valuable  experiments  by  M.  Abria, 
but  which  do  not  admit  of  being  compared  with  the  preceding,  he  obtained  the 
following  results  (Annales  de  Ch.  et  Ph.,  3  se*r.,  xii.  171) : — 

Quantities  of  heat  disengaged  by  the  combination  of  sulphate  of  water, — 

With  1  eq.  water 64.25  degrees. 

2  "        94.69        « 

3  "        113.06        « 

4  «        124.43        « 

5  «        131.66        " 

Excess 165.63         " 

The  anhydrous  acid  S03  disengaged  237.13  degrees  in  combining  with  an  excess 
of  water.  The  value  of  these  last  degrees,  or  the  unit  of  heat,  is  the  quantity  of 
heat  required  to  heat  up  1  gramme  (15.434  grs.)  of  water  1°  Centigrade.  Abria 
concludes  that  in  the  combination  of  anhydrous  sulphuric  acid  with  water,  the  quan- 
tities of  heat  successively  disengaged  by  the  different  equivalents  of  water  have  a 
multiple  relation,  and  correspond  very  closely,  for  the  first  equivalents,  with  the 
numbers — 

1>         $)        6)        T27        A>         2T- 

The  density  of  sulphuric  acid  becomes  always  less  by  dilution,  but  not  exactly  in 
the  ratio  of  the  water  added.  (Table  of  Densities  of  Sulphuric  Acid,  in  Appendix). 

Acid  of  density  1.78  is  the  second  definite  hydrate,  containing  two  eq.  of  water 
to  one  of  acid.  This  hydrate  forms  large  and  regular  crystals,  even  a  little  above 
the  freezing  point  of  water,  and  was  observed  by  Mr.  Keir  to  remain  solid  till  the 

*  [See  Supplemett,  p.  781.] 


300  SULPHUR. 

temperature  rose  to  45°.  If  the  dilute  acid  is  evaporated  at  a  heat  not  exceeding 
400°,  its  water  is  reduced  to  the  proportion  of  this  hydrate.  This  second  eq.  of 
water  is  expelled  by  a  higher  temperature,  but  the  first  eq.  can  only  be  separated 
from  the  acid  by  a  stronger  base.  Sulphuric  acid  forms  still  a  third  hydrate,  of  sp 
gr.  1.632,  containing  three  eq.  of  water,  the  proportion  to  which  the  water  of  a 
more  dilute  acid  is  reduced,  by  evaporation  in  vacuo  at  2J2°.  It  is  also  in  the  pro- 
portions of  this  hydrate  that  the  acid  and  water  undergo  the  greatest  condensation, 
or  reduction  of  volume,  in  combining.  The  following,  then,  are  the  formulae  of  the 
definite  hydrates  of  this  acid,  including  that  derived  by  Mitscherlich  from  the 
Nordhausen  acid  :  — 

HYDRATES   OF    SULPHURIC   ACID. 

Hydrate  in  the  Nordhausen  acid  .........................  H0.2S03 

Oil  of  vitriol,  (sp.  gr.  1.845)  .............................  HO.S03 

Acid  of  sp.  gr.  1.78  ........................................  HO.S03  +  HO 

Acid  of  sp.  gr.  1.632  ..........................  «.  ............  HO.S03+2HO 

The  composition  of  a  hydrate  of  sulphuric  acid  is  ascertained  by  adding  a  known 
weight  of  oxide  of  lead  to  the  liquid,  in  a  capsule,  and  evaporating  to  dryness.  As 
the  sulphuric  acid  abandons  all  its  water  on  combining  with  oxide  of  lead,  and  the 
sulphate  of  lead  may  be  heated  without  decomposition,  the  increase  of  weight  which 
the  oxide  on  the  capsule  undergoes  is  precisely  the  quantity  of  dry  sulphuric  acid  in 
the  hydrate  examined. 

Sulphuric  acid  acts  in  two  different  modes  upon  metals,  dissolving  some,  such  as 
copper  and  mercury,  with  the  evolution  of  sulphurous  acid,  and  others,  such  as  zinc 
and  iron,  with  the  evolution  of  hydrogen  gas.  The  metal  is  oxidated  at  the  expense 
of  the  acid  itself  in  the  one  case,  and  of  the  water  in  combination  with  the  acid  in 
the  other.  The  acid  acts  with  most  advantage  in  the  first  mode  when  concentrated, 
and  in  the  second  when  considerably  diluted. 

The  presence  of  sulphuric  acid  in  a  liquid,  may  always  be  discovered  by  means 
of  chloride  of  barium,  which  produces  with  this  acid  a  white  precipitate  of  sulphate 
of  baryta,  insoluble  in  both  acids  and  alkalies. 

Sulphates.  —  Of  no  class  of  salts  do  chemists  possess  a  more  minute  knowledge 
than  of  the  sulphates.  The  sulphates  of  zinc,  magnesia,  and  other  members  of  the 
magnesian  family,  correspond  closely  with  the  hydrate  of  sulphuric  acid.  Thus  of 
the  seven  eq.  of  water  which  the  crystallized  sulphate  of  magnesia  possesses,  it  retains 
one  at  400°,  and  is  then  analogous  to  the  sulphate  of  water  of  sp.  gr.  1.78;  the 
formula  of  these  two  salts  being, 

MgO.S03+HO, 
HO.S0 


and  the  eq.  of  water  in  both  salts  may  be  replaced  by  sulphate  of  potassa,  when  the 
sulphate  of  water  forms  the  salt  called  the  bisulphate  of  potassa,  and  the  sulphate  of 
magnesia  forms  the  double  sulphate  of  magnesia  and  potassa,  of  which  the  formula) 
also  correspond  :  — 


MgO.S03  +  KO.S03. 

In  all  these  sulphates  there  is  one  eq.  of  acid  to  one  of  base  ;  but  with  potassa,  sul- 
phuric acid  is  supposed  to  form  a  second  salt,  in  which  two  of  acid  are  combined 
with  one  of  base  KO-f-2S03,  and  which  is  said  to  have  lately  been  obtained  in  a 
crystallized  state  by  M.  Jacquelin  (Annal.  de  China,  et  de  Phys.,  Ixx.  311).  This 
would  be  a  true  bisulphate,  and  would  correspond  to  the  red  chromate  or  bichromate 
of  potassa  KO  +  2Cr03;  but  my  own  observations  have  obliged  me  to  call  in  question 
the  existence  of  this  anhydrous  bisulphate  (Mem.  Chem.  Soc.,  i.  120). 

Uses.  —  Sulphuric  acid  is  employed  to  a  large  extent  in  eliminating  nitric  acid 


NITROSULPHURIC    ACID.  301 

from  nitrate  of  potassa,  and  in  the  preparation  of  hydrochloric  acid  and  chlorine  from 
chloride  of  sodium,  and  also  in  the  processes  of  bleaching.  But  the  great  consump- 
tion of  this  acid  is  in  the  formation  of  sulphates,  particularly  of  sulphate  of  soda, 
nearly  all  the  carbonate  of  soda  of  commerce  being  at  present  procured  by  the  de- 
composition of  that  salt. 

CHLOROSULPHURIC   ACID. 

Eq.  67.5  or  843.75;  S02C1;  density  4652  Qj 

Sulphurous  acid  gas  combines  with  an  equal  volume  of  chlorine  under  the  influence 
of  light,  and  condenses  into  oily  drops,  which  are  denser  than  water  (Regnault, 
Annales  de  Chim.  et  o*e  Phys.  Ixix.  170,  and  Ixxi.  445).  Chlorosulphuric  acid  in 
dissolving  decomposes  1  eq.  of  water,  and  is  converted  into  hydrochloric  acid  and 
sulphuric  acid,  —  a  reaction  which  demonstrates  the  original  compound  to  consist  of 
1  eq.  of  sulphurous  acid  with  1  eq.  of  chlorine. 

The  density  of  the  vapour  of  chlorosulphuric  acid  was  found  by  experiment  to  be 
4703,  which  agrees  with  the  theoretical  density,  4652.  It  consists  of  2  volumes 
of  sulphurous  acid  and  2  .volumes  of  chlorine  condensed  into  2  volumes,  which  form 
the  combining  measure  of  the  vapour.  In  its  condensation,  it  resembles  the  vapour 
of  anhydrous  sulphuric  acid.  This  body  also  corresponds  exactly  in  composition 
with  the  compound  hitherto  called  chlorochromic  acid ;  Cr02Cl,  chromium  being 
substituted  in  the  latter  for  the  sulphur  of  the  former. 

With  dry  ammoniacal  gas,  chlorosulphuric  acid  forms  a  white  powder,  which  is  a 
mixture  of  the  hydrochlorate  of  ammonia  (sal  ammoniac)  and  sulphamide,  S02-f-NH2. 
It  does  not  combine,  as  an  acid,  with  bases. 

Chlorosulphuric  acid  may  also  be  represented  as  a  compound  of  sulphuric  acid 
with  a  terchloride  of  sulphur,  3S03-f-S013.  Another  compound  of  the  same  series 
has  been  formed  by  H.  Rose,  which  is  represented  by  5S03+SC13. 

NITRO SULPHURIC   ACID. 

Eq.  62  or  775;  SN04  or  S02.N02;  not  isolable. 

Sir  H.  Davy  made  the  observation  that  binoxide  of  nitrogen  is  absorbed  by  a 
mixture  of  sulphite  of  soda  and  caustic  soda,  and  that  a  compound  is  produced,  of 
which  the  principal  characteristic  is  to  disengage  abundance  of  protoxide  of  nitrogen, 
upon  the  addition  of  an  acid  to  it.  He  concluded  that  the  nitrous  oxide,  which  then 
escapes,  was  previously  united  with  soda,  and  gave  this  as  an  instance  of  the  combi- 
nation of  that  neutral  oxide  with  an  alkali.  As  the  sulphite  of  soda  became  at  the 
same  time  sulphate,  the  conversion  of  the  nitric  oxide  into  nitrous  oxide  appeared  to 
be  explained.  It  was  afterwards  shown  by  Pelouze  that  a  new  acid  is  formed  in  the 
circumstances  of  the  experiment,  to  which  he  has  given  the  name  nitrosulphuric, 
and  which  may  be  considered  as  a  compound  of  sulphurous  acid  and  nitric  oxide,  or 
another  member  of  the  sulphurous  acid  series.  (Pelouze,  in  Taylor's  Scien.  Mem., 
vol.  i.  p.  470 ;  or  Annal.  de  Chiin.  et  de  Phys.  Ix.  151). 

Preparation. — If  a  mixture  be  made  over  mercury  of  2  volumes  of  sulphurous 
acid,  and  4  volumes  of  binoxide  of  nitrogen,  which  are  combining  measures  of  these 
gases,  no  change  occurs;  but  on  throwing  up  a  strong  solution  of  caustic  potassa  into 
the  gases,  they  disappear  entirely  after  some  hours,  combining  with  a  single  equiva- 
lent of  potassa,  and  forming  together  the  nitrosulphate  of  potassa.  But  it  is  better 
to  prepare  the  nitrosulphate  of  ammonia.  A  concentrated  solution  is  made  of 
sulphite  of  ammonia,  which  is  mixed  with  five  or  six  times  its  volume  of  solution  of 
ammonia,  and  into  this  binoxide  of  nitrogen  is  passed  for  several  hours  at  a  low 
temperature.  A  number  of  beautiful  crystals  are  gradually  deposited ;  they  are  to 
be  washed  with  a  solution  of  ammonia,  previously  cooled,  which,  besides  the  advan- 
tage of  retarding  their  decomposition,  offers  that  of  dissolving  less  of  them  than 
pure  water.  When  the  crystals  are  desiccated,  they  should  be  introduced  into  a 


302  SULPHUR. 

well-closed  bottle ;  in  this  state  they  undergo  no  alteration.  The  same  process  is 
applicable  to  the  corresponding  salts  of  potassa  and  soda.  When  a  strong  acid  is 
added  to  a  solution  of  these  salts,  for  the  purpose  of  liberating  the  nitrosulphuric 
acid,  the  latter,  on  being  set  free,  decomposes  spontaneously  into  sulphuric  acid  and 
protoxide  of  nitrogen,  which  comes  off  with  effervescence. 

Properties.  —  The  acid  of  the  nitrosulphates  is  not  precipitated  by  baryta.  The 
nitrosulphate  of  potassa,  when  heated,  becomes  sulphite,  and  evolves  nitric  oxide ; 
but  the  salts  of  soda  and  ammonia  become  sulphates,  and  evolve  nitrous  oxide.  No 
nitrosulphates  of  the  metallic  oxides,  which  are  insoluble  in  water,  have  been  formed, 
or  appear  capable  of  existing ;  for  when  such  salts  as  chloride  of  mercury,  sulphate 
of  zinc  or  of  copper,  sulphate  of  sesquioxide  of  iron  and  nitrate  of  silver,  are  added 
to  the  nitrosulphate  of  ammonia,  they  produce  a  brisk  effervescence  of  nitrous  oxide, 
with  the  formation  of  sulphate  of  ammonia,  or  they  decompose  the  nitrosulphate  of 
ammonia  as  free  acids  do.  Indeed,  the  only  nitrosulphates  which  have  been  formed 
are  those  of  potassa,  soda,  and  ammonia.  These  are  neutral,  and  have  a  sharp  and 
slightly  bitter  taste,  with  nothing  of  that  of  the  sulphites. 

These  salts  rival  the  binoxide  of  hydrogen  in  facility  of  decomposition.  The 
nitrosulphate  of  ammonia  resists  230°,  but  is  decomposed  with  explosion  a  few 
degrees  above  that  temperature,  caused  by  the  rapid  disengagement  of  nitrous  oxide. 
Solutions  of  the  nitrosulphates  are  not  stable  above  the  freezing  point,  but  their 
stability  is  much  increased  by  an  excess  of  alkali.  They  are  resolved  into  sulphate 
and  nitrous  oxide,  by  the  mere  contact  of  certain  substances  which  do  not  themselves 
undergo  any  change ;  such  as  spongy  platinum,  silver  and  its  oxide,  charcoal  powder 
and  binoxide  of  manganese,  by  acids,  even  carbonic  acids,  and  by  metallic  salts. 

Jlzoto-siilpJiuric  acid  of  De  la  Provostaye,  S2N09. — Liquid  sulphurous  acid  and 
peroxide  of  nitrogen,  sealed  up  together  in  a  glass  tube,  react  upon  each  other,  and 
give  rise  to  a  solid  compound  crystallizing  in  rectangular  square  prisms,  which  has 
been  examined  by  M.  de  la  Provostaye.  A  small  portion  of  a  blue  liquid,  possessing 
an  explosive  property,  which  has  not  been  fully  examined,  is  formed  at  the  same 
time.  This  substance  forms  the  "crystals  of  the  leaden  chamber."  It  may  also 
be  produced,  according  to  Gay-Lussac,  by  bringing  peroxide  of  nitrogen  and  oil  of 
vitriol  in  contact : — 

2N04  and  2(HO.S03)  =  HO.N06-fHO  and  S2N09. 

This  substance  fuses  at  about  430°,  and  forms  a  silky  mass  on  cooling;  it  may 
be  distilled  without  decomposition  at  about  620°.  It  is  decomposed  by  water,  sul- 
phuric acid  being  formed,  and  nitrous  vapours  disengaged.  It  has  been  represented 
as  composed  of  2S02  +  N05;  or  as  2S03 -f- N03 ;  orS205  +  N04;  but  nothing  cer- 
tain is  known  of  its  molecular  arrangement. 

Dry  binoxide  of  nitrogen  is  absorbed  by  anhydrous  sulphuric  acid,  according  to 
an  observation  of  H.  Rose. 

HYPOSULPHURIC   ACID. 

Eq.  72  or  900;  S205;  not  isolable. 

Preparation.  —  This  acid  of  sulphur  was  discovered  by  Gay-Lussac  and  Welter, 
in  1819.  To  prepare  it,  a  quantity  of  binoxide  of  manganese,  which  must  not  be 
hydrated,  is  reduced  to  an  extremely  fine  powder,  suspended  by  agitation  in  water, 
and  sulphurous  acid  gas  is  transmitted  through  the  water.  When  ordinary  binoxide 
of  manganese  is  used,  it  should  be  previously  treated  with  nitric  acid,  to  dissolve 
out  the  hydrated  oxide,  and  washed.  The  temperature  is  apt  to  rise  during  the 
absorption  of  the  gas,  but  must  be  repressed,  otherwise  much  sulphuric  acid  is  pro- 
duced,—  the  formation  of  which,  indeed,  it  is  impossible  to  prevent  entirely,  but  of 
which  the  quantity  is  said  to  be  reduced  almost  to  nothing,  when  the  liquid  is  kept 
cold  during  the  operation.  The  binoxide  of  manganese  disappears,  arid  a  solution 
rtf  hyposulphate  of  the  protoxide  of  manganese  is  formed ;  2  equivalents  of  sulphur- 


HYPOSULPHUROUS   ACID.  303 

ous  acid,  and  1  of  binoxide  of  manganese,  forming  one  of  hydrosulphuric  acid  ami 
one  of  protoxide  of  manganese,  or 

2S02  and  Mn02=MnO  -f-S205. 

The  solution  is  filtered,  and  then  mixed  with  a  solution  of  sulphide  of  barium, 
which  occasions  the  precipitation  of  the  insoluble  sulphide  of  manganese,  with  the 
transference  of  the  hyposulphuric  acid  to  baryta.  From  this  hyposulphate  of  baryta, 
the  hyposulphates  of  other  metallic  oxides  may  be  prepared  by  adding  their  sulphates 
to  that  salt,  when  the  insoluble  sulphate  of  baryta  will  precipitate,  and  the  hyposul- 
phate of  the  metallic  oxide  added  remain  in  solution.  But  to  procure  the  hyposul- 
phuric acid  itself,  the  solution  of  hyposulphate  of  baryta  may  be  evaporated  to  dry- 
ness,  and,  being  perfectly  pure,  it  is  reduced  to  a  fine  powder,  weighed,  and  dissolved 
in  water :  for  100  parts  of  it  18.78  parts  of  oil  of  vitriol  are  taken,  which,  after 
dilution  with  three  or  four  times  as  much  water,  are  employed  to  decompose  this  salt 
of  baryta.  The  liberated  hyposulphuric  acid  solution  is  filtered,  and  evaporated  in 
vacua  over  sulphuric  acid,  till  it  attains  a  density  of  1.347,  which  must  not  be 
exceeded,  as  the  acid  solution  begins  then  to  decompose  spontaneously  into  sulphur- 
ous acid,  which  escapes,  and  sulphuric  acid,  which  remains  in  the  liquid. 

Properties.  —  This  acid  has  not  been  obtained  in  the  anhydrous  condition.  Its 
aqueous  solution  has  no  great  stability,  being  decomposed  at  its  temperature  of  ebul- 
lition. The  same  solution  exposed  to  air  in  the.  cold,  slowly  absorbs  oxygen, 
according  to  Heeren,  and  becomes  sulphuric  acid.  But  neither  nitric  acid,  nor 
chlorine,  nor  binoxide  of  manganese,  oxidize  this  acid  unless  they  are  boiled  in  its 
solution.  Its  salts  are  perfectly  stable,  either  when  in  solution  or  when  dry,  and 
are  generally  very  soluble,  having  some  analogy  to  the  nitrates.  A  hyposulphite, 
when  heated  to  redness,  leaves  a  neutral  sulphate,  and  allows  a  quantity  of  sulphur- 
ous acid  to  escape,  which  would  be  sufficient  to  form  a  neutral  sulphite  with  the  base 
of  the  sulphate.  This  class  of  salts  was  particularly  examined  by  Heeren  (Poggen- 
dorff's  Annalen,  v.  vii.  p.  77).  Hyposulphuric  acid  is  imagined  to  exist  in  acid 
compounds  produced  by  the  action  of  sulphuric  acid  on  several  organic  substances. 

The  hyposulphate  of  baryta  may  be  analysed  by  exposing  a  portion  of  it  to  a  red 
heat,  when  it  gives  off  sulphurous  acid,  and  leaves  pure  sulphate  of  baryta  behind, 
tf  an  equal  portion  be  treated  with  boiling  concentrated  nitric  acid,  the  sulphurous 
acid  is  converted  into  sulphuric  acid  ;  and  if  chloride  of  barium  is  afterwards  added, 
a  quantity  of  sulphate  of  baryta  is  obtained  which  is  exactly  double  in  weight  that 
obtained  from  the  first  portion. 

HYPOSULPHUROUS   ACID. 

Eq.  48  or  600;  S202,  or  S02  +  S;  not  isolabh. 

The  hyposulphites  are  better  known  than  hyposulphurous  acid  itself,  which  is  a 
body  of  little  stability,  quickly  undergoing  decomposition  when  liberated  by  a 
stronger  acid  from  a  solution  of  any  of  its  salts,  and  resolving  itself  into  sulphurous 
acid,  hydrosulphuric  acid,  and  sulphur.  These  salts,  long  considered  as  a  species 
of  double  salts,  and  called  sulphuretted  sulphites,  were  first  supposed  to  contain  a 
peculiar  acid  by  Dr.  T.  Thomson  and  by  Gay-Lussac,  —  a  conjecture  afterwards 
verified  by  Sir  John  Herschel,  whose  early  researches  upon  this  acid  form  the 
subject  of  an  interesting  memoir  (Ed.  Phil.  Journ.  vol.  i.  pp.  8  and  396). 

Preparation.  —  Sulphide  of  soda  is  prepared,  in  the  first  instance,  by  saturating 
a  solution  of  carbonate  of  soda  with  sulphurous  acid  gas,  by  the  apparatus  described 
at  page  294).  This  sulphite,  care  being  taken  that  it  is  not  acid,  is  converted  into 
hyposulphite,  by  digesting  it  upon  flowers  of  sulphur  at  a  high  temperature,  but 
without  ebullition.  The  sulphurous  acid  assumes  1  eq.  of  sulphur,  and  remains 
in  combination  with  the  soda;  or,  in  symbols  — 

NaO-f  S02  and  S  =  NaO  +  S02.$. 


304  SULPHUR. 

The  solution  may  afterwards  be  evaporated  (ebullition  being  always  avoided,  as 
the  hyposulphites  are  partially  decomposed  at  21:2°),  and  affords  large  crystals  of 
the  hyposulphite  of  soda.  When  solution  of  caustic  soda  is  digested  upon  sulphur, 
the  latter  is  likewise  dissolved,  and  a  mixture  of  1  eq.  of  hyposulphite  of  soda  with 
2  eq.  of  sulphide  of  sodium  results,  of  which  the  last  always  dissolves  an  excess  of 
sulphur :  — 

3NaO  and  4S=NaO+S202  and  2NaS. 

Exposed  to  the  air,  this  solution  slowly  absorbs  oxygen,  and  if  it  contains  a  certain 
excess  of  sulphur,  passes  entirely  into  hyposulphite  of  soda. 

The  hyposulphite  of  lime  is  also  formed  by  digesting  together  1  part  of  sulphur 
and  3  of  hydrate  of  lime  at  a  high  temperature,  when  changes  of  the  same  nature 
occur  as  with  sulphur  and  caustic  soda,  and  the  solution  becomes  red,  containing 
bisulphide  of  calcium :  a  stream,  of  sulphurous  acid  gas  is  conducted  through  the 
solution  after  it  has  cooled,  and  converts  the  whole  salt  into  hyposulphite,  occasion- 
ing at  the  same  time  a  considerable  deposition  of  sulphur.  The  reaction  here  may 
be  expressed  by  the  following  formula :  — 

2CaS2  and  3S02=2CaO  +  2S202  and  3S. 

If  the  waste-lime,  in  the  porous  state  in  which  it  is  removed  from  the  dry-lime 
purifiers  of  a*  gas-work,  be  exposed  to  air,  it  rapidly  absorbs  oxygen  ;  and,  when 
treated  with  water,  afterwards  gives  much  soluble  hyposulphite  of  lime.  This  is  an 
economical  method  of  preparing  the  salt  on  a  large  scale  (Mem.  Chein.  Soc.  ii.  358). 

Zinc  and  iron  also  dissolve  in  the  solution  of  sulphurous  acid  in  water,  with  little 
or  no  effervescence,  deriving  the  oxygen  necessary  to  convert  them  into  oxides,  not 
from  water,  but  from  the  sulphurous  acid,  two-thirds  of  which  are  thereby  converted 
into  hyposulphurous  acid,  which  combines  with  half  the  oxide  produced;  while  the 
other  third,  remaining  as  sulphurous  acid,  unites  with  the  other  moiety  of  the  same 
oxide :  — 

3S02  and  2Zn  =  ZnO.S202  and  ZnO.S02. 
The  hyposulphite  obtained  by  this  process  is,  therefore,  mixed  with  a  sulphite. 

Properties.  —  The  acid  of  these  salts  undergoes  decomposition  when  they  are 
strongly  heated,  or  treated  with  an  acid.  It  forms  soluble  salts  with  lime  and 
strontia,  in  which  respect  it  differs  from  sulphurous  and  sulphuric  acids;  the  hypo- 
sulphite of  baryta  is  insoluble.  It  also  forms  a  remarkable  salt  with  silver,  which 
has  no  metallic  flavour,  but  tastes  extremely  sweet.  The  existence  of  a  hyposul- 
phite in  a  solution  is  easily  recognised,  by  its  possessing  the  power  to  dissolve  freshly 
precipitated  chloride  of  silver,  and  become  sweet.  Hyposulphite  of  soda  in  solution 
is  apt  to  become  acid  by  the  absorption  of  oxygen,  and  then  its  conversion  into  sul- 
phate of  soda,  with  deposition  of  sulphur,  proceeds  rapidly. 

Uses.  —  The  hyposulphite  of  soda  is  employed  to  distinguish  between  the  earths 
strontia  and  baryta,  —  the  latter  of  which  it  precipitates,  and  not  the  former.  It  is 
also  applied,  in  certain  circumstances,  to  dissolve  the  insoluble  salts  of  silver  in 
photography,  electro-plating,  and  the  treatment  of  silver  ores. 

POLYTHIONIC    SERIES. 

Three  new  acids  of  sulphur  have  lately  been  discovered,  all  containing,  like 
hyposulphuric  acid,  5  eq.  of  oxygen,  but  evidently  more  related  in  constitution  and 
properties  to  hyposulphurous  acid.  They  were  named  by  Berzelius,  from  Occw 
(sulphur);  and  are  composed  as  follows: — 

Trithionic,  or  manosul-hyposulphuric  acid S305,  or  S205  +  S 

Tetrathionic,  or  bisul-hyposulphuric  acid S405,  or  S205  +  2S. 

Pentathionic,  or  trisul-hyposulphuric  acid S505,  or  S206-t-3S. 

Hyposulphurous  acid  becomes  the  ditbionous,  and  hyposulphuric  acid  the  dithionic 
acid,  as  members  of  the  same  series;  all  of  which,  it  will  be  observed,  contain  more 


PENTATHIONIC   ACID.  305 

than  1  equivalent  of  sulphur,  and  are  therefore  polythionic :  but  the  old  names  of 
the  two  acids  last  referred  to  are  too  firmly  established  to  be  changed,  without  a 
greater  necessity  for  the  alteration  than  appears  to  exist. 

Trithionic  or  Monosul-hyposulpkurif  acid;  eq.  88  or  1100,  S305  or  S205-f  S. — 
This  acid  was  first  obtained  by  M.  Langlois  (Annal.  de  Chim.  3  ser.  iv.  77).  It  is 
the  result  of  the  action  of  sulphur  upon  the  soluble  bisulphites,  and  may  be  pre- 
pared from  the  bisulphite  of  baryta.  This  salt  is  digested  with  flowers  of  sulphur 
at  a  temperature  not  exceeding  122°  (50°  C.)  for  several  days;  the  solution  first 
becomes  yellow,  afterwards  loses  all  colour,  and  when  allowed  to  cool  in  this  state, 
deposits  a  salt  in  long  white  silky  crystals,  which  is  the  trithionate  of  baryta.  By 
the  cautious  addition  of  sulphuric  acid  to  a  solution  of  the  new  salt,  the  trithionic 
acid  may  be  liberated  and  obtained  in  solution,  while  the  insoluble  sulphate  of  baryta 
precipitates.  The  acid  solution  may  be  concentrated  in  the  vacuous  receiver  of  an 
air-pump,  but  is  rapidly  decomposed  by  heat  into  sulphurous  acid  and  sulphur. 
The  salt  of  potassa  is  easily  obtained,  either,  according  to  Plessy's  method,  by  passing  t 
sulphurous  acid  into  a  solution  of  hyposulphite  of  potassa ;  or,  according  to  Langlois, 
into  one  of  sulphide  of  potassium  :  in  the  latter  case  hyposulphite  of  potassa  is  first 
formed,  and  from  that  the  trithionate.  (Ressner,  Chem.  Gaz.  vi.  p.  369.)  The 
salts  of  this  acid  appear  to  have  greater  stability  than  the  hyposulphites,  and  are 
formed  when  certain  hyposulphites,  such  as  those  of  zinc,  cadmium^  and  lead,  are 
left  to  spontaneous  decomposition  ;  or  even,  according  to  Fordos  and  Gelis,  by  the 
sole  effect  of  the  concentration  of  solutions  of  these  salts.  This  acid  is  precipitated 
black  by  the  salts  of  the  suboxide  of  mercury,  a  property  which  distinguishes  the 
trithionic  acid  from  the  two  more  highly  sulphured  acids  of  the  same  series,  which 
are  precipitated  yellow  by  the  reagent  in  question. 

Telralhionic  or  Bisul-hyposulphuric  acid',  eq.  104  or  1300;  S405  or  S205  +  S2. 
—  This  acid  was  discovered  by  MM.  Fordos  and  Gelis,  and  is  obtained  by  dissolving 
iodine  in  a  solution  of  the  hyposulphites,  particularly  of  the  hyposulphite  of  baryta. 
The  reaction  in  the  last  case  is  as-  follows : — 

2  (BaO.SA)  and  I  =  Bal  and  BaO.S405. 

The  new  salt,  being  less  soluble  than  the  iodide  of  barium,  is  separated  by  crystal- 
lization, and  affords  the  acid  when  decomposed  by  a  suitable  proportion  of  sulphuric 
acid.  The  solution  of  tetrathionic  acid  has  considerable  stability,  and  may  be  highly 
^concentrated.  The  process  just  described  is  modified  by  Kessner,  who  prepares  first 
the  hyposulphite  of  lead  by  dissolving  2  parts  of  hyposulphite  of  soda  in  hot  water, 
and  pouring  this  solution  into  an  equally  hot  dilute  solution  of  3  parts  of  acetate  of 
lead.  The  precipitate  is  washed  with  a  large  quantity  of  warm  water,  and  mixed 
(still  moist)  with  1  part  of  iodine,  and  the  mass  frequently  stirred ;  in  the  course 
of  a  few  days  the  whole  is  converted  into  iodide  of  lead  and  a  solution  of  tetrathion- 
ate  of  lead.  The  lead  is  now  removed  by  sulphuric  acid  (the  use  of  hydrosulphuric 
acid  being  inadmissible),  any  excess  of  the  latter  by  carbonate  of  baryta,  and  the 
solution  of  the  tetrathionic  acid  evaporated.  When  this  acid  is  saturated  with  car- 
bonate of  soda,  or  its  salt  of  lead  decomposed  by  sulphate  of  soda,  only  products  of 
decomposition  are  obtained,  —  sulphur,  sulphate,  and  hyposulphite  of  soda.  (Chem. 
Gaz.  vi.,  p.  370.)  The  salts  of  this  acid,  therefore,  require  to  be  prepared  directly, 
and  appear  generally  to  be  less  stable  than  the  hydrated  acid. 

Pentathionic  or  Trisul-hyposuIpJiuric  acid ;  =  120  or  1500;  S505  or  S2054-S3. — 
Several  years  ago  Dr.  T.  Thomson  observed  that  when  hydrosulphuric  and  sulphur- 
ous acids  mutually  decompose  each  other  in  presence  of  water,  the  magma  of  sulphur 
precipitated  is  impregnated  by  a  peculiar  acid.  M.  Wackenroder  lately  found  that 
this  acid  is  an  additional  number  of  the  present  series.  To  prepare  the  acid,  Wack- 
enroder supersaturates  water  with  sulphurous  acid,  and  then  causes  hydrosulphurio 
acid  to  stream  through  it  till  the  liquid  has  the  odour  and  reactions  of  the  latter, 
evaporating  afterwards  till  the  excess  of  hydrosulphuric  acid  is  expelled.  The  liquid 
does  not  become  clear  till  after  clean  slips  of  copper  are  left  in  it  for  some  time,  to 
20 


306 


SULPHUR. 


remove  the  suspended  sulphur  :  copper  reduced  from  the  oxide  by  hydrogen  would 
probably  act  more  rapidly.  The  addition  of  chloride  of  sodium,  Or  saturation  with 
a  base,  such  as  an  alkaline  carbonate,  also  facilitates  the  precipitation  of  the  sulphur. 
In  the  opinion  of  Mr.  L.  Thompson,  much^of  this  sulphur,  which  is  supposed  to  be 
suspended,  is  actually  in  solution. 

The  clear  acid  liquid  may  be  concentrated  till  it  attains  a  density  of  1.37;  it  is 
inodorous,  sour,  and  a  little  bitter.  It  may  be  preserved  at  the  temperature  of  the 
air,  without  change  ;  but  when  made  to  boil  it  undergoes  decomposition,  giving  off 
hydrosulphurie  acid,  followed  by  sulphurous  acid,  and  leaving  behind  ordinary  sul- 
phuric acid  and  some  sulphur.  This  acid  is  decomposed,  like  the  last,  by  strong 
bases. 

•  Pentathionic  acid  was  also  found  by  Fordos  and  Gelis  among  the  products  of  the 
decomposition  of  the  chlorides  of  sulphur  by  water.  The  pentothionate  of  baryta 
is  very  soluble,  and  is  easily  altered.  It  was  analysed  by  means  of  chlorine  and  the 
hypochlorites,  which  transform  the  whole  sulphur  into  sulphuric  acid  : 

S505  and  10  01  and  10  HO  =  5  S03  and  10  HC1. 

The  pentathionic  acid  is  distinguished  from  hyposulphurous  acid,  with  which  it  is 
isomeric,  by  the  less  solubility  of  the  pentathionates,  and  by  the  circumstance  that 
the  pentathionates  have  no  action  upon  iodine  (Annales  de  Ch.  3.  ser.  xxii.  66). 
The  sulphur  was  supposed  by  Berzelius  to  exist  in  the  various  polythionic  acids,  in 
its  different  allatropic  conditions. 

SULPHUR   AND    HYDROGEN. 
HYDROSULPHURIC   ACID. 

Syn.   Sulphuretted  hydrogen  gas,  suJfhydric  acid  ;  Eq.  17  or  212.5;  SH;  density 

1191.2; 


FIG.  141. 


Sulphur  does  not  combine  directly  with  hydrogen  even  when  heated  in  that  gas, 
but  with  that  element,  notwithstanding,  sulphur  forms  at  least  two  compounds  ;  one 
of  which,  hydrosulphuric  acid,  is  a  reagent  of  frequent  application  and  considerable 
importance. 

Preparation.  —  (1.)  Of  those  metals  which  dissolve  in  dilute  sulphuric  acid,  with 
the  displacement  of  hydrogen,  the  protosulphides  dissolve  also  in  the  same  acid,  but 
the  hydrogen  then  evolved  carries  off  sulphur  in  combination,  and  appears  as  hydro- 
sulphuric  acid  gas.  The  protosulphide  of  iron,  which  is  commonly  employed  in  this 
operation,  is  obtained  by  depriving  yellow  pyrites,  or  bisulphide  of  iron,  of  a  portion 

of  its  sulphur  by  ignition  in  a  covered  crucible; 
or  formed  directly  by  exposing  to  a  low  red  heat  a 
mixture  of  4  parts  of  coarse  sulphur  and  7  of  iron 
filings  or  borings  in  a  covered  stoneware  or  cast-iron 
crucible.  The  sulphide  of  iron,  thus  obtained,  is 
broken  into  lumps,  and  acted  upon  by  diluted  sul- 
phuric acid  in  a  gas-bottle  (fig.  141),  exactly  as  zinc 
is  treated  in  the  preparation  of  hydrogen  gas. 
Hydrosulphuric  acid  is  evolved  without  the  appli- 
cation of  heat,  and  should  be  collected  over  water 
at  80°  or  90°  ;  or  if  collected  in  a  gasometer  or 
gasholder,  the  latter  may  be  filled  with  bpne,  in 
which  this  gas  is  less  soluble  than  in  pure  water.  ' 
The  gas  obtained  by  this  process  generally  contains 
free  hydrogen,  arising  from  an  intermixture  of  me- 
tallic iron  with  the  sulphide  of  iron  used.  The  gas 
may  also  be  evolved  from  the  action  of  hydrochloric 
«oid  upon  the  sulphide  of  iron,  but  as  it  is  then  impregnated  with  the  vapour  of  the 


HYDROSULPHURIC   ACID. 


307 


latter  acid,  and  may  also,  like  every  gas  produced  with  effervescence,  carry  over 
drops  of  fluid,  it  should  always  be  transmitted  through  water  in  a  wash-bottle,  before 
being  applied  to  any  purpose  as  pure  gas.     The  reaction  by  which  hydro-sulphuric 
acid  is  usually  evolved  is  expressed  in  the  following  equation : 
FeS  and  HO.S03=HS  and  FeO.S03. 

(2.)  Hydrosulphuric  acid,  without  any  admixture  of  free  hydrogen,  is  obtained 
by  digesting  in  a  flask  A,  used  as  a  retort  (fig.  142),  with  a  gentle  heat,  sulphide 

FIG.  142. 


of  antimony  in  fine  powder  with  concentrated  hydrochloric  acid,  in  the  proportion 
of  1  ounce  of  the  former  to  4  'ounce  measures  of  the  latter.  The  gas  of  this  ope- 
ration is  passed  through  water  in  a  wash-bottle  B,  and  collected  over  water  at  80°, 
in  a  bottle  C,  provided  with  a  good  cork.  Or,  after  passing  through  the  wash-bottle, 
it  may  be  carried  over  chloride  of  calcium  in  a  drying  tube,  and  collected  over  mer- 
cury, but  is  gradually  decomposed  by  that  metal,  which  has  a  strong  affinity  for 
sulphur,  and  hydrogen  is  liberated,  without  any  change  of  volume.  The  reaction 
between  hydrochloric  acid  and  sulphide  of  antimony  may  be  thus  expressed : 

3HC1  and  SbS3=3HS  and  SbCl3. 

Properties.  —  Hydrosulphuric  acid  is  a  colourless  gas,  of  a  strong  and  very 
nauseous  odour.  Its  density  is  1191.2,  by  the  experiments  of  Gay-Lussac  and 
Thenard,  and  its  theoretical  sp.  gr.  17  times  that  of  hydrogen.  It  consists  of  2 
volumes  of  hydrogen  and  1  volume  of  sulphur  vapour,  condensed  into  2  volumes, 
which  form  its  combining  measure.  Hydrosulphuric  acid  is  partially  decomposed 
by  heat  into  hydrogen  and  sulphur;  but  to  obtain  complete  decomposition  it  is 
necessary  to  pass  the  gas  a  great  many  times  through  a  porcelain  tube  placed  across 
a  furnace,  and  strongly  heated.  By  a  pressure  of  17  atmospheres  at  50°,  it  is  con- 
densed into  a  highly  limpid  colourless  liquid,  of  sp.  gr.  0.9,  which  is  of  peculiar 
interest  as  the  analogue  of  water  in  the  sulphur  series  of  compounds :  the  solvent 
powers  of  this  liquid  have  not  been  examined.  When  cooled  to  — 122°,  it  solidifies, 
and  is  then  a  white  crystalline  translucent  substance,  heavier  than  the  liquid  (Fara- 
day). The  air  of  a  chamber  slightly  impregnated  by  this  gas  may  be  respired  with- 
out injury,  but  a  small  quantity  of  the  undiluted  gas  inspired  occasions  syncope,  and 
its  respiration,  in  a  very  moderate  proportion,  was  found  by  Thenard  to  prove  fatal, 
—  birds  perishing  in  air  containing  l-1500th?  and  a  dog  in  air  containing  l-800th 


308  SULPHUR. 

part  of  this  gas.  Its  poisonous  effects  are  "best  counteracted  by  a  slight  inhalation 
of  chlorine  gas,  as  the  latter  may  be  obtained  from  a  little  chloride  of  lime  placed  in 
the  folds  of  a  towel  wetted  with  acetic  acid.  Water  dissolves,  at  64°,  2£  volumes 
of  this  gas,  and  alcohol  6  volumes.  These  solutions  soon  become  milky  when 
exposed  to  air,  the  oxygen  of  which  combines  with  the  hydrogen  of  the  gas  and  pre- 
cipitates the  sulphur.  Those  mineral  waters  termed  sulphureous,  such  as  Harrowgate, 
contain  this  gas,  although  rarely  in  a  proportion  exceeding  1^  per  cent,  of  their 
volume.  They  are  easily  recognized  by  their  odour  and  by  blackening  silver.  It 
is  also  found  in  foul  sewers  and  in  putrid  eggs.  Of  deodourizing  fluids  the  solution 
of  nitrate  of  lead,  chloride  of  zinc,  sulphate  of  iron,  and  sulphate  of  manganese, 
appear  to  be  equally  efficacious ;  the  first  alone  decomposing  the  free  gas,  but  that 
salt,  and  all  the  others  named,  decomposing  hydrosulphuric  acid  when  in  combina- 
tion with  ammonia,  the  form  in  which  it  usually  emanates  from  putrefactive  matter. 

Hydrosulphuric  acid  is  highly  combustible,  and  burns  with  a  pale  blue  flame, 
producing  water  and  sulphurous  acid,  and  generally  a  deposit  of  sulphur  when  oxy- 
gen is  not  present  in  excess.  A  little  strong  nitric  acid  thrown  into  a  bottle  of  this 
gas,  occasions  the  immediate  oxidation  of  its  hydrogen,  and  often  a  slight  explosion 
with  flame,  when  the  escape  of  the  vapour  is  impeded  by  closing  the  mouth  of  the 
bottle.  Hydrosulphuric  acid  is  immediately  decomposed  by  chlorine,  bromine,  and 
iodine,  which  assume  its  hydrogen :  hence  the  odour  of  this  gas  in  a  room  is  soon 
destroyed  on  diffusing  a  little  chlorine  through  it.  Tin,  and  many  other  metals, 
heated  in  this  gas,  combine  with  its  sulphur  with  flame,  and  liberate  an  equal  volume 
of  hydrogen,  affording  ready  means  of  demonstrating  the  composition  of  the  gas. 
Potassium  decomposes  one  half  of  the  gas  in  that  manner,  and  becomes  sulphide  of 
potassium,  which  unites  with  the  other  half  without  decomposition,  forming  the 
hydrosulphate  of  the  sulphide  of  potassium.  The  action  of  other  alkaline  metals 
upon  hydrosulphuric  acid  is  similar. 

This  compound  has  a  weak  acid  reaction,  and  forms  one  of  the  hydrogen-acids. 
It  does  not  combine  and  form  salts  with  basic  oxides,  but  it  unites  with  basic  sul- 
phides, such  as  sulphide  of  potassium,  and  forms  compounds  which  are  strictly  com- 
parable with  hydrated  oxides.  When  hydrosulphuric  acid  is  passed  over  lime  at 
a  red  heat,  both  compounds  are  decomposed,  and  water  with  sulphide  of  calcium  is 
formed.  The  oxides  of  nearly  all  the  metallic  salts,  whether  dry  or  in  a  state  of 
solution,  are  decomposed  by  hydrosulphuric  acid  in  a  similar  manner;  but  in  the 
salts  of  those  metals  of  which  the  protosulphide.is  dissolved  by  acids,  such  as  salts 
of  iron,  zinc,  and  manganese,  a  small  quantity  of  a  strong  acid  entirely  prevents 
precipitation.  The  sulphides  are  generally  coloured,  and  many  of  them  are  black ; 
hence  the  effect  of  hydrosulphuric  acid  in  blackening  salts  of  lead  and  silver,  which 
renders  these  compounds  so  sensitive  'as  tests  of  the  presence  of  that  substance. 
Hydrosulphuric  acid  also  tarnishes  certain  metals,  such  as  gold,  silver,  and  brass, 
so  that  utensils  of  which  these  metals  are  the  basis  should  not  be  exposed  to  this 
gas. 

Bisulphide  of  hydrogen,  HS2.  —  When  carbonate  of  potassa  is  fused  with  half  its 
weight  of  sulphur,  a  persulphide  of  potassium  is  formed  containing  a  large  excess 
of  sulphur,  which  affords  a  solution  in  water  of  an  orange  red  colour.  The  proto- 
sulphide  of  potassium,  with  hydrochloric  acid,  gives  hydrosulphuric  acid  and  chloride 
of  potassium  :  HC1  and  KS=HS  and  KC1.  But  when  the  red  solution  of  persul- 
phide of  potassium  is  poured  in  a  small  stream  into  hydrochloric  acid,  diluted  with 
two  or  three  volumes  of  water,  while  chloride  of  potassium  is  formed  as  before,  the 
hydrosulphuric  acid  produced  combines  with  another  equivalent  of  sulphur,  and 
forms  a  yellowish  oily  fluid,  the  bisulphide  of  hydrogen,  which  falls  to  the  bottom 
of  the  acid  liquid.  Supposing  the  persulphide  of  potassium  to  be  a  pure  bisulphide, 
then  HC1  and  KSa=HPa  and  KC1.  The  result  of  the  combination  in  this  case 
appears  rather  capricious ;  for  if  the  acid  and  persulphide  of  potassium  be  mixed  in 
the  other  way,  —  if  the  acid  be  added  drop  by  drop  to  the  alkaline  sulphide, — then 
hydrosulphuric  acid  is  evolved,  the  whole  excess  of  sulphur  precipitates,  and  no  per- 


SULPHUR   AND    CARBON.  309 

sulphide  of  hydrogen  is  formed.  The  oily  fluid  produced  by  the  first  mode  of  mix- 
ing has  considerable  analogy  in  its  properties  to  the  binoxide  of  hydrogen,  and 
appears,  like  that  compound,  to  have  a  certain  degree  of  stability  imparted  to  it  by 
contact  with  acids,  such  as  pretty  strong  hydrochloric  acid,  while  the  presence  of 
^alkaline  bodies,  on  the  contrary,  gives  its  elements  a  tendency  to  separate.  This 
decomposition  has  been  taken  advantage  of  to  obtain  liquid  hydrosulphuric  acid,  by 
sealing  up  bisulphide  of  hydrogen  in  a  Faraday  tube  (page  77). 

Thenard  has  observed  other  points  of  analogy  between  these  compounds.  Like 
binoxide  of  hydrogen,  the  bisulphide  produces  a  white  spot  upon  the  skin,  and 
destroys  vegetable  colours,  so  that  it  has  actually  been  used  in  bleaching.  The 
latter  compound  is  also  resolved  into  hydrosulphuric  acid  and  sulphur  by  all  the 
bodies  which  effect  the  transformation  of  the  former  into  water  and  oxygen;  such 
as  charcoal  powder,  platinum,  indium,  gold,  binoxide  of  manganese,  and  the  oxides 
of  gold  and  silver,  which  last,  when  the  bisulphide  is  dropt  upon  them,  are  decom- 
posed in  an  instant,  and  even  with  ignition.  The  bisulphide  of  hydrogen  undergoes 
spontaneously  the  same  decomposition,  even  in  well-closed  bottles,  which  are  apt, 
on  that  account,  to  be  broken.  It  is  soluble  in  ether,  but  the  solution  soon  deposits 
crystals  of  sulphur.  Thenard  finds  this  body  not  to  be  uniform  in  its  composition, 
the  proportion  of  sulphur  often  exceeding  considerably  2  eq.  to  1  of  hydrogen ;  but 
the  excess  of  sulphur  is  possibly  only  in  solution  (Ann.  de  Ch.  2  ser.  xlviii.  79). 

SULPHUR   AND    NITROGEN. 

Sulphide  of  nitrogen;  eq.  62  or  775;  NS3. — This  is  a  yellow  pulverulent  solid 
substance  of  small  stability,  and  which  cannot  be  formed  by  the  direct  union  of  its 
elements.  The  liquid  bichloride  of  sulphur  absorbs  ammoniacal  gas,  producing  first 
a  flocculent  brown  matter,  NH3.SC12,  and  afterwards,  if  the  action  of  ammonia  is 
continued,  a  yellow  substance,  of  which  the  formula  is  — 

2NH3.SC12. 

Thrown  into  water  this  yellow  matter  undergoes  decomposition,  producing  hydro- 
chlorate  and  hyposulphite  of  ammonia,  which  dissolve,  and  a  yellow  powder,  which 
is  a  mixture  of  sulphur  and  the  sulphide  of  nitrogen.  This  powder  is  quickly 
washed  with  a  little  water,  dried  under  the  receiver  of  an  air-pump,  and  finally 
washed  several  times  with  ether,  which  dissolves  out  the  free  sulphur,  and  leaves 
the  sulphide  of  nitrogen. 

The  sulphide  of  nitrogen  is  a  yellow  powder,  which,  a  little  above  212°,  is 
decomposed  in  a  gradual  manner  into  sulphur  and  nitrogen,  but  when  sharply 
heated,  violently  and  with  explosion.  It  is  also  slowly  decomposed  by  cold  water, 
but  much  more  rapidly  at  the  temperature  of  ebullition.  The  composition  of  sul- 
phide of  nitrogen  is  determined  either  by  boiling  a  known  quantity  in  fuming  nitric 
acid,  which  converts  the  sulphur  into  sulphuric  acid ;  or,  by  heating  a  mixture  of 
this  substance  and  metallic  copper  in  a  glass  tube,  sealed  at  one  end,  and  arranged 
as  a  retort,  so  that  the  gas  evolved  may  be  collected.  The  copper  and  sulphur  unite 
with  avidity,  and  the  nitrogen  is  disengaged  as  gas.  [See  Supplement,  p.  781.] 

SULPHUR   AND    CARBON. 

Bisulphide  of  carbon  ;  sulphocarbonic  acid ;  eq.  38  or  475 ;  CS2.  —  Charcoal 
strongly  ignited  in  an  atmosphere  of  sulphur  vapour,  combines  with  that  element, 
and  forms  a  compound  which  holds  the  same  place  in  the  sulphur  series  that  car- 
bonic acid  occupies  in  the  oxygen  series  of  compounds.  The  bisulphide  of  carbon 
is  a  volatile  liquid,  and  may  be  prepared  by  distilling,  in  a  porcelain  retort,  yellow 
pyrites  or  bisulphide  of  iron,  with  a  fourth  of  its  weight  of  well-dried  charcoal,  both 
in  the  state  of  fine  powder  and  intimately  mixed.  The  vapour  from  the  retort  is 
conducted  to  the  bottom  of  a  bottle  filled  with  cold  water,  to  condense  it.  Or 


310 


SULPHUR. 


Fm.  143. 


sulphur  vapour  may  be  sent  over  fragments  of  well-dried  charcoal  in  a  porcelain 
or  cast  iron  (not  malleable  iron)  tube,  placed  across  a  furnace.  The  product  is 
generally  of  a  yellow  colour,  and  contains  sulphur  in  solution,  to  free  it  from  which 
it  is  redistilled  in  a  glass  retort,  by  a  gentle  heat. 

For  preparing  a  larger  quantity  of  bisulphide  of  carbon, 
M.  Brunner  recommends  an  earthenware  retort  of  the  form 
C  (fig.  143),  two-thirds  filled  with  dry  charcoal,  having  a 
tube,  b,  descending  through  '  the  tubulure  a,  by  which  frag- 
ments of  sulphur  can  be  introduced.  The  retort  is  raised  to 
a  red  heat  in  a  furnace  (fig.  144),  and  the  vapour  which 
comes  over,  carried  through  a  condensing  tube,  c  d,  kept 
cold  by  a  stream  of  water,  and  ultimately  conveyed  to  the 
lower  part  of  a  bottle  surrounded  by  cold  water,  and  also  con- 
taining a  little  water,  which  floats  upon  the  surface  of  the 
condensed  liquid  and  prevents  its  evaporation.  The  sulphur 
is  gradually  introduced  into  the  retort,  and,  being  immedi- 
ately converted  into  vapour,  produces  the  bisulphide  of  carbon 
in  traversing  the  incandescent  charcoal. 

FIG.  144. 


The  bisulphide  of  carbon  is  a  colourless  liquid,  of  high  refracting  power,  and  sp. 
gr.  1.272.  Its  vapour  has  a  tension  of  7.38  Paris  inches  (Marx)  at  50°,  and  the 
liquid  boils  at  110°  j  a  cold  of  — 80°  can  be  produced  by  its  evaporation  in  vacuo. 
This  compound  is  extremely  combustible,  taking  fire  at  a  temperature  which  scarcely 
exceeds  the  boiling  point  of  mercury.  When  a  few  drops  of  the  liquid  are  thrown 
into  a  bottle  of  oxygen  gas,  or  nitric  oxide,  a  combustible  mixture  is  formed,  which 
burns,  when  a  light  is  applied  to  it,  with  a  brilliant  flash  of  flame,  but  without  a 
violent  explosion.  The  bisulphide  of  carbon  is  insoluble  in  water,  but  it  is  soluble 
in  alcohol.  It  dissolves  sulphur,  phosphorus,  and  iodine.  The  solution  of  phos- 
phorus in  this  liquid  is  used  in  electrotyping ;  objects  dipped  in  the  solution  and 
dried  are  left  covered  by  a  film  of  phosphorus,  which  enables  them  to  obtain  a  con- 
ducting metallic  coating  when  plunged  into  a  solution  of  copper. 

The  observed  density  of  the  vapour  of  bisulphide  of  carbon  is  2644.7  (Gay- 
Lussac).  It  consists  of  2  volumes  carbon  vapour  (density  416)  and  2  volumes  sul- 
phur vapour  (density  2216),  condensed  into  2  volumes,  which  form  its  combining 
measure ;  and  is  therefore  quite  analogous  in  condensation  to  carbonic  acid  gas.  A 
complete  analysis  of  the  bisulphide  of  carbon  is  obtained,  by  passing  it  in  vapour 
over  a  mixture  of  carbonate  of  soda  and  oxide  of  copper  in  a  combustion  tube  (page 
287)  at  a  red  heat :  the  sulphur  is  oxidized,  and  remains  in  combination  with  the 


SELENIUM.  311 

soda  as  sulphate  of  soda,  while  the  carbon  is  burnt  also,  and  disengaged  as  carbonic 
acid  gas,  accompanied  by  an  equal  quantity  of  carbonic  acid  liberated  from  the  car- 
bonate of  soda  by  the  sulphuric  acid  formed.  The  carbon  alone  of  this  substance 
may  be  advantageously  determined  as  carbonic  acid,  by  a  similar  combustion  with 
chromate  of  lead. 

The  bisulphide  of  carbon  is  a  sulphur  acid,  and  combines  with  sulphur  bases,  such 
as  the  sulphide  of  potassium,  forming  a  class  of  salts  which  are  called  sulphocarbo- 
nates.  Oxygen  bases  dissolve  it  slowly,  and  are  converted  into  a  mixture  of  car- 
bonate and  sulphocarbonate :  thus  2  equivalents  of  potassa  with  1  of  bisulphide  of 
carbon  yield  2  equivalents  of  sulphide  of  potassium  and  1  of  carbonic  acid,  which 
combine  respectively  with  bisulphide  of  carbon  and  potassa. 

Solid  sulphide  of  carbon.  —  The  charcoal  left  in  the  tube,  after  the  process  for 
the  former  compound,  is  much  corroded,  and  contains  a  portion  of  sulphur  which 
cannot  be  expelled  from  it  by  heat.  Berzelius  considered  this  sulphur  as  in  chemical 
combination  with  the  carbon.  [See  Supplement,  p.  782."] 


SECTION   VIII. 

SELENIUM. 

Eq.  39.28  or  491  (F.  Sacc) ;  Se;  density  of  vapour  unknown. 

This  element  was  discovered  in  1817  by  Berzelius,  in  the  sulphur  of  Fahlun 
employed  in  a  sulphuric  acid  manufactory  in  Sweden,  and  was  named  by  him  sele- 
nium, from  SfT.^,  the  moon,  on  account  of  its  strong  analogy  to  another  element, 
tellurium,  which  derives  its  name  from  tellus,  the  earth.  It  is  ,one  of  the  least 
abundant  of  the  elements,  but  is  found  in  minute  quantity  in  several  ores  of  copper, 
silver,  lead,  bismuth,  tellurium,  and  gold,  in  Sweden  and  Norway ;  and  in  combi- 
nation with  lead,  silver,  copper,  and  mercury,  in  the  Hartz.  It  is  extracte^  from  a 
seleniferous  ore  of  silver  of  a  mine  in  the  latter  district,  and  supplied  for  sale  in 
little  cylinders  of  the  thickness  of  a  goose-quill,  and  three  inches  in  length,  or  in 
the  form  of  small  medallions  of  its  discoverer.  It  has  also  been  found  in  the  Lipari 
islands  associated  with  sulphur,  and  can  sometimes  be  detected  in  the  sulphuric  acid 
both  of  Germany  and  England.  It  is  separated  from  its  combinations  with  sulphur 
and  metals  by  a  very  complicated  process,  for  which  I  must  refer  to  the  works  of 
Berzelius  (Ann.  of  Phil.  vol.  xiii.  401;  or  Ann.  de  Ch.  et  de  Phys.  xi.  160;  also 
Berzelius's  Traite,  ii.  184,  Paris  edit.  Didot,  1846).  [See  Supplement,  p.  784.] 

Properties  of  selenium.  —  This  element  is  allied  to  sulphur,  and,  like  that  body, 
exhibits  considerable  variety  in  its  physical  characters.  When  it  cools  after  being 
distilled,  its  surface  reflects  light  like  a  mirror,  has  a  deep  reddish  brown  colour, 
with  a  metallic  lustre  resembling  that  of  polished  blood-stone ;  its  density  is  between 
4.3  and  4.32.  When  cooled  slowly  after  fusion  its  surface  is  rough,  of  a  leaden 
grey  colour,  its  fracture  fine-grained,  and  the  mass  resembles  exactly  a  fragment  of 
cobalt.  But  as  selenium  does  not  conduct  electricity,  and  its  metallic  characters  are 
not  constant,  it  is  better  classed  with  the  non-metallic  bodies.  Its  powder  is  of  a 
deep  red  colour.  By  heat  it  is  softened,  becoming  semifluid  at  392°,  and  fusing 
completely  at  482°.  It  remains  a  long  time  soft  on  cooling,  and  may  then  be  drawn 
out  like  sealing-wax  into  thin  and  very  flexible  threads,  which  are  grey  and  exhibit  a 
metallic  lustre  by  reflected  light,  but  are  transparent  and  of  a  ruby  red  colour  by 
transmitted  light.  It  boils  about  1292°,  and  gives  a  vapour  of  a  yellow  colour,  less 
intense  than  that  of  sulphur,  but  more  so  than  that  of  chlorine.  The  density  of  this 
vapour  has  not  been  ascertained.  When  heated  to  the  degree  of  ignition,  selenium 
emits  a  powerful  odour,  suggesting  that  of  decaying  horse-radish,  by  means  of  which 
the  smallest  trace  of  this  element  may  be  detected  in  minerals,  when  heated  before 
the  blow-pipe.  The  odour  was  first  ascribed  to  a  gaseous  oxide  of  selenium,  but  it 


312  SELENIUM. 

is  found  by  M.  Sacc  that  selenium  heated  in  perfectly  dry  air  is  inodorous,  and  the 
odour  is  now  referred  to  the  production  of  a  minute  quantity  of  hydroselenic  acid. 

Selenium  combines  in  two  proportions  with  oxygen,  forming  selenious  acid,  which 
corresponds  with  sulphurous  acid,  and  selenic  acid  corresponding  with  sulphuric 
acid.- 

Selenious  acid;  eq.  55.28  or  691;  Se02.  —  Selenium  does  not  burn  in  air,  but 

when  strongly  heated  in  the  bend  of  a 

FlG'  145'  glass  tube  a  b  c,  (fig.  145),  with  a  cur- 

rent of  oxygen  passing  over  it,  selenium 
takes  fire  and  burns  with  a  flame,  white 
at  the  base,  and  of  a  bluish  green  at  the 
point  and  edges,  but  not  strongly  lumin- 
ous j  selenious  acid  at  the  same  time  con- 
denses in  the  upper  part  of  the  tube  as  a 
white  sublimate,  in  long  quadrilateral 
needles.  Its  vapour  has  the  colour  of 
chlorine.  The  same  acid  is  the  only 
product  of  the  action  of  nitric  or  nitro- 
muriatic  acid  upon  selenium,  and  is  ob- 
tained on  slowly  cooling  the  liquor  in 
large  prismatic  crystals,  striated  lengthwise,  which  have  a  considerable  resemblance 
to  nitre.  These  crystals  are  hydrated  selenious  acid.  This  acid  is  largely  soluble, 
both  in  water  and  alcohol.  It  is  decomposed  when  in  solution,  and  selenium  pre- 
cipitated by  zinc,  iron,  or  sulphite  of  ammonia,  with  the  assistance  of  a  free  acid. 
The  selenite  of  ammonia  is  also  decomposed  by  heat,  and  leaves  selenium.  The 
selenious  is  a  strong  acid,  displacing  nitric  and  hydrochloric  acids  from  their  combi- 
nations, but  is  displaced  in  its  turn  by  the  more  fixed  acids,  sulphuric,  boracic,  &c., 
at  a  high  temperature.  (F.  Sacc,  Annales  de  Ch.  3  ser.  xxi.  119.) 

Selenic  acid,  Se03. — Selenium  is  brought  to  this  superior  state  of  oxidation  at  a 
high  temperature,  by  fusion  with  nitre,  a  process  which  affords  the  seleniate  of 
potassa.  The  selenic  acid  is  precipitated  from  that  salt  by  the  nitrate  of  lead ;  and 
the  insoluble  seleniate  of  lead,  after  being  washed,'  is  diffused  through  water  and 
decomposed  by  a  stream  of  hydrosulphuric  acid,  which  converts  the  lead  into  inso- 
luble sulphide  of  lead,  and  liberates  selenic  acid.  A  solution  of  this  acid  may  be 
concentrated  till  its  boiling  point  rises  to  536°,  but  above  that  temperature  it  changes 
rapidly  into  selenious  acid,  with  disengagement  of  oxygen.  Its  density  is  then  2.60, 
and  it  contains  little  more  than  a  single  equivalent  of  water,  and  therefore  corresponds 
with  the  protohydrate  of  sulphuric  acid,  or  oil  of  vitriol.  Selenic  acid  has  not  been 
obtained  in  the  anhydrous  condition.  Zinc  and  iron  are  dissolved  by  this  acid,  with 
the  evolution  of  hydrogen  gas ;  and  with  the  aid  of  heat  it  dissolves  copper  and 
even  gold,  an  operation  in  which  it  is  partially  converted  into  selenious  acid.  But 
it  does  not  dissolve  platinum.  To  precipitate  its  selenium,  the  acid  may  be  digested 
with  hydrochloric  acid,  which  occasions  the  formation  of  selenious  acid  and  the 
evolution  of  chlorine,  and  then  sulphurous  acid  throws  down  the  selenium ;  for  it  is 
singular  that  selenic  acid  is  not  de-oxidized  by  sulphurous  acid,  although  selenious 
acid  is.  The  compounds  of  selenic  acid  with  bases,  so  much  resemble  the  corre- 
sponding sulphates,  in  their  crystalline  form,  colour,  and  external  characters,  that 
they  can  only  be  distinguished  from  them  by  the  property  which  the  seleniates  have 
of  detonating  when  ignited  with  charcoal,  and  causing  a  disengagement  of  chlorine 
when  heated  with  hydrochloric  acid.  To  separate  the  selenic  from  the  sulphuric 
acid,  Berzelius  recommends  the  saturation  of  the  acids  with  potassa,  and  the  ignition 
of  the  dried  salt,  mixed  with  sal-ammoniac;  the  selenic  acid  is  decomposed  by  the 
iinmonia  and  reduced  to  the  state  of  selenium. 


PHOSPHORUS.  313 


SECTION   IX. 

i 

PHOSPHORUS. 

• 

Eq.  400  or  32;  P;  density  of  vapour  4327;  [] 

This  remarkable  element  appears  to  be  essential  to  the  organization  of  the  higher 
animals,  being  found  in  their  fluids,  and  forming,  in  the  state  of  phosphate  of  lime, 
the  basis  of  the  solid  structure  of  the  bones.  It  is  also  found  in  most  plants,  and 
in  a  few  minerals.  Phosphorus  was  first  obtained  by  Brandt  of  Hamburgh  in  1660, 
but  Kunkel  first  made  public  a  process  for  preparing  it,  which  was  afterwards  im- 
proved by  Margraff  and  by  Scheele.  Its  ready  inflammability,  from  which  phos- 
phorus derived  its  name,  has  always  made  this  substance  an  object  of  popular 
interest  ;  while  the  singularity,  importance,  and  variety  of  the  phosphoric  compounds 
have  drawn  to  them  no  ordinary  share  of  the  attention  of  chemists. 

Preparation.  —  Phosphorus  is  not  a  substance  that  can  be  easily  prepared  on  a 
small  scale,  but  ever  since  the  time  of  Godfrey  Hankwitz,  to  whom  Mr.  Boyle 
communicated  a  process  for  preparing  it,  phosphorus  has  been  manufactured  in 
London,  in  considerable  quantity  and  of  great  purity,  for  the  use  of  chemists.  The 
earth  of  bones  is  decomposed  by  2-3ds  of  its  weight  of  sulphuric  acid,  and  the 
insoluble  sulphate  of  lime  separated  by  filtration  from  the  soluble  phosphoric  acid, 
which  passes  through  with  a  quantity  of  phosphate  of  lime  in  solution.  The  acid 
liquor  is  then  evaporated  to  the  consistence  of  a  syrup,  and  mixed  with  charcoal  to 
form  a  soft  paste,  which  is  rubbed  well  in  a  mortar,  and  then  dried  in  an  iron  pot 
with  constant  stirring  till  the  mass  begins  to  be  red-hot.  It  is  allowed  to  cool,  and 
introduced  as  rapidly  as  possible  into  a  stoneware  retort,  previously  covered  with  a 
coating  of  fire-clay.  The  beak  of  the  retort  is  inserted  into  a  wider  copper  tube  of  a 
few  feet  in  length,  the  free  end  of  which  is  bent  downwards  a  few  inches  from  its 
extremity  ;  and  the  descending  portion  introduced  into  a  wide-mouthed  bottle,  con- 
taining enough  of  water  to  cover  the  extremity  of  the  tube  to  the  extent  of  a  line 
or  two.  The  heat  of  the  furnace  in  which  the  retort  is  placed  is  slowly  raised  for 
three  or  four  hours,  and  then  urged  vigorously  till  phosphorus  ceases  to  drop  into 
the  water  from  the  copper  tube,  which  may  continue  from  fifteen  to  thirty  hours, 
according  to  the  size  of  the  retort.  Carbon  at  a  high  temperature  takes  oxygen 
from  the  phosphoric  acid,  and  becomes  carbonic  oxide,  so  that  the  phosphorus  in 
distilling  over  is  accompanied  all  along  by  that  gas. 

Wohler  recommends,  instead  of  the  preceding  process,  to  calcine  ivory  black, 
which  is  a  mixture  of  phosphate  of  lime  and  charcoal,  with  fine  quartzy  sand  and  a 
little  more  ordinary  charcoal,  in  cylinders  of  fire-clay,  at  a  very  high  temperature, 
Each  cylinder  has  a  bent  copper  tube  adapted  to  it,  one  branch  of  which  descends 
into  a  vessel  containing  water.  The  efficiency  of  Wohler's  process  depends  upon 
the  silica  acting  as  an  acid,  and  combining  with  the  lime  of  the  phosphate,  at  a  high 
temperature,  while  the  liberated  phosphoric  acid  is  decomposed  by  the  carbon. 

Properties.  —  At  the  usual  temperature  phosphorus  is  a  translucent  soft  solid  of  a 
light  amber  colour,  which  may  be  bent  or  cut  with  a  knife,  and  the  cut  surface  has 
•a  waxy  Iustr6.  Its  density  is  1.77.  Phosphorus  melts  at  108°,  undergoing  a 
remarkable  dilatation  of  0.0134  of  its  volume,  and  becoming  transparent  and  colour- 
less immediately  before  fusion.  It  forms  a  transparent  liquid,  possessing,  like  most 
combustible  bodies,  a  high  refracting  power.  At  217°  it  begins  to  emit  a  slight 
vapour,  and  boils  at.  550°,  being  converted  into  a  vapour  which  is  colourless,  of  sp. 
gr.  4355,  according  to  the  experiment  of  Dumas,  which  coincides  almost  with  the 
theoretical  density  4327.  Its  combining  measure,  like  that  of  oxygen,  is  1  volume, 
allowing  its  equivalent  to  be  32.  When  fused  and  left  undisturbed,  it  sometimes 
remains  liquid  for  hours  at  the  usual  temperature,  particularly  when  covered  by  an 
alkaline  liquid,  but  becomes  solid  when  touched.  Phosphorus,  when  very  pure, 


314  PHOSPHORUS. 

exhibits,  by  rapid  cooling  from  a  high  temperature,  a  modification  analogous  to  that 
which  sulphur  undergoes  in  the  same  circumstances,  but  which  is  not  so  easily  pro- 
duced. Light  causes  it,  in  all  circumstances,  to  assume  a  red  tint ;  to  avoid  which 
action  phosphorus  is  usually  preserved  in  an  opaque  bottle.  Phosphorus  cannot  be 
crystallized  from  a  state  of  fusion,  for  this  substance  passes  in  a  gradual  manner 
from  the  liquid  to  the  solid  condition,  a  circumstance  which  is  always  opposed  to 
crystallization ;  but  from  its  solution  in  hot  naphtha  it  may  be  obtained,  in  cooling, 
in  rhomboidal  dodecahedrons  of  the  regular  system.  It  is  quite  insoluble  in  water, 
but  soluble  to  a  small  extent,  with  the  aid  of  heat,  in  fixed  and  volatile  oils,  in 
bisulphide  of  carbon,  of  which  100  parts  dissolve  20  of  phosphorus;  in  chloride  of 
sulphur,  sulphide  of  phosphorus,  and  ether. 

[The  red  substance  formed  by  the  action  of  light  appears  to  be  a  modification  of 
phosphorus  exhibiting  chemical  and  physical  characters  different  from  its  ordinary 
condition.  Red  phosphorus  is  formed  not  only  by  exposure  to  light,  but  also  by 
keeping  phosphorus  at  a  high  temperature  (464° — 482°)  for  some  time,  when  it 
assumes  a  carmine  red  colour,  thickens,  and  becomes  perfectly  opaque.  This  change 
takes  place  in  an  atmosphere  of  dry  carbonic  acid,  nitrogen  or  hydrogen.  The 
unaltered  portion  of  the  phosphorus  is  separated  from  the  red  variety  by  means  of 
bisulphide  of  carbon,  in  which  this  latter  is  insoluble,  and  it  may  be  purified  to  a 
greater  extent  by  boiling  it  with  a  solution  of  potassa,  washing  with  water,  then 
with  very  dilute  nitric  acid,  and  finally  again  with  water. 

Red  phosphorus  is  in  the  form  of  a  scarlet  powder.  Its  density  is  1.964.  It 
remains  without  alteration  in  the  air;  and  even  when  heated  gradually  in  a  current 
of  air  it  does  not  take  fire,  requiring  a  temperature  of  500°  to  combine  with  oxygen 
and  become  luminous,  and  for  complete  combustion  that  of  572°.  When  heated  to 
the  boiling  point  in  a  gas  which  has  no  action  on  it,  common  phosphorus  results. 
Chlorine  combines  with  it  at  common  temperatures  without  the  evolution  of  light. 
(Schrceter,  Journ.  Ph.  and  Ch.  Av.  1851).  —  R.  B.]  [fe  Supplement,  p.  785. J 

Phosphorus  undergoes  oxidation  in  the  open  air,  and  diffuses  white  vapours, 
which  have  a  peculiar  odour,  suggesting  to  some  that  of  garlic,  and  are  luminous  in 
the  dark ;  and  at  the  same  time  the  phosphorus  becomes  covered  with  acid  drops, 
which  arise  from  the  phosphorous  acid,  produced  in  these  circumstances,  attracting 
the  humidity  of  the  air.  This  slow  combustion  is  attended  with  a  sensible  evolution 
of  heat,  and  may  terminate  in  the  fusion  of  the  phosphorus,  and  its  inflammation 
with  combustion  at  a  high  temperature.  There  is  a  necessity  for  caution,  therefore, 
in  handling  phosphorus,  a  burn  from  this  body  in  a  state  of  ignition  being  in  general 
exceedingly  severe.  It  is  preserved  under  the  surface  of  water.  The  low  combustion 
of  phosphorus  has  been  particularly  studied.  It  is  not  observed  a  few  degrees  below 
32°,  but  is  sensible  at  that  temperature,  and  increases  perceptibly  a  few  degrees 
above  it.  The  presence  of  certain  gaseous  substances,  even  in  minute  quantity,  has 
a  remarkable  effect  in  preventing  the  slow  combustion  of  phosphorus ;  thus  at  66° 
it  is  entirely  prevented  by  the  presence  of, 

Volumes  of  Air. 

1  volume  of  olefiant  gas  in 450 

1  volume  of  vapour  of  sulphuric  ether  in  150 

1  volume  of  vapour  of  naphtha  in 1820 

1  volume  of  vapour  of  oil  of  turpentine  in 4444 

and  the  influence  of  these  gases  or  vapours  is  not  confined  to  low  temperatures,  a 
certain  admixture  of  all  of  them  defending  phosphorus  from  oxidation  even  at  200°. 
But  on  allowing  such  a  gaseous  mixture  to  expand,  by  diminishing  the  pressure 
upon  it  to  a  half  or  a  tenth,  the  phosphorus  becomes  luminous,  and  the  proportion 
of  foreign  gas  required  to  prevent  the  slow  combustion  must  be  greatly  increased. 
The  only  explanation  of  this  phenomenon  which  can  be  offered  at  present,  is  that 
the  gases  which  exert  this  influence  have  an  attraction  for  oxygen,  and  there  is  reason 
to  believe  are  themselves  undergoing  a  slow  oxidation  at  the  same  time.  Now  when 


OXIDE    OF    PHOSPHORUS.  315 

two  oxidable  bodies  are  in  contact,  one  of  them  often  takes  precedence  in  combining 
with  oxygen,  to  the  entire  exclusion  of  the  other.  Potassium  is  defended  from 
oxidation  in  air  by  the  same  vapours,  although  to  a  less  degree.  (Quarterly  Journal 
of  Science,  N.  S.  vol.  vi.  p.  83).  It  is  curious,  that  in  pure  oxygen,  phosphorus 
may  remain  without  oxidating  at  all,  at  temperatures  below  60°,  but  an  inconsidera- 
ble rarefaction  of  the  gas,  from  diminution  of  the  pressure  upon  it,  will  cause  the 
phosphorus  to  burst  into  the  luminous  condition.  The  dilution  of  the  oxygen  with 
nitrogen,  hydrogen,  or  carbonic  acid,  produces  the  same  effect.  When  gradually 
heated  in  air,  phosphorus  generally  catches  fire,  and  begins  to  undergo  the  high 
combustion,  before  its  temperature  has  risen  to  140°  :  of  this  high  combustion,  the 
sole  product  is  phosphoric  acid.  The  inflammability  of  phosphorus,  however,  is 
greatly  increased  by  its  impurities,  particularly  by  the  presence  of  the  red  oxide  of 
phosphorus. 

The  phosphorus  matches  now  universally  employed  for  procuring  a  light,  are 
generally  the  wooden  sulphur  match,  with  an  additional  coating,  applied  to  its 
extremity,  of  a  paste  containing  phosphorus,  which,  when  dry,  will  ignite  by  friction. 
The  materials  added  to  this  paste,  to  promote  the  combustion  of  the  phosphorus,  are 
chlorate  and  nitrate  of  potassa,  or  certain  metallic  oxides,  such  as  the  binoxide  of 
manganese  or  sesquioxide  of  lead  (minium),  which  abandon  readily  a  portion  of  their 
oxygen.  The  snap,  or  little  detonation  which  attends  the  ignition  of  these  matches, 
is  caused  by  the  chlorate  of  potassa,  and  is  obviated  by  substituting  nitre  for  that 
salt;  although,  to  give  the  proper  inflammability,  a  small  proportion  of  chlorate  is 
found  to  be  indispensable.  The  phosphorus  paste  is  made  by  melting  phosphorus 
in  a  vessel  with  a  certain  quantity  of  water  at  120°.  The  requisite  proportion  of 
chlorate  or  nitrate  of  potassa  is  dissolved  in  this  water,  and  the  metallic  oxides 
added,  if  the  latter  are  used,  and  then  enough  of  gum  to  thicken  the  liquid.  The 
whole  are  well  triturated  together,  in  a  mortar,  till  the  globules  of  phosphorus  cease 
to  be  visible  to  the  eye;  and  the  mass  is  coloured  blue  with  Prussian  blue,  or  led 
with  minium.  The  points  of  the  matches  already  sulphured  are  dipped  into  this 
paste,  so  as  to  cover  their  extremities,  and  then  cautiously  dried  in  a  stove.  The 
gum  on  drying  forms  a  varnish,  which  defends  the  phosphorus  from  oxidation  by 
the  air  till  the*  surface  is  abraded  by  friction,  when  the  phosphorus  first  takes  fire 
and  communicates  its  combustion  to  the  sulphur,  which  again  ignites  the  wood  of 
the  match. 

Phosphorus  is  susceptible  of  four  different  degrees  of  oxidation,  the  highest  of 
which  is  a  powerful  acid,  while  the  acid  character  is  not  absent  even  in  the  lowest. 
These  compounds  are  :  — 

Oxide  of  phosphorus 2P-f  0 

Hypophosphorous  acid P  +  0 

Phosphorous  acid P-f  30 

Phosphoric  acid P+5O 

OXIDE   OP   PHOSPHORUS. 

Eq.  72  or  900;  P20. 

When  burned  in  air  or  oxygen,  phosphorus  generally  leaves  behind  it  a  small 
quantity  of  a  red  matter,  which  is  an  oxide  of  phosphorus.  The  same  compound  is 
obtained,  in  larger  quantity,  by  directing  a  stream  of  oxygen  gas  upon  melted  phos- 
phorus under  hot  water,  and  was  found  by  Pelouze  to  contain  3  equivalents  of 
phosphorus  to  2  of  oxygen  (Annal.  de  Ch.  et  de  Ph.  1.  83). 

But  this  oxide  is  impure,  and  the  definite  oxide  appears  to  have  been  first  obtained 
by  Leverrier  (Annal.  de  Ch.  et  de.  Ph.  Ixv.  257).  His  process  is  to  expose  to  the 
air  small  fragments  of  phosphorus  covered  by  the  liquid  chloride  of  phosphorus 
(PC13),  in  an  open  bolt-head.  Phosphoric  acid  is  formed,  and  also  a  yellow  matter, 
which  he  finds  to  be  a  phosphate  of  the  oxide  of  phosphorus,  and  which  gives  a  yel- 


316   •  PHOSPHORUS. 

low  solution  with  water.  This  solution  is  decomposed  about  176°,  and  a  flocculent 
yellow  matter  subsides,  which  is  a  hydrate  of  the  oxide  of  phosphorus,  nearly  inso- 
luble in  water.  This  compound  abandons  its  combined  water,  when  dried  in  vacuo 
over  sulphuric  acid,  or  when  cooled  below  32°;  when  the  water  separates  as  ice,  and 
oxide  of  phosphorus  remains  perfectly  pure. 

The  oxide  of  phosphorus  is  a  powder  of  a  canary  yellow  colour,  denser  than  water, 
and  soluble  neither  in  water,  alcohol,  nor  ether.  It  may  be  kept  in  dry  air  without 
change.  It  resists  a  temperature  of  570°  without  decomposition,  but  assumes  a 
lively  red  colour;  and  does  not  take  fire  in  the  air  till  heated  a  little  above  the 
boiling  point  of  mercury.  This  oxide  absorbs  dry  ammoniacal  gas,  and  appears  to 
form  feeble  combinations  with  the  fixed  alkalies.  Leverrier  assigns  to  its  hydrate 
the  composition  P20-{-2HO,  and  to  its  phosphate,  2P20+3P05. 

HYPOPHOSPHOROUS    ACID. 

Eq.  40  or  500;  PO;  not  isolable.  Formula  of  a  Hypophosphite,  MO.PO  +  2HO. 

This  acid  was  discovered  in  1816  by  Dulong  (Annal.  de  Ch.  et  de  Ph.  ii.  141). 
It  was  obtained  by  the  action  of  water  upon  the  phosphide  of  barium,  of  which  the 
phosphorus  of  one  portion  oxidates  and  becomes  the  acid  in  question,  at  the  expense 
of  the  water,  while  the  phosphorus  of  another  portion,  combining  with  the  hydrogen 
of  the  water,  produces  phosphuretted  hydrogen  gas.  Rose  prepares  the  same  hypo- 
phosphite  of  baryta  by  boiling  phosphorus  in  a  solution  of  caustic  baryta,  till  all 
the  phosphorus  disappears  and  the  vapours  have  no  longer  the  smell  of  garlic  (H. 
Rose,  sur  les  Hypophosphites,  Annal.  de  Ch.  et  de  Ph.  xxxviii.  258).  Wurtz  uses 
sulphide  of  barium.  To  separate  the  hypophosphorous  acid  from  the  baryta,  diluted 
sulphuric  acid  is  added,  which  precipitates  the  latter.  To  remove  again  the  excess 
of  sulphuric  acid  unavoidably  added,  the  acid  liquid  is  saturated  with  oxide  of  lead, 
which  forms  a  soluble  hypophosphite  of  lead  and  an  insoluble  sulphate  of  lead.  The 
latter  is  separated  by  filtration,  and  the  lead  thrown  down  from  the  filtrate  by  a 
stream  of  hydrosulphuric  acid  gas.  The  acid  remaining  in  solution  may  be  concen- 
trated with  caution  to  the  consistence  of  a  thick  syrup,  but  affords  no  crystals. 
More  strongly  heated,  the  hydrate  of  hypophosphorous  acid  undergoes  decomposi- 
tion, being  converted  into  phosphoric  acid,  with  the  evolution  of  phosphuretted 
hydrogen  and  a  deposition  of  phosphorus.  The  anhydrous  acid  PO  has  never  been 
obtained,  3  eq.  of  water  being  essential  to  its  composition ;  namely,  1  eq.  as  base, 
and  2  eq.,  which  appear  to  form  elements  of  the  acid  itself  (Wurtz).  Hence  the 
formula  of  the  acid  is  HO.PO  +  2HO;  or,  believing  with  Wurtz,  that  both  the 
oxygen  and  hydrogen,  of  2HO,  are  negative  elements  of  the  acid,  like  the  oxygen 
in  phosphoric  acid,  the  formula  is  HO.PH203,  corresponding  with  the  protohydrate 
of  phosphoric  acid  HO.P05. 

Hypophosphorous  acid  is  colourless,  viscid,  and  sour  to  the  taste.  It  withdraws 
oxygen  from  the  sesquioxide  of  lead,  and  some  other  metallic  oxides.  When  heated 
with  sulphuric  acid  it  changes  the  latter  into  sulphurous  acid,  and  also  produces  a 
deposit  of  sulphur,  a  property  by  which  it  is  distinguished  from  phosphorous  acid, 
the  complete  decomposition  of  sulphuric  acid  not  being  effected  by  the  latter  acid. 
Hypophosphorous  acid  also  decomposes  sulphate  of  copper  in  solution,  producing, 
when  the  temperature  is  only  slightly  raised,  a  solid  insoluble  compound  of  that 
metal  with  hydrogen,  the  hydride  of  copper  discovered  by  M.  Wurtz,  and  at  the 
boiling  point  a  deposit  of  metallic  copper  with  the  evolution  of  hydrogen  gas. 

The  hypophosphites  are  all  soluble  in  water,  and  the  salts  of  the  magnesian 
family,  such  as  those  of  magnesia  and  cobalt,  crystallize  well.  They  are  easily 
obtained  by  decomposing  the  hypophosphite  of  baryta  by  the  soluble  sulphates. 
The  dry  hypophosphites  are  permanent  in  air,  but  their  solutions,  evaporated  by 
heat,  absorb  oxygen.  They  all  contain  2  equivalents  of  water,  which  are  essential 
to  the  constitution  of  a  hypophosphite  (Wurtz,  Anrial.  de  Ch.  et  de  Ph.  3  ser.  vii. 
35;  and  xvi.  190;  also,  H.  Hose,  ib.  viii.  364). 


PHOSPHOROUS   ACID.  317 


PHOSPHOROUS   ACID. 

Eq.  56  or  800;  P03.     Formula  of  a  Phosphite,  2MO.P03 

Preparation.  —  This  acid  is  the  principal  product  of  the  slow  combustion  of 
phosphorus,  but  changes  after  its  formation  into  phosphoric  acid,  from  the  further 
absorption  of  oxygen  from  the  air.  It  may  be  obtained  in  the  anhydrous  condition 
by  burning  phosphorus  with  imperfect  access  of  air.  Berzelius  recommended  for 
this  operation  a  tube  of  glass,  about  10  inches  in  length  and  £  inch  in  diameter, 
which  is  nearly  closed  at  one  end,  an  opening  no  greater  than  a  large  pin-hole  being 
left  there,  and  at  a  distance  of  an  inch  from  this  extremity  the  tube  is  bent  at  an 
obtuse  angle.  A  small  fragment  of  phosphorus  is  introduced  into  the  angle  of  the 
tube,  and  heated  till  it  takes  fire.  It  burns  with  a  pale  greenish  flame,  and  the 
phosphorous  acid  produced  is  carried  along  by  the  feeble  current  of  air,  and  condenses 
in  the  ascending  part  of  the  tube,  as  a  white  powder,  volatile,  but  not  in  the  slightest 
degree  crystalline.  The  phosphorus  must  not  be  so  much  heated  as  to  cause  it  to 
sublime  unchanged.  In  contact  with  air,  phosphorous  acid  is  apt  to  inflame,  from. 
the  heat  occasioned  by  the  condensation  of  moisture,  and  is  converted  into  phosphoric 
acid.  The  phosphorous  acid  of  the  preceding  process  is  immediately  soluble  in 
water,  while  the  phosphoric  acid,  which  sometimes  accompanies  it,  remains  for  a 
short  time  undissolved,  in  the  form  of  white  translucent  flocks. 

Hydrated  phosphorous  acid  is  obtained  by  throwing  a  few  drops  of  water  on  the 
liquid  ter-chloride  of  phosphorus  (PC13),  when  that  compound  evolves  hydrochloric 
acid  gas,  arid  gives  hydrated  phosphorous  acid. 

PC13  and  3HO=|P03  and  3HC1. 

The  hydrated  acid  is  also  obtained  by  the  method  of  Droquet.  Two  or  three 
ounces  of  phosphorus  are  melted  in  a  cylindrical  glass  receiver  or  sealed  tube,  of  10 
or  12  inches  in  length,  and  nearly  an  inch  in  diameter,  and  the  tube  filled  up  with 
water.  This  tube,  which  will  contain  a  column  of  fluid  phosphorus  of  5  or  6  inches 
in  height,  is  then  properly  disposed  in  a  bason  or  bolt-head  of  warm  water,  so  as 
to  retain  the  phosphorous  fluid.  Chlorine  gas  is  conveyed  by  a  quill  tube,  from  a 
flask  in  which  it  is  generated,  to  the  bottom  of  the  fluid  phosphorus,  where  combi- 
nation takes  place  with  ignition,  and  the  chloride  of  phosphorus  is  formed.  This 
chloride  is  dissolved  by  the  water  covering  the  phosphorus,  and  converted  into 
hydrochloric  acid  and  phosphorous  acid.  The  chlorine  must  be  transmitted  very 
slowly  through  the  phosphorus,  as  any  portion  of  that  gas  which  reaches  the  water 
converts  the  phosphorous  into  phosphoric  acid;  and  the  absorption  of  the  chlorine 
by  the  phosphorus  is  most  complete  when  it  is  free  from  any  other  gas.  When  the 
remaining  phosphorus  fixes,  upon  cooling,  the  acid  fluid  may  be  poured  oiF,  and  con- 
centrated by  boiling,  till  it  becomes  syrupy  and  the  volatile  hydrochloric  acid  is 
entirely  expelled. 

Properties.  —  In  its  most  concentrated  state,  the  hydrate  of  phosphorous  acid  con- 
tains three  equivalents  of  water,  and  crystallizes  in  transparent  prisms.  When 
heated,  it  is  resolved  into  hydrated  phosphoric  acid,  and  pure  phosphuretted  hydrogen 
gas,  which  is  not  spontaneously  inflammable  as  so  prepared.  The  solution  of  phos- 
phorous acid  absorbs  oxygen  from  the  air  slowly,  if  concentrated,  but  quickly  when 
dilute.  Like  sulphurous  acid,  it  takes  oxygen  from  the  oxide  of  mercury,  when 
heated  with  it,  and  decomposes  also  the  salts  of  gold  and  silver.  It  is  one  of  the 
more  feeble  acids.  ( 

Phosphite's.  —  The  class  of  phosphites,  which  has  been  examined,  is  bibasic,  that 
is,  they  contain  2  eq.  of  base  to  1  of  phosphorous  acid.  They  also  retain  1  eq.  of 
water,  the  elements  of  which  are  proved  by  Wurtz  to  enter  into  the  constitution  of 
the  acid.  Phosphorous  acid  is  thus  represented  with  5  negative  equivalents  PHQ4, 
like  phosphoric  acid  P06.  Much  information  respecting  the  phosphites  is  contained 
in  the  papers  of  Berzelius.  (Annal.  de  Ch.  et  de  Ph.,  ii.  151,  217,  329,  et  x.  278.) 


318  PHOSPHORUS. 

• 

Analysis  of  phosphorous  and  hypophosphorous  acids.  — The  composition  of  both 
phosphorous  ar,d  hypophosphorous  acid  is  determined  by  adding  nitric  acid  to  their 
solutions,  by  which  they  are  converted  into  phosphoric  acid.  But  the  weight  of 
the  resulting  phosphoric  acid  cannot  be  obtained  by  simply  evaporating  its  solution 
to  dryness,  as  that  acid  retains  an  indefinite  quantity  of  water  in  combination.  It 
is  necessary  to  add  to  the  liquid  a  weighed  quantity  of  oxide  of  lead,  more  than  suf- 
ficient to  neutralize  the  phosphoric  acid  and  what  remains  of  the  nitric  acid.  The 
whole  is  then  evaporated  to  dryness  in  a  platinum  capsule,  and  heated  sufficiently  to 
expel  the  nitric  acid  from  the  nitrate  of  lead  formed.  The  water,  previously  com- 
bined with  the  phosphoric  acid,  is  displaced  by  the  oxide  of  lead,  arid  escapes,  leaving 
only  phosphate  of  lead  with  the  excess  of  oxide  of  lead.  This  residue  is  weighed, 
and  the  original  weight  of  oxide  of  lead  is  deducted  from  it  to  obtain  the  weight  of 
dry  phosphoric  acid.  The  composition  of  phosphoric  acid  being  known  (32  phos- 
phorus and  40  oxygen),  the  quantity  of  phosphorus  in  the  phosphoric  acid  of  the 
experiment  is  obtained  by  a  simple  calculation. 

Further,  if  a  stream  of  chlorine  gas  be  transmitted  through  a  solution  of  hypo- 
phosphorous  acid,  it  is  converted  into  phosphoric  acid  by  the  oxygen  of  water  which 
is  decomposed.  The  chlorine  uniting  with  the  hydrogen  of  the  water,  at  the  same 
time,  and  becoming  hydrochloric  acid,  the  quantity  of  the  latter  acid  produced  sup- 
plies a  measure  of  the  oxygen  required  to  convert  the  hypophosphorous  acid  into 
phosphoric  acid. 

The  composition  of  phosphorous  acid  may  also  be  deduced  from  the  analysis  of 
terchloride  of  phosphorus,  which  can  be  made  very  exactly.  One  hundred  grains 
of  that  liquid  compound  being  mixed  with  water  in  a  flask,  it  is  instantaneously 
converted  into  hydrochloric  and  phosphorous  acid;  and  by  the  addition  of  a  little 
nitric  acid  the  latter  acid  is  changed  into  phosphoric  acid.  The  chloride  of  silver, 
precipitated  by  a  solution  of  nitrate  of  silver  added  in  excess  to  the  acid  liquid,  will 
weigh  310.85  grains,  and  contains  76.85  grains  of  chlorine.  Hence  100  grains  of 
terchloride  of  phosphorus  contain  76.85  grains  of  chlorine,  and  the  remaining  23.14 
grains  is  phosphorus.  But  these  numbers  are  in  the  proportion  32  phosphorus  and 
106.5  chlorine,  or  1  eq.  of  the  former,  and  3  eq.  of  the  latter;  giving  PC13  as  the 
composition  of  the  terchloride  of  phosphorus.  Finally,  as  phosphorous  acid  is 
formed  from  the  terchloride  of  phosphorus,  by  replacing  the  chlorine  by  an  equiva- 
lent quantity  of  oxygen,  it  follows  evidently  that  the  composition  of  phosphorous 
acid  is  P03. 

PHOSPHORIC   ACID. 

Eq.  72  or  900 ;  P05 ;  forms  three  hydrates  and  three  classes  of  salts  : 

Formula  of  a  Monobasic  phosphate,  or  Metaphosphate MO.P05 

"         "       Bibasic  phosphate,  or  Pyrophosphate  2M 0. P05 

"         "       Tribasic  phosphate,  or  Phosphate 3MO.P05 

Preparation. — To  obtain  this  acid  in  a  state  of  purity,  a  convenient  process  is  to 
set  fire  to  about  a  drachm  of  phosphorus  upon  a  little  metallic  capsule,  placed  in  the 
centre  of  a  large  stone-ware  plate,  and  immediately  cover  it  by  a  dry  bell  jar  of  the 
largest  size.  The  phosphorus  is  converted  into  white  flakes  of  phosphoric  acid, 
which  are  retained,  with  very  little  loss,  within  the  bell  jar,  and  fall  upon  the  plate 
like  snow. 

The  process  may  be  made  a  continuous  one,  and  a  large  quantity  of  phosphoric 
acid  prepared  by  the  arrangement  of  figure  146.  The  phosphorus  is  burned  within 
a  large  glass  balloon  A,  having  three  tubulures.  which  has  been  well  dried  before- 
hand. The  cork  of  the  upper  tubulure  is  traversed  by  a  long  tube,  a  b,  open  at 
both  ends,  and  about  half  an  inch  in  diameter,  and  which  descends  to  about  the 
centre  of  the  globe.  A  little  capsule  of  platinum  or  porcelain  v  is  attached,  by 
means  of  platinum  wires,  below  the  lower  opening  of  this  tube.  To  the  second 
fcnbulure  d  a  drying  tube  C,  containing  pumice  soaked  in  oil  of  vitriol,  is  attached; 


PHOSPHORIC   ACID. 


319 


It  is  thus  ob- 


and  to  the  third  tubulure  g  a  somewhat  wide  bent  tube,  g  h,  of  which  the  other 
extremity  descends  into  a  well-dried  bottle  B.  This  last  vessel  is  placed  in  com- 
munication, by  means  of  the 

tube  k  Z,  with  any  aspirating  FIG.  146. 

apparatus,  by  means  of  which 
a  continuous  current  of  air  is 
determined,  which  penetrates 
by  the  tube  C,  where  it  is 
dried,  and  traverses  the  whole 
apparatus.  A  fragment  of 
phosphorus  is  now  dropt  upon 
the  capsule  u,  by  the  tube  a  b, 
lighted  by  a  hot  wire,  and  the 
upper  opening  a  then  closed 
by  a  cork.  When  the  com- 
bustion is  completed,  another 
fragment  of  phosphorus  is 
added,  always  taking  care  to 
dry  the  fragment  carefully 
with  filter  paper  before  its  in-  J 
troduction.  The  phosphoric  H 
acid  produced  is  partly  depo- 
sited in  the  globe  A,  and  partly  carried  forward  into  the  bottle  B. 
tained  quite  anhydrous. 

The  dry  phosphoric  acid  is  distinguished  by  the  same  shade  of  white,  absence  of 
crystallization,  and  perfect  opacity,  as  solid  carbonic  acid.  Exposed  for  a  few 
minutes  to  the  air,  it  deliquesces ;  and  when  the  solid  acid  is  collected  in  a  wine- 
glass, and  a  few  drops  of  water  are  thrown  upon  it,  it  is  converted  into  a  hydrate 
with  explosive  ebullition,  from  the  heat  evolved.  The  anhydrous  acid  is  perfectly 
fixed,  unless  in  the  presence  of  aqueous  vapour,  when  it  sublimes  away,  probably  in 
the  state  of  a  hydrate. 

Phosphorus  may  likewise  be  oxidated  by  means  of  nitric  acid.  In  this  operation, 
the  fuming  nitric  acid  should  be  diluted  with  an  equal  bulk  of  water,  to  avoid  acci- 
dents from  the  violent  action  of  the  acid,  which  may  cause  the  phosphorus  to  be 
projected  in  a  state  of  ignition ;  the  diluted  acid  is  boiled  upon  the  phosphorus,  and 
being  afterwards  evaporated  to  dryness,  it  yields  a  hydrated  phosphoric  acid. 

Phosphoric  acid  is  also  obtained  in  large  quantity  from  calcined  bones,  which  are 
reduced  to  a  fine  powder  and  mixed  with  4-5ths  of  their  weight  of  oil  of  vitriol,  pre- 
viously diluted  with  4. or  5  times  its  bulk  of  water,  as  in  the  preparation  of  phos- 
phorus (page  313).  Carbonate  of  ammonia  is  then  added  to  the  filtered  solution  of 
phosphoric  acid,  and  the  resulting  phosphate  of  ammonia  being  evaporated  to  dry- 
ness  and  heated  to  low  redness  in  a  platinum  crucible,  a  hydrated  phosphoric  acid 
remains,  in  a  fused  state,  which  is  known  as  glacial  phosphoric  acid,  from  its  resem- 
blance to  ice. 

To  exhibit  many  of  its  properties,  phosphoric  acid  must  be  first  dissolved  in 
water,  when  the  compound  is  found  to  be  marked  by  an  inconstancy  and  variable 
ness  in  its  characters,  most  unusual  in  a  strong  acid.  This  arises  from  the  circum- 
stance that  it  is  not  actual  phosphoric  acid  which  dissolves  in  water,  any  more  than 
it  is  true  sulphuric  acid  which  dissolves  in  water  when  oil  of  vitriol  is  added  to  that 
fluid.  It  is  a  hydrate  of  both  acids,  which  is  soluble ;  the  phosphate  of  water  in 
the  one  case  and  the  sulphate  of  water  in  the  other.  But  the  phosphoric  acid  differs 
from  the  sulphuric,  in  a  singular  and  almost  peculiar  capacity  to  form  three  different 
salts  of  water,  instead  of  one  only;  and  these  three  phosphates  of  water  are  all 
soluble  without  change,  and  exhibit  properties  so  different,  that  they  might  be  sup- 
posed to  contain  three  different  acids.  When  the  dry  acid  from  the  combustion  of 
phosphorus  is  thrown  into  water,  it  produces  a  mixture,  in  variable  proportions,  of 


320  1HOSPHORUS. 

the  three  hydrates ;  but  each  of  them  may  be  had  separately,  and  in  a  state  of 
purity,  by  a  particular  process.  [Sec  Supplement,  p.  790.] 

Ter hydrate,  or  tribasic  phosphate  of  wafer,  3110  4-  P05-  —  The  common  phos- 
phate of  soda  of  pharmacy  may  be  had  recourse  to  for  all  the  hydrates  of  phosphoric 
acid  ]  but  it  should  be  first  dissolved  and  crystallized  anew  to  purify  it.  To  a  warm 
solution  of  the  pure  phosphate  of  soda  in  a  bason,  a  solution  of  acetate  of  lead  in 
distilled  water  is  added,  so  long  as  it  occasions  a  precipitate ;  the  phosphate  of  soda 
requires  rather  more  than  an  equal  weight  of  acetate  of  lead.  The  dense  insoluble 
phosphate  of  lead  which  precipitates,  is  washed,  and  being  afterwards  suspended  in 
cold  water,  is  decomposed  by  a  stream  of  hydrosulphuric  acid  gas  sent  through  it. 
The  liquid  may  then  be  warmed,  to  expel  the  excess  of  hydrosulphuric  acid,  and 
filtered  from  the  black  sulphide  of  lead  :  it  is  very  sour,  and  contains  the  terhydrate 
of  phosphoric  acid.  The  characters  of  this  acid  solution  are,  to  give  a  yellow  pi  j- 
cipitate  with  nitrate  of  silver,  to  give  a  granular  crystalline  precipitate  with  ammonia 
and  sulphate  of  magnesia  —  the  phosphate  of  magnesia  and  ammonia,  to  yield  the 
common  phosphate  of  soda  when  neutralized  with  carbonate  of  soda,  to  form  salts 
which  have  invariably  3  eq.  of  base  to  1  of  phosphoric  acid,  and  to  be  unalterable 
by  boiling  its  solution  or  keeping  it  for  any  length  of  time.  The  class  of  salts  which 
this  hydrate  forms  are  the  old  phosphates,  which  have  long  been  known,  and  it  is 
convenient  to  allow  them  to  be  particularly  distinguished  as  the  phosphates  or  the 
common  phosphates. 

Deuto-hydrate  of  phosphoric  acid,  or  bibasic  phosphate  of  water,  2HO  +  P05. — 
Dr.  Clark^first  discovered  that  when  the  phosphate  of  soda  is  heated  to  redness,  it  is 
completely  changed,  and  after  being  dissolved  in  water  affords  crystals  of  a  new  salt, 
which  he  named  the  pyrophosphate  of  soda, — an  observation  which  led  to  interesting 
results.  (Ed.  Journ.  of  Science,  vol.  vii.  p.  298,  1826;  or  Annal.  de  Ch.  et  de 
Phys.  xli.  276.)  If  a  solution  of  this  salt,  which  it  is  not  necessary  to  crystallize, 
be  precipitated  by  acetate  of  lead,  the  insoluble  salt  of  lead  washed  and  decomposed 
by  hydrosulphuric  acid,  as  before,  an  acid  liquor  is  obtained  which  contains  the 
deuto-hydrate  of  phosphoric  acid.  It  must  not  be  warmed  to  expel  the  excess  of 
hydrosulphuric  acid,  but  be  left  in  a  shallow  bason  for  twenty-four  hours  to  permit 
the  escape  of  that  gas.  This  acid,  when  neutralized  with  carbonate  of  soda,  gives 
Dr.  Clark's  pyrophosphate  of  soda.  It  also  gives  a  white  precipitate  with  nitrate 
of  silver ;  all  the  salts  which  it  forms  have  uniformly  two  eq.  of  base.  They  were 
named  the  pyrophosphates,  and  since  that  term  has  come  into  use,  it  is  not  likely  to 
be  superseded  by  the  systematic,  but  rather  inconvenient  designation  of  bibasic 
phosphates.  A  dilute  solution  of  the  deuto-hydrate  of  phosphoric  acid  may  be  pre- 
served for  a  month  without  sensible  change,  but  when  the  solution  is  exposed  for 
some  time  to  a  high  temperature,  it  passes  entirely  into  the  terhydrate. 

Protohydrate  of  phosphoric  acid. — If  the  biphosphate  of  soda  be  heated  to  red- 
ness, a  salt  is  formed,  which  treated  in  a  similar  manner  with  the  last,  gives  an  acid 
liquid,  containing  the  protohydrate  of  phosphoric  acid.  To  prepare  the  biphosphate 
itself,  a  solution  of  the  terhydrate  of  phosphoric  acid  is  added  to  a  solution  of  com- 
mon phosphate  of  soda,  till  it  is  found  that  a  drop  of  the  latter  is  no  longer  preci- 
pitated by  chloride  of  barium.  The  biphosphate  of  soda,  which  is  now  in  solution, 
can  only  be  crystallized  in  cold  weather.  The  glacial  phosphoric  acid  also  is  in 
general  almost  entirely  the  protohydrate.  This  hydrate  is  characterized  by  pro- 
ducing a  white  precipitate  in  solution  of  albumen,  which  is  not  disturbed  by  the 
other  hydrates,  and  in  solutions  of  the  salts  of  earths  and  metallic  oxides,  precipi- 
tates which  are  remarkable  semifluid  bodies,  or  soft  solids,  without  crystallization. 
All  these  salts  contain  only  one  eq.  of  base  to  one  of  acid,  like  the  protohydrate  of 
the  acid  itself.  The  name  metaphosphates  was  applied  to  the  class  by  myself,  to 
mark  the  cause  of  the  retention  of  peculiar  properties  by  their  acid,  when  free  and 
in  solution  ;  namely,  that  it  was  not  then  simply  phosphoric  acid,  but  phosphoric  acid 
together  with  water.  (Researches  on  the  Arseniates,  Phosphates,  and  Modifications 
of  Phosphoric  Acid,  Phil.  Trans.  1833,  p.  253 ;  or  Phil.  Mag.  3d  ser.,  vol.  iv.  p. 


PHOSPHATES.  321 

401.)  This  is  the  least  stable  of  the  hydrates  of  phosphoric  acid,  being  converted 
rapidly,  by  the  ebullition  of  its  solution,  into  the  terhydrate.  If  the  terms  meta- 
phnsphoric  acid  and  pyrophosphoric  acid  are  employed  at  all,  it  is  to  be  remembered 
that  they  are  applicable  to  the  proto  and  deutohydrates,  and  not  to  the  acid  itself, 
which  is  the  same  in  all  the  hydrates.  But  to  prevent  the  chance  of  misconception, 
ipetaphosphate  of  water  and  pyrophosphate  of  water  might  be  substituted  for  the 
former  terms. 

A  solution  of  the  terhydrate  of  phosphoric  acid,  evaporated  in  vacuo  over  sulphuric 
acid,  crystallizes  in  thin  plates,  which  are  extremely  deliquescent.  The  deutohydrate 
has  also  been  obtained  in  crystals.  When  heated  to  400°,  the  terhydrate  loses  a 
portion  of  water,  and  becomes  a  mixture  of  the  deuto  and  protohydrates ;  and  by 
heating  it  to  redness  for  some  time,  the  proportion  of  water  may  be  reduced  to  one 
equivalent,  or  perhaps  even  less  than  this;  and  such  is  the  composition  of  glacial 
phosphoric  acid.  But  at  that  high  temperature  much  of  the  hydrated  phosphoric 
acid  passes  off  in  vapour.  The  solution  of  phosphoric  acid  is  not  poisonous,  nor 
when  concentrated  does  it  act  as  a  cautery,  but  it  injures  the  teeth  from  its  property 
of  dissolving  phosphate  of  lime.  The  soluble  phosphates,  which  are  not  acid,  give 
a  precipitate  with  chloride  of  barium,  which  is  the  phosphate  of  baryta.  This 
phosphate,  in  common  with  all  the  insoluble  phosphates,  is  dissolved  by  nitric  acid, 
hydrochloric  acid,  and  even  acetic  acid,  a  property  by  which  it  is  distinguished  from 
sulphate  of  baryta.  A  solution  of  phosphate  of  lime  in  phosphoric  acid  has  been 
prescribed  in  rickets,  a  disease  which  indicates  a  deficiency  of  earthy  phosphates  in 
the  system.  The  phosphate  of  soda,  also,  is  given  as  a  mild  aperient ;  its  taste  is 
saline,  but  not  disagreeably  bitter. 

Phosphates.  —  The  formation  of  three  classes  of  phosphates  from  the  three  basic 
hydrates  of  phosphoric  acid,  affords  an  excellent  illustration  of  the  formation  of 
compounds  by  substitution ;  the  quantity  of  fixed  base,  such  as  soda,  with  which 
phosphoric  acid  combines  in  the  humid  way,  being  entirely  regulated  by  the  propor- 
tion of  water  previously  in  union  with  the  acid,  which  is  simply  replaced  by  the  fixed 
base.  Thus,  the  protohydrate  of  phosphoric  acid  combines  with  no  more  than  one, 
and  the  deutohydrate  with  no  more  than  two  equivalents  of  soda,  although  a  larger 
quantity  of  alkali  be  added  to  it.  The  excess  of  alkali  remains  free.  Again,  sup- 
posing an  equivalent  quantity  of  the  terhydrate  of  phosphoric  acid  in  solution,  and 
one  equivalent  of  soda  added  to  it,  one  equivalent  only  of  water  is  displaced,  and 
two  retained,  and  a  phosphate  formed,  containing  one  of  soda  and  two  of  water  as 
bases ;  the  salt  already  adverted  to  under  its  old  name  of  biphcsphate  of  soda.  Let 
a  second  equivalent  of  soda  be  added  to  this  salt,  and  a  second  basic  equivalent  of 
water  is  displaced,  and  a  tribasic  salt  produced,  containing  two  of  soda  and  one  of 
water  as  bases,  which  is  the  common  phosphate  of  soda  of  pharmacy.  A  third 
equivalent  of  soda  added  to  the  last  salt  displaces  the  last  remaining  equivalent  of 
basic  water,  and  a  tribasic  phosphate  is  formed,  of  which  the  whole  three  equivalents 
of  base  are  soda,  and  which  has  the  name  of  subphosphate  of  soda.  But  this  last 
salt  can  unite  with  no  more  soda.  The  same  three  salts  may  be  formed  by  means 
of  the  tribasic  phosphate  of  water,  in  another  manner.  That  acid  hydrate  decom- 
poses chloride  of  sodium,  but  only  to  a  certain  extent,  expelling  hydrochloric  acid, 
so  as  to  acquire  one  of  soda,  and  becoming  2HO.NaO-fPO5,  or  the  biphosphate  of 
soda  already  referred  to ;  the  same  acid  hydrate  applied  to  the  carbonate  or  the 
acetate  of  soda,  can  assume  two  proportions  of  soda,  displacing  twice  as  much  of  the 
weaker  carbonic  and  acetic  acids,  as  of  the  hydrochloric  acid,  and  so  becomes 
H0.2NaO  +  P05,  or  the  common  phosphate  of  soda;  and  the  same  acid  hydrate 
applied  to  the  hydrate  of  soda  (caustic  soda,)  assumes  three  of  soda,  and  becomes 
3NaO  +  P05,  or  the  subphosphate  of  soda. 

From  soluble  tribasic  phosphates,  such  as  those  mentioned,  insoluble  salts  may  be 
precipitated,  which  are  likewise  tribasic,  by  adding  solutions  of  most  metallic  salts 
Thus  one  equivalent  of  the  common  phosphate  of  soda,  added  to  the  nitrate  of 
silver  in  excess,  decomposes  3  equivalents  of  it,  and  produces  the  yellow  tribasic 


322  PHOSPHORUS. 

phosphate  of  silver,  as  explained  in  the  following  diagram,  in  which  the  name  of  a 
substance  is  understood  to  express  one  equivalent  of  it,  and  the  figures,  numbers  of 
equivalents : — 

Before  decomposition.  After  decomposition. 

™       Ul      ("2  Soda • 7 2  Nitrate  of  soda 

Phosphate    \      mter __y/7  Nitrate  Qf 

of  soda     |     Phosphoric  acid. 

C  2  Nitric  acid. 
8  Nitrate     \      Nitric  acid 

(3  Oxide  of  silver A     Phosphate  of  silver 

(Tribasic  phosp.  silv.) 

Here,  then,  is  exact  mutual  decomposition,  but  it  is  attended  with  a  phenomenon 
which  does  not  occur  when  other  neutral  salts  decompose  each  other.  The  liquid 
does  not  remain  neutral,  but  becomes  highly  acid  after  precipitation ;  the  reason  is, 
that  one  of  the  new  products  is  the  nitrate  of  water,  or  hydrated  nitric  acid ;  and 
consequently  the  products,  although  neutral  in  composition,  are  not  neutral  to  test 
paper. 

The  pyrophosphate  of  soda,  which  is  bibasic,  decomposes,  on  the  other  hand,  two 
proportions  of  nitrate  of  silver,  and  gives  a  pyrophosphate  or  bibasic  phosphate  of 
silver,  which  is  a  white  precipitate ;  thus  — 

Before  decomposition.  After  decomposition. 

Pyrophosphate  C  2  Soda —.2  Nitrate  of  soda 

of  soda        {     Phosphoric  acid ^>^ 

2  Nitrate  of      f  2  Nitric  acid '^^ 

silver         |  2  Oxide  of  silver \  JTW08-  °f  ***• 

(Bibasic  phos.  sil.) 

Here  there  is  no  salt  of  water  among  the  products,  and  consequently  the  liquid  is 
neutral  after  precipitation. 

The  metaphosphate  of  soda,  which  is  monobasic,  like  the  sulphates,  nitrates  and 
other  familiar  salts,  decomposes  like  these  but  one  proportion  of  nitrate  of  silver,  and 
forms  a  white  precipitate ;  thus  — 

Before  decomposition.  After  decomposition. 

Metaphosph.  f  Soda -^  Nitrate  of  soda 

of  soda       (  Phosphoric  acid. 
Nitrate  of      (  Nitric  acid 

silver          (  Oxide  of  silver ^X  Metaphosphate  of  silv. 

(Monobasic  phos.  silv.) 

If  acetate  or  nitrate  of  lead  be  substituted  for  nitrate  of  silver  in  these  decompo- 
sitions, a  tribasic,  bibasic,  or  monobasic  salt  of  lead  is  obtained  in  the  same  manner ; 
and  these  salts,  again,  decomposed  by  hydrosulphuric  acid  gas,  afford  respectively 
the  terhydrate,  deutohydrate,  and  protohydrate  of  phosphoric  acid.  The  statement 
of  the  decomposition  of  the  metaphosphate  of  lead  by  hydrosulphuric  acid  will  be 
sufficient  to  explain  how  a  hydrate  of  phosphoric  acid  comes  to  be  formed  in  all 
these  cases : — 

Before  decomposition.  After  decomposition. 

Metaphosph.  f  ^osphoric  acid -     ^Metaphosph.  of  water 

of  lead       j  OxvSen ?/    (Protohydr.  of  phos.  ac.) 

(Lead <  / 


Hydrosulph .  C  Hydrogen 

acid          (Sulphur ^X  Sulphide  of  lead. 


PHOSPHATES.  323 

It  will  be  observed  that  the  hydrosulphuric  acid  forms  1  equivalent  of  water,  at 
the  same  time  that  it  throws  down  the  sulphide  of  lead.  In  this  phosphate  of  lead, 
there  is  only  1  equivalent  of  oxide  of  lead,  and  consequently  only  1  equivalent  of 
water  is  formed ;  but  if  there  were  2  or  3  equivalents  of  oxide,  there  would  be  2  or 
3  equivalents  of  water  formed  and  conveyed  to  the  acid;  or  the  phosphoric  acid  is 
always  left  in  combination  with  as  many  equivalents  of  water  as  it  previously  pos- 
sessed of  oxide  of  lead.  Thus  the  different  hydrates  of  phosphoric  acid  are  obtained 
from  the  decomposition  of  the  corresponding  phosphates  of  lead. 

In  no  decomposition  of  this  kind  is  there  any  transition  from  one  class  of  phos- 
phates into  another,  because  the  decompositions  are  always  mutual,  and  the  products 
of  a  neutral  character.  Hence  an  argument  for  retaining  the  trivial  names,  common 
phosphates,  pyrophosphates,  and  metaphosphates,  for  there  is  no  changing,  in  de- 
compositions by  the  humid  way,  from  one  to  the  other,  and  the  salts  comport  them- 
selves so  far  quite  as  if  they  had  different  acids.  The  circumstances  may  now  be 
noticed  in  which  a  transition  from  the  one  class  to  the  other  does  occur : — 

1st.  —  Changes  without  the  intervention  of  a  high  temperature.  When  solutions 
of  the  metaphosphate  and  pyrophosphate  of  water  are*  warmed,  they  pass  gradually 
into  the  state  of  common  phosphate,  combining  with  an  additional  quantity  of 
water;  and  the  metaphosphate  of  water  appears  then  to  become  at  once  common 
phosphate,  without  passing  through  the  intermediate  state  of  hydration  of  the  pyro- 
phosphate. The  metaphosphate  of  baryta  also,  which  is  an  insoluble  salt,  is  gra- 
dually dissolved  in  boiling  water,  and  becomes  common  phosphate  by  assuming  2 
eq.  of  basic  water.  The  easy  transition  from  the  one  class  of  phosphates  to  the 
other,  then  witnessed,  forbids  the  supposition  that  they  contain  different  acids,  or 
different  isomeric  modifications  of  phosphoric  acid.  Indeed,  it  might  as  well  be 
supposed  that  in  the  protoxide  and  sesqui-oxide  of  iron,  the  metal  exists  in  different 
isomeric  conditions,  because  these  oxides  possess  peculiar  properties,  and  combine  in 
different  proportions  with  the  same  acid.  Iron  in  its  two  oxides  gives  rise  to  differ- 
ent compounds,  because  they  are  formed  by  substitution ;  and  phosphoric  acid  in 
its  three  hydrates  gives  rise  to  different  compounds,  from  the  same  cause.  The 
degree  of  oxidation  of  the  iron  and  the  degree  of  hydration  of  the  acid  are  anterior 
conditions,  due  to  the  special  unexplained  affinities  with  which  each  element  or  com- 
pound is  invested.  It  is  remarkable  that  pyrophosphates  of  potassa  and  of  ammonia 
exist  in  solution,  and  perfectly  stable,  but  not  in  the  dry  state.  These  salts  do  not 
crystallize.  The  pyrophosphate  of  ammonia,  indeed,  when  allowed  to  evaporate 
spontaneously,  appears  to  crystallize,  but  in  the  act  of  becoming  solid,  it  passes  into 
common  phosphate  (the  biphosphate  of  ammonia,  2HO.NH40-fP05). 

2d. — Changes  with  the  intervention  of  a  high  temperature.  If  a  single  equivalent 
of  phosphoric  acid,  anhydrous,  or  in  any  state  of  hydration,  be  calcined  at  a  tempe- 
rature which  may  fall  short  of  a  red  heat  (1°),  with  1  equivalent  of  soda  or  its  car- 
bonate, the  metaphosphate  of  soda  will  be  formed ;  (2°)  with  2  equivalents  of  soda 
or  its  carbonate,  the  pyrophosphate  of  soda  will  be  formed;  and  (3°)  with  3  equi- 
valents of  soda  or  its  carbonate,  a  common  phosphate  of  soda  will  be  formed. 
Hence,  the  formation  of  none  of  these  classes  is  peculiarly  the  effect  of  a  high  tem- 
perature. Again,  a  tribasic  phosphate,  containing  one  or  two  equivalents  of  a 
volatile  base,  such  as  water  or  ammonia,  loses  the  volatile  base,  when  ignited,  and 
the  acid  remains  in  combination  with  the  fixed  base.  Hence,  common  phosphate 
of  soda  (H0.2NaO-f  P05)  is  converted  by  heat  into  pyrophosphate  (2NaO-f  P05). 
the  original  observation  of  Dr.  Clark ;  and  the  biphosphate  of  soda  (2HO.NaO  +  P05) 
into  metaphosphate  of  soda  (NaO  +  P05).  The  acid  remains  in  combination  with 
the  fixed  base,  and  the  salt  produced  may  be  dissolved  in  water  without  assuming 
basic  water. 

The  metaphosphate  of  soda  is  susceptible  of  a  remarkable  conversion,  by  the 
agency  of  a  certain  temperature,  and  exhibits  a  change  of  nature,  without  a  change 
of  composition,  such  as  often  occurs  in  organic  compounds,  but  rarely  admits  of  so 
satisfactory  an  explanation.  This  particular  salt,  in  common  with  all  the  other 


324  PHOSPHORUS. 

phosphates,  combines  with  water,  which  becomes  attached  to  the  salt,  in  the  state  of 
constitutional  water,  or  water  of  crystallization.  The  inetaphosphate  of  soda,  so 
hydrated,  when  dried  at  212°,  retains  1  equivalent  of  water,  but  that  water  is  not 
basic,  for,  on  dissolving  the  salt  again,  it  is  found  still  to  be  a  inetaphosphate.  But 
let  this  hydrated  inetaphosphate  be  heated  to  300°,  and  without  losing  anything,  it 
changes  completely,  and  becomes  a  pyrophosphate,  —  the  water  which  was  constitu- 
tional before,  being  now  basic.  The  formulae  of  the  salt  in  its  two  states  exhibit  to 
the  eye  the  nature  of  the  internal  change  which  occurs  in  it : 

1. — Hydrated  metaphosphate  of  soda NaO.P05+HO, 

'    2. — Pyrophosphate  of  soda  and  water NaO.HO  +  P05. 

Phosphates  of  the  form  3MO-f2P05.  —  The  recent  investigations  of  Fleitmann 
and  Henneberg  establish  the  existence  of  two  new  classes  of  phosphates,  intermediate 
between  the  monobasic  and  bibasic  classes.  The  soda-salt  of  the  preceding  formula 
is  produced  by  fusing  together,  in  a  platinum  crucible,  100  parts  of  anhydrous 
pyrophosphate  of  soda  and  76.87  parts  of  metaphosphate  of  soda :  the  white  crys- 
talline mass  which  results  is"  reduced  to  powder,  and  quickly  exhausted  with  water  j 
for,  on  long  digestion,  the  ordinary  phosphates  are  obtained.  The  soda-salt  is  soluble 
in  about  twice  its  weight  of  cold  water,  and  has  a  faint  alkaline  reaction.  It  gives, 
by  precipitation  with  nitrate  of  silver  and  with  phosphate  of  magnesia,  salts  corres- 
ponding with  -the  soda-salt,  and  which  have  not  the  properties  of  a  mixture  of  pyro- 
phosphate and  metaphosphate. 

Phosphates  of  the  form  6MO-f5P05.  —  The  soda-salt  was  obtained  by  fusing 
together  100  parts  by  weight  of  pyrophosphate  of  soda  and  307.5  of  metaphosphate. 
The  solution  is  by  no  means  stable,  but  gives,  when  freshly  prepared,  a  precipitate 
in  nitrate  of  silver,  which  is  readily  soluble  in  excess  of  the  soda-salt,  and  possesse? 
the  composition,  when  fused,  of  6AgO  +  5P05.  (Liebig's  Annalen,  Ixv.  304.) 

Modifications  of  metaphosphoric  acid.  —  The  metaphosphates  already  described 
are  prepared  from  the  monobasic  phosphate  of  soda  in  the  vitreous  condition  ]  this 
phosphate,  when  cooled  immediately  from  a  state  of  fusion,  remaining  a  transparent, 
colourless  glas».  But  if  this  glassy  phosphate  be  cooled  very  slowly,  a  beautiful 
crystalline  mass  is  obtained.  On  dissolving  it  in  a  small  quantity  of  hot  water,  the 
liquid  divides  into  two  strata,  the  more  considerable  one  containing  the  crystalline 
salt,  and  the  other  a  portion  of  unaltered  metaphosphate  of  soda.  The  vitreous 
metaphosphate,  and  all  the  salts  derived  from  it,  are  remarkable  for  not  crystallizing, 
but  form  liquid  or  semi-liquid  viscid  hydrates.  But  the  crystalline  metaphosphate 
of  soda  is  described  as  giving  beautiful  crystals  of  the  triclinometric  system,  con- 
taining water  of  crystallization.  Its  solution  is  neutral,  and  has  a  cooling,  pure, 
saline  taste,  while  the  vitreous  metaphosphate  of  soda  is  insipid.  It  is  rapidly  con- 
verted into  the  acid  common  phosphate  by  boiling.  The  corresponding  silver-salt  is 
obtained  by  adding  nitrate  of  silver  to  a  tolerably  concentrated  solution  of  the  soda- 
vsalt.  It  is  white,  crystalline,  and  is  represented  by  the  formula  3(  AgO.P05)  -f  2HO. 

Phosphates  were  obtained  by  Mr.  Maddrell,  by  adding  the  solution  of  sulphates 
of  magnesia,  nickel,  copper,  soda,  lime,  baryta,  alumina,  to  an  excess  of  phosphoric 
acid,  evaporating,  to  expel  the  sulphuric  acid,  and  heating  to  upwards  of  600° ;  in 
the  form  of  a  crystalline  granular  substance,  which  were  all  monobasic.  They  are 
all  anhydrous,  insoluble  in  water  and  diluted  acids,'  but  generally  decomposed  by 
concentrated  sulphuric  acid,  and  appear  to  form  a  class  of  metaphosphates  different 
from  the  preceding  two.  The  magnesian  metaphosphates  of  this  class  have  a  dis- 
position to  combine  wilh  the  corresponding  soda-salt,  when  any  of  that  base  is  present 
in  the  phosphoric  acid  with  which  they  are  ignited.  The  double  salt  of  magnesia 
and  soda  is  represented  by  3(MgO.P05)-f-NaO.POs;  that  of  nickel  and  soda,  by 
6(NiO.P05)  +  NaO.P05).  (Mem.  Chem.  Soc.  iii.  273.) 

The  only  explanation  which  can  be  offered  of  these  modifications  of  the  meta- 
phosphoric acid,  is,  that  they  are  of  a  polymeric  character;  such  as  MO.P06; 
2M0.2P05;  3M0.3P06,  or  perhaps  even  higher  multiples  of  MO.P06.  No  data, 


PHOSPHORIC    ACID.  325 

however,  appear  to  exist  by  which  a  place  in  this  polymeric  series  can  be  ascribed  to 
the  respective  modifications  with  any  degree  of  certainty.  MM.  Fleitmann  and 
Henneberg,  who  have  lately  investigated  the  subject  with  much  ability,  are  disposed 
to  represent  metaphosphoric  acid  by  6M0.6P05 ;  and  certainly  with  this  proportion 
of  base  constant  and  the  phosphoric  acid  variable,  the  other  classes  may  be  consist- 
ently represented :  — 

Common  phosphate '. 6MO  +  2P05 

Pyrophosphate 6MO  +  3P05 

Fleitmann  and  Henneberg's  new  phosphates   -j  5 

Metaphosphate 

The  different  classes  of  phosphates  are  thus  represented  as  all  sex-basic  salts,  with 
a  different  polymeric  acid  in  each,  P20IO,  P3015,  &c.  But  this  theory  does  not  em- 
brace the  modifications  of  metaphosphoric  acid,  n#r  will  it  serve  to  represent  several 
known  double  phosphates ;  such,  for  instance,  as  the  double  pyrophosphate  of  cop- 
per and  soda,  3(2NaO.P05)-h2CuO.P05.  [See  Supplement,  p.  786.] 

Analysis  of  phosphoric  odd  and  of  the  phosphates.  —  Phosphoric  acid  is  pro- 
duced when  the  pentachloride  of  phosphorus  is  thrown  into  water:  — 

PC16  and  5HO=P05  and  5HC1. 

It  may  be  inferred  with  certainty  from  this  decomposition,  that  phosphoric  acid 
contains  5  equivalents  of  oxygen,  in  the  same  manner  as  the  composition  of  phos- 
phorous acid  is  deduced  from  the  decomposition  of  the  terchloride  of  phosphorus  by 
water  (page  318).  The  affinity  of  phosphoric  acid  for  water  is  very  intense,  the 
anhydrous  phosphoric  acid  taking  water  even  from  oil  of  vitriol  and  eliminating 
anhydrous  sulphuric  acid,  at  a  high  temperature.  As  hydrated  phosphoric  acid 
cannot  be  made  anhydrous  by  heat,  the  proportion  of  dry  acid  in  a  solution  of  the 
free  acid  is  determined  by  adding  a  known  weight  of  oxide  of  lead,  evaporating  to 
dryness,  and  heating  the  residue,  as  in  the  case  of  sulphuric  acid.  The  phosphate 
of  lead  formed  being  anhydrous,  the  increase  of  weight  which  the  oxide  of  lead  sus- 
tains represents  exactly  the  weight  of  dry  phosphoric  acyi-  • 

In  determining  the  proportion  of  phosphoric  acid  in  a  salt  of  an  alkaline  or  earthy 
base,  the  acid,  if  not  already  in  the  tribasic  form,  is  first  brought  to  that  condition 
by  boiling  with  a  little  nitric  acid.  1.  The  excess  of  nitric  acid  being  then  neutra- 
lized by  ammonia,  the  phosphate  is  again  dissolved  in  acetic  acid.  If  the  solution 
contains  no  sulphuric  acid  nor  chlorine,  the  phosphoric  acid  may  be  entirely  separated 
by  the  addition  of  nitrate  of  lead,  in  the  form  of  an  insoluble  phosphate  of  lead, 
2PbO.HO.P05,  which  washes  easily,  and  loses  water  and  becomes  pyrophosphate, 
2PbO.P05,  when  calcined  (Heintz).  This  method  is  based  upon  the  insolubility 
of  phosphate  of  lead  in  acetic  acid.  2.  Phosphoric  aoid  may  also  be  thrown  down 
from  the  solution  of  an  alkaline  phosphate,  by  adding  first  carbonate  or  hydrochlorate 
of  ammonia  and  then  sulphate  of  magnesia,  when,  upon  stirring  the  phosphate  of 
magnesia  and  ammonia, 

2MgO.NH4O.P05+  12HO, 

falls  as  a  granular  precipitate.  This  phosphate  must  be  precipitated  in  an  alkaline  solu- 
tion, and  washed  with  water  containing  hydrochlorate  of  ammonia,  as  it  is  very  soluble 
in  acids,  and  even  soluble  in  a  sensible  degree  in  pure  water.  When  ignited  it  loses  its 
volatile  constituents,  and  remains  pyrophosphate  of  magnesia,  2MgO.P05.  3.  The 
phosphoric  acid  not  being  in  combination  with  a  base  which  yields  a  phosphate  insoluble 
in  acetic  acid,  an  addition  is  made  to  the  liquid,  which  may  be  acid,  of  an  excess  of 
the  acetate  of  the  sesqui-oxide  of  iron.  The  phosphate  of  sesqui-oxide  of  iron, 
Fe203.P05,  immediately  separates  as  a  slightly  reddish  yellow  flaky  precipitate, 
which  is  collected  and  washed  upon  a  filter.  This  phosphate  is  dissolved  off  the 
filter  by  a  few  drops  of  hydrochloric  acid,  then  the  salt  of  iron  reduced  to  the  state 
of  protoxide  by  boiling  it  with  sulphite  of  soda,  and  afterwards  the  quantity  of  iroo 


326  PHOSPHORUS. 

ascertained  by  finding  how  much  of  a  solution  of  permanganate  of  potassa  of  known 
composition  is  required  to  peroxidize  the  iron.  The  phosphate  of  iron  being  of 
known  composition,  the  quantity  of  phosphoric  acid  is  calculated  from  the  iron, 
2  eqs.  of  that  metal  being  present  in  the  phosphate  for  1  eq.  of  phosphoric  acid  or 
of  phosphorus;  that  is,  700  parts  iron  representing  900  parts  phosphoric  acid 
(Raewsky  and  Marguerite).  The  acetate  of  sesqui-oxide  of  iron,  which  is  not  per- 
manent, is  best  prepared  extemporaneously  from  solutions  of  100  parts  of  iron-alum 
and  of  98  parts  of  acetate  of  soda  in  equal  quantities  of  water,  of  which  equal 
volumes  are  mixed  at  the  moment  the  acetate  of  iron  is  required. 

In  describing  the  various  classes  of  phosphates,  with  their  relations  to  each  other, 
I  have  been  thus  minute,  partly  because  considerable  explanatory  detail  was  required, 
from  the  extent  of  the  subject,  but  principally  for  the  sake  of  the  light  which  the 
phosphates  throw  upon  the  constitution  of  the  class  of  organic  acids,  and  up6n  the 
function  of  water  in  many  compounds.  Indeed,  phosphoric  acid  is  one  of  the  links 
by  which  mineral  and  organic  compounds  are  connected.  And  it  may  be  reasonably 
supposed  that  it  is  that  pliancy  of  constitution  which  peculiarly  adapts  the  phosphoric, 
above  all  other  mineral  acids,  to  the  wants  of  the  animal  economy. 

PHOSPHORUS  AND  HYDROGEN. 

Solid  hydride  of  phosphorus,  P2H.- — Magnus  formed  a  phosphide  of  potassium 
by  fusing  phosphorus  and  potassium  under  naphtha.  When  this  compound  is 
thrown  into  water,  a  compound  of  phosphorus  and  hydrogen  precipitates  in  the  form 
of  a  yellow  powder.  The  solid  hydride  of  phosphorus  becomes  red  when  exposed 
to  light;  it  does  not  shine  in  the  dark,  nor  take  fire  below  320°  (160°  C.)  It  is 
insoluble  in  water  and  alcohol,  and  is  decomposed  by  alkalies,  with  the  formation 
of  oxide  of  phosphorus,  free  hydrogen,  gaseous  phosphuretted  hydrogen,  and  a 
hypophosphite. 

Phosphuretted  hydrogen  gas;  eq.  19  or  237.5;  PH3.  —  This  gas,  which  is 
remarkable  for^its  occasional  spontaneous  inflammability  in  air,  was  discovered  by 
Gengembre  in  1783,  and  has  been  successively  investigated  by  several  chemists. 
Its  true  nature  was  first  ascertained  by  Rose,  who  proved  it  to  be  a  compound  having 
the  same  proportion  of  hydrogen  as  ammoniacal  gas,  with  phosphorus  in  the  place 
of  nitrogen.  The  pure  gas  is  obtained  by  heating  hydrated  phosphorous  acid,  which 
is  resolved  into  phosphuretted  hydrogen  and  hydrated  phosphoric  acid :  thus  — 

4(3HO  +  P03)  or  12HO  and  4P03=PH3  and  9HO  +  3P05. 

The  gas  so  prepared  does  not  inflame  spontaneously  when  allowed  to  escape  into 
air,  but  kindles  when  a  light  is  applied  to  it,  and  burns  with  the  white  flame  of 
phosphorus.  A  little  air  added  to  the  gas,  which  had  no  effect  at  first,  has  been 
observed  to  produce  occasionally  an  explosion  after  a  time.  The  gas  consists  of  1 
volume  of  phosphorus  vapour  and  6  volumes  of  hydrogen,  condensed  into  4  volumes, 
so  that  it  has  the  same  combining  measure  as  ammoniacal  gas.  Its  density  is  1185. 
Phosphuretted  hydrogen  has  a  disagreeable  alliaceous  odour,  is  but  slightly  soluble 
in  water,  and  has  no  alkaline  reaction. 

The  same  gas,  in  a  self-inflammable  state,  is  obtained  by  boiling  phosphorus  with 
water  and  an  excess  of  lime,  or  in  a  strong  solution  of  caustic  potassa,  in  the  flask 
A  (fig.  147),  at  the  water-trough  B.  The  first  effect  is  the  formation  of  hypophos- 
phite of  lime,  with  the  evolution  of  phosphuretted  hydrogen  gas  : 

4P  and  3CaO  and  3HO  =  PH3  and  3CaO  +  3PO. 

Phosphuretted  hydrogen  is  again  evolved,  but  mixed  with  a  considerable  quantity 
of  free  hydrogen,  when  the  hydrated  hypophosphite  of  lime  is  evaporated  to  dryness, 
phosphate  of  lime  being  the  residuary  product. 


PHOSPHORUS    AND    HYDROGEN 
FIG.  147. 


327 


Each  bubble  of  gas  on  escaping  into  air  takes  fire,  and  produces  a  beautiful  white 
wreath  of  smoke,  consisting  of  phosphoric  acid.  The  spontaneous  inflammability  is 
due  to  the  presence  of  a  small  quantity  of  the  vapour  of  a  liquid  compound  of  phos- 
phorus and  hydrogen,  and  was  first  explained  by  M.  P.  Thenard. 

Phosphuretted  hydrogen  decomposes  some  metallic  solutions,  such  as  those  of 
copper  and  mercury,  and  forms  metallic  phosphides.  When  the  gas  is  pure,  it  is 
entirely  absorbed  by  sulphate  of  copper  and  by  chloride  of  lime.  With  hydriodic 
acid,  phosphuretted  hydrogen  forms  a  crystalline  compound,  which  is  interesting 
from  its  analogy  to  sal  ammoniac.  It  may  be  prepared  by  mixing  together  its  con- 
stituent gases  over  mercury;  or  more  easily  by  introducing  into  a  small  tubulated 
retort  60  parts  of  dry  iodine  with  15  of  phosphorus  finely  granulated,  and  mixing 
these  bodies  intimately  with  pounded  glass ;  8  or  9  parts  of  water  are  then  added  to 
the  mixture,  and  the  vapours  which  immediately  come  off  are  allowed  to  escape  by 
a  glass  tube  open  at  both  ends,  adapted  to  the  beak  of  the  retort  in  which  beautiful 
small  crystals  of  the  salt  condense,  of  a  diamond  lustre.  Rose  observed  that  these 
crystals  do  not  belong  to  the  Regular  System,  and  are,  therefore,  not  isomorphous 
with  sal  ammoniac.  They  are  decomposed  by  water,  with  evolution  of  phosphuretted 
hydrogen. 

Phosphuretted  hydrogen  combines  also,  like  ammonia,  with  the  perchlorides  of 
tin,  titanium,  chromium,  iron,  and  antimony,  forming  white  saline  bodies.  The 
combination  with  bichloride  of  tin  is  decomposed,  with  escape  of  the  gas  in  the  non- 
inflammable  state,  by  water,  and  in  the  spontaneously  inflammable  condition  by 
solution  of  ammonia. 

Liquid  hydride  of  phosphorus,  PH2.  —  This  substance,  which  was  discovered  by 
M.  Paul  Thenard,  is  obtained  by  exposing  the  phosphuretted  hydrogen  gas,  evolved 
by  the  action  of  water,  at  140°  (60°  C.)  on  the  phosphide  of  calcium  Ca2P,  to  a 
freezing  mixture  in  a  condensing  tube.  It  is  a  colourless  liquid,  of  high  refracting 
power,  which  does  not  freeze  at  — 4°  ( — 20°  C.),  but  which  a  temperature  of  +  86° 
(30°  C.)  is  sufficient  to  decompose.  It  is  resolved  under  the  influence  of  light  into 
the  gaseous  and  solid  hydrides  of  phosphorus.  The  same  decomposition  is  produced 
by  contact  with  very  different  substances,  such  as  alcohol,  oil  of  turpentine,  hydro- 
chloric acid,  and  many  pulverulent  matters. 

This  compound  is  one  of  the  most  inflammable  substances  known,  taking  fire 
spontaneously  in  air;  and  burning  with  a  dazzling'  flame.  The  most  minute  trace 


328  PHOSPHORUS. 

of  its  vapour,  diffusing  into  the  different  combustible  gases,  such  as  hydrogen,  car- 
bonic oxide,  cyanogen,  olefiant  gas,  &c.,  communicates  to  them,  as  it  does  to-  phos- 
phuretted  hydrogen,  the  property  of  inflaming  spontaneously  in  air  or  oxygen. 
(P.  ThSnard,  Annal.  de  Ch.  et  Ph.,  3me.  ser.  xiv.  5.) 


PHOSPHORUS   AND    NITROGEN. 

Both  chlorides  of  phosphorus  absorb  ammoniacal  gas,  and  form  solid  white  com- 
pounds. The  combination  of  the  terchloride  contains  2|  equivalents  of  ammonia, 
but  that  of  the  perchloride  was  not  found  equally  definite.  When  exposed  to  a 
strong  red  heat,  without  access  of  oxygen,  these  compounds  leave  a  white  amorphous 
body,  which  was  supposed  to  be  a  nitride  of  phosphorus,  PN2.  (Rose :  Annal.  de 
Ch.  et  Ph.,  liv.  275.)  It  is  most  easily  prepared  by  transmitting  a  stream  of  dry 
carbonic  acid  gas  over  the  ammoniacal  compound,  in  a  tube  of  hard  glass,  heated  by 
a  charcoal  fire,  so  long  as  vapours  of  sal  ammoniac  sublime. 

This  substance,  which  is  remarkable  for  its  fixity,  is  not  soluble  in  any  men- 
struum, nor  acted  upon  by  dilute  acid  or  alkaline  solutions.  It  is  not  affected  even 
when  heated  in  an  atmosphere  of  chlorine  or  sulphur,  but  is  decomposed  when 
heated  in  hydrogen  gas,  with  the  formation  of  ammonia. 

According  to  M.  Gerhard t,  the  pentachloride  of  phosphorus  absorbs  ammonia, 
with  the  evolution  of  some  hydrochloric  acid,  and  the  formation  of  a  compound 
PC13.(NH2)2.  The  nitride  of  phosphorus  also  contains  hydrogen,  and  ought  to  be 
represented  by  the  formula  PN2H  :  its  formation  from  the  perchloride  of  phos- 
phorus and  ammonia  taking  place  according  to  the  equation  : — 

PC15  and  2NH3  =  5HC1  and  PN2H. 

This  compound,  PN2H,  which  is  named  Phospham  by  Gerhardt,  is  decomposed 
by  fusion  with  hydrate  of  potassa,  and  converted  into  ammonia,  and  the  ordinary 
phosphate  of  potassa.  At  a  high  temperature  water  acts  upon  phospham,  giving 
rise  to  ammonia  and  phosphoric  acid. 


PHOSPHORUS  AND  SULPHUR.  —  SULPHIDES  OF  PHOSPHORUS. 

Phosphorus  and  sulphur  combine  in  all  proportions,  with  the  evolution  of  much 
heat,  and  sometimes  with  explosion.  These  elements  most  safely  unite  under  hot 
water,  of  which  the  temperature,  however,  must  not  exceed  160° }  for  otherwise 
hydrosulphuric  and  phosphoric  acids  may  be  produced  with  such  rapidity  as  to  occa- 
sion an  explosion.  The  compounds  obtained  in  this  manner  are  of  a  pale  yellow 
colour,  —  more  fusible  and  more  inflammable  than  phosphorus  itself.  They  were 
supposed  to  be  indefinite  in  composition ',  but  Berzelius  has  shown  that  they  form 
a  series  of  sulphides  of  phosphorus  corresponding  in  composition  with  the  oxides, 
with  one  sulphide  additional.  They  are  represented  by  the  formulae— 

Subsulphide,  P2S corresponding  with  Oxide  of  Phosphorus,  P20. 

Protosulphide,  PS "  "          Hypophosphorous  Acid,  PO. 

Tersulphide,  PS3  "          "          Phosphorous  Acid,  P03. 

Pentasulphide,  PS5 "  "          Phosphoric  Acid,  P06. 

Persulphide,  PS12 without  an  oxygen  analogue. 

These  compounds  may  all  be  formed  directly  by  fusing  sulphur  and  phosphorus 
together  in  the  requisite  proportions,  and  are  generally  crystal lizable.  ^  The  tersul- 
phide  was  originally  obtained  by  Serullas  by  the  action  of  hydrosulphuric  acid  upon 
the  terchloride  of  phosphorus.  They  are  insoluble  in  water,  alcohol,  or  ether ;  but 
combine  readily  with  alkaline  sulphides,  and  form  series  of  sulphur-salts  correspond- 
ing with  thehypophosphites,  phosphites,  and  phosphates,  [See  Supplement,  p.  787.] 
[$ee  Supplement,  p.  787.J 


CHLORINE. 


329 


SECTION  X. 

CHLORINE. 

Eg.  35.5  or  443.75;  Cl;  density  2440 ;  [""["]. 

This  substance  was  discovered  by  Scheele  in  1774,  but  was  believed  to  be  of  a 
compound  nature,  till  Gay-Lussac  and  Thenard,  in  1809,  showed  that  it  might 
reasonably  be  considered  a  simple  substance.  It  is  to  the  powerful  advocacy  of 
Davy,  however,  who  entered  upon  the  investigation  shortly  afterwards,  that  the 
establishment  of  the  elementary  character  of  chlorine  is  principally  due,  and  to  him 
it  is  indebted  for  the  name  it  now  bears,  which  is  derived  from  ^wpo^  yellowish- 
green,  and  refers  to  its  colour  as  a  gas,  elementary  bodies  being  generally  named 
from  some  remarkable  quality  or  important  circumstance  in  their  history.  Chlorine 
is  the  leading  member  of  a  well-marked  natural  family,  to  which  also  bromine, 
iodine,  and  fluorine  belong.  Phosphorus,  carbon,  hydrogen,  sulphur,  and  most  of 
the  preceding  elementary  bodies,  have  little  or  no  action  upon  each  other,  or  upon 
the  mass  of  hydrogenous,  carbonaceous,  and  metallic  bodies  to  which  they  are  ex- 
posed in  the  material  world;  all  these  substances  being  too  similar  in  nature  to  have 
much  affinity  for  each  other.  But  the  class  to  which  chlorine  belongs  ranks  apart, 
and,  with  a  mutual  indifference  to  each  other,  they  exhibit  an  intense  affinity  for 
the  members  of  the  other  great  and  prevailing  class  —  an  affinity  so  general  as  to 
give  the  chlorine  family  the  character  of  extraordinary  chemical  activity,  and  to 
preclude  the  possibility  of  any  member  of  the  class  existing  in  a  free  and  uncom- 
bined  state  in  nature.  The  compounds,  again,  of  the  chlorine  class,  with  the  excep- 
tion of  those  of  fluorine,  are  remarkable  for  solubility,  and  consequently  find  a  place 
among  the  saline  constituents  of  sea  water,  and  are  of  comparatively  rare  occurrence 
in  the  mineral  kingdom;  with  the  single  exception  of  chloride  of  sodium,  which, 
besides  being  present  in  large  quantity  in  sea  water,  forms  extensive  beds  of  rock 
salt  in  certain  geological  formations. 

Preparation. — The  fuming  hydrochloric  acid  or  muriatic  acid  (as  it  is  also  called) 
of  commerce,  is  a  solution  in  water  of  hydrochloric  gas,  a  compound  of  chlorine  and 
hydrogen,  from  which  chlorine  gas  is  easily  procured.  The  liberation  of  chlorine 
results  from  contact  of  the  acid  named  with  binoxide  of  manganese,  and  the  reac- 
tion which  then  occurs  is  made  most  obvious  in  the  following  mode  of  conducting 
the  experiment : — A  few  ounces  of  the  strongly  fuming  hydrochloric  acid  are  intro- 
duced into  a  flask  a  (fig.  148),  with  a  perforated  cork  and  tube  ft,  upon  which  a 
bulb  or  two  have  been  expanded ;  and  that  tube  is  connected,  by  means  of  a  short 

Fio.  148. 


330 


CHLORINE. 


caoutchouc  tube,  with  the  drying  tube  c,  containing  fragments  of  chloride  of  cal- 
cium, and  the  last  is  connected  in  a  similar  manner  with  the  exit  tube  d,  which 
descends  to  the  bottom  of  a  dry  and  empty  bottle  e.  Upon  applying  the  spirit-lamp 
to  a,  the  liquid  in  the  flask  soon  begins  to  boil,  and  the  hydrochloric  gas  passes  off, 
depositing,  perhaps,  a  little  moisture  in  the  bulbs  of  b,  which  may  be  kept  cool  by 
wet  blotting-paper,  and  being  completely  dried  in  passing  through  c.  It  is  con- 
veyed by  d  to  the  bottom  of  the  bottle  e,  and  finally  escapes  and  produces  white 
fumes  in  the  atmosphere,  after  displacing  the  air  of  that  bottle.  The  hydrochloric 
gas  is  obtained  in  e  unchanged,  and  will  redden  and  not  bleach  a  little  blue  infusion 
of  litmus  poured  into  e.  But  between  the  tube  c  and  d,  let  another  tube  be  now 
interposed  having  a  pair  of  bulbs  blown  upon  it  f  and  g  (fig.  149),  one  of  which  f 

FIG.  149. 


contains  a  quantity  of  pounded  anhydrous  binoxide  of  manganese;  the  bottle  e 
remaining  as  before.  Then,  upon  applying  heat  to  the  manganese  bulb  /,  the 
hydrochloric  gas  will  be  found  to  suffer  decomposition  as  it  traverses  that  bulb,  its 
hydrogen  uniting  with  the  oxygen  of  the  manganese,  and  forming  water,  which  will 
condense  in  drops  in  g,  and  disengaged  chlorine  proceeds  on  to  e,  in  which  that  gas 
will  be  perceptible  from  its  yellow  tint,  and  more  so  by  bleaching  the  infusion  of 
reddened  litmus  remaining  in  e.  If  the  transmission  of  hydrochloric  acid  over  the 
binoxide  of  manganese  be  continued  for  sufficient  time,  the  latter  loses  all  its  oxygen, 
and  the  metal  remains  in  the  state  of  protochloride.  Indeed,  only  one-half  of  the 
chlorine  of  the  decomposed  hydrochloric  gas  is  obtained  as  gas,  the  other  half  being 
retained  by  the  manganese,  as  will  appear' by  the  following  diagram : — 


PROCESS   FOR   CHLORINE   FROM   HYDROCHLORIC   ACID   AND   BINOXIDE   OF 

MANGANESE. 
Before  decomposition.  After  decomposition. 

f  Chlorine Chlorine. 

(  Hydrogen 


Water. 

Chloride  of  manganese. 


Hydrochloric  acid 
Binoxide  of  mangan 
Hydrochloric  acid 


C  Oxygen 

.  -^  Manganese. 


(Oxygen. 
f  Chlorine.. 
(  Hydrogen 


Water. 


Or  in  symbols :  — MnO,  +  2HCl=MnCl  and  2HO  and  Cl. 

The  most  convenient  method  of  preparing  chlorine  gas  is  by  mixing  in  a  flask  A 
/'fig.  150),  1  part  of  binoxide  of  manganese  with  4  parts  of  hydrochloric  acid, 


PREPARATION   OF   CHLORINE 
FIG.  150. 


331 


diluted  with  1  of  water.  Effervescence,  from  escape  of  gas,  takes  place  in  the  cold, 
but  is  greatly  promoted  by  the  application  of  a  gentle  heat.  The  gas  is  collected  in 
C  over  water,  of  which  the  temperature  should  not  be  less  than  80°  or  90° ;  other- 
wise a  great  waste  of  the  gas  occurs  from  its  solution  in  the  water,  and  also  a  con- 
sequent annoyance  to  the  operator  from  the  escape  of  the  chlorine  into  the  atmo- 
sphere, by  evaporation  from  the  surface  of  the  water-trough.  If  the  gas  is  not  to 
be  used  immediately,  but  preserved,  it  should  be  collected  in  bottles,  into  which, 
when  filled  with  gas,  their  stoppers  greased  should  be  inserted  before  they  are 
removed  from  the  trough.  Before  the  gas  obtained  by  this  process  can  be  considered 
as  pure,  it  should  be  transmitted  through  water  in  a  wash-bottle  B,  to  remove 
hydrochloric  acid.  If  the  gas  is  to  be  dried,  it  must  be  sent  through  a  tube  con- 
taining chloride  of  calcium,  of  two  or  three  feet  in  length,  some  difficulty  being 
experienced  in  drying  this  gas  in  a  perfect  manner,  owing  to  its  low  diffusive  power. 
Chlorine  cannot  be  collected  over  mercury,  as  it  combines  at  once  with  that  metal. 

A  somewhat  different  process  for  the  preparation  of  chlorine  is  generally  followed 
on  the  large  scale.  About  6  parts  of  manganese  with  8  of  common  salt  are  intro- 
duced into  a  large  leaden  vessel,  of  a  form  nearly  globular,  as  represented  (fig.  151)> 
and  5  or  6  feet  in  diameter,  and  to  these  is  added  as  much  of  the  unconcentrated 
sulphuric  acid  of  the  leaden  chambers  as  is  equiva- 
lent to  13  parts  of  oil  of  vitriol.  The  leaden  vessel 
is  placed  in  an  iron  pan,  or  has  an  outer  casing,  d 
e]  and  to  heat  the  materials,  steam  is  admitted 
by  d  into  the  space  between  the  bottom  and  outer 
casing.  In  the  figure,  which  is  a  section  of  the 
leaden  retort,  a  represents  the  tube  by  which 
the  chlorine  escapes,  b  a  large  opening  for  intro-. 
ducing  the  solid  material  covered  by  a  lid  or  water 
valve,  its  edges  dipping  into  a  channel  containing 
water,  e  a  twisted  leaden  funnel  for  introducing  the 
acid,  f  a  wooden  agitator,  and  c  a  discharge  tube, 
by  which  the  waste  materials  are  run  off  after  the 
process  is  finished.  A  retort  of  lead  cannot  be 
used  with  safety  with  binoxide  of  manganese  and 
hydrochloric  acid  for  chlorine,  owing  to  the  action  of  the  acid  upon  the  lead,  and 


FIG.  161. 


332  CHLORINE. 

the  evolution  of  hydrogen  gas  (which  produces  a  spontaneously-explosive  mixture 
with  chlorine),  or,  it  is  said,  of  euchlorine.  In  the  reaction  which  occurs  in  the 
leaden  retort,  it  may  be  supposed  either  that  hydrochloric  acid  is  first  liberated  from 
chloride  of  sodium  by  sulphuric  acid,  and  afterwards  decomposed  by  binoxide  of 
manganese,  as  in  the  preceding  experiment ;  or  that  sulphates  of  manganese  and 
soda  are  simultaneously  formed,  and  chlorine  liberated  in  consequence,  as  stated  in 
the  following  diagram,  in  which  the  names  express  (as  usual)  single  equivalents : — 

PROCESS  FOR  CHLORINE  FROM  CHLORIDE    OF    SODIUM  (COMMON  SALT),  BINOXIDE 

OF  MANGANESE,  AND  SULPHURIC  ACID. 
Before  decomposition.  After  decomposition. 

„      ,.  (Chlorine . Chlorine. 

Chloride  of  sodium       |  S()dium ^ 

Sulphuric  acid Sulphuric  acid "----•----.^  Sulphate  of  soda. 

Binoxide  of  manganese  {  p^m^ngaueseZlI^f' 

Sulphuric  acid Sulphuric  acid ' """" — ^  Sulph.  of  mangan. 

Or  in  symbols : 

NaCl  and  2S03  and  Mn02=NaO.S03  and  MnO.S03  and  Cl. 

A  new  manufacturing  process  for  chlorine  has  lately  been  applied  by  Mr.  C. 
Tennant  Dunlop,  in  which  the  use  of  binoxido  of  manganese  is  superseded  by  nitric 
acid.  One  equivalent  of  nitric  acid  is  found  to  communicate  two  equivalents  of 
oxygen  to  the  hydrochloric  acid,  and  thus  evolve  two  equivalents  of  chlorine.  The 
decomposed  nitric  acid  is  evolved  in  the  form  of  nitrous  acid  vapour  JST03,  and  it  is 
an  essential  part  of  the  process  to  absorb  that  vapour  by  means  of  sulphuric  acid, 
and  to  introduce  the  nitrous  acid  in -this  form  into  the  leaden  chamber. 

Properties.  —  Chlorine  is  a  dense  gas  of  a  pale  yellow  colour,  having  a  peculiar 
suffocating  odour,  absolutely  intolerable  even  when  largely  diluted  with  air,  and 
occasioning  great  irritation  in  the  trachea,  with  coughing  and  oppression  of  the  chest. 
Some  relief  from  these  effects  is  experienced  from  the  inhalation  of  the  vapour  of 
ether  or  alcohol.  The  density  of  chlorine  gas  is,  by  experiment,  2470  —  by  theory, 
2440.  Under  a  pressure  of  about  4  atmospheres,  chlorine  condenses  into  a  limpid 
liquid  of  a  bright  yellow  colour,  of  sp.  gr.  about  1.33,  and  which  has  not  been 
frozen.  Water  at  60°  dissolves  twice  its  volume  of  this  gas,  and  acquires  the  yel- 
lowish colour,  odour,  and  other  properties  of  chlorine.  To  form  chlorine-water,  a 
stout  bottle  filled  with  the  gas  at  the  water-trough,  may  be  closed  with  a  good  cork, 
and  removed  to  a  basin  of  cold  water :  on  loosening  the  cork  with  the  mouth  of  the 
bottle  under  water,  a  little  water  will  enter  it,  from  the  contraction  of  the  gas  by 
cooling ;  and  this  water  may  be  agitated  in  contact  with  the  gas  by  a  lateral  move- 
ment of  the  bottle  without  removing  it  from  the  water  j  on  loosening  the  cork  again, 
more  water  will  be  found  to  enter  the  bottle,  and  by  repeating  the  agitation  and 
admission  of  water,  the  whole  gas  (if  pure)  is  absorbed,  and  the  bottle  is  in  the  end 
filled  with  water,  which  of  course  contains  an  equal  volume  of  chlorine  gas.  With 
water  near  its  freezing  point,  chlorine  combines  and  forms  a  crystalline  hydrate, 
which  Faraday  found  to  contain  10  eqs.  of  water.  Hence  chlorine  gas  cannot  be 
collected  at  all  over  water  below  40°.  Exposed  to  light,  chlorine  water  soon  loses 
its  properties,  water  being  decomposed  and  hydrochloric  acid  formed,  with  the  evo- 
lution of  oxygen  gas.  But  it  may  be  preserved  for  a  long  time  in  an  opaque  bottle 
properly  closed.  When  diluted  so  far  that  the  water  does  not  contain  above  1  or  1  \ 
per  cent,  of  its  bulk  of  chlorine,  the  odour  is  by  no  means  strong,  and  such  a  solu- 
tion may  be  employed  in  bleaching  without  inconvenience  to  the  workmen,  although 
a  combination  of  chlorine  with  hydrate  of  lime,  called  the  chloride  of  lime,  is  gene- 
rally preferred  for  that  purpose. 


PROPERTIES    OF    CHLORINE. 


333 


Chlorine  does  not  in  any  circumstances  unite  directly  with  oxygen,  although 
several  compounds  of  these  elements  can  be  formed;  nor  is  it  known  to  combine 
directly  with  nitrogen  or  carbon.  Chlorine  and  hydrogen  gases  may  be  mixed  and 
preserved  in  the  dark  without  uniting,  but  combination  is  determined  with  explosion 
by  spongy  platinum  or  the  electric  spark,  or  by  exposure  to  the  direct  rays  of  the 
sun;  even  under  the  diffuse  light  of  day,  combination  of  the  gases  takes  place 
rapidly,  but  without  explosion.  Chlorine,  indeed,  has  a  strong  affinity  for  hydrogen, 
and  decomposes  most  bodies  containing  that  element,  hydrochloric  acid  being  always 
formed.  In  plunging  an  ignited  taper  into  chlorine  gas,  its  flame  is  extinguished, 
but  the  column  of  oily  vapour  rising  from  the  wick  is  rekindled  by  the  chlorine, 
and  the  hydrogenous  part  of  the  combustible  continues  to  burn  with  a  red  and 
smoky  flame,  which  expires  on  removing  the  taper  into  air.  Paper  dipped  in  oil  of 
turpentine  takes  fire  spontaneously  in  this  gas,  and  the  oil  burns,  with  the  deposition 
of  a  large  quantity  of  carbon.  The  affinity  of  chlorine  for  most  metals  is  equally 
great :  antimony,  arsenic,  and  several  others,  showered  in  powder  into  this  gas,  take 
fire,  and  produce  a  brilliant  combustion.  Chlorine  is  absorbed  by  alcohol  and  many 
other  organic  substances,  when  it  generally  eliminates  more  or  less  hydrogen,  as 
hydrochloric  acid,  and  enters  also  by  substitution  into  the  original  compound,  in  the 
place  of  that  hydrogen.  It  bleaches  all  vegetable  and  animal  colouring  matters, 
and  is  believed  then  generally  to  act  in  that  manner.  The  colours  are  destroyed 
and  cannot  be  revived  by  any  treatment. 

A  stream  of  chlorine  gas,  thrown  into  a  bottle  of  dry  ammoniacal  gas,  produces 
a  jet  of  flame  from  the  combustion  of  the  hydrogen  of  the  ammonia.  When  chlorine 
is  passed  through  the  undiluted  solution  of  ammonia,  the  same  decomposition  takes 
place,  and  the  reaction  is  a  convenient  source  of  nitrogen  gas  (page  244). 

Fio.  162. 


The  arrangement  represented  in  fig.  152  may  be  used  for  this  purpose.  It  consists 
of  a  large  globular  flask  A,  in  which  chlorine  is  evolved  from  the  usual  materials  j 
two  wash-bottles,  B  and  C,  containing  solution  of  ammonia,  the  first  placed  in  a 
bason  of  cold  water  to  repress  its  temperature.  The  nitrogen  evolved  passes  through 
a  U-tube,  E,  containing  fragments  of  pumice  impregnated  with  a  solution  of  caustic 
potassa,  to  absorb  any  chlorine  that  may  escape  the  action  of  the  ammonia;  and  the 
gas  is  finally  collected  in  bottles,  F,  filled  with  water  acidulated  with  hydrochloric 
acid,  to  absorb  the  vapour  of  ammonia  with  which  the  nitrogen  is  accompanied. 

Chlorine  when  free  is  easily  recognized  by  its  odour  and  bleaching  power,  and  by 
producing  both  when  free  and  in  the  soluble  chlorides,  with  nitrate  of  silver,  a  white 
curdy  precipitate  of  chloride  of  silver,  which  is  soluble  in  ammonia,  but  not  soluble 
in  cold  or  boiling  nitric  acid. 


334 


CHLORINE. 


Uses. — Chemistry  has  presented  to  the  arts  few  substances  of  which  the  applica- 
tions are  more  valuable.  Chlorine  is  the  discolouring  agent  of  the  modern  process 
of  bleaching,  which,  as  it  is  generally  conducted  with  cotton  goods,  consists  of  the 
following  operations.  The  cloth,  after  being  well  washed,  is  boiled  first  in  lime- 
water  and  then  in  caustic  soda,  which  remove  from  it  certain  resinous  matters  soluble 
in  alkali.  It  is  then  steeped  in.  a  solution  of  chloride  of  lime,  so  dilute  as  just  to 
taste  distinctly,  which  has  little  or  no  perceptible  effect  in  whitening  it ;  but  the 
cloth  is  afterwards  thrown  into  water  acidulated  with  sulphuric  acid,  of  sp.  gr.  be- 
tween 1.010  and  1.020,  when  a  minute  disengagement  of  chlorine  takes  place 
throughout  the  substance  of  the  cloth,  and  it  immediately  assumes  a  bleached 
appearance.  The  cloth  is  boiled  a  second  time  with  caustic  soda,  and  digested  again 
in  dilute  chloride  of  lime  and  in  dilute  sulphuric  acid,  as  before.  The  acid  favours 
the  bleaching  action,  and  is  required  besides  to  remove  the  caustic  alkali,  a  portion 
of  which  adheres  pertinaciously  to  the  cloth.  The  fibre  of  the  cloth  is  not  injured 
by  dilute  sulphuric  acid,  although  digested  in  it  for  days,  provided  the  cloth  is  not 
allowed  to  dry  with  the  acid  in  it,  or  left  above  the  surface  of  the  liquor.  But  it  is 
very  necessary  to  wash  well  after  the  last  souring,  to  get  rid  of  every  trace  of  acid,  with 
which  view  the  cloth  may  be  passed  through  warm  water  as  a  precautionary  measure. 

Chlorine  is  had  recourse  to  in  disinfecting  the  wards  of  hospitals.  Mr.  Faraday, 
in  fumigating  the  Millbank  Penitentiary,  found  that  a  mixture  of  1  part  of  common 
salt  and  1  part  of  the  binoxide  of  manganese,  when  acted  upon  by  2  parts  of  oil  of 
vitriol  previously  mixed  with  1  part  of  water  (all  by  weight),  and  left  till  cold,  pro- 
duced the  best  results.  Such  a  mixture,  at  60°,  in  shallow  pans  of  red  earthenware, 
liberated  its  chlorine  gradually  but  perfectly  in  four  days.  The  salt  and  manganese 
were  well  mixed,  and  used  in  charges  of  3J  pounds  of  the  mixture.  The  acid  and 
water  were  mixed  in  a  wooden  tub,  the  water  being  put  in  first,  and  then  about  half 
the  acid  :  after  cooling,  the  other  half  was  added.  The  proportions  of  water  and  acid 
are  9  measures  of  the  former  to  10  of  the  latter.  (Magazine  of  Science,  1840,  p.  264). 

Chlorides.  —  Chlorine  combines  with  all  the  metals,  and  in  the  same  proportions 
as  oxygen.  With  the  exception  of  the  chlorides  of  silver  and  lead,  and  subchlorides 
of  copper  and  mercury,  these  compounds  are  soluble  and  sapid,  and  they  possess  in 
an  eminent  degree  the  saline  character.  Indeed,  common  salt,  the  chloride  of  sodium, 
has  given  its  name  to  the  class  of  salts,  and  chlorine  is  the  type  of  salt-radicals  or 
halogenous  (salt-producing)  bodies.  Chlorides  of  metals  belonging  to  different 
classes  often  combine  together  and  form  double  chlorides  j  the  chlorides  of  the  pot- 
assium family,  in  particular,  with  some  chlorides  of  the  magnesian  family,  as  with 
chloride  of  copper,  with  chloride  of  mercury,  with  both  the  chlorides  of  tin,  and 
with  perchlorides  generally.  A  chloride  and  oxide  of  the  same  metal  (excepting 
the  potassium  family)  often  combine  together,  forming  oxichloridcs,  which  are  in 
general  insoluble. 

Chlorine  is  also  absorbed  by  alkaline  solutions,  and  combinations  are  formed 
which  bleach  and  exhibit  many  of  the  properties  of  the  free  element.  The  chlorine 
in  these  compounds,  and  also  in  dry  chloride  of  lime,  formed  by  exposing  hydrate 
of  lime  to  chlorine  gas,  is  now  generally  allowed  to  exist  as  hypochlorous  acid.  They 
are  not  permanent  compounds,  and  the  chlorine  eventually  acts  upon  the  metallic 
oxide,  so  as  to  produce  a  chloride  and  a  chlorate  of  the  metal,  as  will  be  afterwards 
explained. 

The  following  chlorides  of  the  non-metallic  elements  will  now  be  particularly 
described : — 


Hydrochloric  acid  H  Cl 

Hypochlorous  acid  Cl  0 

Peroxide  of  chlorine  Cl  O4 

Chloric  acid  Cl  05 

Hyperchlorie  acid Cl  07 

Chloride  of  nitrogen    N  C13 

Chlorocarbonic  acid  .  ..  CO.C1 


Chloride  of  boron B  C13 

Chloride  of  silicon Si  C13 

Chloride  of  sulphur S2  Cl 

Bichloride  of  sulphur  S  C12 

Terchloride  of  phosphorus  ....  P  C13 
Pentachloride  of  phosphorus ...  P  Cl« 


HYDROCHLORIC    ACID. 


335 


HYDROCHLORIC   ACID. 

Syn.  Chlorhydric  acid,  Muriatic  acid ;  Eg.  36.5  or  456.25;  C1H;  density 

f~\ — I 
1269.5;  j-|- 

This  acid  is  one  of  the  most  frequently-employed  reagents  in  chemical  operations, 
and  has  long  been  known  under  the  names  of  spirit  of  salt,  marine  acid,  and 
muriatic  acid  (from  murias,  sea-salt).  It  was  first  obtained  by  Priestley  in  its  pure 
form  of  a  gas  in  1772. 

Preparation. — Hydrochloric  acid  is  always  obtained  by  the  action  of  oil  of  vitriol 
upon  common  salt.  When  the  process  is  conducted  on  a  small  scale  and  in  a  glabs 
retort,  3  parts  of  common  salt,  5  oil  of  vitriol,  and  5  water,  may  be  taken.  The 
oil  of  vitriol  being  mixed  with  two  parts  of  the  water  in  a  thin  flask,  and  cooled,  is 
poured  upon  the  salt  contained  in  a  capacious  retort  A  (fig.  153).  A  flask  B;  con- 

Fio.  163. 


taining  the  remaining  6  parts  of  the  water,  is  then  adapted  to  the  retort  as  a  con- 
denser. Upon  applying  heat  to  the  retort,  hydrochloric  acid  gas  comes  off,  and  is 
condensed  in  the  receiver,  affording  an  aqueous  solution  of  the  acid,  of  about  sp.  gr. 
1.170,  which  contains  34  per  cent,  of  dry  acid;  while  bisulphate  of  soda  remains 
in  the  retort.  Supposing  2  equivalents  of  oil  of  vitriol  and  1  of  chloride  of  sodium 
to  be  employed,  which  the  preceding  proportions  represent,  then  the  rationale  of  the 
action  is  as  follows : — 


PROCESS    FOR    HYDROCHLORIC    ACID. 


58.5  Cloride  of  sodium 


Before  decomposition. 

(Chlorine 35.5 

{Sodium 23 

C  Hydrogen 1 

49      Oil  of  vitriol ^Oxygen 8 

(Sulphu.  acid 40 

49      Oil  of  vitriol..,  .  49 


After  decomposition. 

5.5  hydroc.  acid 


sulph.  of  soda  ") 
sulph.  of  water  j 


156.5  156.5  156.5  ' 

Or  in  symbols:  NaCl  and  HO.S03=HC1  and  NaO.S03+HO.S03. 


336 


CHLORINE. 


The  hydrochloric  acid  coming  off  easily  and  at  a  low  temperature,  when  2  eqs.  of 
sulphuric  acid  are  used,  is  obtained  at  once  pure  and  free  from  sulphuric  acid. 

This  process  is  more  economically  conducted  on  the  large  scale,  as  for  nitric  acid 
(fig.  116,  page  261),  in  a  cast-iron  cylinder,  about  5  feet  in  length  and  2^  in  dia- 
meter, land  upon  its  side,  which  has  moveable  ends,  generally  composed  of  a  thin 
paving-stone  cut  into  a  circular  disc  and  divided  into  two  unequal  segments.  A 
charge  of  three  or  four  hundred  pounds  of  salt  is  introduced  into  the  retort,  and 
after  the  bottom  is  heated,  sulphuric  acid,  as  it  is  withdrawn  from  the  leaden  cham- 
bers, is  added  in  a  gradual  manner  by  means  of  a  long  funnel,  and  in  proportion  not 
exceeding  1  equivalent  for  the  chloride  of  sodium.  In  such  circumstances,  the 
lower  part  of  the  cylinder  exposed  to  the  sulphuric  acid  is  not  much  acted  upon, 
while  the  roof  of  the  cylinder  is  protected  from  the  hydrochloric  acid  fumes  by  a  coating 
of  fire-clay  or  thin  bricks.  The  hydrochloric  acid  gas  is  conducted  by  a  glass  tube 
into  a  series  of  large  jars  of  salt-glaze  ware,  connected  with  each  other  like  Wolfe's 
bottles,  and  containing  water,  in  which  the  acid  condenses. 

Properties.  —  Hydrochloric  acid  is  obtained  in  the  state  of  gas  by  boiling  an 
ounce  or  two  of  the  fuming  aqueous  solution  in  a  small  retort,  or  by  pouring  oil  of 
vitriol  upon  a  small  quantity  of  salt  in  a  retort,  and  is  collected  over  mercury.  It 
is  an  invisible  gas,  of  a  pungent  acid  odour,  and  produces  white  fumes,  when  allowed 
to  escape,  by  condensing  the  moisture  in  the  air.  By  a  pressure  of  40  atmospheres 
at  50°,  it  is  condensed  into  a  liquid  of  sp.  gr.  1.27.  It  is  quite  irrespirable,  but 
much  less  irritating  than  chlorine ;  it  is  not  decomposed  by  heat  alone,  nor  when 
heated  in  contact  with  charcoal.  Hydrochloric  acid  extinguishes  combustion,  and 
is  not  made  to  unite  with  oxygen  by  heat  j  but  when  electric  sparks  are  passed 
through  a  mixture  of  this  gas  and. oxygen,  decomposition  takes  place  to  a  small 
extent,  water  being  formed  and  chlorine  liberated.  It  is  composed  by  volume  of 
one  combining  measure,  or  two  volumes  of  each  of  its  constituents,  united  without 
condensation ;  so  that  its  combining  measure  is  4  volumes,  and  its  theoretical  den- 
sity 1269.5.  It  may  be  formed  directly  by  the  union  of  its  elements. 

If  a  few  drops  of  water  or  a  fragment  of  ice  be  thrown  up  into  a  jar  of  hydrochloric 
acid  over  mercury,  the  gas  is  completely  absorbed  in  a  few  seconds ;  or  if  a  stout 
bottle  filled  with  this  gas  be  closed  by  the  finger  and  opened  under  water,  an  instan- 
taneous condensation  of  the  gas  takes  place,  water  rushing  into  the  bottle  as  into  a 
vacuum.  Dr.  Thomson  found  that  1  cubic  inch  of  water  absorbs  418  cubic  inches 
of  gas  at  69°,  and  becomes  1.34  cubic  inch.  He  constructed  the  following  table, 
from  experiment,  of  the  specific  gravity  of  hydrochloric  acid  of  determinate  strengths 
(First  Principles  of  Cemistry)  :  — 


HYDROCHLORIC   ACID. 


Atoms  of  Water 
to  1  of  Acid. 

Real  Acid  in  100 
of  the  liquid.. 

Specific 
Gravity. 

Atoms  of  Water 
to  1  of  Acid. 

Real  Acid  in  100 
of  the  liquid. 

Specific 
Gravity. 

6 

40.06 

1.203 

14 

22.700 

1.1060 

7 

37.00 

.179 

15 

21.512 

1.1008 

8 

33.95 

.162 

16 

20.442 

1.0960    i 

9 

31.35 

.149 

17 

19.47-4 

1.0902 

10 

29.13 

.139 

18 

18.590 

1.0860 

11 

27.21 

.1285 

19 

17.790 

1.0820    i 

12 

25.52 

1.1.J97 

20 

17051 

1.0780    | 

13 

24.03 

1.1127 

To  this  may  be  added  the  following  useful  table,  for  which  we  are  indebted  to 
Mr.  E.  Davy:  — 


HYDROCHLORIC   ACID. 


337 


HYDROCHLORIC   ACID. 


Specific  Gravity. 

Quantity  of  Acid 
per  cent. 

Specific  Gravity. 

Quantity  of  Acid 
per  cent. 

.21 

42.43 

1.10 

20.20 

.20 

40.80 

1.09 

18.18 

.19 

38.38 

1.08 

16.16 

.18 

36.36 

1.07 

14.14 

.17 

34.34 

1.06 

12.12 

.16 

32.32 

1.05 

10.10 

.15 

30.30 

1.04 

8.08 

.14 

28.28 

1.03 

6.00 

1.13 

26.26 

1.02 

4.04 

1.12 

24.24 

1.01 

2.02 

1.11 

22.22 

It  thus  appears  that  the  strongest  hydrochloric  acid  that  can  be  easily  formed 
contains  six  eqs.  of  water  :  this  liquid  allows  acid  to  escape  when  evaporated  in  air, 
and  comes,  according  to  an  observation  of  my  own,  to  contain  12  eqs.  of  water  to  1 
of  acid.  Distilled  in  a  retort,  it  was  found,  by  Dr.  Dalton,  to  lose  more  acid  than 
water  till  it  attained  the  specific  gravity  1.094,  when  its  boiling  point  attained  a 
maximum  of  230°,  and  the  acid  then  distilled  over  unchanged.  Dr.  Clark  finds  by 
careful  experiments  that  the  acid,  which  is  unalterable  by  distillation,  contains  16.4 
equivalents  of  water. 

The  concentrated  acid  is  a  colourless  liquid,  fuming  strongly  in  air,  highly  acid,  but 
less  corrosive  than  sulphuric  acid ;  not  poisonous  when  diluted.  It  is  decomposed 
by  substances  which  yield  oxygen  readily,  such  as  metallic  peroxides  and  nitric  acid, 
which  cause  an  evolution  of  chlorine,  by  oxidating  the  hydrogen  of  the  hydrochloric 
acid.  A  mixture  of  1  measure  of  nitric  and  2  measures  of  muriatic  acid  forms 
aqua  regia,  which  dissolves  the  less  oxidable  metals,  such  as  gold  and  platinum. 

The  hydrochloric  acid  of  commerce  has  a  yellow  or  straw  colour,  which  is  generally 
due  to  a  little  iron,  but  may  be  occasionally  produced  by  organic  matter,  as  it  is 
sometimes  destroyed  by  light.  This  acid  is  rarely  free  from  sulphuric  acid,  the 
presence  of  which  is  detected  by  the  appearance  of  a  white  precipitate  of  sulphate 
of  baryta  on  the  addition  of  chloride  of  barium  to  the  hydrochloric  acid  diluted  with 
4  or  5  times  its  bulk  of  distilled  water.  Sulphurous  acid  is  also  occasionally  present 
in  commercial  hydrochloric  acid,  and  is  indicated  by  the  addition  of  a  few  crystals 
of  protochloride  of  tin,  which  salt  decomposes  sulphurous  acid,  and  occasions,  after 
standing  some  time,  a  brown  precipitate  containing  sulphur  in  combination  with  tin 
(Girardin).  To  purify  hydrochloric  acid,  it  may  be  diluted  till  its  sp.  gr.  is  about 
1.1,  for  which  the  strongest  acid  requires  an  equal  volume  of  water;  and  with  the 
addition  of  a  portion  of  chloride  of  barium,  the  acid  should  then  be  re-distilled.  As 
the  acid  brings  over  enough  of  water  to  condense  it,  Liebig's  condensing  apparatus 
(fig.  30,  page  73)  can  be  used  in  this  distillation.  The  pure  acid  thus  obtained  is 
strong  enough  for  most  purposes,  and  has  the  advantage  of  not  fuming  in  the  air. 
Hydrochloric  acid,  like  chlorine  and  the  soluble  chlorides,  gives  with  nitrate  of  silver 
a  white  curdy  precipitate,  the  chloride  of  silver,  soluble  in  ammonia,  but  not  dis- 
solved by  hot  or  cold  nitric  acid. 

Hydrochloric  acid  belongs  to  the  class  of  hydrogen  acids  or  hydracids.  On  neu- 
tralizing this  acid  with  soda  or  any  other  basic  oxide,  no  hydrochlorate  of  soda  is 
formed ;  but  the  hydrogen  of  the  acid  with  the  oxygen  of  the  soda  forming  water, 
the  chlorine  and  sodium  combine,  and  produce  a  metallic  chloride.  Zinc,  and  the 
other  metals  which  dissolve  in  dilute  sulphuric  acid,  with  evolution  of  hydrogen, 
dissolve  with  equal  facility  in  this  acid,  with  the  same  evolution  of  hydrogen,  and  a 
chloride  of  the  metal  is  then  formed. 
22 


338  CHLORINE. 


COMPOUNDS    OF    CHLORINE    AND    OXYGEN. 

Chlorine  and  oxygen  gases  in  a  free  state  exhibit  no  disposition  to  combine  with 
each  other  in  any  circumstances,  but  this  is  not  inconsistent  with  their  forming  a 
series  of  compounds,  as  nitrogen  and  oxygen,  which  exhibit  a  similar  indifference  to 
each  other,  also  do.  The  oxides  of  chlorine  are  five  in  number,  namely :  — 

Hypochlorous  acid CIO 

Chlorous  acid C103  4 

Peroxide  of  chlorine,  or  Hypochloric  acid C104 

Chloric  acid C105 

Perchloric  acid C107 

Hypochlorous  and  chloric  acids  are  always  primarily  formed  by  a  reaction  occur- 
ring between  chlorine  and  two  different  classes  of  metallic  oxides ;  and  the  chlorous 
and  perchloric  acids,  again,  are  derived  from  the  decomposition  of  chloric  acid. 

HYPOCLHLOROUS   ACID. 

Eg.  43.5;  CIO;  density  of  vapour  2977 ;     |_| | 

The  discovery  of  this  compound  in  a  separate  state  was  made  by  M.  Balard  in 
1834  (Annal.  de  Ch.  et  de  Ph.  Ivii.  225 ;  or  Taylor's  Scientific  Memoirs,  i.  269).  It 
was  obtained  by  acting  with  chlorine  upon  the  red  oxide  of  mercury.  If  to  a  two- 
pound  bottle  of  chlorine  gas  300  grains  of  red  oxide  of  mercury  in  fine  powder  be 
added,  with  1  £  ounce  of  water,  the  chlorine  will  be  found  to  be  rapidly  absorbed  on 
agitation.  One  portion  of  the  chlorine  unites  with  the  oxygen  of  the  metallic  oxide, 
and  becomes  hypochlorous  acid,  which  is  dissolved  by  the  water;  while  another  por- 
tion forms  a  chloride  with  the  metal,  which  chloride  unites  with  a  portion  of  unde- 
composed  oxide,  and  forms  an  insoluble  oxichloride.  The  liquid  may  be  poured  off 
and  allowed  to  settle :  it  is  a  solution  of  hypochlorous  acid,  with  generally  a  little 
chloride  of  mercury.  This  reaction  is  expressed  in  the  following  diagrkm  :  — 

FORMATION  OF  HYPOCHLOROUS  ACID. 

Before  decomposition.  After  decomposition. 

Chlorine Chlorine __^  Hypochlorous  acid 

Oxide  of  mercury 

Chlorine Chlorine _  H^=^  Chloride  of  mercury  j 

Oxide  of  mercury     Oxide  of  mercury Oxide  of  mercury       j  C( 

Or  in  symbols : 

2C1  and  2HgO=C10  and  HgCl.HgO. 

But  the  oxichloride  formed  seems  not  always  to  contain  the  same  proportion  of 
oxide.  The  proportion  of  hypochlorous  acid  in  the  liquid  may  be  increased  by  intro- 
ducing the  same  solution  into  a  second  bottle  of  chlorine,  with  an  additional  quan- 
tity of  red  oxide  of  mercury.  The  oxide  of  zinc  and  black  oxide  of  copper,  diffused 
through  water,  and  exposed  to  chlorine,  give  rise  to  a  similar  formation  of  hypo- 
chlorous  acid. 

If  red  oxide  of  mercury  in  fine  powder  be  added  to  chlorine-water  so  long  as  the 
oxide  is  dissolved,  a  solution  of  hypochlorous  acid  and  chloride  of  mercury  is  formed, 
without  any  insoluble  compound:  2C1  and  HgO=C10  and  HgCl  (Gay-Lussac). 

On  the  other  hand,  hypochlorous  acid,  free  from  water,  arid  in  the  liquid  state, 
may  be  obtained  by  passing  dry  chlorine  gas  in  a  gradual  manner  over  red  oxide  of 


HYPOCHLOROUS   ACID.  339 

mercury  in  a  glass  tube  a  b  (fig.  154) ;  care  being  taken  to  prevent  elevation  of 
temperature,  by  surrounding  the  tube  with  fragments  of  ice,  or  immersing  it  in  cold 

FIG.  154. 


water,  as  otherwise  nothing  but  oxygen  will  be  disengaged.  The  chlorine  is  evolved 
from  the  usual  materials  in  the  flask  A,  passed  through  water  in  the  wash-bottle  B 
to  arrest  any  hydrochloric  acid,  and  afterwards  dried  over  chloride  of  calcium  tube  C. 
Chloride  of  mercury  is  formed  as  in  the  other  processes,  and  a  yellow  gas,  which  is 
liquefied  in  the  bent  tube  D,  kept  cold  by  a  freezing  mixture  of  ice  and  salt.  The 
oxide  of  mercury  which  answers  best  for  this  experiment  is  that  precipitated  from 
chloride  or  nitrate  of  mercury  by  potassa,  washed  and  dried  at  a  temperature  of 
abouti572°  (300°  C.)  —  Regnault's  Traite". 

Hypochlorous  acid  is  a  liquid  of  an  orange-yellow  colour,  which  boils  at  about  68° 
(20°  C.)  Its  vapour  is  of  a  pale  yellow  colour,  very  similar  to  chlorine.  It  is 
composed  of  2  volumes  of  chlorine  and  1  volume  of  oxygen,  condensed  into  2  volumes, 
which  gives  a  theoretical  density  of  2992,  while  2977  has  been  obtained  by  experi- 
ment. It  is  resolved  by  a  slight  elevation  of  temperature  into  its  constituent  gases; 
a  property  which  allows  it  to  be  analyzed,  by  determining  the  proportions  -of  the 
mixed  chlorine  and  oxygen  gases.  Water  dissolves  about  200  volumes  of  this  gas, 
and  assumes  a  fine  yellow  colour. 

Hypochlorous  acid  is  also  formed  when  chlorine  is  absorbed  by  woak  so/utions  of 
alkalies  and  by  hydrate  of  lime,  and,  as  the  acid  of  the  bleaching  chlorides,  possesses 
considerable  interest.  It  displaces  the  carbonic  acid  of  alkaline  carbonates,  but  has 
not  much  analogy  to  other  acids.  Its  taste  is  extremely  strong  and  acrid,  but  not 
sour,  and  its  odour  penetrating  and  different  from,  although  somewhat  similar  to, 
chlorine.  It  attacks  the  epidermis  like  nitric  acid,  and  is  exceedingly  corrosive. 
It  bleaches  instantly,  like  chlorine,  and  is  a  powerful  oxidizing  agent.  A  concen- 
trated solution  of  it  is  exceedingly  unstable,  small  bubbles  of  chlorine  gas  being 
spontaneously  evolved  and  chloric  acid  formed.  This  decomposition  is  promoted  by 
the  presence  of  angular  bodies,  such  as  pounded  glass,  and  also  by  heat  and  light. 

Of  the  elementary  bodies,  hydrogen  has  no  action  upon  hypochlorous  acid.  Sul- 
phur, selenium,  phosphorus,  and  arsenic,  act  upon  it  with  great  energy,  and  are  all 
of  them  raised  to  their  highest  degree  of  oxidation,  with  the  evolution  of  chlorine 
gas;  selenium  even  being  converted  into  selenic  acid,  although  it  is  converted  into 
selenious  acid  only  by  the  action  of  nitric  acid.  Iodine  is  also  converted  into  iodie 
acid.  Iron  filings  decompose  it  immediately,  and  chlorine  gas  comes  off.  Copper 
and  mercury  combine  with  both  elements  of  the  acid,  and  form  oxichlorides.  Many 
other  metals  are  not  acted  upon  by  it,  unless  another  acid  be  present,  such  as  zinc, 
tin,  antimony,  and  lead.  Silver  has  a  different  action  upon  hypochlorous  acid  from 
that  of  most  bodies,  combining  with  its  chlorine,  and  causing  an  evolution  of  oxygen 
gas.  Hydrochloric  and  hypochlorous  acid  mutually  decompose  each  other,  water 
being  formed,  and  chlorine  liberated ;  if  the  liquids  are  both  cooled  to  a  very  low 


340 


CHLORINE. 


degree,  before  mixture,  the  chlorine  is  not  disengaged,  but  combines  with  water  to 
form  the  hydrate  of  chlorine,  and  causes  the  liquid  to  become  a  solid  mass.  The 
presence  of  soluble  chlorides  is  equally  incompatible  with  the  existence  of  hypo- 
chlorous  acid. 

Hypochlorites.  —  The  direct  combination  of  hypochlorous  acid  with  powerful 
bases  is  accompanied  by  heat,  which  is  apt  to  convert  the  hypochlorite  into  a  mix- 
ture of  chlorate  and  chloride;  but  by  adding  the  acid  in  a  gradual  manner  to  the 
alkaline  solution,  hypochlorites  of  potassa,  soda,  lime,  baryta,  and  strontia,  may  be 
formed,  and  may  even  be  obtained  in  a  solid  state  by  evaporation  in  vacuo,  if  a  con- 
siderable excess  of  alkali  be  present,  which  appears  to  give  a  certain  degree  of  stabi- 
lity to  these  salts.  They  bleach  powerfully,  and  their  odour  and  colour  are  identi- 
cally the  same  as  the  corresponding  decolourizing  compounds  of  chlorine,  formed  by 
exposing  solutions  of  the  highly  basic  oxides  named  to  chlorine  gas,  from  which  it  is 
impossible  to  distinguish  them  by  their  physical  properties.  When  chlorine,  then, 
is  absorbed  by  a  weak  solution  of  potassa,  without  heat  being  applied,  the  hypo- 
chlorite of  potassa  is  formed,  with  chloride  of  potassium,  both  of  which  remain  in 
solution :  — 

2C1  and  2KO=KO.C10  and  KC1. 


FIG.  155. 


The  hypochlorites  are  salts  of 
a  very  changeable  constitution  ;  a 
slight  increase  of  temperature, 
the  influence  of  solar  light,  even 
diffused  light,  converts  them  into 
chloride  and  chlorate. 

The  euchlorine  gas  of  Davy,  to 
which  he  assigned  the  composition 
of  hypochlorous  acid,  has  been 
found  to  be  a  mixture  of  chlorine 
gas  and  chlorochloric  acid.  That 
mixture  is  obtained  by  the  action 
of  hydrochloric  acid  of  sp.  gr.  1.1 
upon  chlorate  of  potassa,  aided  by 
a  gentle  heat.  It  has  a  very  yel- 
low colour  (euchlorine),  and  ex- 
plodes feebly  when  a  hot  wire  is 
introduced  into  it,  becoming  nearly 
colourless  when  the  chlorochloric 
.acid  is  decomposed.  A  tube  re- 
tort A  (fig.  155),  is  employed  for 
the  evolution  of  this  gas,  and  it 
is  collected  in  the  phial  B  by  dis- 
placement. 


CHLORIC   ACID. 

Eq.  75.5  or  943.75;  HO.C105. 

When  a  stream  of  chlorine  gas  is  transmitted  through  a  strong  solution  of  caustic 
potassa,  the  gas  is  absorbed,  and  a  solution  is  formed  which  bleaches  at  first,  but 
loses  that  property  without  any  escape  of  gas,  and  becomes  a  mixture  of  chloride  of 
potassium  and  chlorate  of  potassa;  the  latter  of  which,  being  the  least  soluble,  sepa- 
rates in  shining  tabular  crystals.  Five  equivalents  of  potassa  (the  oxide  of  potas- 
sium) are  decomposed  by  6  of  chlorine,  5  of  which  unite  with  the  potassium,  and 
form  5  equivalents  of  chloride  of  potassium,  while  the  5  of  oxygen  form  chloric  acid 
with  the  remaining  equivalent  of  chlorine,  as  stated  in  the  following  diagram,  in 
which  the  numbers  exp^oss  equivalents : — 


CHLORIC   ACID.  341 


ACTION    OP   CHLORINE    UPON   POTASSA. 

Before  decomposition.  After  decomposition. 

5  Chlorine 5  Chlorine ^  5  Chloride  of  Potassium. 

I  5  Potassium 
|  5  Oxygen 

Chlorine Chlorine ^ »  Chloric  acid  ")  Chlorate  of 

Potassa Potassa Potassa j      potassa. 

Or  in  symbols :  6C1  and  6KO  =  KO.C105  and  5KC1.  Such  is  the  nature  of  the 
action  of  chlorine  upon  the  soluble  and  highly  alkaline  metallic  oxides,  when  their 
solutions  are  concentrated,  or  heat  applied. 

The  chlorate  of  baryta  may  be  formed  by  transmitting  chlorine  through  caustic 
baryta  in  the  same  manner;  and  from  a  solution  of  the  pure  chlorate  of  baryta, 
chloric  acid  may  be  obtained  by  the  cautious  addition  of  sulphuric  acid,  so  long  as 
ft  occasions  a  precipitate  of  sulphate  of  baryta.  The  solution  may  be  evaporated  by 
a  very  gentle  heat  till  it  becomes  a  syrupy  liquid,  which  has  no  odour,  but  a  very 
acid  taste,  is  decomposed  above  100°,  and  when  distilled  at  a  still  higher  tempera- 
ture gives  water,  then  a  mixture  of  chlorine  and  oxygen  gases,  and  hyperchloric 
acid;  which  last  acid  may  be  prepared  in  this  way  without  difficulty.  Chloric 
acid  is  not  isolable,  being  incapable  of  existing  except  in  combination  with  water 
or  a  fixed  base.  This  acid  first  reddens  litmus  paper,  but  after  a  time  the  colour 
is  bleached,  and  if  the  acid  has  been  highly  concentrated,  the  paper  often  takes 
fire.  It  dissolves  zinc  and  iron  with  disengagement  of  hydrogen.  Chloric  acid  is 
decomposed  by  hydrochloric  acid,  with  escape  of  chlorine,  and  by  most  combustible 
bodies  and  acids  of  the  lower  degrees  of  oxidation,  such  as  sulphurous  and  phos- 
phorous acids,  which  oxidate  themselves  at  its  expense. 

This  acid,  when  free  or  in  combination,  may  be  recognized  by  several  properties. 
It  is  not  precipitated  by  chloride  of  barium  or  nitrate  of  silver,  and  its  salts  have  no 
bleaching  power ;  sulphuric  acid  causes  the  disengagement  from  it  of  a  yellow  gas, 
having  a  peculiar  odour,  which  bleaches  strongly;  and  its  salts,  when  heated  to 
redness,  afford  oxygen,  and  deflagrate  with  combustibles. 

Chlorates.  —  This  class  of  salts  is  remarkable  for  a  general  solubility,  like  the 
nitrates.  Those  of  them  which  are  fusible  detonate  with  extreme  violence  with 
combustibles.  The  chlorate  of  potassa,  of  which  the  preparation  and  properties  will 
be  described  under  the  salts  of  potassa,  has  become  a  familiar  chemical  product, 
being  largely  consumed  in  the  manufacture  of  deflagrating  mixtures.  The  chlorates 
were  at  one  time  termed  hyperoxymuriates,  and  their  acid,  the  existence  of  which 
was  originally  observed  by  Mr.  Chenevix,  was  first  obtained  in  a  separate  state  by 
Gay-Lussac. 

The  composition  of  chloric  acid  is  ascertained  by  decomposing  a  known  quantity 
of  chlorate  of  potassa  by  heat,  and  ascertaining  the  loss  of  weight  which  is  due  to 
the  expulsion  of  6  eqs.  of  oxygen.  The  chloride  of  potassium  which  forms  the  fixed 
residue  is  dissolved,  and  the  chlorine  precipitated  by  nitrate  of  silver.  The  chlorine 
is  thus  obtained  in  the  form  of  chloride  of  silver,  of  which  the  composition 'is  known. 
The  relation  between  the  equivalents  of  chlorine  and  oxygen  is  also  established  by 
the  analysis  of  the  chlorate  of  potassa  (Note,  p.  104). 

HYPERCHLORIC  ACID. 

Eg.  91.5  or  1143.75;  HO.C107. 

This  acid,  which  is  also  named  perchloric  and  oxichloric  acid,  is  obtained  from 
chlorate  of  potassa  in  different  ways.  At  that  particular  point  of  the  decomposition 
of  chlorate  of  potassa  by  heat,  when  the  evolution  of  oxygen  is  about  to  become 
very  violent*,  the  fused  salt  is  in  a  pasty  state,  and  contains,  as  was  first  observed  by 


342  CHLORINE. 

Serullas,  a  considerable  quantity  of  perchlorate,  the  oxygen  extricated  from  one  por- 
tion of  chlorate  being  retained  by  another  portion  of  the  same  salt.  This  salt  is 
rubbed  to  powder,  and  dissolved  in  boiling  water,  from  which  the  perchlorate  is  first 
deposited,  on  cooling,  owing  to  its  sparing  solubility.  It  is  stated  by  M.  Millon, 
that  from  50  to  53  per  cent,  of  perchlorate  may  be  obtained  by  stopping  when  9J 
litres  of  gas  (580  c.  i.)  are  collected  from  100  grammes  (1543  grains)  of  chlorate, 
instead  of  13  litres.  (Annal.  de  Ch  et  Ph.,  3e  ser.  vii.  335.)  The  same  salt  may 
also  be  prepared  by  throwing  chlorate  of  pdtassa,  in  fine  powder,  and  well  dried, 
into  oil  of  vitriol  gently  heated  in  an  open  basin,  by  a  few  grains  at  a  time,  when 
the  liberated  chloric  acid  resolves  itself  into  peroxide  of  chlorine  and  hyperchloric 
acid,  the  former  coming  off  as  a  yellow  gas ;  thus  : — 


RESOLUTION    OP   CHLORIC   ACID   INTO   PEROXIDE   OF   CHLORINE   AND    HYPER- 
CHLORIC  ACID. 

Before  decomposition.  After  decomposition. 

(  2  Chlorine ^  2  Perox.  chlorine. 


3  Chloric  acid 

I    i  uxygen  — _____ 

Hyperchloric  acid. 

Of  the  3  equivalents  of  potassa,  previously  in  combination  with  the  chloric  acid, 
one  remains  with  hyperchloric  acid  as  hyper«hlorate  of  potassa,  and  the  other  two 
are  converted  into  bisulphate  of  potassa.  The  whole  reaction  between  the  acid  and 
salt  may,  therefore,  be  thus  expressed : — 

3(KO.C105)  and  4(HO.S03)  =  2C104  and  KO.C107 
and  (2HO.S03  +  KO.S03)  and  2HO. 

In  conducting  this  operation,  the  greatest  caution  is  necessary,  owing  to  the  ex- 
plosive property  of  peroxide  of  chlorine ;  for  if  the  order  of  mixing  the  substances 
be  reversed,  and  the  acid  poured  upon  the  chlorate,  or  if  too  much  chlorate  be  added 
at  a  time  to  the  acid,  a  most  violent  and  dangerous  detonation  may  occur.  But  this 
reaction  is  chiefly  interesting  as  affording  peroxide  of  chlorine ;  for  hyperchlorate  of 
potassa  may  be  obtained  from  chlorate  by  the  action  of  nitric  acid,  lately  observed 
by  Professor  Penny,  without  danger  or  inconvenience.  The  chlorate  is  tranquilly 
decomposed  in  nitric  acid  gently  heated  upon  it,  the  chlorine  and  oxygen  at  3  equi- 
valents of  peroxide  of  chlorine  being  evolved  in  a  state  of  mixture  and  not  of  com- 
bination :  the  saline  residue  consists  of  3  equivalents  of  nitrate  and  1  of  perchlorate 
of  potassa,  which  may  be  separated  by  dissolving  them  in  the  smallest  adequate 
quantity  of  boiling  water.  On  cooling,  the  perchlorate  separates  in  small  shining 
crystals,  which  may  be  dissolved  a  second  time  to  obtain  them  perfectly  pure. 

Perchloric  acid  may  be  prepared  from  the  last  salt  by  boiling  it  with  an  excess 
of  fluosilicic  acid,  which  forms,  .with  potassa,  a  salt  nearly  insoluble.  After  cooling, 
a  clear  liquid  is  decanted  and  evaporated  by  the  water-bath.  To  eliminate  a  small 
excess  of  hydrofluoric  acid,  a  little  silica  in  fine  powder  is  added  to  the  liquid,  which 
at  a  certain  degree  of  concentration  carries  off  the  former  as  fluosilicic  acid.  After 
being  still  further  concentrated,  the  acid  liquid  may  be  distilled  in  a  retort  by  a 
sand-bath  heat.  A  very  dilute  acid  comes  over  first,  but  the  temperature  of  ebulli- 
tion rises  till  it  attains  392°,  after  which  the  receiver  should  be  changed,  because 
what  then  passes  over  is  a  concentrated  acid  of  sp.  gr.  1.65.  This  acid  is  a  colour- 
less liquid  which  fumes  slightly  in  the  air.  It  may  be  still  farther  concentrated  by 
distilling  it  with  4  or  5  times  its  weight  of  strong  sulphuric  acid,  when  the  greater 
part  of  it  is  decomposed  into  chlorine  and  oxygen ;  but  a  portion  condenses  in  a 
mass  of  small  crystals,  and  also  in  long  four-sided  prismatic  needles  terminated  by 
dihedral  summits,  which  were  found  by  Serullas  to  be  two  different  hydrates  of  the 
acid,  the  last  containing  least  water  and  being  most  volatile.  The  crystals  and  the 


CHLOROUS    ACID.  343 

concentrated  solution  of  the  acid  have  a  great  affinity  for  water;  the  acid  itself 
(C107)  appears  not  to  be  isolable. 

Perchloric  acid  is  much  the  most  stable  of  the  oxides  of  chlorine ;  it  does  not 
bleach,  is  not  altered  by  the  presence  of  sulphuric  acid,  and  is  not  decomposed  by 
sulphurous  acid  or  by  hydrosulphuric  acid.  It  dissolves  zinc  and  iron  with  effer- 
vescence, and,  in  point  of  affinity,  is  one  of  the  most  powerful  acids.  Perchloric 
acid  is  recognized  by  producing,  with  potassa,  a  salt  of  the  same  sparing  solubility 
as  bitartrate  of  potassa.  It  is  an  interesting  acid  from  its  composition,  and  as  being 
the  most  accessible  of  the  small  class  containing  periodic  and  permanganic  acids,  to 
which  it  belongs.  The  alkaline  perchlorates  emit  much  oxygen  when  heated,  and 
leave  metallic  chlorides ;  they  do  not  deflagrate  so  powerfully  with  combustibles  as 
the  chlorates. 

CHLOROUS   ACID. 

Eq.  59.5  or  743.75;  C103;  density  2.646. 

This  is  a  gaseous  compound  of  chlorine  and  oxygen,  which  is  not  liquefied  at  5° 
( — 15°  C.),  and  is  therefore  remarkable  for  its  fixity.  It  was  discovered  and  studied 
by  M.  Millon  (Annal.  de  Ch.  et  Ph.,  3  ser.  vii.)  Chlorous  acid  is  formed  by  the 
deoxidation  of  chloric  acid  in  various  circumstances.  It  is  readily  obtained  from  a 
mixture  of  three  parts  of  arsenious  acid  and  four  of  chlorate  of  potassa,  pulverized 
together,  and  made  into  a  thin  paste  with  water ;  twelve  parts  of  ordinary  nitric  acid 
diluted  with  four  of  water  being  added,  the  whole  is  introduced  into  a  flask,  which 
is  filled  to  the  neck  with  the  mixture,  and  heated  cautiously  by  a  water-bath. 

Chlorous  acid  is  a  gas  of  a  greenish-yellow  colour,  of  which  water  dissolves  five 
or  six  times  its  volume,  assuming  a  golden-yellow  tint  of  considerable  intensity.  It 
bleaches  litmus  and  indigo,  but  does  not  attack  gold,  platinum,  nor  antimony.  It  is 
decomposed  by  heat,  in  general  at  134.6°  (57°  C.),  into  perchloric  acid,  chlorine, 
and  oxygen:  3C103—  C107  and  20  and  2C1.  Chlorous  acid  combines  with  bases, 
and  forms  crystallizable  salts;  the  affinity  of  this  and  some  other  anhydrous  acids  is 
gradually  exerted,  and  requires  time  for  its  action.  On  pouring  a  solution  of  chlo- 
rite of  potassa  into  a  solution  of  nitrate  of  lead,  a  yellowish-white  precipitate  of 
chlorite  of  lead  is  obtained,  PbO.C103,  which  is  easily  subjected  to  analysis  by 
transforming  it  into  sulphate  by  means  of  sulphuric  acid ;  or,  if  the  chlorite  of  lead 
be  fused  in  a  crucible  with  carbonate  of  soda,  the  whole  chlorine  of  the  chlorous 
acid  is  obtained  in  the  form  of  chloride  of  potassium,  and  may  be  precipitated  from 
an  acid  solution  by  nitrate  of  silver,  and  estimated  as  chloride  of  silver. 

According  to  M.  Millon,  the  gas  which  forms  when  chlorate  of  potassa  is  treated 
with  hydrochloric  acid  (euchlorine),  ought  to  be  considered  a  compound  of  chloric 
and  chlorous  acid,  2C105.C103.  It  is  named  chlorochloric  acid.  Another  double 
acid,  which  Millon  has  named  chloroperchloric  acid,  is  formed  when  humid  chlorous 
acid  is  exposed  to  light,  and  condenses  as  a  red  liquid,  2C107.C103. 

PEROXIDE   OF   CHLORINE. 

Hypochloric  acid;  eq.  67.5  or  843.75:  C104. 

This  substance  cannot  be  obtained  in  a  state  of  purity  without  considerable  dan- 
ger. Gray-Lussac  recommends,  in  preparing  it,  to  mix  chlorate  of  potassa  in  the 
state  of  a  paste  with  sulphuric  acid  previously  diluted  with  half  its  weight  of  water 
and  cooled,  and  to  distil  the  mixture  in  a  small  retort  by  a  water-bath.  It  comes 
off  as  a  gas,  of  a  yellow  colour  considerably  deeper  than  chlorine,  which  cannot  be 
collected  over  mercury,  as  it  is  instantly  decomposed  by  that  metal,  nor  over  water, 
which  dissolves  it  in  large  quantity.  It  is  composed  of  2  volumes  of  chlorine  with 
4  volumes  of  oxygen,  condensed  into  4  volumes,  which  gives  it  a  density  of  2337.5. 
This  gas  is  decomposed  gradually  by  light,  but  between  200°  and  212°  its  elements 
separate  in  an  instantaneous  manner,  with  the  disengagement  of  light  and  a  violent 


344  CHLORINE. 

explosion,  which  breaks  the  vessels.  "Water  dissolves  about  20  times  its  volume  of 
this  gas :  the  gas  itself  is  liquefied  by  cold,  and  forms  a  red  liquid,  which  boils  at 
68°  (20°  C.)  It  bleaches  damp  litmus  paper,  without  first  reddening  it,  and  is 
absorbed  by  alkaline  solutions  with  the  formation  of  a  mixture  of  a  chlorate  and 
chlorite.  This  compound,  then,  resembles  peroxide  of  nitrogen,  N04,  and  is  not 
a  peculiar  acid,  but  may  be  represented  as  a  compound  of  chlorous  and  chloric 
acids:  2C104=C10?+C105. 

Peroxide  of  chlorine  has  a  violent  action  upon  combustibles,  kindling  phosphorus, 
sulphur,  sugar,  and  other  combustible  substances  in  contact  with  which  it  is  evolved. 
Its  action  upon  phosphorus  may  foe  shown  by  throwing  a  drachm  or  two  of  crystal- 
lized chlorate  of  potassa  into  a  deep  foot-glass  (fig.  156)  filled  with  cold  water,  to  the 
bottom  of  which  the  salt  falls  without  any  loss  by  solution.    Oil 
FIG.  156.  Of  vitriol  is  then  conducted  to  the  salt,  in  a  small  stream,  from 

a  tube  funnel,  the  lower  end  of  which  has  been  drawn  out  into 
a  jet  with  a  minute  opening.  A  gas  of  a  lively  yellow  colour 
is  evolved  with  slight  concussions,  and  immediately  dissolved  by 
the  water,  to  which  it  imparts  the  same  colour.  If,  while  this 
is  occurring,  a  piece  of  phosphorus  be  thrown  into  the  glass,  it 
is  ignited  by  every  bubble  of  gas  evolved,  and  a  brilliant  com- 
bustion is  produced  under  the  water,  forming  a  beautiful  expe- 
riment wholly  without  danger.  If  a  few  grains  of  chlorate  of 
potassa  in  fine  powder  and  loaf-sugar  be  mixed  upon  paper  by 
the  fingers,  (rubbing  these  substances  together  in  a  mortar  may 
be  attended  with  a  dangerous  explosion),  and  a  single  drop  of 
sulphuric  acid  be  allowed  to  fall  from  a  glass  rod  upon  the  mix- 
ture, an  instantaneous  deflagration  takes  place,  occasioned  by  the  evolution  of  the 
yellow  gas,  which  ignites  the  mixture.  Captain  Manby  used  to  fire  in  this  manner 
the  small  piece  of  ordnance,  which  he  proposed,  as  a  life-preserver,  to  throw  a  rope 
over  a  stranded  vessel  from  the  shore ;  and  the  same  mixture  was  afterwards  em- 
ployed, with  sulphuric  acid,  in  various  forms  of  the  instantaneous  light-match,  all 
of  which,  however,  are  now  superseded  by  other  mixtures  ignited  by  friction  with- 
out sulphuric  acid. 

CHLORINE   AND   BINOXIDE   OF   NITROGEN. 

Mr.  E.  Davy  appears  first  to  have  obtained  a  gaseous  compound  of  chlorine  and 
binoxide  of  nitrogen  in  1830,  and  a  combination  of  the  same  constituents  was  dis- 
tilled from  aqua  regia  and  liquefied  by  M.  Baudrimont  in  1843.  It  is  only  lately, 
however,  that  the  nature  of  the  mutual  action  of  nitric  and  hydrochloric  acids  has 
been  fully  explained  by  the  investigations  of  M.  Gay-Lussac  on  aqua  regia.  (Ann. 
de  Ch.  et  Ph.,  3me  ser.  xxiii.  203;  or,  Chemical  Gazette,  1848,  p.  269). 

When  nitric  and  hydrochloric  acids  are  mixed,  a  reaction  soon  commences  if  the 
acids  are  concentrated  j  the  liquid  becomes  of  a  red  colour,  and  effervescence  takes 
place,  from  the  escape  of  chlorine  and  a  chloro-nitric  vapour.  On  passing  this 
gaseous  mixture  through  a  U  tube,  the  angle  of  which  is  immersed  in  a  freezing 
mixture  of  ice  and  salt,  the  chloro-nitric  compound  condenses  as  a  dark-coloured 
liquid,  and  is  thus  separated  from  the  free  chlorine  which  accompanied  it. 

Chloro-nitric  acid,  N02C12-  —  This  forms  the  principal  part  of  the  chloro-nitric 
vapour :  it  may  be  represented  as  a  peroxide  of  nitrogen  in  which  two  equivalents 
of  oxygen  are  replaced  by  two  equivalents  of  chlorine.  A  third  equivalent  of  chlo- 
rine, due  to  the  third  equivalent  of  oxygen  yielded  by  the  nitric  acid,  is  disengaged 
as  gas^  and  is  the  agent  by  which  aqua  regia  dissolves  gold,  platinum,  and  other 
metals  having  a  weak  affinity  for  oxygen,  converting  them  into  chlorides  :  the  chlnro- 
nitric  acid  takes  no  part  in  the  action.  This  compound  is  also  formed  by  the  mix- 
ture of  the  two  gases  in  equal  volumes,  which  assume  a  brilliant  orange  colour,  and 
suffer  a  condensation  amounting  to  exactly  one-third  of  their  original  volume.  The 
theoretical  density  of  this  vapour  is  1740.2. 


CHLQRIDE   OF    CARBON.  345 

Chloro-nitrous  acid,  N02C1.  —  This  second  compound,  which  corresponds  with 
nitrous  acid,  N03,  always  appears  simultaneously  with  the  other  in  variable  propor- 
tions. It  is  a  vaporous  liquid  of  similar  properties,  of  which  the  vapour  density 
is  inferred  to  be  2259.4.  The  vapours  of  both  compounds,  when  conducted  into 
water,  are  instantly  decomposed  into  hydrochloric  acid  and  peroxide  of  nitrogen  or 
nitrous  acid — a  decomposition  which  affords  the  means  of  determining  the  propor- 
tion of  chlorine  which  they  contain.  The  chloro-nitric  compounds  are  also  decom- 
posed by  mercury,  the  chlorine  combining  with  the  metal  and  leaving  pure  binoxide 
of  nitrogen.  The  solution  of  the  vapours  in  water  decolorizes  a  solution  of  per- 
manganate of  potassa,  owing  to  the  peroxide  of  nitrogen  it  contains,  but  does  not 
bleach  indigo  because  it  contains  no  free  chlorine. 

CHLORIDE   OF   NITROGEN. 

This  is  one  of  the  most  formidable  of  explosive  compounds,  and  great  caution  is 
necessary  in  its  preparation  to  avoid  accidents.  Four  ounces  of  sal  ammoniac  (which 
must  not  smell  of  animal  matter  or  of  nitrate  of  ammonia),  are  dissolved  in  a  small 
quantity  of  boiling  water,  filtered,  and  made  up  to  3  pounds  with  distilled  water  j  a 
two-pound  bottle  of  chlorine  is  inverted  in  a  basin  containing  this  solution  at  80°, 
being  supported  by  the  ring  of  a  retort  stand,  with  its  mouth  over  a  small  leaden 
saucer.  The  chlorine  gas  is  absorbed,  and  upon  the  surface  of  the  liquid,  which 
rises  into  the  bottle,  an  oily  substance  condenses,  which,  when  it  accumulates,  preci- 
pitates in  large  drops,  and  is  received  in  the  leaden  saucer.  During  the  whole 
operation,  the  bottle  must  not  be  approached,  unless  the  face  is  protected  by  a  sheet 
of  wire  gauze,  and  the  hands  by  thick  woollen  gloves ;  agitation  of  the  bottle,  to 
make  the  suspended  drop  fall,  is  a  common  cause  of  explosion.  The  leaden  saucer, 
when  it  contains  the  chlorine,  may  be  withdrawn  from  under  the  bottle,  without 
disturbing  the  latter,  and  then  no  harm  can  result  from  the  explosion,  if  it  does  not 
occur  in  contact  with  glass. 

M.  Balard  finds  that  this  compound  may  also  be  produced  by  suspending  a  mass 
of  sulphate  of  ammonia  in  a  strong  solution  of  hypochlorous  acid. 

The  chloride  of  nitrogen  is  a  volatile  oleaginous  liquid  of  a  deep  yellow  colour, 
and  sp.  gr.  1.653,  of  which  the  vapour  is  irritating  like  chlorine,  and  attacks  the 
eyes.  It  may  be  distilled  at  160°,  but  effervesces  strongly  at  200°,  and  explodes 
between  205°  and  212°,  producing  a  very  loud  detonation,  and  shattering  to  pieces 
glass  or  cast-iron,  but  producing  merely  an  indentation  in  a  leaden  cup.  It  is  re- 
solved into  chlorine  and  nitrogen  gases,  the  instantaneous  production  of  which  with 
heat  and  light,  is  the  cause  of  the  violence  of  the  explosion.  The  chloride  of 
nitrogen  is  decomposed  by  most  organic  matters  containing  hydrogen ;  and  may  be 
safely  exploded  by  touching  it  with  the  point  of  a  cane- rod,  which  has  been  previously 
dipped  in  oil  of  turpentine. 

This  compound  is  represented  by  NC14,  but  the  properties  of  this  compound  render 
its  accurate  analysis  almost  impossible,  and  the  correctness  of  the  formula  usually 
assigned  to  it  is  very  doubtful.  M.  Millon  has  shown  that  it  may  contain  hydrogen, 
and  is  possibly  a  nitride  of  chlorine  with  ammonia,  Cl3N-f  2H3N.  He  formed  from 
it  corresponding  compounds,  containing  bromine,  iodine,  and  cyanogen,  by  double 
decomposition  •  a  bromide,  iodide,  or  cyanide  of  potassium  being  introduced  into  the 
chloride  of  nitrogen  for  that  purpose.  (Annales  de  Chim.  et  de  Phys.  Ixix.  75.)  [See 
Supplement,  p.  791. 

CHLORIDES   OP   CARBON. 

Sesquichloride  of  carbon,  C4C16.  —  The  compounds  of  these  elements  are  not 
formed  directly,  but  were  produced  by  Mr.  Faraday  by  the  action  of  chlorine  upon 
a  certain  compound  of  carbon  and  hydrogen ;  the  circumstances  of  their  formation 
were  explained  with  singular  felicity  by  M.  Regnault.  Chlorine  and  olefiant  gas 
C4H4  combine  together  in  equal  volumes,  and  condense  as  Dutch  liquid  (page  28(5). 


346  CHLORINE. 

Chemists  are  now  generally  agreed  that  the  rational  formula  of  this  liquid  is  not 
C4H4  +  2C1,  but  that  its  elements  are  thus  arranged  : — 

Dutch  liquid C4H3.C1  +  HC1. 

It  is  considered  a  combination  of  hydrochloric  acid  HC1,  with  the  chloride  of  acetyl 
C4H3.C1.  When  a  stream  of  chlorine  gas  is  transmitted  through  Dutch  liquid,  a 
second  e"q.  of  hydrogen  is  carried  off,  as  hydrochloric  acid,  and  1  eq.  of  chlorine  left 
in  its  place;  thus  Dutch  liquid,  C4H3C1  +  HC1  becomes  — 

C4H2C12+H01. 

This  second  product,  which  is  a  liquid,  being  submitted  to  the  action  of  a  stream 
of  chlorine,  gives  rise  to  a  third  liquid  product,  in  which  the  hydrochloric  acid  of  the 
last  formula  disappears,  and  the  remaining  portion  assumes  2  additional  eqs.  of  chlo- 
rine, forming  — 

C4H2C14. 

This  third  liquid  is  changed  by  the  prolonged  action  of  chlorine  into  the  sesqui- 
chloride of  carbon,  but  to  hasten  the  action  it  is  convenient  to  conduct  the  operation 
in  the  light  of  the  sun ;  its  two  remaining  eqs.  of  hydrogen  being  carried  off  in  the 
form  of  hydrochloric  acid,  and  2  eqs.  of  chlorine  left  in  their  place,  which  gives  the 
formula 

Sesquichloride  of  carbon C4C16,  or  C4C14  -f  C12. 

This  view  of  the  derivation  and  constitution  of  the  sesquichloride  of  carbon  is 
confirmed  by  the  density  of  its  vapour,  which  Regnault  found  by  experiment  to  be 
8157.  It  should  from  its  formula  contain 

8  volumes  carbon  vapour 3371 

12  volumes  chlorine..,  ...29284 


32655 

If  these  form  a  combining  measure  of  4  volumes,  the  most  usual  of  all  comlining 
measures,  the  weight  of  1  volume,  or  density  of  the  vapour,  is  8164,  which  almost 
coincides  with  the  experimental  result.1 

The  sesquichloride  of  carbon  is  a  volatile  crystalline  solid,  having  an  aromatic 
odour  resembling  that  of  camphor,  fusible  at  320°  and  boiling  at  360°  (Faraday), 
of  sp.  gr.  2,  soluble  in  alcohol,  ether,  and  oils.  It  was  prepared  by  Mr.  Faraday  by 
exposing  Dutch  liquid  to  sunlight  in  an  atmosphere  of  chlorine,  which  was  several 
times  renewed  as  the  chlorine  was  absorbed. 

Protochloride  of  carbon,  C4C14.  —  This  compound  was  prepared  by  Faraday  by 
passing  the  vapour  of  the  sesquichloride  through  a  glass  tube  filled  with  fragments 
of  glass,  and  heated  to  redness.  A  great  quantity  of  chlorine  becomes  free,  and  a 
colourless  liquid  is  obtained,  which  when  purified  from  sesquichloride  of  carbon  and 
chlorine  as  much  as  possible,  boils  at  248°  (Regnault),  has  a  sp.gr.  of  1.5526,  and 
in  its  chemical  relations  is  very  analogous  to  the  sesquichloride  of  carbon.  The 
density  of  the  vapour  of  the  protochloride  decides  the  nature  of  its  constitution.  It 
was  found  by  Regnault  to  be  5820,  which  corresponds  to  the  composition  by 
volume :  — 

8  volumes  carbon  vapour 3371 

8  volumes  chlorine 19523 

22894 
Density  = =  5724. 


1  Regnault,  De  1' Action  du  Chlore  sur  la  liqueur  des  Hollandais  et  sur  le  Chlorure  d'Ald&- 
hydene.  Ann.  de  Ch.  et  de  Ph.  t.  69,  p.  151.  Idem,  Sur  les  Chlorures  de  Carbon,  ib.  t.  70, 
p.  104. 


CHLORIDES   OF   CARBON.  347 

It  must,  therefore,  contain  4  eqs.  of  carbon  and  4  of  chlorine,  and  its  formula  be 
C4C14,  or  it  represents  olefiant  gas  C4H4  with  its  whole  hydrogen  replaced  by  chlorine. 
It  is  interesting  to  observe  how  a  body  retains,  after  so  many  mutations,  such  distinct 
traces  of  its  origin.  From  its  analysis  it  might  be  a  compound  of  single  equivalents, 
C  01,  of  the  simplest  nature,  and  so  it  was  considered  when  named  protochloride  of 
carbon. 

Subchloride  of  carbon,  C4C12.  —  Another  compound  of  this  class  exists,  of  which 
a  specimen  produced  accidentally  was  examined  by  Messrs.  Phillips  and  Faraday. 
Regnault  has  formed  it  by  making  the  preceding  liquid  compound  pass  several  times 
through  a  tube  at  a  bright  red  heat.  It  condenses  in  the  coldest  parts  of  the"  tube 
in  very  fine  silky  crystals,  which  may  be  taken  up  by  ether,  and  obtained  perfectly 
pure  by  a  second  sublimation. 

Perchloride  of  carbon,  C2C14,  was  obtained  by  Regnault  from  the  prolonged 
action  of  chlorine  on  hydrochloric  ether,  wood-spirit,  or  chloroform,  and  by  M.  Kolbe 
by  passing  chlorine  gas  impregnated  with  the  vapour  of  bisulphide  of  carbon 
through  a  porcelain  tube  heated  to  redness.  It  is  a  colourless  liquid,  of  density  1.6, 
boiling  at  172°  (78°  C.)  By  passing  the  vapour  of  this  chloride  through  a  tube 
heated  to  dull  redness,  Regnault  obtained  another  chloride  of  carbon,  isomeric  with 
Faraday's  sesquichloride,  but  of  which  the  vapour  density  was  4.082.  Kolbe 
formed  a  crystallizable  compound  of  perchloride  of  carbon  and  sulphurous  acid, 
which  has  the  formula  2(S02)  +  C2C14. 

Another  chloride  of  carbon,  of  the  formula  C20C18,  was  obtained  by  M.  Laurent, 
by  the  action  of  chlorine  upon  naphthaline,  020H8,  in  the  form  of  a  crystalline  solid, 
soluble  in  boiling  petroleum. 

C/iloroxicarbonic  gas,  CO.C1.  —  This  gas  is  formed  by  exposing  equal  measures 
of  chlorine  and  carbonic  oxide  to  sunshine,  when  rapid  but  silent  combination  ensues, 
and  they  contract  to  one  half  their  volume  (page  275).  [See  Supplement,  p.  791. 

Chloride  of  boron,  B  C13. — A  gaseous  compound  of  these  elements  was  obtain 
by  Berzelius,  by  transmitting  chlorine  over  boron  heated  in  a  glass  tube,  and  by 
Dumas  by  transmitting  the  same  gas  over  a  mixture  of  boracic  acid  and  carbon 
ignited  in  a  porcelain  tube  placed  across  a  furnace  (fig.  157).  Its  density  was  found 
to  be  4079  by  Dumas,  and  it  is  considered  a  terchloride. 

Fia.  157. 


Chloride  of  silicon;  127.85  or  1598.12;  Si013.  —  When  silicon  is  heated  in  a 
stream  of  chlorine  gas  it  takes  fire,  and  this  compound  is  formed.  It  is  also  obtained 
in  quantity  by  a  process  analogous  to  that  of  Dumas  for  the  chloride  of  boron,  which 
it  greatly  resembles.  Silicic  acid  is  not  decomposed  when  heated  with  carbon,  but 
if  chlorine  gas  be  present,  then  the  simultaneous  action  of  the  latter  element  upon 
the  silicon  favours  the  action  of  the  carbon  on  the  oxygen,  and  carbonic  oxide  with 


348 


CHLORINE. 


chloride  of  silicon  results.  Precipitated  silica  (page  290),  which  is  in  a  highly 
divided  state,  is  mixed  with  an  equal  weight  of  lamp-black,  and  made  into  a  stiff 
paste  with  a  little  oil ;  this  is  divided  into  balls,  which  are  rolled  in  charcoal  powder, 
and  then  exposed  to  a  strong  red  heat  in  a  covered  crucible.  These  ignited  balls 
form  the  mixture  of  silica  and  charcoal  which  is  introduced  into  the  porcelain  tube 
(fig.  157),  and  heated  strongly  by  a  charcoal  furnace,  while  chlorine  gas,  washed  by 
water  and  dried  in  a  chloride  of  calcium  tube,  is  carried  through  the  porcelain  tube. 
The  chloride  of  silicon  is  condensed  in  a  U  tube  placed  in  an  inverted  bell-jar,  with 
an  opening  at  the  lower  part;  a  short  straight  tube  is  cemented  to  the  lower  part 
of  the'  U  tube,  and,  passing  through  the  tubulure  of  the  jar,  terminates  in  a  small, 
thoroughly  dry  bottle,  where  the  liquefied  chloride  of  silicon  is  collected.  (Regnault's 
Traite). 

The  chloride  of  silicon  is  a  colourless,  highly  mobile  liquid,  of  density  1.52; 
which  boils  at  138°  (59°  C.),  and  fumes  in  the  air.  It  is  instantly  decomposed  by 
contact  with  water,  and  resolved  into  hydrochloric  acid  and  silica :  — 

SiCl3  and  3HO=Si03  and  3HC1. 

This  property  affords  the  means  of  analyzing  the  chloride  of  silicon,  as  the  chlo- 
rine of  the  hydrochloric  acid  formed  may  be  precipitated  by  nitrate  of  silver,  and  its 
amount  determined.  The  proportion  of  oxygen  in  silicic  acid  may  also  be  deduced 
from  the  same  experiment,  as  the  oxygen  must  necessarily  be  equivalent  to  the 
chlorine  in  the  chloride. 


CHLORINE   AND    SULPHUR. 

Chlorine  and  sulphur  appear  to  combine  in  several  different  proportions,  some  of 
these  compounds  being  formed  only  in  combination  with  certain  other  chlorides. 
But  two  compounds  of  these  elements  have  been  obtained  in  a  separate  state.* 

Subchloride  of  sulphur;  67.5  or  843.75;  S2C1.  —  This  compound  was  first 
obtained  by  Dr.  T.  Thomson  in  1804.  To  prepare  it,  a  few  ounces  of  flowers  of 
sulphur  are  introduced  into  the  tubulated  retort  D  (fig.  158),  and  fused  by  a  lamp 

FIG.  158. 


below.  Chlorine  gas  is  evolved  from  hydrochloric  acid  and  binoxide  of  manganese 
in  the  flask  A,  transmitted  through  the  wash-bottle  B  containing  water,  and  after- 
wards dried  by  chloride  of  calcium,  before  the  gas  reaches  the  sulphur  in  D.  The 
chlorine  is  rapidly  absorbed,  and  a  yellowish  red  dense  liquid  distils  over,  and  is 
condensed  in  the  flask  with  two  openings  E,  which  is  kept  cool  by  a  stream  of  water 
from  F.  It  contains  an  excess  of  sulphur  in  solution,  but  is  obtained  pure  by 

*  [See  Supplement,  p.  793.] 


PHOSPHATES.  349 

redistilling  the  liquid  at  a  moderate  temperature  (Rose,  Annal.  de  Ch.  et  de  Ph.  1. 
92).  The  subchloride  of  sulphur  boils  at  about  280°,  and  has  a  disagreeable  odour, 
somewhat  resembling  that  of  sea-weed,  but  much  stronger.  Its  density  in  the  liquid 
state  is  1.687;  the  density  of  its  vapour  has  been  found  4668  by  experiment.  This 
compound  is  capable  of  dissolving  a  large  quantity  of  sulphur,  which  may  be  obtained 
in  crystals  from  a  solution  saturated  at  a  high  temperature.  It  is  decomposed  by 
water,  and  hydrochloric  acid  with  acids  of  sulphur  formed. 

In  one  of  the  processes  for  vulcanizing  caoutchouc,  the  subchloride  of  sulphur  is 
employed.  This  compound  is  dissolved  in  50  times  its  bulk  of  well  rectified  coal 
naphtha,  and  the  articles  of  caoutchouc  immersed  in  the  fluid  for  one  minute,  then 
taken  out  and  dried  without  heat.  The  caoutchouc  thus  acquires  a  small  portion  of 
sulphur,  with  which  it  appears  to  combine,  and  is  improved  greatly  in  elasticity  and 
strength. 

ProtocJiloride  of  sulphur,  51.5  or  643.75;  SCI.  —  If  chlorine  be  passed  through 
the  former  compound,  the  gas  is  absorbed  in  large  quantity,  and  a  liquid  compound 
of  a  deep  red  colour  formed,  which  contains  twice  as  much  chlorine.  The  new 
compound  dissolves  an  excess  of  chlorine,  which  must  be  expelled  by  ebullition. 
When  pure,  this  chloride  boils  at  147°.2  (64°  C.)  Its  density  in  the  liquid  form 
is  1.620,  and  in  the  state  of  vapour  3549.  It  is  decomposed  like  the  preceding 
compound  when  agitated  with  water,  all  its  chlorine  becoming  hydrochloric  acid,  the 
quantity  of  which  may  be  determined  by  the  usual  means.  Polythionic  acids  are 
also  formed,  with  a  deposit  of  sulphur.  This  compound,  of  which  the  formula  is 
SCI,  may  correspond  with  hypochlorous  acid  CIO,  or  with  hyposulphurous  acid; 
but  the  subchloride  of  sulphur,  S2C1,  has  no  analogue  among  the  known  compounds 
of  oxygen  and  chlorine,  or  of  oxygen  and  sulphur. 

When  chlorine  is  passed  over  the  bisulphide  of  tin,  the  gas  is  absorbed,  the  sul- 
phide fuses,  and  a  compound  is  formed  in  yellow  crystals,  which  consists  of  SnCl24- 
SC12.  The  sulphur  of  the  sulphide  of  titanium  and  of  the  sulphides  of  antimony 
and  arsenic  is  converted  by  chlorine  in  the  same  manner  into  bichloride,  and  the 
metal  itself  obtains  the  same  proportions  of  chlorine  as  it  had  of  sulphur  previously, 
the  new  products  also  remaining  in  combination  with  each  other  (Rose;  Annal.  de 
Ch.  et  de  Ph.  Ixx.  270). 

CHLORIDES    OF   PHOSPHORUS.* 

Terchloride  of  phosphorus,  PC13.  —  This  chloride,  which  corresponds  with  phos- 
phorous acid,  is  obtained  by  passing  chlorine  through  melted  phosphorus,  as  for 
chloride  of  sulphur  (fig.  158);  a  clear  and  volatile  liquid  distils  over,  of  sp.  gr.  1.45. 
It  is  capable  of  dissolving  phosphorus ;  when  mixed  with  water,  it  is  resolved  into 
hydrochloric  and  phosphorous  acids. 

Pentachloride  of  phosphorus,  PC15.  —  Phosphorus  takes  fire  spontaneously  in  a 
vessel  of  dry  chlorine,  and  produces  a  snow-white  woolly  sublimate,  which  is  very 
volatile,  rising  in  vapour  below  212°.  It  is  converted  by  water  into  hydrochloric 
and  phosphoric  acids. 

The  variation  of  the  vapour-density  of  this  substance  observed  by  M.  Cahours, 
has  already  been  referred  to  (page  138).  This  compound  is  considered  by  Cahours 
as  a  direct  combination  of  the  terchloride  with  2  eq.  chlorine,  PC13+  C12. 

Chloroxide  of  phosphorus,  PC1302.  —  The  vapour  of  water  produces  with  the 
pentachloride  of  phosphorus  a  compound  so  named,  discovered  by  M.  Wurtz.     It  is 
a  colourless  and  very  limpid  liquid,  of  density  1.7,  which  fumes  in  air.    Jt  is  decom-k 
posed  by  water. 

Chloro-sulphide  of  phosphorus,  PC13S2.  —  It  was  discovered  by  Serullas,  and  is 
obtained  by  the  action  of  hydrosulphuric  acid  on  the  pentachloride  of  phosphorus. 
It  is  liquid,  boils  at  262°  (128°  C.);  is  not  decomposed  by  water.  The  alkaline 
oxides  transform  it  into  a  suJphoxiphosphate,  a  metallic  chloride  being,  produced  at 
the  same  time  :  PC13S2  and  6NaO=3NaO.P03S2  and  3NaCl. 

*  [See  Supplement,  p.  794.J 


350  BROMIXE. 

These  salts,  which  correspond  with  the  tribasic  phosphates,  maybe  crystallized. 
The  sulphoxiphosphate  of  soda  crystallizes  with  24  eq.  water,  3NaO.PQ3S2  +  24HO, 
and  has,  therefore,  a  composition  exactly  similar  to  the  phosphate  of  soda,  3NaO 
P05  +  24HO,  but  the  form  is  different.  Here,  then,  sulphur  is  not  isomorphous 
with  oxygen  (Wurtz,  Annal.  de  Ch.  3me  s^r.  xx.  472). 


SECTION  XI. 

BROMINE. 

Eq.  78.26  or  978.30;  Br;  density  of  vapour  5393;  |~|~"|  • 

This  element  was  discovered  by  M.  Balard  of  Montpellier  in  1826.  Its  name  is 
derived  from  Spu^o?,  mal-odour,  and  was  applied  to  it  on  account  of  its  strong  and 
disagreeable  odour.  Like  the  other  members  of  the  chlorine  family,  it  is  found 
principally  in  solution,  being  present  in  an  exceedingly  minute  but  appreciable  pro- 
portion in  sea- water,  under  the  form  of  bromide  of  sodium  or  magnesium,  also  in 
the  water  of  the  Dead  Sea,  and  in  nearly  all  the  saline  springs  of  Europe,  of  which 
that  of  Theodorshall  near  Kreuznach  in  Germany  is  the  principal  source  of  bromine, 
as  an  article  of  commerce.  Bromine  is  interesting  from  its  chemical  relations,  par- 
ticularly from  the  extraordinary  parallelism  in  properties  with  chlorine  which  it 
exhibits. 

Preparation.  —  Bromine  in  combination  is  discovered  by  means  of  chlorine-water, 
a  few  drops  of  which  cause  the  colourless  solution  of  a  bromide  to  become  orange- 
yellow,  like  nitrous  acid,  by  disengaging  bromine,  while  an  excess  of  chlorine  weakens 
the  indication,  by  forming  a  chloride  of  bromine  which  is  nearly  colourless.  Before 
the  application  of  this  test,  the  saline  water  in  which  bromine  is  contained  must 
always  be  greatly  concentrated,  and,  indeed,  the  greater  part  of  its  salts  should  be 
separated  by  crystallization.  The  bromides  are  highly  soluble,  and  remain  in  the 
crystallizable  liquor  which  is  called  the  mother-ley,  or  bittern  in  the  case  of  sea- 
water.  The  bromide  of  magnesium  may  lose  hydrobromic  acid  during  the  farther 
concentration  of  the  mother-ley,  by  evaporation,  on  which  account  Desfosses  recom- 
mends the  addition  of  hydrate  of  lime  to  the  liquid,  which  throws  down  magnesia, 
and  produces  a  bromide  of  calcium  which  may  be  evaporated  without  loss  of  bromine. 
Instead  of  using  free  chlorine  to  extricate  the  bromine,  binoxide  of  manganese  and 
a  little  hydrochloric  acid  may  be  added  to  the  liquid.  Upon  distilling,  bromine  is 
liberated  and  comes  off  completely  before  the  liquid  boils.  The  watery  vapour  which 
condenses  in  the  receiver  along  with  the  bromine  contains  a  portion  of  chloride  of 
bromine,  from  which  the  bromine  may  be  separated  by  adding  baryta  to  the  liquid, 
and  forming  a  chloride  of  barium  and  bromate  of  baryta ;  evaporating  the  liquor  to 
dryness,  heating  to  redness,  and  treating  with  alcohol. 

Properties.  —  Bromine  condenses  in  the  preceding  process  as  a  dense  liquid  under 
the  water,  the  sp.  gr.  of  bromine  being  2.966.  In  mass,  it  is  opaque  and  of  a  dark 
brown  red,  but  in  a  thin  stratum,  transparent  and  of  a  hyacinth  red.  Its  odour  is 
powerful  and  very  like  that  of  chlorine.  When  cooled  10  or  15  degrees  below  zero, 
it  freezes,  and  remains  solid  at  10° ;  it  then  has  a  leaden  gray  colour,  and  a  lustre 
almost  metallic.  Bromine  at  the  usual  temperature  is  decidedly  volatile,  and  to 
retard  its  evaporation  it  is  generally  covered  by  water  in  the  bottle  in  which  it  is 
kept.  It  boils  at  116°. 5,  and  affords  a  vapour  very  similar  to  the  ruddy  fumes  of 
peroxide  of  nitrogen.  Bromine  is  soluble  to  a  small  extent  in  water,  and  gives 
an  orange-coloured  solution ;  it  is  more  solubje  in  alcohol,  and  considerably  more  so 
in  ether. 

Bromine  bleaches  like  chlorine,  and  acts  in  a  similar  manner  upon  the  volatile 
oils  and  many  organic  substances  containing  hydrogen,  which  element  it  eliminates 
in  the  form  of  hydrobromic  acid.  Many  metals  combine  with  bromine  with  ignition, 


HYDROBROMIC   ACID.  351 

as  they  do  with  chlorine ;  it  acts  as  a  caustic  on  the  skin,  and  stains  it  yellow,  like 
nitric  acid.  It  forms  a  compound  with  starch,  which  is  of  a  yellow  colour;  like 
chlorine  it  forms  a  crystalline  hydrate  with  water  at  32°,  which  is  of  a  beautiful  red 
tint. 

Hydrobromic  acid;  79.26  or  990.8;  HBr.  —  This  is  a  gas,  in  which  2  volumes 
of  each  constituent  are  united  without  condensation,  as  in  hydrochloric  acid,  and 
which  has  the  great  attraction  for  water  of  that  acid.  Hydrogen  and  bromine  do 
not  unite  at  the  usual  temperature,  and  a  mixture  of  them  is  not  exploded  by  flame, 
but  they  unite  in  contact  with  the  flame  and  form  hydrobromic  acid.  The  same 
acid  is  more  readily  prepared  by  the  action  of  bromine  upon  certain  compounds  of 
hydrogen,  such  as  hydrosulphuric  acid,  phosphuretted  hydrogen,  and  hydriodic  acid. 
The  gas  may  also  be  obtained  by  the  mutual  action  of  bromine,  phosphorus,  and 
water,  and  must  be  collected  over  mercury. 

For  the  last  process,  a  tube-apparatus,  represented  fig.  159,  is  recommended  by 
M.  Regnault.    It  contains  a  little  bromine  in  the 
bend  b,  and  small  portions  of  phosphorus  at  dt  *IQ~  *""• 

this  bend  being  filled  up  with  fragments  of  glass, 
and  a  very  minute  quantity  of  water  added.  The 
open  end  a  of  the  tube  being  closed  with  a  cork, 
heat  is  applied  to  b,  so  as  to  vapourize  the  bro- 
mine in  a  gradual  manner.  A  bromide  of  phos- 
phorus is  produced,  which  is  immediately  decom- 
posed by  the  water,  while  hydrobromic  acid  is 
disengaged  and  escapes  by  the  tube  e. 

Hydrobromic  acid,  like  all  the  other  bromides,  is  decomposed  by  chlorine,  which 
is  more  powerful  in  its  affinities  than  bromine,  but 'it  is  not  decomposed  by  iodine. 
Its  action  with  metals  is  precisely  similar  to  that  of  hydrochloric  acid.  Hydro- 
bromic acid  is  not  decomposed  when  heated  with  oxygen,  and  water  is  not  decom- 
posed by  bromine,  so  that  the  affinity  of  bromine  and  oxygen  for  hydrogen  may  be 
inferred  to  be  nearly  equal.  This  acid,  or  a  soluble  bromide,  produces  white  preci- 
pitates with  the  nitrates  of  silver,  lead,  and  suboxide  of  mercury,  which  are  very 
similar  to  the  chlorides  of  these  metals.  The  other  metallic  bromides  correspond  in 
solubility  with  the  chlorides.  The  bromide  of  silver,  like  the  chloride,  is  soluble  in 
ammonia. 

Bromic  acid,  Br05.  —  Bromine  is  dissolved  by  the  strong  alkaline  bases,  and 
occasions  a  decomposition  exactly  similar  to  that  produced  by  chlorine,  in  which  a 
bromide  of  the  metal  and  bromate  of  the  metallic  oxide  are  formed.  The  bromic 
acid  may  be  separated  from  bromate  of  baryta  by  sulphuric  acid,  and  its  solution 
may  be  concentrated  to  a  certain  point,  like  chloric  acid,  beyond  which  it  undergoes 
decomposition.  It  has  not  been  isolated.  The  chief  points  of  difference  between 
chloric  and  bromic  acid  are,  that  the  latter  alone  is  decomposed  by  sulphurous  and 
phosphorous  acids,  and  by  hydrosulphuric  acid;  and  while  all  the  chlorates  are 
soluble,  the  bromates  of  silver  and  suboxides  of  mercury  are  insoluble,  the  former 
being  a  white  and  the  latter  a  yellowish  white  precipitate.  Bromic  acid  is  the  only 
known  oxide  of  bromine. 

Chloride  of  bromine,  BrCl5.  —  Chlorine  gas  is  absorbed  by  bromine,  and  a  vola- 
tile fluid  of  a  reddish  yellow  colour  produced.  This  chloride  appears  to  dissolve  in 
water,  without  decomposition,  but  in  an  alkaline  solution  it  is  converted  into  chloride 
and  bromate. 

Bromide  of  sulphur.  —  Bromine  combines  when  mixed  with  flowers  of  sulphur, 
forming  a  fluid  of  an  oily  appearance  and  reddish  tint,  much  resembling  subchloride 
of  sulphur  in  appearance  and  properties.  This  bromide  dissolves  both  sulphur  and 
bromine,  and  has  not  been  obtained  in  a  state  of  sufficient  purity  for  analysis. 

Bromides  of  phosphorus,  PBr3  and  PBr5.  —  If  bromine  and  phosphorus  are 
brought  into  contact,  in  a  flask  filled  with  carbonic  acid  gas,  a  violent  action  with 
ignition  takes  place,  of  which  the  products  are  a  volatile  crystalline  solid  and  a  yel 


352  IODINE. 

kowish  liquid.  The  former,  when  decomposed  by  water,  affords  hydrobromic  and 
phosphoric  acids,  which  proves  it  to  be  PBr5;  and  the  latter  affords  hydrochloric 
ind  phosphorous  acids,  which  proves  it  to  be  PBr3.  The  liquid  bromide  does  not 
freeze  at  5°,  and,  like  the  liquid  chloride  of  phosphorus,  is  capable  of  dissolving  a 
large  quantity  of  phosphorus. 

Bromide  of  silicon —  Is  prepared  by  a  similar  process  as  the  chloride  of  silicon. 
It  is  a  liquid  boiling  at  302°,  and  freezing  at  10°.  By  water  it  is  resolved  into 
hydrobromic  acid  and  silica. 

[/See  Supplement,  p.  795.] 


SECTION  XII. 

IODINE. 

Eq.  126.36  or  1579.5;  I;  density  of  vapour  8707;    |     |     | 

Iodine  was  discovered  in  1811,  by  M.  Courtois  of  Parig,  in  kelp,  a  substance  from 
which  he  prepared  carbonate  of  soda.  Its  chemical  properties  were  examined  by 
Clement,  and  afterwards,  more  completely,  by  Davy  and  Gay-Lussac,  particularly 
by  the  latter  (Davy,  Phil.  Trans,  for  1814  aud  1815;  Gay-Lussac,  Annal.  de  Ch. 
txxxviii.,  xc.,  etxci.)  A  trace  of  iodine  has  been  observed  in  sea-water  (Schweitzer), 
but  it  is  more  abundant  in  the  fuci,  ulvi,  and  other  marine  plants,  and  also  in  sponge, 
the  ashes  of  which  contain  iodide  of  sodium.  It  is  known  also  to  exist  in  one  mine- 
ral, a  silver  ore  of  Albaradon  in  Mexico.  [See  Supplement,  p.  796.] 

Preparation.  —  The  greater  part  of  the  iodine  of  commerce  is  prepared  at  Glasgow 
from  the  kelp  of  the  west  coast  of  Ireland  and  western  islands  of  Scotland.  The  sea- 
weed thrown  upon  the  beach  is  collected,  dried,  arid  afterwards  burned  in  a  shallow 
pit,  in  which  the  ashes  accumulate  and  melt  by  the  heat,  being  of  a  fusible  material. 
The  fused  mass  broken  into  lumps  forms  kelp,  which  was  prepared  and  chiefly  valued 
at  one  time  for  the  carbonate  of  soda  it  contains,  which  varies  in  quantity  from  2  to 
5  per  cent.  It  is  not  all  equally  rich  in  iodine.  According  to  the  observation  of 
Mr.  Whitelaw,  the  long  elastic  stems  of  the  fucus  palmatus  afford  most  of  the  iodine 
contained  in  kelp,  and  the  kelp  prepared  from  this  plant  may  be  recognized  by  the 
presence  of  charred  portions  of  the  stems.  This  being  a  deep  sea  plant,  iodine  is 
found  in  largest  quantity  in  the  sea-wreck  of  exposed  coasts.  A  high  temperature 
in  the  preparation  of  the  kelp,  which  increases  the  proportion  of  alkaline  carbonate, 
diminishes  that  of  the  iodine,  owing  to  the  volatility  of  the  iodide  of  sodium  at  a  full 
red  heat.  The  kelp  which  contains  most  iodine  generally  contains  also  most  chloride 
of  potassium,  and  it  is  for  these  two  products  that  the  substance  is  now  valued,  more 
than  for  its  alkali. 

The  kelp  broken  into  small  pieces  is  lixiviated  in  water,  to  which  it  yields  about 
naif  its  weight  of  salts.  The  solution  is  evaporated  down  in  an  open  pan,  and  when 
concentrated  to  a  certain  point,  begins  to  deposit  its  soda  salts,  —  namely,  common 
salt,  carbonate  and  sulphate  of  soda,  —  which  are  removed  from  the  boiling  liquor 
by  means  of  a  shovel  pierced  with  holes  like  a  colander.  The  liquid  is  afterwards 
run  into  &  shallow  pan  to  cool,  in  which  it  deposits  a  crop  of  crystals  of  chloride  of 
potassium :  the  same  operations  are  repeated  upon  the  mother-ley  of  these  crystals 
until  it  is  exhausted.  A  dense  dark-coloured  liquid  remains,  which  contains  the 
iodide,  in  the  form,  it  is  believed,  of  iodide  of  sodium,  but  mixed  with  a  large  quan- 
tity of  other  salts ;  and  this  is  called  the  iodine  ley. 

To  this  ley,  sulphuric  acid  is  gradually  added  in  such  quantity  as  to  leave  the 
liquid  very  sour,  which  causes  an  evolution  of  carbonic  acid,  sulphuretted  hydrogen, 
and  sulphurous  acid  gases,  with  a  considerable  deposition  of  sulphur.  After  stand- 
ing for  a  day  or  two,  the  ley  so  prepared  is  heated  with  binoxide  of  manganese,  to 
separate  the  iodine.  This  operation  is  conducted  in  a  leaden  retort  a  (see  fig.  ICO) 
of  a  cylindrical  form,  supported  in  a  sand-bath,  which  is  heated  by  a  small  fire  below. 


PREPARATION   OF    IODINE. 


353 


The  retort  has  a  large  opening,  to  Fl°- 

which  a  capital,  b  c,  resembling 
the  head  of  an  alembic,  is  adapted, 
and  luted  with  pipe-clay.  In  the 
capital  itself  there  are  two  openings, 
a  larger  and  a  smaller,  at  b  and  c, 
closed  by  leaden  stoppers.  A  series 
of  bottles  d,  having  each  two  open- 
ings, connected  together  as  repre- 
sented in  the  figure,  and  with  their 
joinings  luted,  are  used  as  con- 
densers. The  prepared  ley  being 
heated  to  about  140°  in  the  retort, 
the  manganese  is  then  introduced, 
and  b  c  luted  to  a.  Iodine  imme- 
diately begins  to  come  off,  and 
proceeds  on  to  the  condensers,  in 
which  it  is  collected ;  the  progress 
of  its  evolution  is  watched  by  oc- 
casionally removing  the  stopper 
at  c;  and  additions  of  sulphuric  acid  or  manganese  are  made  by  b,  if  deemed  neces- 
sary. The  success  of  the  experiment  depends  much  upon  its  being  slowly  conducted, 
and  upon-the  proper  management  of  the  temperature,  which  is  more  easily  regulated 
when  the  quantities  of  materials  are  considerable,  than  when  the  experiment  is 
attempted  with  small  quantities  in  glass  flasks.  In  the  latter  circumstances,  chlorine 
is  often  evolved  with  the  iodine,  which  escapes  in  acrid  fumes,  as  the  chloride  of 
iodine,  and  is  lost ;  but  this  accident  can  be  avoided  in  the  manufacturing  process. 
A  little  cyanide  of  iodine  often  accompanies  the  iodine,  which  being  more  volatile, 
condenses  in  the  form  of  white,  flexible,  prismatic  crystals,  in  the  bottle  most  distant 
from  the  leaden  retort. 

In  this  operation  the  binoxide  of  manganese  will  be  in  contact  at  once  with 
hydriodic,  hydrochloric,  and  sulphuric  acids ;  and  the  iodine  of  the  hydriodic  acid 
may  be  liberated,  from  the  union  with  its  hydrogen  of  the  oxygen  of  the  manga- 
nese, and  the  formation  of  water;  or  hydrochloric  acid  may  be  first  decomposed  by 
the  manganese,  and  chlorine  decompose  the  hydriodic  acid  and  liberate  iodine.  If 
a  considerable  excess  of  sulphuric  acid  be  employed,  iodine  is  obtained  without  the 
use  of  binoxide  of  manganese,  the  oxygen  required  by  the  hydrogen  of  the  hydriodic 
acid  being  supplied  by  the  sulphuric  acid,  a  part  of  which  is  converted  into  sul- 
phurous acid.  The  presence  of  iodine  in  the  prepared  ley  may  be  observed  by  sud- 
denly mixing  it  with  an  equal  volume  of  oil  of  vitriol,  when  violet  fumes  of  iodine 
appear.  But  the  quantity  of  iodine  may  be  more  accurately  estimated  by  means 
of  a  solution  consisting  of  1  part  of  crystallized  sulphate  of  copper  and  2J  cr.  pro- 
sulphate  of  iron,  which  throws  down  an  insoluble  subiodide  of  copper,  almost  white. 
It  may  also  be  determined  approximatively  by  precipitation  by  the  ammonio-nitrate 
of  silver. 

Properties.— Iodine  is  generally  in  crystalline  scales  of  a  bluish  black  colour  and 
metallic  lustre.  It  is  obtained,  from  solution,  in  modifications  of  an  elongated  octo- 
hedron  with  rhomboidal  base  (fig.  161.)  The  density  of  iodine  is  4-948;  it  fuses 
at  225°,  and  boils  at  347° ;  but  it  evaporates  at  the  usual  temperature,  and  more 
rapidly  when  damp  than  when  dry,  diffusing  an  odour  having  considerable  resem- 
blance to  chlorine,  but  easily  distinguished  from  it.  Iodine  stains  the  skin  of  a 
yellow  colour,  which  however  disappears  in  a  few  hours.  Its  vapour  is  of  a  splendid 
violet  colour,  which  is  seen  to  great  advantage  when  a  scruple  or  two  of  iodine  is 
thrown  at  once  upon  a  hot  brick.  Hence  its  name,  from  'Iw^^,  violet-coloured. 
The  vapour  of  iodine  is  one  of  the  heaviest  of  gaseous  bodies,  its  density  being  8716 
23 


354 


IODINE. 


according  to  the  experiment  of  Dumas,  and  8707.7  according  to  calculation  from  its 
atomic  weight. 

FIG.  161. 


Pure  water  dissolves  about  1 -7000th  of  its  weight  of  iodine,  and  acquires  a  brown 
colour;  but  when  charged  with  salt,  particularly  the  nitrate  or  hydrochlorate  of 
ammonia,  water  dissolves  a  considerably  greater  quantity  of  iodine.  The  solution 
of  iodine  does  not  disengage  oxygen  in  the  light  of  the  sun,  and  does  not  destroy 
vegetable  colours,  but  after  a  time  it  becomes  colourless,  and  then  contains  hydriodic 
and  iodic  acids.  In  other  respects,  iodine  generally  comports  itself  like  chlorine, 
but  its  affinities  are  much  less  powerful.  Iodine  is  soluble  in  alcohol  and  ether, 
with  which  it  forms  dark  reddish-brown  liquids.  Solutions  of  iodides,  too,  all  dis- 
solve much  iodine,  and  become  of  a  deep  red  colour.  A  liquid  containing  20  grains 
of  iodine  and  30  grains  of  iodide  of  potassium  in  1  ounce  of  water,  is  known  as 
Lugol's  solution,  and  preferred  to  the  tincture  in  medicine,  because  the  iodine  is  not 
precipitated  from  it  by  dilution  with  water. 

A  solution  of  starch  forms  a  compound  with  iodine,  of  a  deep  blue  colour,  soluble 
in  pure  water  but  insoluble  in  acid  and  saline  solutions,  the  production  of  which  is 
an  exceedingly  delicate  test  of  iodine.  If  the  iodine  be  free,  starch  produces  at 
<t once  the  blue  compound,  but  if  the  iodine  be  in  combination  as  a  soluble  iodide,.  DO 
change  takes  place  till  chlorine  is  added  to  liberate  the  iodine.  If  more  chlorine, 
however,  be  added  than  is  necessary  for  that  purpose,  the  iodine  is  withdrawn  from 
the  starch,  chloride  of  iodine  formed,  and  the  blue  compound  destroyed.  Dr.  A.  T. 
Thomson,  after  adding  the  starch  with  a  drop  of  sulphuric  acid  to  the  liquid  con- 
taining an  iodide,  in  a  cylindrical  vessel,  allows  the  vapour  only  from  the  chlorine- 
water  bottle  to  fall  upon  the  solution,  and  not  the  chlorine-water  itself.  In  this 
way,  the  danger  of  adding  an  excess  of  chlorine  is  easily  avoided,  and  the  test  indi- 
cates in  a  sensible  manner  an  exceedingly  minute  quantity  of  iodine.  The  iodide 
of  starch,  in  water,  becomes  colourless  when  heated,  but  recovers  its  blue  colour  if 
immediately  cooled.  The  soluble  iodides  give,  with  the  nitrate  of  silver^  an  insoluble 
iodide  of  silver,  of  a  pale  yellow  colour,  insoluble  in  ammonia ;  with  salts  of  lead, 
an  iodide  of  a  rich  yellow  colour,  and  with  corrosive  sublimate,  a  fine  scarlet  iodide 
of  mercury. 

In  ascertaining  the  quantity  of  iodine  in  the  mixed  chlorides,  and  iodides  of 
mineral  waters  and  other  solutions,  Rose  recommends  the  addition  of  nitrate  of 
silver,  which  throws  down  a  mixture  of  chloride  and  iodide  of  silver,  which  is  fused 
and  weighed.  This  is  afterwards  heated  in  a  tube  and  chlorine  passed  over  it,  by 
which  the  iodine  is  expelled,  and  the  whole  becomes  chloride  of  silver.  It  is 
weighed  again,  and  a  loss  is  found  to  have  occurred,  owing  to  the  equivalent  of  the 
replacing  chlorine  being  less  than  that  of  the  replaced  iodine.  This  loss,  multiplied 
by  1-389,  gives  the  quantity  of  iodine  originally  present,  which  has  been  expelled 
by  the  chlorine.  (Handbuch  der  analyt.  Chem.  von  Heinrich  Rose,  B.  2,  p.  577). 
J)r.  Schweitzer  employs  a  similar  method  in  estimating  the  quantity  of  iodine  when 
mixed  with  bromine,  heating  the  iodide  and  bromide  of  silver  in  an  atmosphere  of 
bromine.  The  difference  of  weight  multiplied  by  2.627  gives  the  proportion  of 
iodine,  and  multiplied  by  1.627  the  proportion  of  bromine.  (Phil.  Mag.;  3d  series, 
xv.  p.  57.) 


HTDEIODIC    ACID. 


355 


Uses. — Iodine  is  employed  in  the  laboratory  for  many  chemical  preparations,  and 
as  a  test  of  starch.  It  was  first  introduced  into  medicine  by  Coindet  of  Geneva, 
who  employed  it  with  success,  in  the  treatment  of  goitre,  dissolved  in  alcohol,  in 
solution  of  iodide  of  potassium,  or  as  iodide  of  sodium  j  and  since  tint  application, 
most  mineral  waters  to  which  the  virtue  of  curing  goitre  was  ascribed,  have  been 
found  to  contain  iodine.  M.  Boussingault  has  adduced  striking  confirmations  of 
the  efficacy  of  iodine  in  that  disease,  in  his  interesting  memoir  on  the  iodiferous 
mineral  waters  of  the  Andes.  (Annal.  de  Chim.  et  de  Phys.,  liv.  163.)  It  appears 
to  have  a  specific  action  in  causing  the  absorption  of  glandular  swellings,  and  is  also 
administered  as  a  tonic.  Iodine  swallowed  in  the  solid  state  causes  ulceration  of 
the  mucous  membrane  of  the  stomach,  and  death.  But  the  iodide  of  potassium  or 
sodium  is  not  poisonous  in  considerable  doses,  nor  is  the  iodide  of  starch  hurtful 
(Dr.  A.  Buchanan).  Iodine  and  bromine  have  also  found  an  interesting  application 
to  form  the  film  of  iodide  or  bromide  of  silver,  in  the  silver-plates  of  the  daguerreo- 
type, which  is  so  sensitive  to  light. 

Iodides.  —  Iodine  does  not  form  a  hydrate  like  chlorine,  but  it  combines  with 
another  compound  body,  ammonia;  dry  iodine  absorbing  dry  ammoniacal  gas  and 
running  into  a  brown  liquid,  which  Bineau  found  to  contain  20.4  ammonia  to  100 
iodine,  quantities  in  the  proportion  of  3  equivalents  of  ammonia  to  2  of  iodine. 
(Annal.  de  Chim.  et  de  Phys.,  Ixvii.  226.)  This  liquid  dissolves  iodine.  Iodine 
does  not  combine  with  dry  iodide  of  potassium,  but  with  the  addition  of  a  small 
quantity  of  water,  it  forms  what  appears  to  be  a  ternary  compound  of  iodide  of 
potassium,  water  and  iodine,  which  is  usually  fluid,  but  was  obtained  in  crystals  by 
Bauer.  Iodine  forms  similar  compounds  with  other  hydrated  metallic  iodides. 
With  the  metals  generally  iodine  combines,  with  the  same  facility,  and  nearly  with 
as  much  energy  as  chlorine  does.  The  iodide  of  zinc  and  protiodide  of  iron,  which 
are  very  soluble,  are  formed  by  simply  bringing  the  metals  into  contact  with  iodine, 
in  water.  All  the  iodides  are  decomposed  by  bromine,  as  well  as  by  chlorine. 

The  compounds  of  iodine  may  be  shortly  described  in  the  following  order : — 


Hydriodic  acid HI 

*Iodic  acid I05 

Periodic  acid I07 

Iodide  of  nitrogen  ...  NI3 


Iodide  of  sulphur 
Iodides  of  phosphorus 
Chlorides  of  iodine 
Bromides  of  iodine. 


COMPOUNDS   OF   IODINE. 


Hy anodic  add;  127.36  or 
1 592 ;  HI.  —  Hydriodic  acid 
cannot  be  prepared  with  ad- 
vantage by  treating  the  iodide 
of  sodium  or  potassium  with 
hydrated  sulphuric  acid,  as  the 
latter  is  partially  converted 
into  sulphurous  acid  by  hy- 
driodic  acid,  with  the  separa- 
tion of  iodine.  It  may  be 
obtained  in  the  state  of  gas, 
by  forming  an  iodide  of  phos- 
phorus, 9  parts  of  dry  iodine 
and  1  of  phosphorus  being  in- 
troduced into  a  tube  sealed  at 
one  end,  to  be  used  as  a  retort, 
and  the  mixture  covered  by 
pounded  glass,  and  combina- 
tion determined  by  a  gentle 
heat ;  and  afterwards  decom- 
posing this  iodide  of  phos- 

*  [See  Supplement,  p.  796.] 


FIG.  162. 


356  IODINE. 

phorus  by  a  few  drops  of  water.  Hydriodic  acid  instantly  comes  off  as  gas,  and 
hydrated  phosphorous  acid  remains  in  the  tube : 

PI3  and  6HO=3HI  and  3HO  +  P03. 

A  slight  heat  may  be  applied  to  the  tube,  when  the  action  abates,  to  expel  the  last 
portions  of  hydriodic  acid ;  but  if  the  temperature  be  elevated,  the  residuary  hy- 
drated phosphorous  acid  is  decomposed,  with  evolution  of  phosphuretted  hydrogen 
gas,  which  may,  therefore,  be  obtained  by  the  same  operation.  This  gas  is  very 
soluble  in  water,  and  soon  decomposed  over  mercury,  which  combines  with  its  iodine 
and  liberates  hydrogen ;  so  that  it  is  collected  in  a  dry  bottle,  B,  by  the  method  of 
displacement,  and  the  bottle  is  closed  with  a  glass  stopper  when  full  of  gas.  Hy- 
driodic gas  is  colourless,  of  density  4443  by  experiment  and  4385  by  theory,  and 
consists  of  2  volumes  of  iodine  vapour  and  2  volumes  of  hydrogen  gas  united  with- 
out condensation,  or  forming  4  volumes,  which  are,  therefore,  the  combining  measure 
of  the  gas.  In  the  combination  of  its  constituents  by  volume,  hydriodic  acid  re- 
sembles hydrochloric  acid  gas  and  all  the  other  hydrogen  acids.  Hydriodic  acid  gas  is 
gradually  decomposed  by  oxygen,  with  the  formation  of  water :  iodine  is  liberated. 

The  solution  of  this  acid  in  water  may  be  obtained  by  transmitting  hydrosulphuric 
acid  gas  through  water  in  which  iodine  is  suspended :  the  iodine  combines  with  the 
hydrogen -of  that  compound  and  liberates  the  sulphur.  The  liquid  may  afterwards 
be  warmed  to  expel  the  excess  of  hydrosulphuric  acid,  and  filtered.  It  is  colourless 
at  first,  but  in  a  few  hours  becomes  red,  owing  to  the  decomposition  of  hydriodic 
acid  by  the  oxygen  of  the  air,  and  solution  of  the  iodine  in  the  acid. 

The  solution  has  its  maximum  boiling  point,  which  lies  between  257°  and  262°, 
when  of  sp.  gr.  1.7,  according  to  Gay-Lussac.  Nitric  and  sulphuric  acids  decompose 
it,  and  are  decomposed  themselves  with  the  formation  of  water;  the  starch  test  then 
indicates  free  iodine. 

lodlc  acid;  166.36  or  2079.5;  I05.  —  Iodine  does  not  afford  a  peculiar  acid 
compound  with  red  oxide  of  mercury  and  those  metallic  oxides  which  yield  free 
hypochlorous  acid  with  chlorine.  Nor  is  it  absorbed,  like  chlorine,  by  hydrate  of 
lime  or  alkaline  solutions,  to  form  a  class  of  bleaching  salts.  Such  compounds  are 
wanting  in  the  series  of  oxides  of  iodine,  which  is  limited  to  hypoiodic,  iodic,  and 
periodic  acids.  Sementini  imagined  that  he  had  formed  inferior  oxides  of  iodine, 
but  he  is  evidently  mistaken.  The  iodate  of  soda  combines  with  iodide  of  sodium 
in  several  proportions,  one  of  which  was  supposed  by  Mitscherlich,  when  he  discovered 
it,  to  be  an  iodite  of  soda;  but  that  this  is  a  double  salt  of  the  constitution  first 
mentioned  is  more  probable. 

A  few  grains  of  iodic  acid  may  easily  be  prepared  by  the  method  of  Mr.  Connel, 
which  consists  in  heating  the  most  concentrated  nitric  acid,  free  from  nitrous  vapour, 
upon  a  little  iodine,  in  a  wide  glass  tube,  and  allowing  the  liquid  to  cool ;  the  iodine 
is  oxidated  at  the  expense  of  the  nitric  acid,  and  the  greater  part  of  the  iodic  acid 
is  deposited  in  crystals.  When  a  larger  quantity  is  required,  a  convenient  process 
is  to  form,  in  the  first  place,  an  iodate  of  soda,  as  suggested  by  Liebig.  An  ounce 
or  two  of  iodine  in  powder  may  be  suspended  in  a  pound  of  water,  with  occasional 
agitation,  and  a  stream  of  chlorine  be  passed  through  till  the  whole  iodine  is  dissolved. 
Carbonate  of  soda  is  then  added  to  the  liquid,  which  is  of  a  brown  colour  and  strongly 
acid,  till  it  becomes  slightly  alkaline,  when  a  large  precipitation  of  iodine  occurs, 
which  may  be  separated  and  collected  on  a  filter.  This  iodine  may  be  suspended  in 
water,  and  exposed  to  a  stream  of  chlorine  as  before. 

501  and  5HO  and  I=5HC1  and  I06. 

The  filtered  solution  contains  iodate  of  soda  and  chloride  of  sodium,  with  a  trace 
of  carbonate,  which  may  be  neutralized  by  hydrochloric  acid.  On  afterwards  adding 
chloride  of  barium  to  the  filtered  solution,  so  long  as  a  precipitate  is  produced,  the 
whole  iodic  acid  is  thrown  down  as  iodate  of  baryta,  which  may  be  collected  on  a 
filter  and  dried.  This  iodate  is  anhydrous,  and  may  be  decomposed  completely,  by 


IODATES.  357 

boiling  9  parts  of  it  for  half  an  hour  with  2  parts  of  oil  of  vitriol,  diluted  with,  10 
or  12  parts  of  water.  The  liberated  iodic  acid  dissolves,  and  being  separated  from 
the  sulphate  of  baryta  by  filtration,  is  obtained  as  a  crystalline  mass  when  evaporated 
to  dryness  by  a  gentle  heat. 

This  acid  is  also  prepared  very  easily,  according  to  M.  Millon,  by  digesting  iodine 
in  a  mixture  of  nitric  acid  and  chlorate  of  potassa  j  the  proportions  recommended  are 
4  of  iodine,  7.5  chlorate  of  potassa,  10  of  nitric  acid,  and  40  of  water.  The  iodic 
acid  is  afterwards  precipitated  in  the  form  of  iodate  of  baryta,  as  in  the  preceding 
process,  the  iodate  of  baryta  then  decomposed  by  sulphuric  acid. 

Iodic  acid  crystallizes  from  a  strong  solution,  as  a  hydrate,  HO.I05,  in  large  and 
transparent  crystals,  which  are  six-sided  tables.  This  acid  is  not  sublimed,  but  de- 
composed into  iodine  and  oxygen,  by  a  high  temperature,  without  any  formation  of 
periodic  acid.  Another  definite  hydrate  of  iodic  acid  was  obtained  by  M.  Millon, 
containing  only  one-third  of  an  equivalent  of  water,  by  maintaining  the  protohydrate 
at  a  temperature  of  266°  (130°  C.),  so  long  as  it  continued  to  lose  weight.  It  is 
also  formed  when  the  protohydrate  is  mixed  with  an  excess  of  anhydrous  alcohol. 
By  drying  either  of  these  hydrates  at  338°  (170°  C.),  iodic  acid  is  obtained  entirely 
anhydrous  (I05). 

Iodic  acid  is  very  soluble  in  watef ;  and  after  reddening,  bleaches  litmus,  paper. 
It  oxidates  all  metals  with  which  it  has  been  tried,  except  gold  and  platinum.  It 
is  deoxidized  by  sulphurous  acid  and  hydrosulphuric  acid,  .and  iodine  liberated,  but 
an  excess  of  sulphurous  acjjd  causes  the  iodine  again  to  disappear  as  hydriodic  acid, 
water  being  decomposed  by  the  simultaneous  action  of  sulphurous  acid  and  iodine 
upon  its  elements.  Iodic  acid  is  easily  decomposed  by  heat,  disengaging  oxygen  and 
vapours  of  iodine.  It  is  soluble  in  water,  alcohol,  and  ether. 

lodales. — The  salts  of  iodic  acid  have  a  general  resemblance  to  chlorates ;  when 
thrown  upon  burning  embers  they  enliven  the  combustion,  but  with  less  vivacity  than 
chlorates.  The  iodate  of  potassa  is  converted  by  heat  into  iodide  of  potassium  and 
oxygen ;  so  that  the  composition  of  iodic  acid  may  be  determined  from  that  of  iodate 
of  potassa,  in  the  same  manner  as  the  composition  of  chloric  acid  is  determined  from 
that  of  chlorate  of  potassa.  The  iodate  of  soda,  however,  loses  iodine  as  well  as 
oxygen,  when  heated,  and  a  yellow,  sparingly  soluble,  alkaline  matter  remains,  which 
Liebig  supposes  to  contain  the  salt  of  an  iodous  acid,  resolvable  into  an  iodate  and 
iodide  by  solution  in  water,  but  which  requires  further  investigation.  The  iodates 
of  metallic  protoxides,  with  the  exception  of  the  potassa  family,  are  all  sparingly 
soluble  or  insoluble  salts.  The  iodate  of  lime  contains  water,  and  when  heated 
affords  no  iodide  of  calcium,  but  caustic  lime. 

Fixed  acids,  which  have  little  affinity  for  water,  such  as  iodic  acid,  appear  often 
to  combine  in  several  proportions  with  oxides  of  the  potassa  family.  The  ordinary 
biniodate  of  potassa  contains  1  eq.  of  basic  water,  but  at  a  high  temperature  it  is 
made  anhydrous,  and  then  a  salt  remains  containing  2  eq.  of  acid  to  1  of  potassa. 
Mr.  Penny  has  crystallized  a  biniodate  and  teriodate  of  soda,  both  anhydrous. 

Iodic  acid  likewise  combines  with  other  acids.  These  compounds  generally  pre- 
cipitate in  a  crystalline  form,  when  another  acid  is  added  to  a  hot  and  concentrated 
solution  of  iodic  acid.  Compounds  of  sulphuric,  nitric,  phosphoric,  and  boracic 
acids,  with  iodic  acid,  have  been  formed.  It  has  been  observed  by  M.  Millon,  that 
when  the  compound  with  sulphuric  acid  is  submitted  to  heat,  oxygen  is  evolved,  and 
a  hypoiodic  acid  or  peroxide  of  iodine  formed,  of  which  the  formula  is  I04.  There 
is  formed  besides  in  this  decomposition,  according  to  M.  Millon,  a  peculiar  double 
acid,  which  may  be  considered  a  compound  of  iodous  and  hypo-iodic  acid,  having  for 
formula  4I04  +  I03.  When  vegetable  acids  are  dissolved  in  iodic  acid,  they  are 
immediately  decomposed  by  it,  carbonic  acid  being  disengaged  with  effervescence,  and 
iodine  precipitated. 

.  Periodic  acid,  Hyperiodic  acid',  182.36  or  2279.5;  I07. — This  acid,  which  was 
discovered  by  Magnus  and  Ammermuller,  is  formed  by  transmitting  a  current  of 
chlorine  through  a  solution  of  iodate  of  soda;  to  which  a  portion  of  carbonate  is 


358  IODINE. 

added,  and  the  whole  maintained  in  constant  ebullition.  On  allowing  the  solution 
to  cool,  a  basic  periodate  of  soda  is  deposited  in  tufts  of  silky  crystals,  and  the 
chloride  of  sodium,  formed  at  the  same  time,  retained  in  solution.  This  basic 
periodate  of  soda,  which  is  almost  insoluble  in  cold  water,  is  dissolved  in  nitric  acid, 
and  nitrate  of  silver  added,  which  throws  down  a  basic  periodate  of  silver,  also  of 
sparing  solubility.  The  last  salt  may  be  washed,  and  afterwards  dissolved  in  boiling 
nitric  acid,  and  the  solution  on  cooling  yields  orange-yellow  crystals  of  neutral 
periodate  of  silver.  It  is  remarkable  that  when  these  crystals  are  thrown  into  water 
they  are  decomposed,  the  whole  oxide  of  silver  precipitating  with  half  the  periodic 
acid,  as  the  former  basic  periodate,  while  half  of  the  acid  is  dissolved  by  the  water 
without  a  trace  of  silver,  and  obtained  in  a  state  of  purity.  This  solution  when 
evaporated  affords  periodic  acid  in  crystals,  which  are  unalterable  in  the  air,  and  of 
which  the  solution  in  water  is  not  changed  by  ebullition.  The  crystals  fuse  about 
266°  (130°  C.)  The  solution,  treated  with  hydrochloric  acid,  affords  chlorine  and 
iodic  acid,  water  being  formed.  Periodic  acid  is  resolved  into  oxygen  and  iodine  by 
a  high  temperature.  , 

Periodates. —  Besides  neutral  salts  of  this  acid,  subsalts  of  the  potassa  family 
exist  which  contain  two  of  base  to  one  of  acid.  The  sparing  solubility  of  the  basic 
salt  of  soda  is  the  most  remarkable  character  of  periodic  acid.  True  subsalts  of  the 
potassa  family  are  so  extremely  unusual,  that  it  is  more  probable  that  periodic  acid 
forms  a  second  and  bihasic  class  of  salts,  to  which  they  belong.  (PoggendorfFs 
Annalen,  xxviii.  514).  The  periodates  are  decomposed  by  heat  like  the  iodates,  but 
yield  more  oxygen. 

Iodide  of  nitrogen.  —  Dry  iodine  and  ammonia  unite  directly,  and  form  a  brown 
liquid,  of  which  the  formula  is  3(H3N).I2.  But  when  digested  in  the  solution  of 
ammoniaj  iodine  acts  upon  that  substance  as  chlorine  does,  and  forms  an  insoluble 
black  powder,  which  is  powerfully  detonating,  and  analogous  to  the  chloride  of 
nitrogen.  The  iodide  detonates  more  easily,  but  less  violently,  than  the  chloride, 
always  exploding  spontaneously  when  it  dries.  Another  process  is  to  mix  a  great 
excess  of  ammonia  with  a  saturated  solution  of  iodine  in  alcohol,  and  afterwards  to 
add  water  so  long  as  iodide  of  nitrogen  precipitates.  The  filter  with  the  humid 
precipitate  should  be  divided  into  several  pieces,  otherwise  the  whole  may  explode 
at  once  upon  drying.  \_See  Supplementj  p.  797.] 

Although  named  the  iodide  of  nitrogen,  this  substance  contains  hydrogen  as  a 
constituent,  according  to  the  observations  of  M.  Biueau,  and  may  be  represented  by 
I2HN ;  or  ammonia  in  which  2  eqs.  of  hydrogen  are  replaced  by  2  eqs.  of  iodine. 
The  same  substance  is  represented  by  Millon,  as  I3N-f2H3N. 

When  caustic  soda  is  added  to  the  solution  of  iodine  in  alcohol  or  wood-spirit,  a 
yellow  substance  of  a  saffron  odour  precipitates,  which  was  supposed  at  one  time  to 
be  the  periodide  of  carbon,  but  is  really  iodojorm,  of  which  the  formula  is  C2HI3. 
No  true  iodide  of  carbon  is  known. 

Iodide  of  sulphur.  —  This  compound  is  formed  by  fusing  together  4  parts  of 
iodine  and  one  of  sulphur.  It  has  a  radiated  crystalline  structure,  but  its  elements 
are  easily  Disunited,  the  iodine  escaping  entirely  from  this  compound  when  it  is  left 
exposed  in  the  air. 

Iodides  of  phosphorus. — Iodine  appears  to  combine  with  phosphorus  in  several 
proportions,  when  they  are  brought  in  contact  and  slightly  heated.  In  all  these 
combinations  the  mass  becomes  hot  without  inflaming,  if  the  phosphorus  is  not  at 
the  same  time  in  contact  with  air.  One  part  of  phosphorus  with  6,  12,  and  20  parts 
of  iodine,  forms  fusible  solids,  which  may  be  sublimed  without  change,  but  which 
are  decomposed  by  water,  all  of  them  yielding  hydriodic  acid,  and  the  first  affording, 
besides,  phosphorus  and  phosphorous  acid,  the  second  phosphorous  acid,  and  the 
third  phosphoric  acid.  [See  Supplement,  p.  798.] 

Chlorides  of  iodine.  —  Chlorine  is  readily  absorbed  by  dry  iodine ;  when  the 
latter  is  in  excess,  a  protochloride,  Id,  appears  to  be  formed ;  and  when  the  chlo- 
rine is  in  excess,  a  terchloride,  IC13. 


FLUORINE.  359 

Berzelius  produced  the  protocliloride  by  distilling  a  mixture  of  1  part  of  iodine 
with  4  parts  or  more  of  chlorate  of  potassa.  There  is  formed  in  the  retort  a  mixture 
of  iodate  and  perchlorate  of  potassa,  at  the  same  time  that  oxygen  gas  is  disengaged, 
and  the  chloride  of  iodine  is  produced,  which  condenses  in  the  receiver.  This  com- 
pound is  a  yellow  or  reddish  liquid,  of  an  oily  consistence,  of  a  sharp  and  peculiar 
odour,  and  taste  which  is  feebly  acid,  but  very  astringent  and  rough.  It  is  soluble 
in  water  and  alcohol ;  and  ether  extracts  it  from  its  aqueous  solution  unaltered,  so 
that  it  is  not  decomposed  by  water. 

i  When  iodine  is  saturated  with  chlorine,  it  forms  a  compound  which  is  solid  and 
crystallizable,  and  of  a  yellow  colour ;  fusible  by  heat,  but  which  cannot  be  sublimed 
without  loss  of  chlorine.  It  fumes  in  air,  and  has  an  acrid  odour.  When  this  ter- 
chloride  of  iodine  is  dissolved  in  water,  and  the  solution  saturated  with  carbonate  of 
soda,  chloride  of  sodium  is  formed,  and  some  iodate  of  soda ;  while  at  the  same  time 
a  large  quantity  of  iodine  precipitates.  By  the  continued  action  of  chlorine  upon 
iodine  in  a  considerable  quantity  of  water,  the  liquid  becomes  at  last  entirely  colour- 
less, and  then  contains  nothing  but  hydrochloric  and  iodic  acids. 

Bromides  of  iodine. — Iodine  likewise  forms  two  bromides,  which  are  both  soluble 
in  water.  The  solution  bleaches  litmus  paper  without  first  reddening  it. 

SECTION   XIII. 

FLUORINE. 

Eq.  18.70  or  233.8;  F;  density  (hypothetical)  1292;  j     j     | 

This  elementary  body  is  most  frequently  found  in  the  mineral  kingdom  in  com- 
bination with  calcium,  as  fluoride  of  calcium,  which  constitutes  the  mineral  fluor- 
spar; it  exists  in  small  quantity  in  amphibole,  mica,  and  most  of  the  natural  phos- 
phates :  a  trace  of  it  also  occurs  in  the  enamel  of  the  teeth,  and  in  the  bones  of 
animals.  Of  all  bodies,  fluorine  appears  to  possess  the  most  powerful  and  general 
affinities,  and  to  be,  therefore,  the  most  difficult  to  isolate  and  preserve  .for  the  study 
of  its  properties.  Indeed,  we  have  hitherto  learned  little  more  of  fluorine  than  that 
it  exists  and  may  be  isolated.  Several  of  its  compounds,  however,  are  of  less  difficult 
preparation,  and  well  known.  \_See  Supplement,  p.  800. J 

Sir  H.  Davy  made  several  attempts  to  isolate  fluorine.  He  exposed  the  fluoride 
of  silver  in  a  glass  tube  to  gaseous  chlorine,  at  a  high  temperature,  and  found  that 
chloride  of  silver  was  produced,  and  fluorine  therefore  liberated ;  but  it  was  absorbed 
and  replaced  by  oxygen,  which  it  disengaged  from  the  silica  and  soda  of  the  glass. 
When  Davy  repeated  the  same  experiment  in  a  platinum  vessel,  the  metal  became 
covered  with  fluoride  of  platinum.  He  proposed  afterwards  to  construct  vessels  of 
fluor-spar  for  the  reception  of  the  fluorine,  which  he  expected  to  disengage  from  the 
fluoride  of  phosphorus  by  burning  it  in  oxygen  gas ;  but  he  does  not  appear  to  have 
carried  this  project  into  execution.  The  Messrs.  Knox  and  M.  Louyet  have  an- 
nounced that  they  have  separated  fluorine  from  the  fluorides  of  silver  and  mercury, 
by  treating  these  bodies  with  chlorine  or  iodine  in  vessels  of  fluor-spar,  when  fluorine 
was  disengaged  in  the  form  of  a  colourless  gas.  Grold  and  platinum  did  not  appear 
to  be  acted  upon  by  fluorine,  except  when  it  was  in  the  nascent  state. 

No  compound  of  fluorine  and  oxygen  is  yet  known,  but  a  compound  of  fluorine 
and  hydrogen  is  easily  formed,  and  is  of  importance  from  its  applications. 

HYDROFLUORIC   ACID. 

Eq.  19.7  or  246.3;  HF. 

Schwankhardt,  of  Nuremberg,  observed  in  1670,  that  it  was  possible  to  etch  upon 
lass  by  means  of  fluor-spar  and  sulphuric  acid,  but  it  was  not  till  1771  that  Scheelo 
iferred  this  action  to  a  particular  acid  which  sulphuric  acid  disengaged  from  fluor- 


360  FLUORINE. 

spar.  Wenzel  first  obtained  the  true  hydrofluoric  acid,  exempt  from  silica,  by  pre- 
paring it  in  proper  metallic  vessels ;  the  acid  collected  by  Scheele  being  the  fluosilicic, 
and  not  the  hydrofluoric.  The  preparation  and  properties  of  the  pure  acid  were 
more  fully  studied  by  Gay-Lussac  and  Thenard  in  1810.  It  was  then  known  as 
fluoric  acid,  and  was  supposed,  according  to  the  doctrine  of  the  day,  to  contain 
oxygen.  The  idea  of  its  being  a  hydrogen  acid  was  first  suggested,  a  few  years 
afterwards,  by  M.  Ampere,  whose  views  in  theoretical  chemistry  were  often  marked 
by  much  acuteness  and  originality.  The  view  of  Ampere  was  generally  assented  to, 
and  is  confirmed  by  the  isomorphism  of  the  fluorides  with  the  chlorides,  bromides, 
and  iodides,  observed  by  M.  Louyet. 

Preparation.  —  To  obtain  hydrofluoric  acid,  a  specimen  of  fluor-spar  is  selected, 
free  from  silicious  minerals  and  galena ;  this  is  reduced  to  an  impalpable  powder, 
and  distilled  in  a  retort  of  lead  (fig.  163),  by  a  gentle  heat,  such  as  that  of  an  oil- 
bath,  with  twice  its  weight  of  highly  concentrated 
FIG.  163.  Oii  Of  vitriol.     The  materials  become  viscid  and 

swell  considerably,  and  an  acid  vapour  distils  over, 
which  is  even  more  acrid  and  suffocating  than  chlo- 
rine, and  produces  severe  sores  if  allowed  to  con- 
dense upon  the  hands  of  the  operator.  This  vapour 
is  received  in  a  bent  tube,  likewise  of  lead,  used  as 
a  receiver,  and  kept  cold  by  a  freezing  mixture,  in 
which  the  hydrofluoric  acid  condenses  without  the 
presence  of  water.  The  acid  thus  obtained  may  be 
preserved  in  vessels  of  platinum  or  gold,  provided 
with  stoppers  of  the  same  metal  which  fit  accurately; 
or  in  vessels  of  lead  formed  without  tin  solder,  tin  being  rapidly  acted  upon  by 
hydrofluoric  acid.  If  a  dilute  solution  of  this  acid  in  water  is  required,  the  extre- 
mity of  the  leaden  tube,  from  the  retort,  may  be  allowed  to  touch  the  surface  of 
water  in  a  platinum  crucible  or  capsule,  by  which  the  acid  vapour  is  readily  con- 
densed ;  and  the  dilute  acid  may  be  preserved,  without  much  contamination,  in  a 
glass  bottle  which  has  been  previously  heated,  and  coated  internally  with  melted 
bees' -wax. 

Fluor-spar,  which  is  employed  in  this  operation,  is  the  fluoride  of  calcium,  upon 
which  the  action  of  hydrated  sulphuric  acid  is  similar  to  its  action  upon  chloride  of 
sodium,  when  hydrochloric  acid  is  produced.  Water  is  decomposed,  by  the  hydrogen 
and  oxygen  of  which  the  fluorine  and  calcium  are  converted  respectively  into  hydro- 
fluoric acid  and  lime,  the  former  coming  off  as  vapour,  while  the  latter  remains  in 
the  retort  as  sulphate  of  lime.  In  symbols — 

CaF  and  HO.S08=HF  and  CaO.S03. 

Properties. — The  acid  liquid  obtained  by  the  preceding  process,  which  has  hitherto 
been  considered  as  the  anhydrous  acid,  is,  according  to  M.  Louyet,  a  hydrate.  Dis- 
tilled with  anhydrous  phosphoric  acid,  it  loses  water,  and  gives  rise  to  a  colourless 
gas,  fuming  in  air  like  hydrochloric  acid,  which  is  the  true  anhydrous  hydrofluoric 
acid.  M.  Louyet  finds  this  gaseous  acid  to  have  no  sensible  action  upon  dry  glass. 

The  former  product  is  a  colourless,  fuming,  and  very  volatile  liquid,  boiling  not 
much  above  60°;  and  which  does  not  freeze  at  4°.  Its  sp.  gr.,  which  is  1.0609,  is 
increased  to  1.25  by  the  addition  of  a  certain  quantity  of  water,  for  which  it  has  an 
intense  affinity.  Hydrofluoric,  like  hydrochloric  acid,  dissolves  the  more  oxidable 
metals  with  the  evolution  of  hydrogen  gas.  Mixed  with  nitric  acid,  it  dissolves 
ignited  silicon  and  titanium,  with  disengagement  of  nitric  oxide;  but  that  acid 
mixture  has  no  action  upon  the  nobler  metals,  such  as  gold  and  platinum,  which  are 
dissolved  by  aqua  regia.  Several  insoluble  acid  bodies,  which  are  not  acted  on  by 
sulphuric,  nitric,  or  hydrochloric  acid,  are  dissolved  with  facility  by  hydrofluoric 
acid;  such  as  silica,  titanic,  tantalic,  molybdic  and  tungstic  acids.  Water  is  then 
formed  from  the  oxygen  of  these  acids  and  the  hydrogen  of  hydrofluoric  acid,  and 


FLUORIDE    OF   BORON.  361 

fluorides  of  silicon  or  of  the  metals  of  the  acids  enumerated  are  likewise  produced; 
which  fluorides  appear  to  combine  with  undecomposed  hydrofluoric  acid,  when  water 
is  present.  This  acid  destroys  glass  by  acting  upon  its  silica.  If  a  drop  of  the 
concentrated  acid  be  allowed  to  fall  upon  a  glass  plate,  it  becomes  hot,  enters  into 
ebullition  and  volatilizes  in  a  thick  smoke,  leaving  the  spot  with  which  it  was  in 
contact  deeply  corroded,  and  covered  by  a  white  powder  composed  of  the  elements 
of  the  glass,  excepting  a  portion  of  the  silica,  which  has  passed  off  as  gaseous  fluo- 
ride of  silicon. 

The  diluted  solution,  or  the  vapour  of  hydrofluoric  acid,  is  sometimes  used  to 
etch  upon  glass.  The  purity  of  the  acid  being  of  little  moment  in  this  application 
of  it,  the  sulphuric  acid  and  fluor-spar  may  be  mixed  in  a  stone-ware  evaporating 
basin.  The  glass  is  warmed  sufficiently  to  melt  bees'-wax  rubbed  upon  it,  and 
thereby  covered  with  a  coating  of  that  substance,  which  is  afterwards  removed  from 
the  parts  to  be  etched,  by  a  pointed  rod  of  lead  or  tin,  employed  as  a  graver.  A 
gentle  heat  being  applied  to  the  basin,  acid  fumes  are  evolved,  to  which  the  etched 
surface  of  the  glass  is  exposed  for  a  minute  or  two,  care  being  taken  not  to  melt  the 
wax.  The  wax  is  afterwards  removed  by  warming  the  glass,  and  wiping  it  with  tow 
and  a  little  oil  of  turpentine,  when  the  exposed  lines  are  found  engraved  to  a  depth 
proportional  to  the  time  they  have  been  exposed  to  the  acid  fumes.  But  in  taking 
impressions  upon  paper  from  glass  plates  engraved  in  this  way,  as  from  a  copper- 
plate, they  are  too  apt  to  be  broken  from  the  pressure  applied  in  printing. 

To  discover  the  minute  quantity  of  hydrofluoric  acid  which  exists  in  many  mine- 
rals, Berzelius  recommends  that  the  substance  to  be  examined  be  reduced  to  fine 
powder  and  mixed  with  concentrated  sulphuric  acid,  in  a  platinum  crucible  covered 
by  a  small  plate  of  glass,  waxed  and  engraved  as  described.  The  crucible  is  then 
exposed  to  a  gentle  heat,  insufficient  to  melt  the  wax,  and,  in  half  an  hour,  the  glass 
plate  may  be  removed  and  cleaned.  If  the  mineral  submitted  to  the  test  contains 
fluorine,  the  design  will  be  perceived  upon  the  glass;  when  the  quantity  of  fluorine, 
however,  is  very  small,  the  engraving  does  not  appear  immediately,  but  becomes 
visible  on  passing  the  breath  over  the  glass.  The  presence  of  silica  in  the  mineral 
interferes  with  this  operation,  but  an  indication  may  then  be  obtained  by  heating  a 
fragment  of  the  mineral  to  redness  upon  a  piece  of  platinum  foil  slipped  into  a  glass 
tube,  8  or  10  inches  in  length,  and  open  at  both  ends.  The  tube  is  held  obliquely 
with  the  mineral  near  the  lower  end,  and  so  that  part  of  the  vapour  from  the  flame 
passes  up  the  tube.  The  moisture  thus  introduced  carries  away  the  gaseous  fluoride 
of  silicon,  and  condenses  in  drops  in  the  upper  part  of  the  tube.  These  drops,  when 
afterwards  evaporated,  in  drying  the  tube,  leave  a  white  spot,  which  consists  of  silica, 
resulting  from  the  decomposition  of  the  fluoride  of  silicon  by  the  water  with  which  it 
condensed.  (Berzelius). 

Fluoride  of  boron,  Jluoboric  acid;  67'0  or  837-5;  BF3.  —  This  compound  is 
gaseous,  and  is  obtained  when  dry  boracic  acid  is  brought  in  contact  with  concen- 
trated hydrofluoric  acid;  When  boracic  acid  is  ignited  with  fluor  spar;  and  most 
conveniently  by  heating  together  in  a  glass  retort,  1  part  of  vitrified  boracic  acid  in 
fine  powder,  2  of  fluor  spar,  and  12  of  concentrated  sulphuric  acid,  although  this 
process  does  not  give  it  free  from  fluosilicic  acid.  The  reaction  by  which  the  fluo- 
boric  acid  is  then  produced  may  bo  thus  expressed : — 

3CaF  and  B03  and  3(HO.S03)  =  3(CaO.S03)  and  3HO  and  BF3. 

Fluoboric  acid  gas  has  no  action  upon  glass,  and  may  be  collected  in  glass  vessels 
over  mercury.  It  is  colourless,  but  produces  thick  fumes  when  allowed  to  escape 
into  the  atmosphere.  Its  density,  according  to  Dr.  J.  Davy,  is  2371,  and  2312 
according  to  Dumas,  who  finds  1  volume  of  this  gas  to  contain  1|  vol.  of  fluorine. 
Fluoboric  gas  is  not  decomposed  by  iron  and  the  ordinary  metals,  even  at  a  bright 
red  heat,  but  on  the  contrary,  potassium,  with  the  metals  of  the  alkalies  and  alka- 
line earths,  decomposes  it  at  a  red  heat;  boron  is  liberated  by  potassium,  and  a 
double  fluoride  of  boron  and  potassium  also  formed.  Water  absorbs  fluoboric  acid 


832 


FLUORINE. 


gas  with  the  greatest  avidity,  taking  up,  according  to  J.  Davy,  700  times  its  volume, 
which  increases  its  bulk  considerably,  and  raises  its  density  to  1.77.  Sulphuric  acid 
can  dissolve  50  times  its  volume  of  the  fluoride  of  boron.  The  most  ready  mode  of 
preparing  the  aqueous  solution  of  this  acid  is  to  dissolve  crystallized  boracic  acid  in 
hydrofluoric  acid.  The  acid  is  extremely  caustic  and  corrosive,  charring  and  destroy- 
ing wood  and  organic  matters,  when  concentrated,  like  sulphuric  acid,  probably  from 
its  avidity  for  moisture. 

A  dilute  solution  of  fluoride  of  boron  undergoes  spontaneous  decomposition,  ac- 
cording to  Berzelius,  depositing  one-fourth  of  its  boron  in  the  form  of  boracic  acid, 
which  crystallizes  at  a  low  temperature ;  while  a  compound  of  hydrofluoric  acid  and 
fluoride  of  boron  remains  in  solution,  which  he  termed  hydrofluoboric  acid.  The 
fluoride  of  boron  has  a  great  disposition  to  form  double  fluorides,  and  acts  upon  basic 
metallic  oxides  like  the  following  compound. 

Fluoride  of  silicon,  fluosilicic   acid;   77.45  or 

•      FIG.  164.  968.12  ;  Si  F3.— This  gas  is  obtained  in  the  follow- 

ing manner : — Equal  parts  of  fluor  spar  and  broken 
glass  or  quartzy  sand,  in  fine  powder,  are  mixed  in 
a  glass  flask  a  (fig.  164),  to  be  used  as  a  retort,  with 
six  parts  of  concentrated  sulphuric  acid,  and  stirred 
well  together.  A  disengagement  of  gas  immediately 
takes  place,  and  the  mass  swells  up  considerably. 
After  a  time,  a  gentle  heat  is  required  to  aid  the 
operation.  Muosilicic  gas  is  collected  over  mercury. 
In  its  physical  characters  it  resembles  fluoboric  gas. 
It  is  colourless  and  fumes  in  air;  it  extinguishes 
bodies  in  combustion,  and  does  not  attack  glass.  Its 
density  is  3574  according  to  J.  Davy,  and  3600  ac- 
cording to  Dumas ;  it  contains  twice  its  volume  of 
fluorine. 

In  transmitting  this  gas  into  water,  the  tube  must  not  dip  in  the  fluid,  for  it  would 
speedily  be  choked  by  the  deposition  of  silica  produced  by  the  action  of  water  upon 
the  gas.  In  the  arrangement  figured,  the  extremity  of  the  exit  tube  is  covered  by 
a  small  column  of  mercury  m,  in  the  lower  part  of  the  jar,  through  which  the  gas 
passes  before  it  reaches  the  water  w.  Every  bubble  of  gas  exhibits  a  remarkable 
phenomenon,  as  it  enters  the  water,  becoming  invested  with  a  white  bag  of  silica, 
which  rises  to  the  surface.  It  often  happens,  in  the  course  of  the  operation,  that 
the  gas  forms  tubes  of  silica  in  the  water,  through  which  it  gains  the  surface  with- 
out decomposition,  if  they  are  not  broken  from  time  to  time.  When  water  is  com- 
pletely saturated  with  the  fluoride  of  silicon,  it  has  taken  up  about  once  and  a  half 
its  weight,  and  is  a  gelatinous,  semi-transparent  mass,  which  fumes  in  the  air.  The 
liquid  contains  two  equivalents  of  water  to  one  of  the  original  fluoride  of  silicon : 
but  one-third  of  the  fluoride  has  been  decomposed  by  the  water  and  converted  into 
hydrofluoric  acid  and  silica.  The  hydrofluoric  acid  and  fluoride  of  silicon,  in  solu- 
tion, were  supposed  to  be  in  combination  by  Berzelius,  forming  3HF-f  2SiF3,  which 
was  termed  by  him  hydrofluosilicic  acid.  When  this  liquid  is  placed  in  a  mode- 
rately warm  situation,  the  whole  of  it  gradually  evaporates ;  the  free  hydrofluoric 
acid  reacting  upon  the  deposited  silica,  with  formation  of  water,  and  fluoride  of  sili- 
con being  revived. 

The  most  remarkable  property  of  the  fluoride  of  silicon  is  to  produce,  with  neutral 
salts  of  potassa,  soda  and  lithia,  precipitates  which  are  gelatinous,  and  so  transparent 
as  to  be  scarcely  visible  at  first  in  the  liquid ;  and  with  salts  of  baryta,  a  white  and 
crystalline  precipitate,  which  appears  in  a  few  seconds.  It  is  often  employed  to 
decompose  a  salt  of  potassa,  for  the  purpose  of  isolating  its  acid.  It  also  serves  to 
distinguish  salts  of  baryta  from  salts  of  strontia;  the  salts  of  baryta  producing  with 
this  acid  a  salt  scarcely  soluble  in  water,  while  the  salts  of  stroutia  are  not  pre- 
cipitated. 


METALLIC   ELEMENTS. 


363 


Almost  all  the  basic  metallic  oxides  decompose  this  acid,  when  they  are  employed 
in  excess,  separating  silica,  and  giving  rise  to  metallic  fluorides.  When,  on  the 
other  hand,  no  more  of  the  base  is  applied  than  the  quantity  required  to  neutralize 
the  free  hydrofluoric  acid,  combinations  are  obtained  with  all  bases,  which  are  ana- 
logous to  double  salts;  consisting  of  a  metallic  fluoride  combined  with  fluoride  of 
silicon,  the  proportion  of  the  latter  containing  twice  as  much  fluorine  as  the  former. 
The  formula  of  one  of  these  compounds,  the  double  fluoride  of  silicon  and  potassium, 
is  2SiF3  4-  3KF;  and  those  of  other  metals  are  similar.  The  ratio  of  2  to  3,  in  the 
equivalents  of  the  two  fluorides  which  form  these  double  salts,  is  unusual.  But  the 
double  fluorides  in  question  may  be  represented  by  single  equivalents  of  fluoride  of 
silicon  and  metallic  fluoride,  as  was  suggested  by  Dr.  Clark,  by  adopting  the  low 
equivalent  of  silicon  12.6,  when  silica  is  made  to  consist  of  1  equivalent  of  silicon 
and  2  equivalents  of  oxygen,  and  the  fluoride  of  silicon  of  1  equivalent  of  silicon 
and  2  equivalents  of  fluorine. 


CHAPTER  VI. 

METALLIC    ELEMENTS, 


GENERAL    OBSERVATIONS. 

THE  metallic  class  of  elements  is  considerably  more  numerous  than  the  non- 
metallic  class,  embracing  forty-eight  elementary  bodies.  Of  these  seven  only  were 
known  to  the  ancients,  and  of  the  remainder,  a  large  proportion  are  of  recent  dis- 
covery. Their  names  and  their  densities,  when  accurately  determined,  with  the 
dates  and  authors  of  their  discovery,  are  contained  in  the  following  table,  compiled 
chiefly  from  the  work  of  Dr.  Turner : — 

Table  of  Metals. 


Name. 

Density. 

Dates  and  Authors  of  the  Discovery. 

Gold  

19-257  Brisson   to  19-361  ] 

Silver.  

10-474,  ditto  

Iron  
Copper  

7-778,  ditto  
8-895   Hatchett 

Known  to  the  Ancients 

Mercury  
Lead  

13-596,  at  32°  Regnault. 
11-352,  Brisson  

Tin     .. 

7-291    ditto 

Antimony  
Bismuth  

6-702,  ditto  
9-822,  ditto  

1490,  described  by  Basil  Valentine. 
1530,  described  by  Agricola. 

Zinc             . 

6-861  to  7'1   ditto 

16th  century  first  mentioned  by  Paracelsus 

Arsenic    ...... 

5-884   Turner                    " 

Cobalt  

8-538   Haiiy    

; 

1733,  Brandt. 

Platinum  
Nickel  

20-336   Brisson,  to*  22-069 
8-279  Richter 

1741,  Wood,  assay  -master,  Jamaica. 
1751    Cronstedt 

Manganese  ... 

7.500'                    

1774  Gahn  and  Scheele. 

Tungsten  

17-6       D'Elhuyart  

1781,  D'Elhuyart. 

Tellurium  

6-115   Klaproth  

1782,  Miiller. 

Molybdenum  . 

7-400  Hielm             

1782,  Hielm. 

Uranium  

9-000  Bucholz  

1789,  Klaproth. 

Titanium  

5-3,      Wollaston  

1791,  Gregor. 

Chromium  .... 
Tantalum  

5-9,  

1797,  Vauquelin. 
1802,  Hatchett. 

364 


METALLIC   ELEMENTS. 


Table  of  Metals  —  continued. 


Name. 

Density. 

Dates  and  Authors  of  the  Discovery. 

Palladium  .... 

11-3  to  11-8,  Wollaston...  ) 
10-649                        .          J 

1803,  Wollaston. 

Iridium 

18-680    [21-8   Hare]  

1803,  Descotils  and  Smithson  Tennant. 

10-0  

1803,  Smithson  Tennant. 

1804,  Hisinger  and  Berzelius. 

Potassium  
Sodium  

0-865  \  Gay  Lussac  and  ] 
0-972  /      ThSnard  

Barium 

1807,  Davy. 

Strontium  

Calcium 

Cadmium  

8-604   Stromeyer  

1818,  Strorneyer. 

1818,  Arfwedson. 

Zirconium 

1824   Berzelius 

Aluminum  .... 

1828,  Wohler. 

Yttrium 

Thorium  

1829,  Berzelius. 

1829,  Bussy. 

Vanadium 

1830   Sefstrb'm 

Lantanum 

, 

1839   Mosander. 

Erbium  

Since  1840,  Mosander. 

Terbium  . 

1844,  Klaus. 

..  ) 

Niobium... 

::::::           t 

1845,  H.  Rose. 

Of  the  physical  properties  of  metals  and  their  combinations  with  each  other,  the 
most  characteristic  is  their  lustre  and  power  to  reflect  much  of  the  light  which  falls 
upon  them,  —  a  property  exhibited  in  a  high  degree  by  burnished  steel,  speculum 
metal,  and  the  reflecting  surface  of  mercury  in  glass  mirrors.  Metals  are  also  re- 
markable for  their  opacity,  although  they  have  a  certain  degree  of  transparency  in 
a  highly  attenuated  state,  as  fine  gold-leaf  allows  light  of  a  green  colour  to  pass 
through  it.  They  are  peculiarly  the  conductors  of  electricity,  and  also  the  best  con- 
ductors of  heat.  The  most  dense  substances  in  nature  are  found  among  the  metals, 
— gold,  for  instance,  being  upwards  of  nineteen,  and  laminated  platinum  twenty-two 
times  heavier  than  an  equal  bulk  of  water.  But  some  of  the  metals,  notwithstanding, 
are  very  light,  potassium  and  sodium  floating  upon  the  surface  of  water. 

Certain  metals  possess  a  valuable  property,  malleability,  depending  upon  a  high 
tenacity  with  a  certain  degree  of  softness;  particularly  gold,  silver,  copper,  tin, 
platinum,  palladium,  cadmium,  lead,  zinc,  iron,  nickel,  potassium,  sodium,  and  solid 
mercury.  These  metals  may  all  be  hammered  out  into  plates,  or  even  into  thin 
leaves.  In  zinc  this  property  is  found  in  the  highest  degree  between  300°  and 
400°,  and  in  iron  at  a  degree  of  temperature  exceeding  a  red  heat.  The  same 
metals  are  likewise  ductile,  or  may  be  drawn  into  wires,  although  the  ductility  of 
different  metals  is  not  always  proportional  to  their  malleability,  iron  being  highly 
ductile,  although  it  cannot  be  beaten  into  very  thin  leaves.  By  a  peculiar  method, 
Dr.  Wollaston  formed  gold  wire  so  small  that  it  was  only  l-5000th  of  an  inch  in 
diameter,  and  550  feet  of  it  were  required  to  weigh  one  grain.  He  also  obtained  a 
wire  of  platinum  not  more  than  l-30,000th  of  an  inch  in  diameter,  (Phil.  Trans. 
1813.)  The  tenacity  of  different  metals  is  determined  by  ascertaining  the  weight 
required  to  break  wires  of  them  having  the  same  diameter.  Iron  appears  to  possess 
that  property  in  the  greatest,  and  lead  in  the  least  degree.  It  has  been  observed 
by  M.  Baudrimont  that  the  tenacity  of  wires  of  iron,  copper,  and  brass,  is  much 
injured  by  annealing  them,  (Annal.  de  Chim.  et  de  Phys.  Ix.  78.)  A  few  of  the 


GENERAL   OBSERVATIONS. 


365 


malleable  metals  can  be  welded,  or  portions  of  them  joined  into  one  by  hammering 
them  together.  Pieces  of  iron  or  platinum  may  be  united  in  this  manner  at  a  bright 
red  heat,  and  fragments  of  potassium  may  be  made  to  adhere  by  pressing  them  to- 
gether with  the  hand  at  the  temperature  of  the  air.  Many  metals  are  only  ma-lleable 
in  a  low  degree,  and  some  are  actually  brittle,  —  such  as  bismuth,  antimony,  and 
arsenic. 

The  metals,  with  the  exception  of  mercury,  are  all  solid  at  the  temperature  of  the 
air,  but  they  may  be  liquefied  by  heat.  Their  points  of  fusion  are  very  different, 
as  will  appear  from  the  following  table : 

Table  of  the  Fusibility  of  different  Metals. 

FAHR.  DIFFERENT  CHEMISTS. 

Mercury — 39° 

Potassium  ...  136    ") 

oOQlVHH    ..........*................       190      ) 

Tin 442    ) 

Bismuth 497    Icrichton. 

Fusible  "below  o>  •*•••••••••••••••••••••••••••••     ux*-    j 

red  heat.  gible  th&n  lead Klaproth. 

Arsenic  —  undetermined. 

Zinc.. 773       Daniell. 

Antimony  —  a  little  below  a 

red  heat. 
Cadmium 442       Stromeyer. 

Silver 1873°) 

Copper 1996    I  Daniell. 

Gold 2016   J 

Cobalt  —  rather  less  fusible  \ 

than  iron.  * 

Iron,  cast 2786       Daniell. 

Iron,  malleable 1    Requiring  the  highest  heat  of  a  smith's 

Manganese J        forge. 

Nickel  —  nearly  the  same  as  cobalt. 

Infusible  below  a  1  Molybdenum  ^  Aimost  infusible,  and  not  t  >  be  }  Fusible     before    the 
Uranium I      procured  in  buttons  by  the  L      oxi-hydrogen  blow- 
Tungsten  ..  ..  J      heat  of  a  smith's  forge.  J      pipe. 
Chromium 
Titanium .. 

Cerium 

Osmium ,  Infusible  in  the  heat  of  a  smith's  forge,  but  fusible  be- 

Iridium f      fore  the  oxi-hydrogen  blow-pipe. 

Rhodium 

Platinum 

.Columbium.. 


The  metallic  elements  are,  in  general,  highly  fixed  substances,  although  it  is  pro- 
bable that  all  of  them  may  be  dissipated  at  the  highest  temperatures.  The  following 
metals  are  so  volatile  as  to  be  occasionally  distilled, — cadmium,  mercury,  arsenic, 
tellurium,  sodium,  potassium,  and  zinc. 

All  the  metals  are  capable  of  uniting  with  oxygen,  but  they  differ  greatly  from 
each  other  in  their  affinity  for  that  element.  The  greater  number  of  them  absorb 
oxygen  from  dry  air  at  the  usual  temperature,  and  undergo  oxidation,  which  is  only 
slight  and  superficial  in  many,  when  they  are  in  mass,  but  may  be  complete  and 
perfect  in  the  same  metals,  when  they  are  highly  divided,  and  in  a  favourable  state 
for  combination,  as  in  the  lead  and  iron  pyrophorus  exposed  to  air.  The  same  metals 
exhibit,  at  a  high  temperature,  a  more  intense  affinity  for  oxygen,  and  combine  with 
the  phenomena  of  combustion. 

The  metals  have  been  arranged  in  six  groups  or  sections,  differing  in  their  degrees 


366  METALLIC   ELEMENTS. 

of  oxidability :  1.  Metals  which  decompose  water  even  at  32°,  with  lively  efferves- 
cence— namely,  potassium,  sodium,  lithium,  barium,  strontium,  calcium.  2.  Metals 
which  do  not  decompose  water  at  32°,  like  the  metals  of  the  preceding  class;  they 
do  not  decompose  it  with  a  lively  effervescence,  except  at  a  temperature  approaching 
212°,  or  even  higher,  but  always  much  below  a  red  heat.  In  this  class  are  found 
magnesium,  glucinum,  aluminum,  zirconium,  thorium,  yttrium,  cerium,  and  manga 
nese.  3.  Metals  which  do  not  decompose  water  except  at  a  red  heat,  or  at  the 
ordinary  temperature  with  the  presence  of  strong  acids.  This  section  comprehends 
iron,  nickel,  cobalt,  zinc,  cadmium,  tin,  chromium,  and  probably  vanadium.  Iron 
is  rapidly  corroded  in  water  containing  carbonic  acid,  with  the  evolution  of  hydrogen. 
4.  Metals  which  decompose  the  vapour  of  water  at  a  red  heat  with  considerable 
energy,  but  which  do  not  decompose  water  in  presence  of  the  strong  acids.  They 
are  tungsten,  molybdenum,  osmium,  tantalum,  titanium,  antimony,  and  uranium. 
These  metals  appear  to  be  incapable  of  decomposing  water  in  contact  with  acids,  be- 
cause their  oxides  have  but  a  small  basic  power,  being,  indeed,  bodies  which  are 
ranked  among  the  acids.  5.  Metals  of  which  the  oxides  are  not  decomposed  by  heat 
alone,  and  which  decompose  water  only  in  a  feeble  manner  and  at  a  very  high  tem- 
perature. They  are  also  distinguished  from  the  preceding  class  by  their  tendency 
to  form  basic  and  not  acid  oxides.  These  metals  are  copper,  lead,  and  bismuth.  6. 
Metals  of  which  the  oxides  are  reducible  by  heat  alone  at  a  temperature  more  or  less 
elevated :  these  metals  do  not  decompose  water  in  any  circumstances.  They  are 
mercury,  silver,  palladium,  platinum,  gold,  and  probably  rhodium  and  iridium. 
(Regnault,  Annal.  de  Chim.  et  de  Phys.  Ixii.  368.)  It  is  to  be  remarked  of  nearly 
all  the  metals  which  decompose  the  vapour  of  water,  and  consequently  separate  hy- 
drogen from  oxygen  at  a  certain  temperature,  that  their  oxides  are  reduced,  notwith- 
standing, with  great  facility  by  hydrogen  gas,  and  within  the  same  limits  of  tempe- 
rature. This  anomalous  result  has  already  been  adverted  to  in  regard  to  iron 
(page  181). 

Of  the  non-metallic  elements,  hydrogen  only  forms  an  oxide  capable  of  uniting  as 
a  base  with  acids.  It  is  a  general  character  of  the  metals,  on  the  contrary,  to  form 
such  oxides,  if  tellurium  be"  excepted,  which  is  more  analogous  in  its  chemical  pro- 
perties to  sulphur  than  to  the  metals.  Hence,  as  the  former  class  are  principally 
salt-radicals,  the  latter  are  principally  basyls. 

The  protoxides  of  metals  are  uniformly  and  strongly  basic,  but  this  feature  becomes 
less  distinct  in  their  superior  oxides,  and  passes  into  the  acid  character  in  the  high 
•  degrees  of  oxidation  of  which  some  metals  are  susceptible.  Thus,  of  manganese,  the 
protoxide  is  a  strong  base ;  the  sesquioxide  basic,  but  in  a  less  degree  than  the  pro- 
toxide ',  the  binoxide  indifferent  j  and  the  still  higher  oxides  are  the  manganic  and 
permanganic  acids,  which  are  respectively  isomorphous  with  sulphuric  and  perchloric 
acids.  A  few  metals  which  have  no  protoxides,  such  as  arsenic  and  antimony,  are 
most  remarkable  for  the  acids  they  form  with  oxygen,  and  thus  more  resemble  in 
their  chemical  history  the  elements  of  the  non-metallic  class.  It  is,  indeed,  impos- 
sible to  draw  an  exact  line  of  demarcation  between  the  two  classes  of  elements, 
either  with  reference  to  their  physical  or  chemical  properties. 

Besides  combining  with  oxygen,  metals  combine  with  sulphur,  chlorine,  and  with 
other  salt-radicals,  whether  simple  or  compound;  and  hence  sulphides,  chlorides, 
and  numerous  other  series  of  metallic  compounds.  Of  these  series  the  sulphides 
most  resemble  the  corresponding  oxides  of  the  same  metals ;  the  chlorides  and  other 
series  partake  more  strongly  of  the  saline  character.  Each  metal,  or  class  of  metals, 
effects  combination  with  oxygen  in  certain  proportions,  and  combines  also  with  sul- 
phur, chlorine,  &c.  in  the  same  proportions.  Hence,  given  the  formulae  of  the 
oxides  of  a  metal,  the  formulae  of  its  sulphides,  chlorides,  &c.  may  generally  be  pre- 
dicated, as  they  correspond  with  the  former.  Thus  the  oxides  of  iron  being  FeO 
and  Fe203,  the  sulphides  are  FeS  and  Fe2S3,  and  the  chlorides  FeCl  and  Fe2Cl3 ; 
the  oxides  of  arsenic,  or  arsenious  and  arsenic  acids,  being  As03  and  As05,  the  sul- 
phides of  that  metal  are  AsS3  and  AsS6,  and  the  chlorides  AsCla  and  AsCl6.  But 


GENERAL   OBSERVATIONS.  367 

sometimes  a  metal  unites  with  sulphur  in  more  ratios  than  with  oxygen ;  both  iron 
and  arsenic,  for  example,  possessing  each  a  sulphide  to  which  they  have  no  corre- 
sponding oxide,  namely,  iron  pyrites  and  realgar,  of  which  the  formulae  are  FeS2  and 
AsS2.  The  potassium  family  of  metals  combine  also  with  three  and  five  equivalents 
of  sulphur,  without  all  uniting  with  oxygen  in  such  high  proportions.  Again,  cer- 
tain metals  of  the  magnesian  and  its  allied  families,  such  as  manganese  and  chro- 
mium, form  acid  compounds  with  oxygen,  to  which  no  corresponding  sulphides  exist, 
such  as  manganic  and  chromic  acids,  Mn03  and  Cr03.  But  the  circumstance  that 
these  acids  are  isomorphous  with  sulphuric  acid,  and  the  metals  they  contain  isomor- 
phous  with  sulphur,  appears  to  be  a  sufficient  reason  why  there  should  not  be  similar 
sulphur  acids.  The  chlorides  of  a  metal  generally  correspond  in  number,  as  they 
always  do  in  composition,  with  the  oxides  j  in  some  cases  they  are  less  numerous, 
but  never,  I  believe,  more  numerous  than  the  oxides  of  the  same  metal. 

Combination  takes  place  within  a  series  j  that  is,  oxides  combine  with  oxides, 
sulphides  with  sulphides.  Those  members  of  the  same  series  which  differ  greatly 
in  chemical  characters  being  most  disposed  to  combine  together,  —  as  oxygen  acids 
with  oxygen  bases,  sulphur  acids  with  sulphur  bases.  Chlorides  also  combine  with 
chlorides,  to  form  double  chlorides,  and  iodides  with  iodides. 

Compounds  belonging  to  different  series,  on  the  contrary,  do  not  in  general  com- 
bine together,  but  often  mutually  decompose  each  other  when  brought  into  contact. 
Thus  hydrochloric  acid  and  potassa  do  not  unite,  one  belonging  to  the  chlorine  and 
the  other  to  the  oxygen  series,  but  form  water  and  chloride  of  potassium,  by  mutual 
decomposition,  as  explained  in  the  following  diagram  :  — 

Before  decomposition.  After  decomposition. 

^    Water 
>rine 


Hydrochloric  acid  {  Hyd 


Potassa.... {potassium ^  Chloride  of  potassium. 

In  the  game  manner,  sesqui-oxide  of  iron,  when  dissolved  in  hydrochloric  acid, 
produces  water  and  a  perchloride  of  iron  corresponding  with  the  peroxide :  — 

3HC1  and  Fe203=3HO  and  Fe2Cl3. 

And  in  all  cases  when  a  metallic  oxide  dissolves  in  hydrochloric  acid,  without 
evolution  of  chlorine,  the  chloride  produced  necessarily  corresponds  with  the  oxide 
dissolved.  Again,  orpiment,  or  sulph-arsenious  acid,  does  not  combine  with  potassa, 
when  dissolved  in  that  alkaline  oxide,  the  first  being  a  sulphur  and  the  second  an 
oxygen  compound,  but  gives  rise  to  the  formation  of  certain  proportions  of  arsenioua 
acid  and  sulphide  of  potassium  :  — 

Before  decomposition.  After  decomposition. 

c,  ,  ,          .          ..,    (Arsenic _  Arsenious  acid 

Sulpharsemous  acid   •]  0  n  . 

(  3  Sulphur 


3  Potassa j  3  Oxygen... . 

(  3  Potassium  • 


3  Sulphide  of  potassium. 


Two  pairs  of  compounds  of  different  series,  then,  co-exist  in  the  liquid,  —  an 
oxygen  acid,  arsenious  acid,  which  unites  with  the  oxygen  base,  potassa,  and  a  sulphur 
base,  sulphide  of  potassium,  which  unites  with  undecomposed  sulpharsenious  acid. 
Hence  the  result  of  dissolving  orpiment  in  potassa  is  the  decomposition  of  both  com- 
pounds and  formation  of  two  salts  of  different  series,  arsenite  of  potassa  and  sulph- 
arsenite  of  sulphide  of  potassium. 

The  union  of  metallic  compounds  of  the  oxygen  and  sulphur  series  is  a  rare  occur- 
rence. But  the  red  ore  of  antimony  is  such  a  combination,  and  oxisulphides  of 
mercury  also  exist.  Compounds  of  metallic  oxides  with  metallic  chlorides,  and  with 


368  ARRANGEMENT   OF   METALLIC   ELEMENTS. 

other  highly  saline  binary  compounds,  are  more  frequent ;  but  they  are  not  to  be 
placed  in  the  same  category  with  the  compounds  of  individuals  both  belonging  to 
the  same  series,  which  last  are  neutral  salts.  For  a  metallic  oxichloride  may  gene- 
rally, if  not  always,  be  viewed  as  a  chloride  to  which  a  certain  proportion  of  metallic 
oxide  is  attached,  like  constitutional  water  in  a  hydrated  salt.  That  metallic  oxide 
is  likewise  always  of  the  magnesian  class,  or  of  a  class  allied  to  it.  Oxichlorides 
are  then  to  be  associated  with  those  salts  of  oxygen-acids  usually  denominated  sub- 
salts  (page  162) ;  the  oxichlorides  of  lead  and  of  copper, — 

PbCl  +  3PbO  and  CuCl  +  CuO, 
with  the  subacetates  and  subsulphates  of  the  same  metals. 

Arrangement  of  metallic  elements.  —  A  distribution  of  the  metals  into  three 
classes  is  generally  made,  composed  respectively  of  the  metals  of  the  alkalies  and 
alkaline  earths,  the  metals  of  the  earths,  and  the  metals  proper.  The  latter  class 
again  is  subdivided,  according  to  the  affinity  of  the  metals  contained  in  it  for  oxygen, 
into  two  groups  —  the  noble  and  common  metals ;  the  oxides  of  the  former,  such  as 
gold,  silver,  &c.,  abandoning  their  oxygen  at  a  high  temperature,  while  the  oxides 
of  the  latter,  lead,  copper,  &c.,  are  undecomposable  by  heat  alone.  In  treating  of 
the  metals,  I  shall  introduce  them  in  the  order  which  appears  to  facilitate  most  the 
study  of  their  combinations,  with  a  general  reference  to  this  classification.  For  sub- 
divisions, I  shall  avail  myself  of  the  natural  families  into  which  the  elements  have 
been  arranged  (page  144),  which  have  the  advantage  of  bringing  together  those 
metals  of  which  the  compounds  are  most  frequently  isomorphous.  The  different 
metals  will  therefore  be  grouped  under  the  following  orders :  — 

I.  Metallic  bases  of  the  alkalies  —  three  metals  :  — 

Oxides. 

Potassium Potassa 

Sodium Soda 

Lithium Lithia 

II.  Metallic  bases  of  the  alkaline  earths  —  four  metals :  — 

Oxides. 

Barium Baryta 

Strontium Strontia 

Calcium Lime 

Magnesium Magnesia 

III.  Metallic  bases  of  the  earths  proper  —  seven  metals :  — 

Oxides. 

Aluminum Alumina 

Glucinum Glucina 

Zirconium Zirconia 

Yttrium Yttria 

Terbium Terbia 

Erbium Erbia 

Thorium  Thorina 

IV.  Metals  proper,  of  which  the  protoxides  are  isomorphous  with 
eight  metals :  — 


Manganese 
Iron 
Cobalt 
Nickel 


Zinc 

Cadmium 
Copper 
Lead 


POTASSIUM.  369 

V.  Other  metals  proper  having  isomorphous  relations  with  the  magnesian  family 
—  seven  metals :  — 


Tin 

Titanium 
Chromium 
Vanadium 


Tungsten 

Molybdenum 

Tellurium 


VI.  Metals  isomorphous  with  phosphorus  —  three  metals :  — 


Arsenic 
Antimony 


Bismuth 


VII.  Metals  proper,  not  included  in  the  foregoing  classes,  of  which  the  oxides 
are  not  reduced  by  heat  alone  —  eight  metals :  — 


Uranium. 
Cerium. 
Lantanum. 
Didymium. 


Titanium. 

Tantalum  or  Columbium. 

Pelopium. 

Niobum. 


VIII.  Metals  proper,  of  which  the  oxides  are  reduced  to  the  metallic  state  by 
heat  (noble  metals) — three  metals  : — 


Mercury. 
Silver. 


Gold. 


IX.  Metals  found  in  native  platinum  (noble  metals)  —  six  metals  :•— 


Platinum. 

Palladium. 

Iridium. 


Osmium. 

Rhodium. 

Ruthenium. 


ORDER  I. 

METALLIC   BASES   OP   THE   ALKALIES. 

SECTION  I. 

POTASSIUM. 

Syn.  KALIUM.     Eg.  39  or  487.5;  K. 

The  alkalies  and  earths  have  long  been  named  and  distinguished  from  each  other, 
but  they  were  not  known  to  be  the  oxides  of  peculiar  metals  till  a  recent  period. 
The  terms  applied  to  the  new  metallic  bases  are  formed  from  the  names  of  their 
oxides,  as  potassium  from  potash,  and  calcium  from  calx,  a  name  sometimes  given 
to  liine ;  while  the  original  names  of  the  oxides  are  still  retained,  as  those  of  ordi- 
nary objects,  and  not  superseded  by  appellations  indicating  their  relation  to  the 
metals,  such  as  oxide  of  potassium  for  potassa,  or  oxide  of  calcium  for  lime. 

Preparation. — In  1807,  Sir  H.  Davy  made  the  memorable  discovery  that  potassa 
is  resolved  by  a  powerful  voltaic  battery  into  potassium  and  oxygen.  He  placed  a 
moistened  fragment  of  hydrate  of  potassa  on  mercury,  introducing  the  terminal  wire 
from  the  zinc  extremity  of  an  active  battery  (the  chloroid)  into  the  fluid  metal,  and 
touching  the  potassa  with  the  other  terminal  wire  (the  zincoid) ;  bubbles  of  oxygen 
gas  appeared  at  the  latter  wire,  and  potassium  was  liberated  at  the  former,  and  dis- 
solving in  the  mercury,  was  protected  from  oxidation  by  the  air.  To  effect  this 
24 


370 


POTASSIUM. 


decomposition,  Davy  employed  a  battery  of  200  pairs  of  four-inch  plates ;  but  an 
amalgam  of  potassium  may  be  as  readily  obtained  by  a  more  simple  voltaic  apparatus, 
in  the  manner  described  at  page  221.  These  processes,  however,  afford  potassium 
only  in  minute  quantity.  Soon  after  the  existence  of  this  metal  was  known,  Gay- 
Lussac  and  Thenard  discovered  that  potassa  is  decomposed  by  iron  at  a  white  heat, 
and  they  contrived  a  process  by  which  a  more  abundant  supply  of  the  metal  was 
obtained.  It  was  afterwards  noticed  by  Curaudau,  that  potassa,  like  the  oxides  of 
common  metals,  is  decomposed  by  charcoal  as  well  as  by  iron,  which  is  the  basis  of 
the  process  for  potassium  now  always  followed. 

This  interesting  process  is  described  by  Mitscherlich,  as  it  is  successfully  pursued 
in  Germany.  Whenever  charcoal  is  used  to  deprive  a  metallic  oxide  of  its  oxygen, 
the  former  must  be  in  a  state  of  minute  division,  and  be  intimately  mixed  with  the 
latter.  Carbonate  of  potassa  requires  this  precaution  the  more,  that  it  fuses  at  a 
red  heat,  and  is  thus  apt  to  separate  from  the  charcoal,  and  sink  below  it.  It  is 
found  that  the  best  means  to  obtain  a  proper  mixture  of  these  substances  is  to  calcine 
a  salt  of  potassa  containing  a  vegetable  acid,  which  leaves  a  large  quantity  of  char- 
coal when  decomposed.  Crude  tartar  (bitartrate  of  potassa)  is  preferred,  and  for 
one  operation  six  pounds  of  that  salt  are  ignited  in  a  large  crucible  or  melting-pot 
provided  with  a  lid,  so  long  as  combustible  gases  are  disengaged.  The  crucible  is 
then  withdrawn  from  the  fire,  and  is  found  to  contain  a  black  mass,  which  is  the 
mixture  of  charcoal  and  carbonate  of  potassa,  known  as  black  flux.  It  is  reduced 
to  powder,  while  still  warm,  and  immediately  mixed  with  about  ten  ounces  of  wood- 
charcoal  in  small  pieces,  -or  in  a  coarse  powder,  from  which  the  dust  has  been  sepa- 
rated by  a  sieve.  The  use  of  this  additional  charcoal  is  to  act  as  a  sponge,  and 
absorb  the  potassa  when  liquefied  by  heat.  The  mixture  is  introduced  into  a  bottle 
of  wrought  iron,  and  a  mercury  bottle  (page  224)  answers  well  for  the  purpose,  bur, 
must  be  heated  to  redness  beforehand,  to  expel  a  little  mercury  that  remains  in  it. 
The  mouth  of  the  bottle  is  enlarged  a  little  by  means  of  a  round  file,  and  a  straight 
iron  tube  of  4  or  5  inches  in  length  fitted  into  the  opening,  by  grinding.  The  bottle 
and  tube  thus  form  a  retort,  which  is  supported  horizontally  in  a  brick  furnace,  as 
represented  (fig.  165)  in  which  a  is  the  iron  bottle  resting  upon  two  bars  of  iron  oo, 
to  which  it  may  also  be  firmly  bound  by  iron  wire.  These  bars  cross  the  furnace  at 


PREPARATION  OF   POTASSIUM.  371 

a  height  of  5  or  6  inches  above  the  grate-bars.     A  mixture  of  equal  parts  of  coal 
and  coke  makes  an  excellent  fuel  for  this  furnace.    The  tube  b  of  the  bottle  projects 
through  an  aperture  in  the  side-wall  of  the  furnace,  and  enters  a  receiver  of  a  pecu- 
liar construction  required  to  condense  the  potassium,  which  distils'  over.     This 
receiver  is  composed  of  two  separate  copper  cylinders  or  oval  boxes,  hard  soldered, 
similar  in  form  and  size,  which  are  represented  in  section  (fig.  166),  the  one,  b  n  d, 
being  introduced  within  the  other,  ghk,  and  thus  forming  together 
FIG.  166.          a  vessel  of  which  bnd  is  the  cover.     It  will  also  be  observed  that 
«  b  d  is  divided  into  two  cells  by  a  diaphragm,  t,  of  the  same  length 

as  the  cylinder,  and  descending  with  it  to  within  two  inches  of 
the  bottom,  h,  of  ghk.  A  ribbon  of  copper,  g,  is  soldered  around 
bnd,  so  as  to  form  a  ledge,  which  is  seen  in  both  figures,  and 
serves  as  a  support  for  a  cage  of  iron-wire,  c  d,  placed  over  the 
receiver  during  the  distillation,  to  hold  ice,  and  also  to  shed  the 
water  from  the  liquefaction  of  that  ice,  which  falls  into  a  tray,  jo, 
below,  and  flows  off  by  the  tube,  I.  The  cover  has  also  two  short 
copper  tubes,  d  and  b,  of  which  the  copper  of  b  is  notched  so  as  to  clasp  firmly  by 
its  elasticity  the  tube  b  from  the  iron  bottle,  which  is  fitted  into  it.  The  other  tube, 
d,  which  is  exactly  opposite  to  b,  is  fitted  with  a  cork,  and  the  diaphragm,  i,  has  a 
small  hole  in  it  to  allow  of  a  rod  being  passed  through  b  and  d.  In  the  same  part 
of  the  apparatus  is  a  third  opening,  to  which  a  glass  tube,  x,  is  fitted  by  a  cork,  for 
the  escape  of  uncondensible  gases.  The  receiver  is  filled  to  about  one-third  with 
rectified  petroleum,  a  liquid  containing  no  oxygen,  so  as  to  come  nearly  to,  but  not 
to  cover,  the  bottom  of  the  partition,  i.  The  length  of  the  bottle  is  11  inches,  its 
width  4,  arid  the  other  parts  of  the  apparatus  are  designed  upon  the  same  scale. 

Potassium  and  carbonic  oxide  gas  are  the  principal  products  of  the  decomposition 
of  the  carbonate  of  potassa,  but  other  substances  besides  these  are  found  in  the 
receiver ;  namely,  a  black  mass  very  rich  in  potassium,  some  oxalate  and  croconate 
of  potassa  and  free  potassa,  with  a  portion  of  charcoal  powder  carried  over  mecha- 
nically. Part  of  these  products  appears  to  be  formed,  after  the  reduction  of  the 
potassium,  by  the  mutual  reaction  of  that  metal,  carbonic  oxide  and  petroleum.  The 
process  is  found  to  succeed  best  when  the  iron  tube,  ft,  is  so  short  that  it  can  be 
maintained  at  a  red  heat  through  its  whole  length  during  the  operation,  while  the 
receiver  is  kept  at  a  very  low  temperature ;  the  potassium  then  falls  from  the  tube, 
drop  by  drop,  into  the  receiver,  and  does  not  remain  long  in  contact  with  carbonic 
oxide,  which  is  known  to  combine  readily  with  that  metal.  One  or  two  other  points 
should  always  be  attended  to.  The  connexion  between  the  tube  ft  and  the  receiver 
is  not  made  till  the  iron  bottle  has  been  heated  to  redness,  to  allow  'of  the  escape 
of  a  little  water,  and  of  a  trace  of  mercury,  which  had  remained  in  the  bottle  in  the 
state  of  vapour,  and  which  come  off  first.  The  joining  of  the  tube  b  is  not  air-tight 
at  first,  and  allows  a  little  potassium  vapour  to  escape,  but  this  burns  and  forms 
potassa,  which  immediately  closes  the  openings.  This  tube  being  always  incandescent 
and  the  refrigeration  properly  made,  the  reduction  sometimes  proceeds  without 
interruption.  But  the  tube  is  sometimes  obstructed,  as  appears  by  the  gases  ceasing 
to  escape  by  x.  Haste  must  then  be  made  to  open  the  tube  ft,  and  to  clear  it  by 
means  of  a  flattened  iron  rod,  I,  slightly  hooked  at  its  anterior  extremity.  Care 
has  been  taken  to  mark  on  this  rod,  with  the  scratch  of  a  file,  how  far  it  has  to 
penetrate  into  the  apparatus  to  reach  the  mouth  of  the  bottle,  jjnd  it  must  not  be 
introduced  farther.  The  current  of  air  through  the  furnace  is  regulated  by  a  register 
valve  in  the  chimney,  and  the  fire  stirred  frequently  so  as  to  prevent  the  formation 
of  cavities ;  the  operator  being  guided  in  the  management  of  the  fire  by  the  rapidity 
of  the  current  of  gas  which  escapes  by  the  tube  x.  To  terminate  the  operation,  the 
grate  bars  may  be  thrown  down,  by  which  the  fuel  will  fall  into  the  ash-pit.  The 
quantity  of  crude  tartar  mentioned  yields  about  4  ounces  of  potassium,  which  is 
about  4  per  cent,  of  its  weight.  The  potassium  thus  obtained,  containing  a  little 
carbon  chemically  combined  with  it,  is  submitted,  together  with  the  black  mass 


372  COMPOUNDS  OF   POTASSIUM. 

f  ;und  in  the  receiver,  to  a  second  distillation.  For  this  purpose  a  smaller  iron  bottle 
with  a  bent  tube  may  be  employed,  the  end  of  which  is  covered  by  rectified  petro- 
leum in  a  capacious  flask,  used  as  a  receiver.  (Mitscherlich,  Siemens  de  Chimie, 
iii.  8).  [See  Supplement,  p.  805.] 

Properties.  —  Potassium  is  solid  at  the  usual  temperature,  but  so  soft  as  to  yield 
like  wax  to  the  pressure  of  the  fingers.  A  fresh  surface  has  a  white  colour,  with  a 
shade  of  blue,  like  steel,  but  is  almost  instantly  covered  by  a  dull  film  of  oxide  when 
exposed  to  air.  The  metal  is  brittle  at  32°,  and  has  been  observed  crystallized  in 
cubes :  it  is  semi-fluid  at  70°,  and  becomes  completely  liquid  at  150°.  It  may  be 
distilled  at  a  low  red  heat,  and  forms  a  vapour  of  a  green  colour.  Potassium  is  con- 
siderably lighter  than  water,  its  density  being  0.865  at  60°. 

Potassium  oxidates  gradually  without  combustion  when  exposed  to  air  j  but  heated 
till  it  begins  to  vaporize,  it  takes  fire  and  burns  with  a  violet  flame.  The  avidity 
of  this  metal  for  oxygen  is  strikingly  exhibited  when  a  fragment  of  it  is  thrown 
upon  water.  It  instantly  decomposes  the  water,  and  so  much  heat  is  evolved  as  to 
kindle  the  potassium,  which  moves  about  upon  the  surface  of  the  water,  burning 
with  a  strong  flame,  of  which  the  vivacity  is  increased  by  the  combustion  of  the 
hydrogen  gas  disengaged  at  the  same  time.  A  globule  of  fused  potassa  remains, 
which  continues  to  swim  about  upon  the  surface  of  the  water  for  a  few  seconds,  but 
finally  produces  an  explosive  burst  of  steam,  when  its  temperature  falls  to  a  certain 
point,  illustrating  the  phenomenon  of  a  drop  of  water  on  a  hot  metallic  plate 
(page  64.) 

Potassium  appears  to  have  the  greatest  affinity  of  all  bodies  for  oxygen  at  tempe- 
ratures which  are  not  exceedingly  elevated.  It  decomposes  nitrous  and  nitric  oxides, 
and  also  carbonic  oxide  gas  at  a  red  heat,  although  potassa  is  reduced  to  the  metallic 
state  by  charcoal  at  a  white  heat.  It  has  already  been  stated  that  the  oxides  and 
fluorides  of  boron  and  silicon  are  decomposed  by  potassium,  and  besides  these  ele- 
ments, several  of  the  metallic  bases  of  the  earths  are  obtained  by  means  of  this 
inetal.  It  is,  indeed,  a  reducing  agent  of  the  greatest  value. 


COMPOUNDS   OF  POTASSIUM. 

Potassa,  or  potash ;  KO;  590  or  47.26. — Potassium  exposed  in  thin  slices  to 
dry  air  becomes  a  white  matter,  which  is  the  protoxide  of  potassium  or  potassa. 
This  compound  is  fusible  at  a  red  heat,  and  rises  in  vapour  at  a  strong  white  heat. 
It  unites  with  water,  with  ignition,  and  forms  a  fusible  hydrate,  which  is  the  ordinary 
condition  of  caustic  potassa. 

The  hydrate  of  potassa  is  obtained  in  quantity  from  the  carbonate  of  potassa. 
Equal  weights  of  that  salt  and  of  quicklime  are  taken,  the  latter  of  which  is  slaked 
with  water,  and  falls  into  a  powder  consisting  of  hydrate  of  lime ;  the  former  is 
dissolved  in  from  6  to  10  times  its  weight  of  water,  and  both  boiled  together  for 
half  an  hour  in  a  clean  iron  pan.  The  lime  abstracts  carbonic  acid  from  the  potassa 
and  becomes  carbonate  of  lime  j  a  reaction  which  may  be  illustrated  by  adding  lime- 
water  to  a  solution  of  carbonate  of  potassa,  when  a  precipitate  of  carbonate  of  lime 
falls.  When  the  potassa  has  been  deprived  entirely  of  carbonic  acid,  a  little  of  the 
clear  liquid  taken  from  the  pan  will  be  found  not  to  effervesce  upon  the  addition  of 
an  acid  to  it.  It  is  remarkable  that  the  decomposition  is  never  complete  if  the  car- 
bonate of  potassa  Be  dissolved  in  less  than  the  prescribed  quantity  of  water.  Liebig 
has  observed  that  a  concentrated  solution  of  potassa  decomposes  carbonate  of  lime, 
and  consequently  hydrate  of  lime  could  not,  in  the  same  circumstances,  decompose 
carbonate  of  potassa.  The  pan,  being  covered  by  a  lid,  may  be  allowed  to  cool ; 
when  the  insoluble  carbonate  of  lime  and  the  excess  of  hydrate  of  lime  subside,  a 
considerable  quantity  of  the  clear  solution  of  potassa  may  be  drawn  off  by  a  syphon, 
and  the  remainder  may  be  obtained  clear  by  filtration.  In  the  latter  operation  a 
large  glass  funnel  may  be  employed,  to  support  a  filter  of  washed  cotton  calico,  into 


POTASSA.  373 

which  what  remains  in  the  pan  is  transferred.  A  small  portion  of  liquid,  which 
passes  through  turbid  at  first,  should  be  returned  to  the  filter.  As  the  solution  of 
potassa  absorbs  carbonic  acid,  it  is  proper  to  conduct  its  filtration  with  as  little  ex- 
posure to  air  as  possible ;  on  which  account  the  mouth  of  the  the  funnel  should  be 
covered  by  a  plate,  and  the  liquid  which  flows  from  it  be  immediately  received  in  a 
bottle,  in  the  mouth  of  which  the  funnel  may  be  supported.  The  bottle  in  which 
potassa  is  preserved  should  not  be  of  crystal,  or  of  a  material  containing  lead,  as  the 
alkali  corrodes  such  glass,  particularly  when  its  natural  surface  has  been  cut. 

To  obtain  the  solid  hydrate  of  potassa,  the  preceding  solution  is  rapidly  evaporated 
in  a  clean  iron  pan  or  silver  basin,  till  an  oily  liquid  remains  at  a  high  temperature, 
which  contains  no  more  than  a  single  equivalent  of  water.  This  liquid  is  poured 
into  cylindrical  iron  moulds  to  obtain  it  in  the  form  of  sticks,  which  are  used  by 
surgeons  as  a  cautery,  and  are  the  potassa  or  potassa  fusa  of  the  Pharmacopeia;  a 
form  in  which  it  is  also  convenient  to  have  potassa  for  some  chemical  purposes.  Tne 
sticks  generally  contain  a  portion  of  carbonate  of  potassa,  besides  a  little  oxide  of  iron 
and  peroxide  of  potassium,  the  last  of  which  gives  occasion  to  the  evolution  of  a  little 
oxygen  gas  when  the  sticks  are  dissolved  in  water.  To  obtain  hydrate  of  potassa 
free  from  carbonate,  the  sticks  are  dissolved  in  alcohol,  in  which  the  foreign  impu- 
rities are  insoluble,  and  the  alcoholic  solution  is  evaporated  to  dryness. 

The  pure  and  fused  hydrate  of  potassa  is  a  solid  white  mass  of  a  structure  some- 
what crystalline,  of  sp.  gr.  1.706,  fusible  at  a  heat  under  redness.  It  is  a  protohy- 
drate,  and  cannot  be  deprived  of  its  combined  water  by  the  most  intense  heat.  It 
destroys  animal  textures.  It  rapidly  deliquesces  in  damp  air,  from  the  absorption 
of  moisture :  is  soluble  in  half  its  weight  of  water,  and  also  in  alcohol.  Mixed  in 
powder  with  a  small  quantity  of  water,  it  forms  a  second  crystalline  combination, 
which  is  a  terhydrate ;  and  its  solution  in  water  affords,  at  a  very  low  temperature, 
crystals  in  the  forms  of  four-sided  tables  and  octohedrons,  which  are  a  pentahy- 
drate,  KO.HO-f4HO.  [See  Supplement,  p.  806.] 

The  solution  of  potassa,  or  potassa  ley,  has  a  slight  but  peculiar  odour,  character- 
istic of  caustic  alkalies,  which  they  acquire  from  their  action  upon  organic  matter, 
derived  from  the  atmosphere  or  other  sources.  The  skin  and  other  animal  substances 
are  dissolved  by  this  liquid.  It  is  highly  caustic,  and  its  taste  intensely  acrid.  It 
has  those  properties  which  are  termed  alkaline,  in  an  eminent  degree.  It  neutral- 
izes the  most  powerful  acids,  restores  the  blue  colour  of  reddened  litmus,  changes 
the  blue  infusion  of  cabbage  into  green,  but  in  a  short  time  altogether  destroys  these 
vegetable  colours.  It  acts  upon  fixed  oils,  and  converts  them  into  soaps,  which  are 
soluble  in  water.  It  absorbs  carbonic  acid  with  great  avidity  from  the  air,  on  which 
account  it  should  be  preserved  in  well-stopped  bottles. 

The  presence  of  free  potassa  or  soda,  in  solutions  of  their  carbonates,  may  be 
discovered  by  nitrate  of  silver,  the  oxide  of  which  is  precipitated  of  a  brown  colour 
by  the  caustic  alkali,  while  the  white  carbonate  of  silver  only  is  precipitated  by  the 
pure  carbonated  alkali.  Potassa,  whether  free  or  in  combination  with  an  acid  as  a 
soluble  salt,  may  be  discovered  and  distinguished  from  soda  and  other  substances, 
by  means  of  certain  acids,  &c.,  which  form  sparingly  soluble  compounds  with  that 
alkali.  A  strong  solution  of  tartaric  acid  produces  a  precipitate  of  bitartrate  of 
potassa,  in  a  liquid  containing  1  per  cent,  of  any  potassa  salt.  The  precipitate  is 
crystalline,  and  does  not  appear  immediately,  but  is  thrown  down  on  stirring  the 
liquid  strongly,  and  soonest  upon  the  lines  which  have  been  described  on  the  glass 
by  the  stirrer.  A  similar  precipitation  is  occasioned  in  salts  of  potassa  by  perchloric 
acid.  Also  by  bichloride  of  platinum,  which  forms  the  double  chloride  of  platinum 
and  potassium,  in  granular  octohedrons  of  a  pale  yellow  colour.  In  the  separation 
of  potassa  for  its  quantitative  estimation,  the  last  reagent  is  preferred,  and  is  added 
in  excess  to  the  potassa  solution,  together  with  a  few  drops  of  hydrochloric  acid, 
which  is  then  evaporated  by  a  steam  heat  to  dryness.  The  dry  residue  is  washed 
with  alcohol,  which  dissolves  up  everything  except  the  double  chloride  of  platinum 
and  potassium.  Ammonia,  also,  is  thrown  down  by  bichloride  of  platinum ;  but 


374  POTASSIUM. 

when  the  chloride  of  platinum  and  ammonium  is  heated  to  redness,  nothing  is  left 
except  spongy  platinum,  while  the  chloride  of  platinum  and  potassium  leaves  all  its 
potassium  in  the  state  of  chloride  mixed  with  the  platinum.  Potassa  is  likewise 
separated  from  acids  by  means  of  fluosilicic  acid,  which  throws  down  a  light  gelati- 
nous precipitate,  the  double  fluoride  of  silicon  and  potassium.  Carbazotic  acid  also 
produces  a  yellow  crystalline  precipitate  in  solution  of  potassa. 

Salts  of  potassa,  more  particularly  the  chloride,  nitrate,  and  carbonate,  communi- 
cate to  flame  a  pale  violet  tint. 

Potassa  is  the  base  which  in  general  exhibits  the  highest  affinity  for  acids ;  it 
precipitates  lime  and  the  insoluble  metallic  oxides  from  their  solutions  in  acids. 
This  alkali  is  employed  indifferently  with  soda  for  a  variety  of  useful  purposes.  The 
principal  combinations  of  potassa  with  acids  will  be  described  after  the  binary  com- 
pounds of  potassium. 

Peroxide  of  potassium,  K03.  —  Heated  strongly  in  air  or  oxygen,  potassium 
combines  with  three  equivalents  of  oxygen.  The  ultimate  residue  on  calcining 
nitrate  of  potassa  at  red  heat  has  been  said  to  be  the  same  compound,  but  Mitscher- 
lich  finds  that  residue  to  be  potassa.  The  peroxide  of  potassium  is  decomposed  by 
water,  being  converted  into  hydrate  of  potassa,  with  evolution  of  oxygen  gas. 

When  potassium  is  burned  with  an  imperfect  supply  of  air,  a  grey  matter  is 
formed,  which  Berzelius  believed  to  be  a  suboxide  of  potassium.  It  is  not  more 
stable  than  the  peroxide. 

Sulphides  of  potassium.  —  Sulphur  and  potassium,  when  heated  together,  unite 
with  incandescence,  and  in  several  proportions,  two  of  which  correspond  respectively 
with  the  protoxide  and  peroxide  of  potassium.  The  protosulphide  may  be  obtained 
by  transmitting  hydrogen  gas  over  sulphate  of  potassa,  heated  in  a  bulb  of  hard 
glass  to  full  redness,  when  the  whole  oxygen  of  the  salt  is  carried  off  as  water,  and 
the  sulphur  remains  in  combination  with  potassium,  forming  a  fusible  compound  of 
a  light  brown  colour.  Sulphate  of  potassa  calcined  with  one-fourth  of  its  weight  of 
pounded  charcoal  or  pit-coal,  in  a  covered  Cornish  crucible,  at  a  bright  red  heat,  is 
converted  into  a  black  crystalline  mass,  which  is  also  protosulphide  of  potassium, 
with  generally  a  small  quantity  of  a  higher  sulphide,  arising  from  the  combination 
of  the  silica  of  the  crucible  with  potassa  of  the  sulphate.  If  lamp-black  be  used 
instead  of  charcoal,  the  sulphide  of  potassium  formed  having  a  great  affinity  for 
oxygen,  and  being  in  a  highly  divided  state,  takes  fire  when  exposed  to  the  air,  and 
forms  a  pyrophorus.  The  solution  of  the  protosulphide  in  water  is  highly  caustic ; 
it  is  decomposed  by  acids  with  effervescence,  from  the  escape  of  hydrosulphuric  acid, 
but  without  any  deposit  of  sulphur.  Being  a  sulphur  base,  it  combines  without 
decomposition  with  sulphur  acids. 

This  sulphide  unites  directly  with  hydrosulphuric  acid,  forming  KS.HS ;  and  the 
compound  may  be  otherwise  formed,  namely,  by  transmitting  a  stream  of  hydrosul- 
phuric acid  through  caustic  potassa,  so  long  as  the  gas  is  absorbed.  It  is  often 
named  the  bihydrosulphate  of  potassa.  It  is  analogous  in  composition  to  hydrate 
of  potassa  (KO.HO)  in  the  oxygen  series. 

The  trisulphide  is  formed  when  anhydrous  carbonate  of  potassa,  mixed  with  half 
its  weight  of  sulphur,  is  maintained  at  a  low  red  heat  so  long  as  carbonic  acid  gas 
comes  off.  Of  four  proportions  of  potassa,  three  become  sulphide  of  potassium,  while 
sulphuric  acid  is  formed,  which  neutralizes  the  fourth  proportion  of  potassa :  4KO 
and  10S  =  3KS3  and  KO.S03.  With  carbonate  of  potassa  and  sulphur,  in  equal 
weights  a  similar  action  occurs,  at  a  temperature  above  the  fusing  point  of  sulphur, 
but  five,  instead  of  three,  proportions  of  sulphur  then  unite  with  one  of  potassium, 
and  a  penlasulphide  is  formed.  With  a  larger  proportion  of  carbonate  of  potassa 
the  same  sulphide  is  also  produced,  provided  the  temperature  does  not  much  exceed 
the  boiling  point  of  sulphur,  and  the  excess  of  carbonate  fuses  along  with  it,  without 
undergoing  decomposition.  A  sulphide  obtained  by  fusing  sulphur  and  carbonate 
of  potassa  together  has  a  liver-brown  colour,  and  hence  its  old  pharrnaceutic  name 
hepar  sulp/turis.  The  three  sulphides  described  are  deliquescent,  and  are  all  soluble 


IODIDE    OF    POTASSIUM.  375 

in  water,  the  higher  sulphides  giving  red  solutions.  They  may,  indeed,  be  prepared 
by  heating  sulphur,  in  proper  proportions,  with  caustic  potassa.  A  simultaneous 
formation  of  hyposulphurous  acid  then  occurs,  as  already  explained  (page  304). 
The  preparation,  precipitated  sulphur,  is  obtained  by  adding  an  excess  of  hydro- 
chloric acid  to  these  solutions,  when  much  sulphur  is  thrown  down,  although  the 
potassium  be  only  in  the  state  of  protosulphide,  'for  the  hydrosulphuric  acid,  arising 
from  the  action  of  the  acid  on  that  sulphide,  meets  hyposulphurous  evolved  at  the 
same  time  from  the  decomposition  of  the  hyposulphite,  with  the  formation  of  water 
and  sulphur.  The  excess  of  sulphur  in  the  alkaline  sulphide  also  precipitates  at, 
the  same  time.  The  peculiar  whiteness  of  precipitated  sulphur  is  owing,  according 
to  Rose,  to  its  containing  a  little  bisulphide  of  hydrogen. 

Chloride  of  potassium ;  eq.  74.5  or  931.25;  KC1.  —  Formed  by  the  combustion 
of  potassium  in  chlorine,  or  by  neutralizing  hydrochloric  acid  by  potassa  or  its  car- 
bonate. It  is  also  derived  in  considerable  quantity  from  kelp  (page  352).  It  crys- 
tallizes in  cubes  and  rectangular  prisms,  resembles  common  salt  in  taste,  and  is  con- 
siderably more  soluble  in  hot  than  in  cold  water.  According  to  the  observations  of 
Gay-Lussac,  100  parts  of  water  dissolve  of  this  salt  29.21  parts  at  0°  C. ;  34.53 
parts  at  19°. 35;  43.59  parts  at  52°. 39;  50.93  parts  at  79°.5S,  and  59.26  parts  at 
109°. 6  C.  When  pulverised  and  dissolved  in  four  times  its  weight  of  cold  water,  it 
produces  a  depression  of  temperature  of  20^  degrees ;  while  chloride  of  sodium,  dis- 
solved in  the  same  manner,  lowers  the  temperature  only  3.4  degrees.  Upon  the 
difference  between  two  salts  in  this  property,  M.  Gay-Lussac  founded  a  method  of 
estimating  their  proportions  in  a  mixture.  Chloride  of  potassium  is  principally  con- 
sumed in  the  manufacture  of  alum.  Rose  observed  that  chloride  of  potassium  unites 
with  anhydrous  sulphuric  acid,  KC1+2S03.  The  same  salt  unites  with  terchloride 
of  iodine,  KC1.IC13. 

Iodide  of  potassium ;  eq.  165.36  or  2067  ;  KI.  —  This  salt  is  obtained  by  dis- 
solving iodine  in  solution  of  potassa  till  neutral,  evaporating  to  dryness,  and  heating 
to  redness,  to  decompose  the  portion  of  iodate  of  potassa  formed.  M.  Freundt 
recommends  to  add  a  little  charcoal  to  the  mixed  iodide  and  iodate.  Iodide  of 
potassium  is  more  soluble  in  water  than  the  chloride,  and  may  be  obtained  in  cubes 
or  rectangular  prisms,  which  are  generally  white  and  opaque,  and  have  an  alkaline 
reaction  from  the  presence  or  a  trace  of  carbonate  of  potassa.  Iodide  of  potassium 
is  also  dissolved  by  alcohol,  but  in  a  much  less  proportion  than  by  water.  The  dry 
salt  does  not  combine  with  more  iodine,  but  in  conjunction  with  a  small  quantity  of 
water  (I  believe  4  equivalents)  it  absorbs  the  vapour  of  iodine  with  great  avidity, 
and  runs  into  a  liquid  of  a  deep  red,  almost  black,  colour.  According  to  Baup,  a 
saturated  solution  of  iodide  of  potassium  may  dissolve  so  much  as  two  equivalents  of 
iodine,  but  allows  one  equivalent  ttf  precipitate  when  diluted.  Iodide  of  potassium, 
which  is  often  called  the  hydriodate  of  potassa,  is  much  used  in  medicine;  it  is  not 
poisonous  even  in  doses  of  several  drachms.  Its  solution  is  also  employed  as  a 
vehicle  for  iodine  itself,  20  grains  of  iodine  and  30  grains  of  iodide  of  potassium 
being  usually  dissolved  together  in  1  ounce  of  water.  The  bromide  of  potassium  ia 
capable  also  of  dissolving  bromine,  but  the  solution  of  chloride  of  potassium  has  no 
affinity  for  chlorine. 

Ferrocyanide  of  potassium.  Yellow  prussiate  of  potassa ;  K2.FeCy3  +  3HO ; 
eq.  184  +  27  or  2300  +  337.5.  —  This  important  salt  is  formed  when  carbonate  of 
potassa  is  fused  at  a  red  heat  in  an  iron  pot,  with  animal  mat- 
ter, such  as  dried  blood,  hoofs,  clippings  of  hides,  &c.,  and  is  the  FIG.  167. 
product  of  a  reaction  to  be  hereafter  described.  This  salt  occurs 
in  a  state  of  great  purity  in  commerce.  It  is  of  a  lemon  yel- 
low colour,  and  crystallized  in  large  quadrangular  tables,  with 
truncated  angles  and  edges,  belonging  to  the  square  prismatic 
system.  The  crystals  contain  3  equivalents  of  water,  which  they 
lose  at  212°,  are  soluble  in  4  parts  of  cold  and  2  parts  of  boil- 
ing water,  and  are  insoluble  in  alcohol.  The  taste  of  this  salt  is  saline,  and  it  is  not 


376  POTASSIUM. 

poisonous.  By  a  red  heat  it  is  converted,  with  escape  of  nitrogen  gas,  into  carburet 
of  iron  and  cyanide  of  potassium ;  but  with  exposure  to  air  the  latter  salt  absorbs 
oxygen,  and  becomes  cyanate  of  potassa.  This  salt  is  represented  by  Liebig  as  con- 
taining a  salt-radical,  Ferrocyanogen,  composed  of  1  eq.  of  iron  and  3  eq.  of  cyano- 
gen, or  FeCy3.  This  salt-radical  is  bibasic,  and  is  in  combination  with  2  eq.  potas- 
sium in  the  salt,  as  will  be  seen  by  reference  to  its  formula.  The  same  salt  has 
been  represented  by  myself  as  a  compound  of  a  tribasic  salt-radical  prussine  (3Cy), 
with  Fe-{-2K.  But  its  reactions  with  other  salts  are  most  easily  stated  on  the  former 
view  of  its  constitution.  The  iron  in  this  salt  is  not  precipitated  by  alkalies.  When 
ferrocyanide  of  potassium  is  added  to  salts  of  lead  and  various  other  metallic  solu- 
tions, it  produces  precipitates,  in  which  two  equivalents  of  the  lead  or  other  metal 
are  substituted,  in  combination  with  ferrocyanogen,  for  the  two  equivalents  of  potas- 
sium. In  salts  of  sesquioxide  of  iron,  ferrocyanide  of  potassium  produces  the  well- 
known  precipitate,  Prussian  blue. 

Ferricyanide  of  potassium,  Red  prussiate  of  potassa;  3K.Fe2Cy6;  eq.  329  or 
4112.5.  —  This  salt,  which,  like  the  last,  is  a  valuable  reagent,  is  formed  by  trans- 
mitting chlorine  gas  through  a  solution  of  the  ferrocyanide  of  potassium,  till  it  ceases 
to  give  a  precipitate  of  Prussian  blue  with  a  persalt  of  iron,  and  no  longer.  One- 
fourth  of  the  potassium  of  the  ferrocyanide  is  converted  into  chlodde,  from  which 
the  resulting  ferricyanide  may  be  separated  by  crystallization.  It  forms  right  rhom- 
bic prisms,  which  are  transparent  and  of  a  fine  red  colour.  The  crystals  are  anhy- 
drous, soluble  in  3.8  parts  of  cold,  and  in  less  hot  water.  They  burn  with  brilliant 
scintillations  when  held  in  the  flame  of  a  candle.  The  solution  of  this  salt  is  a  deli- 
cate test  of  iron  in  the  state  of  protoxide,  throwing  down  from  its  salts  a  variety  of 
Prussian  blue,  in  which  the  3K  of  the  formula  are  replaced  by  3Fe.  Liebig  views 
the  red  prussiate  of  potassa  as  containing  a  salt-radical,  Ferricyanogen,  or  ferridcya- 
nogen,  Fe2Cy6,  differing  from  ferrocyanogen  in  having  twice  its  atomic  weight  and 
in  being  tribasic. 

Cyanide  of  potassium;  eq.  65  or  812.5;  KCy.  —  The  preparation  of  this  salt  is 
attended  with  difficulty,  owing  to  the  action  of  the  carbonic  acid  of  the  air  upon  its 
solution,  which  evolves  hydrocyanic  acid,  and  the  tendency  of  the  solution  itself  to 
undergo  spontaneous  decomposition,  even  in  close  vessels.  It  may  be  formed  by 
adding  absolute  hydrocyanic  acid,  or  a  strong  solution  of  that  acid,  to  a  solution  of 
potassa  in  alcohol ;  a  portion  of  the  cyanide  falls  down  as  a  white  crystalline  preci- 
pitate, which  should  be  washed  with  alcohol  and  dried,  and  an  additional  quantity 
is  obtained  by  evaporating  the  liquid  in  a  retort.  But  it  is  prepared  with  more 
advantage  from  the  ferrocyanide"  of  potassium,  already  described.  That  salt  is  care- 
fully dried  and  reduced  to  a  fine  powder,  8  parts  of  which  are  mixed  with  3  parts 
of  carbonate  of  potassa  and  1  part  of  charcoal,  and  exposed  to  a  strong  red  heat  in  a 
closed  iron  crucible,  or  other  convenient  vessel.  The  mass  is  reduced  to  powder, 
placed  in  a  funnel,  moistened  with  a  little  alcohol,  and  then  washed  with  cold  water. 
The  strong  solution  of  cyanide  of  potassium  which  comes  through  is  colourless,  and 
must  be  rapidly  evaporated  to  dryness  in  a  porcelain  basin,  and  fused  at  a  red  heat. 
The  crude  salt,  obtained  by  ignition  without  charcoal,  contains  a  little  cyanate  of 
potassa,  but  this  does  not  interfere  with  its  use  for  forming  and  dissolving  cyanides 
of  gold  and  silver,  for  the  processes  of  voltaic  gilding  and  plating. 

Cyanide  of  potassium  crystallizes  in  colourless  cubes,  which  become  opaque  and 
deliquesce  in  damp  air,  and  are  very  soluble  in  water.  It  bears  a  red  heat  without 
decomposition  in  close  vessels,  but  with  exposure  to  air  absorbs  oxygen,  and  becomes 
cyanate  of  potassa  (KO.CyO).  Its  solution  smells  of  hydrocyanic  acid,  being  de- 
composed by  carbonic  acid.  The  action  of  cyanide  of  potassium  upon  the  animal 
economy  is  equally  powerful  with  that  of  hydrocyanic  acid,  and  as  the  dry  salt  may 
be  preserved  in  a  well-stopped  bottle  without  change,  it  is  preferable  to  the  acid, 
which  is  far  from  stable.  Red  oxide  of  mercury  dissolves  freely  in  the  solution  of 
cyanide  of  potassium,  cyanide  of  mercury  being  formed  and  potassa  set  free.  The 


CARBONATE   OF   POTASSA.  377 

purity  of  the  alkaline  cyanide  may  be  ascertained  from  this  property ;  12  grains  of 
the  pure  cyanide  dissolving  20  grains  of  finely-pulverised  oxide  of  mercury. 

Hydrocyanic  acid  for  medical  purposes  is  conveniently  prepared  from  this  cyanide. 
2  i  grains  of  cyanide  of  potassium,  56  grains  of  tartaric  acid  in  crystals,  and  1  ounce 
of  water,  are  agitated  together  in  a  stout  phial  closed  by  a  cork.  The  liquid  is  after- 
wards separated  by  filtration  from  the  precipitate  of  bitartrate  of  potassa ;  it  contains 
10  grains  of  hydrocyanic  acid,  or  rather  more  than  2  per  cent.  (Dr.  Clark). 

Sulphocyanide  of  potassium  ;  K.CyS2;  1222.2  or  97.92.  —  Sulphocyanogen  is 
a  salt-radical  consisting  of  2  eq.  sulphur  and  1  eq.  cyanogen,  which  is  formed  on 
fusing  the  ferrocyanides  with  sulphur.  To  obtain  it  in  combination  with  potassium, 
the  ferrocyanide  of  potassium,  made  anhydrous  by  heat  and  reduced  to  a  fine  powder, 
is  mixed  with  an  equal  weight  of  flowers  of  sulphur  in  a  common  cast-iron  pot  (pitch 
pot),  and  kept  in  a  state  of  fusion  for  half  an  hour  at  a  temperature  above  the  melt- 
ing point  of  sulphur,  but  below  that  at  which  bubbles  of  gas  escape  through  the 
melted  mass.  No  cyanogen  is  evolved  or  decomposed,  and  the  residuary  matter  is 
a  mixture  of  sulphocyanide  of  potassium  and  protosulphocyanide  of  iron,  with  the 
excess  of  sulphur.  Both  sulphocyanides  dissolve  in  water,  and  give  a  solution  which 
is  colourless  at  first,  but  soon  becomes  red  from  oxidation  of  the  sulphocyanide  of 
iron.  To  get  rid  of  the  iron,  carbonate  of  potassa  is  added  to  the  boiling  solution, 
so  long  as  a  precipitate  of  carbonate  of  iron  falls,  and  the  liquid  is  afterwards  filtered. 
This  solution  gives  crystals  of  sulphocyanide  of  potassium,  when  evaporated,  which 
may  be  freed  from  any  adhering  carbonate  of  potassa  by  dissolving  them  in  alcohol. 
The  salt  crystallizes  in  long  white  striated  prisms,  which  are  anhydrous,  and  resemble 
nitrate  of  potassa  in  their  appearance  and  taste.  They  deliquesce  in  a  damp  atmo- 
sphere, and  are  very  soluble  in  hot  alcohol,  from  which  the  salt  crystallizes  on 
cooling.  The  sulphocyanide  of  potassium  communicates  a  blood-red  colour  to  solu- 
tions of  salts  of  sesquioxide  of  iron,  and  is  consequently  employed  as  a  test  of  that 
metal  in  its  higher  state  of  oxidation.  The  red  solution  is  made  perfectly  colourless 
by  a  moderate  dilution  with  water,  when  the  iron  is  not  present  in  excess.  The 
sulphocyanide  of  potassium  has  been  detected  in  the  saliva  of  man  and  the  sheep. 

SALTS   OF   OXIDE   OF   POTASSIUM. 

Carbonate  of  potassa  ;  KO.C02;  eq.  69  or  862.5.  —  This  useful  salt  is  princi- 
pally obtained  from  the  ashes  of  plants.  Potassa  is  always  contained  in  a  state  of 
combination  in  clay  and  other  minerals  which  form  the  earthy  part  of  soil,  and 
appears  to  be  a  constituent  of  soil  essential  to  vegetation.  The  alkali  is  appropriated 
by  plants,  and  is  found  in  their  sap  combined  with  vegetable  acids,  particularly  with 
oxalic  and  tartaric  acids ;  also  with  silicic  and  sulphuric  acids,  and  as  chloride  of 
potassium.  When  the  plants  are  dried  and  burned,  the  salts  of  the  vegetable  acids 
are  destroyed,  and  leave  carbonate  of  potassa :  shrubs  yielding  three,  and  herbs  five 
times  as  much  saline  matters  as  trees ;  and  the  branches  of  trees  being  more  pro- 
ductive than  their  trunks — a  distribution  which  may  depend  upon  the  potassa  exist- 
ing chiefly  in  the  sap.  The  whole  ashes  from  wood  seldom  exceed  1  per  cent,  of  its 
weight,  of  which  l-6th  may  be  saline  matter.  The  solution,  evaporated  to  dryness, 
yields  potashes  ;  and  these,  partially  purified  and  ignited,  form  pearlash.  The  car- 
bonate is  mixed  in  the  latter  with  about  20  per  cent,  of  foreign  salts,  principally 
sulphate  of  pota.ssa  and  chloride  of  potassium.  The  carbonate  of  potassa  is  obtained, 
in  a  state  of  greater  purity,  by  dissolving  pearlash  in  an  equal  weight  of  water,  then 
separating  the  solution  from  undissolved  salts,  and  evaporating  it  to  dryness. 

Carbonate  of  potassa  is  prepared  of  greater  purity  for  chemical  purposes,  by 
igniting  bitartrate  of  potassa  j  or  better,  by  burning  together  2  parts  of  that  salt  arid 
1  of  nitre.  In  the  latter  process,  the  carbon  and  hydrogen  of  the  tartaric  acid  are 
destroyed  by  t'he  oxygen  of  the  nitric  acid,  and  carbonate  of  potassa  remains  mixed 
with  charcoal,  from  which  it  may  be  separated  by  solution  and  filtration. 

Carbonate  of  potassa  has  an  acrid,  alkaline  taste,  but  is  not  caustic.     It  gives  a 


378 


SULPHATES   OF   POTASSA. 


FIG.  168. 


FIG.  169. 


green  colour  to  the  blue  infusion  of  cabbage.  This  salt  is  highly  deliquescent,  and 
soluble  in  less  than  an  equal  weight  of  water  at  60°.  It  may  be  crystallized  with 
two  equivalents  of  water.  Added  to  solutions  of  salts  of  lime,  lead,  &c.,  it  throws 
down  insoluble  carbonates.  It  is  more  frequently  used  than  the  caustic  alkali,  to 
neutralize  acids  and  to  form  the  salts  of  potassa. 

Bicarbonate  of  potassa ;  HO.C02  +  KO.C02;  eg.  100  or  1250. 
—  Formed  by  transmitting  a  stream  of  carbonic  acid  gas  through 
a  saturated  cold  solution  of  the  neutral  carbonate.  It  is  soluble 
in  four  times  its  weight  of  water  at  60°,  and  in  less  water  at  212°. 
The  solution  has  an  alkaline  taste  and  reaction,  but  is  not  acrid  j 
it  does  not  thrown  down  magnesia  from  its  soluble  salts ;  it  loses 
carbonic  acid  when  evaporated  at  all  temperatures,  and  becomes 
neutral  carbonate.  The  salt  contains  one  proportion  of  water, 
which  is  essential  to  it,  and  crystallizes  well  in  prisms  of  eight 
sides,  having  dihedral  summits.  The  existence  of  a  sesquicarbo- 
nate  of  potassa  is  doubtful. 

Sulphate  of  potassa  ;  KO.S03;  eq.  87  or  1087.5.  — This  salt 
precipitates  when  oil  of  vitriol  is  added,  drop  by  drop,  to  a  concen- 
trated solution  of  potassa.  It  is  generally  prepared  by  neutralizing 
the  residue,  composed  of  bisulphate  of  potassa,  of  the  nitric  acid 
process  (page  260),  and  crystallizes  in  double  pyramids  of  six  faces, 
or  in  oblique  four-sided  prisms.  The  crystals  are  anhydrous,  un- 
alterable in  air,  and  they  decrepitate  strongly  when  heated  \  their 
density  is  2.400.  The  sulphate  is  one  of  the  least  soluble  of  the 
neutral  salts  of  potassa :  100  parts  of  water  dissolve  8.36  parts  of 
this  salt  at  82°,  and  0.09666  parts  more  for  each  degree  above  that  point. 

Hydrated  bisulphate  of  potassa,  or  sulphate  of  water  and  potassa ;  HO.S03  + 
KO.S03;  eq.  136  or  1700:  the  fusible  salt  remaining,  when  nitrate  of  potassa  is 
decomposed  in  a  retort  by  two  equivalents  of  oil  of  vitriol.  Below  386.6°  (197°  C.), 
it  is  a  white  crystalline  mass.  This  salt  is  very  soluble  in 
water,  but  is  partially  decomposed  by  that  liquid,  and  de- 
posits sulphate  of  potassa.  It  crystallizes  from  a  strong  solu- 
tion in  rhombohedral  crystals,  of  which  the  form  is  identical 
with  one  of  the  forms  of  sulphur.  But  this  salt  is  dimor- 
phous, and  crystallizes  from  a  state  of  fusion  by  heat  in  large 
crystals,  which  have  the  form  of  felspar  (Mitscherlich).  Its 
density  is  2.163.  The  excess  of  acid  in  this  salt  acts  upon  metals  and  alkaline 
bases  very  much  as  if  it  were  free. 

Hydrated  sesquisulphate  of  potassa  ;  HO.S03  -f  2(KO.S03).  — A  salt  in  pris- 
matic needles  discovered  by  Mr.  Phillips,  and  which  has  also  accidentally  occurred 
since  to  Mr.  Jacquelin.  It  is  decomposed  by  water;  the  circumstances  necessary 
for  its  formation  are  unknown. 

Sulphate  of  potassa  combines  with  hydrated  nitric  and  phosphoric  acids,  as  well 
as  with  hydrated  sulphuric  acid.  On  dissolving  the  neutral  salt  in  nitric  acid,  a 
little  nitre  and  hydrated  bisulphate  of  potassa  are  formed,  with  a  large  quantity  of 
a  salt  in  oblique  prisms,  of  which  the  formula  is  HO.NO(:  +  2(KO.S03).  This  last 
'salt  fuses  at  302°  (150°  0.) ;  its  density  is  2.38  (Jacquelin).  The  compound  with 
phosphoric  acid  is  formed  by  dissolving  sulphate  of  potassa  in  a  syrupy  solution  of 
that  acid,  and  crystallizes  in  oblique  prisms  of  six  sides,  which  fuse  at  464°  (240°  C.), 
and  of  which  the  density  is  2.296  (Jacquelin).  Its  formula  is  3HO.P05  +  2(KO.S03). 
It  will  be  observed  that  both  these  compounds  agree  with  Mr.  Phillips's  sesquisul- 
phate in  having  2  eq  sulphate  of  potassa  to  1  eq.  of  hydrated  acid.  (Annales  de 
Chimie,  Ixx,). 

Nitrate  of  potassa,  Nitre,  Saltpetre;  KO.N05;  eq.  101  or  1262.5.  —  Nitric 
acid  is  formed  in  the  decomposition  of  animal  matters  containing  nitrogen,  when 
they  are  exposed  to  air;  and  are  in  contact  with  alkaline  substances.  It  appears 


FIG.  170. 


GUNPOWDER.  379 

to  be  largely  produced  in  this  way  in  the  soil  of  certain  districts  of  India,  from  which 
nitrate  of  potassa  is  obtained  by  lixiviation.  Nitrous  soils  always  contain  much 
carbonate  of  lime,  the  debris  of  tertiary  calcareous  rocks,  in  which  the  oxygen  and 
nitrogen  of  the  air  unite,  according  to  some,  assisted  by  the  porous  structure  of  the 
rock,  and  under  the  influence  of  an  alkaline  base,  so  as  to  generate  nitric  acid  with- 
out the  intervention  of  animal  matter.  But  this  conjecture  is  not  founded  upon 
experiment  •  nor  is  it  a  necessary  hypothesis,  since  nitrifiable  rocks  are  never  entirely 
destitute  of  organic  matter.  Nitrate  of  potassa  is  also  prepared  in  some  countries 
of  Europe,  by  imitating  the  natural  process,  in  artificial  nitre  beds,  wherein  nitrate 
of  lime  is  formed,  and  afterwards  converted  into  nitrate  of  potassa  by  the  addition 
of  wood-ashes  to  the  lixivium.1 

Nitrate  of  potassa  generally  crystallizes  in  long  stri- 
ated six-sided  prisms,  is  anhydrous,  unalterable  in  the 
air,  fusible  into  a  limpid  liquid  by  a  heat  under  red- 
ness, in  which  condition  it  is  cast  in  moulds,  and  forms 
sal  prunelle.  Its  density  is  1.933  (Dr.  Watson). 
According  to  Gay-Lussac  100  parts  of  water  dissolve 
13.3  parts  of  this  salt  at  32°,  29  parts  at  64.4°,  74.6 
parts  at  96.8°,  and  236  parts  at  206.6°.  The  taste  of 
the  solution  is  cooling  and  peculiar ;  it  has  considerable 
antiseptic  properties.  Nitre  is  insoluble  in  absolute 
alcohol. 

From  the  large  quantity  of  oxygen  which  nitre  contains,  and  the  facility  with 
which  it  imparts  that  element  to  combustibles  at  a  red  heat,  it  is  much  employed  in 
making  gunpowder  and  other  deflagrating  mixtures.  An  intimate  mixture  of  nitre 
in  fine  powder  with  one-third  of  its  weight  of  wood-charcoal,  when  touched  by  a 
body  in  ignition,  burns  with  great  brilliancy,  but  without  explosion.  A  mixture  of 
3  parts  of  nitre,  2  of  dry  carbonate  of  potassa,  and  1  of  sulphur,  forms  pulvis  ful- 
minans,  which,  heated  gently  till  it  enters  into  fusion,  inflames  suddenly,  and 
explodes  with  a  deafening  report.  The  violence  of  the  explosion  is  caused  by  the 
reaction  between  the  sulphur  and  nitre  being  instantaneous,  from  their  fusion -and 
perfect  intermixture,  and  the  consequent  sudden  formation  of  much  nitrogen  gas 
from  the  decomposition  of  nitric  acid.  Gunpowder  contains  both  sulphur  and  char- 
coal, of  which  the  former  serves  the  purpose  of  accelerating  the  process  of  deflagra- 
tion and  supplying  heat,  while  the  latter  supplies  much  of  the  gas,  to  the  formation 
of  whick  the  available  force  of  the  explosion  is  due.  Gunpowder  yields  about  300 
times  its  volume  of  gas,  measured  when  cold ;  but  its  explosive  force  is  greater  than 
this  indicates,  from  the  high  temperature  of  the  gas,  and  not  less  than  1000  atmo- 
spheres. The  ordinary  proportions  of  gunpowder  approach  very  nearly  I  eq.  of 
nitre,  1  of  sulphur,  and  3  of  carbon,  as  will  be  seen  by  the  following  comparison  :  — 


Composition  of  Gunpowder. 
Theoretical  Mixture.             English. 
Sulphur  ---   lift  195   

Prussian. 
.  11  5 

Charcoal  t  

Nitre.., 

....  13.6  .... 
.  74.6  . 

12.5  

.  75. 

...  13.5 
.  75. 

100.0  100.0  100.0 


1  The  observations  and  original  experiments  upon  nitrification,  of  Professor  Kuhlman,  are 
valuable,  but  do  not  lead  to  any  general  theory  of  the  process.  He  did  not  succeed  in  causing 
oxygen  and  nitrogen  gases  to  combine  by  means  of  spongy  platinum,  but  he  found  that 
under  the  influence  of  that  substance  (1°)  all  vaporisable  compounds  of  nitrogen,  including 
ammonia,  mixed  with  air,  with  oxygen,  or  with  an  oxidating  gas,  change  into  nitric  acid  or 
peroxide  of  nitrogen ;  and  (2°)  that  all  the  vaporisable  compounds  of  nitrogen,  including 
nitric  acid,  mixed  with  hydrogen  or  a  hydrogenous  acid,  give  rise  to  ammonia. — (Memoirs 
of  the  Academy  of  Sciences  of  Lille,  1838,  and  Liebig's  Annalen,  xxix.  272,  1839.) 


380  CHLORATE   OF    POTASSA. 

By  the  combustion  of  the  mixture,  carbonic  acid  and  nitrogen  gases  are  formed, 
with  a  solid  residue  of  protosulphide  of  potassium.  Thus  :  — 

Deflagration  of  Gunpowder. 
Before  decomposition.  After  decomposition. 

3  Carbon 3  Carbon ^^3  Carbonic  acid 

f  6  Oxygen &J#*tt- 

Nitrate  of  potassa  •<  Nitrogen Nitrogen 

(^  Potassium ^^^ 

Sulphur Sulphur """--»  Sulphide  of  potassium. 

A  portion  of  the  potassa  is  always  converted  into  sulphate  of  potassa,  which  must 
interfere  with  the  exactness  of  this  decomposition.  Blasting  powder  is  composed  of 
20  sulphur,  15  charcoal,  and  65  nitre  ;  the  proportion  of  sulphur  being  increased, 
by  which  a  more  powerfully  explosive  mixture  is  obtained,  but  which  is  not  suitable 
for  fire-arms,  as  they  are  injured  by  an  excess  of  sulphur.  The  most  inflammable 
charcoal  is  employed  in  making  gunpowder ;  which  is  obtained  by  calcining  branches 
of  about  fths  of  an  inch  in  diameter,  in  an  iron  retort,  for  a  considerable  time,  at  a 
heat  scarcely'  amounting  to  redness,  and  which  has  a  brown  colour  without  lustre. 
The  granulation  of  gunpowder  increases  its  explosive  force.  A  charge  is  thus  made 
sufficiently  porous  to  allow  flame  to  penetrate  it,  and  to  kindle  every  grain  composing 
it  at  the  same  time.  But  still  the  discharge  of  gunpowder  is  not  absolutely  instan- 
taneous ;  and  it  is  remarkable  that  other  explosive  compounds  which  burn  more 
rapidly  than  gunpowder,  such  as  fulminating  mercury,  are  not  adapted  for  the  move- 
ment of  projectiles.  Their  action  in  exploding  is  violent  but  local ;  if  substituted 
for  gunpowder  in  charging  ordinary  fire-arms,  they  would  shatter  them  to  pieces, 
and  not  project  the  ball.  It  is  a  common  practice  to  mix  with  the  charge  of  blast- 
ing powder,  used  in  mining,  a  considerable  bulk  of  sawdust,  which  renders  the  com- 
bustion of  the  powder  still  slower,  but  productive  of  a  sustained  effort,  most  effectual 
in  moving  large  masses. 

Chlorate  of  potassa;  KO.C105:  eq.  122.5  or  1531.25.  —This  salt  is  the  result 
of  a  reaction  between  chlorine  and  potassa,  which  has  already  been  explained  (page 
341).  In  the  preparation  of  chlorate  of  potassa,  a  strong  solution  of  two  or  three 
pounds  of  carbonate  of  potassa  is  made,  and  chlorine  passed  through  it.  The  gas 
is  conducted  into  the  liquid  by  a  pretty  wide  tube,  or  better  by  a  tube  terminated 
by  a  funnel,  to  prevent  its  being  choked  by  the  solid  salt  which  is  formed.  A  stage 
in  the  process  can  be  observed  before  the  liquid  has  discharged  much  carbonic  acid, 
when  bicarbonate,  chlorate,  and  hypochlorite  of  potassa  exist  together  in  solution, 
and  a  considerable  quantity  of  chloride  of  potassium  is  deposited.  The  latter  salt  is 
removed,  and  the  current  of  chlorine  continued  till  the  liquid,  which  is  often  red 
from  hypermanganic  acid,  becomes  colourless  or  yellow,  and  ceases  to  absorb  the  gas. 
A  considerable  quantity  of  chlorate  of  potassa  is  deposited  in  tubular  shining  crystals, 
which  are  purified  by  solution  and  a  second  crystallization }  and  more  of  the  same 
salt  is  obtained  from  the  liquid  evaporated  and  set  aside  to  crystallize ;  the  separa- 
tion of  the  chlorate  from  chloride  of  potassium  depending  upon  the  solubility  at  a 
low  temperature  of  the  former  salt  being  greatly  less  than  that  of  the  latter. 

The  chlorate  of  potassa  may  be  prepared  more  economically  by  exposing  to  a 
current  of  chlorine  gas  a  mixture  of  7.6  parts  of  carbonate  of  potassa,  and  16.8 
hydrate  of  lime  in  a  dry  or  only  slightly  damp  state.  Chlorate  of  potassa  is  formed 
with  carbonate  of  lime  and  chloride  of  calcium.  The  mass  is  treated  with  boiling 
water,  which  dissolves  the  chloride  of  calcium  and  chlorate  of  potassa.  The  latter 
salt  is  purified  by  crystallization.  It  is  stated  that  other  salts  of  potassa,  particularly 
the  sulphate,  may  be  substituted  for  the  carbonate  in  this  process;  and  that  the 
potassa  salt  and  lime  are  mixed  with  hot  water  when  exposed  to  the  chlorine  gas. 

This  salt  is  anhydrous.     It  appears  in  flat  crystals  of  a  pearly  lustre,  of  which  the 


IODATE  OF  POTASSA.  381 

forms,  according  to  Brooke,  belong  to  the  oblique  prismatic  system.  Its  density  is 
1.989  (Hassenfratz).  It  has  a  cooling,  disagreeable  taste,  like  that  of  nitre.  Ac- 
cording to  Gay-Lussac,  100  parts  of  water  dissolve  3£  parts  of  chlorate  of  potassa  at 
32°,  6  at  59°,  12  at  95°,  19  at  120.2°,  and  60  at  219.2°,  the  point  of  ebullition 
of  a  saturated  solution.  This  salt  fuses  readily  in  a  glass  retort  or  tube,  enters  into 
ebullition,  and  discharges  oxygen  below  a  red  heat.  At  a  certain  period  in  the 
decomposition,  when  the  mass  becomes  thick,  hyperchlorate  of  potassa  is  formed,  but 
ultimately  chloride  of  potassium  is  the  sole  residue. 

Chlorate  of  potassa  deflagrates  with  combustibles  more  violently  than  the  nitrate. 
A  grain  or  two  of  it  rubbed  in  a  warm  mortar  with  an  equal  quantity  of  sulphur, 
occasions  smart  explosions,  with  the  formation  of  sulphurous  acid  gas.  Inclosed 
with  a  little  phosphorus  in  paper,  and  struck  by  a  hammer,  it  produces  a  powerful 
explosion ;  but  this  experiment  may  be  attended  with  danger  to  the  operator  from 
the  projection  of  the  flaming  phosphorus.  A  mixture  which,  when  dry,  inflames  by 
percussion,  and  which  was  applied  to  lucifer  matches,  is  composed  of  this  salt,  sul- 
phur, and  charcoal.  One  of  the  simplest  receipts  for  this  percussion  powder  consists 
in  washing  out  the  nitre  from  10  parts  of  ordinary  gunpowder  with  water,  and 
mixing  the  residue  intimately,  while  still  humid,  with  5 1  parts  of  chlorate  of  potassa 
in  an  extremely  fine  powder.  This  mixture  is  highly  inflammable  when  dry,  and 
dangerous  to  preserve  in  that  state.  Phosphorus  and  nitre,  however,  are  now  more 
generally  used  for  these  matches  (page  315).  More  chlorate  of  potassa  is  employed 
in  the  processes  of  calico-printing,  as  an  oxidizing  agent. 

Perchlorate  of  potassa;  KO.C107;  eq.  138.5  or  1731.25.  —  Processes  for  pre- 
paring this  salt  have  already  been  described  under  perchloric  acid  (pag£  342).  It 
is  also  formed  in  a  strong  solution  of  chlorate  of  potassa  contained  in  the  decom- 
posing cell  of  a  voltaic  battery,  this  salt  being  deposited  in  small  crystals  upon  the 
zincoid,  and  no  oxygen  liberated  there.  It  requires  55  parts  of  water  to  dissolve  it 
at  59°,  but  is  largely  soluble  in  boiling  water.  It  crystallizes  in  octohedrons  with 
a  square  base,  which  are  generally  small :  they  are  anhydrous.  It  deflagrates  less 
strongly  with  combustibles  than  the  chlorate,  loses  oxygen  at  400°,  and  is  com- 
pletely decomposed  at  a  red  heat,  chloride  of  potassium  being  left. 

lodate  of  potassa,  KO.I05;  eq.  213.36  or  2667.  — This  salt  may  be  formed  by 
neutralizing  the  chloride  of  iodine  with  carbonate  of  potassa,  instead  of  carbonate  of 
soda  (p.  356).  It  gives  small  anhydrous  crystals,  which  fuse  by  heat  and  lose  all 
their  oxygen.  lodic  acid  likewise  forms  a  biniodate  and  a  teriodate  of  potassa, 
according  to  Serullas.  (Annal.  de  Chim.  et  de  Phys.  xliii.)  The  biniodate  is 
obtained  by  adding  an  additional  proportion  of  iodic  acid  to  a  solution  of  neutral 
iodate  saturated  at  a  high  temperature :  it  contains  an  equivalent  of  water,  but  may 
be  made  anhydrous  by  a  strong  heat,  according  to  my  own  observations.  It  occurs 
in  prisms  with  dihedral  summits,  and  requires  75  parts  of  water  at  59°  to  dissolve 
it.  The  teriodate  is  obtained  on  mixing  a  strong  acid,  such  as  nitric,  hydrochloric, 
or  sulphuric,  with  a  hot  saturated  solution  of  the  neutral  iodate,  and  allowing  it  to 
cool  slowly.  It  crystallizes  in  rhombohedrons,  and  requires  25  parts  of  water  to 
dissolve  it. 

Serullas  has  observed  that  the  biniodate  of  potassa  has  a  great  disposition  to  form 
double  salts.  A  compound  with  chloride  of  potassium,  to  which  he  assigned  the 
formula  KCl-f  KO.I2Oi0?  is  obtained  on  adding  a  little  hydrochloric  acid  to/a  solu- 
tion of  iodate  of  potassa,  and  allowing  the  solution  to  evaporate  spontaneously.  This 
salt  crystallizes  well,  but  afterwards  loses  its  transparency  in  the  air.  It  is  decom- 
posed by  water,  and  cannot  be  formed  by  uniting  its  constituent  salts.  Another, 
compound  contains  bisulphate  of  potassa:  KO.S2064-KO.I2010.  These  compounds 
of  iodic  acid  have  also  been  lately  examined  by  M.  Millon. 


382 


SODIUM. 


SECTION  II. 


SODIUM. 

Syn.  Natrium.     Eq.  23  or  287.5;  Na. 

•Davy  obtained  this  metal  by  the  voltaic  decomposition  of  soda,  immediately  after 
the  discovery  of  potassium.  An  intimate  mixture  of  charcoal  and  carbonate  of  soda 
is  formed  by  calcining  acetate  of  soda,  from  which  sodium  is  commonly  prepared, 
according  to  the  method  described  for  potassium,  and  with  greater  facility,  owing  to 
the  lower  affinity  of  sodium  for  oxygen.  [See  Supplement,  p.  806.] 

Sodium  is  a  white  metal  having  the  aspect  of  silver.  Its  density  is  0.972,  at  59°, 
according  to  Gay-Lussac  and  Thenard.  This  metal  is  so  soft,  at  the  usual  tempera- 
ture, that  it  may  be  cut  with  a  knife,  and  yields  to  the  pressure  of  the  fingers ;  it  is 
quite  liquid  at  194°.  It  oxidates  spontaneously  in  the  air,  although  not  so  quickly 
as  potassium ;  and  when  heated  nearly  to  redness  takes  fire  and  burns  with  a  yellow 
flame.  Thrown  upon  water,  it  oxidates  with  great  vivacity,  but  without  inflaming, 
evolving  hydrogen  gas,  and  forming  an  alkaline  solution  of  soda.  When  a  few  drops 
only  of  water  are  applied  to  sodium,  it  easily  becomes  sufficiently  hot  to  take  fire. 

As  potassium  is  in  some  degree  characteristic  of  the  vegetable  kingdom,  so  sodium 
is  the  alkaline  metal  of  the  animal  kingdom,  its  salts  being  found  in  all  animal 
fluids.  Both  of  these  elements  occur  in  the  mineral  world ;  of  the  two,  perhaps 
potassium  is  most  extensively  diffused ;  felspar,  the  most  common  of  minerals,  con- 
taining 12  «per  cent,  of  potassa,  but  from  the  existence  everywhere  of  a  soluble 
compound  of  sodium,  its  chloride,  the  sources  of  that  element  are  the  more  accessi- 
ble, if  not  the  most  abundant. 

The  anhydrous -protoxide  of  sodium  and  the  peroxide  are  prepared  in  the  same 
manner  as  the  corresponding  oxides  of  potassium,  which  they  greatly  resemble  in 
properties.  The  composition  of  the  peroxide  of  sodium,  however,  is  different,  being 
expressed  by  the  formula  2Na-jr30  (Thenard).  It  is  supposed  by  M.  Millon  to  be 
Na  +  20. 

COMPOUNDS   OF   SODIUM. 

Soda;  NaO;  eq.  31  or  387.5. — A  solution  of  soda  is  obtained  by  decomposing 
the  crystallized  carbonate  of  soda,  dissolved  in  four  or  five  times  its  weight  of  water, 
by  means  of  half  its  weight  of  hydrate  of  lime  \  the  same  points  being  attended  to 
as  in  the  preparation  of  potassa.  A  preference  is  given  to  this  alkali  from  its  cheap- 
ness, for  most  manufacturing  purposes,  and  in  the  laboratory  it  may  frequently  be 
substituted  for  potassa,  where  a  caustic  alkali  is  required.  On  the  large  scale  it  is 
prepared  from  salts  of  soda,  a  carbonate  containing  chloride  of  sodium  and  sulphate 
of  soda.  The  solution  of  soda  is  purified  from  these  salts  by  concentrating  it  consi- 
derably, upon  which  the  foreign  salts  cease  to  be  soluble  in  the  liquid,  and  precipi- 
tate. (Mr.  W.  Blythe). 

The  following  table,  constructed  by  Dr.  Dalton,  exhibits  the  quantity  of  caustic 
soda  in  solutions  of  different  densities  :  — 

\ 
Solution  of  Caustic  Soda. 


Density  of  the  Solu- 
tion. 

Alkali  per  cent. 

Density  of  the  Solu- 
tion. 

Alkali  per  cent. 

2-00 
•85 
•72 
•63 
•56 
•50 
•47 
•44 

77-8 
63-6 
53-8 
46-6 
41-2 
36-8 
34-0 
31-0 

1-40 
1-36 
1-32 
1-29 
1-23 
1-18 
1-12 
1-06 

29-0 
26-0 
23-0 
19-0 
16-0 
13-0 
9-0 
4-7 

CHLORIDE   OF   SODIUM.  383 

The  solid  hydrate  of  soda  is  obtained  by  evaporating  a  solution  of  soda,  precisely 
in  the  same  manner  as  the  corresponding  preparation  of  potassa.  It  is  soluble  in  all 
proportions  in  water  and  alcohol. 

Soda  is  distinguished  from  potassa  and  other  bases  by  several  properties:  —  1st. 
All  its  salts  are  soluble  in  water,  and  it  is  therefore  not  precipitated  by  tartaric  acid, 
chloride  of  platinum,  or  any  other  reagent.  *  2d.  With  sulphuric  acid  it  affords  a 
salt  which  crystallizes  in  large  efflorescent  prisms,  easily  recognised  as  Glauber's 
salt.  3d.  Its  salts  communicate  a  rich  yellow  tint  to  flame. 

Sulphides  of  sodium.  —  These  compounds  so  closely  resemble  the  sulphides  of 
potassium  as  not  to  require  a  particular  description.  The  protosulphide  of  sodium 
crystallizes  from  a  strong  solution  in  octohedrons.  This  salt  contains  water  of 
crystallization ;  in  contact  with  air  it  rapidly  passes  into  caustic  soda,  and  the  hypo- 
sulphite of  the  same  base. 

Chloride  of  sodium,  Sea  salt,  Common  salt,  NaCl;  eq.  58.5  or  731.25. — Sodium 
takes  fire  in  chlorine  gas,  and  combining  with  that  element,  produces  this  salt.  The 
chloride  of  sodium  is  also  formed  on  neutralizing  hydrochloric  acid,  by  soda  or,  its 
carbonate,  and  is  obtained  thus  in  the  greatest  purity.  Sea-water  contains  2.7  per 
cent,  of  chloride  of  sodium,  which  is  the  most  considerable  of  its  saline  constituents : 
(analysis  of  sea-water,  page  242).  Salt  is  obtained  from  that  source  in  warm 
climates,  as  at  St.  Ubes,  in  Portugal,  on  the  coast  of  the  Mediterranean  near  Mar- 
seilles, and  other  places  where  spontaneous  evaporation  proceeds  rapidly;  the  sea- 
water  being  retained  in  shallow  basins  or  canals,  on  the  surface  of  which  a  saline 
crust  forms,  with  the  progress  of  evaporation,  which  is  broken  and  raked  out.  Sea- 
water  is  also  evaporated  artificially,  by  means  of  culm,  or  waste  coal,  as  fuel,  on  some 
parts  of  the  coast  of  Britain,  but  as  much  for  the  sake  of  the  bittern  as  of  the 
common  salt  it  affords.  The  evaporation  is  not  carried  to  dryness,  but  when  the 
greater  part  of  the  chloride  of  sodium  is  deposited  in  crystals,  the  mother  liquid, 
which  forms  the  bittern,  is  drawn  off;  it  is  the  source  of  a  portion  of  the  Epsom 
salt  and  other  magnesian  preparations  of  commerce.  Other  inexhaustible  sources 
of  common  salt  are  the  beds  of  sal-gem  or  rock  salt,  which  occur  in  several  geologi- 
cal formations  posterior  to  the  coal,  as  at  Northwich  in  Cheshire,  in  Spain,  Poland, 
and  many  other  localities.  These  beds  appear  to  have  been  formed  by  the  evapora- 
tion of  salt  lakes  without  an  outlet,  in  which  the  saline  matter,  continually  supplied 
by  rivers,  had  accumulated,  till  the  water  being  saturated,  a  deposition  of  salt  took 
place  upon  the  bottom  of  the  lake.  The  Dead  Sea  is  such  a  lake,  and  the  bottom 
of  it  is  found  to  be  covered  with  salt.  The  salt  is  sometimes  sufficiently  pure  for  its 
ordinary  uses,  as  it  is  taken  from  these  deposits,  but  more  generally  it  is  coloured 
brown  from  an  admixture  of  clay,  and  requires  to  be  purified  by  solution  and  filtra- 
tion. Instead  of  sinking  a  shaft  to  the  bed  of  the  rock  salt,  and  mining  it,  the 
superior  strata  are  often  pierced  by  a  bore  of  merely  a  few  inches  in  diameter,  by 
which  water  is  admitted  to  the  bed,  and  the  brine  formed  drawn  off  by  a  pump  and 
pipe  of  copper  suspended  in  the  same  tubular  opening. 

Chloride  of  sodium  crystallizes  from  solution  in  water  in  cubes,  and  sometimes 
from  urine  and  liquids  containing  phosphates  in  the  allied  form  of  the  regular  octo- 
hedron.  Its  crystals  are  anhydrous,  but  decrepitate  when  heated,  from  the  expan- 
sion of  water  confined  between  their  plates.  According  to  Fuchs,  pure  chloride  of 
sodium  Jias  exactly  the  same  degree  of  solubility  in  hot  and  cold  water,  requiring 
2.7  parts  of  water  to  dissolve  it  at  all  temperatures;  but  it  has  been  proved  by  Gay- 
Lussac,  and  also  by  Poggiale,  that  the  solubility  of  this  salt  increases  sensibly, 
although  not  considerably,  with  the  temperature.  According  to  Poggiale  100  parts 
of  water  dissolve  of  chloride  of  sodium  35.52  parts  at  32°;  35-87  parts  at  57.2 
(14°  C.);  39.61  parts  at  212°  (100°  C.);  and  40.35  parts  at  229.46°  (109-7°  0.), 
the  temperature  of  ebullition  of  a  saturated  solution  (Annales  de  Ch.  3me  Ser.  viii. 
469).  Gay-Lussac  also  makes  the  boiling  point  of  a  saturated  solution  2^9.5°,  but 
that  temperature  is  too  high  (I  believe)  for  a  solution  of  pure  chloride  of  sodium. 
When  a  saturated  solution  is  exposed  to  a  low  temperature  between  14°  and  5°,  the 


384  SODIUM. 

salt  crystallizes  in  hexagonal  tables,  which  have  two  sides  larger  than  the  others. 
Fuchs  found  these  crystals  to  contain  6,  and  Mitscherlich  4  equivalents  of  water. 
If  their  temperature  is  allowed  to  rise  above  14°,  they  undergo  decomposition,  and 
are  converted  into  a  congeries  of  minute  cubes,  from  which  water  separates. 

The  little  increase  of  the  solubility  of  chloride  of  sodium  at  a  high  temperature, 
makes  it  impossible  to  crystallize  this  salt  by  cooling  a  hot  solution,  but  Mr.  Arrott 
finds  that  with  the  addition  of  chloride  of  calcium  to  the  solution,  a  greater  inequality 
of  solubility  at  high  and  low  temperatures  takes  place,  and  a  portion  of  the  chloride 
of  sodium  crystallizes  from  a  hot  saturated  solution  on  cooling.  In  the  evaporation 
of  brine  for  salt,  certain  inconveniences  attend  the  deposition  of  salt  from  the  boiling 
solution,  which  Mr.  Arrott  proposes  to  obviate  by  the  presence  of  chloride  of  cal- 
cium. 

Pure  chloride  of  sodium  has  an  agreeable  saline  taste,  deliquesces  slightly  in 
damp  weather,  and  dissolves  largely  in  rectified  spirits,  but  is  very  slightly  soluble 
in  absolute  alcohol.  Its  density  is  2.557  (Mohs).  It  fuses  at  a  bright  red  heat, 
and  at  a  higher  temperature  rises  in  vapour.  It  is  immediately  decomposed  by  oil 
of  vitriol,  with  the  evolution  of  hydrochloric  acid.  Besides  being  used  as  a  season- 
ing for  food,  chloride  of  sodium  is  employed  in  the  preparation  of  the  sulphate  and 
carbonate  of  soda.  When  ignited  in  contact  with  clay  containing  oxide  of  iron,  the 
sodium  of  this  salt  becomes  soda,  and  unites  with  the  silica  of  the  clay,  while  the 
chlorine  combines  with  iron,  and  is  volatilized  as  sesquichloride  of  iron.  On  this 
decomposition  is  founded  the  mode  of  communicating  the  salt-glaze  to  pottery :  a 
quantity  of  salt  is  thrown  into  the  kiln,  where  it  is  converted  into  vapour  by  the 
heat,  and  condensing  upon  the  surface  of  the  pottery  causes  its  vitrification,  which 
is  attended  with  the  formation  of  hydrochloric  acid,  and  of  sesquichloride  of  iron, 
if  sesquioxide  of  iron  be  present.  When  chloride  of  sodium  and  silica,  both  dry, 
are  heated  together,  no  decomposition  takes  place ;  but  if  steam  is  passed  over  the 
mixture,  hydrochloric  acid  is  evolved  and  silicate  of  soda  formed.  These  decompo- 
sitions are  represented  by  the  following  equations  :  — 

Si03  and  3NaCl  and  Fe203=3NaO.Si03  and  Fe2Cl3 
Si03  and  NaCl  and  HO=NaO.Si03  and  HC1. 

The  second  reaction  has  not  been  applied  successfully  to  the  preparation  of  soda 
from  the  chloride  of  sodium,  owing,  it  is  said,  to  the  vitrification  of  the  silicate  of 
soda  produced,  which  covers  the  undecomposed  chloride  of  sodium,  and  protects  it 
from  the  steam.  Mr.  Tilghman  substitutes  for  the  silica  precipitated  alumina,  which 
is  made  up  into  balls  with  the  chloride  of  sodium,  and  exposed  to  steam  in  a  rever- 
beratory  furnace  at  an  elevated  temperature.  Hydrochloric  acid  escapes,  and  an 
aluminate  of  soda  is  formed,  which  may  be  decomposed,  when  cold,  by  dry  carbonic 
acidj  the  carbonate  of  soda  is  dissolved  out  by  water;  the  alumina  is  made  up  again 
into  balls  with  chleride  of  sodium,  to  be  ignited  and  decomposed  by  steam  as  before. 
The  bromide  and  iodide  of  sodium  crystallize  in  cubes,  and  resemble 

FIG.  172.       in  properties  the  corresponding  compounds  of  potassium. 

SALTS   OF   OXIDE   OF   SODIUM. 

Carbonate  of  soda;  NaO.C02  +  10HO;  eq.  53  +  90,  or  662.5  + 
1125.  — This  useful  salt  is  found  nearly  pure  in  commerce,  in  large 
crystals,  which  effloresce  when  exposed  to  air.  These  crystals  contain 
10  equivalents  of  water,  and  consist,  in  100  parts,  of  21.81  soda, 
15.43  carbonic  acid,  and  62.76  water.  According  to  Dr.  Thomson, 
they  generally  contain  about  |  per  cent,  of  sulphate  of  soda  as  an 
accidental  impurity :  they  belong  to  the  oblique  prismatic  system. 
Their  density  is  1.623  :  100  parts  of  water  dissolve  20.64  of  the 
crystals  at  58.25°;  and  more  than  an  equal  weight  at  the  boiling 


CARBONATE   OF   SODA.  385 

temperature  (Dr.  Thomson).  In  warm  weather,  the  carbonate  of  soda  sometimes 
crystallizes  in  another  form,  which  is  not  efflorescent,  and  of  which  the  proportion 
of  water  is  8  equivalents.  The  ordinary  crystals,  by  efflorescing  in  dry  air,  are  re- 
duced to  a  hydrate  of  5  equivalents  of  water,  NaO.C02+5HO.  The  same  hydrate 
appears  when  a  solution  of  carbonate  of  soda  is  made  to  crystallize  at  93°  (34°  C.), 
in  crystals  derived  from  an  octohedron  with  a  square  base.  Again,  a  solution  of 
this  salt  evaporated  between  158°  and  176°  (70°  and  80°  C.),  deposits  quadrilateral 
crystals,  containing  1  equivalent  of  water,  or  14.77  per  cent.  Carbonate  of  soda, 
therefore,  appears  to  be  capable  of  forming  four  definite  hydrates,  containing  HO, 
5HO,  8HO,  and  10HO.  The  density  of  the  anhydrous  salt  is  2.509  (Filhol). 

The  solubility  of  the  carbonate  of  soda,  supposed  to  be  anhydrous,  at  various 
temperatures,  was  observed  by  M.  Poggiale  to  be  as  follows : — 

100  parts  of  water  at  32°  (0°  C.)  dissolve  7.08  of  carbonate  of  soda. 
100     «  "          50°  (10°  C.)      "      16.66  "       .         " 

100     «  "          68°  (20°  C.)      "      25.83 

100     "  "          86°  (30°  C.)      "      35.90  "  « 

100     "  "     219.2°  (104°  C.)    "      48.50  "  " 

To  obtain  such  determinations  of  the  solubility  of  a  salt  at  a  given  temperature, 
water  is  kept  in  contact  with  a  considerable  excess  of  the  salt  in  the  state  of  powder 
for  at  least  half  an  hour,  at  the  fixed  temperature,  with  occasional  agitation.  About 
two  ounces  of  the  solution  is  then  transformed  into  a  light  glass  flask  (fig.  173),  and 

FIG.  173. 


after  being .  accurately  weighed,  is  evaporated  either  over  the  gas,  or  by  a  small 
furnace,  taking  care  to  hold  the  neck  at  an  angle  of  45°,  to  avoid  drops  of  fluid 
being  thrown  out  by  the  ebullition.  After  the  salt  is  dry,  the  heat  is  still  continued, 
to  expel  the  water  of  crystallization,  the  escape  of  the  latter  being  promoted  by 
blowing  air  gently  into  the  flask  while  hot  by  means  of  bellows  having  a  bent  glass 
tube  attached  to  the  nozzle.  [See  Supplement,  p.  807.]  « 

This  salt  has  a  disagreeable  alkaline  taste.  When  heated,  it  undergoes  the  watery 
fusion  ]  its  water  is  soon  dissipated,  and  a  white  anhydrous  salt  remains,  which  again 
becomes  liquid  at  a  red  heat,  undergoing  then  the  igneous  fusion,  and  by  a  greater 
heat  it  loses  no  carbonic  acid.  A  mixture  of  carbonates  of  potassa  and  soda  is  more 
fusible  than  either  salt  separately. 

Carbonate  of  soda  is  decomposed  at  a  bright  red  heat  by  the  vapour  of  water, 
which  disengages  all  the  carbonic  acid,  and  produces  hydrate  of  soda,  NaO.HO. 
The  carbon  of  its  acid  is  also  set  at  liberty  by  phosphorus  at  a  hign  temperature, 
and  the  phosphate  of  soda  formed.  Lime,  baryta,  strontia,  and  magnesia,  decompose 
a  solution  of  carbonate  of  soda,  assuming  its  carbonic  acid  and  liberating  soda. 

Carbonate  of  soda  is  manufactured  by  a  process  which  will  be  described  imme- 
25 


386 


SODIUM 


diately  under  the  head  of  sulphate  of  soda.  Much  of  the  carbonate  of  commerce 
is  not  crystallized,  but  simply  evaporated  to  dryness,  and  is  then  known  as  salts  of 
soda,  soda-salt,  or  soda-ash.  In  this  form  it  generally  contains  chloride  of  sodium, 
sulphate  of  soda,  hydrate  of  soda,  and  often  insoluble  matter,  and  varies  consider- 
ably in  value.  The  soda  which  is  caustic,  and  that  in  combination  with  carbonic 
acid  alone  of  the  acids,  are  available  in  the  application  of  the  salt  as  an  alkaline 
substance.  The  pure  anhydrous  carbonate  of  soda  consists  of  58.58  soda  and  41. 42 
carbonic  acid,  and  the  best  soda-salts  of  commerce  contain  from  50  to  53  per  cent. 
of  available  soda.  The  operation  of  ascertaining  the  proportion  of  alkali  in  these 
salts,  and  in  other  forms  of  the  carbonate  of  soda,  is  a  process  of  importance  from 
its  frequent  occurrence,. and  of  high  interest  and  value  as  a  general  method  of 
analysis  of  easy  execution,  and  applicable  to  a  great  variety  of  substances.  I  shall 
therefore  describe  minutely  the  mode  of  conducting  it. 


Fia.  175. 


-— -3fl 


ALKALIMETRY. 

The  experiment  is,  to  find  how  many  measures  of  a  diluted  acid  are  required  to 
destroy  the  alkaline  reaction  of,  and  to  neutralize  100  grains  of  a  specimen  of  soda- 
salt.     (1.)  The  acid  is  measured  in  the  alkalimeter,  which  is  a  straight  glass  tube, 
or  very  narrow  jar,  with  a  lip  (fig.  174),  about  5-8ths  of  an  inch  in  width,  and  14 
»r  15  inches  in  height,  generally  mounted  upon  a  foot,  which  is  by  no  means  ad- 
vantageous, as  a,  (fig.  175),  capable  of 
FIG.  174.    containing  at  least  1000  grs.  of  water. 
It  is  graduated  into  100  parts,  each  of 
which  holds  ten  grains  of  water.     In 
the  operation  of  dividing  such  an  instru- 
ment, it  is  more  convenient  to  use  mea- 
sures of  mercury  than  water, — 135.68 
grains  of  mercury  being  in  bulk  equal 
to  10  grains   of  water,  678.40  grains 
will  be  equal  to  50  grains  of  water.     A 
unit  measure  may  be  formed  of  a  pipette, 
b,  made  to   hold  the  last  quantity  of 
mercury,  into  which  the  metal  is  poured, 
the  opening  at  the  point  of  the  pipette 
being   closed   by   the   finger,    and    the 
height   of    the   mercury   in    the    tube 
marked  by  a  scratch  on  the  glass  made 
by  a  triangular  file.     The  bulk  of  twice 

that  quantity  of  mercury,  or  100  water  grain  measures,  may  likewise  be 
marked  upon  the  tube.  The  former  quantity  of  mercury  is  then  decanted 
from  the  tube  into  the  alkalimeter  to  be  graduated,  and  a  scratch  made 
upon  the  latter  at  the  mercury  surface :  this  is  5  of  the  10-gruin  water 
measures.  Another  measure  is  added,  and  its  height  marked;  and  the  s mi e  re- 
peated till  20  measures,  of  mercury  in  all  have  been  added,  which  are  100  ten-grain 
water  measures.  The  subdivision  of  each  of  these  measures  into  5  is  best  made  by 
the  eye,  and  is  also  marked  on  the  alkalimeter.  The  divisions  are  lastly  numbered, 
0,  5, 10,  &c.,  counting  from  above  downwards,  and  terminating  with  100  on  the  sole 
of  the  instrument.  Several  alkalimeters  may  be  graduated  at  the  same  time,  with 
little  more  trouble  than  one,  the  measured  quantities  of  mercury  being  transferred 
from  one  to  the  others  in  succession. 

(2.)  To  form  the  teot  acid,  4  ounces  of  oil  of  vitriol  are  diluted  with  20  ounces 
of  water  ;  or  larger  quantities  of  acid  and  water  are  mixed  in  these  proportions. 
About  three-fourths  of  an  ounce  of  bicarbonate  of  soda  is  heated  strongly  by  a  lamp 
for  an  hour,  to  obtain  pure  carbonate  of  soda;  of  which  171  grains  are  immediately 
weighed;  that  quantity,  or  more  properly  170.6  grains,  containing  100  grains  of 


ALKALIMETRY.  387 

soda.  This  portion  of  carbonate  of  soda  is  dissolved  in  4  or  5  ounces  of  hot  water, 
contained  in  a  basin,  and  kept  in  a  state  of  gentle  ebullition ;  and  the  alkalimeter  is 
filled  up  to  0  with  the  dilute  acid.  The  measured  acid  is  poured  gradually  into  the 
soda  solution,  till  the  action  of  the  latter  upon  test-paper  ceases  to  be  alkaline,  and 
becomes  distinctly  acid,  and  the  measures  of  acid  necessary  to  produce  that  change 
accurately  observed.  The  last  portions  of  the  acid  must  be  carefully  added  by  a 
single  drop  at  a  time,  which  is  most  easily  done  by  using  a  short  glass  rod  to  conduct 
the  stream  of  acid  from  the  lip  of  the  alkalimeter.  It  may  probably  require  about 
90  measures.  But  it  is  convenient  to  have  the  acid  exactly  of  the  strength  at  which 
100  measures  of  it  saturate  100  grains  of  soda.  A  plain  cylindrical  jar,  c,  of  which 
the  capacity  is  about  a  pint  and  a  half,  is  graduated  into  100  parts,  each  containing 
100  grain  measures  of  water,  or  ten  times  as  much  as  the  divisions  of  the  alkalimeter. 
The  divisions  of  this  jar,  however,  are  numbered  from  the  bottom  upwards,  as  is 
usual  in  measures  of  capacity.  This  jar  is  filled  up  with  the  dilute  acid  to  the  extent 
of  90,  or  whatever  number1  of  the  alkalimeter  divisions  of  acid  were  found  to  neu- 
tralize 100  grains  of  soda;  and  water  is  added  to  make  up  the  acid  liquid  to  100 
measures.  Such  is  the  test  acid,  of  which  100  alkalimeter  measures  neutralize,  and 
are  equivalent  to,  100  grains  of  soda;  or  1  measure  of  acid  to  1  grain  of  soda.  It 
is  transferred  to  a  stock  bottle.  The  remainder  of  the  original  dilute  acid  is  diluted 
with  water  to  an  equal  extent,  in  the  same  instrument,  and  added. to  the  bottle.  The 
density  of  this  acid  is  1.0995  or  1.0998,  which  is  sensibly  the  same  as  1.1.  The 
protohydrate  of  sulphuric  acid  diluted  with  5J  times  its  weight  of  water,  gives  this 
test  acid  exactly ;  but  as  oil  of  vitriol  varies  in  strength,  it  is  better  to  form  the  test 
acid  exactly ;  but  as  oil  of  vitriol  varies  in  strength,  it  is  better  to  form  the  test  acid 
in  the  manner  described  than  to  trust  to  that  mixture.  Twenty-two  measures  of  the 
test  acid  should  neutralize  100  grains  of  cr.  carbonate  of  soda;  and  58^  measures, 
100  grains  of  pure  anhydrous  carbonate  of  soda. 

(3.)  In  applying  the  test-acid,  it  is  poured  from  the  alkalimeter,  as  before,  upon 
100  grains  of  the  soda-salt  to  be  tested,  dissolved  in  two  or  three  ounces  of  hot 
water,  the  liquid  being  well  stirred  by  a  glass  rod  after  each  addition  of  acid.  The 
salt  contains  so  many  grains  of  soda  as  it  requires  measures  of  acid  to  neutralize  it; 
and,  therefore,  so  much  alkali  per  cent.  The  first  trial,  however,  should  only  be 
considered  an  approximation,  as  much  greater  accuracy  will  be  obtained  on  a  repeti- 
tion of  it.  The  experiment  is  often  made  in  the  cold,  but  it  is  very  advantageous 
to  have  the  alkaline  solution  in  a  basin,  in  which  it  is  heated  and  evaporated  during 
the  addition  of  the  test-acid.  The  indications  of  the  test-paper  then  become  greatly 
more  clear  and  decisive,  both  from  the  expulsion  of  the  carbonic  acid  and  the  con- 
centration of  the  solution.  With  such  precautions  the  proportion  of  soda  may  be 
determined  to  0.1  grain  in  100  grains  of  salt,  and  an  alkalimetrical  determination, 
made  in  a  few  minutes,  is  not  inferior  in  precision  to  an  ordinary  analysis. 

If  the  soda-salt  is  mixed  with  insoluble  matter,  its  solution  must  be  filtered  before 
the  test-acid  is  applied  to  it.  In  examining  a  soda-salt  which  blackens  salts  of  lead, 
and  contains  carbonate  of  soda  with  sulphide  of  sodium  and  hyposulphite  of  soda, 
100  grains  are  tested  as  above,  and  the  whole  alkali  in  the  salts  thus  determined. 
A  neutral  solution  of  chloride  of  calcium  is  also  added  in  excess  to  the  solution  of  a 
second  hundred  grains,  by  which  the  carbonate  of  soda  is  converted  into  chloride  of 
sodium,  while  carbonate  of  lime  precipitates.  The  filtered  liquid  is  still  alkaline, 
and  contains  all  the  sulphide  of  sodium  and  hyposulphite  of  soda ;  the  quantity  of 
soda  corresponding  with  which  is  ascertained  by  means  of  the  test-acid.  This  quan- 
tity is  to  be  deducted  from  the  whole  quantity  of  alkali  observed  in  the  first  ex- 
periment. 

Borax  may  be  analysed  by  the  same  test-acid,  and  will  be  found,  when  pure,  to 
contain  16.37  per  cent,  of  soda.  The  carbonates  of  potassa  may  also  be  examined 
by  the  same  means;  but  the  per  centage  of  alkali  must  then  be  estimated  higher 
than  the  measures  of  acid  neutralized,  in  the  proportion  of  the  equivalent  of  soda  to 
that  of  potassa,  which  are  to  each  other  as  31  to  47. 


388  SODIUM. 

The  test-paper  employed  in  alkalimetry  must  be  delicate.  It  should  be  prepared 
on  purpose,  by  applying  a  filtered  infusion  of  litmus  several  times  to  good  letter- 
paper  (not  unsized  paper),  and  drying  it  after  each  immersion,  till  the  paper  is  of  a 
distinct  but  not  deep  purple  colour.  If  the  test-acid  be  added  to  the  alkaline  solu- 
tion in  the  cold,  the  operator  must  make  himself  familiar  with  the  diiference  between 
the  slight  reddening  of  his  test-paper  by  carbonic  acid  which  is  disengaged,  and  the 
unequivocal  reddening  which  is  produced  by  the  smallest  quantity  of  a  strong  acid. 
The  former  is  a  purple  or  wine-red  tint ;  the  latter  a  pale  or  yellow  red,  without 
blue,  like  the  skin  of  an  onion. 

Method  of  Gay-Lussac. — The  directions  for  proceeding  given  by  M.  Gay-Lussac 
are  recommended  by  the  general  utility  of  the  French  measures  employed  for  scien- 
tific purposes.  It  is  commercial  potassa  which  is  supposed  to  be  examined,  and  its 
value  is  expressed  in  anhydrous  oxide  of  potassium. 

The  acid  employed  is  the  sulphuric,  as  before,  of  which  5  grammes  at  its  maxi- 
mum of  concentration,  that  is,  the  acid  HO.S03,  are  taken  as  a  unit.  This  quantity 
of  acid  is  diluted  with  water,  so  that  the  mixture  occupies  fifty  cubic  centimeters,  or 
one  hundred  half  cubic  centimeters.1  It  is  capable  of  neutralizing  4.816  grammes 
of  pure  potassa,  and  one-half  cubic  centimeter  of  the  dilute  acid  will  consequently 
indicate  0.04816  gramme  of  potassa. 

To  prepare  the  normal  acid  fluid,  as  the  test-acid  is  called,  it  is  necessary  to  have 
the  pure  monohydrated  sulphuric  acid.  The  acid  sold  as  distilled  sulphuric  acid  is 
sufficiently  free  from  fixed  impurities,  but  generally  contains  a  little  water  in  excess. 
By  evaporating  off  one-fourth  of  this  acid,  the  remaining  three-fourths  are  left  of  the 
maximum  degree  of  concentration.  One  hundred  grammes  of  the  monohydrated 
sulphuric  acid  are  accurately  weighed  in  a  small  glass  bottle.  A  thin  glass  flask  is 
also  provided,  which  holds  a  liter  of  water  when  filled  to  a  mark  on  the  neck.  The 
sulphuric  acid  already  weighed  is  added  in  a  gradual  manner  to  this  flask,  about 
half  filled  with  water  at  first,  a  circular  motion  being  given  to  the  vessel  in  order  to 
mix  the  liquids  rapidly.  The  acid  bottle  is  well  rinsed  out  with  water,  which  is 
added  to  the  flask ;  and  when  the  whole  cools,  more  water  is  added  to  fill  up  the 
flask  to  the  mark  on  the  neck.  The  normal  acid  fluid,  thus  prepared,  should  be 
preserved  for  use  in  a  well-stopped  bottle. 

In  making  an  examination  of  commercial  potashes,  a  fair  sample  of  the 
FIG.  176.  mass  }s  first  taken,  and  reduced  to  powder;  of  this,  48.16  grammes  are 
accurately  weighed  out,  and  dissolved  in  a  quantity  of  water,  so 
that  the  volume  of  the  solution  is  exactly  half  a  liter.     If  one-    FlG-  177< 
tenth  of  this  liquid  be  taken,  that  is,  fifty  cubic  centimeters,  we 
shall  of  course  have  the  quantity  which  contains  4.816  grammes 
of  the  potashes.    To  draw  off  this  portion  conveniently,  a  pipette 
is  used  (fig.  176),  which  holds  fifty  cubic  centimeters  when 
filled  up  to  a  mark  a  on  its  stem.     The  pipette  is  emptied  into 
a  plain  glass  jar,  the  last  drop  of  liquid  being  made  to  flow  out 
by  blowing  into  the  pipette.    A  sufficiently  distinct  blue  tint  is 
given  to  the  liquid  in  the  jar  by  the  addition  of  a  few  drops  of 
an  infusion  of  litmus,  and  the  jar  placed  upon  a  sheet  of  white 
letter-paper,  in  order  to  observe  the  changes  of  colour  afterwards 
with  more  facility. 

To  measure  the  normal  acid  fluid,  a  glass  tube  of  the  form  fig.  177  is 
used,  12  or  14  millimeters  in  internal  diameter,  which  is  called  a  burette. 
It  is  divided  into  half  cubic  centimeters,  and  the  divisions  marked  on 
the  large  tube  in  an  inverse  order,  as  in  the  former  alkalimeter.  The 
beak  may  be  greased  below  the  aperture,  to  prevent  the  liquid  running 

1  The  Gramme  is  15.4336  grains ;  the  Cubic  Centimeter,  0.06103  English  cubic  inch ;  the 
Liter  or  1000  cubic  centimeters,  61.03  cubic  inches,  0.22017  English  imperial  gallon,  or 
1.76133  pint. 


BICARBONATE   OF   SODA.  389 

down  the  outside  of  the  glass.  The  acid  is  poured  from  the  burette,  filled  to  the 
division  0,  into  the  jar  containing  the  potassa-solution,  the  liquid  in  the  latter  being 
constantly  stirred.  The  change  to  the  wine-colour  is  first  observed,  and  the  addition 
of  acid  is  afterwards  continued  with  the  greatest  caution,  drop  by  drop,  till  the  liquid 
assumes  at  once  the  onion-skin  red.  A  few  drops  of  acid  in  excess  are  inevitably 
added,  owing  to  the  slowness  of  the  action  of  the  last  portions  of  acid  upon  the 
colouring  matter.  The  number  of  these  drops  in  excess  is  discovered  by  drawing  a 
line  with  the  liquid  upon  a  slip  of  blue  litmus  paper,  after  the  addition  of  each  drop. 
The  lines  become  red  after  the  lapse  of  some  time,  where  the  acid  is  in  excess,  and 
give  the  number  of  drops  to  be  deducted ;  of  these,  five  are  in  general  equivalent  to 
one  measure  of  the  burette.  The  quantity  of  potassa  is  calculated  from  the  measures 
of  normal  acid  fluid  prepared,  each  measure  representing  0.04816  gramme  of  potassa, 
as  already  stated. 

The  chief  objection  to  the  practice  of  this  method  is  the  delicacy,  and  in  some 
degree  uncertainty,  of  the  mode  of  determining  the  number  of  drops  of  acid  always 
added  in  excess.  This  difficulty  is  best  avoided,  I  believe,  by  operating  upon  the 
alkaline  solution  while  hot  and  undergoing  evaporation,  as  directed  in  the  preceding 
method  of  alkalimetry.1 

The  object  of  an  alkalimetrical  process  may  also  be  obtained  by  determining  the 
quantity  of  carbonic  acid  in  a  specimen  of  soda-ash  or  potashes.  The  quantity  of 
carbonic  acid  is  ascertained  by  decomposing  the  carbonate  by  sulphuric  acid,  and 
observing  the  loss  of  weight  occasioned  by  the  escape  of  the  gas.  The  evolution 
of  hydrosulphuric  acid  gas  at  the  same  time,  by  the  decomposition  of  sulphide  of 
sodium,  is  prevented  by  adding  a  little  bichromate  of  potassa  to  the  sulphuric  acid, 
so  as  to  oxidize  the  former  acid  gas.  For  every  equivalent  of  carbonic  acid,  or  22 
parts,  an  equivalent  quantity  of  soda  or  potassa  is  allowed  to  be  present ;  namely, 
31  parts  of  soda  or  47  parts  of  potassa.  The  process  may  be  conducted  by  means 
of  the  well-devised  arrangements  of  Dr.  Will,  described  in  works  upon  Analytical 
Chemistry.  It  would,  however,  be  a  subject  of  regret  if  this  latter  method  should 
be  allowed  to  supersede  the  use  of  normal  fluids  and  the  burette,  which  are  capable 
of  being  usefully  applied  in  numerous  other  investigations  besides  alkalimetry,  and, 
in  fact,  form  the  basis  of  an  interesting  department  of  chemical  analysis. 

Bicarbonate  of  soda  ;  HO.C02  +  NaO.CO^  84  or  1050.  —  This  salt  is  formed 
when  a  stream  of  carbonic  acid  gas  is  transmitted  through  a  saturated  solution  of 
the  neutral  carbonate ;  it  is  then  deposited  as  a  farinaceous  powder,  but  may  be  ob- 
tained in  crystals  from  a  weaker  solution,  which  are  rectangular  prisms.  But  it  is 
generally  prepared  on  the  large  scale  by  exposing  the  crystals  of  neutral  carbonate, 
placed  on  trays  in  a  wooden  case,  to  an  atmosphere  of  carbonic  acid  gas :  the  matter 
then  changes  entirely  into  bicarbonate,  which  appears  in  amorphous  and  opaque 
masses.  One  hundred  parts  of  water  dissolve  of  it  10.04  parts  at  50°  (10°  C.)  and 
16.69  parts  at  158°  (70°  C.),  according  to  M.  Poggiale.  Although  containing  two 
equivalents  of  acid,  this  salt  is  alkaline  to  test-paper,  but  its  taste  is  much  less  un- 
pleasant than  the  neutral  carbonate,  and  indeed  is  scarcely  perceived  when  mixed 
with  a  little  common  salt.  The  crystallized  salt  is  permanent  in  dry  air,  but  its 
solution  loses  carbonic  acid,  slowly  at  the  temperature  of  the  air,  and  rapidly  above 
160°,  passing  into  the  state  of  sesquicarbonate,  and  ultimately  of  neutral  carbonate. 
A  solution  of  bicarbonate  of  soda  does  not  produce  a  precipitate  in  salts  of  magnesia 
in  the  cold,  nor  does  it  disturb  immediately  a  solution  of  chloride  of  mercury ;  by 
which  properties  it  is  distinguished  from  the  neutral  carbonate. 

The  bicarbonate  of  soda  is  obtained  otherwise  by  an  interesting  reaction.  Equal 
weights  are  taken  of  common  salt  and  of  the  carbonate  of  ammonia  of  the  shops, 
which  is  chiefly  bicarbonate ;  the  former  is  dissolved  in  three  times  its  weight  of 

1  The  apparatus  and  methods  of  alkalimetry  have  received  much  attention  from   Mi 
Griffin.    His  improved  apparatus  and  test-paper  may  be  procured  at  the  Chemical  Museum, 
53,  Baker  Street. 


390  SODIUM. 

water,  and  the  latter  added  in  the  state  of  fine  powder  to  this  solution,  the  whole 
stirred  well  together,  and  allowed  to  stand  for  some  hours.  The  bicarbonate  of 
oxide  of  ammonium  present  reacts  upon  chloride  of  sodium,  producing  the  more 
sparingly  soluble  bicarbonate  of  soda,  which  precipitates  in  crystalline  grains  and 
causes  the  liquid  to  become  thick,  with  chloride  of  ammonium  (sal-ammoniac), 
which  remains  in  solution  :  — 

HO.C02+NH4O.C02  and  NaCl= 
HO.C02+NaO.C02  and  NH4C1. 

The  solid  bicarbonate  of  soda  is  separated  from  the  liquid  by  pressure  in  a  screw 
press  y  but  retains  a  portion  of  chloride  of  sodium.  Messrs.  Hemming  and  Dyer, 
who  first  observed  this  reaction,  proposed  it  as  a  process  for  obtaining  carbonate  of 
soda  from  common  salt. 

Sesquicarbonate  of  soda;  2NaO+3C02+4HO;  164  or  2050.  —This  salt  pre- 
sents itself  occasionally  in  small  prismatic  crystals,  but  cannot  be  prepared  at 
pleasure.  It  is  unalterable  in  the  air,  but  is  decomposed  in  the  dry  state  by  a  less 
degree  of  heat  than  the  bicarbonate,  notwithstanding  its  containing  a  smaller  excess 
of  carbonic  acid.  The  theoretical  carbonate  of  water,  supposed  to  resemble  the  car- 
bonate of  magnesia,  will  be  HO.C02+  HO+2HO ;  which  gives  the  salt  in  question, 
if  the  last  2HO  are  replaced  by  two  proportions  of  protohydrated  carbonate  of  soda. 
Substitutions  of  this  character  appear  to  be  common  in  the  formation  of  double  car- 
bonates and  oxalates.  The  bicarbonate  of  potassa  may  be  formed  by  the  substitu- 
tion of  carbonate  of  potassa  for  the  first  HO,  in  the  same  carbonate  of  water,  while 
the  other  2HO  disappear.  The  sesquicarbonate  of  soda  occurs  native  in  several 
places,  particularly  on  the  banks  of  the  lakes  of  Soda  in  the  province  of  Sukena,  in 
Africa,  whence  it  is  exported  under  the  name  of  Trona  j  in  Egypt,  Hungary,  and 
in  Mexico,  and  has  the  same  proportion  of  water  as  the  artificial  salt. 

Double  carbonate  of  potassa  and  soda.  —  The  carbonates  of  potassa  and  soda 
unite  readily  by  fusion.  A  compound  was  also  obtained  by  M.  Margueritte,  in 
transparent  crystals,  by  submitting  a  solution  of  the  two  carbonates,  in  different  pro- 
portions, to  evaporation,  of  which  the  formula  is  2(NaO.C02)  +  (KO.C02)+lSHO. 
These  crystals  may  be  dissolved  without  injury  in  a  solution  of  carbonate  of  potassa, 
but  when  dissolved  in  pure  water  they  are  in  great  part  decomposed,  and  allow  crys- 
tals of  carbonate  of  soda  to  be  deposited.  This  double  salt  may  be  analysed  by  eva- 
porating to  dryness,  after  first  adding  hydrochloric  acid,  to  convert  the  bases  into 
chlorides  of  potassium  and  sodium,  and  then  precipitating  the  former  by  means  of 
bichloride  of  platinum,  as  described  at  page  373. 

Sulphite  of  soda;  NaO.S02  +  10HO;  63+  90,  or  787.5  -j-  1125.  —  This  salt 
crystallizes  in  oblique  prisms,  and  is  efflorescent  like  the  sulphate  of  soda,  which  it 
much  resembles.  Its  taste  is  sulphureous,  and  its  reaction  feebly  alkaline.  When 
heated  strongly  in  a  close  vessel,  it  gives  sulphate  of  soda  mixed  with  sulphide  of 
sodium.  It  is  prepared  by  passing  a  stream  of  sulphurous  acid  through  a  solution 
of  the  carbonate  of  soda  (page  294),  or  on  the  large  scale  by  exposing  the  crystals 
of  carbonate  of  soda,  moistened,  to  the  vapour  of  burning  sulphur.  This  salt,  and 
also  the  sulphite  of  lime,  are  much  employed  as  an  antichlore,  or  to  remove  the 
last  traces  of  chlorine.from  bleached  cloth  and  the  pulp  of  paper.  A  bisulphite  of 
soda  also  exists,  which  appears  in  irregular  and  opaque  crystals. 

Hyposulphite  of  soda ;  NaO.S202-f  5HO;  79  +  45,  or  987.5+ 562.5. —  This 
salt,  of  which  the  preparation  and  some  of  the  properties  have  already  been  described 
(page  303),  is  inodorous,  persistent  in  air,  very  soluble  in  water,  and  insoluble  in 
alcohol.  It  crystallizes  in  large  rhomboidal  prisms,  terminated  by  oblique  faces,  of 
which  the  acute  angles  are  replaced  by  planes.  When  heated  in  a  covered  vessel, 
it  first  loses  its  water,  and  then  undergoes  decomposition,  and  is  resolved  into  sul- 
phate of  soda  and  pentasulphide  of  sodium.  The  hyposulphite  of  soda  readily  dis- 
solves chloride  of  silver,  forming  a  double  salt  of  soda  and  oxide  of  silver,  which  has 
an  intensely  sweet  taste.  It  also  dissolves  the  red  oxide  of  mercury  easily,  forming 


SULPHATE   OF    SODA.  391 

a  double  salt,  which  readily  decomposes  with  deposition  of  sulphide  of  mercury. 
With  chloride  of  gold,  it  gives  rise  to  the  formation  of  chloride  of  sodium,  tetrathi- 
onate  of  soda,  and  a  double  hyposulphite  of  soda  and  oxide  of  gold,  of  which  the 
formula  is 

Au2O.S202-f  3(NaO.S202)4-4HO  (Fordos  and  Gelis). 
The  use  of  this  last  salt  is  recommended  for  fixing  the  daguerreotype  image. 

Sulphate  of  soda,  Glauber's  salt;  NaO.S03+10HO ;  71+90,  or  887.5  +  1125.— 
This  salt  occurs  crystallized  in  nature,  and  also  dissolved  in  mineral  waters,  and  is 
formed  on  neutralizing  carbonate  of  soda  by  sulphuric  acid.  But  it  is  more  gene- 
rally prepared  by  decomposing  common  salt  with  sulphuric  acid,  as  in  the  process  for 
hydrochloric  acid  (page  335).  The  sulphate  of  soda  crystallizes  readily  in  long 
prisms,  of  which  the  sides  are  often  channelled,  which  have  a  cooling  and  bitter 
taste,  and  contain  55.76  per  cent,  of  water,  or  10  equivalents ;  in  which  they  fuse 
by  a  slight  elevation  of  temperature,  and  which  they  lose  entirely  by  efflorescence 
in  dry  air  even  at  40°.  At  32°,  100  parts  of  water  dissolve  5.02  parts  of  anhydrous 
sulphate  of  soda,  16.73  parts  at  64.2°  (17.91°  C.),  50.65  parts  at  91°,  which  is  the 
temperature  of  maximum  solubility  of  this  salt,  and  42.65  parts  at  the  boiling  tem- 
perature of  a  saturated  solution,  which  is  217.6°  (103.1°  C.),  as  observed  by  Gay- 
Lussac.  In  a  supersaturated  solution  of  this  salt  (page  239),  crystals  are  sometimes 
slowly  deposited,  which  are  different  in  form  and  harder  than  Glauber's  salt;  they 
are  long  prisms  with  rhombic  bases,  and  contain  8  equivalents  of  water,  or  possibly 
only  7  equivalents  (Loewel,  Annal.  de  Ch.  et  de  Phys.  3  ser.  xxix.  62 ;  or  Chem. 
Soc.  Quart.  Journ.  in.,  164).  [See  Supplement,  p.  807.] 

M.  Loewel  finds  these  crystals  to  have  a  greater  solubility  than  the  ten-atom 
hydrate.  The  sulphate  of  soda  no  doubt  exists  in  the  supersaturated  solution  as 
eight-atom  hydrate,  and  the  salt  is  induced  to  crystallize  by  causes  which  make  it  to 
assume  two  additional  equivalents  of  water,  and  form  the  less  soluble  hydrate.  It 
is  proved  that  the  action  of  air  in  causing  crystallization  is  not  from  its  pressure 
(Gay-Lussac,  Annal.  de  Ch.  et  de  Ph.  2  ser.  ii.  296) ;  but,  as  I  have  shown,  from 
the  solubility  of  air  in  the  saline  solution,  carbonic  acid  exceeding  air  in  activity 
(Edinb.  Trans,  xi.  114).  Loewel  observes,  among. other  curious  circumstances,  that 
a  rod  of  glass  or  metal,  which  determines  the  formation  of  the  ten-atom  hydrate 
when  plunged  into  the  supersaturated  solution,  loses  this  property  if  it  is  left  in 
contact  with  water  for  twelve  hours,  or  if  it  has  been  previously  heated  to  between 
40°  and  100°  C.,  and  continues  incapable  of  inducing  crystallization  for  ten  days  or 
a  fortnight  at  the  ordinary  temperature,  if  preserved  from  free  contact  with  the  air. 
I  had  previously  put  up  clean  glass  beads  into  supersaturated  solutions  contained  in 
jars  inverted  over  mercury,  without  determining  crystallization,  a,nd  would  ascribe 
the  action  of  the  glass  surface  to  adhering  soluble  matter,  rather  than  the  molecular 
condition  of  the  glass,  as  supposed  by  M.  Loewel. 

A  saturated  solution  of  sulphate  of  soda,  kept  at  a  temperature  between  91°  and 
104°,  affords  octohedral  crystals  with  a  rhombic  base,  which  are  anhydrous.  They 
are  isomorphous  with  the  hyperinanganate  of  baryta.  Their  density  is  2.642.  The 
anhydrous  salt  fuses  at  a  bright  red  heat,  without  loss  of  acid.  Sulphate  of  soda 
was  at  one  time  the  saline  aperient  in  general  use,  but  is  now  superseded  by  sulphate 
of  magnesia;  It  is  still,  however,  occasionally  associated  with  the  tartrate  of  potassa 
and  soda,  in  Seidlitz  powders. 

The  crystallized  sulphate  of  soda  dissolves  freely  in  hydrochloric  acid,  or  in  dilute 
sulphuric  acid,  and  produces  a  great  degree  of  cold,  by  which  water  may  easily  be 
frozen  in  summer.  A  suitable  apparatus  for  this  purpose  consists  of  a  hollow7  cylin- 
der C  C  (figs.  178  and  179),  intended  for  the  reception  of  the  freezing  mixture, 
itself  surrounded  by  a  space  to  contain  the  water  to  be  frozen,  having  the  external 
opening  M,  and  the  whole  protected  by  a  double  casing,  B  B,  filled  with  cotton  or 
tow  to  prevent  access  of  heat.  The  cylinder  A  is  hollow,  and  may  also  have  water 
placed  in  it  to  be  frozen.  This  cylinder  is  turned  on  a  pivot  by  the  handle  above, 


392 


SODIUM. 


FTG.  178. 


FIG.  179. 


and  has  projections  or  vanes,  by  which  the  salt  and  acid  are  conveniently  agitated 
The  upper  part,  D,  of  this  cylinder  is  filled  with  a  non-conducting  material.  The 
freezing  mixture  is  added  in  charges  of  about  3  pounds  of  pulverized  sulphate 
of  soda,  and  2  pound  measures  of  hydrochloric  acid,  at  a  time ;  which  are  repeated 
after  ten  minutes,  and  the  stopcock  opened  to  allow  the  acid  solution  to  flow  into  the 
vessel  V  below,  where  its  low  temperature  may  be  further  employed  to  cool  wine  or 
other  beverages.  With  12  pounds  of  sulphate  of  soda,  and  about  10  pounds  of 
acid,  from  10  to  12  pounds  of  ice  may  be  formed  in  the  course  of  an  hour  in  this 
manner. 

The  anhydrous  sulphate  of  soda  also  forms  the  mineral  Thenardite,  which  was 
discovered  by  M.  Casasecu  in  the  neighbourhood  of  Madrid. 


FIG.  180. 


PREPARATION  OF  CARBONATE  OF  SODA  FROM  THE  SULPHATE. 

The  sulphate  of  soda  is  chiefly  formed  as  a  step  in  the  process  of  preparing  soda 
from  common  salt.  The  same  manufacture  gives  rise  to  the  preparation  of  large 
quantities  of  sulphuric  acid,  of  which  80  pounds  are  required  for  100  pounds  of  salt. 

From  the  last,  upwards  of  50,000  tons  of  soda- 
ash,  and  20,000  tons  of  crystallized  carbonate  of 
soda,  were  manufactured  in  1838 ;  and  the  pro- 
duction has  since  greatly  increased. 

A  reverberatory  furnace  is  employed  in  soda- 
making  and  various  other  chemical  manufactures, 
to  afford,  the  means  of  exposing  a  considerable 
quantity  of  materials  to  a  strong  heat,  of  which  a 
perpendicular  and  a  horizontal  section  are  given 
in  fig.  180.  It  consists  of  a  fire-place,  a,  in  which 
the  fuel  is  burned,  of  which  b  is  the  ash-pit",  with 
a  horizontal  flue  expanding  into  a  small  chamber 
or  oven,  d  d,  which  is  raised  to  a  strong  red  heat 
by  the  reverberation  on  its  walls  of  the  flame  or 
heated  air  from  the  fire,  on  its  passage  to  the 
chimney.  The  matters  to  be  heated  are  placed 
upon  the  floor  of  this  chamber.  It  has  an  open- 


PREPARATION    OF    CARBONATE    OF    SODA. 


393 


ing,  f,  in  the  side,  for  the  introduction  of  materials,  and  another  opening,  g,  at  the 
end  'most  distant  from  the  fire.  The  chimney  is  provided  with  a  damper,  p}  by 
which  the  draught  is  regulated. 

(1.)  The  sulphate  of  soda  is  prepared  by  throwing  600  pounds  of  common  salt  into 
the  chamber  of  the  furnace,  already  well  heated,  and  running  down  upon  it,  from  an 
opening  in  the  roof,  an  equal  weight  of  sulphuric  acid  of  density  1.600,  in  a  moderate 
stream.  Hydrochloric  acid  is  disengaged  and  carried  up  the  chimney,  and  the  con- 
version of  the  salt  into  sulphate  of  soda  is  completed  in  four  hours.  (2.)  The  sul- 
phate thus  prepared  is  reduced  to  powder  and  100  parts  of  it  mixed  with  103  parts 
of  ground  chalk,  and  62  parts  of  small  coal  ground  and  sifted.  This  mixture  is  in- 
troduced into  a  very  hot  reverberatory  furnace,  about  two  hundred  weight  at  a  time. 
It  is  frequently  stirred  until  it  is  uniformly  heated.  In  about  an  hour  it  fuses ;  it 
is  then  well  stirred  for  about  five  minutes,  and  drawn  out  with  a  rake  into  a  cast- 
iron  trough,  in  which  is  is  allowed  to  cool  and  solidify.  This  is  called  ball  soda,  or 
black-ash,  and  contains  about  22  per  cent,  of  alkali.  (3.)  To  separate  the  salts 
from  insoluble  matter,  the  cake  of  ball  soda,  when  cold,  is  broken  up,  put  into  vats, 
and  covered  by  warm  water.  In  six  hours  the  solution  is  drawn  off  from  below, 
and  the  washing  repeated  about  eight  times,  to  extract  all  the  soluble  matter. 
These  liquors  being  mixed  together  are  boiled  down  to  dryness,  and  afford  a  salt 
which  is  principally  carbonate  of  soda,  with  a  little  caustic  soda  and  sulphide  of 
sodium.  (4.)  For  the  purpose  of  getting  rid  of  the  sulphur,  the  salt  is  mixed  with 
one-fourth  of  its  bulk  of  sawdust,  and  exposed  to  a  low  red  heat  in  a  reverberatory 
furnace  for  about  4  hours,  which  converts  the  caustic  soda  into  carbonate,  while  the 
sulphur  also  is  carried  off.  This  product  contains  about  50  per  cent,  of  alkali,  and 
forms  the  soda-salt  of  best  quality.  (5.)  If  the  crystallized  carbonate  is  required, 
the  last  salt  is  dissolved  in  water,  allowed  to  settle,  and  the  clear  liquid  boiled  down 
until  a  pellicle  appears  on  its  surface.  The  solution  is  then  run  into  shallow  boxes 
of  cast-iron,  to  crystallize  in  a  cool  place ;  and  after  standing  for  a  week  the  mother 
liquor  is  drawn  off,  the  crystals  drained,  and  broken  up  for  the  market.  (6.)  The 
mother  liquor,  which  contains  the  foreign  salts,  is  evaporated  to  dryness,  for  a  soda- 
salt,  which  serves  for  soap  or  glass  making,  and  contains  about  30  per  cent,  of  alkali. 

In  fig.  181,  a  soda-furnace  is  represented,  consisting  of  two  compartments :  the 
first,  A,  in  which  the  sulphate  of  soda  is  decomposed,  and  the  second,  B,  in  which 


sulphuric  acid  is  applied  to  the  chloride  of  sodium,  and  the  sulphate  of  soda  formed. 
The  heat  from  the  furnace  is  further  economized  by  being  applied  to  evaporate  solu- 
tions of  carbonate  of  soda  in  C  and  D. 

The  most  essential  part  of  this  process  is  the  fusion  of  sulphate  of  soda  with  coal 
and  carbonate  of  lime :  by  the  first,  the  sulphate  is  converted  into  sulphide  of  sodium 
(page  383) ;  and  by  the  second,  the  sulphide  of  sodium  is  converted  into  carbonate 
of  soda.  These  changes  may  be  effected  separately  to  a  considerable  extent,  but  not 
completely,  by  calcining  the  sulphate  at  a  higher  temperature  with  coal  and  carbo- 
nate of  lime  in  succession.  The  lime  becomes  at  the  same  time  sulphide  of  calcium, 


394 


SODIUM. 


or  it  is  more  generally  supposed  to  form  an  oxi-sulphide  of  calcium,  SCaS.CaO,  a 
compound  which  would  destroy  the  carbonate  of  soda,  if  it  was  dissolved  along  with 
that  salt,  in  the  subsequent  lixiviation  of  the  ball  soda.  But  the  sulphide  of  calcium 
being  nearly  insoluble  of  itself,  or  rendered  entirely  so  by  its  combination  with  lime, 
does  not  dissolve  to  a  sensible  extent  in  the  experiment.  The  application,  however, 
of  very  hot  water  to  the  ball  soda  is  to  be  avoided.  The  following  diagram  is  used 
to  represent  the  chemical  changes  in  this  process,  supposing  for  simplicity  that  char- 
coal is  employed  instead  of  coal,  and  lime  instead  of  its  carbonate ;  the  numbers 
denoting  equivalents : — 

REACTION  IN  THE  SODA  PROCESS. 


Before  decomposition. 
4  Carbon 4  Carbon... 

Sulphate  of  (40*ygea.. 
-I  t    Sodium. 

1     Sulphur 
(^     Calcium 


Lime 


Lime 


After  decomposition. 
4  Carbonic  oxide. 

Soda. 


Sulphide  of  calcium 
Lime 


Mr.  Gossage  considers  the  additional  |  equiv.  of  lime  as  superfluous,  although 
not  injurious  in  the  process.  The  soda  derives  carbonic  acid  from  the  carbonate  of 
lime  or  from  the  gases  of  the  fire,  and  is  therefore  entirely  carbonate.  No  hydrate 
of  soda  is  dissolved  out  of  the  ball  soda  by  alcohol,  but  a  portion  of  the  carbonate 
appears  often  to  become  caustic  by  the  action  of  the  caustic  lime,  in  the  subsequent 
lixiviation.1 

The  insoluble  sulphide  of  calcium  of  this  process  is  known  as  soda-waste. '  It  is 


1  The  analysis,  by  Mr.  F  Claudet  in  my  laboratory,  of  a  specimen  of  black-ash  from 
Birmingham,  in  which  a  minimum  of  lime  appears  to  have  been  used,  gave  the  following 
results  :— 

Carbonate  of  Soda 35.42 

Sulphide  of  Sodium 1.45 

Sulphate  of  Soda 78 

Chloride  of  Sodium 2.62 

Silicic  acid 58 

Oxide  of  Iron,  Alumina 15 

r  Sulphide  of  Calcium  ...  ...  32.90  ==  /  SulPhur  14'6 


I 


Carbonate  of  Lime 3.73: 

Magnesia 56 

Oxide  of  Iron 1.98 

Alumina 3.59 

Sand  and  Silicic  acid 4.95 

Charcoal 10.57 

.  Water .72 


\  Calcium  18.9 
Lime  2.09 


100.00 


The  lime  found  is  not  in  quantity  sufficient  to  form  the  oxi-sulphide  of  calcium,  3CaS.CaO ; 
confirming  the  view  of  the  process  taken  by  Mr.  Gossage.  No  hydrate  of  soda,  or  sulphide 
of  sodium,  was  dissolved  out  of  this  black-ash  by  alcohol.  The  portion  of  the  latter  salt  ob- 
tained in  the  analysis  appeared  to  be  the  result  of  over-washing;  the  sulphide  of  calcium 
having  a  tendency  to  pass  into  lime  and  the  soluble  hydrosulphate  of  sulphide  of  calcium, 
which  decompose  a  portion  of  the  carbonate  of  soda.  Although  this  important  process  has 
been  much  studied,  its  theory  is  still  incomplete.  The  furnacing  of  the  sulphate  of  soda  is 
promoted  by  aqueous  vapour,  and  a  loss  of  sulphur  occurs  in  a  way  which  is  not  understood. 
See  the  papers  of  Mr.  J.  Brown  (Phil.  Mag.  xxxiv.  15),  of  M.  B.  Unger  (Ann.  Ch.  Pharm., 
Ixi.  Ixiii.  and  Ixvii.),  and  the  Annual  Report  on  the  Progress  of  Chemistry  of  Liebig  and 
Kopp,  edited  by  Hoffmann  and  De  la  Rue,  ii.  292,  1847-48. 


NITRATE   OF   SODA.  395 

not  merely  valueless,  but  troublesome  to  the  manufacturer.  But  the  attempt  has 
been  made  to  turn  it  to  account  as  a  source  of  sulphur.  As  means  are  now  taken 
to  condense  the  hydrochloric  acid,  formerly  sent  up  the  chimney,  this  acid  is  applied 
to  the  soda-waste,  from  which  it  disengages  hydrochloric  and  carbonic  acids.  But- 
hydrochloric  acid  is  not  produced,  in  the  soda  process,  in  adequate  quantity  for  this 
application  of  it,  and  the  carbonic  acid  evolved  with  the  hydrosulphuric  acid  might 
interfere  with  the  combustion  of  the  latter.  These  difficulties,  however,  are  in  a 
great  degree  removed  by  the  discovery  of  Mr.  Gossage,  that  sulphide  of  calcium, 
when  moistened  with  water,  is  decomposed  easily  and  completely  by  a  single  equiva- 
lent of  carbonic  acid.  Hence  the  application  of  hydrochloric  acid  to  the  waste  may 
be  made,  with  the  evolution  of  nothing  but  hydrosulphuric  acid ;  and  the  deficiency 
in  the  quantity  of  hydrochloric  acid  may  be  made  up  by  a  supply  of  carbonic  acid, 
to  be  applied  to  the  waste,  from  any  other  source.  The  hydrosulphuric  acid  would 
be  burned,  instead  of  sulphur,  in  the  leaden  chamber,  to  produce  sulphuric  acid. 

Many  changes  have  been  proposed  upon  the  soda  process.  Sulphate  of  iron,  pro- 
duced by  the  oxidation  of  iron-pyrites,  is  a  cheap  salt,  and  may  be  applied  to  convert 
chloride  of  sodium  into  sulphate  of  soda. — (1.)  By  igniting  a  mixture  of  these  salts 
in  a  reverberatory  furnace,  when  sulphate  of  soda,  sesquioxide  of  iron,  and  volatile 
sesquichloride  of  iron  are  produced.  (2.)  By  dissolving  the  salts  together  in  water, 
and  allowing  the  solution  to  fall  to  a  low  temperature,  when  sulphate  of  soda  crystal- 
lizes, and  chloride  of  iron  remains  in  solution  (Mr.  Phillips);  or  (3.)  By  concen- 
trating the  last  solution  at  the  boiling-point,  when  the  same  decomposition  occurs, 
anhydrous  sulphate  of  soda  precipitates,  and  may  be  raked  out  of  the  liquor.  The 
roasting  of  bisulphide  of  iron  with  common  salt  in  a  reverberatory  furnace  may  also 
be  made  to  furnish  sulphate  of  soda.  Sulphate  of  magnesia  has  been  substituted 
for  sulphate  of  iron,  in  these  three  modes  of  application ;  but  the  unavoidable  for- 
mation of  double  salts  of  magnesia  and  soda  makes  the  separation  of  the  sulphate 
of  soda  always  imperfect.  It  has  been  proposed,  instead  of  furnacing  the  sulphate 
of  soda,  to  decompose  it  by  caustic  baryta,  or  by  strontia,  the  last  earth  being  pro- 
cured by  Mr.  Tilghmann,  for  this  application  of  it,  by  decomposing  the  native 
sulphate  of  strontia  from  Bristol,  by  a  current  of  steam  at  a  red  heat.  Such  a  pro- 
cess should  also  furnish  the  sulphuric  acid  required  to  decompose  chloride  of  sodium 
and  form  sulphate  of  soda.  Chloride  of  sodium  may  also  be  decomposed  by  moist- 
ening and  rubbing  it  in  a  mortar  with  4  or  6  times  its  weight  of  litharge,  when  an 
oxichloride  of  lead  is  formed,  and  caustic  soda  liberated.  The  decomposition  of 
chloride  of  sodium  by  the  carbonate  of  ammonia,  with  formation  of  bicarbonate  of 
soda,  has  already  been  noticed  (page  389).  It  appears,  however,  that  the  soda- 
process  first  described,  which  was  invented  towards  the  end  of  the  last  century  by 
Leblanc,  is  still  generally  preferred  to  all  others. 

The  old  sources  of  carbonate  of  soda,  namely  barilla,  or  the  ashes  of  the  salsola 
soda,  which  is  cultivated  on  the  coasts  of  the  Mediterranean,  and  kelp,  the  ashes  of 
sea- weeds,  have  ceased  to  be  of  importance,  at  least  in  England.  Barilla  contains 
about  18,  and  kelp  about  2  per  cent,  of  alkali. 

Bisulphate  of  soda,  HO.S03  +  NaO.S03;  120  or  1500.  This  salt  is  obtained 
in  large  crystals  on  adding  an  equivalent  of  oil  of  vitriol  to  sulphate  of  soda,  and 
evaporating  the  solution  till  it  attains  the  degree  of  concentration  necessary  for 
crystallization.  If  half  an  equivalent  only  of  oil  of  vitriol  is  added,  a  sesquisul- 
phate  of  soda  is  obtained  in  fine  crystals,  according  to  Mitscherlich.  The  ordinary 
bisulphate  of  soda  contains  basic  water,  but  it  may  be  rendered  anhydrous  by  a 
degree  of  heat  approaching  to  redness.  The  salt  thus  obtained  is  a  true  bisulphate 
of  soda,  and  gives  anhydrous  sulphuric  acid  when  distilled  at  a  red  heat. 

Nitrate  of  soda;  Na().N05j  85  or  1062.5.  — This  salt  crystallizes  in  the  rhom- 
boidal  form  of  calc-spar;  density  2.260.  It  is  soluble  in  twice  its  weight  of  water, 
and  has  a  tendency  to  deliquesce  in  damp  air.  It  burns  much  slower  with  combus- 
tibles than  nitrate  of  potassa,  and  cannot  therefore  be  substituted  for  that  salt  in  the 
manufacture  of  gunpowder.  It  is  now  generally  had  recourse  to,  as  the  source  of 


396  SODIUM. 

nitric  acid,  and  is  also  largely  used  in  agriculture.  Nitrate  of  soda  is  found  abun- 
dantly in  the  soil  of  some  parts  of  India;  and  it  forms  a  thin  but  very  extensive 
bed  covered  by  clay  at  Atacama  in  Peru,  from  which  it  is  exported  in  great 
quantity. 

Chlorate  of  soda  (NaO.C105)  is  formed  by  mixing  strong  solutions  of  bitartrate 
of  soda  and  chlorate  of  potassa,  when  the  bitartrate  of  potassa  precipitates,  and  the 
chlorate  of  soda  remains  in  solution.  It  crystallizes  in  fine  tetrahedrons,  and  is 
considerably  more  soluble  than  chlorate  of  potassa. 

Phosphates  of  soda.  —  There  are  three  crystallizable  phosphates  of  soda  belonging 
to  the  tribasic  class,  which  I  shall  describe  under  their  most  usual  names. 

Phosphate  of  soda ;  H0.2NaO.P05  +  24HO;  359  or  4487.5.  — This  is  the  salt 
known  in  pharmacy  as  phosphate  of  soda,  and  formed  by  neutralizing  phosphoric 
acid  from  burnt  bones  (page  319)  with  carbonate  of  soda.  It  crystallizes  in  oblique 
rhombic  prisms,  which  are  efflorescent,  and  essentially  alkaline.  M.  Malaguti  is,  I 
believe,  mistaken  in  ascribing  26  equivs.  of  water  to  this  salt.  The  taste  of  phos- 
phate of  soda  is  cooling  and  saline,  and  less  disagreeable  than  sulphate  of  magnesia, 
for  which  it  may  be  substituted  as  an  aperient.  It  dissolves  in  4  times  its  weight 
of  cold  water,  and  fuses  in  its  water  of  crystallization,  when  moderately  heated. 
When  evaporated  above  90°,  this  salt  crystallizes  in  another  form  with  14  instead 
of  24  atoms  of  water  (Clark).  It  is  deprived  of  half  its  alkali  by  hydrochloric  acid 
in  the  cold,  but  not  by  acetic  acid. 

Subphosphate  of  soda;  3NaO.P05+24HO;  381  or  4762.5.  —  Formed  when  an 
excess  of  caustic  soda  is  added  to  the  preceding  salt.  It  crystallizes  in  slender  six- 
sided  prisms,  with  flat  terminations,  which  are  unalterable  in  air;  but  the  solution 
of  this  salt  rapidly  absorbs  carbonic  acid,  and  is  deprived  of  one-third  of  its  alkali 
by  the  weakest  acids.  The  crystals  dissolve  in  5  times  their  weight  of  water  at  60°, 
and  undergo  the  watery  fusion  at  170°.  This  salt  continues  tribasic  after  being 
exposed  to  a  red  heat. 

Biphosphate  of  soda;  2HO.NaO.P05  +  2HO;  139  or  1737.5.  —  Obtained  by 
adding  tribasic  phosphate  of  water  to  phosphate  of  soda,  till  the  latter  ceases  to  pro- 
duce a  precipitate  with  chloride  of  barium.  The  solution  affords  crystals,  in  cold 
weather,  of  which  the  ordinary  form  is  a  right  rhombic  prism,  having  its  larger 
angle  of  93°  54'.  But  this  salt  is  dimorphous,  occurring  in  another  right  rhombic 
prism,  of  which  the  smaller  angle  is  78°  30',  terminated  by  pyramidal  planesT 
isomorphous  with  binarseniate  of  soda.  The  biphosphate  of  soda  is  very  soluble, 
and  has  a  distinctly  acid  reaction.  Like  all  the  other  soluble  tribasic  phosphates,  it 
gives  a  yellow  precipitate  with  nitrate  of  silver,  which,  is  tribasic  phosphate  of 
silver. 

Phosphate  of  soda  and  ammonia,  Microcosmic  salt ;  HO.NH4O.NaO.P05  +  8HO; 
201  or  2512.5.  —  This  salt  is  obtained  by  heating  together  6  or  7  parts  of  crystal- 
lized phosphate  of  soda,  and  2  parts  of  water,  till  the  whole  is  liquid,  and  then 
adding  1  part  of  pulverized  sal-ammoniac.  Chloride  of  sodium  separates,  and  the 
solution,  filtered  and  concentrated,  affords  the  phosphate  in  prismatic  crystals.  It  is 
purified  by  a  second  crystallization.  This  salt  occurs  in  urine.  It  is  much  employed 
as  a  flux  in  blow-pipe  experiments.  By  a  slight  heat  it  loses  8110,  by  a  stronger 
heat  it  is  deprived  of  its  remaining  water  and  ammonia,  and  converted  into  meta- 
phosphate  of  soda,  which  is  a  very  fusible  salt.  It  will  be  observed  that  the  three 
atoms  of  base  in  this  phosphate  are  all  different, —  namely,  water,  oxide  of  ammo- 
nium, and  soda ;  of  which  the  two  last  belong  to  the  same  natural  family,  for  bases 
of  the  same  family  may  exist  together  in  the  salts  of  bibasic  and  tribasic  acids, 
forming  stable  compounds,  but  not  in  ordinary  double  salts.  No  phosphate  exists, 
corresponding  with  microcosmic  salt,  but  containing  potassa  instead  of  oxide  of 
ammonium;  the  phosphate  of  soda,  with  14HO,  has  been  mistaken  for  such  a  salt. 

Pyrophosphate  of  soda;  2NaO.P05  -f  10HO;  134  +  90,  or  1675  +  1125.— 
Procured  by  heating  the  phosphate  of  soda  to  redness,  when  it  loses  its  basic  water 
as  well  as  its  water  of  crystallization.  The  residual  mass  dissolved  in  water  affords 


BIBORATE   OF   SODA.  397 

a  salt,  which  is  less  soluble  than  the  original  phosphate,  and  crystallizes  in  prismatic 
crystals,  which  are  permanent  in  air,  and  contain  ten  atoms  of  water.  Its  solution 
is  essentially  alkaline.  This  salt  is  precipitated  white,  by  nitrate  of  silver.  It  is  to 
be  remarked  that  insoluble  pyrophosphates,  including  pyrophosphate  of  silver,  are 
soluble  to  a  considerable  degree  in  the  solution  of  pyrophosphate  of  soda.  The 
pyrophosphates  of  potassa  and  of  ammonia  can  exist  in  solution,  but  pass  into  tribasic 
salts  when  they  crystallize. 

A  bipyrophosphate  of  soda  (HO.NaO.P05)  exists,  obtained  by  the  application 
of  a  graduated  heat  to  the  biphosphate  of  soda,  but  it  does  not  crystallize.  Its  solu- 
tion has  an  acid  reaction. 

Metaphosphate  of  soda;  NaO.P05,  103  or  1287.5.  —  The  biphosphate  of  soda, 
containing  only  one  equivalent  of  fixed  base,  affords  the  metaphosphate  of  soda, 
when  heated  to  redness.  The  metaphosphate  of  soda  fuses  at  a  heat  which  does 
not  exceed  low  redness,  and  on  cooling  rapidly  forms  a  transparent  glass,  which  is 
deliquescent  in  damp  air,  and  very  soluble  in  water,  but  insoluble  in  alcohol :  its 
solution  has  a  feebly  acid  reaction,  which  can  be  negatived  by  the  addition  of  4  per 
cent,  of  carbonate  of  soda.  When  evaporated,  this  solution  does  not  give  crystals, 
but  dries  into  a  transparent  pellicle,  like  gum,  which  retains  at  the  temperature  of 
the  air  somewhat  more  than  a  single  equivalent  of  water.  Added  to  neutral,  and 
not  very  dilute  solutions  of  earthy  and  metallic  salts,  metaphosphate  of  soda  throws 
down  insoluble  hydrated  metaphosphates,  of  which  the  physical  condition  is  remark- 
able. They  are  all  soft  solids,  or  semifluid  bodies;  the  metaphosphate  of  lime 
having  the  degree  of  fluidity  of  Venice  turpentine. 

The  bipyrophosphate  of  soda  appears  to  undergo  several  changes  under  the  influ- 
ence of  heat  before  it  becomes  metaphosphate.  At  a  temperature  of  500°,  the  salt 
becomes  nearly  anhydrous,  and  affords  a  solution  which  is  neutral  to  test-paper,  but 
in  other  respects  resembles  the  bipyrophosphate.  But  at  temperatures  which  are 
higher,  but  insufficient  for  fusion,  the  salt  being  anhydrous,  appears  to  have  lost  its 
solubility  in  water ;  at  least  it  is  not  affected  at  first  when  thrown  in  powder  into 
boiling  water,  but  gradually  dissolves  by  continued  digestion,  and  passes  into  the 
preceding  variety.— (Phil.  Trans.  1833,  p.  275). 

When  the  fused  metaphosphate  of  soda  is  slowly  cooled,  it  forms  a  crystalline 
mass,  as  observed  by  Fleitmann  and  Henneberg,  and  gives  a  crystallizable  meta- 
phosphate of  soda  (page  324). 

Borax,  Biborate  of  soda,  Na0.2B03  +  10HO;  100.8  -f- 90  or  1260.  +  1125.— 
This  salt  is  met  with  in  commerce  in  large  hard  crystals.  It  is  found  in  the  water 
of  certain  lakes  in  Transylvania,  Tartary,  China,  and  Thibet,  and  is  deposited  in 
their  beds  by  spontaneous  evaporation.  It  is  imported  from  India  in  a  crude  state, 
and  enveloped  in  a  fatty  matter,  under  the  name  of  Tinkal,  and  afterwards  purified. 
But  nearly  the  whole  borax  consumed  in  England  is  at  present  formed  by  neutral- 
izing, with  carbonate  of  soda,  the  acid  from  the  boracic  lagoons  of  Tuscany.  The 
ordinary  crystals  of  borax  are  prisms  of  the  oblique  system,  containing  10  atoms  of 
water,  of  density  1.692 ;  but  it  also  crystallizes  at  133°  in  regular  octohedrons, 
which  contain  on4y  5  atoms  of  water.  This  salt  has  a  sweetish,  alkaline  taste ;  for, 
although  containing  an  excess  of  acid,  it  has  an  alkaline  reaction,  like  the  bicarbonate 
of  soda,  and  is  soluble  in  10  parts  of  cold,  and  2  parts  of  boiling  water. 

The  anhydrous  salt  is  very  fusible  by  heat,  and  forms  a  glass  of  density  2.367. 

This  glass  possesses  the  property  of  dissolving  most  metallic  oxides,  the  smallest 

portions  of  which  colour  it.     As  the  metal  may  often  be  discovered  by  the  colour, 

borax  is  valuable  as  a  flux  in  blow-pipe  experiments.     For  this  purpose  a  thin  pla-, 

tinum  wire  is  generally  used,  one  end  of  which  is  bent  into  a  hook  (fig.  182.)     The 

loop  being  slightly  moistened,  is  dipped  into  a  fine  powder 

Fia.  182.  Of  anhydrous  borax,  and  a  minute  portion  of  the  metallic 

— -__ — ~~O  oxide  which  we  wish  to  determine  is  also  taken  up  on  the 

loop.  The  matter  is  then  fused  in  the  flame  of  a  candle 
or  spirit-lamp  directed  upon  it  by  means  of  a  mouth  blow-pipe  (fig.  183.)  Often 


398  SODIUM. 

two  different  colourations  are  obtained  when  the  metal  has  more  than  one  oxide,  ac- 
cording as  the  substance  is  heated  in  the  reducing  or  white  portion  of  the  flame, 
which,  in  the  blow-pipe  flame,  is  at  b  (fig.  184),  or  in  the  oxidating  spheres  a  a,  and 

FIG.  183.  FIG.  184. 


at  the  point  c,  where  there  is  an  excess  of  atmospheric  air.  To  produce  the  colour 
of  the  protoxide,  we  expose  to  the  reducing  flame ;  and  to  produce  the  colour  of  the 
peroxide,  we  expose  to  the  oxidizing  flame. 

As  pieces  of  metal  could  not  be  soldered  together  if  covered  by  oxide,  borax  is 
fused  with  the  solder  upon  the  surface  of  the  metals  to  be  joined,  to  remove  the 
oxide.  Borax  is  also  a  constituent  of  the  soft  glass,  known  as  jewellers'  paste,  which 
is  coloured  to  imitate  precious  stones.  But  the  most  considerable  consumption  of 
this  salt  is  in  the  potteries,  in  the  formation  of  a  glaze  for  porcelain. 

A  neutral  borate  of  soda  is  formed  by  calcining  strongly  1  eq.  of  borax  with  1 
eq.  of  carbonate  of  soda,  when  carbonic  acid  is  expelled.  The  solution  yields  a  salt 
belonging  to  the  oblique  prismatic  system,  of  which  the  formula  is,  NaO.B03  +  8HO. 
When  heated,  it  fuses  in  its  water  of  crystallization,  and  is  expanded  into  a  vesicular 
mass  of  extraordinary  magnitude  by  the  vaporization  of  that  water. 

When  borax  is  fused  with  carbonate  of  soda  in  excess,  the  quantity  of  carbonic 
acid  which  escapes  indicates  the  formation  of  a  borate,  3NaO  +  2B03,  but  which  has 
not  been  farther  examined.  Notwithstanding  this,  a  solution  of  borax  in  water  is 
decomposed,  and  the  boracic  acid  entirely  liberated,  by  a  stream  of  either  carbonic 
or  hydrosulphuric  acid.  Silicic  acid,  however,  in  its  soluble  modification,  has  no 
decomposing  action  upon  a  solution  of  borax.  Boracic  acid,  therefore,  appears  to 
stand  in  the  scale  of  acids  above  silicic,  but  below  carbonic  acid.  A  saturated  solu- 
tion of  borax  readily  dissolves  a  large  amount  of  arsenious  acid,  forming  a  compound 
remarkable  for  its  great  solubility  in  water.  This  contains,  according  to  Prof.  E. 
Schweizer,  arsenite  of  soda,  borate  of  soda,  and  a  compound  of  arsenious  and  boracic 
acids,  and  is  probably  represented  by  the  formula  — 

NaO.  As03  +  2(Na0.2B03)  +  2(B032  As03)  +  10HO. 

A  salt  is  said  to  exist,  formed  of  NaO  +  4B03,  but  to  crystallize  with  difficulty, 
produced  on  combining  borax  with  a  quantity  of  boracic  acid  equal  to  what  it  already 
contains.  M.  Laurent  has  also  shown  that  a  sexborate  of  soda  exists  in  solution, 
but  is  not  crystallizable.  (Ann.  de  Ch.  et  de  Phys.  Ixvii.,  218.)  The  boratcs  of 
potassa  have  also  been  examined  by  Laurent.  The  sexborate  crystallizes  well;  its 
formula  is  K0.6B03-f  10HO.  A  triborate  is  represented  by  K0.3B03-f8HO; 
the  biborate  corresponds  in  composition  with  octohedral  borax,  but  has,  notwith- 
standing, a  different  and  incompatible  form. 

A  simple  and  very  accurate  method  of  analyzing  borax  is,  to  add  an  excess  of  hy- 
drochloric acid  to  a  solution  of  the  salt,  and  evaporate  to  dryness  on  the  water-bath, 
adding  a  few  more  drops  of  hydrochloric  acid  towards  the  end  of  the  operation. 
The  mass,  when  perfectly  dry,  is  re-dissolved  in  water,  a  little  nitric  acid  mixed  with 
the  solution,  and  the  chlorine  precipitated  by  nitrate  of  silver ;  from  the  amount  of 
chloride  of  silver  that  of  the  chlorine  is  deduced,  and  from  the  latter  the  quantity 
of  soda.  The  alkaline  bases  of  all  the  other  borates  may  be  obtained  wholly  as 
chloride  by  a  similar  treatment.  (Schweitzer,  Chein.  Gaz.  1850,  p.  281.) 


GLASS.  399 

Silicates  of  soda. — The  earth  silica,  or  silicic  acid,  Si03  (page  290),  is  dissolved 
by  caustic  soda,  and  gives,  by  slow  evaporation,  a  crystallized  silicate  of  soda, 
8Na0.2Si03  (Fritzsche).  A  concentrated  solution  of  caustic  soda  at  a  high  tempe- 
rature under  pressure  dissolves  silica  freely  even  in  the  form  of  flint  or  of  quartzy 
sand,  and  gives  a  similar  silicate,  which  is  used  by  Mr.  Ransome  of  Ipswich  for  the 
induration  of  plaster  and  cements,  and  the  formation  of  artificial  stone. 

When  silicic  acid  is  thrown  into  carbonate  of  potassa  or  soda,  in  a  state  of  fusion 
by  heat,  a  fusible  silicate  is  formed,  in  which,  judging  from  the  quantity  of  carbonic 
acid  expelled,  3  eq.  of  soda  are  also  combined  with  2  eq.  of  silicic  acid,  and  the 
oxygen  in  the  soda  is  to  that  in  the  silicic  acid  as  1  to  2.  This  silicate  dissolves  in 
the  clear  and  liquid  carbonate.  When,  on  the  other  hand,  a  greater  proportion  of 
silicic  acid  is  fused  with  the  carbonate,  the  whole  carbonic  acid  of  the  latter  is 
expelled,  and  the  excess  of  silicic  acid  then  dissolves  in  the  silicate.  The  silicic  acid 
and  silicate  of  such  mixtures  do  not  separate  by  crystallization,  but  uniformly  solidify 
together,  on  cooling,  as  a  homogeneous  glass,  whatever  their  proportions  may  be.  It 
is  thus  impossible  to  obtain  alkaline  silicates,  which  are  certainly  definite  combina- 
tions, in  the  dry  way.  A  mixture  of  silicic  acid  with  potassa  or  soda,  in  which  the 
oxygen  of  the  former  is  to  that  of  the  latter  as  18  to  1,  is  said  still  to  be  fusible  by 
the  heat  of  a  forge;  but  when  the  proportion  is*  as  30  to  1,  the  mixture  merely  ag- 
glutinates, or  frits.  These  combinations,  even  with  a  large  quantity  of  silicic  acid, 
continue  to  be  soluble  in  water. 

A  compound,  known  as  soluble  glass,  is  obtained  by  fusing  together  8  parts  of 
carbonate  of  soda  (or  10  of  carbonate  of  potassa)  with  15  of  fine  sand  and  1  of 
charcoal.  The  object  of  the  charcoal  is  to  facilitate  the  combination  of  the  silicic 
acid  with  the  alkali,  by  destroying  the  carbonic  acid,  which  it  converts  into  carbonic 
oxide.  This  glass,  when  reduced  to  powder,  is  not  attacked  by  cold  water,  but  is 
dissolved  by  4  or  5  parts  of  boiling  water.  The  solution  may  be  applied  to  objects 
of  wood,  and,  when  dried  by  a  gentle  heat,  forms  a  varnish,  which  imbibes  a  little 
moisture  from  the  air,  but  is  not  decomposed  by  carbonic  acid,  nor  otherwise  alterable 
by  exposure.  Stuffs  impregnated  with  the  solution  lose  much  of  their  combusti- 
bility, and  wood  is  also  defended  by  it,  to  a  certain  degree,  from  combustion. 

GLASS. 

The  alkaline  silicates,  cooled  quickly  or  slowly,  never  exhibit  a  crystalline  struc- 
ture, but  are  uniformly  vitreous  (p.  151).  They  are  the  bases  of  the  ordinary 
varieties  of  glass,  which  contain  earthy  silicates  besides,  but  appear  to  owe  the 
vitreous  character  to  the  silicates  of  potassa  and  soda.  The  silicate  of  lime,  and  the 
silicate  of  the  protoxide  of  iron,  crystallize  on  cooling;  so  does  the  silicate  of  It-ad, 
unless  it  contains  a  large  excess  of  oxide  of  lead.  The  addition  of  the  silicate  of 
potassa  or  soda  deprives  them  entirely  of  this  property ;  the  silicate  of  alumina  con- 
siderably diminishes  it.  But  if  silicates  of  potassa  or  soda  are  heated  for  a  long 
time,  the  alkali  may  in  part  escape  in  vapour,  and  if  other  bases  exist  in  the  com- 
pound, it  then  often  assumes  a  crystalline  structure  on  cooling.  The  alkaline  silicates 
by  themselves  are  soluble  in  water,  and  decomposed  by  acids ;  the  silicate  of  lime 
is  also  dissolved  by  acids,  but  the  double  silicates,  on  the  contrary,  resist  the  action 
of  acids,  particularly  when  they  contain  an  excess  of  silicic  acid,  and  form  an  avail- 
able glass.  The  following  table  exhibits  the  composition  of  the  best  known  kinds 
of  glass,  from  the  analyses  of  Dumas  and  of  Faraday : — 


400 


GLASS. 


COMPOSITION    OF   VARIETIES    OF    GLASS. 


Silicic 
acid. 

Potassa. 

Lime. 

Ox.  lead. 

Alumina. 

Water. 

69 

12 

9 

o 

10 

o 

Crown-glass             

63 

22 

12 

o 

3 

0 

69 

11  soda 

13 

o 

7 

o 

54 

5 

29 

6  ox   iron 

0 

o 

Flint-glass             

45 

12 

o 

43 

o 

o 

Crystal    

61 

6 

o 

33 

o 

o 

Strass   

38 

8 

0 

53 

1 

o 

Soluble  glass      ...           . 

62 

26 

o 

o 

o 

12 

- 

The  analysis,  by  Mr.  T.  Rowney,  of  the  superior  Bohemian  glass,  which,  on 
account  of  its  difficult  fusibility,  is  employed  for  combustion-tubes,  gave  silicic  acid 
73.13,  potassa  11.49,  soda  3.07,  lime  10.43,  alumina  0.30,  sesquioxide  of  iron  0.13, 
magnesia  0.26,  protoxide  of  manganese  0.46=99.27.  The  oxygen  of  the  bases  is 
to  that  of  the  silicic  acid  as  1  to  6.  The  specimen  was  decomposed  by  fusion  with 
carbonate  of  soda,  for  the  earths,  and  by  fusion  with  hydrate  of  baryta  for  the  alka- 
lies (Mem.  Chem.  Soc.  iii.  299). 

Silicate  of  soda  and  lime.  —  To  form  window-glass,  100  parts  of  quartzy  sand 
are  taken,  with  35  to  40  parts  of  chalk,  30  to  35  parts  of  carbonate  of  soda,  and 
180  parts  of  broken  glass.  These  materials  are  first  fritted,  or  heated  so  as  to  cause 
the  expulsion  of  water  and  carbonic  acid,  and  to  produce  an  agglutination  of  their 
particles,  and  afterwards  completely  fused  in  a  large  clay  crucible  of  a  peculiar  con- 
struction ;  or  fused  at  once,  the  fritting  being  now  generally  discontinued.  For  the 
first  formation  of  the  glass  a  higher  temperature  is  required  than  that  at  which  it  is 
most  thick  and  viscid,  and  in  the  proper  condition  for  working  it.  At  the  latter 
temperature  the  substance  possesses  an  extraordinary  degree  of  ductility,  and  may 
be  drawn  out  into  threads  so  fine  as  to  be  scarcely  visible  to  the  eye.  A  portion  of 
the  plastic  mass,  on  the  extremity  of  an  iron  tube  used  as  a  blow-pipe,  may  be 
expanded  into  a  globular  flask,  and  pressed  or  bent  into  vessels  of  any  form,  which 
may  be  pared  and  fashioned  by  the  scissors.  At  a  lower  temperature,  glass  vessels 
become  rigid,  and,  when  cold,  brittle  in  the  extreme,  unless  they  be  annealed)  that 
is,  kept  for  several  hours  at  a  temperature  progressively  lowered  from  the  highest 
degree  which  the  glass  can  bear  without  softening  to  the  temperature  of  the  atmo- 
sphere. The  well-known  glass  tears,  or  Prince  Rupert's  drops,  as  they  are  called, 
which  are  made  by  allowing  drops  of  melted  glass  to  fall  into  water,  illustrate  the 
peculiar  properties  of  unannealed  glass.  The  surface  becoming  solid  by  the  sudden 
cooling,  while  the  interior  is  still  at  a  high  temperature,  and  consequently  dilated, 
the  drop  is  of  greater  volume  than  it  would  be  if  cooled  slowly  and  equally  through- 
out its  mass.  Its  particles  are  thus  in  a  state  of  extreme  tension,  and  an  injury  to 
any  part  causes  the  whole  mass  to  fly  to  pieces.  The  fracture  of  unannealed  vessels, 
which  is  the  immediate  consequence  of  scratching  their  surface,  has  been  compared 
to  the  effect  upon  a  sheet  of  cloth  forcibly  stretched,  of  injuring  its  edge  in  the 
smallest  degree  by  a  knife  or  scissors.  It  then  ceases  to  preserve  its  integrity  by 
resisting  the  tension,  and  is  torn  across.  The  relative  proportions  of  the  ingredients 
of  this  and  other  species  of  glass  is  subject  to  some  variation.  But  the  oxygen  in 
the  bases  of  window-glass  is  to  the  oxygen  of  the  silicic  acid  nearly  as  1  to  4 ;  the 
composition  approaching  the  formula  3Na0.3CaO-r-8Si03.  This  glass  has  a  green 
tint,  which  is  very  obvious  in  a  considerable  mass  of  it,  occasioned  in  part,  it  may 
be,  by  the  impurities  of  the  materials,  but  a  certain  degree  of  which  appears  to  be 
essential  to  a  soda-glass.  For  in  all  the  finer  and  entirely  colourless  varieties  of  glass 
it  is  necessary  to  use  potassa. 

Silicates  of  potassa  and  lime.  —  Plate-glass  used  for  mirrors,  crown-glass,  and 


GLASS.  401 

the  beautiful  Bohemian  glass,  are  of  this  composition.  In  the  most  remarkable 
varieties  the  oxygen  of  the  bases  is  to  that  of  the  acid  as  1  to  6,  and  the  oxygen  of 
the  lime  to  that  of  the  potassa  in  proportions  which  vary  from  1  and  f  to  1  and  1. 
Its  composition  approaches  the  formula  KO.CaO  +  4SiO3.  This  is  the  glass  of 
most  difficult  fusibility,  and  therefore  most  suitable  for  the  combustion-tubes  employed 
in  organic  analysis.  From  its  purity,  and  the  absence  of  oxide  of  lead,  it  is  also 
made  the  basis  of  most  coloured  glasses,  and  of  stained  glass.  To  produce  coloured 
glasses  certain  metallic  oxides  are  mixed  with  the  fused  glass  in  the  pot;  oxide  of 
cobalt,  for  instance,  for  a  blue  colour,  oxide  of  copper  for  green,  binoxide  of  manga- 
nese in  small  proportion  for  an  amethystine  glass,  and  in  large  proportion  for  a  black 
glass,  peroxide  of  uranium  for  a  delicate  lemon-yellow  tint,  and  gold  for  a  ruby  glass. 
In  stained  glass,  on  the  other  hand,  the  metal  or  metallic  oxide  is  merely  applied 
with  a  proper  flux  to  the  surface  of  the  glass,  which  is  then  exposed  in  an  oven  to  a 
temperature  sufficient  to  fuse  the  colouring  matter,  without  distorting  the  sheet  of 
glass.  Different  shades  of  yellow  and  orange  are  thus  produced  by  means  of  silver 
and  antimony,  and  a  superb  ruby-red  by  a  proper,  but  difficult,  application  of  sub- 
oxide  of  copper.  The  beautiful  avanturine  glass  contains  crystals  of  metallic  copper. 
The  green  shade  of  ordinary  glass  is  chiefly  due  to  protoxide  of  iron,  and  is  corrected 
by  a  small  addition  of  binoxide  of  manganese  (hence  called  pyrolusite),  which  raises 
the  iron  to  the  state  of  sesquioxide,  in  which  it  is  not  injurious,  while,  at  the  same 
time,  the  binoxide  of  manganese,  by  losing  oxygen,  passes  into  the  state  of  the 
colourless  protoxide  of  that  metal. 

Silicates  of  potassa  and  lead.  —  These  substances  enter  into  the  composition  of 
the  purer  and  more  brilliant  species  of  glass  in  use  in  this  country ;  such  as  that 
called  crystal,  of  which  most  drinking  vessels  are  made,  flint-glass  for  optical  purposes, 
and  strass,  which  is  employed  in  imitations  of  the  precious  stones.  For  crystal,  the 
materials  are  taken  in  the  following  proportions:  120  parts  of  fine  sand,  about  40 
of  purified  potashes,  35  of  litharge  or  minium,  and  12  of  nitre.  In  this  glass  the 
oxygen  of  the  bases  is  to  that  of  the  silicic  acid  as  1  to  a  number  which  may  vary 
from  7  to  9,  and  the  oxygen  of  the  potassa  is  to  that  of  the  oxide  of  lead  as  1  to  a 
number  varying  from  1  to  2.5.  In  flint-glass,  and  in  strass,  the  oxygen  of  the  bases 
is  to  that  of  the  silicic  acid  as  1  to  4,  and  the  oxygen  of  the  potassa  is  to  that  of  the 
oxide  of  lead  as  2  to  3  in  flint-glass,  and  as  1  to  3  in  strass  (Dumas).  The  more 
oxide  of  lead  glass  contains,  the  higher  its  density  •  the  density  of  this  kind  of  glass 
exceeding  3.6,  while  that  of  the  Bohemian  glass  does  not  rise  higher  than  2.4. 
Glass  containing  oxide  of  lead  is  recommended  by  its  greater  fusibility  and  softness, 
by  which  it  is  more  easily  fashioned  into  various  forms,  and  by  its  great  brilliancy, 
which  is  remarkable  in  lustres  and  other  objects  of  cut  glass.  The  presence  of  lead 
in  glass  is  at  once  discovered  by  its  surface  acquiring  a  metallic  lustre  when  heated 
to  redness  in  the  reducing  flame.  Enamel  is  a  white  and  very  fusible  glass,  con- 
taining a  white  opaque  substance  suspended  in  its  mass.  It  is  generally  prepared 
from  the  stannate  of  lead,  formed  by  heating  and  oxidizing  together  15  parts  of  tin 
and  100  of  lead.  This  is  afterwards  fused  with  50  parts  of  sand  and  40  parts  of 
carbonate  of  potassa.  Besides  binoxide  of  tin,  arsenious  acid,  oxide  of  antimony, 
phosphate  of  lime,  and  sulphate  of  potassa,  are  employed  to  give  opacity  to  enamel. 

Silicates  of  alumina,  of  the  oxides  of  iron,  magnesia,  and  potassa  or  soda. — 
Green  or  bottle-glass,  of  which  wine-bottles,  carboys,  and  glass  articles  of  low  price 
consist,  is  a  mixture  of  these  silicates.  It  is  formed  of  the  cheapest  materials,  such 
as  sand,  with  soap-makers'  waste,  lime  that  has  been  used  to  render  alkali  caustic, 
&c.  In  the  bottle-glass  of  this  country  the  small  quantity  of  alkali  is  chiefly  soda. 
The  alkaline  sulphates,  when  fused  with  silicic  and  carbonaceous  matter,  lose  their 
sulphuric  acid,  and  become  silicates ;  even  common  salt  is  decomposed  by  the  united 
action  of  silicic  acid  and  the  aqueous  vapour  in  flame,  but  much  of  it  is  lost  from  its 
own  volatility.  The  proportion  of  silicic  acid  to  the  bases  is  much  less  in  this  than 
in  the  other  kinds  of  glass,  the  oxygen  of  the  former  being  to  the  latter  as  2  to  1  ; 
and  the  oxygen  of  the  alumina  and  sesquioxide  of  iron  equal  to  that  of  the  potassa 


402  LITHIUM. 

and  lime.  This  glass  is,  in  fact,  a  mixture  of  neutral  and  subsilicates,  and,  when  it 
contains  an  excess  of  lime,  is  more  apt  than  any  of  the  preceding  species  to  assume 
a  crystalline  structure  when  maintained  long  in  a  soft  condition  by  heat. 

A  bottle  of  green  glass. may  be  devitrified,  or  converted  into  what  is  called  Reau- 
mur's porcelain,  by  enveloping  it  in  sand,  and  placing  it  where  its  temperature  is 
kept  high  for  several  weeks,  as  in  a  brick-kiln  or  porcelain-furnace.  Glass  of  all 
kinds,  when  strongly  and  repeatedly  heated,  loses  alkali,  from  its  volatility ;  the  glass 
then  becomes  harder  and  less  fusible,  and  is  not  so  easily  wrought, —  a  circumstance 
which  may  sometimes  be  remarked  in  blowing  a  bulb  upon  a  tube  which  has  been 
too  long  exposed  to  the  blow-pipe  flame.  Glass  of  all  kinds,  when  well  manufac- 
tured, is  supposed  to  be  insoluble  in  water,  but  it  is  eventually  acted  upon,  and 
soonest  when  its  natural  surface  is  broken ;  water  tending  to  resolve  glass  into  a 
soluble  alkaline  silicate  and  an  insoluble  earthy  silicate.  Glass  bottles  containing  a 
large  proportion  of  lime  may  be  corroded  through  by  sulphuric  acid.  An  excess  of 
alumina  also  makes  glass  very  easily  attacked  by  acids,  even  by  the  bitartrate  of 
potassa  in  wines.  In  common  with  all  natural  and  artificial  silicates,  glass  is  attacked 
by  hydrofluoric  acid,  with  the  formation  of  the  volatile  fluoride  of  silicon.  (See  tho 
Treatise  on  Glass,  in  Knapp's  Chemical  Technology,  edited  by  Ilonalds  and  Richard 
son,  vol.  ii.) 

Ultramarine. — This  beautiful  blue  pigment  is  extracted  by  mechanical  operations 
from  the  mineral  Lapis  lazuli.  The  structure  of  the  mineral  is  granular  and  slightly 
laminated  :  its  constituents  are,  silicic  acid  45.40,  alumina  31.67,  soda  9.09,  sulphu- 
ric acid  5.89,  sulphur  0.95,  lime  3.52,  iron  0.86,  chlorine  0.42,  water  0.12  =  97.92. 
It  was  first  imitated  successfully  by  M.  Guimet  in  1827.  The  process,  according  to 
M.  Debette,  appears  to  be  first  the  preparation  of  a  polysulphide  of  sodium,  which 
is  afterwards  calcined  with  prepared  clay  and  protosulphate  of  iron,  so  as  to  form 
sulphide  of  iron.  The  last  product  in  fine  powder  is  heated  in  a  muffle  with  exposure 
to  air  for  several  hours,  when  it  becomes  in  succession  brown,  red,  green,  and  blue. 
The  excess  of  sulphide  of  sodium  and  other  salts  is  washed  out  of  the  powder,  which, 
dried  and  washed  again  at  a  moderate  temperature,  gives  an  ultramarine  of  a  magni- 
ficent blue  tint.  '  The  process  is  an  extremely  delicate  one,  and  the  nature  of  the 
substance  which  gives  the  blue  colour  is  very  obscure.  A  sulphide  of  sodium  is 
supposed  to  be  essential  to  its  composition,  as  the  colour  is  destroyed  by  acids,  with 
evolution  of  the  hydrosulphuric  acid ;  while  the  substitution  of  carbonate  of  potassa 
for  carbonate  of  soda  gives  a  compound  corresponding  to  ultramarine,  but  which  is 
colourless.  (Pelouze  et  Freuiy,  Cours  de  Chirn.  G£ner.  ii.  117). 

SECTION  III. 

LITHIUM. 

Eg.  6.43  or  80.37 ;  Li. 

Lithium  is  the  metallic  basis  of  a  rare  alkaline  oxide,  lithia,  discovered  in  1818 
by  Arfwedson.  (Ann.  de  Ch.  et  de  Ph.  x.  82).  The  name  lithia  (from  \i0cu*, 
stony)  was  applied  to  it,  from  its  having  been  first  derived  from  an  earthy  mineral. 
The  metal  was  obtained  by  Davy  by  the  voltaic  decomposition  of  lithia,  and  observed 
to  be  white,  resembling  sodium,  and  to  be  highly  oxidable.  The  equivalent  of 
lithium  is  much  smaller  than  that  of  any  other  metal,  and  its  oxide  has-  therefore  a 
high  saturating  power. 

Lithia ;  LiO.  —  The  only  known  oxide  of  lithium  is  a  protoxide.  It  exists  in 
small  quantities  in  the  minerals  spodumene  or  triphane,  petalite,  and  lepidolite ;  but 
the  mineral  containing  lithia,  which  is  most  abundant,  is  a  native  phosphate  occurring 
at  Rabenstein  in  Bavaria,  and  which  consists  of  phosphoric  acid  42.64,  oxide  of  iron 
49.16,  oxide  of  manganese  4.75,  and  lithia  3.45.  This  mineral  is  dissolved  in 
hydrochloric  acid,  the  iron  peroxidized  by  a  little  nitric  acid,  the  solution  diluted 


BARIUM.  403 

with  water,  and  then  ammonia  added,  which  precipitates  the  insoluble  phosphate  of 
sesquioxide  of  iron.  The  manganese  is  afterwards  removed  by  hydrosulphuric  acid, 
the  liquid  filtered,  evaporated  to  dryness,  and  the  residue  calcined  to  volatilize  the 
ammoniacal  salts ;  the  chloride  of  lithium  is  then  taken  up  by  alcohol. 

The  hydrate  of  lithia  resembles  hydrate  of  potassa  in  causticity,  but  is  less  soluble 
in  water,  and  loses  its  combined  water  at  an  elevated  temperature.  Sulphur  acts 
upon  it  in  the  same  manner  as  upon  potassa.  Its  salts  are  colourless. 

The  chloride  is  very  soluble  in  water,  as  well  as  in  absolute  alcohol,  and  fuses  at 
a  high  temperature.  It  crystallizes  in  cubes  containing  4  HO. 

The  carbonate  of  lithia  has  a  certain  degree  of  solubility,  and  its  solution  has  an 
alkaline  reaction,  properties  upon  which  the  claim  of  lithia  to  be  ranked  among  the 
alkalies,  instead  of  the  alkaline  earths,  is  chiefly  rested.  The  fluoride  of  lithium 
has  the  sparing  solubility  of  the  carbonate. 

The  sulphate  of  lithia  is  soluble,  and  presents  itself  in  fine  crystals,  which  are 
persistent  in  air.  It  forms  a  double  salt  with  sulphate  of  soda,  of  which  the  formula 
is  LiO.SO3  +  NaO.S03+6HO.  The  nitrate  and  acetate  are  both  very  soluble  and 
deliquescent. 

Tbe  neutral  phosphate  of  lithia  is  slightly  soluble  in  water,  but  considerably  more 
so  than  the  double  phosphate  of  lithia  and  soda,  which  remains  as  an  insoluble 
powder  when  the  solution  of  lithia  is  evaporated  to  dryness  with  that  of  phosphate 
of  soda.  Hence  phosphate  of  soda  is  used  as  a  test  of  lithia.  The  salts  of  lithia 
are  also  recognized,  when  heated  on  platinum  wire  before  the  blow-pipe,  by  tinging 
the  flame  of  a  red  colour. 

[See  Supplement,  p.  811.] 


OKDER  II. 

METALLIC   BASES   OP   THE   ALKALINE   EARTHS. 
SECTION     I. 
BARIUM. 

Eq.  68.64. or  858 ;  Ba. 

Barium,  the  metallic  basis  of  the  earth  baryta,  was  obtained  by  Davy  in  1808, 
by  the  voltaic  decomposition  of  moistened  carbonate  of  baryta  in  contact  with  mer- 
cury :  it  may  likewise  be  procured  by  passing  potassium  in  vapour  over  baryta 
heated  to  redness  in  an  iron  tube,  and  afterwards  withdrawing  the  reduced  barium, 
which  the  residue  contains,  by  means  of  mercury.  The  latter  metal  is  separated  by 
distillation  in  a  glass  retort,  care  being  taken  not  to  raise  the  temperature  to  redness, 
for  the  barium  then  decomposes  glass.  Barium  is  a  white  metal  like  silver,  fusible 
under  a  red  heat,  denser  than  oil  of  vitriol,  in  which  it  sinks.  It  oxidates  with 
vivacity  in  water,  disengages  hydrogen,  and  is  converted  into  baryta.  It  is  named 
barium  (from  jSopwss  heavy),  in  allusion  to  the  great  density  of  its  compounds. 

Baryta;  BaO,  76.64  or  958.  —  This  earth  exists  in  several  minerals,  of  which 
the  most  abundant  are  sulphate  of  baryta  or  heavy-spar,  and  the  carbonate  of  baryta 
or  witherite.  The  earth  is  obtained  in  the  anhydrous  condition  and  pure,  by  cal- 
cinating nitrate  of  baryta,  at  a  bright-red  heat,  in  a  porcelain  retort,  or  in  a  well- 
covered  crucible  of  porcelain  or  silver,  but  not  of  platinum.  Baryta  is  a  grey  pow- 
der, of  which  the  density  is  about  4.  When  heated  to  redness  in  a  porcelain  tube, 
and  oxygen  gas  passed  over  it,  it  absorbs  that  gas  with  avidity,  and  becomes  binoxide 
of  barium,  the  compound  for  the  preparation  of  which  anhydrous  baryta  is  chiefly 
required.  Baryta  slakes  and  falls  to  powder  when  water  is  thrown  upon  it,  com- 


404  BARIUM. 

bining  with  one  equivalent  of  water  with  the  evolution  of  so  much  heat  as  to  become 
incandescent. 

Hydrate  of  baryta  is  a  valuable  reagent.  Of  the  different  processes  for  this  sub- 
stance, one  of  the  most  convenient  is  that  from  the  native  sulphate.  This  is  a  soft 
mineral,  and  easily  reduced  to  an  impalpable  powder,  which  is  intimately  mixed 
with  one-eighth  of  its  weight  of  coal  pounded  and  sifted,  or  with  one-third  charcoal- 
powder  and  one-fourth  resin ;  the  mixture  is  introduced  into  a  Cornish  crucible,  and 
exposed  in  a  furnace  to  a  bright-red  heat  for  an  hour.  The  sulphate  is  converted  by 
this  treatment  into  sulphide  of  barium ;  the  last  salt  is  dissolved  out  of  the  black 
residuary  mass  by  boiling  water,  and  the  solution,  which  generally  has  a  yellow  tint 
but  is  sometimes  colourless,  is  filtered  while  still  hot.  The  solution,  if  strong,  may 
crystallize  on  cooling,  in  thin  plates.  As  the  sulphide  absorbs  oxygen  from  the  air, 
and  returns  to  the  state  of  sulphate  of  baryta,  it  must  not  be  exposed  long  in  open 
vessels.  To  a  boiling  solution  of  sulphide  of  barium  in  a  flask,  black  oxide  of 
copper  from  the  nitrate  is  added,  in  successive  small  portions,  till  a  drop  of  the  liquid 
ceases  to  blacken  a  solution  of  lead,  and  precipitates  it  entirely  white :  the  liquid 
then  contains  only  hydrate  of  baryta  in  solution.  It  may  immediately  be  filtered, 
with  little  access  of  air,  to  prevent  absorption  of  carbonic  acid.  The  decomposition 
in  this  process,  for  which  we  are  indebted  to  Dr.  Mohr  of  Coblentz,  is  rather  com- 
plicated. Six  eq.  of  sulphide  of  barium  and  8  eq.  of  oxide  of  copper  producing  5 
eq.  of  baryta,  1  eq.  of  hyposulphite  of  baryta,  and  4  eq.  of  subsulphide  of  copper, 
of  which  the  first  only  is  soluble : 

6  BaS  and  8CuO=5BaO  and  BaO.S202  and  4Cu2S. 

Binoxide  of  manganese  may  be  substituted  in  this  process  for  oxide  of  copper,  but 
generally  gives  a  solution  of  baryta  coloured  by  some  impurity.  The  reaction  is 
then  similar : 

6BaS  and  4Mn02=5BaO  and  BaO.S202  and  4MnS. 

If  the  solution  of  sulphide  of  barium  has  been  concentrated,  the  greater  part  of  the 
hydrate  of  baryta  separates  on  cooling  in  voluminous  and  transparent  crystals,  con- 
taining 10HO. 

Hydrate  of  baryta  may  also  be  obtained  by  adding  caustic  potassa  to  a  saturated 
solution  of  chloride  of  barium ;  hydrate  of  baryta  precipitates,  and  must  be  redis- 
solved  in  boiling  water,  and  crystallized  by  cooling,  to  purify  it.  It  is  soluble  in  3 
parts  of  boiling  water,  and  in  20  parts  of  water  at  60°.  Baryta  retains  1  eq.  of 
water  with  great  force  like  the  fixed  alkalies.  This  combination  is  fusible  a  little 
below  redness,  and  runs  like  an  oil;  it  congeals  into  a  crystalline  mass,  which 
attracts  carbonic  acid  very  slowly  from  air,  and  is  therefore  the  most  favourably 
position  in  which  to  preserve  hydrate  of  baryta. 

The  solution  of  baryta  is  strongly  caustic,  although  less  so  than  potassa  or  soda, 
and  disorganizes  organic  matter  rapidly ;  it  is  poisonous,  in  common  with  all  the 
soluble  preparations  of  barium.  Chlorine  decomposes  baryta  in  the  same  manner  as 
it-  does  the  alkalies.  Sulphur  is  dissolved  in  the  solution  of  baryta  with  the  aid  of 
heat,  and,  according  to  the  temperature,  a  sulphate  or  hyposulphite  is  formed,  with 
the  trisulphide  of  barium  of  a  green  colour.  When  heated  to  redness  in  the  vapour 
of  phosphorus,  baryta  is  converted  into  phosphate  of  baryta  and  phosphide  of  barium. 
On  dropping  oil  of  vitriol  upon  dry  baryta  and  strontia,  the  combination  is  said  to 
produce  light  with  the  first,  but  not  with  the  second.  Baryta,  whether  free  or  in 
combination  with  an  acid  as  a  soluble  salt,  is  discovered  by  means  of  sulphuric  acid, 
which  throws  down  sulphate  of  baryta,  a  compound  not  decomposed  by,  nor  soluble 
in,  nitric  and  hydrochloric  acids. 

Binoxide  of  barium;  Ba02;  84.64  or  1058. — This  compound  is  prepared  by 
exposing  anhydrous  baryta,  from  the  nitrate,  to  pure  oxygen  at  a  red  heat;  or  by 
heating  pure  baryta  to  low  redness  in  a  porcelain-crucible,  and  then  gradually  adding 
chlorate  of  potassa,  in  the  proportion  of  about  1  part  of  the  latter  to  4  of  the  former. 


BARIUM.  405 

The  chloride  of  potassium  formed  at  the  same  time,  is  removed,  by  cold  water,  from 
the  binoxide  of  barium,  while  the  latter  unites  with  6HO.  Binoxide  of  barium, 
when  decomposed  by  dilute  acids  with  proper  precautions,  affords  binoxide  of 
hydrogen. 

Chloride  of  barium;  BaCl-f2HO;  104.14+18  or  1301.76+225.  — A  reagent 
of  constant  use,  which  is  obtained  by  dissolving  native  carbonate  of  baryta  in  pure 
hydrochloric  acid  diluted  with  3  or  4  times  its  bulk  of  water,  or  by  neutralizing  sul- 
phide of  barium  by  the  same  acid.  It  crystallizes  from  a  concentrated  solution  in 
flat  four-sided  tables,  bevelled  at  the  edges.  The  crystals  contain  2HO  (14.75  per 
cent,  of  water),  which  they  lose  h,elow  212°.  They  are  said  to  be  loluble  in  400 
parts  of  anhydrous  alcohol :  100  parts  of  water  dissolve  43.5  parts  at  60°,  and  78 
parts  at  222°,  which  is  the  boiling-point  of  the  solution. 

Carbonate  of  baryta;  BaO.C02;  98.64  or  1233.01.  — This  salt  consists  in  100 
parts  of  22.41  carbonic  acid,  and  77.59  baryta.  The  density  of  the  native  carbonate 
is  4.331 ;  it  is  not  attacked  by  sulphuric  acid,  and  retains  its  carbonic  acid  at  the 
highest  temperatures.  The  precipitated  carbonate  is  decomposed  by  sulphuric  acid, 
and  loses  its  carbonic  acid  when  calcined  at  a  white  heat,  in  contact  with  carbonaceous 
matter.  It  is  obtained  of  greater  purity  when  precipitated  by  the  carbonate  of  am- 
monia, than  by  the  carbonate  of  potassa  or  soda,  portions  of  which  are  apt  to  go 
down  in  combination  with  carbonate  of  baryta.  Although  reputed  an  insoluble  salt, 
carbonate  of  baryta  is  soluble  in  2300  parts  of  boiling  water,  and  in  4300  parts  of 
cold  water.  It  is  still  more  soluble  in  water  containing  carbonic  acid,  and  is  highly 
poisonous.  The  precipitated  carbonate  of  baryta,  or,  better,  the  hydrate  of  baryta, 
is  employed  in  the  analysis  of  silicious  minerals,  containing  an  alkali,  which  are  not 
soluble  in  an  acid.  The  mineral,  in  the  state  of  an  impalpable  powder,  is  intimately 
mixed  with  4  or  5  times  its  weight  of  the  hydrate,  and  exposed  in  a  silver-crucible 
to  a  red  heat,  which  occasions  a  semi-fusion  of  the  mixture  and  the  decomposition 
of  the  silicates;  the  mineral  afterwards  dissolving  entirely  in  an  acid,  with  the 
exception  of  its  silica. 

Sulphate  of  baryta;  BaO.S03;  116.64  or  1458.01.  — This  salt  consists,  in  100 
parts,  of  34.37  sulphuric  acid  and  65.63  baryta.  The  density  of  heavy-spar,  or  the 
native  sulphate,  varies  from  4  to  4.47.  It  occurs  in  considerable  quantities  in  trap 
and  other  igneous  rocks,  forming  often  veins  of  several  feet  in  thickness,  and  miles 
in  extent.  It  is  mined  for  the  purpose  of  being  substituted  for  carbonate  of  lead,  or 
being  mixed  with  that  substance,  when  used  as  a  pigment.  When  chloride  of  barium 
is  added  to  sulphuric  acid,  or  to  a  soluble  sulphate,  at  the  boiling  temperature,  sul- 
phate of  baryta  precipitates  readily,  in  a  dense  crystalline  powder,  which  may  easily 
be  collected  and  washed  on  a  filter.  It  is  completely  insoluble  in  water  and  dilute 
acids,  but  is  soluble  in  concentrated  and  boiling  sulphuric  acid,  fromVLieh  it  crys- 
tallizes on  cooling.  Precipitated  sulphate  of  baryta  is  partially  decomposed  in  a 
concentrated  and  boiling  solution  of  carbonate  of  potassa  or  soda,  and  ca/bonate  of 
baryta  formed.  • 

Nitrate  of  baryta;  BaO.N05;  130.64  or  1633.01.  —  This  salt  crystallizes  in 
fine  transparent  octohedrons,  which  are  anhydrous.  It  is  obtained  by  dissolving 
carbonate  of  baryta  in  nitric  acid  diluted  with  8  or  10  times  its  weight  of  water;  or 
by  mixing  the  acid,  also  in  a  diluted  state,  with  the  solution  of  sulphide  of  barium. 
It  requires  12  parts  of  water  at  60°,  and  3  or  4  parts  of  boiling  water,  for  solution ; 
it  is  insoluble  in  alcohol.  The  nitrate  pf  baryta  is  employed  as  a  reagent,  and 
also  in  procuring  anhydrous  baryta. 

The  chlorate  and  hyposulphate  of  baryta  are  soluble,  the  iodate,  sul^"  ;ta  hypo- 
sulphite and  phosphates  of  baryta,  insoluble  salts. 

[See  Supplement,  p.  812.] 


406  STRONTIA. 

SECTION   II. 

STRONTIUM. 

Eq.  43.84  or  548.02.     Sr. 

Strontium  is  prepared  iii  the  same  way  as  barium,  which  it  greatly  resembles.  It 
is  a  white  metal,  denser  than  oil  of  vitriol.  It  derives  its  name  from  Strontian,  a 
mining  village  in  Argyleshire. 

Strontia,  Strontian,  or  Strontites ;  SrO;  51.84  or  648.02.  —  The  native  carbo- 
nate of  strontia  was  first  distinguished  from  carbonate  of  baryta  by  Dr.  Crawford,  in 
1790,  who  conceived  the  idea  that  the  former  mineral  might  contain  a  new  earth. 
This  conjecture  was  verified  in  1793,  by  Dr.  Hope  (Edinb.  Trans,  iv.  14);  and 
much  about  the  same  time  also  by  Klaproth.  The  earth,  strontia,  is  to  baryta  what 
soda  is  to  potassa.  It  occurs  in  nature  as  carbonate  and  more  abundantly  as  sul- 
phate. Strontia  may  be  prepared  by  a  strong  calcination  of  the  native  carbonate  in 
contact  with  carbon.  It  is  lighter  than  baryta,  and  has  a  taste  which  is  less  acrid 
and  caustic,  but  stronger  than  that  of  lime.  It  is  said  not  to  be  poisonous.  The 
hydrate  crystallizes  with  9HO,  but  retains  only  one  equivalent  at  212°  (Mr.  Smith). 
This  last  hydrate  enters  into  fusion  at  a  very  high  temperature,  without  losing  its 
combined  water.  The  anhydrous  earth,  like  baryta,  is  infusible.  The  crystallized 
hydrate  requires  52  parts  of  water  to  dissolve  it  at  60°,  but  only  twice  its  weight 
at  212°. 

The  soluble  salts  of  strontia  are  prepared  from  the  carbonate.  They  are  precipi- 
tated by  sulphuric  acid  and  by  soluble  sulphates,  but  not  so  completely  as  the  salts 
of  baryta,  the  sulphate  of  strontia  having  a  small  degree  of  solubility.  Hence, 
when  sulphate  of  soda  is  added  in  excess  to  a  salt  of  strontia,  and  the  precipitate 
separated  by  filtration,  so  much  sulphate  of  strontia  remains  in  solution,  that  the 
liquid  yields  a  white  precipitate  with  carbonate  of  soda  (Dr.  Turner).  Most  of  the 
salts  of  strontia,  when  heated  on  platinum-wire  before  the  blow-pipe,  communicate  a 
red  colour  to  the  flame.  Baryta  and  strontia  in  solution  may  be  separated  by  hydro- 
fluosilicic  acid,  which  precipitates  baryta,  but  forms  with  strontia  a  salt  very  soluble 
in  a  slight  excess  of  acid.  Hyposulphite  of  strontia  being  soluble,  while  hyposul- 
phite of  baryta  is  insoluble,  these  earths  may  also  be  distinguished  by  means  of 
hyposulphite  of  soda. 

Binoxide  of  strontium,  obtained  by  Thenard  in  brilliant  crystalline  scales,  on 
adding  binoxide  of  hydrogen  to  a  solution  of  strontia.  It  contains  two  eq.  of 
oxygen. 

Chloride  of  strontium  crystallizes  'in  slender  prisms,  which  contain  9HO,  and 
are  slightly  deliquescent.  This  salt  is /soluble  in  three-fourths  of  its  weight  of  cold 
water,  and  in  all  proportions  in  boiling  water.  At  the  ordinary  temperature  it  dis- 
solves in  24  parts  of  anhydrous  alcohol,  and  in  19  parts  of  alcohol  boiling.  In  this 
respect  it  differs  from  chloride  of  barium,  which  is  insoluble  in  alcohol.  Chloride 
of  strontium  communicates  to  flame  a  fine  red  tint.  In  the  anhydrous  condition  this 
chloride  absorbs  4  eq.  of  ammonia,  and  becomes  a  white  bulky  powder. 

Carbonate  of  strontia  forms  the  mineral  strontianite,  which  generally  has  a 
fibrous  texture,  and  is  sometimes  transparent  and  colourless,  but  generally  has  a 
tinge  of  yellow  or  green.  Its  density  varies  from  3.4  to  3.726.  This  salt  is  said 
to  be  soluble  in  1536  parts  of  boiling  water.  It  is  more  soluble  in  water  containing 
carbonic  acid,  and  occurs  in  some  mineral  waters.  It  retains  its  carbonic  acid  when 
calcined. 

Sulphate  of  strontia  is  known  as  celesfine,  and  occurs  in  regular  crystals  of  the 
same  form  as  sulphate  of  baryta.  Its  density  is  about  3.89.  It  is  soluble  in  from 
3000  to  4000  parts  of  water,  and  the  solution  is  sensibly  precipitated  by  chloride  of 
barium.  The  mineral  is  found  in  considerable  quantity  associated  with  volcanic  sul- 


LIME.  407 

phur,  and  in  other  formations.  A  large  deposit  of  it  exits  in  the  neighbourhood  of 
Bristol,  from  which  it  may  be  obtained  in  sufficient  quantity  for  any  application  in 
the  arts.  The  various  compounds  of  strontium  may  be  prepared  from  the  sulphate 
of  strontia  precisely  in  the  same  manner  as  those  of  barium  from  the  sulphate  of 
baryta. 

Hyposulphite  of  strontia  is  crystallizable,  and  soluble  in  4  parts  of  cold,  and  If 
parts  of  boiling  water.  It  loses  31  per  cent,  of  water  of  crystallization  between  122° 
and  140°,  without  any  other  change. 

Nitrale  of  strontia  crystallizes  at  a  high  temperature  in  regular  octohedrons,  of 
density  2.857,  which  are  anhydrous,  but  it  is  generally  obtained  at  a  low  tempera- 
ture in  crystals,  which  contain  5HO,  of  density  2.113  (Filhol).  The  anhydrous 
salt  dissolves  in  5  parts  of  cold  water,  and  in  1  part  of  boiling  water.  A  deflagrating 
mixture,  which  produces  an  intensely  red  illumination,  is  formed  of  40  parts  of 
nitrate  of  strontia,  13  parts  of  flowers  of  sulphur,  5  parts  of  chlorate  of  potassa,  and 
4  parts  of  sulphide  of  antimony. 

The  salts  of  baryta,  strontia,  and  protoxide  of  lead,  are  strictly  isomorphous,  and 
greatly  resemble  each  other  in  solubility  and  other  properties.  Hydrofluosilicic  acid 
is  employed  to  separate  baryta  from  strontia,  as  it  precipitates  the  former  but  not 
the  latter.  Neutral  chromate  of  potassa,  which  precipitates  salts  of  baryta  imme- 
diately, precipitates  only  slowly  the  salts  of  strontia.  In  analysis,  strontia  is  gene- 
rally estimated  as  sulphate,  but  as  the  latter  is  not  completely  insoluble,  an  addition 
of  alcohol  is  made  to  the  water  employed  to  wash  the  precipitate. 
[See  Supplement,  p.  814.] 

SECTION  III. 

CALCIUM. 

Eg.  20,  or  250  j  Ca. 

Davy  obtained  evidence  of  the  existence  of  this  metal,  and  of  its  analogy  to  the 
preceding  metals.  It  is  the  basis  of  lime.  The  name  applied  to  it  is  derived  from 
calx.  [See  Supplement,  p.  815.] 

Lime ;  CaO ;  28,  or  350. — Uncombined  lime,  or  quicklime,  as  it  is  termed  in  the 
arts,  is  obtained  by  heating  masses  of  limestone  (carbonate  of  lime)  to  redness  in 
an  open  fire,  or  lime-kiln.  The  escape  of  the  carbonic  acid  is  favoured  by  the  pre- 
sence of  aqueous  vapour  and  the  gases  of  the  fire,  into  which  that  gas  can  diffuse 
(page  181).  In  a  covered  crucible,  carbonate  of  lime  may  be  fused  by  heat  with- 
out decomposition.  The  lime,  properly  burnt,  remains  in  porous  masses,  which  may 
be  easily  separated  from  the  ashes  of  the  fuel,  and  are  sufficiently  hard  to  be  trans- 
ported from  place  to  place  without  falling  to  pieces.  Although  these  masses  appear 
light,  the  density  of  lime  is  not  less  than  2.3,  or  even  3.08,  according  to  Royer  and 
Pumas.  Water  thrown  upon  them,  is  first  imbibed,  and  afterwards  combines  with 
the  lime,  which  falls  to  powder  in  the  state  of  hydrate,  and  is  then  said  to  be  slaked. 
In  this  combination  the  temperature  may  rise  to  572°,  (300°  C.),  or  sufficiently 
high  to  char  wood.  From  its  affinity  for  water,  quicklime  is  applied  to  deprive  cer- 
tain liquids,  such  as  alcohol,  of  the  water  they  contain.  To  obtain  pure  lime,  the 
crystallized  carbonate  should  be  calcined,  such  as  calcareous  spar,  or  Carrara  marble. 
Lime,  in  common  with  other  infusible  earths,  phosphoresces  strongly  when  heated  to 
full  redness. 

The  only  hydrate  of  lime  known  contains  1  eq.  of  water,  which  it  loses  at  a  low- 
red  heat.  It  is  sparingly  soluble  in  water,  but  more  soluble  in  cold  than  in  hot 
water.  According  to  Dalton,  lime-water  formed  at  60°,  130°,  and  212°,  contains  1 
grain  of  lime  in  778, 972,  and  1270  grains  of  water.  Hence  water  saturated  in  the 
cold  deposits  hydrate  of  lime  when  boiled.  By  evaporating  the  solution  in  vacuo, 
Gay-Lussac  obtained  the  same  hydrate  of  lime  in  small  transparent  crystals  of  the 


408  CALCIUM. 

hexahedral  form.  The  milk  or  cream  of  lime  is  merely  the  hydrate  diffused  through 
water.  In  preparing  lime-water,  3  or  4  ounces  of  slaked  lime  are  agitated  several 
times,  during  two  or  three  hours,  with  two  quarts  of  distilled  water,  and  then 
allowed  to  settle.  The  lime-water  first  drawn  off  generally  contains  a  little  potassa, 
and  should  not  therefore  be  considered  pure.  Lime-water  has  a  harsh  acrid  taste,  is 
alkaline,  and,  to  a  certain  extent,  caustic.  It  precipitates  carbonic,  silicic,  boracic, 
and  phosphoric  acids  from  solutions  of  their  alkaline  salts.  It  dissolves  oxide  of 
lead.  Lime-water  absorbs  carbonic  acid  rapidly  from  the  air,  and  becomes  covered 
by  a  pellicle  of  carbonate  of  lime.  Hydrate  of  lime  has  the  same  property,  absorb- 
ing about  half  an  equivalent  of  carbonic  acid  with  avidity,  but  not  acquiring  quite 
so  much  as  three-fourths  of  an  equivalent  by  two  or  three  weeks'  exposure  to  an 
atmosphere  of  the  gas.  Fuchs  observed,  that  when  hydrate  of  lime  is  exposed  to 
air,  it  absorbs  only  half  an  equivalent  of  carbonic  acid,  and  that  a  definite  compound 
of  hydrate  and  carbonate  was  formed.  In  the  anhydrous  condition,  lime  exhibits 
no  affinity  for  carbonic  acid. 

Lime  is  characterized  by  affording  a  bulky  precipitate  of  sulphate  of  lime,  when 
sulphuric  acid  is  added  to  its  soluble  salts.  But  as  the  sulphate  of  lime  has  a  certain 
degree  of  solubility,  this  precipitate  does  not  appear  in  very  dilute  solutions  of  these 
salts,  nor  in  lime-water,  a  property  by  which  lime  may  be  distinguished  from  baryta 
and  strontia.  Sulphate  of  lime  may  also,  when  precipitated,  be  re-dissolved  by  the 
addition  of  nitric  acid.  Lime  is  entirely  precipitated  from  neutral  solutions  by 
oxalate  of  ammonia,  the  oxalate  of  lime  being  completely  insoluble.  In  the  quan- 
titative estimation  of  this  earth,  it  is  therefore  generally  thrown  down  as  oxalate,  and 
afterwards  obtained  as  carbonate  of  lime,  by  heating  the  oxalate  nearly  to  redness 
in  a  platinum  crucible,  in  which  a  small  fragment  of  carbonate  of  ammonia  is  dissi- 
pated' at  the  same  time,  to  prevent  any  lime  becoming  caustic  by  loss  of  carbonic 
acid. 

Lime  is  applied  to  a  variety  of  useful  purposes  in  ordinary  life  and  in  the  arts,  of 
which  the  most  important  are  its  applications  as  a  manure  for  land,  and  as  mortar. 
In  the  first  application,  lime  appears  to  be  chiefly  useful,  (1)  in  promoting  the  oxi- 
dation and  decomposition  of  the  insoluble  organic  matters  which  the  soil  contains, 
and  thereby  rendering  them  capable  of  sustaining  vegetable  life ;  (2)  in  decomposing 
clay  and  rendering  its  potassa  soluble,  and  (3)  in  restoring  to  the  soil  the  calcareous 
element  which  is  annually  removed  in  the  crop.  In  the  formation  of  mortar,  the 
hydrate  of  lime  is  mixed  with  2  parts  of  coarse,  or  3  parts  of  fine  sand,  and  made 
into  a  paste  with  water.  In  building,  a  stone  is  laid  upon  a  bed  of  this  paste,  which 
it  compresses  by  its  weight,  imbibing  moisture  also  from  the  mortar,  which  escapes 
principally  through  the  porous  stone.  On  drying,  the  mortar  binds  the  stones  be- 
tween which  it  is  interposed,  and  its  own  particles  cohere  so  as  to  form  a  hard  mass, 
solely  by  the  attraction  of  aggregation,  for  no  chemical  combination  takes  place  be- 
tween the  lime  and  sand,  and  the  stones  are  simply  united  as  two  pieces  of  wood  are 
by  glue.  The  sand  is  useful  in  rendering  insignificant  by  its  mass  the  contraction 
of  the  mortar  on  drying,  and  also,  from  the  large  size  of  its  grains,  in  rendering  the 
dry  mortar  less  short  and  friable.  The  mortar  is  subject  to  an  ulterior  change,  from 
the  slow  absorption  of  carbonic  acid,  but  even  in  the  oldest  mortar  the  conversion 
of  the  hydrate  of  lime  into  carbonate  is  never  complete.  The  lime  which  is  called 
fat  slakes  easily,  and  with  considerable  increase  of  volume ;  lean  or  poor  lime  slakes 
imperfectly,  owing  frequently  to  the  presence  of  magnesia  in  a  proportion  exceeding 
10  or  12  per  cent  ]  the  latter  earth  having  a  comparatively  feeble  affinity  for  water. 
Magnesian  lime  is  also  generally  considered  prejudicial  in  agriculture,  owing,  it  is 
supposed,  to  the  magnesia  long  remaining  caustic  in  the  soil. 

Some  limestones,  containing  about  20  per  cent  of  clay  or  silicate  of  alumina,  afford 
lime  which  possesses  a  valuable  property,  that  of  forming  with  water  a  mass  which 
becomes  solid  in  a  few  minutes,  and  therefore  hardens  in  structures  covered  by 
water.  An  excellent  hydraulic  mortar  of  this  kind  is  obtained  from  concretionary 
masses  found  in  marl,  and  also  as  isolated1  blocks  in  the  bed  of  tbr>  Thames.  This 


LIME.  409 

lime  being  burnt,  ground,  and  sifted,  when  mixed  with  water  to  form  a  paste,  sets 
RS  quickly  as  Paris  plaster ;  its  solidity  increases  with  the  time  it  has  been  submerged, 
and  it  ends  by  acquiring  the  hardness  of  limestone.  Sand  is  added  to  it  when  it  is 
used  as  common  mortar,  or  in  covering  buildings  to  imitate  stone.  From  the  minute 
division  of  the  silicic  acid  and  alumina  in  this  mortar,  their  combination  with  lime 
is  more  likely  to  occur  than  in  ordinary  mortar.  Still  the  first  setting  of  hydraulic 
mortar  seems  to  be  due  simply  to  the  fixation  of  water,  and  formation  of  a  solid 
hydrate  like  gypsum.  Hydraulic  mortar  is  sometimes  made  by  mixing  together 
clay  and  chalk,  and  calcining  the  mixture,  or  more  frequently  by  adding  to  hydrate 
of  lime  puzzolano  ground  to  fine  powder.  The  latter  is  a  silicious  substance  of 
volcanic  origin,  composed  principally  of  pumice,  of  which  a  stratum  is  excavated  in 
the  neighbourhood  of  Naples.  The  mortar  which  it  makes  with  lime  has  obtained 
the  name  of  Roman  cement. 

The  hydrate  of  binoxide  of  calcium  precipitates  on  adding  lime-water,  drop  by 
drop,  to  a  solution  of  binoxide  of  hydrogen.  It  contains,  according  to  Thenard,  2 
eq.  of  oxygen. 

The  protomJphide  of  calcium  is  procured  by  decomposing  sulphate  of  lime,  at  a 
red  heat,  by  hydrogen  or  charcoal.  When  newly  prepared,  it  phosphoresces  in  the 
dark.  It  is  only  very  sparingly  soluble  in  water,  but  it  is  decomposed  by  boiling 
water,  according  to  M.  H.  Rose,  into  hydrosulphate  of  sulphide  of  calcium,  which 
is  soluble,  and  hydrate  of  lime.  Sulphide  of  calcium,  when  moistened  with  water, 
is  readily  decomposed  by  a  stream  of  carbonic-acid  gas,  with  the  evolution  of  hydro- 
sulphuric  acid : 

CaS.HO  and  C02=CaO.C02+HS. 

When  hydrate  of  lime  is  boiled  with  sulphur  and  water,  and  the  liquor  allowed 
to  cool  before  it  is  completely  saturated  with  sulphur,  yellow  crystals  separate  from 
it,  which  are  a  bisulphide  of  calcium,  combined  with  3HO,  according  to  the  obser- 
vations of  Herschel.  When  lime,  or  protosulphide  of  calcium,  is  boiled  with  excess 
of  sulphur,  it  dissolves  sulphur  till  a  pentasulphide  of  calcium  is  formed,  which  re- 
sembles in  properties  the  corresponding  degree  of  sulphuration  of  potassium. 

Phosphide  of  calcium.  —  Small  fragments  of  quicklime  being  heated  to  redness 
by  a  spirit-lamp,  in  a  small  mattrass  with  a  long  neck,  and  fragments  of  phosphorus 
dropped  into  the  same  vessel,  a  mixture  is  obtained  of  phosphate  of  Jime  and  phos- 
phide of  calcium.  The  compound  has  a  chocolate-brown  colour.  When  the  tem- 
perature is  raised  too  high,  the  affinities  change,  and  phosphorus  escaping  in  vapour, 
nothing  but  lime  remains.  According  to  M.  P.  Thenard,  in  the  reaction  which 
gives  phosphide  of  calcium,  7  eq.  of  phosphorus  act  upon  14  eq.  of  lime : 

UCaO  and  7P=2(2CaO.P05)  and  5Ca2P. 

The  phosphide,  therefore,  contains  2  eq.  of  calcium  to  1  eq.  of  phosphorus,  and 
is  analogous  to  the  liquid  hydride  of  phosphorus  PH2.  When  thrown  into  water, 
it  is  immediately  transformed  into  the  hydride  of  phosphorus  referred  to,  which  is 
spontaneously  inflammable,  and  hypophosphite  of  lime,  which  is  dissolved. 

Chloride  of  calcium;  CaCl ;  55.50  or  693.75. — Obtained  by  neutralizing  hydro- 
chloric acid  with  carbonate  of  lime,  or  as  a  residue  in  several  processes ;  a  concen- 
trated solution  affords  crystals  in  large  striated  four-sided  prisms,  which  contain  6 
eq.  of  water.  Dried  with  stirring,  above  212°,  it  affords  a  crystalline  powder,  con- 
taining 2  eq.  of  water,  which  produces  an  intense  degree  of  cold  when  mixed  with 
snow  (p.  62).  The  same  hydrate  was  produced  on  drying  the  crystals  in  vacuo  over 
sulphuric  acid  for  ten  days.  The  crystals  are  soluble  in  one-fifteenth  of  their  weight 
of  water  at  60°,  and  exceedingly  deliquescent.  The  salt  is  made  anhydrous  by  heat, 
and  undergoes  the  igneous  fusion  at  a  red  heat.  The  liquid  chloride  is  poured  upon 
a  slab,  and  the  transparent  cake  of  solid  salt  immediately  broken  into  pieces,  and 
preserved  in  a  stoppered  bottle.  It  is  nynch  employed,  from  its  great  affinity  for 
water,  to  dry  gases  and  absorb  moisture.  Chloride  of  calcium  always  acquires  by 


410  CALCIUM. 

fusion  a  slight  but  sensibly  alkaline  reaction  from  partial  decomposition ;  on  which 
account  Liebig  prefers  the  salt  strongly  dried,  but  not  fused,  as  the  hygrometric 
agent  in  organic  analysis.  Ignited  with  the  sulphates  of  baryta  and  strontia,  chlo- 
ride of  calcium  gives  rise  to  sulphate  of  lime  and  the  chlorides  of  barium  and 
strontium.  Ten  parts  of  anhydrous  alcohol  dissolve  7  parts  of  chloride  of  calcium, 
ftt  the  boiling-point,  and  the  solution,  in  cold  weather,  affords  crystals  in  rectangular 
scales,  which  are  an  alcoholate,  containing  2  eq.  of  alcohol,  instead  of  water  of 
crystallization;  CaCl-f  2C4H602.  Anhydrous  chloride  of  calcium  likewise  absorbs 
4  equivalents  of  arnmoniacal  gas,  and  forms  a  bulky  white  powder,  CaCl  +  4NH3, 
from  which  the  ammonia  may  be  easily  expelled  again  by  heat. 

A  solution  of  chloride  of  calcium,  when  boiled  with  hydrate  of  lime,  dissolves 
that  substance,  and  the  solution  filtered  hot,  deposits  an  oxichloride  of  calcium, 
3CaO.CaCl  +  15HO,  in  long  flat  and  thin  crystals.  The  salt  is  decomposed  by 
water  and  alcohol. 

A  compound  of  chloride  of  calcium  with  oxalate  of  lime  containing  water  of 
crystallization,  is  obtained  in  good  crystals,  which  are  persistent  in  air,  by  dissolving 
oxalate  of  lime  to  saturation  in  hot  hydrochloric  acid,  and  allowing  the  solution  to 
cool.  It  consists  of  1  eq.  of  each  salt,  with  7  eq.  of  water.  Oxalate  of  lime  is 
known  to  combine  with  2  eq.  of  water,  of  which  1  eq.  appears  to  remain  in  this 
double  salt,  while  the  other  is  replaced  by  chloride  of  calcium  carrying  its  6  eq.  of 
water  of  crystallization  along  with  it;  CaO.C203  +  (HO.CaCl)  +  6HO.  A  similar 
replacement  is  observed  in  the  formation  of  quadroxalate  of  potassa  (p.  164).'  This 
salt  becomes  anhydrous  without  decomposition  at  266°  (130°  C.)  It  is  decomposed 
by  pure  water. 

Fluoride  of  calcium,  Fluor-spar ;  CaF;  38.70  or  483.80.  —  This  salt  is  pecu- 
liarly a  constituent  of  mineral  veins,  and  occurs  massive,  or  in  transparent  crystals 
which  are  cubes  or  octohedrons,  and  is  often  of  beautiful  colours,  generally  green  or 
purple.  It  is  cut  into  ornamental  forms,  and  is  believed  to  be  the  substance  of 
which  the  vasa  murrina  of  the  Romans  were  .composed.  In  minute  quantity  fluo- 
ride of  calcium  is  very  generally  diffused,  being  found  in  the  earthy  deposit  from 
sea- water  when  boiled  (G-.  Wilson).  It  forms  a  few  thousandths  of  the  earth  of 
bones,  and  a  somewhat  larger  proportion  of  the  enamel  of  the  teeth  :  in  fossil  bones 
the  proportion  of  fluoride  of  calcium  is  considerably  greater  (J.  Middleton,  Mem. 
Chem.  Soc.  ii. -134).  It  is  dissolved  to  a  small  extent  by  water  containing  carbonic 
acid,  like  the  other  insoluble  salts  of  lime;  its  density  varies  from  3.14  to  3.17. 
When  heated  gently,  on  a  plate  of  metal,  it  becomes  luminous  in  the  dark  for  a 
short  time ;  the  phosphorescent  property  may  be  restored  by  passing  electric  sparks 
through  the  crystal  (Griffiths).  Fluoride  of  calcium  is  obtained  in  a  granular  con- 
dition, when  hydrofluoric  acid  is  neutralized  by  freshly  precipitated  carbonate  of 
lime.  But  when  a  neutral  salt  of  lime  is  mixed  with  a  soluble  fluoride,  the  fluoride 
of  calcium  appears  as  a  translucent  gelatinous  mass.  This  fluoride,  whether  artificial 
or  natural,  is  not  decomposed  by  sulphuric  acid  at  a  low  temperature,  but  imbibes 
that  acid,  and  forms  a  thick  ropy  liquid.  At  104°  (40°  C.),  this  mixture  begins  to 
decompose,  and  emits  hydrofluoric  acid.,  Fluoride  of  calcium  resists  the  action  of  a 
solution  of  hydrate  of  potassa,  but  is  easily  decomposed  in  the  dry  way  by  fusion 
with  carbonate  of  potassa,  and  fluoride  of  potassium  is  formed. 


SALTS   OF   LIME. 


Carbonate  of  lime  ;  CaO.C02;  50,  or  625. — This  is  one  of  the  most  abundantly 
diffused  salts  in  nature,  forming  the  basis  of  limestones,  marbles,  marls,  coral-reefs, 
shells,  &c.  It  is  anhydrous,  and  occurs  in  two  incompatible  crystalline  forms,  the 
rhomboidal  crystal  of  Iceland  spar  and  calc-spar,  which,  with  its  numerous  modifica- 
tions, is  much  the  most  abundant,  and  the  six-sided  prism  of  arragonite,  isoraorpbous 
with  carbonate  of  strontia,  which  last  ma^  be  readily  recognized  by  falling  to  powder 
when  heated.  The  grains  of  this  powder  have  the  form  of  calc-spar.  The  density 


SALTS   OF   LIME.  411 

of  carbonate  of  lime  in  these  two  forms  is  sensibly  different,  that  of  calc-spar  being 
2.719,  and  of  arragonite  2.949  (Gr.  Rose).  Carbonate  of  lime  consists  of  56  lime 
and  44  carbonic  acid  in  100  parts. 

Carbonate  of  lime  may  also  be  obtained  in  the  state  of  a  hydrate  by  heating  toge- 
ther very  slightly  1  part  of  hydrate  of  lime,  3  parts  of  sugar,  and  6  parts  of  water, 
filtering  the  solution,  and  leaving  it  exposed  in  a  shallow  vessel.  In  twenty-four 
hours  crystals  appear  upon  the  surface  of  the  liquid,  and  in  fifteen  days  the  whole 
lime  is  generally  converted  into  hydrated  carbonate,  in  the  form  of  sharp  transparent 
rhombs.  The  carbonic  acid  is  absorbed  from  the  atmosphere.  These  crystals  con- 
tain 5  eq.  of  water;  by  boiling  them  in  anhydrous  alcohol,  a  second  definite  hydrate 
is  obtained  containing  3  eq.  of  water,  as  ascertained  by  Pelouze.  The  first  of  these 
hydrates  has  also  been  found  native  in  a  running  stream,  by  Scheerer.  The^two 
hydrates  of  carbonate  of  lime  correspond  in  composition  with  two  crystalline  hydrates 
of  carbonate  of  magnesia. 

Carbonate  of  lime  is  considered  an  insoluble  salt,  although,  according  to  Fresenius, 
one  part  of  carbonate  of  lime  dissolves  in  8834  parts  of  boiling  water,  and  in  10601 
parts  of  water  at  .ordinary  temperatures :  the  solution  is  sensibly  alkaline  to  test- 
paper.  When  recently  precipitated,  carbonate  of  lime  is  much  more  soluble  in  salts 
of  ammonia :  the  solution  of  carbonate  of  lime  in  hydrochlorate  of  ammonia  in 
excess  is  completely  resolved  by  spontaneous  evaporation  into  chloride  of  calcium 
and  carbonate  of  ammonia,  which  escapes.  Sea-water  appears  to  be  essentially 
alkaline  from  the  presence  of  carbonate  of  lime,  a  circumstance  calculated,  therefore, 
to  prevent  the  accumulation  in  the  sea  of  ammonia  in  the  form  of  fixed  salts,  and  to 
cause  the  restoration  of  that  base  to  the  atmosphere.  Carbonate  of  lime  is  soluble 
in  water  containing  carbonic  acid,  and  is  generally  present  in  the  water  of  wells,  and 
in  some  mineral  waters  to  a  considerable  extent.  It  is  deposited  from  the  latter, 
when  exposed  to  air  in  a  gradual  manner  and  in  possession  of  a  crystalline  structure, 
forming  stalactites  and  stalagmites  in  mountain  caverns,  and  calcareous  petrifications, 
when  it  flows  over  wood  and  other  organic  and  destructible  matters,  of  which  it  pre- 
serves the  form.  When  a  current  of  carbonic-acid  gas  is  passed  through  lime-water, 
the  greater  portion,  but  not  the  whole,  of  the  carbonate  of  lime  first  precipitated  is 
re-dissolved  by  the  excess  of  carbonic  acid.  This  solution  yields  on  evaporation  the 
anhydrous  carbonate,  and  no  crystalline  bicarbonate  of  lime  has  been  obtained. 
Carbonate  of  lime  is  decomposed  with  effervescence  by  acids.  At  a  red  heat  it 
parts  with  carbonic  acid,  arid  is  converted  into  quicklime  in  the  manner  already 
described. 

A  crystalline  mineral  was  discovered  by  Boussingault  at  Merida  in  America, 
which  he  ascertained  to  be  a  double  carbonate  of  soda  and  lime,  with  5  eq.  of  water, 
and  named  gaylussite,  in  honour  of  Gay-Lussac.  It  may  be  made  anhydrous  by 
heat,  and  its  two  salts  are  then  separated  by  water. 

The  hardness  of  well  and  river-water,  so  far  as  it  is  due  to  carbonate  of  lime  in 
solution,  may  be  removed  by  a  proper  addition  of  lime-water,  the  free  carbonic  acid 
becoming  carbonate  of  lime,  and  precipitating  together  with  the  portion  of  carbonate 
of  lime  formerly  held  in  solution ;  colouring  and  other  organic  matter  is  carried 
down  at  the  same  time.1  This  elegant  process  has  been  found  to  act  satisfactorily 
on  a  large  scale.  The  proportion  of  carbonate  of  lime,  where  it  is  the  only  alkaline 
substance  in  solution,  may  be  determined  with  great  accuracy  by  neutralizing  8750 
grains  of  the  water  (one  pint),  by  means  of  a  normal  acid  solution  containing 
0.4562  per  cent,  of  hydrochloric  acid  (this  is  319.37  grs.  of  HC1  in  one  gallon,  or 
70000  grs.  of  water,  or  as  much  acid  as  would  neutralize  one  ounce  or  437.5  grs. 

Professor  Clark:  Repertory  of  Patent  Inventions,  October  1841;  a  pamphlet  entitled 
"A  New  Process  for  Purifying  Waters  supplied  .to  the  Metropolis,"  published  by  K.  and  J. 
E.  Taylor;  and  "  On  the  Examination  of  Water  for  its  Hardness,"  Pharmaceutical  Journal, 
vi.  520.  The  instruments  and  test-liquids  required  in  the  examination  of  waters  by  Prof. 
Clark's  method  may  be  obtained  at  Mr.  Griffin's,  in  Baker  street,  London. 


CALCIUM. 

FIG.  185.  of  carbonate  of  lime).  This  test-acid  is  prepared  by  means  of 
pure  carbonate  of  soda,  as  in  the  process  of  alkalimetry  (page  886), 
or  from  the  analysis  of  the  dilute  acid  by  nitrate  of  silver.  The 
measured  quantity  of  water  is  placed  in  an  evaporating  basin,  and 
being  found  alkaline  by  delicate  red  litmus-paper,  the  normal  acid 
is  added  from  the  small  burette  (fig.  185)  graduated  into  ten-grain 
measures,  each  of  which  is  subdivided  into  five,  till  the  point  of 
neutralization  is  reached,  the  liquid  being  heated  towards  the  end 
of  the  operation.  A  small  portion  of  30  or  40  grains  of  the  water 
is  transferred  to  a  small  conical  wine-glass,  and  the  test-paper  left 
in  it  for  several  minutes,  to  obtain  the  indication  of  alkalinity.  To 
save  time,  a  series  of  six  of  these  wine-glasses  is  conveniently  em- 
ployed, each  containing  a  sample  of  the  water  after  successive  ad- 
ditions of  the  test-acid.  Each  ten-grain  measure  of  the  acid  re- 
quired indicates  1  grain  of  carbonate  of  lime  in  1  gallon  of  the 
water,  or  0.000014286  per  cent,  of  carbonate  of  lime.  By  such 
means  a  minutely  accurate  determination  of  alkalinity  may  be  ob- 
tained; one-hundredth  of  a  grain  of  carbonate  of  lime  in  a  pint 
of  water  is  thus  observed.  (Prof.  Clark). 
Sulphate  of  lime,  Gypsum ;  CaO.S03  +  2HO ;  68  +  18  or  850  -f  225.  —  This 
salt  precipitates  as  a  bulky  and  gritty  powder,  when  sulphuric  acid  is  added  to  a 
soluble  salt  of  lime.  Sulphate  of  lime  appears  to  have  nearly  the  same  degree  of 
solubility  at  all  temperatures,  and  requires  460  parts  of  water  for  solution,  according 
to  Bucholz,  or  380  parts  of  cold,  and  388  parts  of  boiling  water,  according  to  Geise. 
It  occurs  in  nature  in  well-formed  crystals,  and  also  in  large  crystalline  masses, 
forming  beds  of  gypsum;  a  mineral  which  contains  2  eq.  of  water,  and  of  which  the 
density  is  2.322  (Royer  and  Dumas).  Prof.  Johnston  likewise  obtained  small  pris- 
matic crystals  of  sulphate  of  lime,  deposited  in  a  steam-boiler,  which  contain  only 
half  an  equivalent  of  water  2(CaO.S03)  +  HO.  Sulphate  of  lime  occurs  in  a  crys- 
talline form,  without  water,  forming  the  mineral  anhydrite.,  of  which  the  density  is 
about  2.96.  Sulphate  of  lime  fuses  at  a  strong  red  heat,  without  decomposition, 
and  on  cooling  assumes  the  crystalline  form  of  the  last  mineral.  To  form  plaster 
of  Paris,  gypsum,  in  pieces  about  the  size  of  a  pigeon's  egg,  is  heated  in  an  oven 
till  it  is  nearly  anhydrous,  and  then  reduced  to  a  powder.  When  this  is  made  into 
a  paste  with  a  little  water,  it  forms  a  hard  coherent  mass,  or  sets,  in  a  minute  or  two, 
with  a  slight  evolution  of  heat.  This  artificial  hydrate,  or  stucco,  has  the  same  com- 
position as  native  gypsum.  If  sulphate  of  lime  has  been  heated  above  300°,  in  dry- 
ing, it  refuses  to  set  afterwards  when  mixed  with  water. 

The  powder  of  hydrated  gypsum  solidifies  also  when  mixed  with  a  solution  of 
potassa,  or  various  salts  of  potassa,  such  as  the  carbonate,  bicarbonate  (in  this  case 
with  violent  effervescence),  sulphate,  and  silicate,  but  not  with  the  chlorate  or 
nitrate  of  potassa,  nor  with  any  salt  of  soda.  Double  salts  are  probably  formed,  as 
it  is  the  alkaline  salts  only  which  are  capable  of  forming  double  salts,  and  are  con- 
sidered bibasic  by  M.  Herhardt,  that  possess  the  remarkable  property  in  question 
(Emmet,  Am.  Jouni.  of  Scien.,  xxiii.  209).  [See  Supplement,  p.  816.] 

Hyposulphite  of  lime  is  formed  by  transmitting  sulphurous  acid  through  sulphide 
of  calcium,  suspended  in  water,  till  the  solution  is  neutral  and  colourless.  The 
solution  is  decomposed  when  heated  above  140°  (60°  C.)  into  sulphur  and  sulphite 
of  lime.  If  evaporated  below  that  temperature,  it  yields  large  hexagonal  prisms  of 
hyposulphite  of  lime,  on  cooling,  which  are  colourless.  They  contain  5  eq.  of  water, 
and  are  persistent  in  air.  The  same  salt  may  be  obtained  very  economically  by  ex- 
posing to  air  the  waste-lime  of  the  dry-lime  gas  purifiers. 

Nitrate  of  lime  is  a  highly  deliquescent  salt,  which  crystallizes  with  6  eq.  of 
water,  like  the  nitrates  of  the  maguesian  class.  It  is  soluble  in  alcohol. 

Phosphates  of  lime. — On  adding  chloride  of  calcium  to  the  tribasic  subphosphate 
tf  soda;  a  corresponding  phosphate  of  lime  precipitates  in  bulky  gelatinous  flakes, 


HTPOCHLORITE   OF   LIME.  413 

of  which  the  formula  is  3CaO.P05.  This  phosphate  occurs  in  nature  in  combina- 
tion with  fluoride  of  calcium  in  the  form  of  hexagonal  prisms,  in  the  minerals  apatite 
and  moroxite.  The  formula  of  apatite  is  CaF  +  3(3CaO.P05).  The  native  phos- 
phates of  lead  occur  in  the  same  form,  with  chloride  of  lead  in  the  place  of  fluoride 
of  calcium.  Hedyphan  is  the  same  mineral,  in  which  a  portion  of  phosphoric  acid 
is  replaced  by  arsenic  acid.  \_See  Supplement,  p.  816.] 

Another  tribasic  phosphate  of  lime  is  obtained  on  adding  the  solution  of  common 
phosphate  of  soda,  drop  by  drop,  to  chloride  of  calcium.  This  precipitate  is  slightly 
crystalline.  Its  formula,  exclusive  of  its  water  of  crystallization,  is  H0.2CaO.P05. 
Again,  when  a  solution  of  phosphate  of  ammonia,  supersaturated  with  ammonia,  is 
treated  with  a  solution  of  chloride  of  calcium,  till  about  one-half  of  the  phosphoric 
acid  is  precipitated,  the  precipitate  contains  51.263  per  cent  of  lime,  and  corresponds 
to  the  formula  8Ca0.3P05  (Berzelius).  A  biphosphate  of  lime  is  also  described  by 
Berzelius,  obtained  on  evaporating  a  solution  of  any  of  the  preceding  salts  in  nitric 
acid  to  the  point  of  crystallization,  of  which  the  probable  formula  is  2HO.CaO.P05. 
There  also  exist  a  pyrophosphate  and  metaphosphate  of  lime.  The  insoluble  phos- 
phates of  lime  are  soluble  in  water  containing  carbonic  acid.  It  is  possibly  in  this 
manner  that  phosphate  of  lime  is  dissolved  by  the  alkaline  animal  fluids. 

Hypochlorite  of  lime  ;  Chloride  of  lime  ;  Bleaching  powder. — This  compound, 
remarkable  for  its  valuable  applications  in  the  arts,  is  generally  prepared  by  exposing 
hydrate  of  lime,  from  the  purest  lime,  to  chlorine-gas,  the  latter  being  supplied  so 
gradually  as  to  prevent  the  heat,  occasioned  by  the  combination,  from  rising  above 
62°.  Chlorine  is  not  absorbed  by  quicklime,  nor  by  the  carbonate  of  lime.  When 
dried  at  212°,  hydrate  of  lime,  I  find,  absorbs  afterwards  little  or  no  chlorine;  but 
dried  over  sulphuric  acid,  without  heat,  it  is,  on  the  contrary,  in  the  most  favourable 
condition  for  becoming  chloride  of  lime.  A  dry,  white,  pulverulent  compound  is 
obtained  by  exposing  the  last  hydrate  to  chlorine,  which  contains  41.2  to  41.4  chlo- 
rine in  100  parts ;  but  of  this  chlorine  about  39  parts  only  are  available  for  bleach- 
ing, owing  to  2  parts  of  that  element  going  to  the  formation  of  chloride  of  calcium 
and  chlorate  of  lime.  A  slight  addition  of  moisture  to  hydrate  of  lime  does  not 
increase  the  proportion  of  chlorine  absorbed,  and  renders  the  compound  less  stable. 
The  above  appears  to  be  the  maximum  absorption  of  chlorine  by  dry  hydrate  of 
lime,  and  is  greater  than  it  would  be  advisable  to  attempt  in  the  manufacture  of 
bleaching  powder,  owing  to  the  occurrence  of  the  partial  decomposition  adverted  to. 
Yet  this  proportion  is  considerably  short  of  1  eq.  of  chlorine  to  1  of  hydrate  of  lime, 
which  are  48.57  chlorine  and  51.43  hydrate  of  lime,  in  100  parts.  The  excess  of 
Time  appears  to  be  useful  in  adding  to  the  stability  of  the  compound.  Labarraque 
mixes  the  hydrate  of  lime  with  ^th  of  its  weight  of  chloride  of  sodium,  by  which 
means  the  absorption  of  chlorine  is  greatly  promoted.  The  bleaching  powder  of 
commerce  may  contain,  when  newly  prepared,  about  30  per  cent,  of  chlorine ;  but 
after  being  kept  for  several  months,  the  proportion  of  available  chlorine  is  found 
more  frequently  below  than  above  10  per  cent.,  so  much  does  it  deteriorate  by 
keeping. 

The  reaction  which  occurs  in  the  formation  of  hypochlorite  of  lime  is  represented 
as  follows : — 

2CaO  and  2C1  =  Ca.Cl  and  CaO.ClO. 

Or  the  product  is  a  mixture  of  chloride  of  calcium  and  hyperchlorite  of  lime. 

The  same  compound  is  obtained  in  solution  by  transmitting  a  stream  of  chlorine-l 
gas  through  hydrate  of  lime  suspended  in  water.  The  lime  then  absorbs  a  full* 
equivalent  of  chlorine,  and  dissolves  entirely. 

Ten  parts  of  water  take  up  the  bleaching  combination  from  one  part  of  dry  chlo- 
ride of  lime,  leaving  undissolved  the  hydrate  of  lime  contained  in  excess.  The 
solution  has  a  slight  odour  of  hypochlorous  acid^  a  rough  astringent  taste,  and  alka- 
line reaction.  It  destroys  most  organic  matters  containing  hydrogen,  including 
colouring  matters.  But  its  bleaching  action  is  not  instantaneous,  unless  an  acid  be 


414  CALCIUM. 

added  to  it,  which  liberates  the  chlorine.  Hence,  when  Turkey-red  cloth,  having  a 
pattern  printed  upon  it  with  tartaric  acid  thickened  by  gum,  is  immersed  for  about 
one  minute  in  this  solution,  it  comes  out  with  the  colour  discharged  where  the  acid 
was  present,  but  elsewhere  uninjured.  In  this  manner  white  figures  are  produced 
upon  a  coloured  ground.  The  solution  of  chloride  of  lime  also  absorbs  and  destroys 
contagious  matters  in  the  atmosphere,  and  is  slowly  decomposed  by  carbonic  acid, 
with  escape  of  chlorine.  The  powder  or  its  solution,  when  heated,  or  when  kept 
for  a  considerable  time,  undergoes  decomposition;  18  eq.  of  chlorine  then  leaving 
17  eq.  of  chloride  of  calcium,  and  1  eq.  of  chlorate  of  lime,  and  disengaging  12  eq. 
of  oxygen-gas,  according  to  the  observations  of  M.  Morin. 


CHLORIMETRY. 

The  bleaching  power  of  hypochlorite  of  lime  is  often  estimated  by  the  quantity 
of  a  solution  of  sulphate  of  indigo,  which  a  constant  weight  of  the  substance  can 
deprive  of  its  blue  colour,  or  render  yellow.  But  as  the  indigo-solution  alters  by 
keeping,  this  method  is  not  unobjectionable.  A  more  exact  method  is  that  in  which 
sulphate  of  iron  is  used.  This  method  reposes  upon  the  circumstance  that  the  chlo- 
rine of  hypochlorite  of  lime  converts  a  salt  of  the  protoxide  into  a  salt  or  the  sesqui- 
oxide of  iron ;  half  an  equivalent,  or  222  parts  of  chlorine,  effecting  that  change 
upon  a  whole  equivalent,  or  1728  parts  of  cr.  protosulphate  of  iron.  Protoxide  of 
iron  is  convertible  into  sesquioxide  by  half  an  equivalent  of  oxygen,  which  the  half 
equivalent  of  chlorine  may  be  supposed  to  supply,  by  decomposing  water,  in  be- 
coming hydrochloric  acid.  It  follows,  by  proportion,  that  10  grains  of  chlorine  are 
capable  of  peroxidizing  77.9  grains  of  cr.  protosulphate  of  iron. 

A  few  ounces  of  good  crystals  of  protosulphate  of  iron  are  reduced  to  powder, 
and  dried  by  strong  pressure  between  folds  of  cloth ;  the  salt  may  afterwards  be 
preserved  in  a  bottle  without  change.  In  a  chlorimetric  experiment,  78  grains 
(equivalent  to  10  grains  of  chlorine)  of  this  salt  are  dissolved  in  about  two  ounces 
of  water,  which  may  be  acidulated  by  a  few  drops  of  sulphuric  or  hydrochloric  acid. 
Fifty  grains  of  the  chloride  of  lime  to  be  examined  are  dissolved  in  about  two  ounces 
of  tepid  water,  by  rubbing  them  together  in  a  mortar,  and  the  whole  poured  into 
the  alkalimeter  (page  386),  which  is  afterwards  filled  up  to  0  on  the  scale,  by  the 
addition  of  water,  and  the  whole  mixed  by  inverting  the  alkalimeter  upon  the  palm 
of  the  hand.  The  solution  of  chloride  of  lime,  being  thus  made  up  to  100  measures, 
is  poured  gradually  into  the  sulphate  of  iron,  till  the  latter  is  completely  peroxidized, 
and  the  .number  of  measures  of  chloride  required  to  produce  that  effect  observed. 
The  change  in  the  degree  of  oxidation  of  the  iron-solution  is  discovered  by  means 
of  red  prussiate  of  potassa,  which  gives  a  precipitate  of  Prussian  blue  with  a  salt  of 
the  protoxide  of  iron  only,  and  not  with  a  salt  of  the  sesquioxide.  By  means  of  a 
glass-stirrer,  a  white  stoneware  plate  is  spotted  over  with  small  drops  of  the  prus- 
siate. A  drop  of  the  iron-solution  is  mixed  with  one  of  these,  after  every  addition 
of  chloride  of  lime,  and  the  additions  continued,  so  long  as  a  deep  blue  precipitate 
is  produced.  The  liquid  may  continue  to  be  coloured  green  by  the  iron-salt,  but 
that  is  of  no  moment.  The  richer  the  specimen  of  chloride  of  lime  is  in  chlorine, 
the  fewer  measures  of  its  solution  are  required  to  peroxidize  the  iron,  the  number 
of  measures  containing  10  grains  of  chlorine  always  producing  that  effect.  The 
quantity  of  chlorine  in  the  fifty  grains  of  bleaching  powder  is  now  known,  being 
ascertained  by  the  proportion,  as  m  measures  (the  number  poured  out  by  the  alkali- 
meter)  is  to  10  grains  of  chlorine,  so  100  is  to  the  total  grains  of  chlorine.  In  a 
particular  experiment  the  78  grains  of  sulphate  of  iron  required  72  measures  of  the 
bleaching  solution.  Hence,  as  72  is  to  10,  so  100  is  to  18.89  chlorine  in  50  grains 
of  the  chloride  of  lime.  The  quantity  of  chlorine  in  100  grains  of  the  chloride,  or 
the  percentage  of  chlorine,  is  obtained  by  doubling  that  number ;  and  was  therefore, 
in  this  instance,  27.78  per  cent,  or  28  per  cent.  The  arithmetical  process  may 


MAGNESIA.  415 

always  be  reduced  to  that  of  dividing  2000  by  the  number  of  measures  poured  from 
the  alkalimeter :  thus  in  the  last  example  — 

^=27.78. 

72 


SECTION  IV. 

t 

MAGNESIUM. 

Eg.  12.2,  or  152.5;  Mg. 

To  obtain  magnesium,  sodium  in  a  test-tube  of  hard  glass  is  covered  by  frag- 
ments of  anhydrous  chloride  of  magnesium,  and  heated  to  redness  by  a  lamp.  The 
alkaline  metal  unites  with  chlorine,  with  strong  ignition.  After  extracting  the 
chloride  of  sodium  by  means  of  water,  the  magnesium  remains  in  little  globules, 
which  may  be  reunited  by  fusing  them  under  a  stratum  of  chloride  of  potassium  at 
a  moderate  red-heat.  \_Sec  Supplement,  p.  817.] 

Magnesium  has  the  colour  and  lustre  of  silver;  it  is  very  ductile,  and  capable  of 
being  beaten  into  thin  leaves,  fuses  at  a  gentle  heat,  and  crystallizes  in  octahedrons. 
Magnesium  is  oxidized  superficially  by  moist  air,  but  undergoes  no  change  in  dry 
air  or  oxygen.  Heated  to  redness,  it  burns  with  great  brilliancy,  forming  magnesia. 
It  is  evidently  more  analogous  to  zinc  than  to  the  preceding  metals. 

Magnesia ;  MgO;  20.2,  or  252.5.  —  This  is  the  only  known  oxide  of  magne- 
sium. As  usually  prepared,  by  a  gentle  but  long  calcination  of  the  artificial  carbo- 
nate of  magnesia,  it  forms  a  white  soft  powder,  the  magnesia  usta  of  pharmacy. 
Magnesia  is  of  density  3.61  after  ignition  in  a  porcelain-furnace  (H.  Rose),  and 
highly  infnsible.  It  combines  with  water,  but  with  much  less  avidity  than  lime 
does,  forming  a  protohydrate.  The  native  hydrate  of  magnesia  has  the  same  com- 
position, and  so  has  the  compound  obtained  by  precipitating  magnesia  from  its  soluble 
salts  (by  means  of  hydrate  of  potassa)  and  washing  well,  when  dried  either  without 
heat  or  at  212°.  These  preparations  have  a  silky  lustre  and  a  softness  to  the  touch, 
characteristic  of  magnesian  minerals,  such  as  is  observed  in  asbestos  and  soapstone. 

According  to  M.  Fresenius,  magnesia  requires  for  solution  55368  parts  of  water, 
either  boiling  or  at  ordinary  temperatures;  the  solution  is  feebly  alkaline,  and  gives 
a  sensible  precipitate  on  the  addition  of  phosphate  of  soda,  followed  by  ammonia. 
When  this  earth  and  its  salts  are  moistened  with  nitrate  of  cobalt,  and  strongly 
ignited  before  the  blow-pipe,  they  assume  a  fine  rose-colour :  phosphate  of  magnesia 
takes  more  of  a  violet  tint.  Magnesia  is  precipitated  from  its  soluble  salts  by  lime- 
water,  but  is  still  a  strong  base  capable  of  neutralizing  acids  perfectly.  Ammonia 
never  throws  down  more  than  half  of  the  magnesia  from  the  solution  of  a  salt  of 
magnesia,  owing  to  the  formation  of  a  soluble  double  salt  of  magnesia  and  ammonia; 
and  the  flaky  precipitate  produced  by  ammonia  in  the  solution  of  a  salt  of  magnesia 
disappears  again  completely  on  the  addition  of  hydrochlorate  of  ammonia.  Magnesia 
is  precipitated  from  its  salts  by  the  carbonates,  but  not  by  the  bicarbonates,  of  po- 
tassa and  soda.  It  is  most  correctly  estimated  by  precipitation  by  the  phosphate  of 
soda  with  caustic  ammonia,  washing  with  water  containing  hydrochlorate  of  ammo- 
nia, and  igniting  the  precipitated  phosphate  of  magnesia  and  ammonia;  the  whole 
magnesia  being  ultimately  obtained  in  the  form  of  bibasic  phosphate  of  magnesia, 
2MgO.P05. 

Chloride  of  magnesium,  made  by  neutralizing  carbonate  of  magnesia  with  hydro- 
chloric acid,  crystallizes  in  thin  needles,  which  contain  6  eq.  of  water,  and  are  highly 
deliquescent.  When  we  attempt  to  make  this  salt  anhydrous  by  heat,  hydrochloric 
acid  escapes,  and  magnesia  remains.  But  the  pure  chloride  of  magnesium,  which  is 
employed  in  preparing  the  metal,  may  be  obtained  by  dividing  a  quantity  of  hydro- 


416  MAGNESIUM. 

chloric  acid  into  two  equal  portions,  neutralizing  one  with  magnesia  and  the  other 
with  ammonia,  mixing  and  evaporating  these  two  solutions  to  dryness,  when  an 
anhydrous  double  chloride  of  magnesium  and  ammonia  is  formed.  On  heating  this 
salt  to  redness  in  a  covered  porcelain-crucible,  sal-ammoniac  sublimes,  and  chloride 
of  magnesium  remains  in  a  state  of  fusion,  which  becomes  a  translucent,  crystalline 
mass  on  cooling.  This  chloride  is  decomposed  by  oxygen,  which,  at  a  high  tempe- 
rature, displaces  its  chlorine,  and  magnesia  is  formed.  According  to  M.  Poggiale, 
the  chloride  of  magnesium  forms  with  chloride  of  sodium  a  double  salt,  which  has 
the  formula  aMgCl.NaCl+2HO. 

Carbonate  of  magnesia.  —  This  salt  occurs  native,  and  then  always  in  the  anhy- 
drous condition,  as  a  white,  hard,  compact  mineral  of  an  earthy  fracture,  which  is 
known  as  magnesite,  and  sometimes  in  rhombohedral  crystals,  similar  to  those  of 
carbonate  of  lime.  It  is  prepared  artificially  by  precipitating  a  soluble  salt  of  mag- 
nesia, by  means  of  carbonate  of  potassa  at  the  boiling-point.  The  precipitate  is 
diffused  in  pure  water,  and  a  stream  of  carbonic  acid  sent  through  it,  by  which  the 
carbonate  of  magnesia  is  dissolved.  On  allowing  this  solution  to  evaporate  sponta- 
neously, the  excess  of  carbonic  acid  escapes,  and  carbonate  of  magnesia  is  deposited 
in  small  hexagonal  prisms  with  right  summits.  These  crystals  contain  3  eq.  of 
water.  They  effloresce  in  dry  air,  and  then  lose  2  eq.  of  water,  according  to  my 
own  observations.  Carbonate  of  magnesia  has  also  been  obtained  in  crystals,  with 
5  eq.  of  water,  from  the  solution  in  carbonic  acid,  at  a  low  temperature.  There  are, 
consequently,  three  hydrates  of  this  salt,  of  which  the  formulae  are  — 

MgO.C02.HO; 

MgO.C02. 

MgO.C02. 


The  fact  that  the  carbonate  of  magnesia  dissolves  in  carbonic  acid-water  is  not  to 
be  held  as  a  proof  of  the  existence  of  a  bicarbonate  of  magnesia.  Various  insoluble 
salts,  such  as  phosphate  of  lime  and  fluoride  of  calcium,  dissolve  in  the  same  liquid, 
which  appears  to  possess  a  specific  solvent  power.  In  the  analogous  solution  of  car- 
bonate of  lime  in  carbonic  acid-water,  the  proportion  of  the  carbonate  was  found  by 
Berthollet  to  have  a  variable  and  indefinite  relation  to  the  acid.  On  theoretical 
grounds,  supersalts,  of  the  ordinary  constitution,  of  magnesia,  and  the  magnesian 
family  of  oxides,  are  not  to  be  expected,  as  they  would  be  double  salts  of  water  and 
another  magnesian  oxide. 

Magnesia  alba,  or  the  subcarbonate  of  magnesia  of  pharmacy,  is  prepared  by  pre- 
cipitating a  boiling  solution  of  sulphate  of  magnesia  or  chloride  of  magnesium,  by 
means  of  carbonate  of  potassa.  Carbonate  of  soda  is  not  so  suitable  as  a  precipitant 
of  magnesia,  as  a  portion  of  it  is  ap^  to  go  down  in  combination  with  the  magnesian 
carbonate,  but  it  may  be  used  provided  the  quantity  applied  be  less  than  is  required 
to  decompose  the  whole  magnesian  salt  in  solution.  Magnesia  alba,  when  washed 
with  hot  water,  is  very  white,  light,  and  bulky.  A  portion  of  carbonic  acid  is  lost, 
the  magnesia  not  being  in  combination  with  a  full  equivalent  of  that  acid.  Berzelius 
found  magnesia  alba  to  contain,  in  100  parts,  35.77  carbonic  acid,  44.75  magnesia, 
and  19.48  water;  or  to  consist  of  3  eq.  of  carbonic  acid,  4  eq.  of  magnesia,  and  4 
eq.  of  water.  It  is  viewed  as  a  combination  of  3  eq.  of  protohydrated  carbonate  of 
magnesia  with  1  eq.  of  protohydrate  of  magnesia;  of  which  the  formula  is  3(MgO. 
C02.HO)  +  MgO.HO.  This  compound  requires  2500  parts  of  cold,  and  9000  of 
hot  water  for  solution  (Dr.  Fyfe). 

Bicarbonate  of  potassa  and  magnesia.  —  This  salt  was  formed  by  Berzelius  by 
mixing  a  solution  of  nitrate  of  magnesia  or  chloride  of  magnesium  (not  the  sulphate 
of  magnesia)  with  a  saturated  solution  of  bicarbonate  of  potassa  in  excess,  and 
allowing  the  liquor  to  rest.  In  the  course  of  a  few  days,  the  double  salt  is  deposited 
in  large  regular  crystals.  These  crystals  are  insipid;  insoluble  in  pure  water,  but 
slowly  decomposed  by  it.  The  composition  of  this  salt  corresponds  with  1  eq.  of 
potassa,  2  of  magnesia,  4  of  carbonic  acid,  and  9  of  water.  It  contains  the  elements 


SALTS  OF  MAGNESIA.  417 

of  1  eq.  of  a  hydrated  bicarbonate  of  potassa,  and  of  2  eq.  of  hydrated  carbonate  of 
magnesia. 

MgO.C02.HO  +  2HO 

HO.G02.(KO.C02)+2HO 

MgO.C02.HO+2HO. 

It  appears  an  association,  or  compound,  of  three  salts  of  similar  constitution.  .This 
salt,  I  find,  loses  8HO  at  212°,  or  all  its  combined  water,  except  the  single  basic 
equivalent  of  the  bicarbonate  of  potassa.  A  corresponding  bicarbonate  of  soda  and 
magnesia  also  exists. 

Dolomite,  a  magnesian  limestone,  very  extensively  diffused  in  nature,  is  a  mixture 
or  combination  of  the  carbonates  of  lime  and  magnesia,  having  the  crystalline  form 
of  calc-spar.  The  two  salts  unite  in  all  proportions,  but  are  most  frequently  found 
in  the  proportion  of  single  equivalents.  It  is  remarkable  that  when  this  rock  is 
exposed  to  the  solvent  action  of  water  containing  carbonic  acid,  the  carbonate  of 
lime  is  dissolved  exclusively,  and  a  magnesian  limestone  remains  in  the  form  of  a 
porous  and  crystalline  mass.  It  is  not  unusual  to  find  whole  mountains  of  magnesian 
limestone  thus  altered. 

Sulphate  of  magnesia;  MgO.S03.HO  +  6HO;  60.2  +  63,  or  752.5  +  787.5.  — 
This  salt  exists  in  many  mineral  springs,  in  the  waters  of  Epsom,  of  Seidlitz  in 
Bohemia,  &c.,  from  which  it  was  first  procured  by  evaporation.  It  is  now  obtained 
from  the  bittern  of  sea-water,  which  consists  principally  of  chloride  of  magnesium 
and  sulphate  of  magnesia,  and  is  converted  wholly  into  sulphate  by  the  addition  of 
sulphuric  acid.  Or  magnesia  is  precipitated  from  sea-water  confined  in  a  tank,  by 
means  of  hydrate  of  lime,  and  the  earth  thus  obtained  afterwards  neutralized  by 
sulphuric  acid.  Magnesian  limestone  is  also  had  recourse  to  for  magnesia.  It  is 
burned  and  slaked  with  water,  to  obtain  it  in  a  divided  state,  and  then  neutralized 
by  sulphuric  acid.  The  mixed  sulphates  are  easily  separated,  that  of  lime  being 
soluble  to  a  minute  extent  only,  while  that  of  magnesia  is  highly  soluble  in  water. 
A  solution  of  sulphate  of  lime  is  also  decomposed  by  carbonate  of  magnesia,  with 
the  formation  of  sulphate  of  magnesia ;  and  this  reaction  is  often  witnessed  in  beds 
of  magnesian  limestone,  when  water  containing  sulphate  of  lime  percolates  through 
them. 

The  crystals  of  sulphate  of  magnesia  are  four-sided  rectangular  prisms,  which, 
when  pure,  have  a  slight  disposition  to  effloresce  in  dry  air.  One  hundred  parts  of 
water  at  32°  dissolve  25.76  parts  of  the  anhydrous  salt,  and  for  every  degree  above 
that  temperature  they  take  up  0.26564  part  additional  (see  Gay-Lussac's  table  of 
the  solubility  of  salts,  at  page  178).  The  solution  has  a  bitter  disagreeable  taste, 
which  is  characteristic  of  all  the  soluble  salts  of  magnesia.  It  is  not  precipitated  in 
the  cold  by  the  alkaline  bicarbonates,  by  common  carbonate  of  ammonia,  nor  by 
oxalate  of  ammonia  if  the  solution  of  sulphate  of  magnesia  be  dilute.  This  salt 
crystallizes  at  32°  with  12HO  (Fritzsche);  it  is  also  generally  stated  to  crystallize 
about  70°,  with  6HO. 

Sulphate  of  magnesia  loses  6HO  considerably  under  300°,  but  retains  1  eq.  of 
water  even  at  400.°  The  last  equivalent  is  replaced  by  sulphate  of  potassa,  forming 
the  double  sulphate  of  magnesia  and  potassa,  which  is  considerably  less  soluble  than 
the  sulphate  of  magnesia,  and  crystallizes  with  6HO.  Sulphate  of  magnesia  unites 
directly  with  sulphate  of  ammonia  also,  at  the  ordinary  temperature,  and  with  sul- 
phate of  soda  above  100°  (Mr.  Arrott). 

Sulphate  of  magnesia,  when  ignited  in  contact  with  charcoal,  leaves  magnesia! 
with  very  little  sulphide  of  the  metal ;  it  is  the  last  of  the  earths  which  exhibits 
any  analogy  of  this  kind  to  the  alkalies.  The  hydrosulphate  of  sulphide  of  magne- 
sium is  soluble  in  water,  and  appears  to  be  formed  when  sulphate  of  magnesia  is 
precipitated  by  sulphide  of  barium. 

Hyposulphate  of  magnesia  forms  crystals,  which  are  persistent  in  air,  very  soluble, 
and  contain  36.77  per  cent,  or  6  eq.  of  water,  like  the  following  salt. 


418  MAGNESIUM. 

Nitrate  of  magnesia  is  a  very  soluble  and  highly  deliquescent  salt.  It  crystal- 
lizes with  6 HO. 

Phosphate  of  magnesia  is  formed  on  mixing  cold  solutions  of  common  phosphate  of 
soda  and  sulphate  of  magnesia,  and  allowing  to  stand  for  24  hours.  The  salt  ap- 
pears in  tufts  of  slender  prisms,  which  effloresce  in  dry  air.  They  are  soluble  in 
about  1000  times  their  weight  of  water.  The  composition  of  this  salt,  which  I 
carefully  examined,  may  be  expressed  by  the  following  formula  —  H0.2MgO.P05 
+  2HO  +  12HO.  (Phil.  Trans.  1837.) 

Phosphate  of  magnesia  and  ammonia.  —  This  is  the  well-known  granular  preci- 
pitate which  appears  when  a  tribasic  phosphate  and  a  salt  of  ammonia  are  dissolved 
together,  and  any  salt  of  magnesia  is  added  to  the  mixture.  Its  formation  is  had 
recourse  to  as  a  test  of  the  presence  of  magnesia.  Although  insoluble  in  a  liquid 
containing  salts,  it  is  so  soluble  in  pure  water  that  it  cannot  be  washed  without  sen- , 
sible  loss.  It  is  readily  dissolved  by  acids.  The  same  substance  forms  the  basis 
of  the  variety  of  urinary  calculus  known  as  the  ammoniaco-magnesian  phosphate. 
It  is  a  tribasic  phosphate,  of  which  the  3  eq.  of  base  are  1  eq.  of  oxide  of  ammonium 
and  2  eq.  of  magnesia,  with  12  eq.  of  water  of  crystallization  :  ten  of  the  latter  may 
be  expelled  without  any  loss  of  ammonia.  The  formula  of  this  salt  is  therefore 
NH40.2MgO.P05  +  2HO+10HO.  The  same  salt  was  found  in  crystals  of  consi- 
derable magnitude,  by  Dr.  Ulex,  in  the  old  soil  of  the  city  of  Hamburgh,  and 
named  struvite,  as  a  new  mineral  species.  It  has  also  been  found  in  guano,  and 
hence  named  guanite  by  Mr.  Teschemacher.  Dr.  Otto  has  observed  a  corresponding 
tribasic  phosphate  of  protoxide  of  iron  and  ammonia,  which  contains  only  2  eq.  of 
water ;  and  also  an  arseniate  of  manganese  and  ammonia,  of  which  the  water  of 
crystallization  appears  to  be  the  same  as  that  of  the  phosphate  of  magnesia  and 
ammonia.  By  igniting,  without  fusing,  phosphate  of  magnesia  with  a  small  quan- 
tity of  carbonate  of  potassa,  an  insoluble  double  salt  of  similar  constitution, 
'  2MgO.KO.P05,  was  obtained  by  H.  Rose.  Corresponding  double  phosphates, 
containing  2  eq.  of  lime,  baryta,  and  strontia,  in  the  place  of  the  2  eq.  of  magnesia, 
were  prepared  in  a  similar  manner. 

Borate  of  magnesia. — The  neutral  salt  was  obtained  by  M.  Wphler,  in  the  form 
of  crystals,  by  heating  a  mixture  of  the  solutions  of  sulphate  of  magnesia  and  borax 
to  the  boiling  point,  so  as  to  form  a  precipitate,  which  is  re-dissolved  on  cooling,  and 
leaving  the  liquid  at  a  temperature  only  a  few  degrees  above  32°  for  some  months. 
There  were  formed  on  the  sides  of  the  vessel  thin  crystalline  needles,  transparent, 
brilliant,  hard,  and  having  much  of  a  mineral  character,  insoluble  in  hot  or  cold 
water,  and  having  the  composition  MgO.B03  +  8HO.  Boracic  acid  forms  also  an 
insoluble  triborate  of  magnesia,  3MgO.B03  +  9HO;  a  soluble  terborate,  Mg0.3B03 
+  8HO;  and  a  soluble  sexborate,  Mg0.6B03+18HO. 

The  mineral  boracite,  which  occurs  in  the  cube  and  its  allied  forms,  is  an  anhy- 
drous compound  of  magnesia  and  boracic  acid,  in  the  ratio  of  3  eq.  of  magnesia  to 
4  eq.  of  boracic  acid,  which  is  represented  by  Mg0.2B03-f2(MgO.B03).  This 
mineral  becomes  electrical  by  heat.  The  rare  mineral,  hydroboracit.e,  is,  according 
to  Hess,  a  compound  of  a  borate  of  lime  and  borate  of  magnesia,  in  both  of  which 
the  acid  and  base  are  in  the  same  ratio  as  in  boracite,  with  18  eq.  of  water. 

Silicates  of  magnesia. — Magnesia  is  found  combined  with  silicic  acid  in  various 
proportions,  forming  several  mineral  species,  of  which  the  formulae  are  as  follows  : — 

Steatite 5(MgO.Si03)  +  2HO. 

Meerschaum MgO.Si03  +  2HO. 

Picrosmine  and  pyrallolite 6Mg0.4Si03-}-3HO. 

Peridote  (olivine,  or  chrysolyte)  ....     3MgO.Si03. 


Serpentine    (hydrate    of    magnesia 

with  subsilicate  of  magnesia 

Pyroxene  or  augite  (silicate  of  lime 


and  magnesia) 
Amphibole,  or  hornblende  (silicate 
of  lime  and  magnesia) 


2(3MgO  -f  2Si03)  +  3(Mg0.2HO). 
3Ca0.2Si03  +  3Mg0.2Si03. 
CaO.Si03+3Mg0.2Si03. 


ALUMINUM.  419 

In  these  minerals,  particularly  the  two  last,  the  magnesia  is  often  replaced,  in 
whole  or  in  part,  by  protoxide  of  iron,  which  gives  them  a  green,  and  sometimes 
black  colour.  Fine  crystals  of  pyroxene  are  often  found  among  the  scoriae  of  blast- 
furnaces. Serpentine  is  easily  decomposed  by  acids,  and  may  be  employed  in  the 
preparation  of  sulphate  of  magnesia.  A  variety  of  other  minerals  are  formed  of 
silicic  acid  and  magnesia,  anhydrous  or  hydrated ;  such  as  talc,  metaxite,  &c. 


ORDER  III. 

METALLIC   BASES   OF   THE   EARTHS. 

SECTION  I. 

ALUMINUM. 

Eq.  13.7  or  171.2;  Al. 

This  element  is  named  from  alumen,  the  Latin  term  for  alum,  which  is  a  double 
salt,  consisting  of  sulphate  of  alumina  and  sulphate  of  potassa. 

Like  the  preceding  metal,  aluminum  is  obtained  from  its  chloride  by  the  action 
of  potassium.  In  order  to  diminish  the  violence  of  the  reaction,  M.  Wohler  recom- 
mends that  about  20  grains  of  perfectly  dry  potassium  be  introduced  into  a  small 
platinum-crucible,  which  is  placed  within  another  larger  crucible,  also  of  platinum, 
containing  the  anhydrous  chloride  of  aluminum.  The.  cover  of  the  larger  crucible 
is  then  fastened  down  by  an  iron-wire,  and  heat  applied  with  caution.  The  alumi- 
num is  afterwards  separated  from  the  chloride  of  potassium,  with  which  it  is  mixed, 
by  digesting  the  crucible  and  its  contents  in  a  considerable  quantity  of  cold  water. 
The  metal  appears  as  a  grey  powder,  resembling  spongy  platinum,  but  is  seen  in  a 
strong  light,  while  suspended  in  water,  to  consist  of  small  scales  or  spangles  having 
the  metallic  lustre.  It  is  not  a  conductor  of  electricity  when  in  this  divided  state, 
but  becomes  one  when  its  particles  are  approximated  by  fusion.  Wohler  finds  that 
iron  resembles  aluminum  in  that  respect.  [See  Supplement,  p.  818.] 

Aluminum  has  no  action  upon  water  at  the  usual  temperature,  but  decomposes  it 
to  a  small  extent  at  the  boiling  temperature,  with  the  evolution  of  hydrogen.  It 
undergoes  oxidation  more  rapidly  in  solutions  of  potassa,  soda,  and  ammonia,  and 
the  resulting  alumina  is  dissolved  by  these  alkalies.  Aluminum  requires  for  fusion 
a  temperature  higher  than  that  at  which  cast-iron  melts.  Heated  in  open  air,  it 
takes  fire  and  burns  with  a  vivid  light,  and  in  oxygen-gas  with  the  production  of  so 
much  heat  as  to  fuse  the  alumina,  which  then  has  a  yellowish  colour,  and  is  equal 
in  hardness  to  the  native  crystallized  aluminous  earth,  corundum. 

•Alumina ;  1A1203 :  51.4  or  642.5. — This  earth  is  the  only  degree  of  oxidation  of 
which  aluminum  is  susceptible,  so  far  as  is  known  at  present.  In  its  constitution, 
alumina  is  presumed  to  resemble  sesquioxide  of  iron,  because  it  occurs  crystallized 
in  the  same  form  as  the  native  sesquioxide  of  iron,  and  the  salts  into  which  it  enters 
are  strictly  isomorphous  with  the  corresponding  salts  of  that  oxide.  To  3  eq.  of 
oxygen  it  must,  therefore,  contain  2  eq.  of  metal,  such  being  the  composition  of 
sesquioxide  of  iron.  Aluminum  is  not  known  to  enter  into  combination  in  any  other 
proportion  than  that  of  two  equivalents  of  the  metal  to  three  of  the  halogenous  con- 
stituent. [See  Supplement,  p.  819.] 

Alumina  occurs  in  a  state  of  purity,  with  the  exception  of  a  trace  of  colouring 
matter,  in  two  precious  stones,  the  sapphire  and  ruby ;  the  first  of  which  is  blue, 
and  the  other  red.  They  are  not  inferior  in  hardness  to  the  diamond.  Their  den- 
sity is  from  3.9  to  3.97.  Alumina  may  be  obtained  by  calcining  the  sulphate  of 


420  ALUMINUM. 

alumina  and  ammonia,  or  ammoniacal  alum,  very  strongly.  But  alumina  so  pre- 
pared is  insoluble  in  acids.  It  is  obtained  in  tha  state  of  a  hydrate  from  common 
alum  by  dissolving  the  latter  in  boiling  water,  and  adding  a  solution  of  ammonia 
(or  better,  of  the  carbonate  of  ammonia),  and  boiling.  This  earth  is  still  more  per- 
fectly precipitated  by  the  hydrosulphate  of  ammonia,  according  to  MM.  Malaguti 
and  Durocher.  The  precipitate,  which  is  white,  gelatinous,  and  very  bulky,  must 
be  carefully  washed,  by  mixing  it  several  times  with  a  large  quantity  of  distilled 
water,  allowing  it  to  settle,  and  pouring  off  the  clear  liquid.  By  drying  in  air,  alu- 
mina is  reduced  to  a  few  hundredths  of  the  bulk  of  the  humid  mass.  It  is  still  a 
hydrate,  but,  when  ignited  at  a  high  temperature,  it  gives  anhydrous  alumina.  One 
hundred  parts  of  alum  furnish  10.3  parts  of  alumina. 

Alumina  is  white  and  friable.  It  has  no  taste,  but  adheres  to  the  tongue.  Before 
the  oxihydrogen-blow-pipe  it  melts  into  a  colourless  glass.  After  being  ignited,  it 
is  dissolved  by  acids  with  great  difficulty.  It  is  highly  hygrometric,  condensing 
about  15  per  cent,  of  moisture  from  the  atmosphere  in  damp  weather.  If  ignited 
alumina  contains  a  small  portion  of  magnesia,  it  becomes  warm  when  moistened 
with  water :  this  property  is  very  sensible,  even  when  the  proportion  of  magnesia 
does  not  exceed  half  a  per  cent.  It  appears  to  be  due,  not  to  chemical  combination, 
but  to  heat  disengaged  by  humectation,  —  a  phenomenon  first  observed  by  Pouillet. 

The  hydrate  of  alumina,  when  moist,  is  gelatinous  and  semi-transparent,  like 
starch,  but  dries  up  into  gummy  masses.  It  is  completely  insoluble  in  water,  but 
is  readily  dissolved  by  acids,  and  also  by  the  fixed  alkalies ;  this  earth  standing  in 
the  relation  of  an  acid  to  the  stronger  bases.  Caustic  ammonia  dissolves  it  only  in 
small  quantity.  The  hydrate  of  alumina  is  deposited  in  crystals  when  the  solution 
of  this  earth  in  potassa  is  allowed  to  absorb  carbonic  acid  slowly  from  the  air.  The 
crystals  are  white  and  transparent  at  the  edges,  and  contain  3  eq.  of  water,  which 
they  do  not  lose  at  212°.  .  The  mineral  gibsite  is  a  native  hydrate  of  alumina  of 
the  same  composition,  A1203  +  3  HO.  Another  native  hydrate  exists,  containing 
less  water,  Al203-f  2HO.  It  is  called  diaspore  by  mineralogists,  from  decrepitating 
and  falling  to  powder  when  heated,  —  a  property  which  the  artificial  hydrate  in 
gummy  masses  likewise  exhibits. 

Hydrated  alumina  has  a  peculiar  attraction  for  organic  matter,  which  it  withdraws 
from  solution ;  and  hence  this  earth  is  apt  to  be  coloured  when  washed  with  water 
not  absolutely  pure.  This  affinity  is  so  strong,  that,  when  digested  in  solutions  of 
vegetable  colouring  matters,  alumina  combines  with  and  carries  down  the  colouring 
matter,  which  is  removed  entirely  from  the  liquid,  if  the  alumina  is  in  sufficient 
quantity.  The  pigments  called  lakes  are  such  aluminous  compounds.  The  fibre 
of  cotton,  when  charged  with  this  earth,  attracts  and  retains  with  force  the  same 
colouring  matters.  Hence  the  great  application  of  aluminous  salts  in  dyeing,  to 
impregnate  cloth  or  yarn  with  alumina,  and  thus  enable  it  to  fix  the  colouring  matter, 
and  produce  a  fast  colour.  Alumina  is  then  said  to  be  a  mordant :  binoxide  of  tin 
and  sesquioxide  of  iron  have  an  equal  attraction  for  organic  colouring  matters. 

Alumina,  it  will  be  observed,  is  not  a  protoxide,  and  is  greatly  inferior  to  the 
preceding  earths  in  basic  power.  It  is  dissolved  by  acids,  but  never  neutralizes 
them  completely.  Hence,  alum  and  all  the  salts  of  alumina  have  an  acid  reaction. 
Their  solutions  have  an  astringent  and  sweetish  taste,  which  is  peculiar  to  them. 
Alumina  dissolves,  to  the  extent  of  several  equivalents,  in  some  acids,  particularly 
hydrochloric  acid,  forming  feeble  compounds,  which  are  even  deprived  of  a  portion 
of  their  alumina  by  filtering  them  through  paper.  It  is  usually  supposed  that  alu- 
mina does  not  combine  with  some  of  the  weaker  acids,  such  as  carbonic  acid ;  and 
that  an  alkaline  carbonate  throws  down  alumina  from  alum,  and  not  a  carbonate  of 
that  earth.  The  carbonate  of  ammonia,  however,  according  to  Mr.  Dansori,  gives  a 
subcarbonate  of  alumina,  which,  dried  in  vacuo  at  a  low  temperature,  formed  a  light 
bulky  powder,  having  the  composition  3A1203.2C02  -f  16HO.  Alumina  dissolves 
readily  in  solution  of  potassa  or  soda,  formrag  compounds  in  which  it  must  play  the 
part  of  an  acid.  The  alurninate  of  potassa  is  deposited,  on  evaporating  a  solution 


SALTS   OF   ALUMINA.  421 

of  alumina  in  potassa,  in  white  granular  crystals,  sweet  to  the  taste,  and  having  a 
strongly  alkaline  reaction  :  its  formula  is  KO.A1203,  according  to  M.  Fremy.  Such 
combinations  occur  in  nature  :  spinell,  a  very  hard  mineral  crystallizing  in  octohe- 
drons,  being  an  aluminate  of  magnesia,  MgO.Al203;  and  gahnite,  an  aluminate  of 
zinc,  ZnO.Al203. 

Sulphide  of  aluminum  is  formed  by  burning  the  metal  in  the  vapour  of  sulphur. 
It  is  a  black  semi-metallic  mass,  which  is  rapidly  transformed,  by  contact  with  water, 
into  alumina  and  hydrosulphuric  acid.  Hydrosulphate  of  ammonia  has  the  same 
effect  upon  the  solution  of  a  salt  of  alumina  as  ammonia  has  itself,  neutralizing  the 
acid  of  the  salt,  and  throwing  down  alumina,  while  hydrosulphuric  acid  escapes. 

Chloride  of  aluminum;  A12C13;  133.9  or  1673.75.  —  When  alumina  is  dissolved 
in  hydrochloric  acid,  it  is  to  be  supposed  that  water  and  a  chloride  of  the  metal  are 
formed;  3HC1  and  A1203  =  A12C13  and  3HO.  The  solution,  when  concentrated  by 
spontaneous  evaporation  in  a  very  dry  atmosphere,  yields  crystals,  which  Bonsdorff 
found  to  contain  12  eq.  of  water.  But  it  generally  forms  a  saline  mass,  which  de- 
liquesces quickly  in  the  air.  When  it  is  attempted  to  make  this  salt  anhydrous  by 
heat,  the  chlorine  goes  off  in  the  form  of  hydrochloric  acid,  and  pure  alumina  is  left. 

The  anhydrous  chloride  was  discovered  by  Oersted,  who  made  known  a  nlethod 
of  preparing  it  which  has  since  had  numerous  applications.  Pure  alumina,  free 
from  potassa,  is  intimately  mixed  with  oil  and  lamp-black,  made  up  into  pellets,  and 
strongly  calcined  in  a  crucible.  The  alumina  is  thus  made  anhydrous,  without 
being  otherwise  altered.  It  is  then  introduced  into  a  porcelain-tube,  which  is  placed 
across  a  furnace  and  exposed  to  a  red  heat.  Chlorine-gas,  carefully  dried,  is  con- 
ducted over  the  materials  in  the  tube,  when,  under  the  conjoint  influence  of  carbon 
and  chlorine,  the  alumina  is  decomposed  ;  its  oxygen  is  carried  off  by  the  carbon  as 
carbonic-oxide  gas,  and  chlorine  unites  with  the  aluminum  itself.  The  chloride  of 
aluminum,  being  volatile,  sublimes  and  condenses  in  the  cool  part  of  the  porcelain- 
tube.  A  glass-tube,  a  little  smaller  than  the  porcelain-tube,  should  be  introduced 
into  this  part  of  the  latter,  which  may  afterwards  be  drawn  out,  containing  the  con- 
densed chloride.  The  salt  is  partly  in  the  state  of  long  crystalline  needles,  and 
partly  in  the  form  of  a  firm  and  solid  mass,  which  is  easily  detached  from  the  glass. 

Chloride  of  aluminum  is  of  a  pale  greenish-yellow  colour,  and  to  a  certain  degree 
translucent.  In  air  it  fumes  slightly,  diffuses  an  odour  of  hydrochloric  acid,  and, 
runs  into  a  liquid  by  the  absorption  of  moisture.  It  is  very  soluble  in  wate^but 
cannot  again  be  recovered  in  the  anhydrous  condition.  It  is  equally  soluble  in 
alcohol.  Chloride  of  aluminum  combines  with  hydrosulphuric  acid,  phosphuretted 
hydrogen,  and  also  with  ammonia. 

The  fluoride  of  aluminum  can  only  be  obtained  by  dissolving  pure  aluminum  in 
hydrofluoric  acid  :  it  does  not  crystallize.  This  fluoride  unites  in  two  proportions 
with  fluoride  of  potassium,  for  which  it  has  a  strong  affinity.  Both  the  compounds 
are  gelatinous  precipitates,  which  become  white  and  pulverulent  after  being  washed 
and  dried.  Berzelius  assigned  to  them  the  formulae,  3KF+  A12F3  and  2KF_-f  A12F3. 
Fluoride  of  aluminum  exists  in  two  crystalline  minerals,  one  of  which,  on  account 
of  its  transparency,  hardness,  and  brilliancy,  is  reckoned  among  the  precious  stones  :—  - 

Topaz  .............................  3(Al203.Si03)  +  (Al203+Al2F3) 

Pyknite  ...........................  3(Al203.Si03 


The  sulphocyanide  of  aluminum  crystallizes  in  octohedrons,  which  are  persistent 
in  air. 

SALT§   OF   ALUMINA. 

Sulphate  of  alumina;  A1203.3S03  +  18HO;  171.4  +  162  or  2142.5  +  2025.— 
Obtained  by  dissolving  alumina  in  sulphuric  acid.  It  crystallizes  in  thin  flexible 
plates  of  a  pearly  lustre,  has  a  sweet  and  astringent  taste,  and  is  soluble  in  twice  its 
weight  of  cold  water,  but  does  not  dissolve  in  alcohol.  When  heated,  it  fuses  in  its 
water  of  crystallization,  swells  up,  and  forms  a  light  porous  mass,  which  appears  at 


422  ALUMINUM. 

first  to  be  insoluble  in  water,  but  dissolves  completely  after  a  time.  Heated  to  red- 
ness, it  is  entirely  decomposed ;  the  residue  is  pure  alumina.  This  salt  has  been 
found,  in  the  crystalline  form,  in  the  volcanic  Island  of  Milo  in  the  Archipelago. 
Sulphuric  acid  arid  alumina  combine  in  several  proportions,  but  this  is  considered 
the  neutral  sulphate,  as  it  possesses  the  same  number  of  equivalents  of  acid  as  it 
contains  equivalents  of  oxygen  in  the  base. 

Another  sulphate  of  alumina  (A1203.3S034-  A1203)  was  obtained  by  Maus  by 
saturating  sulphuric  acid  with  alumina,  which  contains  twice  as  much  alumina  as 
the  neutral  sulphate.  After  evaporation,  this  subsalt  presents  itself  in  a  gummy 
mass,  which  dissolves  in  a  small  quantity  of  water,  but  is  decomposed  when  the 
solution  is  diluted  with  a  large  quantity  of  water,  or  boiled ;  ip  that  case  the  neutral 
salt  remains  in  solution,  and  the  following  salt  precipitates.  Subtrisulphate  of 
alumina,  A1203.3S03  +  2A1203  +  9HO,  precipitates,  on  adding  ammonia  to  the  sul- 
phate of  alumina,  as  a  white  insoluble  powder.  This  subsalt  forms  the  mineral 
aluminite,  which  is  found  near  Newhaven  in  England,  and  at  Halle  in  Ger- 
many. 

Alum;  sulphate  of  alumina  and  potassa;  KO.S03  +  A1203.3S03  +  24HO; 
258.4  +  216,  or  3230  +  2700.  —  Sulphate  of  alumina  has  a  strong  affinity  for  sul- 
phate of  potassa,  in  consequence  of  which  octohedral  crystals  of  this  double  salt 
precipitate  when  a  salt  of  potassa  is  added  to  a  strong  solution  of  sulphate  of  alumina. 
Alum  is  a  salt  of  which  large  quantities  are  consumed  in  dyeing.  It  is  prepared  by 
several  processes,  or  derived  from  different  sources.  It  may  be  prepared  by  decom- 
posing clay  with  sulphuric  acid ;  the  decomposition  is  sometimes  effected  by  igniting 
pure  clay,  grinding  it  afterwards  to  powder,  and  mixing  it  with  0.45  of  sulphuric 
acid,  of  1.45  density.  This  mixture  is  heated  in  a  reverberatory  furnace  till  the 
mass  becomes  very  thick ;  afterwards  left  to  itself  for  at  least  a  month,  and  then 
treated  with  water  to  wash  out  the  sulphate  of  alumina  formed.  This  salt  forms,  on 
cooling,  a  mass  of  interlaced  crystals,  being  the  sulphate  of  alumina  already  de- 
scribed, A1203.3S03  +  18HO.  Some  clays  and  aluminous  schists  do  no£  require  to 
be  heated  before  being  treated  with  sulphuric  acid.  The  addition  of  sulphate  of 
potassa  converts  the  last  salt  into  alum. 

The  old  mode  of  making  alum  is  still  largely  practised  in  England.  A  series 
of  beds  occur  low  in  many  of  the  coal  measures,  which  contain  much  bisulphide  of 
iron.  One  of  these,  known  as  alum-slate,  is  a  silicious  clay,  containing  a  considerable 
portion  of  coaly  matter,  and  of  the  metallic  sulphide  in  a  state  of  minute  division. 
When  this  mineral  is  exposed  to  air  and  moisture,  it  soon  exfoliates,  from  the  for- 
mation of  sulphate  of  iron,  the  bisulphide  of  iron  absorbing  oxygen  like  a  pyro- 
phorus.  The  excess  of  sulphuric  acid  formed  attacks  the  other  bases  present,  of 
which  the  most  considerable  is  alumina.  Aluminous  schists  often  require  to  be 
moderately  calcined  or  roasted  before  they  undergo  this  change  in  the  atmosphere. 
The  mineral  being  lixiviated,  after  a  sufficient  exposure,  affords  a  solution  of  sul- 
phate of  alumina  and  protosulphate  of  iron,  from  which  the  latter  salt  is  first  sepa- 
rated by  'crystallization.  The  subsequent  addition  of  sulphate  of  potassa  to  the 
liquor  causes  the  formation  of  alum ;  the  chloride  of  potassium  answers  the  same 
purpose,  and  has  the  advantage  over  the  sulphate  that  it  converts  the  remaining 
sulphates  of  iron  into  chlorides,  which  are  very  soluble,  and  from  which  the  alum  is 
most  easily  separated  by  crystallization.  A  very  pure  alum  is  also  obtained  in  the 
Roman  states  from  alum-stone,  which  is  simply  heated  till  sulphurous  acid  begins 
to  escape  from  it,  and  the  residue  of  this  calcination  treated  with  water.  This 
mineral  contains  an  insoluble  subsulphate  of  alumina  with  sulphate  of  potassa.  The 
heating  has  the  effect  of  separating  the  excess  of  alumina,  so  {hat  a  neutral  sulphate 
of  alumina  is  formed.  Alum-stone  appears  to  be  continually  produced  at  the 
Solfatara,  near  Naples,  and  other  volcanic  districts,  by  the  joint  action  of  sulphur- 
ous acid  and  oxygen  upon  trachyte,  a  volcanic  rock  composed  almost  entirely  of 
felspar.  [/See  Supplement,  p.  820.] 


SALTS  OF  ALUMINA.  423 

The  solubility  of  crystallized  alum,  according  to  M.  Poggiale,  is  as  follows:—- 

100  parts  of  water  at  32°    (0°  C.)  dissolve  3.29  parts  of  alum. 
at  50°  (10°  C.)     —      9.52 

—  at  86°  (30°  C.)     —     22.00 

—  at  140°  (60°  C.)    —     31.00 

—  .     at  158°  (70°  C.)    —    90.00 

at  212°  (100°  C.)  —  357.00 

It  crystallizes  very  readily  in  regular  octohedrons,  of  which  the  apices  are  always 
more  or  less  truncated,  from  the  appearance  of  faces  of  the  cube  ;  their  density  is 
1.71.  The  taste  of  alum  is  sweet  and  astringent,  and  its  action  decidedly  acid;  it- 
dissolves  metals,  with  evolution  of  hydrogen,  as  readily  as  free  sulphuric  acid.  The 
crystals  effloresce  slightly  in  air,  and,  when  heated,  melt  in  their  water  of  crystalli- 
zation, which  amounts  to  45.5  per  cent,  of  their  weight,  or  24  equivalents.  The 
fused  salt,  in  losing  this  water,  becomes  viscid,  froths  greatly,  and  forms  a  light 
porous  mass,  known  as  burnt  alum.  When  submitted  to  a  graduated  temperature, 
alum  loses  10  equivalents  of  water  at  212°,  and  9  equivalents  more  at  248°  (120° 
C.)  ,  leaving  alum  combined  with  5  eq.  of  water.  This  last  substance  can  support  a 
temperature  of  320°  (160°  C.)  without  losing  more  water.  At  356°  (180°  C.)  it 
loses  4  equivalents  of  water  j  a  salt  then  remains  which  parts  with  J  eq.  of  water 
at  392°  (200°  C.),  leaving  alum  in  combination  with  J  eq.  of  water  (Hertwig). 

A  pyrophorus  is  formed  from  an  intimate  mixture  of  3  parts  of  alum  and  1  of 
sugar,  which  are  first  evaporated  to  dryness  together,  and  then  introduced  into  a 
small  stoneware-bottle,  and  this  placed  in  a  crucible  and  surrounded  with  sand.  The 
whole  is  heated  to  redness  till  a  blue  flame  appears  at  the  mouth  of  the  bottle,  which 
is  allowed  to  burn  for  a  few  minutes,  and  the  mouth  then  closed  by  a  stopper  of 
chalk.  After  cooling,  the  bottle  is  found  to  contain  a  black  powder,  which  becomes 
red-hot  when  exposed  to  air,  and  catches  fire  also  and  burns  with  peculiar  vivacity 
in  oxygen-gas.  This  property  appears  to  depend  upon  the  highly  divided  state  of 
sulphide  of  potassium,  which  is  intermixed  with  charcoal  and  sulphate  of  alumina. 
A  pyrophorus  can  be  produced  from  sulphate  of  potassa  alone,  without  the  sulphate 
of  alumina  ;  but  it  does  not  so  certainly  succeed. 

If  the  quantity  of  carbonate  of  soda  necessary  to  neutralize  a  portion  of  alum  be 
divided  into  three  equal  portions,  and  added  in  a  gradual  manner  to  the  aluminous 
solution,  it  will  be  found  that  the  alumina  at  first  precipitated  is  re-dissolved  upon 
stirring,  and  that  no  permanent  precipitate  is  produced  till  nearly  two  parts  of  alka- 
line carbonate  are  added.  It  is  in  the  condition  of  this  partially  neutralized  solution 
that  alum  is  generally  applied  as  a  mordant  to  cloth.  Animal  charcoal  readily 
withdraws  the  excess  of  alumina  from  this  solution,  and  so  does  vegetable  fibre, 
probably  from  a  similar  attraction  of  surface.  When  this  solution  is  concentrated 
by  evaporation,  alum  crystallizes  from  it,  generally  in  the  cubic  form,  and  the  excess 
of  alumina  is  precipitated. 

Basic  alum  is  a  granular  crystalline  compound,  which  precipitates  when  gelatinous 
alumina  is  boiled  in  a  solution  of  alum.  The  formula  of  this  salt  is  HO.S03  + 
3(A1203.S03)  +  9HO  :  the  alum-stone  used  in  preparing  the  Roman  alum  has  the 
same  composition. 

Sulphate  of  ammonia  may  be  substituted  for  sulphate  of  potassa  in  alum,  giving 
rise  to  ammoniacal  alum, 


which  agrees  very  closely  in  properties  with  potassa-alum. 

Sulphate  of  alumina  also  combines  with  sulphate  of  soda,  forming  soda-alum, 
which  crystallizes  in  the  same  form  as  common  alum,  and  also  contains  24HO,  the 
formula  of  soda-alum  being, 

NaO.S03+  A1203-3S03+24HO. 


424  ALUMINUM. 

Crystals-  are  obtained  by  mixing  the  sulphates  of  soda  and  alumina,  and  leaving  a 
concentrated  solution  to  spontaneous  evaporation  ;  or  by  pouring  spirits  of  wine 
upon  the  surface  of  such  a  solution  contained  in  a  bottle,  which  deposits  crystals  as 
the  alcohol  gradually  diffuses  through  it.  This  salt  effloresces  in  air  as  rapidly  as 
sulphate  of  soda.  It  is  very  soluble  in  water,  10  parts  of  water  at  60°  dissolving 
11  parts  of  this  salt. 

Sulphate  of  alumina  also  combines  with  the  sulphate  of  protoxide  of  iron,  when 
dissolved  with  that  salt  and  a  considerable  admixture  of  sulphuric  acid  (Klauer). 
The  double  salt  was  found  to  contain  1  eq.  of  protosulphate  of  iron  (FeO.S03),  1  eq 
of  sulphate  of  alumina  (A1203.3S03),  and  24  eq.  of  water  (24HO),  which  indicates 
a  similarity  in  composition  to  alum.  But  it  is  deposited  in  long  acicular  crystals, 
which  do  not  belong  to  the  octohedral  system,  and  has  therefore  no  claim  to  be  con- 
sidered an  alum.  A  similar  salt  with  magnesia  was  obtained  in  the  same  way. 
Another  combination  of  the  same  class,  containing  the  sulphate  of  manganese,  forms 
a  white  fibrous  mineral  found  in  a  cave  upon  Bushman's  river  in  South  Africa. 
This  native  sulphate  of  alumina  and  manganese  has  been  carefully  examined  by  Dr. 
Apjolm  and  by  Sir  R.  Kane,  and  found  to  contain  25HO.  It  is  probable  that  if 
the  proportion  of  water  in  Klauer's  salts  were  accurately  determined,  it  would  be 
found  to  be  the  same.  These  salts  may  be  represented  as  compounds  of  a  magnesian 
sulphate,  retaining  its  single  equivalent  of  constitutional  water,  with  sulphate  of  alu- 
mina ;  the  manganese  compound  thus  :  — 

MnO.S03.H04-Al203.3S03+24HO. 

Certain  salts  have  been  formed,  isomorphous  with  alum,  and  strictly  analogous  in 
composition,  in  which  the  alumina  is  replaced  by  metallic  oxides  isomorphous  with 
it,  namely,  by  sesquioxide  of  iron,  sesquioxide  of  manganese,  and  sesquioxide  of 
chromium.  To  these  salts  the  generic  term  alum  is  applied,  and  the  species  is  dis- 
tinguished by  the  name  of  the  metallic  sesquioxide  it  contains ;  as  iron-alum,  man- 
ganese-alum, and  chrome-alum. 

Alumina  dissolves  freely  in  most  acids,  but,  like  metallic  peroxides  in  general,  it 
affords  few  crystalline  salts,  except  double  salts.  The  oxalate  of  potassa  and  alumina 
is  the  only  other  of  these  that  has  been  fully  examined.  It  is  remakable  for  its 
composition,  containing  3  eq.  of  oxalate  of  potassa  to  1  eq.  of  oxalate  of  alumina, 
with  6  eq.  of  water.  Its  formula  is,  therefore, 

3(KO.C203)+A1203.3C203+6HO. 

Like  alum  it  is  the  type  of  a  genus  of  double  salts.  The  corresponding  oxalates, 
containing  soda,  crystallize  with  10HO.  — (Phil.  Trans.  1837,  p.  54.) 

Nitrate  of  alumina  is  said  to  crystallize  with  difficulty  in  prismatic  crystals  radi- 
ating from  a  centre.  \See  Supplement,  p.  820.] 

An  insoluble  phosphate  of  alumina  precipitates  when  phosphate  of  soda  is  added 
to  a  solution  of  alum.  By  fusion  it  gives  a  glass,  like  porcelain  :  its  composition  is 
2A1203.3P05  (Berzelius).  This  salt,  dissolved  in  an  acid  and  precipitated  by  am- 
monia in  excess,  gives  a  more  highly  basic  phosphate,  of  which  the  formula  is 
4A1/)3.3P05  (Berzelius).  The  last  phosphate  of  alumina  occurs  in  nature,  in  com- 
bination with  fluoride  of  aluminum,  in  the  form  of  radiating  crystals,  and  is  named 
wavellite,  of  which  the  formula  is  A12F3  + 3(4A1203.3P03)  +  36HO.  A  phosphate 
of  alumina  and  lithia,  containing  the  same  subphosphate  of  alumina,  forms  the  rare 
mineral  amUygonite,  and  may  be  prepared  artificially :  its  formula  is  2LiO.P05-f- 
4A1203-3P05. 

SILICATES   OP   ALUMINA. 

The  varieties  of  clay  are  essentially  silicates  of  alumina,  but  composed  as  they 
are  of  the  insoluble  matter  of  various  rocks  destroyed  by  the  action  of  water,  it  is 
not  to  be  expected  that  they  will  be  uniform  in  composition.  Mitscherlich  considers 
it  probable  that  the  bat  is  of  clay  is  usually  a  subsilicate  of  alumina,  of  which  the 


SILICATES   OF   ALUMINA.  425 

formula  is  2Al203.3Si03;  and  which  contain  57.42  parts  of  silicic  acid  and  42.58 
of  alumina  in  100  parts.  But  from  the  analysis  of  Mosander,  the  refractory  clay 
of  Stourbridge  (a  fire-clay)  is  a  neutral  silicate  of  alumina,  Al203.3Si03.  China-clay 
or  kaolin,  which  is  prepared  from  decaying  granite,  being  the  result  of  the  decom- 
position of  the  felspar  and  mica  of  that  mineral,  is  not  uniform  in  its  composition. 
The  clay  from  a  white  bed  of  the  Plastic  Clay  formation,  which  is  worked  for  the 
purposes  of  pottery  in  the  neighbourhood  of  Farnham,  gave  Mr.  Way  the  following 
results :  — 

White  clay  dried  at  212°  contained  in  100  parts  — 

(  Silicic  acid 42.28 

Alumina 11.45 

Insoluble  in  acids,  58.03  <j  Oxide  of  iron  ..: 3.53 

Lime 0.55 

[Magnesia 0.22 

C  Silicic  acid 18.73 

Alumina 12.15 

Oxide  of  iron 2.11 

Lime 0.27 

Magnesia 0.29 

Potassa 0.86 

Soda 1.41 

Water  of  combination...  6.15 


Soluble  in  acids,  41.97 


100.00 

Clay,  and  soils  in  general  from  the  clay  which  they  contain,  possess  a  remarkable 
power  of  separating  salts  of  ammonia  and  potassa  from  their  solutions,  and  retaining 
these  bases,  first  observed  with  reference  to  ammonia  by  Mr.  H.  0.  Thomson,  and 
since  ably  investigated  by  Professor  Way.  A  light  soil  digested  with  a  weak  solu- 
tion of  caustic  ammonia  for  two  hours,  withdrew  0.3438  per  cent,  of  its  weight  of 
that  base,  and  0.3478  per  cent,  of  ammonia  from  a  solution  of  the  hydrochlorate  of 
ammonia,  the  latter  salt  being  decomposed,  and  chloride  of  calcium  found  in  solu- 
tion. The  sulphate  of  ammonia  was  decomposed  by  the  same  soil  and  by  the  clay 
above  described,  in  a  similar  manner,  sulphate  of  lime  appearing  in  solution.  Hence, 
when  putrid  urine  and  other  soluble  manures  are  filtered  through  clay  or  soil,  the 
ammonia  is  entirely  retained,  while  the  water  drains  away  containing  only  earthy 
salts.  This  absorptive  power  of  clay  is  not  destroyed  by  boiling  the  clay  with  an 
acid,  nor  by  drying  it  between  150°  and  200° ;  but  the  property  is  nearly  lost  in 
thoroughly  burnt  clay.  The  lime  present  in  clay,  which  appears  to  be  necessary  to 
this  action,  is  not  entirely  withdrawn  by  boiling  with  an  acid,  as  will  be  observed  ID 
the  preceding  analysis  of  clay.  From  the  hydrochlorate  of  ammonia  0.2010  per 
cent,  of  ammonia  was  withdrawn  by  the  white  clay,  and  0.4366  per  cent,  of  potassa, 
from  the  nitrate  of  potassa,  by  the  same  clay.  The  only  solutions  of  lime  which 
came  under  the  influence  of  this  absorbing  power  of  clay  and  soils  were  those  of 
hydrate  of  lime,  and  of  carbonate  of  lime  in  carbonic  acid  water.  Mr.  Way  doea 
not  propose  any  rationale  of  this  remarkable  action  of  clay,  but  excludes  the  suppo- 
sition of  its  being  due  to  free  alumina  and  silicic  acid  (Journal  of  the  Royal  Agri- 
cultural Society  of  England,  xi.  313,  1850). 

A  subsilicate  of  alumina  exists,  forming  a  very  hard  crystallized  mineral,  disthene 
or  cyanite,  of  which  the  formula  is  2Al203.Si03. 

Double  silicates  of  alumina  and  potassa  are  extensively  diffused  in  the  mineral 
kingdom,  forming  a  very  considerable  portion  of  the  solid  crust  of  the  globe.  The 
most  usual  of  these  double  salts  are  the  following : 

Potash-Felspar,  which  is  crystallized  in  oblique  rhomboidal  prisms,  of  density 
2.5,  is  composed  of  single  equivalents  of  the  neutral  silicates  of  potassa  and  alumina. 


426    /  EARTHENWARE  AND   PORCELAIN. 

Its  formula  is  therefore  analogous  to  that  of  anhydrous  alum,  silicon  being  substi- 
tuted for  sulphur;  KO.Si03-hAl203.3Si03.  It  is  one  of  the  three  principal  consti- 
tuents of  granite  and  gneiss.  This  species  of  felspar  is  named  orthose.  Otherx 
varieties  of  felspar  are  albite,  or  soda-felspar,  containing  silicate  of  soda,  NaO.Si03, 
in  the  place  of  silicate  of  potassa;  lithia-felspar  (petalite,  triphane),  LiO.Si03-f- 
Al203-3Si03;  and  lime-felspar  (labradorite,  anorthite),  CaO.Si03-f  Al203.3Si03. 
The  alkaline  base  of  felspars  is  often  partially  replaced  by  lime  and  magnesia,  and 
the  most  general  formula  for  a  felspar  would  be  — 

KO     -| 

CaO      fSi03+Al208.3Si03. 
MgO   J 

•flmphigen  or  leucile  occurs  principally  in  the  lava  of  Vesuvius  in  a  crystallized 
state.  The  relation  between  the  potassa  and  alumina  is  the  same  as  in  orthose,  but 
it  contains  one-third  less  silicic  acid.  Hence  the  formula  3K0.2Si03-f  3(A1203. 
2Si03).  A  similar  combination  is  obtained  by  precipitating  a  saturated  solution  of 
alumina  in  potassa,  by  a  solution  of  silicate  of  potassa  (Berzelius). 

When  a  mixture  of  silicic  acid  and  alumina  is  fused  with  an  excess  of  potassa, 
and  the  fused  mass  washed  with  water,  to  withdraw  everything  soluble,  a  powder 
remains  in  which  the  potassa  and  alumina  are  still  in  the  ratio  of  single  equivalents, 
but  in  which  the  oxygen  of  the  silicic  acid  is  equal  to  that  of  the  bases.  This  double 
salt  has  consequently  the  formula,  3KO.Si03-f  3Al203.3Si03. 

Analcime  is  the  soda  silicate  proportional  to  amphigen.  It  is  crystallized  like 
amphigen,  but  contains  6  eq.  of  water.  Its  formula  is  3Na0.2Si03  +  3(A1203. 
2Si03)  +  6HO. 

A  third  compound  may  be  prepared,  corresponding  with  the  artificial  potassa- 
compound  above.  It  occurs  also  in  hexagonal  prisms  in  the  lava  of  Vesuvius, 
forming  the  mineral  nephelin. 

Garnet  is  a  double  basic  silicate  of  lime  and  alumina,  of  which  the  formula  is 
3Ca03.Si03-4-  Al203.Si03. 

The  silicates  of  lime  and  of  alumina  combine  in  many  different  proportions, 
forming  a  great  variety  of  minerals.  Most  of  them  contain  water,  in  consequence 
of  which  they  froth  when  heated  before  the  blow-pipe,  and  hence  are  called  zeolites. 
One  of  these,  named  stilbite,  from  its  shining  lustre,  corresponds  in  composition 
with  felspar,  but  contains  in  addition  6  eq.  of  water :  its  formula  is 

CaO.Si02+  Al203.3Si03+ 6HO. 

A  small  portion  of  one  or  other  of  the  alkalies  is  often  found  in  these  minerals,  be- 
sides small  quantities  of  protoxide  of  iron  and  other  magnesian  oxides,  replacing,  it 
may  be  presumed,  the  lime  in  part.  This  extensive  class  of  minerals  has  been  very 
fully  studied  by  Dr.  Thomson,  who  has  added  considerably  to  their  number. — 
(Outlines  of  Mineralogy  and  Geology,  vol.  i.) 

EARTHENWARE  AND   PORCELAIN. 

The  silicate  of  alumina  is  the  basis  of  all  the  varieties  of  pottery.  When  mois- 
tened with  water,  clay  possesses  a  high  degree  of  plasticity,  and  can  be  extended 
into  the  thinnest  plates,  fashioned  into  form  by  the  hand,  by  pressure  in  moulds,  or, 
when  dried  to  a  certain  point,  be  modelled  on  the  turning  lathe.  It  loses  its  water 
also  in  drying,  without  cracking,  provided  it  is  allowed  to  contract  equally  in  all 
directions,  and  acquires  greater  solidity.  When  heated  more  strongly  in  the  potter's 
kiln,  in  which  it  is  not  fused  nor  its  particles  agglutinated  by  partial  fusion,  it  be- 
comes a  strong  solid  mass,  which  adheres  to  the  tongue  and  absorbs  water  with 
avidity.  To  render  it  impermeable  to  that  liquid,  it  is  covered  with  a  vitreous 
matter,  which  is  fused  at  a  high  temperature,  and  forms  an  insoluble  glaze  or  varnish 


EARTHENWARE   AND   PORCELAIN.  427 

upon  its  surface.     But  the  interior  mass  of  ordinary  pottery  has  always  an  earthy 
fracture,  and  presents  no  visible  trace  of  fusion. 

When  an  addition  is  made  to  the  clay,  of  some  compound,  which  softens  or  fuses 
at  the  temperature  at  which  the  earthenware  is  fired,  such  as  felspar  in  powder,  then 
the  clay  is  agglutinated  by  the  fusible  ingredient,  and  the  mass  is  rendered  semi- 
transparent,  in  the  same  manner  as  paper  that  has  imbibed  melted  wax  remains 
translucent  after  the  latter  has  fixed.  The  accidental  presence  of  lime,  potassa, 
protoxide  of  iron,  or  any  similar  base  in  the  clay,  may  produce  the  same  effect  by 
forming  a  fusible  silicate  diffused  through  the  clay  in  excess.  Such  is  the  constitu- 
tion of  porcelain,  and  of  brown  salt-glaze  ware  of  which  stoneware  bottles  are  made, 
which  is  indeed  a  sort  of  porcelain.  When  these  kinds  of  ware  are  covered  by  a 
fusible  material,  similar  to  that  which  has  entered  into  the  cgmposition  of  their  body, 
and  a  second  time  fired,  they  acquire  a  vitreous  coating.  Their  fracture  is  vitreous 
and  not  earthy,  the  broken  surface  does  not  adhere  to  the  tongue,  and  the  mass  has 
much  greater  solidity  and  strength  than  the  former  kinds  of  earthenware.  In  com- 
bining the  ingredients  of  porcelain,  an  excess  of  the  fusible  material  is  to  be  avoided, 
as  it  may  cause  the  vessels  to  soften  so  much  in  the  kiln  as  to  lose  their  shape,  or 
even  to  run  down  into  a  glass ;  while  on  the  other  hand  if  the  verifiable  constituent 
is  in  too  small  a  proportion,  the  heat  of  the  furnace  may  be  inadequate  to  soften  the 
mass,  and  to  agglutinate  it  completely. 

Felspar  mixed  with  a  little  clay  is  used  as  the  glaze  for  the  celebrated  porcelain 
of  Levres.  Elsewhere  a  mixture  of  sulphate  of  lime,  ground  porcelain  and  flint,  is 
sometimes  used  as  a  glaze.  In  painting  porcelain,  the  same  metallic  oxides  are  em- 
ployed as  in  staining  glass.  They  are  combined  with  a  vitrifiable  material,  generally 
made  thin  with  oil  of  turpentine,  and  applied  to  the  pottery,  sometimes  under  and 
sometimes  above  the  glaze.  To  fuse  the  latter  colours,  the  porcelain  must  be  exposed 
a  third  time  to  heat,  in  the  enamel  furnace.. 

Stoneware.  —  The  principal  varieties  of  clay  used  here,  according  to  Mr.  Brande, 
are  the  following:  —  1.  Marly  clay,  which,  with  silicic  acid  and  alumina,  contains 
a  portion  of  carbonate  of  lime :  it  is  much  used  in  making  pale  bricks,  and  as  a 
manure,  and  when  highly  heated  enters  into  fusion.  2.  Pipe-clay,  which  is  very 
plastic  and  tenacious,  and  requires  a  "higher  temperature  than  the  preceding  for 
fusion :  when  burned  it  is  of  a  cream  colour,  and  is  used  for  tobacco-pipes  and  white 
pottery.  3.  Potters'  clay  is  of  a  reddish  or  grey  colour,  and  becomes  red  when 
heated ;  it  fuses  at  a  bright-red  heat ;  mixed  with  sand  it  is  manufactured  into  red 
bricks  and  tiles,  and  is  also  used  for  coarse  pottery  (Manual  of  Chemistry,  p.  1131). 
The  glaze  is  applied  to  articles  of  ordinary  pottery  after  they  are  fired,  and  in  the 
condition  of  biscuit- ware.  They  are  dipped  into  a  mixture  of  about  60  parts  of  red 
lead,  10  of  clay,  and  20  of  ground  flint  diffused  in  water  to  a  creamy  consistence, 
and  when  taken  out  enough  adheres  to  the  piece  to  give  a  uniform  glazing  when 
again  heated.  To  cover  the  red  colour  which  iron  gives  to  the  common  clays  when 
burnt,  the  body  of  the  ware  is  sometimes  coloured  uniformly  of  a  dull  green,  by  an 
admixture  of  oxide  of  chromium,  or  made  black  by  oxides  of  manganese  and  iron ; 
or  oxide  of  tin  is  added  to  the  materials  of  the  glaze,  to  render  it  white  and  opaque. 
The  patterns  on  ordinary  earthenware  are  generally  first  printed  upon  tissue-paper, 
in  an  oily  composition,  from  an  engraved  plate  of  copper,  and  afterwards  transferred 
by  applying  the  paper  to  the  surface  of  the  biscuit  ware,  to  which  the  colour  adheres. 
The  paper  is  afterwards  removed  by  a  wet  sponge.  The  fusion  of  the  colouring 
matters  takes  place  with  that  of  the  glaze,  which  is  subsequently  applied,  in  the 
second  firing.  The  prevailing  colours  of  these  patterns  are  blue  from  oxide  of  cobalt, 
green  from  oxide  of  chromium,  and  pink  from  that  compound  of  oxide  of  tin,  lime, 
and  a  small  quantity  of  oxide  of  chromium,  known  as  pink  colour. 


428  GLUCINUM. 

SECTION   II. 

GLUCINUM,  YTTRIUM,   THORIUM,   ZIRZONIUM 

GLUCINUM. 
Eg.  6.97  or  87.06;  Gl. 

Syn.  Beryllium. — The  compounds  of  this  metal  have  a  considerable  analogy  to 
those  of  aluminum.  Glucinum  is  obtained  from  its  chloride,  which  is  decomposed 
by  potassium  in  the  same  manner  as  the  chloride  of  aluminum.  This  metal  is  fusible 
with  great  difficulty,  not  oxidable  by  air  or  water  at  the  usual  temperature,  but  it 
takes  fire,  in  oxygen,  at  a  red-heat,  and  burns  with  a  vivid  light.  It  derives  its 
name  from  yhvxvf,  sweet,  in  allusion  to  the  sweet  taste  of  the  salts  of  its  oxide, 
glucina. 

Glucina,  Bcryllia;  G1203  is  a  comparatively  rare  earth,  but  contained  to  the 
extent  of  13 f  per  cent,  in  the  emerald  and  beryl,  of  which  specimens  that  are  not 
transparent  and  well  crystallized  can  be  procured  in  considerable  quantity.  To 
decompose  this  mineral,  which  is  a  silicate  of  glucina  and  alumina,  it  must  be 
reduced  to  an  extremely  fine  powder,  the  grosser  particles  which  fall  first  when  the 
powder  is  suspended  in  water,  being  submitted  again  to  pulverization,  and  the  pow- 
der calcined  with  3  times  its  weight  of  hydrate  of  potassa.  The  calcined  mass  is 
moistened  with  water,  and  then  treated  with  hydrochloric  acid,  added  in  small  por- 
tions till  it  is  in  excess.  The  potassa,  alumina,  and  glucina,  are  thus  converted  into 
chlorides,  and  dissolved.  The  solution  is  evaporated  to  dryness  on  a  water-bath, 
and  the  residue  acidulated  by  a  few  drops  of  hydrochloric  acid  :  the  silicic  acid 
remains  undissolved.  On  adding  afterwards  carbonate  of  ammonia  in  considerable 
excess  to  the  filtered  liquid,  the  alumina  is  precipitated  together*  with  the  lime  and 
oxides  of  iron  and  chromium  which  are  usually  present,  while  the  glucina  alone 
remains  in  solution.  The  liquor  is  filtered,  and  the  carbonate  of  ammonia  being 
then  expelled  from  it  by  ebullition,  carbonate  of  glucina  precipitates.  The  earthy 
carbonate  is  ignited,  and  leaves  glucina  in  the  state  of  a  white  and  light  powder, 
tasteless,  infusible  by  heat,  insoluble  in  water  and  caustic  ammonia,  but  soluble  in 
caustic  potassa  and  soda.  Its  density  is  nearly  3.  It  is  distinguished  from  alu- 
mina, which  it  greatly  resembles,  by  absorbing  carbonic  acid  from  the  air,  and 
readily  forming  a  carbonate ;  and  most  remarkably  by  being  soluble,  when  freshly 
precipitated,  in  a  cold  solution  of  carbonate  of  ammonia.  It  is  capable  of  decom- 
posing the  salts  of  ammonia  in  a  hot  solution,  and  replaces  that  base.  The  salts  of 
glucina  do  not  form  an  alum  when  treated  with  sulphate  of  potassa ;  nor  do  they 
become  blue,  like  the  salts  of  alumina,  when  heated  before  the  blow-pipe  with  nitrate 
of  cobalt. 

Glucina  combines  with  sulphuric  acid  in  several  proportions,  forming  a  bisulphate, 
G1203.6S03,  which  is  cry  stall  i  zable  ;  a  neutral  sulphate,  G1203.3S08  +  12  HO, 
which, forms  fine  crystals;  a  soluble  subsalt,  G1203.2S03,  and  an  insoluble  subsalt, 
G1203.S03. 

Emerald  or  beryl  is  a  double  silicate  of  glucina  and  alumina,  of  the  composition 
expressed  by  GI2O3.Si03-f  Al203.Si03;  but  contains  besides,  lime  and  some  chro- 
mium and  iron.  This  mineral  crystallizes  in  six-sided  prisms,  which  are  very  hard. 
When  coloured  green  by  oxide  of  chromium  it  forms  the  true  emerald,  and  when 
colourless  and  transparent  aqua  marina,  which  are  both  ranked  among  the  precious 
etones.  The  density  of  the  emerald  is  2.58  to  2.732. 

Euclase  is  also  a  silicate  of  glucina  and  alumina.  It  is  a  very  rare  mineral, 
which  crystallizes  in  limpid,  greenish  prisms. 

Chrysoberyl,  one  of  the  finest  of  the  gems,  consists  essentially  of  1  equivalent 
of  glucina  combined  with  6  equivalents  of  alumina,  G1203,  6A1203. 

Jt  is  very  doubtful  whether  glucina  is  a  sesquioxide,  G1203,  analogous  in  compo- 


THORIUM.  429 

sition  to  alumina.     It  is  indeed  quite  as  probable  that  glucina  is  a  protoxide,  G10, 
analogous  to  magnesia.    The  equivalent  of  glucinum  would  then  be  reduced  to  4.64 
on  the  hydrogen-scale,  and  58.04  on  the  oxygen-scale. 
[See  Supplement,  p.  821.] 


YTTRIUM,    ERBIUM,   AND   TERBIUM. 

Eg.  32.20  or  402.5;  Y. 

The  earth  yttria  was  discovered  in  1794,  by  Gradolin,  in  a  mineral  from  Ytterby 
in  Sweden,  which  is  now  called  gadolinite.  It  has  since  been  found  in  several  other 
minerals,  but  all  of  which  are  exceedingly  rare.  The  metal  was  isolated  from  its 
chloride  by  Wbhler,  precisely  in  the  same  manner  as  the  two  preceding  metals.  It 
is  of  a  darker  colour  than  these  metals,  and  in  oxidability  resembles  glucinum. 

Yttria  is  considered  a  protoxide,  YO.  Its  density  is  even  greater  than  baryta, 
being  4.842.  It  is  absolutely  insoluble  in  the  caustic  alkalies,  is  precipitated  by 
yellow  prussiate  of  potassa,  and  its  sulphate  and  some  others  of  its  salts  have  an 
amethystine  tint,  properties  which  distinguish  it  from  the  preceding  earths.  The 
nitrate  of  yttria  is  colourless  and  crystallizable.  The  chloride  of  yttrium  is  deli- 
quescent, and  does  not  appear  to  be  voktile. 

In  what  has  hitherto  been  distinguished  as  yttria  two  new  bases  have  lately  been 
discovered  by  M.  Mosander,  which  have  been  named  erbia  and  terbia.  These 
oxides  are  less  soluble  in  dilute  sulphuric  acid  than  yttria,  and  are  thereby  separated 
from  that  earth.  From  a  solution  in  nitric  acid  of  the  two  new  earths,  oxide  of 
erbium  is  precipitated  by  saturating  the  liquid  with  sulphate  of  potassa,  in  the  form 
of  a  sparingly  soluble  double  salt,  while  the  oxide  of  terbium  remains  in  solution. 
Each  of  these  bases  may  then  be  precipitated  singly  by  means  of  potassa. 

The  sulphate  and  nitrate  of  terbia  readily  crystallize ;  the  former  salt  is  efflores- 
cent. The  salts  of  terbia  are  apt  on  dessiccation  to  assume  a  red  amethystine  tint. 

Erbia  assumes  a  deep-yellow  tint  when  made  anhydrous,  which  appears  to  be  due 
to  oxidation,  as  the  earth  becomes  colourless  in  a  stream  of  hydrogen.  The  sulphate 
of  erbia,  which  is  crystallizable  and  colourless,  does  not  effloresce  in  air,  like  the 
sulphate  of  terbia. 

THORIUM,    OR   THORINUM. 

Eq.  59.59  or  744.9;  Th. 

This  element  was  discovered  by  Berzelius,  in  1824,  in  a  black  mineral,  like  obsi- 
dian, since  called  thorite,  from  the  coast  of  the  North  Sea.  This  mineral  contains 
57  per  cent,  of  the  thorina.  This  element  has  been  named  from  the  Scandinavian 
deity  Thor.  The  metal  was  obtained  from  the  chloride,  and  exhibited  a  general 
resemblance  to  aluminum.  Like  yttrium,  it  burns  in  oxygen  with  a  degree  of  bril- 
liancy which  is  quite  extraordinary:  the  resulting  oxide  does  not  exhibit  the  slightest 
trace  of  fusion. 

Thorina  is  considered. a  protoxide,  ThO.  Its  density  is  9.402,  and  therefore 
superior  to  that  of  all  other  earths.  Thorina  forms  a  hydrate,  ThO.HO,  which  is 
soluble  in  alkaline  carbonates  and  in  all  the  acids.  It  resembles  yttria  in  being 
insoluble  in  the  caustic  alkalies,  but  differs  from  that  earth  in  the  peculiar  property 
of  its  sulphate,  to  be  precipitated  by  ebullition,  and  to  redissolve  entirely,  although 
in  a  slow  manner,  in  cold  water.  Its  sulphate  also  forms  a  double  salt  with  sulphate 
of  potassa,  which  dissolves  in  water,  but  is  insoluble  in  a  liquid  saturated  with  sul- 
phate of  potassa.  The  solutions  of  thorina  are  precipitated  white  by  the  ferrocyanide 
of  potassium,  a  property  by  which  thorina  is  distinguished  from  zirconia.  Thorina 
is  also  precipitated  from  solutions  to  which  an  excess  of  acid  has  been  added,  011 
afterwards  introducing  sufficient  ammonia,  by  which  it  is  distinguished  from  magnesia. 


430  ZIRCONIUM. 

ZIRCONIUM. 

Eq.  33.62  or  420.2;  Zr. 

Zirconium  is  obtained  by  heating  the  double  fluoride  of  zirconium  and  potassium, 
with  potassium,  in  a  glass  or  iron  tube.  On  throwing  the  cooled  mass  into  water, 
the  zirconium  remains  in  the  form  of  a  black  powder,  very  like  charcoal.  It  con- 
tains an  admixture  of  hydrate  of  zirconia,  which  may  be  withdrawn  from  it  by  diges- 
tion in  hydrochloric  acid,  at  104°  (40°  C.)  The  zirconium  is  afterwards  washed 
with  sal-ammoniac  to  remove  completely  chloride  of  zirconium,  and  then  with  alcohol 
to  withdraw  the  sal-ammoniac.  If  washed  with  pure  water,  it  is  apt  to  pass  through 
the  filter.  After  being  thus  treated,  the  powder  assumes,  under  the  burnisher,  the 
lustre  of  iron,  and  is  compressed  into  scales  which  resemble  graphite.  When 
heated  in  air  it  takes  fire  below  redness.  It  is  very  slightly  attacked  by  either 
alkalies  or  acids,  with  the  exception  of  hydrofluoric  acid,  which  dissolves  zirconium 
with  evolution  of  hydrogen. 

The  constitution  of  zirconia  is  not  certainly  known,  but  it  is  believed  to  be  ana- 
logous to  that  of  alumina,  Zr203.  It  was  first  recognized  as  a  peculiar  earth  by 
Klaproth  in  1789,  who  discovered  it  in  the  zircon  of  Ceylon,  a  silicate  of  zirconia; 
which  is  also  found  in  the  syenitic  mountains  of  the  south-east  side  of  Norway. 
The  hyacinth  is  the  same  mineral,  of  a  red-colour ;  it  is  found  in  volcanic  sand  at 
Expailly  in  France,  in  Ceylon,  and  some  other  localities.  The  earth  is  obtained 
from  this  mineral,  which  is  more  difficult  of  decomposition  than  most  others,  by 
processes  for  which  I  must  refer  to  Berzelius.1 

Zirconia  is  a  white  earth,  like  alumina  in  appearance,  of  density  4.3.  Its  hydrate, 
after  being  boiled,  is  soluble  with  difficulty  in  acids.  "When  heated,  it  parts  with  its 
water,  afterwards  glows  strongly,  from  a  discharge  of  heat,  becomes  denser,  and  less 
susceptible  of  being  acted  on  by  reagents.  Zirconia  forms  a  carbonate.  When  once 
separated  from  its  combinations,  it  is  insoluble  in  carbonate  of  potassa  or  soda,  but 
dissolves  in  them  in  the  nascent  state.  The  salts  of  zirconia  have  a  purely  astrin- 
gent taste.  It  agrees  with  thorina  in  being  precipitated,  when  any  of  its  neutral 
salts  are  boiled  with  a  solution  of  sulphate  of  potassa.  The  chloride  of  zirconium  is 
volatile,  but  less  so  than  the  chloride  of  silkmim ;  a  property  which  has  been  taken 
advantage  of  by  M.  Wohler  in  preparing  zirconia. 

1  TraitS  de  Chimie,  ii.  171.     Paris,  1846. 


MANGANESE.  431 


ORDER   IY. 

METALS '  PROPER   HAVING   PROTOXIDES    ISOMORPHOUS   WITH    MAGNESIA. 

SECTION    I. 

MANGANESE. 

p 

Eq.  27-67  or  345-9;  MD. 

THIS  element  is  found  in  the  ashes  of  plants,  in  the  bones  of  animals,  and  in 
many  minerals,  of  which  that  employed  in  the  preparation  of  oxygen  is  one  of  the 
richest.  The  black  oxide  of  manganese  was  long  known  as  magnesia  niyra,  from 
a  fancied  relation  to  magnesia  alba;  but  was  first  thoroughly  studied  by  Scheele, 
in  1774,  and  immediately  afterwards  by  Gahn,  who  obtained  from  it  the  metal 
now  called  manganese. 

From  its  strong  affinity  for  oxygen,  and  the  very  high  temperature  which  it 
requires  for  fusion,  manganese  is  one  of  the  most  difficult  of  all  the  metals  proper, 
to  reduce  and  fuse  into  a  button.  Hydrogen  and  charcoal,  at  a  red  heat,  reduce 
the  superior  oxides  of  this  metal  to  the  state  of  protoxide,  without  eliminating  the 
pure  metal  at  that  temperature ;  but  at  a  white  heat,  charcoal  deprives  the  metal 
of  the  whole  of  its  oxygen.  The  following  process  is  recommended  by  M.  John 
for  the  reduction  of  manganese  :  it  illustrates  the  chief  points  to  be  attended  to  in 
the  reduction  of  the  less  tractable  metals.  Instead  of  a  native  oxide,  an  artificial 
oxide  of  manganese,  obtained  by  calcining  the  carbonate  in  a  well-closed  vessel,  is 
operated  upon.  This  oxide,  which  is  preferred  from  being  in  a  high  state  of  divi- 
sion, is  mixed  with  oil  and  ignited  in  a  covered  crucible,  so  as  to  convert  the  oil 
into  charcoal.  After  several  repetitions  of  this  treatment,  the  carbonaceous  mass 
is  reduced  to  powder,  and  made  into  a  firm  paste  by  kneading  it  with  a  little  oil. 
Finally,  this  paste  is  introduced  into  a  crucible  lined  with  charcoal  (creuset 
brasque),  the  unoccupied  portion  of  which  is  filled  up  with  charcoal  powder.  The 
crucible  is  first  heated  merely  to  redness  for  half  an  hour,  to  dry  the  mass  and 
decompose  the  oil;  after  which  its  cover  is  carefully  luted  down,  and  it  is  exposed 
for  an  hour  and  a  half  to  the  most  violent  heat  of  a  wind-furnace  that  the  crucible 
itself  can  support  without  undergoing  fusion.  The  metal  is  obtained  in  the  form 
of  a  semi-globular  mass  or  button  in  the  lower  part  of  the  crucible,  but  not  quite 
pure,  as  it  contains  traces  of  carbon  and  silicon  derived  from  the  ashes  of  the  char- 
coal. By  igniting  the  metal  a  second  time  in  a  charcoal  crucible,  with  a  portion 
of  borax,  John  obtained  it  more  fusible  and  brilliant,  and  so  free  from  charcoal, 
that  it  left  no  black  powder  when  dissolved  in  an  acid. 

Manganese. is  a  greyish  white  metal,  having  the  appearance  of  hard  cast  iron. 
Its  density,  according  to  John,  is  8-013;  while  M.  Eerthier  finds  it  to  be  7'05, 
and  Bergmann  made  it  6-850:  according  to  Hjelm,  it  is  7'0.  From  its  close  re- 
semblance to  iron,  manganese  may  be  oxpected  to  be  susceptible  of  magnetism ; 
but  its  magnetic  powers  are  doubtful.  Pe"clet  has  endeavoured  to  show  that  man- 
ganese can  assume  and  preserve  magnetic  polarity  from  the  temperature  —  4°  up 
to  70°,  but  loses  it  again  at  higher  temperatures.  The  small  difference  between 
the  atomic  weights  of  iron,  manganese,  cobalt,  and  nickel,  which  are  respectively 
28,  27'67,  29-52,  and  29-57,  is  remarkable,  attended  as  it  is  by  a  great  analogy 
between  these  metals  in  many  other  respects. 

Manganese  oxidates  readily  in  air,  soon  falling  down  as  a  black  powder;  in 


432 


MANGANESE. 


water  it  occasions  a  disengagement  of  hydrogen  gas.  It  is  best  preserved  in 
naphtha,  like  potassium,  or  over  mercury.  Manganese  exhibits  five  degrees  of 
oxidation,  with  two  intermediate  or  compound  oxides. 


OXIDES    OP    MANGANESE. 

Protoxide  or  manganous  oxide  ..................  MnO. 

Sesquioxide  or  manganic  oxide  ..................  Mn203. 

Bioxide  or  Peroxide  ..............................  Mn02. 

Manganoso-manganic  oxide  or  red  oxide  ......  Mn3O4,  or  MnO-f  Mn203. 

Varvicite  ......  .  .....................................  Mn407,  or  Mn203  +  2Mn02. 

Manganic  acid  .......  •.  .............................  Mn03. 

Permanganic  acid  .................................  Mn207. 

Protoxide  of  manganese  :  Manganous  oxide;  MnO,  35-67  or  445-9.  —  This  is 
the  oxide  existing  in  the  ordinary  salts  of  manganese,  which  are  isomorphous  with 
the  salts  of  magnesia.  It  may  be  obtained  by  fusing  at  a  red  heat  in  a  platinum 
crucible,  a  mixture  of  equal  parts  of  pure  chloride  of  manganese  and  carbonate  of 
soda,  with  a  small  quantity  of  sal  ammoniac.  By  the  reaction  between  the  first- 
mentioned  salts,  chloride  of  sodium  is  produced,  together  with  the  carbonate  of 
manganese,  which  is  decomposed  at  a  red  heat,  leaving  the  protoxide  of  that 
metal.  The  hydrogen  of  the  sal-ammoniac  at  the  same  time  reduces  to  the  state 
of  protoxide  any  bioxide  which  may  be  formed  by  absorption  of  oxygen  from  the 
air.  Any  one  of  the  superior  oxides  of  manganese,  in  the  state  of  fine  powder, 
may  be  converted  into  protoxide  by  passing  hydrogen  gas  over  it,  in  a  porcelain 
tube  at  a  red  heat  :  the  bioxide  obtained  by  igniting  the  nitrate  of  the  protoxide 
of  manganese  was  recommended  by  Dr.  Turner  as  the  most  easily  deoxidated. 

Protoxide  of  manganese  is  a  powder  of  a  greyish  green  colour,  more  or  less  deep. 
When  obtained  by  mears  of  hydrogen  at  a  low  temperature,  it  absorbs  oxygen  from 
the  air,  soon  becoming  brown  throughout  its  whole  mass,  and  is,  indeed,  sometimes 
a  pyrophorus  ;  but  when  prepared  by  hydrogen  at  a  high  temperature,  it  acquires 
more  cohesion,  and  is  permanent. 

Protoxide  of  manganese  dissolves  readily  in  acids,  and  is  a  strong  base.  Its 
salts  are  of  a  pale  rose  tint,  which  is  not  destroyed  by  sulphurous  or  hydrosulphuric 
acid,  and  must  be  considered  as  a  peculiar  character  of  manganous  salts.  When 
the  solution  is  colourless,  as  it  sometimes  is,  the  fact"  is  explained,  according  to 
M.  Grbrgeu,  by  the  presence  of  a  salt  of  iron,  nickel,  or  copper;  the  green  or  blue 
tint  of  the  latter  metals  producing  white  or  a  scarcely  perceptible  violet  shade 
when  combined  with  the  rose  tint  of  a  salt  of  manganese.  Caustic  alkalies  added 
to  solutions  of  manganous  salts  throw  down  the  protoxide  of  manganese  in  the 
form  of  a  white  hydrate,  which  soon  absorbs  oxygen  from  the  air  and  becomes 
brown  ;  when  collected  on  a  filter  and  washed,  it  ultimately  changes  into  a  blackish 
brown  powder,  which  is  the  hydrate  of  the  sesquioxide.  A  similar,  change  is  in- 
stantaneously produced  by  the  action  of  chlorine-  water  upon  the  white  hydrate,  or 
by  the  addition  of  chloride  of  lime  to  a  salt  of  the  protoxide  of  manganese  ;  but 
then  the  hydrated  bioxide  is  formed.  Protoxide  of  manganese  resembles  magnesia 
and  protoxide  of  iron,  in  being  but  partially  precipitated  by  ammonia.  The  alka- 
line monocarbonates  precipitate  white  carbonate  of  manganese,  which  does  not  turn 
brown  in  the  air,  and  dissolves  sparingly  in  a  cold  solution  of  sal-ammoniac. 
Bicarbonate  of  potash  precipitates  a  strong  solution  immediately,  and  renders  a 
dilute  solution  slightly  turbid  ;  but  if  the  solution  contains  a  free  acid,  so  that  an 
excess  of  carbonic  acid  is  set  free,  no  precipitate  is  formed.  The  earthy  carbon- 
ates do  not  precipitate  manganous  salts.  Ilydrosulphuric  arid  forms  no  precipi- 
tate in  neutral  solutions  of  manganous  salts  containing  any  of  the  stronger  acids. 
In  a  neutral  solution  of  the  acetate,  a  flesh-coloured  precipitate  is  formed  after 
some  time;  but  not  if  the  solution  contains  free  acetic  acid.  Sulphide  of  ammo- 


OXIDES    OF    MANGANESE.  433 

nium  forms  in  neutral  solutions  of  manganous  salts  a  flesh-coloured  precipitate  of 
hydrated  sulphide  of  manganese,  insoluble  in  excess  of  sulphide  of  ammonium,  but 
readily  soluble  in  acids.  When  exposed  to  the  air,  it  turns  brown  on  the  surface, 
from  oxidation.  The  least  trace  of  iron  or  cobalt  colours  it  black.  Ferrocyanide 
of  potassium  forms  in  neutral  solutions  of  manganous  salts  a  white  precipitate, 
having  a  tinge  of  red,  and  soluble  in  free  acids.  Ferricyanide  of  potassium  forms 
a  reddish  precipitate,  which  is  insoluble  in  acids.  Manganous  salts,  and  indeed 
all  compounds  of  manganese,  heated  with  borax  or  phosphorus-salt  in  the  outer 
blowpipe  flame,  form  an  amethyst-coloured  bead  containing  manganoso-manganic 
oxide,  which  becomes  colourless  in  the  inner  flame  by  reduction  of  that  oxide  to 
the  protoxide.  This  character  distinguishes  manganese  from  all  other  metals. 
The  minutest  trace  of  manganese  is  discovered  by  heating  the  solution  with  a  little 
bioxide  of  lead  and  nitric  acid,  when  a  red  tint  appears  due  to  the  formation  of 
permanganic  acid  (W.  Crum).  An  equally  delicate  reaction  is  obtained  in  the 
dry  way  by  heating  the  substance  supposed  to  contain  manganese  with  carbonate 
of  soda  on  platinum  foil  in  the  outer  blowpipe  flame.  The  smallest  trace  of  man- 
ganese is  indicated  %  the  formation  of  green  manganate  of  soda.  The  delicacy 
of  the  reaction  may  be  increased  by  adding  a  little  nitre  to  the  carbonate  of  soda. 

Protosulphide  of  manganese  may  be  procured  in  the  dry  way,  by  heating  a 
mixture  of  bioxide  of  manganese  and  sulphur.  Sulphurous  acid  is  disengaged, 
and  a  green  powder  remains,  which  dissolves  in  acids  with  disengagement  of  hy- 
drosulphuric  acid.  The  same  compound  is  obtained  in  the  humid  way,  when 
acetate  of  manganese  is  decomposed  by  hydrosulphuric  acid,  or  any  manganous 
salt  precipitated  by  an  alkaline  sulphide.  Protosulphate  of  manganese,  decom- 
posed by  hydrogen  at  a  red  heat,  yields  an  oxisulphide.  A  crystalline  sulphide  is 
obtained  by  passing  the  vapour  of  bisulphide  of  carbon  over  hydrated  manganic 
oxide  ignited  in  a  porcelain  tube :  the  crystals  are  iron-black  rhombic  prisms, 
having  a  tinge  of  green,  and  yielding  a  dingy  green' powder  (Yb'lker). 

Phosphide  of  manganese  is  obtained  by  exposing  an  intimate  mixture  of  10 
parts  of  pure  ignited  bioxide  of  manganese,  10  parts  of  white  burnt-bones,  5 
parts  of  white  quartz-sand,  and  3  parts  of  ignited  lamp-black  for  an  hour  in  a 
closed  Hessian  crucible  to  a  heat  sufficient  to  melt  cast-iron, — or  by  strongly  igni- 
ting 10  parts  of  ignited  phosphate  of  manganese,  3  parts  of  ignited  lamp-black, 
and  2  parts  of  calcined  borax  in  a  crucible  lined  with  charcoal.  The  product  is 
a  very  brittle,  crystalline  regulus  of  the  colour  of  grey  cast-iron,  and  of  specific 
gravity  5-951.  It  is  permanent  in  the  air,  glows  when  heated  in  contact  with  air, 
and  burns  with  an  intense  light  when  heated  with  nitre.  It  appears  to  contain 
Mn5P,  and  is  probably  a  mixture  of  Mn3P  and  Mn7P,  the  latter  of  which  com- 
pounds is  left  behind  when  the  substance  is  treated  with  hydrochloric  acid,  while 
the  former  dissolves,  with  evolution  of  non-spontaneously  inflammable  phosphu- 
retted  hydrogen  (Wb'hler). 

Protochloride  of  manganese:  MnCl+4HO;  63-17  -f-  36  or  789-63  +  450.— 
This  salt  crystallizes  in  thick  tables,  which  are  oblong  and  quadrilateral,  and  of  a 
rose  colour;  it  is  very  soluble  in  water,  and  slightly  deliquescent.  The  residuary 
liquid  obtained  in  preparing  chlorine  by  dissolving  bioxide  of  manganese  in  hydro- 
chloric acid,  consists  of  chloride  of  manganese  contaminated  with  a  portion  of 
sesquichloride  of  iron.  To  remove  the  latter  and  obtain  a  pure  chloride  of  man- 
ganese, the  solution  should  be  boiled  down  considerably  to  expel  the  excess  of 
acid,  diluted  afterwards  with  water,  and  boiled  again  with  carbonate  of  manganese, 
which  salt  precipitates  the  whole  of  the  sesquioxide  of  iron,  forming  chloride  of 
manganese  with  its  acid  (Everitt).  If  about  one-fourth  of  the  impure  solution 
of  chloride  of  manganese  be  reserved,  and  precipitated  by  carbonate  of  soda,  a 
quantity  of  carbonate  of  manganese  will  be  obtained  sufficient  to  precipitate  the 
iron  from  the  other  three-fourths  of  the  liquid,  and  applicable  to  that  purpose 
after  it  has  been  washed.  The  iron  may  likewise  be  separated  by  evaporating  the 
solution  of  the  impure  chloride  to  dryness,  heating  the  residue  to  low  redness  in 


434  MANGANESE. 

a  crucible,  as  long  as  hydrochloric  acid  continues  to  escape;  then  leaving  it  to 
cool,  exhausting  with  boiling  water,  and  filtering.  The  hydrated  chloride  of  iron 
is  resolved  by  the  heat  into  hydrochloric  acid  and  sesquioxide,  while  the  chloride 
of  manganese  remains  unaltered,  and  is  easily  dissolved  out  by  water,  all  the  iron 
remaining  behind.  Chloride  of  manganese,  when  free  from  iron,  is  precipitated 
white,  without  any  shade  of  blue,  by  ferrocyanide  of  potassium.  The  crystals 
retain  one  of  their  four  equivalents  of  water  at  212°  (Brandes),  but  may  be  ren- 
dered anhydrous  at  a  higher  temperature.  Brandes  finds  100  parts  of  water  to 
dissolve  at  50°,  38-3  ;  at  88°,  46-2;  at  144-5°,  55  parts  of  the  anhydrous  salt. 
A  higher  temperature,  instead  of  increasing  the  solubility  of  this  salt,  diminishes 
it.  From  the  aqueous  solution,  chlorine,  with  the  aid  of  heat,  throws  down  the 
black  hydrated  bioxide  of  manganese.  Hypochlorous  acid  produces  a  similar 
result,  with  evolution  of  free  chlorine.  Absolute  alcohol  dissolves  half  its  weight 
of  the  anhydrous  chloride  of  manganese,  and  affords,  by  evaporation  in  vacuo,  a 
crystalline  alcoate,  containing  two  equivalents  of  alcohol. 

Chloride  of  manganese  forms  two  crystalline  double  salts  with  chloride  of  am- 
monium. One  of  these,  MnCl.  NH4C1,  forms  cubical  crystals,  containing  1  equiv. 
water,  according  to  Rammelsberg,  and  2  eq.  according  to  Hauer.  These  crystals 
when  ignited  leave  manganoso-manganic  oxide  in  microscopic  pyramids  resembling 
Hausmanite.  The  other  salt,  2MnCl.NH4Cl-t-4HO,  forms  crystals  belonging  to 
the  oblique  prismatic  system  (Hautz).  Solution  of  chloride  of  manganese  con- 
taining chloride  of  ammonium,  yields,  on  addition  of  ammonia  and  exposure  to 
the  air,  a  precipitate  of  hydrated  manganoso-manganic  oxide  (Otto). 

Protocyanide  of  manganese  is  obtained  in  the  form  of  a  yellowish  or  reddish- 
white  precipitate,  on  adding  cyanide  of  potassium  to  the  solution  of  a  manga nous 
salt.  It  quickly  turns  brown  on  exposure  to  the  air.  It  is  decomposed  by  the 
stronger  acids,  and  dissolves  in  alkaline  cyanides. 

The  corresponding  fluoride  of  manganese  forms,  with  fluoride  of  silicon,  a 
double  salt  which  is  very  soluble  in  water  and  crystallizes  in  long  regular  prisms 
of  six  sides.  The  formula  of  this  double  salt  is,  according  to  Berzelius,  2SiF3-f- 
3MnF  +  21HO. 

Carbonate  of  manganese  is  a  white  insoluble  powder,  which  acquires  a  brown 
tint  when  exposed  in  the  dry  state  at  140°.  It  is  decomposed  by  a  red  heat. 
Carbonate  of  manganese  occurs  in  the  mineral  kingdom,  in  the  form  of  manga- 
nese-spar 3  but  never  in  a  state  of  purity,  being  mixed  with  the  carbonates  of  lime 
and  iron,  which  have  the  same  crystalline  form,  viz.  the  rhombohedral.  Its  pre- 
sence in  spathic  carbonate  of  iron  is  said  to  be  the  cause  why  the  latter  yields  an 
iron  peculiarly  adapted  for  the  manufacture  of  steel. 

Protosulphate  of  manganese  ;  Manganous  sulphate  ;  MnO,  S03  +  7HO.  —  A 
solution  of  this  salt,  used  in  dyeing  and  entirely  free  from  iron,  is  prepared  by 
igniting  bioxide  of  manganese  mixed  with  about  one-tenth  of  its  weight  of 
pounded  coal  in  a  gas  retort.  The  protoxide  thus  formed  is  dissolved  in  sulphuric 
acid,  with  the  addition  of  a  little  hydrochloric  acid  towards  the  end  of  the  pro- 
cess ;  the  sulphate  is  evaporated  to  dryness,  and  again  heated  to  redness  in  the  gas 
retort.  The  iron  is  found  after  ignition  in  the  state  of  sesquioxide  and  insoluble, 
the  persulphate  of  iron  being  decomposed,  while  the  sulphate  of  manganese  is  not 
injured  by  the  temperature  of  ignition,  and  remains  soluble.  The  salt  may  also 
be  obtained  by  heating  bioxide  of  manganese,  previously  freed  from  the  carbonates 
of  lime  and  magnesia  by  boiling  with  dilute  sulphuric  acid,  with  an  equal  weight 
of  strong  oil  of  vitriol,  and  gently  igniting  the  resulting  mass  for  an  hour,  to 
decompose  the  sulphates  of  iron  and  copper  formed  at  the  same  time.  The  inan- 
ganous  sulphate,  which  remains  unaltered,  is  then  dissolved  in  water,  and  the 
solution  evaporated  to  the  crystallizing  point.  The  solution  is  of  an  amethystine 
colour,  and  does  not  crystallize  readily.  When  cloth  is  passed  through  sulphate 
of  manganese  and  afterwards  through  a  caustic  alkali,  protoxide  of  manganese  is 
precipitated  upon  it,  and  rapidly  becomes  brown  in  the  air;  or  it  is  peroxidized  at 


OXIDES    OF    MANGANESE.  435 

once  by  passing  the  cloth  through  a  solution  of  chloride  of  lime.  The  colour 
thus  produced  is  called  manganese-brown. 

Crystallized  under  42°,  the  sulphate  of  manganese  gives  crystals  containing 
7 HO,  which  have  the  same  form  as  sulphate  of  iron.  The  crystals  which  form 
between  45°  and  68°,  contain  5HO,  and  are  isomorphous  with  sulphate  of  copper. 
By  a  higher  temperature,  from  68°  to  86°,  a  third  set  of  crystals  is  obtained,  which 
contain  4HO :  their  form  is  a  right  rhombic  prism.  The  sulphate  of  iron  and 
other  sulphates  also  assume  the  same  form  (Mitscherlich).  This  salt  loses  3HO 
at  243°,  but  retains  1  eq.  even  at  400°,  like  the  other  magnesian  sulphates.  M. 
Kuhn  finds,  that  when  a  strong  solution  of  the  sulphate  of  manganese  is  mixed 
with  sulphuric  acid  and  evaporated  by  heat,  a  granular  salt  is  precipitated,  which 
contains  only  one  equivalent  of  water.  This  sulphate  also  forms  with  sulphate  of 
potash  a  double  salt  containing  6HO.  The  anhydrous  salt  is  soluble,  according 
to  Brandes,  in  2  parts  of  water  at  59°,  in  1  part  at  122° ;  but  above  the  latter 
temperature,  the  salt  becomes  less  soluble.  The  tetra-hydrated  salt  dissolves  in 
0-883  part  of  water  at  43-3°;  in  0-79  part  at  50°;  in  0-82  part  at  65.8;  in  0-67 
part  at  99  5°;  and  in  1-079  part  at  2-1°.  Manganous  sulphate  is  insoluble  in 
absolute  alcohol,  but  dissolves  in  500  parts  of  spirit  of  the  strength  of  55  per 
cent. 

Hypomlphate  of  manganese  ;  MnO  .  S205-f-()HO.  For  the  preparation,  see  p. 
253. — The  bioxide  of  manganese  used  in  preparing  it  should  be  previously  treated 
with  nitric  acid,  to  dissolve  out  the  hydrated  oxide,  and  be  well  washed.  The 
salt  forms  rose-coloured,  generally  indistinct,  crystals,  belonging  to  the  doubly 
oblique  prismatic  system  (Marignac).  The  oxalate  of  manganese  is  a  highly  inso- 
luble salt.  The  acetate  is  soluble  in  3?  parts  of  cold  water,  and  also  in  alcohol. 
Bitartrate  of  potash  dissolves  protoxide  of  manganese,  and  forms  a  very  soluble 
double  salt,  the  tartrate  of  potash  and  manganese,  which  can  be  obtained,  although 
with  difficulty,  in  regular  crystals. 

Sesquioxide  of  manganese  ;  Manganic  oxide  ;  Mn203;  79-34  or  991-8. — This 
oxide  is  left  of  a  dark  brown,  almost  black  colour,  when  the  nitrate  of  the  pro- 
toxide is  gently  ignited.  It  also  occurs  crystallized  in  the  mineral  kingdom, 
although  rarely;  its  density  is  4-818,  and  it  is  named  Iraunite  as  a  mineral  spe- 
cies. The  hydrate  of  manganic  oxide  is  formed  by  the  oxidation  in  air  of  man- 
ganous  hydrate.  Manganic  hydrate  also  frequently  occurs  in  nature  of  a  black 
colour,  both  crystallized  and  amorphous,  and  is  often  mixed  with  the  bioxide  of 
manganese.  It  constitutes  the  mineral  species  manganite,  of  which  the  density 
is  4-3  to  44,  and  the  formula  Mn203,  HO.  This  hydrate  may  be  artificially  pre- 
pared by  heating  finely  divided  bioxide  of  manganese  with  monohydrated  sulphuric 
acid,  decomposing  the  resulting  manganic  sulphate  with  water,  and  washing  it 
thoroughly  (Carius).  This  oxide  colours  glass  of  a  red  or  violet  tint.  The  com- 
mon violet  or  purple  stained  glass  contains  manganic  oxide ;  also  the  amethyst. 

Manganic  oxide  is  a  base  isomorphous  with  alumina  and  sesquioxide  of  iron. 
It  dissolves  in  cold  hydrochloric  acid  without  decomposition.  Concentrated  sul- 
phuric acid  combines  with  it  at  a  temperature  a  little  above  212°,  but  does  not 
form  a  solution.  Dilute  sulphuric  acid  does  not  dissolve  it,  either  in  the  cold  or 
when  gently  heated,  unless  manganous  oxide  is  present,  even  in  very  small  quan- 
tities, in  which  case  a  violet  solution  is  formed ;  hence  the  commonly  received 
statement  that  manganic  oxide  forms  a  red  solution  with  sulphuric  acid  (Carius). 
At  somewhat  elevated  temperatures,  acids  reduce  the  sesquioxide  of  manganese  to 
protoxide,  with  evolution  of  oxygen. 

Manganic  sulphate;  Mn203 .  3  S03. — Prepared  by  mixing  finely  divided  bioxide 
of  manganese  (obtained  by  passing  chlorine  gas  through  a  solution  of  carbonate  of 
soda  in  which  carbonate  of  manganese  is  suspended)  with  monohydrated  sulphuric 
acid  to  the  consistence  of  a  pulp,  and  gradually  heating  the  mixture  in  an  oil-bath 
to  about  276°,  &  which  point  the  mass  becomes  dark  green  and  more  mobile.  It 


436  MANGANESE. 

is  then  drained  on  a  plate  of  pumice-stone  to  remove  the  greater  part  of  the  sul- 
phuric acid ;  afterwards  stirred  up  in  a  warm  basin  with  the  strongest  nitric  acid 
(free  from  nitrous  acid) }  again  drained  on  pumice-stone ;  and  this  treatment  re- 
peated several  times :  lastly,  it  is  dried  in  the  oil-bath  at  266°,  and  preserved  in 
carefully  dried  tubes.  —  Manganic  sulphate  thus  obtained  is  a  dark  green  powder 
which  exhibits  no  traces  of  crystallization.  It  may  be  heated  to  320°  without  de- 
composition, but  at  higher  temperatures  gives  off  oxygen  and  is  reduced  to  man- 
ganous  sulphate.  At  ordinary  temperatures  it  is  all  but  insoluble  in  concentrated 
sulphuric  and  nitric  acid ;  with  the  former  it  may  be  heated  nearly  to  the  boiling 
point  without  alteration,  but,  when  boiled  with  the  acid,  it  dissolves  as  manganous 
sulphate,  with  evolution  of  oxygen.  Heated  with  concentrated  nitric  acid  to  212°, 
it  turns  brown,  but  resumes  its  green  colour  when  the  acid  is  evaporated  at  the 
lowest  possible  temperature.  In  strong  hydrochloric  acid,  it  dissolves,  like  the 
pure  sesquioxide,  forming  a  brown  solution,  which  when  heated  gives  off  chlorine 
till  all  the  sesquioxide  of  manganese  is  reduced  to  protoxide.  Organic  substances, 
heated  with  the  dry  salt,  decompose  it  with  considerable  violence.  The  salt  ab- 
sorbs moisture  very  rapidly,  so  that  it  must  always  be  kept  in  sealed  tubes.  Small 
quantities  of  it  deliquesce  in  a  few  seconds,  forming  a  violet  solution,  which,  how- 
ever, soon  becomes  brown  and  turbid  from  separation  of  the  hydrated  oxide. 
Water  decomposes  the  salt  rapidly,  especially  when  heated,  separating  the  pure 
hydrated  sesquioxide.  Hence  the  mode  of  preparing  the  hydrate  above  men- 
tioned. Sulphuric  acid,  somewhat  diluted,  decomposes  manganic  sulphate,  con- 
verting it  into  a  red-brown  powder,  which  appears  to  be  a  basic  salt.*  Manganic 
sulphate  forms  an  alum  with  sulphate  of  potash  (Mitscherlich)  :  this  salt  occurs 
native  in  needle-shaped  crystals  at  Alum  Point,  on  the  Great  Salt  Lake  in  North 
America  (L.  D.  Gale). 

SesquicMoride  of  manganese  (Mn2Cl3)  is  formed  when  the  sesquioxide  is  dis- 
solved in  hydrochloric  acid  at  a  low  temperature.  The  solution  is  yellowish  brown 
or  black,  according  to  its  degree  of  concentration,  and  fs  decomposed  by  a  slight 
elevation  of  temperature,  with  evolution  of  chlorine.  A  corresponding  sesqui- 
fluoride  may  be  crystallized. 

Sesquicyanide  of  manganese, — A  compound  of  this  cyanide  is  formed,  when 
manganous  acetate  is  mixed  with  hydrocyanic  acid  in  excess,  then  neutralized  with 
potash  and  evaporated.  The  manganous  cyanide  then  absorbs  oxygen,  and  is  con- 
verted into  hydrated  manganic  oxide  and  manganic  cyanide,  which  last  combines 
with  cyanide  of  potassium,  and  appears,  on  the  cooling  of  a  concentrated  solution, 
in  red  crystals,  which  dissolve  easily  in  water  (Mitscherlich).  This  salt  is  analo- 
gous to  red  prussiate  of  potash,  containing  manganese  instead  of  iron,  and 
may,  therefore,  be  represented  as  containing  manganicyanogen  —  a  manganicy- 
anide  of  potassium,  K3(Mn2Cy6).  As  a  double  cyanide,  its  formula  would  be, 
3KCy.Mn2Cy3. 

Red  oxide  of  manganese,  MnO.Mn2,03,  named  by  Berzelius  manganoso-man- 
ganic  oxide,  is  always  produced  when  any  oxide  of  manganese  is  heated  strongly 
in  air.  It  is  a  double  oxide,  being  a  compound  of  single  equivalents  of  protoxide 
and  bioxide  of  manganese.  It  forms  the  mineral  Hausmamte,  which  differs  from 
manganite  in  having  manganous  oxide  in  place  of  water.  Its  density  is  4-722. 
Berthier  finds  that  strong  nitric  acid  dissolves  out  the  protoxide  of  manganese 
from  the  red  oxide,  and  leaves  a  remarkable  hydrate  of  the  bioxide,  of  which  the 
formula  is  4Mn02-f  HO. 

Bioxide  or  Peroxide  of  manganese  ;  Slack  oxide  of  manganese;  Mn02j  43 '67 
or  545-9.  —  This  is  the  well-known  ore  of  manganese  employed  in  the  preparation 
of  oxygen  and  chlorine.  It  generally  occurs  massive,  of  an  earthy  appearance, 
and  contaminated  with  various  substances,  such  as  sesquioxide  of  iron,  silica,  and 
carbonate  of  lime ;  but  sometimes  of  a  fibrous  texture,  consisting  of  small  prisms 

*  Carius,  Ann.  Ch.  Pharm.  xcviii.,  53. 


VALUATION  OF  BIOXIDE  OF  MANGANESE.        437 

radiating  from  a  common  centre.  Its  density  varies  from  4-819  to  4-94-  as  a 
mineral  species  it  has  been  named  pyrolucite*  Another  important  variety  of  this 
ore,  known  as  ivad,  is  essentially  a  hydrate,  containing,  according  to  Dr.  Turner, 
1  eq.  of  water  to  2  eq.  of  peroxide.  A  hydrated  bioxide,  consisting  of  single 
equivalents  of  its  constituents,  is  formed  by  precipitating  the  protosalts  of  manga- 
nese with  chloride  of  lime  ;  and  the  same  compound  results  from  the  decomposition 
of  the  acids  of  manganese,  when  diluted  with  water  or  an  acid.  It  is  possible  that 
the  equivalent  of  this  oxide  should  be  doubled,  and  that  its  proper  formula  is 
Mn204,  corresponding  with  peroxide  of  chlorine,  C104. 

Bioxide  of  manganese  loses  one-fourth  of  its  oxygen  at  a  low  red  heat,  and  is 
is  changed  into  sesquioxide;  at  a  bright  red  heat  it  loses  more  oxygen,  and 
becomes  red  oxide,  the  condition  into  which  all  the  oxides  of  manganese  pass 
when  ignited  strongly  in  the  open  air.  The  bioxide  does  not  unite  either  with 
acids  or  with  alkalies.  When  boiled  with  sulphuric  acid,  it  yields  oxygen  gas 
and  a  sulphate  of  the  protoxide.  In  hydrochloric  acid  it  dissolves  with  gentle 
digestion,  evolving  chlorine  gas,  and  forming  protochloride  of  manganese  (page 
433).  It  is  extensively  used  in  the  arts  for  preparing  chlorine,  and  also  to  pre- 
serve glass  colourless  by  its  oxidating  action.  In  the  last  application,  it  is  added 
to  the  vitreous  materials  in  a  relatively  small  proportion,  and  becomes  protoxide, 
which  is  not  a  colouring  oxide,  while  as  sesquioxide  it  would  stain  glass  purple. 
At  the  same  time  it  destroys  carbonaceous  matter,  and  converts  protoxide  of  iron, 
which  colours  glass  green,  into  sesquioxide,  which  is  less  injurious. 

The  mineral  varvicite  was  discovered  by  Mr.  K.  Phillips  among  some  ores  of 
manganese  from  Hartshill  in  Warwickshire.  It  is  distinguished  from  the  bioxide 
by  being  much  harder,  having  more  of  a  larnellated  structure,  and  by  yielding 
water  freely  when  heated  to  redness.  Its  density  is  4-531.  It  may  be  supposed 
to  consist  of  1  eq.  of  sesquioxide,  and  2  eq.  of  bioxide  with  1  eq.  of  water  (Dr. 
Turner);  its  formula  is,  therefore,  Mn203  .  Mn204 


*  VALUATION    OF   BIOXIDE   OF   MANGANESE. 

The  numerous  applications  of  the  higher  oxides  of  manganese  depending  upon 
the  oxygen  which  they  can  furnish,  render  it  important  to  have  the  means  of 
easily  and  expeditiously  estimating  their  value  for  such  purposes.  The  value  of 
these  oxides  is  exactly  proportional  to  the  quantity  of  chlorine  which  they  produce 
when  dissolved  in  hydrochloric  acid,  and  the  chlorine  can  be  estimated  by  the 
quantity  of  protosulphate  of  iron  which  it  oxidizes.  Of  pure  bioxide  of  manganese 
43-7  parts  (1  eq.)  produce  35-5  parts  of  chlorine,  which  oxidize  278  parts  (2  eq.) 
of  crystallized  protosulphate  of  iron.  Hence  50  grains  of  bioxide  of  manganese 
yield  chlorine  sufficient  to  oxidize  317  grains  (more  exactly,  316-5  grs.)  of  proto- 
sulphate of  iron. 

50  grains  of  the  powdered  oxide  of  manganese  to  be  examined  are  weighed  out, 
and  also  any  known  quantity,  not  less  than  317  grains,  of  the  sulphate  of  iron 
(copperas)  employed  in  chlorimetry.  The  oxide  of  manganese  is  thrown  into  a 
flask  containing  an  ounce  and  a  half  of  strong  hydrochloric  acid,  diluted  with 
half  an  ounce  of  water,  and  a  gentle  heat  applied.  The  sulphate  of  iron  is  gradu 
ally  added  in  small  quantities  to  the  acid,  so  as  to  absorb  the  chlorine  as  it  is 
evolved  ;  and  the  addition  of  that  salt  continued,  till  the  liquid,  after  being  heated, 
gives  a  blue  precipitate  with  the  red  prussiate  of  potash,  and  has  no  smell  of 
chlorine,  which  are  indications  that  the  protosulphate  of  iron  is  present  in  excess. 
By  weighing  what  remains  of  the  sulphate  of  iron,  the  quantity  added  is  ascer- 
tained ;  say  m  grains.  If  the  whole  manganese  were  bioxide,  it  would  require 
317  grains  of  sulphate  of  iron,  and  that  quantity  would,  therefore,  indicate  100 
per  cent,  of  bioxide  in  the  specimen  ;  but  if  a  portion  of  the  manganese  only  is 

*  From  n-vp,  fire,  and  Xvw,  I  wash  ;  in  allusion  to  its  being  employed  to  discharge  the  brown 
and  green  tints  of  glass. 


438  MANGA  NE  SE. 

bioxide,  it  will  consume  a  proportionally  smaller  quantity  of  the  sulphate,  which 
quantity  will  give  the  proportion  of  the  bioxide,  by  the  proportion  :  as  317  : 
100  ::m:  per-centage  required.  The  per-centage  of  bioxide  of  manganese  is  thus 
obtained  by  multiplying  the  number  of  grains  of  sulphate  of  iron  oxidized  by 
0-317.  It  also  follows  that  the  per-centage  of  chlorine  which  the  same  specimen 
of  manganese  would  afford,  is  obtained  by  multiplying  the  number  of  grains  of 
sulphate  of  iron  oxidized  by  0-2588. 

Another  mode  of  estimation  is  to  pass  the  chlorine  gas,  obtained  by  heating  the 
manganese  in  a  flask  with  hydrochloric  acid,  into  a  solution  of  sulphurous  acid, 
quite  free  from  sulphuric  (it  should  give  no  precipitate  with  chloride  of  barium)  ; 
the  chlorine  converts  an  equivalent  quantity  of  sulphurous  acid  into  sulphuric. 
The  liquid  is  then  mixed  with  chloride  of  barium,  and  boiled  to  expel  the  excess 
of  sulphurous  acid,  after  which  the  sulphate  of  baryta  is  thrown  on  a  filter,  washed, 
dried,  ignited,  and  weighed.  The  116-64  gr.,  or  1  eq.  of  sulphate  of  baryta, 
correspond  to  43-7  gr.,  or  1  eq.  of  bioxide  of  manganese. 

The  value  of  commercial  oxide  of  manganese  may  also  be  estimated  by  heating 
it  with  hydrochloric  acid  and  oxalic  acid.  The  disengaged  chlorine  then  converts 
the  oxalic  acid  into  carbonic  acid,  —  2  eq.  of  carbonic  acid  representing  1  eq  of 
chlorine,  and  therefore  1  eq.  of  bioxide  of  manganese  : 


A  convenient  apparatus  for  the  determination  is  a  small  light  glass  flask  (fig. 
186),  of  3  or  4  oz.  capacity,  having  a  lipped  edge,  and  fitted  with  a  perforated 
cork.  A  piece  of  tube,  about  3  inches  long,  drawn  out  at 
one  end,  and  filled  with  fragments  of  chloride  of  calcium, 
to  absorb  water,  is  fitted  by  means  of  a  small  cork  and  a 
bent  tube  to  the  mouth  of  the  flask.  A  short  tube  closed 
at  one  end,  and  small  enough  to  go  into  the  flask,  is  used 
to  contain  the  hydrochloric  acid.  Fifty  grains  of  the  mine- 
ral, in  the  state  of  very  fine  powder,  are  introduced  into  the 
flask,  together  with  about  half  an  ounce  of  cold  water,  and 
100  grains  of  strong  hydrochloric  acid  in  the  tube,  as  shown 
in  the  figure  :  50  grains  of  crystallized  oxalic  acid  are  then 
added,  the  chloride  of  calcium  tube  fitted  on,  and  the  whole  quickly  weighed.  The 
flask  is  then  tilted  so  as  to  allow  the  hydrochloric  acid  to  flow  out  of  the  tube,  and 
come  in  contact  with  the  mixture  of  manganese  and  oxalic  acid,  and  a  gentle  heat 
applied  to  determine  the  action.  Carbonic  acid  is  then  evolved,  and  escapes 
through  the  chloride  of  calcium  tube.  To  expel  the  last  portions  of  carbonic  acid, 
the  liquid  must  be  ultimately  heated  till  it  boils  ;  after  which  it  is  left  to  cool, 
and  weighed  :  the  loss  of  weight  gives  the  quantity  of  carbonic  acid.  Now,  as 
43-67,  the  equivalent  of  bioxide  of  manganese,  is  nearly  double  that  of  carbonic 
acid,  which  is  22,  the  loss  of  weight  in  the  apparatus  may  be  taken  to  represent 
the  quantity  of  real  bioxide  in  the  50  grains  of  the  sample.  [For  other  methods, 
see  Appendix.] 

To  obtain  a  complete  appreciation  of  the  value  of  a  sample  of  manganese,  it  is 
not  sufficient  to  know  the  per-centage  of  real  bioxide  in  it,  —  or,  which  comes  to 
the  same  thing,  the  quantity  of  chlorine  it  is  capable  of  yielding,  —  but  we  must 
also  know  the  quantity  of  hydrochloric  acid  which  must  be  consumed  for  evolving 
this  chlorine.  If  the  sample  consists  of  pure  bioxide,  half  the  acid  used  will  give 
up  its  chlorine  ;  if  it  be  pure  sesquioxide,  only  a  third  of  the  acid  will  be  changed 
into  chlorine.  The  quantity  of  acid  required  will  therefore  be  greater  in  the  latter 
case  than  in  the  former  in  the  ratio  of  3  :  2.  Lastly,  if  the  oxide  contains  lime, 
baryta,  or  oxide  of  iron,  these  bases  will  neutralize  a  portion  of  the  acid  without 
supplying  any  chlorine.  To  determine  the  expenditure  of  acid,  a  known  weight 
of  the  oxide  is  heated  with  a  known  quantity  of  hydrochloric  acid  of  given  strength, 


VALUATION    OF    BIOXIDE    OF    MANGANESE.       439 

the  chlorine  being  suffered  to  escape,  but  the  hydrochloric  acid  which  would 
otherwise  escape  un decomposed  being  collected  in  a  small  receiver  moistened  on 
the  inside.  When  the  action  is  over,  the  acid  thus  condensed  is  added  to  that  in 
the  flask,  the  whole  diluted  with  water,  and  the  quantity  of  free  acid  determined 
by  adding  a  graduated  alkaline  solution,  till  the  precipitate  which  forms  no  longer 
redissolves  on  agitation.  The  quantity  of  free  acid  thus  determined  is  then  to  be 
deducted  from  the  original  quantity,  and  the  difference  gives  the  quantity  con- 
sumed. 

Manganic  acid;  Mn03;  51-67  or  645-9.  —  When  bioxide  of  manganese  is 
strongly  ignited  with  hydrate  or  carbonate  of  potash  in  excess,  manganic  acid  is 
formed,  under  the  influence  of  the  alkali,  together  with  a  lower  oxide  of  man- 
ganese. Ignition  in  open  vessels,  or  with  an  admixture  of  nitrate  of  potash, 
increases  the  production  of  the  acid,  by  the  absorption  of  oxygen  which  then 
occurs.  The  product  has  long  been  known  as  mineral  chameleon,  from  the  pro- 
perty of  its  solution,  which  is  green  at  first,  to  pass  rapidly  through  several  shades 
of  colour.  But  a  more  convenient  process  for  preparing  manganate  of  potash  is 
that  recommended  by  Dr.  Gregory.  He  mixes  intimately  4  parts  of  bioxide  of 
manganese  in  fine  powder  with  3 £  parts  of  chlorate  of  potash,  and  adds  them  to  5 
parts  of  hydrate  of  potash  dissolved  in  a  small  quantity  of  water.  The  mixture  is 
evaporated  to  dryness,  powdered,  and  afterwards  ignited  in  a  platinum  crucible, 
but  not  fused,  at  a  low  red  heat.  The  ignited  mass,  digested  in  a  small  quantity 
of  cold  water,  forms  a  deep  green  solution  of  the  alkaline  manganate,  which  may 
be  obtained  in  crystals  of  the  same  colour  by  evaporating  the  solution  over  sul- 
phuric acid  in  the  air-pump.  Zwenger,  by  igniting  bioxide  of  manganese  with  3 
parts  of  nitric  acid,  and  evaporating  the  aqueous  solution  in  vacuo,  obtained 
reddish-brown  crystals  containing  KO.Mn03.  On  exposure  to  the  air,  they 
became  dull  and  dark  green.  The  manganates  were  discovered  by  Mitscherlich 
to  be  isomorphous  with  the  sulphates  and  chromates.  It  has  not  yet  been  found 
possible  to  isolate  manganic  acid.  Its  salts  in  solution  readily  undergo  decompo- 
sition, unless  an  excess  of  alkali  is  present;  and  are  also  destroyed  by  contact  of 
organic  matter,  such  as  paper. 

Permanganic  acid,  Mn207;  111-34  or  1391 -8. — When  the  green  solution  of 
manganate  of  potash,  prepared  as  above  directed,  is  diluted  with  boiling  water, 
hydrated  bioxide  of  manganese  subsides,  and  the  liquid  assumes  a  beautiful  pink 
or  violet  colour.  The  manganic  acid  is  resolved  into  bioxide  of  manganese  and 
hypermanganic  acid : 

3Mn03  =  Mn02  -f  Mn207- 

The  permanganate  of  potash  should  be  rapidly  concentrated,  without  contact  of 
organic  matter,  and  allowed  to  crystallize.  A  better  process  for  obtaining  this 
salt  is  to  mix  1  part  of  bioxide  of  manganese,  in  very  fine  powder,  with  1  part  of 
chlorate  of  potash;  introduce  this  mixture  into  a  solution  of  H  part  of  caustic 
potash  in  the  smallest  possible  quantity  of  water;  evaporate  to  dryness,  during 
which  process  a  considerable  quantity  of  manganate  of  potash  is  formed;  then 
heat  the  mixture  slowly  to  dull  redness;  boil  the  product  in  water;  filter  through 
asbestos,  and  concentrate  by  evaporation  :  the  liquid,  on  cooling,  deposits  perman- 
ganate of  potash  in  crystals.  It  may  be  purified  by  solution  in  a  small  quantity 
of  boiling  water,  and  recrystallization.  The  crystals  are  of  a  dark  purple  colour, 
almost  black,  and  soluble  in  sixteen  times  their  weight  of  cold  water;  they  were 
found  by  Mitscherlich  to  be  isomorphous  with  perchlorate  of  potash ;  they  dis- 
solve in  16  parts  of  water  at  60°  (Regnault).  The  permanganates  give  out  oxygen 
when  heated,  and  are  reconverted  into  manganates.  Their  solutions  have  a  rich 
purple  colour,  and  are  so  stable  that  they  may  be  boiled,  if  concentrated.  A  small 
portion  of  a  permanganate  imparts  a  purple  colour  to  a  very  large  quantity  of 
water. 

When  a  strong  solution  of  caustic  potash  is  added  to  a  dilute  solution  of  per- 


440  MANGANESE. 

manganate  of  potash,  the  liquid  changes  colour,  assuming  first  a  violet,  and  after- 
wards an  emerald-green  tint.  The  permanganate  is  in  fact  converted  into  man- 
ganate, a  double  quantity  of  potash  having  entered  into  combination  with  the  acid  : 

KO.Mn207  +  KO  =  2(KO.Mn03)  +  0. 

The  oxygen  thus  liberated  remains  dissolved  in  the  water.  This  transformation  is 
due  to  the  great  basic  power  of  the  potash.  Acids  produce  the  contrary  effect, 
that  is  to  say,  they  convert  manganates  into  permanganates. 

The  insoluble  manganate  of  baryta  may  be  formed  by  fusing  bioxide  of  man- 
ganese with  nitrate  of  baryta;  and  when  mixed  with  a  little  water,  and  decom- 
posed by  an  equivalent  quantity  of  sulphuric  acid,  affords  free  permanganic  acid. 
In  Mitscherlich's  experiments,  the  free  acid  appeared  to  be  a  body  not  more  stable 
than  bioxide  of  hydrogen,  being  decomposed  between  86°  and  104°,  with  escape 
of  oxygen  gas  and  precipitation  of  hydrated  bioxide  of  manganese.  It  bleached 
powerfully,  and  was  rapidly  destroyed  by  all  kinds  of  organic  matter.  M.  Hiine- 
feld,  on  the  other  hand,  obtained  permanganic  acid  in  a  state  in  which  it  could  be 
preserved,  evaporated,  redissolved,  &c.  He  washed  the  manganate  of  baryta  with 
hot  water,  by  which  it  is  resolved  into  bioxide  of  manganese  and  permanganate  of 
baryta,  and  then  added  to  it  the  quantity  of  phosphoric  acid  exactly  necessary  to 
neutralize  the  baryta.  The  liberated  permanganic  acid  was  dissolved  out,  evaporated 
to  dryness,  and  by  a  second  solution  and  evaporation,  obtained  in  the  form  of  a 
reddish-brown  mass,  crystalline  and  radiated,  which  exhibited  the  lustre  of  indigo 
at  some  points  and  was  entirely  soluble  in  water.  When  dry  permanganic  acid 
was  fused  in  a  retort  with  anhydrous  sulphuric  acid,  and  afterwards  distilled  at  a 
higher  temperature,  an  acicular  sublimate  of  a  crimson  red  colour  was  obtained, 
which  appeared  to  be  a  combination  of  permanganic  and  sulphuric  acids.  (Ber- 
zelius's  Traite,  i.  522.)  When  monohydrated  sulphuric  acid  is  poured  upon  a 
somewhat  considerable  quantity  of  crystallized  permanganate  of  potash,  the  salt  is 
decomposed  with  great  evolution  of  heat,  red  flames  bursting  out,  oxygen  being 
evolved,  and  manganic  oxide  set  free  in  dark-brown  flakes  and  shreds  like  spider- 
lines.  The  red  flames  seem  to  show  that  permanganic  acid  is  gaseous  at  the  high 
temperature  produced  by  the  reaction.  (Wohler.) 

Perchloride  of  manganese,  Mn2Cl7,  is  a  greenish  yellow  gas,  which  condenses 
at  0°  F.  into  a  liquid  of  a  greenish-brown  colour.  This  liquid  diffuses  purple 
fumes,  owing  to  the  formation  of  hydrochloric  and  permanganic  acids,  by  the 
decomposition  of  the  moisture  of  the  air.  It  was  formed  by  Dumas  by  dissolving 
manganate  of  potash  in  oil  of  vitriol,  pouring  the  solution  into  a  tubulated  retort, 
and  adding  by  degrees  small  portions  of  chloride  of  sodium  or  potassium,  com- 
pletely freed  from  water  by  fusion.  The  perchloride  of  manganese  is  the  result 
of  a  reaction  between  the  liberated  hypermanganic  and  hydrochloric  acids  : 

Mn207  +  7HC1  =  Mn2017  +  7HO. 

A  corresponding  perfluoride  of  manganese  was  formed  by  Wohler  by  distilling, 
in  a  platinum  retort,  a  mixture  of  manganate  of  potash  and  fluor-spar  in  powder, 
with  fuming  sulphuric  acid.  It  is  a  greenish-yellow  gas,  which  likewise  produces 
purple  fumes  in  damp  air. 

Isomorphous  relations  of  manganese.  —  There  is  no  other  element  whose  com- 
pounds enter  into  so  many  isomorphous  groups,  and  connect  so  large  a  proportion 
of  the  elements  by  the  tie  of  isomorphism,  as  manganese.  The  salts  of  its  prot- 
oxide are  strictly  isomorphous  with  the  salts  of  magnesia  and  its  class;  so  that 
manganese  belongs  to  find  represents  the  magnesian  family  of  elements.  The 
same  metal  connects  the  sulphur  family  with  the  magnesian,  by  the  isomorphism 
of  the  sulphates  and  manganates;  and,  therefore,  sulphur,  selenium,  and  tellurium 
are  thus  allied  to  the  magnesian  metals.  An  equally  interesting  relation  is  that 


IRON.  4'!1 

of  permanganic  with  perchloric  acid,  and  the  isomorphism,  which  it  establishes, 
of  2  equivalents  of  manganese  with  1  equivalent  of  chlorine,  and  the  other  mem- 
bers of  its  family. 

ESTIMATION    OF     MANGANESE,    AND     METHODS    OF    SEPARATING   IT   FROM    THE 

PRECEDING    METALS. 

The  usual  method  of  precipitating  manganese  from  the  solution  of  a  manganous 
salt,  is  to  add  carbonate  of  soda  at  a  boiling  heat.  The  precipitated  carbonate  of 
manganese  is  then  well  washed  with  boiling  water,  and  calcined  at  a  strong  red 
heat,  whereby  it  is  converted  into  manganoso-manganic  oxide,  Mn304,  containing 
72'11  per  cent,  of  manganese.  If  the  solution  contains  a  considerable  quantity 
of  ammoniacal  salts,  it  must  be  evaporated  after  mixing  it  with  excess  of  car- 
bonate of  soda,  and  the  soluble  salts  dissolved  out  of  the  residue  by  water. 

Manganese  is  separated  from  the  alkali-metals  by  means  of  carbonate  of  soda  or 
sulphide  of  ammonium,  which  latter  precipitates  it  in  the  form  of  sulphide.  The 
sulphide  is  washed  with  water  containing  a  small  quantity  of  sulphide  of  ammo- 
nium;  then  redissolved  in  acid;  and  the  manganese  precipitated  from  the  solution 
by  carbonate  of  soda. 

From  barium  and  strontium,  manganese  is  easily  separated  by  means  of  sul- 
phate of  soda,  which  throws  down  the  baryta  and  strontia  as  sulphates ;  also  by 
sulphide  of  ammonium.  From  lime  arid  manganese  it  is  separated  by  sulphide  of 
ammonium,  which,  if  the  solution  be  sufficiently  dilute,  precipitates  the  manga- 
nese alone  in  the  form  of  sulphide.  The  separation  from  lime  may  also  be  eifected 
by  means  of  oxalate  of  ammonia,  after  the  addition  of  chloride  of  ammonium  to 
keep  the  manganese  in  solution. 

From  alumina  and  glucina,  manganese,  if  in  small  or  moderate  quantity  only, 
may  be  separated  by  boiling  the  solution  with  potash  in  an  open  vessel.  The 
manganese  is  then  precipitated  in  the  form  of  sesquioxide,  while  the  alumina  and 
glucina  are  dissolved  by  the  potash.  If,  however,  the  proportion  of  manganese  be 
considerable,  this  method  cannot  be  used,  because  the  oxide  of  manganese  carries 
down  with  it  considerable  quantities  of  alumina  and  glucina.  In  this  case,  the 
liquid  must  be  mixed  with  sal-ammoniac  and  the  alumina  and  glucina  precipitated 
by  ammonia.  The  precipitate,  however,  always  contains  small  quantities  of  man- 
ganese, which  must  be  separated  by  subsequent  treatment  with  potash. 


SECTION    II. 

IRON. 

Eq.  28  or  350;  Fe  (ferrum). 

The  most  remarkable  of  the  metals;  the  production  of  which,  from  the  nume- 
rous and  important  applications  it  possesses,  appears  to  be  an  indispensable  con- 
dition of  civilization.  Meteoric  masses  of  iron,  often  so  pure  as  to  be  malleable, 
are  found  widely  although  thinly  scattered  over  the  earth's  surface,  and  probably 
first  attracted  the  attention  of  mankind  to  this  metal.  Of  the  occurrence  of  me- 
tallic iron  as  a  terrestrial  mineral  in  situ,  the  best  established  instances  are  the 
species  of  native  iron  which  accompanies  the  Uralian  platinum,  and  a  thin  vein 
about  two  inches  in  thickness,  observed  in  chlorite  slate,  near  Canaan  in  the 
United  States.  In  a  state  of  combination,  iron  is  extensively  diffused,  being 
found  in  small  quantity  in  the  soil,  and  in  most  minerals,  and  as  sulphide,  oxide, 
and  carbonate,  in  quantities  which  afibrd  an  inexhaustible  supply  of  the  metal  and 
its  preparations,  for  economical  purposes. 

Iron  diifers  from  all  other  metals  in  two  points,  which  greatly  affect  the  methods 


442  IRON. 

of  reducing  it.  Its  particles  agglutinate  at  a  full  red  heat,  although  the  pure 
metal  is  nearly  infusible.  The  oxides  of  iron,  which  are  easily  reduced  by  com- 
bustible matter,  thus  yield  in  the  furnace  a  spongy  metallic  mass,  which  may 
admit  of  being  compacted  by  subsequent  heating  and  hammering,  if  the  oxide 
has  originally  been  free  from  earthy  and  other  foreign  matter.  Such  probably 
was  everywhere  the  earliest  mode  of  treating  the  ores  of  iron,  and  we  find  it  still 
followed  among  rude  nations.  But  iron  is  also  singular  in  forming,  at  an  elevated 
temperature,  a  fusible  compound  with  carbon  (cast  iron),  the  production  of  which 
facilitates  the  separation  of  the  metal  from  every  thing  extraneous  in  the  ore,  and 
is  the  basis  of  the  only  method  of  extracting  iron  extensively  practised. 

The  ore  of  iron  most  abundant  in  the  primary  formations  is  the  black  oxide  or 
magnetic  ore,  which  affords  the  most  celebrated  and  valuable  irons  of  Sweden  and 
the  north  of  Europe,  but  of  which  the  application  is  greatly  circumscribed  from 
its  not  being  associated  with  coal.  In  the  secondary  and  tertiary  formations,  the 
anhydrous  and  hydrated  sesquioxide  of  iron,  red  and  broicn  hematite,  occur  occa- 
sionally in  considerable  quantity,  often  massive,  reniform,  and  quite  pure,  at  other 
times  pulverulent  and  mixed  with  clay.  It  is  employed  to  some  extent  in  Eng- 
land in  the  last  condition,  but  only  for  the  purpose  of  mixing  with  the  more 
common  ore.  The  crystallized  carbonate  of  iron,  or  spathic  iron,  is  smelted  in 
some  parts  of  the  continent,  and  gives  an  iron  often  remarkable  for  a  large  pro- 
portion of  manganese.  The  celebrated  iron  of  Elba  is  derived  from  specular  or 
oligistic  iron,  a  crystallized  sesquioxide.  But  the  consumption  of  all  these  ores 
is  inconsiderable,  compared  with  that  of  the  clay  ironstone  of  the  coal  measures. 
This  is  the  carbonate  of  the  protoxide  of  iron  mixed  with  variable  quantities  of 
clay  and  carbonates  of  lime,  magnesia,  &c. ;  it  is  often  called  the  argillaceous  car- 
bonate of  iron.  It  is  a  sedimentary  rock  wholly  without  crystallization,  resembling 
a  dark-coloured  limestone,  but  of  higher  density,  from  2-936  to  8-471,  and  not 
effervescing  so  strongly  in  an  acid.  It  occurs  in  strata,  beds,  or  bands,  as  trhey 
are  also  named,  from  2  to  10  or  14  inches  in  thickness,  alternating  with  beds  of 
coal,  clay,  bituminous  schist,  and  often  limestone.  The  proportion  of  iron  in  this 
ore  varies  considerably,  but  averages  about  30  per  cent.,  and  after  it  has  been  cal- 
cined, to  expel  carbonic  acid  and  water,  about  40  per  cent.* 

SMELTING   CLAY   IRON-STONE. 

The  blast  furnace,  in  which  the  ore  is  reduced,  is  of  the  form  represented 
below,  40  to  65  feet  in  height,  with  an  interior  diameter  of  from  14  to  17  feet  at 
the  widest  part.  The  cavity  of  the  furnace  is  entirely  filled  with  fuel  and  the 
other  materials,  which  are  continuously  supplied  from  an  opening  near  the  top ; 
and  the  combustion  maintained  by  air  thrown  in  at  two  or  more  openings,  called 
tuyeres,  near  the  bottom,  under  a  pressure  of  about  6  inches  of  mercury,  from  a 
blowing  apparatus,  so  as  to  maintain  the  whole  contents  of  the  furnace  in  a  state 
of  intense  ignition.  When  the  air  to  support  the  combustion  has  attained  a 
temperature  of  600°  or  700°,  by  passing  through  heated  iron  tubes,  before  it  is 
thrown  into  the  furnace,  raw  coal  may  be  used  as  the  fuel ',  but  with  cold  air,  the 
coal  must  be  previously  charred  to  expel  its  volatile  matter,  and  converted  into 
coke,  otherwise  the  heat  produced  by  its  combustion  is  insufficient.  With  the 
ore  and  fuel,  a  third  substance  is  added,  generally  limestone,  the  object  of  which 
is  to  form  a  fusible  compound  with  the  earthy  matter  of  the  ore  ;  it  is,  therefore, 
called  a  flux.  Two  liquid  products  accumulate  at  the  bottom  of  the  furnace, 
namely,  a  glass  composed  of  the  flux  in  combination  with  the  earthy  impurities 

*  Accurate  analyses  of  several  Scotch  varieties  of  this  ore  have  been  published  by  Dr.  H. 
Colquhoun  (Brewster's  Journal,  vii.  234;  or  Dr.  Thomson's  Outlines  of  Mineralogy  and 
Geology,  i.  446) ;  and  of  the  French  ores,  by  M.  Berthier,  in  his  Traite  des  essais  par  la  vote 
skche,  ii.  252,  a  work  which  is  invaluable  for  the  metallurgic  student,  and  Mitchell's  Practi- 
cal Assaying,  8vo. 


SMELTING    CLAY    IRON-STONE. 


443 


of  the  ore,  which  when  drawn  off  forms  a  solid  slag,  and  the  carbide  of  iron,  or 
metal,  which  is  the  heavier  of  the  two.     It  may  be  drawn  from  observations  made 

FIQ.  187. 


by  Dr.  Clark,  in  1833,  on  the  working  of  the  Scotch  blast  furnaces,  under  the  hot 
blast,  that  the  relative  proportions  of  the  materials,  including  air,  and  product  of 
cast  iron,  are  as  follows  :  *  — 

Weight. 

Coal 5 

Roasted  iron-stone 5 

Limestone 1 

Air 11 

Average  product  of  cast  iron 2 

The  ultimate  fixed  products  are  the  slag  and  carburet  of  iron,  but  the  formation 
of  these  is  preceded  by  several  interesting  changes  which  the  ore  successively 
undergoes  in  the  course  of  its  descent  in  the  furnace.  A  portion  of  the  oxide  of 
iron  is  certainly  reduced  to  the  metallic  state,  soon  after  its  introduction,  in  the 
upper  part  of  the  furnace,  by  carbonic  oxide  and  volatile  combustible  matter;  but 
the  reduced  metal  does  not  then  fuse.  A  large  portion  of  the  oxide  of  iron  must 
combine  also,  at  the  same  time,  with  the  silica  and  alumina  present  in  the  ore, 
which  act  as  acids,  and  a  glass  be  formed,  the  oxide  of  iron  in  which  is  scarcely 
reducible  by  carbon.  But  this  injurious  effect  of  the  acid  earths  is  counteracted 
by  the  lime  of  the  flux,  which,  being  a  more  powerful  base  than  oxide  of  iron, 

*  Edinburgh  Phil.  Trans,  vol.  13. 


444  IRON. 

liberates  that  oxide  from  the  glass  when  the  proportions  of  the  materials  introduced 
into  the  furnace  are  properly  adjusted,  and  neutralizes  the  silica ;  so  that  the  slag 
eventually  becomes  a  silicate  of  lime  and  alumina,  with  scarcely  a  trace  of  oxide 
of  iron.  The  whole  oxide  of  iron  comes  thus  to  be  exposed  to  the  reducing 
action  of  the  volatile  combustible,  and  consequently  the  whole  iron  is  probably,  at 
one  time,  in  the  condition  of  pure  or  malleable  iron.  But  when  the  metal  de- 
scends somewhat  farther  in  the  furnace,  it  attains  the  high  temperature  at  which 
it  combines  with  the  carbon  of  the  coke  in  contact  with  it,  and  it  fuses  for  the 
first  time,  in  the  form  of  carburet  of  iron.  It  has  not  yet,  however,  attained  its 
ultimate  condition.  When  it  reaches,  in  its  descent,  the  region  of  the  furnace 
where  the  heat  is  most  intense,  its  carbon  reacts  on  the  silica,  alumina,  lime,  and 
other  alkaline  oxides  contained  in  the  fluid  slag  with  which  it  is  accompanied,  re- 
ducing portions  of  silicon,  aluminum,  calcium,  and  other  alkaline  metals,  which 
combine  with  the  iron.  The  proportion  of  carbon  replaced  by  silicon  and  metallic 
bases  is  generally  found  to  be  greater  in  iron  prepared  by  the  hot  than  by  the  cold 
blast,  owing,  it  is  presumed,  to  the  higher  temperature  of  the  furnace  with  the 
hot  blast. 

The  introduction  of  air  already  heated  to  support  the  combustion  of  the  blast 
furnace,  for  which  a  patent  was  obtained  by  Mr.  J.  B.  Neilson,  has  greatly  re- 
duced the  proportion  of  coal  required  to  smelt  a  given  weight  of  ore,  enabling  the 
iron-master,  indeed,  to  effect  a  saving  of  more  than  three-fourths  of  the  coal  where 
it  is  of  a  bituminous  quality.  The  air  is  heated  between  the  blowing  apparatus 
and  the  furnace,  by  being  made  to  circulate  through  a  set  of  arched  tubes  of 
moderate  diameter,  heated  by  a  fire  beneath  them.  The  air  can  be  heated  in  this 
manner  to  low  redness,  or  to  near  1000°,  but  there  is  found  to  be  no  proportional 
advantage  in  raising  its  temperature  much  above  the  melting  point  of  lead  (612°), 
which  is  already  higher  than  the  point  at  which  charcoal  inflames.  Considering 
the  great  weight  of  air  that  enters  the  furnace,  the  temperature  of  that  material 
must  greatly  affect  the  whole  temperature  of  the  furnace,  particularly  of  the  lower 
part,  wvhere  the  air  is  admitted,  and  which  part  it  is  desirable  should  be  hottest. 
Now  a  certain  elevated  temperature  is  required  for  the  proper  smelting  of  the  ore, 
and,  unless  attained  in  the  furnace,  the  fuel  is  consumed  to  no  purpose.  The  re- 
moval of  the  negative  influence  of  the  low  temperature  of  the  air,  appears  to  per- 
mit the  heat  to  rise  to  the  proper  point,  which  otherwise  is  attained  with  difficulty 
and  by  a  wasteful  consumption  of  fuel.  Professor  Reich,  of  Freiberg,  has  ob- 
served that  heating  the  air  likewise  alters  the  relative  temperatures  of  different 
parts  of  the  furnace,  depressing  in  particular,  and  bringing  nearer  the  tuyeres, 
the  zone  of  highest  temperature.  The  admixture  of  steam  with  the  air  has,  he 
finds,  precisely  the  opposite  effect,  elevating  the  zone  of  highest  temperature  in 
the  furnace ;  so  that  the  effect  of  the  hot  blast  may  be  exactly  neutralized  by 
mixing  steam  with  the  hot  air. 

Cast  iron. — The  fused  metal  is  run  into  channels  formed  in  sand,  and  thus  cast 
into  ingots  or  pigs,  as  they  are  called.  Cast  iron  is  an  exceedingly  variable  mix- 
ture of  reduced  substances,  of  which  the  principal  is  iron  combined  with  carbon. 
The  theoretical  constitution  to  which  that  variety  of  it,  most  definite  in  its  com- 
position, approaches,  is  the  following :  — 

WHITE   CAST   IRON. 

4  equivalents  of  iron 94  9 

1  equivalent  of  carbon 5-1 

100-0 

The  difference  in  appearance  and  quality  of  the  varieties  of  cast  iron  is  not  well 
accounted  for  by  their  composition.  The  grey  or  mottled  cast  iron,  forming  the 


WHITE    CAST    IRON. 


445 


qualities  Nos.  1  and  2,  presents  a  fracture  composed  of  small  crystals,  is  easily  cut 
by  the  file,  and  is  preferred  for  castings.  It  is  generally  supposed  that  a  portion 
of  uncombined  carbon  is  diffused  through  the  iron  of  these  qualities,  in  the  form 
of  graphite.  No.  3,  or  white  cast  iron,  is  more  homogeneous ;  its  fracture  exhibits 
crystalline  plates,  like  that  of  antimony,  and  is  nearly  white ;  it  is  exceedingly 
hard  and  brittle. 

Malleable  iron.  —  The  great  proportion  of  cast  iron  manufactured  is  afterwards 
refined,  or  converted  into  bar  or  malleable  iron.  The  mode  of  effecting  this  con- 
version varies  with  the  nature  of  the  fuel.  Where  coal  or  coke  is  used,  as  in  this 
country,  the  process  consists  of  two  stages.  In  the  first,  which  is  called  refining, 
the  pig-iron  is  heated  in  contact  with  the  fuel  in  small  low  furnaces  called  refineries, 
while  air  is  blown  over  its  surface  by  means  of  tuyeres.  The  effect  of  this  opera- 
tion is  to  deprive  the  iron  of  a  great  portion  of  the  carbon  and  nearly  all  the 
silicon  associated  with  it.  The  metal  thus  far  purified  is  run  out  into  a  trench, 
and  suddenly  cooled  by  pouring  cold  water  upon  it.  It  then  forms  a  greyish-white 
very  brittle  mass,  blistered  on  the  surface.  In  this  state  it  is  called  fine  metal. 

Fio.  188. 


It  is  then  ready  for  the  second  and  principal  operation,  called  the  puddling  process, 
which  consists  in  heating  masses  of  the  iron  with  a  certain  access  of  air  in  a  kind 
of  reverberatory  furnace,  called  the  puddling  furnace,  of  which  Fig.  188  repre- 
sents a  vertical  section.  This  furnace  has  four  doors,  two  of  which,  F  and  G, 
serve  for  the  introduction  of  fuel  to  the  grate ;  the  charge  of  metal  is  introduced 
at  E ;  and  D  serves  for  the  insertion  of  a  long  poker  or  spatula,  with  which  the 
metal  is  stirred  about.  The  hearth  of  the  furnace  has  an  aperture  B  at  the  back, 
for  removing  the  slag.  The  furnace  having  been  brought  to  a  bright  red  heat, 
about  four  or  five  hundred  weight  of  fine  metal  is  introduced,  together  with  one 
hundred  weight  of  rich  scoriae  or  forge  cinders  (scale-oxide).  The  metal  then 
fuses,  and  in  this  state  the  workman  stirs  it  about  with  the  poker,  so  as  to  expose 
every  part  to  the  flame.  The  carbon  is  thus  gradually  burnt  out,  partly  by  the 
direct  action  of  oxygen  in  the  flame,  and  partly  by  cementation  with  the  oxide  of 
iron ;  and  the  metal  becomes  less  fusible,  and  thick  and  tenacious,  so  that  it  sticks 
together,  and  is  easily  formed  into  four  or  five  large  balls,  called  blooms.  In  this 
condition  it  is  removed  by  tongs,  compressed  into  a  cylindrical  form  by  a  few  blows 
of  a  loaded  hammer,  and  quickly  converted  into  a  bar,  by  pressing  it  between 
grooved  rollers.  The  tenacity  of  the  metal  is  further  increased  by  welding  several 


446  IRON. 

bars  together ;  a  faggot  of  bars  is  brought  to  a  white  heat  in  an  oblong  furnace, 
and  then  extended  between  the  grooved  rollers  into  a  single  bar. 

The  texture  of  malleable  iron  IF,  fibrous.  Although  the  purest  commercial  form 
of  the  metal,  it  still  contains  about  one-half  per  cent,  of  carbon,  with  traces  of 
silicon  and  other  metals. 

Pure  iron  may,  however,  be  obtained  by  introducing  into  a  Hessian  crucible  4 
parts  of  iron  wire  cut  into  small  pieces,  and  1  part  of  black  oxide  of  iron  •  placing 
above  these  a  mixture  of  white  sand,  lime,  and  carbonate  of  potash,  in  the  propor- 
tions used  for  glass-making;  covering  the  crucible  with  a  closely  fitting  lid;  and 
exposing  it  to  a  very  high  temperature.  A  button  of  pure  metal  is  thus  obtained, 
the  traces  of  carbon  and  silicon  in  the  iron  having  been  removed  by  the  oxygen 
of  the  oxide.  (Mitscherlich.) 

Steel.  —  Only  the  best  qualities  of  malleable  iron,  those  prepared  from  a  pure 
ore,  and  reduced  by  means  of  charcoal,  such  as  thje  Swedish  iron,  are  converted 
into  steel.  An  iron  box  is  filled  with  flat  bars  of  such  iron  and  charcoal  powder, 
in  alternate  layers,  and  kept  at  a  red  heat  for  forty-eight  hours,  or  longer.  The 
surface  of  the  bars  is  found  afterwards  to  be  blistered,  and  they  have  absorbed 
from  1-3  to  1'75  per  cent,  of  carbon.  This  is  the  process  of  cementation.  It  is 
known  that  iron  can  be  converted  into  steel  without  being  in  actual  contact  with 
charcoal,  provided  the  iron  and  charcoal  are  in  a  close  vessel  together,  and  oxygen 
be  present,  the  carbon  reaching  the  surface  of  the  metal  in  the  form  of  carbonic 
oxide  gas.  The  iron  becomes  harder  by  this  change,  and  more  fusible,  but  can 
still  be  hammered  into  shape,  and  cut  with  a  file.  The  property  in  which  steel 
differs  most  from  soft  iron,  is  the  capacity  it  has  acquired  of  becoming  excessively 
hard  and  elastic,  when  heated  to  redness  and  suddenly  cooled  by  plunging  it  into 
cold  water  or  oil.  This  hardness  makes  steel  invaluable  for  files,  knives,  and  all 
kinds  of  cutting  instruments.  But  the  steel,  when  hardened  in  the  manner 
described,  is  harder  than  is  required  for  most  of  its  applications,  and  also  very 
brittle.  Any  portion  of  its  original  softness  can  be  restored  to  the  steel  by  heating 
it  up  *o  particular  temperatures,  —  which  are  judged  of  by  the  colour  of  the  film 
of  oxide  upon  its  surface,  which  passes  from  pale  yellow  at  about  430°,  through 
straw  yellow,  brown  yellow,  and  red  purple  into  a  deep  blue  at  580°,  —  and 
allowing  the  steel  afterwards  to  cool  slowly.  Articles  of  steel  are  tempered  in  this 
manner. 

A  simple  and  expeditious  method  of  converting  crude  or  pig-iron  into  malleable 
iron  and  steel,  without  the  aid  of  fuel,  has  lately  been  proposed  by  Mr.  H.  Besse- 
mer. This  process  consists  in  causing  cold  air  to  bubble  through  the  liquid  iron  ; 
under  which  circumstances  the  oxygen  of  the  air  combines  with  the  carbon  of  the 
iron,  removing  it  in  the  form  of  carbonic  oxide,  and  generating  sufficient  heat  to 
keep  the  iron  in  the  liquid  state  without  external  heating,  and  to  sustain  the  action 
till  the  whole,  or  any  required  proportion,  of  the  carbon  is  burnt  away.  As  the 
quantity  of  carbon  in  the  metal  diminishes,  part  of  the  oxygen  combines  with  the 
iron,  converting  it  into  an  oxide,  which,  at  the  very  high  temperature  then  exist- 
ing in  the  vessel,  melts,  and  forms  a  powerful  solvent  for  the  earthy  bases  associated 
with  the  iron.  At  a  certain  stage  of  the  process,  the  whole  of  the  crude  iron  is 
said  to  be  converted  into  cast  steel  of  ordinary  quality.  By  continuing  the  process, 
the  steel  thus  formed  is  gradually  deprived  of  its  small  remaining  portion  of  carbon, 
and  passes  successively  from  hard  to  soft  steel,  steely  iron,  and  ultimately  to  very 
soft  iron.* 

Properties  of  iron.  —  Iron  is  of  a  bluish-white  colour,  and  admits  of  a  high 
polish.  It  is  remarkably  malleable,  particularly  at  a  high  temperature,  and  of  great 
tenacity.  Its  mean  density  is  7*7,  which  is  increased  by  fusion  to  7-8439.  When 
kept  for  a  considerable  time  at  a  red  heat,  its  particles  often  form  large  cubic  or 

*  Chemical  Gazette,  1856,  p.  336. 


PASSIVE    CONDITION    OF    IRON.  447 

octohedral  crystals,  and  the  metal  becomes  brittle.  Malleable  iron  softens  before 
entering  into  fusion,  and  in  this  state  it  can  be  welded,  or  two  pieces  united  by 
hammering  them  together.  The  point  of  fusion  of  cast  iron  is  3479°  ;  that  of 
malleable  iron  is  much  higher.  Cast-iron  expands  in  becoming  solid,  and  there- 
fore takes  the  impression  of  a  mould  with  exactness.  Iron  is  attracted  by  the 
magnet  at  all  temperatures  under  an  orange-red  heat.  It  is  then  itself  magnetic 
by  induction,  but  immediately  loses  its  polarity,  if  pure,  when  withdrawn  from  the 
magnet.  If  it  contains  carbon,  as  steel  and  cast  iron,  it  is  affected  less  strongly, 
but  more  durably,  by  the  proximity  of  a  magnet,  becoming  then  permanently 
magnetic.  Among  the  native  compounds  of  iron,  the  black  oxide,  which  forms 
the  loadstone,  and  the  corresponding  sulphide,  are  those  which  share  this  property 
with  the  metal  in  the  highest  degree.  A  steel  magnet  loses  it  polarity  at  the  boil- 
ing point  of  almond  oil;  a  loadstone,  just  below  visible  ignition  (Faraday). 

Iron  reduced  from  the  oxide  by  hydrogen  at  a  heat  under  redness,  forms  a 
spongy  mass,  which,  when  exposed  to  air,  takes  fire  spontaneously  at  the  usual 
temperature,  oxide  of  iron  being  reproduced  (Magnus).  But  iron,  in  mass,  appears 
to  undergo  no  change  in  dry  air,  and  to  be  incapable  of  decomposing  pure  water 
at  ordinary  temperatures.  Nor  does  it  appear  to  be  acted  upon  by  oxygen  and 
water  together;  but  the  presence  of  carbonic  acid  in  the  water  causes  the  iron  to 
be  rapidly  oxidated,  with  evolution  of  hydrogen  gas.  In  the  ordinary  rusting  of 
iron,  the  carbonate  of  the  protoxide  appears  to  be  first  produced,  but  that  com- 
pound gradually  passes  into  the  hydrated  sesquioxide,  and  the  carbonic  acid  is 
evolved.  The  rust  of  iron  always  contains  ammonia,  probably  absorbed  from  the 
air;  the  native  oxides  of  iron  also  contain  ammonia.  Iron  remains  bright  in  solu- 
tions of  the  alkalies  and  in  lime-water,  which  appear  to  protect  it  from  oxidation ; 
but  neutral,  and  more  particularly  acid  salts,  have  the  opposite  effect.  The  corro- 
sion of  iron  under  water  appears,  in  general,  to  be  immediately  occasioned  by  the 
formation  of  a  subsalt  of  that  metal  with  excess  of  oxide,  the  acid  of  which  is  sup- 
plied by  the  saline  matter  in  solution.  Articles  of  iron  may  be  completely  de- 
fended from  the  injury  occasioned  in  this  way,  by  contact  with  the  more  positive 
metal  zinc,  as  in  galvanized  iron  (p.  201),  while  the  protecting  metal  itself  wastes 
away  very  slowly.  Cast  iron  is  converted  into  a  species  of  graphite  by  many  years' 
immersion  in  sea-water,  the  greater  part  of  the  iron  being  dissolved  while  the 
carbon  remains.*  In  open  air,  iron  burns  at  a  high  temperature  with  vivacity, 
and  its  surface  becomes  covered  with  a  fused  oxide,  which  forms  smithy  ashes. 
Iron  also  decomposes  steam  at  a  red  heat,  and  the  same  oxide  is  formed  as  by  the 
combination  of  the  metal  in  air,  namely,  the  magnetic  or  black  oxide,  FeO,Fe203. 

Iron  dissolves  readily  in  diluted  acids,  by  substitution  for  hydrogen,  which  is 
evolved  as  gas.  Strong  nitric  acid  acts  violently  upon  iron,  yielding  oxygen  to  it, 
and  undergoing  decomposition.  But  the  relations  of  iron  to  that  acid  when 
slightly  diluted  are  exceedingly  singular ;  they  have  been  particularly  studied  by 
Professor  Schbnbein. 

Passive  condition  of  iron.  —  Pure  malleable  iron,  such  as  a  piece  of  clean  stock- 
ing wire,  usually  dissolves  in  nitric  acid  of  sp.  gr.  1-3  to  1-35,  with  effervescence; 
but  it  may  be  thrown  into  a  condition  in  which  it  is  said  by  Schonbein  to  bejpas- 
sive,  as  it  is  no  longer  dissolved  by  that  acid,  and  may  be  preserved  in  it  for  any 
length  of  time,  without  change:  —  1.  By  oxidating  the  extremity  of  the  wire 
slightly,  by  holding  it  for  a  few  seconds  in  the  flame  of  a  lamp,  and  after  it  is  cool 
dipping  it  gradually  in  the  nitric  acid,  introducing  the  oxidated  end  first.  2.  By 
dipping  the  extremity  of  the  wire  once  or  twice  in  concentrated  nitric  acid,  and 
washing  it  with  water.  3.  By  placing  a  platinum  wire  first  in  the  acid,  and  then 
introducing  the  iron  wire,  preserving  it  in  contact  with  the  former,  which  may 

*  Mr.  Mallett  has  collected  much  information  respecting  the  corrosion  of  iron,  in  his  First 
Report  to  the  British  Association,  on  the  action  of  sea  and  river  water  upon  cast  and  wrought 
iron,  1839. 


448  IRON. 

afterwards  be  withdrawn.  4.  A  fresh  iron  wire  may  be  introduced  in  the  same 
manner  into  the  nitric  acid,  in  contact  with  a  wire  already  passive ;  this  may  ren- 
der passive  a  third  wire,  and  so  on.  5.  By  making  the  wire  the  positive  pole  or 
zincoid  of  a  voltaic  battery,  introducing  it  after  the  negative  pole  or  chloroid  has 
been  placed  in  the  acid.  Oxygen  gas  is  then  evolved  from  the  surface  of  the  iron 
wire,  without  combining  with  it,  as  if  the  wire  were  of  platinum.  As  the  passive 
state  can  be  communicated  by  contact  of  passive  iron,  so  it  may  be  destroyed  by 
contact  with  active  iron  (or  zinc)  undergoing,  at  the  moment,  solution  in  the  acid. 
If  passive  iron  be  made  a  negative  pole  (chlorous)  in  nitric  acid,  it  also  ceases  tc 
resist  solution.  The  indifference  to  chemical  action  exhibited  by  iron  when  pas- 
sive, is  not  confined  to  nitric  acid  of  the  density  mentioned,  but  extends  to  various 
saline  solutions  which  are  usually  acted  upon  by  iron.  An  indifference  to  nitric 
acid  of  the  same  kind  can  also  be  acquired  by  other  metals  as  well  as  iron,  particu- 
larly by  bismuth  (Dr.  Andrews),  but  in  a  much  less  degree.  To  account  for  this 
remarkable  phenomenon  various  theories  have  been  proposed.  Schonbein  and 
Wetzlar  attribute  it  to  a  peculiar  electro-dynamic  condition  of  the  surface  of  the 
metal,  similar  to  that  of  the  platinum  in  Grove's  gas  battery  (pp.  208 — 209). 
Mousson  attributes  it  to  a  coating  of  nitrous  acid.  By  others  again  it  has  been 
ascribed  to  a  peculiar  antagonism  between  two  forces  acting  simultaneously  on  the 
metal,  the  one  tending  to  oxidate  it  at  the  expense  of  the  nitric  acid,  the  other  to 
cause  it  to  take  the  place  of  hydrogen  in  the  nitrate  of  water,  just  as  when  it  dis- 
solves in  sulphuric  acid.*  But  perhaps  the  most  probable  explanation  is  that 
which  attributes  the  passive  condition  of  iron  to  the  formation  on  its  surface  of  a 
thin  film  of  anhydrous  ferric  oxide,  similar  to  specular  iron.  This  view  is  sup- 
ported by  the  fact  that  iron  which  has  been  ignited,  and  is  therefore  completely 
covered  with  black  oxide,  exhibits  the  same  characters,  excepting  that,  from  the 
greater  thickness  of  the  coating,  the  passive  state  is  more  complete.  It  may  also 
be  observed,  that  iron  becomes  passive  only  in  liquids  which  give  up  oxygen,  and 
that  in  the  voltaic  circuit  it  becomes  passive  precisely  under  the  circumstances  in 
which  it  is  exposed  to  oxidation,  i.  e.,  when  it  is  made  the  zincoid  or  positive  pole, 
and  that  it  becomes  active  again  when  made  the  negative  pole,  that  is  to  say,  when 
the  oxide  is  reduced.  The  same  view  is  supported  by  the  observation  that  iron 
rendered  passive  in  nitric  acid  immediately  begins  to  dissolve  on  the  addition  of 
hydrochloric  acid. 

PROTOCOMPOUNDS   OF   IRON;    FERROUS    COMPOUNDS. 

Protoxide  of  iron,  Ferrous  oxide  ;  FeO;  36  or  450.  —  Iron  appears  to  admit 
of  three  degree  of  oxidation,  the  protoxide  and  sesquioxide,  which  are  both  basic 
and  correspond  respectively  with  manganous  and  manganic  oxide,  and  ferric  acid. 
The  protoxide  is  not  easily  obtained  in  a  dry  state,  from  the  avidity  with  which  it 
absorbs  oxygen.  The  purest  anhydrous  protoxide  is  obtained  by  igniting  the 
oxalate  out  of  contact  of  air ;  but  even  this,  according  to  Liebig,  contains  a  small 
quantity  of  metallic  iron.  The  protoxide  exists  in  the  sulphate  and  other  salts  of 
iron,  formed  when  the  metal  dissolves  in  an  acid  with  evolution  of  hydrogen. 

Solutions  of  ferrous  salts  have  a  green  colour.  Potash  or  soda  added  to  them 
throws  down  the  protoxide  as  a  white  hydrate,  which  becomes  black  on  boiling, 
from  loss  of  water.  The  colour  of  the  white  precipitate  changes  by  exposure  to 
air,  to  grey,  then  to  green,  bluish  black,  and  finally  to  an  ochrey  red,  when  it  is 
entirely  sesquioxide.  Ammonia  exercises  a  similar  action,  but  does  not  precipi- 
tate the  whole  of  the  oxide,  because  the  precipitate  dissolves  in  the  ammoniacal 

*  Dr.  Andrews  indeed  concludes  from  observation,  that  the  ordinary  chemical  action  of  a 
hydrated  acid  upon  the  mptals  which  dissolve  in  it,  is  in  general  diminished,  when  the  acid 
is  concentrated,  by  the  voltaic  association  of  these  metals  with  such  metals  as  gold,  platinum, 
&c. ;  while,  on  the  contrary,  it  is  increased  when  the  acid  is  diluted.  —  Trans,  of  the  Royal 
Irish  Academy,  1«38;  or,  Becquerel,  vol.  v.  pt.  2,  p.  187. 


FERROUS    COMPOUNDS.  449 

salt  produced.  Alkaline  carbonates  form  a  precipitate  of  carbonate  of  iron,  which 
is  white  at  first,  but  soon  becoinos  of  a  dirty  green,  and  undergoes  the  same  subse- 
quent changes  from  oxidation.  Ferrous  salts  are  not  precipitated  by  hydrosul- 
phuric acid,  the  sulphide  of  iron  being  dissolved  by  strong  acids,  but  give  a  black 
sulphide  with  solutions  of  alkaline  sulphides.  They  give  a  white  precipitate  with 
ferrocyanide  ofpofaxswm,  which  gradually  becomes  of  a  deep  blue  when  exposed 
to  air  j  with  the  ferriryanide,  a  precipitate  which  is  at  once  of  an  intense  blue, 
being  one  of  the  varieties  of  prussian  blue.  The  infusion  of  y all-nuts  does  not 
affect  a  solution  of  the  protoxide  of  iron  when  completely  free  from  sesquioxide. 

Protosulphide  of  iron  is  prepared  by  heating  to  redness,  in  a  covered  crucible, 
a  mixture  of  iron  filings  and  crude  sulphur,  in  the  proportion  of  7  of  the  former 
to  4  of  the  latter.  It  dissolves  in  sulphuric  and  hydrochloric  acids,  with  evolu- 
tion of  hydrosulphuric  acid  gas  (p.  306.). 

A  subsulphide  of  iron,  Fe2S,  appears  to  be  formed  when  the  sulphate  of  iron  is 
reduced  by  hydrogen,  one-half  of  the  sulphur  coming  off  in  the  form  of  sulphu- 
rous acid.  This  subsulphide  is  analogous  to  the  subsulphides  of  copper  and  lead, 
which  crystallize  in  octahedrons. 

Protochloride  of  iron  crystallizes  with  4HO,  and  is  very  soluble.  Like  all  so- 
luble ferrous  salts,  it  is  of  a  green  colour,  gives  a  green  solution,  and  has  a  great 
avidity  for  oxygen. 

Protiodide  of  iron  is  formed  when  iodine  is  digested  with  water  and  iron  wire, 
the  latter  being  in  excess,  and  is  obtained  as  a  crystalline  mass  by  evaporating  to 
dryness.  It  was  introduced  into  medical  use  by  Dr.  A.  T.  Thomson.  A  piece  of 
iron  wire  is  placed  in  the  solution  of  this  salt  to  preserve  it  from  oxidizing.  The 
protiodide  of  iron  dissolves  a  large  quantity  of  iodine,  without  becoming  periodide, 
as  the  excess  of  iodine  may  be  precipitated  by  starch. 

Protocyanide  of  iron,  C2NFe  or  FeCy,  is  as  difficult  to  obtain  as  the  protoxide 
of  iron.  When  cyanide  of  potassium  is  added  to  a  protosalt  of  iron,  a  yellowish- 
red  precipitate  appears,  which  dissolves  in  an  excess  of  the  alkaline  cyanide,  and 
forms  the  ferrocyanide  of  potassium  (p.  375.).  A  grey  powder  remains  on  dis- 
tilling the  ferrocyanide  of  ammonium  at  a  gentle  heat ;  and  a  white  insoluble  sub- 
stance on  digesting  recently  precipitated  prussian  blue  in  sulphuretted  hydrogen 
water,  contained  in  a  well-stopped  phial ;  these  products,  although  they  differ  con- 
siderably in  properties,  have  both  been  looked  upon  as  protocyanide  of  iron.  This 
compound  is  also  obtained  as  a  white  deposit  on  boiling  an  aqueous  solution  of 
hydroferrocyanic  acid,  H2FeCy3.  The  same  solution  heated  with  red  oxide  of 
mercury  forms  cyanide  of  mercury  and  white  protocyanide  of  iron.  The  most 
remarkable  property  of  this  cyanide  is  its  tendency  to  combine  with  other  cyanides 
of  all  classes,  and  to  form  double  cyanides,  or  to  enter  as  a  constituent  into  the 
salt-radicals,  ferrocyanogen  and  ferricyanogen,  Cy3Fe  and  Cy6Fe2. 

Hydroferrocyanic  acid;  H2FeCy3  or  2HCy,FeCy.  This  compound  was  disco- 
vered by  Mr.  Porrett.  It  may  be  obtained  by  decomposing  ferrocyanide  of  barium 
with  sulphuric  acid,  or  ferrocyanide  of  potassium  with  an  alcoholic  solution  of  tar- 
taric  acid,  or  ferrocyanide  of  lead  with  hydrosulphuric  acid.  It  is  soluble  in  water 
and  alcohol,  insoluble  in  ether,  and  crystallizes  by  spontaneous  evaporation  in  cubes 
or  four-sided  prisms,  or  sometimes  in  tetrahedrons.  When  dry,  it  may  be  kept 
for  a  long  time  without  alteration  in  close  vessels ;  but  is  decomposed  on  exposure 
to  the  air  with  evolution  of  hydrocyanic  acid,  and  formation  of  prussian  blue. 

Hydroferrocyanic  acid  unites  with  most  salifiable  bases,  forming  the  salts  called 
ferroryanides,  whose  general  formula  is  M2FeCy3,  the  symbol  M  denoting  a  metal. 
The  ferrocyanides  of  ammonium,  potassium,  sodium,  barium,  strontium,  calcium, 
and  magnesium,  dissolve  readily  in  water;  the  rest  are  insoluble  or  sparingly 
soluble.  Some  of  them,  as  the  copper  and  uranium  salts,  are  very  highly  coloured. 
Ferrocyanide  of  potassium  has  been  already  described  (p.  375.) 

Ferrocyanide  of  potassium  and  iron;  KFe2Cy3  =  (KFe);(Cy3Fe). — The  bluish- 
29 


450  IRON. 

white  precipitate  which  falls  on  testing  a  protosalt  of  iron  with  the  ferrocyanide 
of  potassium  or  yellow  prussiate  of  potash,  e.  g.,  with  the  protochloride  : 

K2FeCy3  -f  Fed  ==  KC1  +  KFe2Cy3. 

It  is  also  obtained  in  the  form  of  a  white  crystalline  salt  (mixed  with  bisulphate 
of  potash),  in  the  preparation  of  hydrocyanic  acid,  by  distilling  ferrocyanide  of 
potassium  with  dilute  sulphuric  acid  : 

2K2FeCy3+6S03  +  6HO  =  3(KO,HO,2S03)  +  3HCy  +  KFe2Cy3. 

Exposed  to  the  air,  it  absorbs  oxygen  and  becomes  blue.  It  then  affords  ferro- 
cyanide of  potassium  to  water,  and  after  all  soluble  salts  are  removed,  a  compound 
remains,  which  Liebig  names  the  basic  sesquiferrocyanide  of  iron,  and  represents 
by  the  formula  Fe4.3(Cy3Fe)-f  Fe203,  corresponding,  as  will  be  seen  hereafter, 
with  1  eq.  of  prussian  blue  -f-  1  eq.  of  sesquioxide  of  iron.  This  basic  compound 
is  dissolved  entirely  by  continued  washing,  and  affords  a  beautiful  deep  blue  solu* 
tion.  The  addition  of  any  salt  causes  the  separation  of  this  compound.  Its  solu- 
tion may  be  evaporated  to  dryness  without  decomposition.  The  white  ferrocyanide 
of  iron  and  potassium  likewise  turns  blue  when  treated  with  chlorine-water  or 
nitric  acid,  being  thereby  converted  into  ferricyanide  of  iron  and  potassium 
(KFe4Cy6). 

2KFe2Cy3  -f  Cl  =  KFe4Cy6  -f  KC1. 

This  latter  compound,  which  when  dry  is  of  a  beautiful  violet  colour,  may  be  re- 
garded as  ferricyanide  of  potassium,  K3Fe2Cy6,  in  which  2  eq.  of  potassium  are 
replaced  by  iron  (Williamson). 

Ferricyanide  of ^  iron,  Turnbull's  blue;  Fes(Cy6Fe2). —  This  is  the  beautiful 
blue  precipitate  which  falls  on  adding  the  ferricyanide  of  potassium  (red  prussiate 
of  potash)  to  a  protosalt  of  iron.  It  is  formed  by  the  substitution  of  3  eq.  of  iron 
for  the  3  eq.  of  potassium  of  the  latter  salt  (p.  376).  The  same  blue  precipitate 
may  be  obtained  by  adding  to  a  protosalt  of  iron  a  mixture  of  yellow  prussiate  of 
potash,  chloride  of  soda,  and  hydrochloric  acid.  The  tint  of  this  blue  is  lighter 
and  more  delicate  than  that  of  prussian  blue.  It  is  occasionally  used  by  the 
calico-printer,  who  mixes  it  with  pernmriate  of  tin,  and  prints  the  mixture,  Which 
is  in  a  great  measure  soluble,  upon  Turkey-red  cloth,  raising  the  blue  colour  after- 
wards by  passing  the  cloth  through  a  solution  of  chloride  of  lime  containing  an 
excess  of  lime.  The  chief  'object  of  that  operation  is  indeed  different,  namely,  to 
discharge  the  red  and  produce  white  patterns,  where  tartaric  acid  is  printed  upon 
the  cloth ;  but  it  has  also  the  effect  incidentally  of  precipitating  the  blue  pigment 
and  peroxide  of  tin  together  on  the  cloth,  by  neutralizing  the  acid  of  the  permu- 
riate  of  tin.  This  blue  is  believed  to  resist  the  action  of  alkalies  longer  than 
ordinary  prussian  blue.  It  is  distinguished  from  prussian* blue  by  yielding,  when 
treated  with  caustic  potash  or  carbonate  of  potash,  a  solution  of  ferrocyanide  of 
potassium,  and  a  residue  of  ferroso-ferric  oxide : 

3Fe5Cy6  +  4KO  =  2K2FeCy3  +  Fe304; 

whereas  prussian  blue  treated  in  the  same  manner  yields  ferric  oxide  (Williamson). 
Carbonate  of  iron  is  obtained  on  adding  carbonate  of  soda  to  the  protosulphate 
of  iron,  as  a  white  or  greenish-white  precipitate,  which  may  be  washed  and  pre- 
served in  a  humid  condition  in  a  close  vessel,  but  cannot  be  dried  without  losing 
carbonic  acid  and  becoming  sesquioxide  of  iron.  It  is  soluble,  like  the  carbonate 
of  lime,  in  carbonic  acid  water,  and  exists  under  that  form  in  mos,t  natural  chaly- 
beates.  Carbonate  of  iron  occurs  also  crystallized  in  the  rhombohedral  form  of 
calc-spar,  forming  the  mineral  spathic  iron,  which  generally  contains  portions  01 
the  carbonates  of  lime,  magnesia,  and  manganese.  It  is  generally  of  a  cream 
colour  or  black,  and  its  density  rarely  exceeds  3-8.  This  anhydrous  carbonate 


FERRIC     COMPOUNDS.  451 

does  not  absorb  oxygen  from  the  air.  Carbonate  of  iron  is  also  the  basis  of  clay 
iron-stone.  There  is  no  carbonate  of  the  scsquioxide. 

Protosulphate  of  iron,  Ferrous  sulphate,  Green  vitriol,  Copperas;  FeO.S03, 
HO  -f  6HO;  76  +  63  or  950  +  787-5.  —  This  salt  may  be  formed  by  dissolving 
iron  in  sulphuric  acid  diluted  with  4  or  5  times  its  bulk  of  water,  filtering  the 
solution  while  hot,  and  setting  it  aside  to  crystallize.  But  the  large  quantities  of 
sulphate  of  iron  consumed  in  the  arts  are  prepared  simultaneously  with  alum,  by 
the  oxidation  of  iron  pyrites  (p.  422). 

The  commercial  salt  forms  large  crystals,  derived  from  an  oblique  rhomboidal 
prism,  which  effloresce  slightly  in  dry  air,  and,  when  at  all  damp,  absorb  oxygen 
and  become  of  a  rusty  red  colour;  hence  the  origin  of  the  French  term  couperose 
applied  to  this  salt,  and  corrupted  in  our  language  into  copperas.  If  these  crys- 
tals be  crushed  and  deprived  of  all  hygrometric  moisture  by  strong  pressure 
between  folds  of  cotton  cloth  or  filter  paper,  they  may  afterwards  be  preserved  in 
a  bottle  without  any  change  from  oxidation.  Of  the  7HO  which  sulphate  of  iron 
contains,  it  loses  6HO  at  238°,  but  retains  1  eq.  even  at  535°.  It  may,  however, 
be  rendered  perfectly  anhydrous,  with  proper  caution,  without  any  appreciable 
loss  of  acid.  The  anhydrous  salt  is  also  obtained  in  very  small  crystalline  scales 
by  immersing  the  hydrated  crystals  in  strong  boiling  sulphuric  acid,  and  leaving 
the  liquid  to  cool.  The  salt  was  observed  by  Mitscherlich  to  crystallize  at  176°, 
with  4HO,  in  a  right  rhombic  prism,  like  the  corresponding  sulphate  of  manga- 
nese. When  its  solution  containing  an  excess  of  acid  is  evaporated  by  heat,  a 
saline  crust  is  deposited,  which,  according  to  Kuhn,  contains  3HO.  The  sul- 
phate of  iron  appears  to  form  neither  acid  nor  basic  salts.  One  part  of  copperas 
requires  to  dissolve  it,  the  following  quantities  of  water,  at  the  particular  tempe- 
ratures indicated  above  each  quantity,  according  to  the  observations  of  Brandes 
and  Firnhaber : — 

50°     59°     75-2°     109-4°     114-°     140-0°     183-2°     194°     212° 
.  1-64    1 43     0.87       0-66       0-44      0-38         0.37      0-27     0-30 

Ferrous  sulphate  undergoes  decomposition  at  a  red  heat,  changing  into  ferric 
sulphate,  and  leaves,  after  all  the  acid  is  expelled,  the  red  sesquioxide  known  as 
colcothar.  This  sulphate,  like  all  the  magnesian  sulphates,  forms  with  sulphate 
of  potash  a  double  salt  containing  6HO.  A  solution  of  the  sulphate  of  iron 
absorbs  nitric  oxide,  and  becomes  quite  black;  according  to  Peligot,  it  takes  up 
the  gas  in  the  proportion  of  9  parts  to  100  anhydrous  salt,  or  one-fourth  of  an 
equivalent  (p.  257). 

Protonitrate  of  iron,  Ferrous  nitrate,  may  be  formed  by  dissolving  the  proto- 
sulphide  in  cold  dilute  nitric  acid ;  the  solution  evaporated  in  vacuo  yields  pale 
green,  very  soluble  crystals.  The  solution  of  the  neutral  salt  is  decomposed  near 
the  boiling  heat,  with  evolution  of  nitric  acid  and  copious  precipitation  of  a  ferric 
subnitrate.  Iron  turnings  dissolve  in  dilute  nitric  acid  and  form  the  same  salt, 
without  evolution  of  gas,  the  water  and  acid  being  decomposed  in  such  a  manner 
as  to  form  ammonia,  at  the  same  time  that  they  oxidate  the  iron. 

Protoacetate  of  iron,  Ferrous  acetate,  is  obtained  by  dissolving  the  metal  or  its 
sulphide  in  acetic  acid.  It  forms  small  green  prisms  which  decompose  very  readily 
in  the  air. 

Tartrate  of  potash  and  iron,  Potassio-ferrous  tartrate,  is  prepared  by  boiling 
bitartrate  of  potash  with  half  its  weight  of  iron  turnings  and  a  small  quantity  of 
water.  Hydrogen  is  evolved,  and  a  white,  granular,  sparingly  soluble  salt  formed 
which  blackens  in  the  air  from  absorption  of  oxygen.  It  is  used  medicinally, 
The  iron  of  this  salt  is  not  precipitated  by  hydrate  or  carbonate  of  potash, 

SESQUICOMPOUNDS   OP   IRON;    FERRIC   COMPOUNDS. 

Sesquioxide  of  iron;  Peroxide  of  iron;  Ferric  oxide,  80  or  1000.  —  Occurs 
very  abundantly  in  nature :  1.  as  oligistic  or  specular  iron,  in  crystals  derived 


452  IRON. 

from  a  rhombohedron  very  near  the  cube,  which  are  of  a  brilliant  metallic  black 
and  highly  iridescent.  Their  powder  is  red;  their  density,  from  5-01  to  5-22. 
This  oxide  forms  the  celebrated  Elba  ore.  — 2.  As  red  hematite,  in  fibrous,  mam- 
niillated,  or  kidney-shaped  masses,  of  a  dull  red  colour,  very  hard,  and  of  sp.  gr. 
from  4-8  to  5-0.  This  mineral  when  cut  forms  the  burnishers  of  bloodstone. — 3. 
also  in  combination  with  water,  as  brown  hematite,  which  is  much  more  abun- 
dantly diffused  than  the  anhydrous  sesquioxide,  the  granular  variety  supplying, 
according  to  M.  Berthier,  more  than  three-fourths  of  the  iron-furnaces  in  France. 
Its  density  is  3-922;  its  powder  is  brown  with  a  shade  of  yellow,  and  it  dissolves 
readily  in  acid,  which  the  anhydrous  sesquioxide  does  not.  From  analyses  by  Dr. 
Thomson  and  M.  Berthier,  this  mineral  appears  to  unite  with  1  eq.  of  water,  as 
HO.Fe203,  analogous  to  the  magnetic  oxide  of  iron,  FeO.Fe203.  The  hydrated 
sesquioxide  produced  by  the  oxidation  of  iron  pyrites,  of  which  it  retains  the 
form,  contains  1  eq.  of  water,  or  10-31  per  cent.,  and  that  from  the  oxidation  of 
the  carbonate  of  iron,  3  eq.  of  water,  or  14-71  per  cent.,  to  2  eq.  of  sesquioxide 
(Mitscherlich,  Lehrbuch,  II.  23,  1840).  The  hydrate  is  the  yellow  colouring 
matter  of  clay,  and  with  silica  and  clay  it  forms  the  several  varieties  of  ochre. 

When  metallic  iron  is  oxidated  gradually  in  a  large  quantity  of  water,  there 
forms  around  it  a  light  precipitate  of  a  bright  orange  yellow  colour,  which,  accord- 
ing to  Berzelius,  is  a  ferric  hydrate,  and  of  which  the  empirical  formula  is  2Fe203 
+  3HO,  the  usual  composition  of  brown  hematite.  When  iron  is  oxidated  in 
deep  water,  it  is  converted,  according  to  E.  Davy,  into  the  magnetic  oxide,  which 
is  possibly  formed  by  cementation  from  the  hydrated  sesquioxide.  The  hydrated 
sesquioxide  is  also  obtained,  by  precipitation  from  ferric  salts,  by  ammonia  and  by 
hydrated  or  carbonated  alkali ;  but  never  pure,  as  when  an  insufficient  quantity 
of  alkali  is  added,  a  sub-salt  containing  acid  is  precipitated ;  and  when  the  alkali 
is  added  in  excess,  a  portion  of  it  goes  down  in  combination  with  the  oxide,  and 
cannot  be  entirely  removed  by  washing.  When  ammonia  is  used,  the  water  and 
excess  of  the  precipitant  may  be  expelled  by  ignition,  and  the  pure  sesquioxide 
obtained.  The  latter  is  not  magnetic,  and  after  ignition  dissolves  with  difficulty 
in  acids.  When  ignited  strongly,  it  loses  oxygen  and  becomes  magnetic. 

Ferric  oxide  and  its  compounds  are  strictly  isomorphous  with  alumina  and  the 
compounds  of  that  earth,  and  remarkably  analogous  to  them  in  properties.  It  is 
a  weak  base,  of  which  the  salts  have  a  strong  acid  reaction,  and  are  decomposed 
by  all  the  magnesian  carbonates,  as  well  as  by  the  magnesian  oxides  themselves. 
The  solution  of  its  salts,  which  are  neutral  in  composition,  have  generally  a  yellow 
tint;  but  they  are  all  capable,  when  rather  concentrated,  of  dissolving  a  great 
excess  of  ferric  oxide,  and  then  become  red.  Very  dilute  solutions  of  the  neu- 
tral salts  of  ferric  oxide  are  decomposed  by  ebullition,  and  the  oxide  entirely  pre- 
cipitated, the  acid  of  the  salt  then  uniting  with  water  as  a  base  (Scheerer). 

Iron  is  most  conveniently  distinguished  by  tests,  or  precipitated  for  quantitative 
estimation,  when  in  the  state  of  sesquioxide.  The  solution  of  a  ferrous  salt  is 
usually  oxidized  by  transmitting  a  current  of  chlorine  through  it,  or  by  adding  to 
it,  at  the  boiling  point,  nitric  acid,  in  small  quantities,  so  long  as  effervescence  is 
occasioned  from  the  escape  of  nitric  oxide.  Alkalies  and  alkaline  carbonates 
throw  down  a  red-brown  precipitate  of  hydrated  sesquioxide.  IJydrosulpliuric 
acid  converts  a  sesquisalt  of  iron  into  a  protosalt,  with  precipitation  of  sulphur. 
Ferrocyanide  of  potassium  throws  down  prussian  blue,  but  the  ferricyanide  has 
no  effect  upon  ferric  salts  beyond  slightly  changing  the  colour  of  the  solution. 
Sulphocyanide  of  potassium  produces  a  deep  wine-red  solution  with  ferric  salts, 
which  becomes  perfectly  colourless  when  considerably  diluted  with  water,  provided 
the  iron  salt  is  not  in  great  excess.  Infusion  of  gall-nuts  produces  a  bluish-black 
precipitate  —  the  basis  of  common  writing  ink. 

A  remarkable  insoluble  modification  of  the  hydrated  sesquioxide  is  produced  by 
boiling  the  ordinary  hydrate  (precipitated  from  the  chloride  of  ammonia)  in  watei 
for  7  or  8  hours.  The  colour  then  changes  from  ochre-yellow  to  brick-red,  and 


FERRIC    COMPOUNDS.  453 

the  hydrate  thus  altered  is  scarcely  acted  upon  by  strong  boiling  nitric  acid,  and 
but  very  slowly  by  hydrochloric  acid.  In  acetic  acid,  or  dilute  nitric  or  hydro- 
chloric acid,  it  dissolves,  forming  a  red  liquid,  which  is  clear  by  transmitted,  but 
turbid  by  reflected  light ;  is  precipitated  by  the  smallest  quantity  of  an  alkali-salt 
or  a  sulphate ;  and  on  addition  of  strong  nitric  or  hydrochloric  acid,  yields  a  red 
granular  precipitate  which  re-dissolves  on  diluting  the  liquid  with  water.  The 
modified  hydrate  does  not  form  prussian  blue  with  ferrocyanide  of  potassium  and 
acetic  acid.  It  appears  to  be  Fe203.HO,  the  ordinary  precipitated  hydrate,  after 
drying  in  vacuo,  being  2Fe203.3HO.  This  insoluble  hydrate  is  likewise  precipi- 
tated when  a  solution  of  the  ordinary  hydrate  in  acetic  acid  is  rapidly  boiled. 
The  same  solution,  if  kept  for  some  time  at  212°  in  a  close  vessel,  becomes  light 
in  colour,  no  longer  forms  prussian  blue  with  ferrocyanide  of  potassium,  or  exhibits 
any  deepening  of  colour  on  addition  of  a  sulphocyanide ;  strong  hydrochloric  or 
nitric  acid,  or  a  trace  of  an  alkali-salt,  or  sulphuric  acid,  throws  down  all  the  ferric 
oxide  in  the  form  of  the  insoluble  hydrate.*  It  has  also  been  observed  that  ferric 
hydrate  becomes  crystalline  and  less  soluble  by  long  immersion  in  water,  and  by 
exposure  to  a  low  temperature. 

Black  or  magnetic  oxide  of  iron,  Ferroso-ferric  oxide,  FeO.Fe203,  an  import- 
ant ore  of  iron,  is  a  compound  of  the  two  oxides.  It  crystallizes  in  regular  octo- 
hedrons.  In  this  compound,  the  sesquioxide  of  iron  may  be  replaced  by  alumina 
and  by  oxide  of  chromium,  and  the  protoxide  of  iron  by  oxide  of  zinc,  magnesia, 
and  protoxide  of  manganese,  without  change  of  form.  It  was  produced  artificially, 
by  Liebig  and  Wbhler,  by  mixing  the  dry  protochloride  of  iron  with  an  excess  of 
carbonate  of  soda,  calcining  the  mixture  in  a  crucible,  and  treating  the  mass  with 
water.  The  double  oxide  then  remains  as  a  black  powder,  which  may  be  washed 
and  dried  without  further  oxidation.  The  same  chemists,  by  dissolving  the  bli^E  . 
oxide  in  hydrochloric  acid,  and  precipitating  by  ammonia,  obtained  a  hydrate  of 
the  double  oxide.  It  was  attracted  by  the  magnet,  even  when  in  the  state  of  a 
flocculent  precipitate  suspended  in  water.  When  ignited  and  anhydrous,  this 
double  oxide  is  much  more  magnetic  than  iron  itself. 

Scale-oxide,  6FeO  .  Fe203.  —  When  iron  is  heated  to  redness  in  contact  with 
air,  two  layers  of  scale-oxide  are  formed,  which  may  be  easily  separated.  The 
inner  layer,  which  has  the  composition  just  given,  is  blackish  grey,  porous,  brittle, 
and  attracted  by  the  magnet.  The  outer  layer  contains  a  larger  proportion  of 
ferric  oxide ;  it  is  of  a  reddish  iron-black  colour,  dense,  brittle,  yields  a  black 
powder,  and  is  more  strongly  attracted  by  the  magnet  than  the  inner  layer.  The 
proportion  of  ferric  oxide  in  the  outer  layer  is  between  32  and  37  per  cent.,  and 
on  the  very  surface  as  much  as  52-8  per  cent.  (Mosander).  The  specific  gravity 
of  the  scale-oxide  is  548  (Boullay). 

Sesquisulphide  of  iron,  or  Ferric  sulphide,  Fe2S3,  corresponding  with  the 
sesquioxide,  may  be  prepared  by  pouring  a  solution  of  a  sesquisalt  of  iron,  drop 
by  drop,  into  a .  solution  of  an  alkaline  sulphide,  the  latter  being  preserved  in 
excess.  At  a  low  red  heat,  it  loses  2-9  ths  of  its  sulphur,  and  becomes  magnetic 
pyrites.  The  common  yellow  iron  pyrites  is  the  bisulphide  of  iron.  It  crystallizes 
in  cubes  or  other  forms  of  the  regular  system;  its  density  is  4-981.  It  may  be 
formed  artificially  by  mixing  the  protosulphide  with  half  its  weight  of  sulphur, 
and  distilling  in  a  retort  at  a  temperature  short  of  redness.  The  metallic  sulphide 
combines  with  a  quantity  of  sulphur  equal  to  that  which  it  already  possesses,  and 
forms  a  bulky  powder  of  a  deep  yellow  colour  and  metallic  lustre,  upon  which 
sulphuric  and  hydrochloric  acids  have  no  action.  This  sulphide  appears  to  be  of 
a  stable  nature,  but  the  lower  sulphides  of  iron  oxidate,  when  moistened,  with 
great  avidity.  Stromeyer  found  the  native  magnetic  sulphide  of  iron  to  consist 
of  100  parts  of  iron  combined  with  68  of  sulphur;  and  the  sulphide  left  on  dis- 
tilling iron  with  sulphur  at  a  high  temperature,  to  be  of  the  same  composition.  It 

*  P6an  de  St.  Giles,  Ann.  Ch.  Phys.  [3],  xlvi.  47. 


454  IRON. 

may  be  viewed  as  5Fe  S.  Fe2S3  (Berzelms).  It  is  said  to  be  this  compound  which 
is  almost  always  formed  when  sulphide  of  iron  is  prepared  in  the  usual  manner. 

Sesquichloride  of  iron,  Ferric  chloride,  Fe2  C13,  is  formed  when  iron  is  burned 
in  an  excess  of  chlorine.  It  is  volatile  at  a  red  heat.  Its  solution,  which  is  used 
in  medicine,  is  obtained  by  dissolving  the  hydrated  sesquioxide  of  iron  in  dilute 
hydrochloric  acid.  When  greatly  concentrated,  the  solution  of  sesquichloride  of 
iron  yields,  sometimes  orange-yellow  crystalline  needles,  radiating  from  a  centre, 
wliich  are  Fe2Cl3  +  12.HO,  at  other  times,  large  dark  yellowish-red  crystals, 
Fe2013  +  5HO.  Mixed  with  sal-ammoniac,  and  evaporated  in  vacuo,  it  affords 
beautiful  ruby-red  octohedral  crystals,  consisting  of  2  eq.  of  chloride  of  am- 
monium, and  1  eq.  of  sesquichloride  of  iron,  with  2  eq.  of  water,  Fe2Cl3. 
2NH4Cl  +  2Hp.  Of  this  water,  the  double  salt  loses  1  eq.  at  150°,  and  the 
other  when  dried  above  300°  (Graham).  There  is  a  similar  double  salt,  contain- 
ing chloride  of  potassium,  but  not  so  easily  formed.  Sesquichloride  of  iron  is 
soluble  both  in  alcohol  and  ether.  A  strong  aqueous  solution  was  found  by  Mr. 
R.  Phillips  to  dissolve  not  less  than  4  eq.  of  freshly  precipitated  ferric  hydrate, 
becoming  deep  red  and  opaque. 

Sesqui-iodide  of  iron  is  formed  in  similar  circumstances  to  the  preceding  sesqui- 
chloride. 

Sesquicyanide  of  iron,  Ferric  cyanide,  Fe2Cya,  is  unknown  in  the  pure  state. 
A  solution  of  it,  which  is  decomposed  by  evaporation,  is  obtained  by  precipitating 
the  potash  of  the  red  prussiate  of  fluoride  of  silicon.  It  forms  a  numerous  class 
of  double  cyanides.  A  compound  of  the  two  cyanides  of  iron,  like  the  compound 
oxide,  is  obtained  as  a  green  powder,  when  a  solution  of  the  yellow  prussiate  of 
potash,  charged  with  excess  of  chlorine,  is  heated  or  exposed  to  air.  The  precipi- 
tate should  be  boiled  with  eight  or  ten  times  its  weight  of  concentrated  hydro- 
chloric acid,  and  well  washed.  Its  formula  is,  FeCy.Fe2Cy3  -f-  4HO.* 

Hydroferricyanic  acid  ;  H3Fe2Cy6,  or  H3.(Cy3Fc)2,  or  3IICy.Fe2Cy3,  is  obtained 
by  decomposing  ferricyanide  of  lead  with  sulphuric  or  hydrosulphuric  acid.  The 
decanted  yellow  solution  yields,  by  careful  evaporation,  brownish  needles,  which 
redden  litmus  strongly,  and  have  a  rough  sour  taste.  This  solution  gives  a  deep 
blue  precipitate  (Turnbull's  blue),  with  ferrous  salts.  This  acid,  united  with 
salifiable  bases,  forms  iheferricynides,  M3Fe2Cy6.  The  potassium  salt  is  described 
on  p.  376. 

Prussian  blue,  Fe3  •  3(Cy3Fe),  or  3FeCy.2Fe2Cy3.  —  This  remarkable  substance 
is  precipitated  whenever  the  yellow  prussiate  of  potash  is  added  to  a  sesquisalt 
of  iron.  Thus  with  the  sesquichloride  : 

3K2FeCy3  +  2Fe2Cl3  =  Fe4.3(Cy3Fe)  +  6KC13. 

Care  must  be  taken  to  avoid  an  excess  of  the  yellow  prussiate,  as  the  precipitate 
is  apt  to  carry  down  a  portion  of  that  salt.  The  precipitate  also  contains  water 
which  cannot  be  separated  from  it  without  decomposition.  On  the  large  scale, 
prussian  blue  is  sometimes  prepared  by  precipitating  green  vitriol  with  yellow 
prussiate  of  potash,  and  subjecting  the  white  precipitate,  KFe2Cy3,  to  the  action 
of  oxidizing  agents,  such  as  chlorine  or  nitric  acid.  This  process,  however,  is 
likely  to  yield  ferricyanide  of  iron  and  potassium,  KFe4Cy6  (p.  40.),  rather  than 
Prussian  blue,  properly  so  called. 

Prussian  blue,  dried  at  the  temperature  of  the  air,  is  a  light  porous  body,  of  a 
rich  velvety  blue  colour;  dried  at  a  higher  temperature  it  is  more  compact,  and 
exhibits  in  mass  a  coppery  lustre.  It  is  tasteless,  and  not  poisonous.  Alkalies 
decompose  it,  precipitating  sesquioxide  of  iron  and  reproducing  an  alkaline  ferro- 
cyanide.  This  renders  prussian  blue  of  little  value  in  dyeing,  as  it  is  injured  by 
washing  with  soap.  Red  oxide  of  mercury  boiled  with  prussian  blue,  affords  the 
soluble  cyanide  of  mercury,  with  an  insoluble  mixture  of  oxide  and  cyanide  of 

*  Pelouze,  Ann.  Ch.  Phys.  [2],  Ixix.  40. 


FERRIC     NITRATE.  455 

iron.     Prussian  blue  is  destroyed  by  fuming  nitric  acid,  but  combines  with  oil  of 
vitriol,  forming  a  white  pasty  mass,  which  is  decomposed  by  water. 

The  combination  of  prussian  blue  and  sesquioxide  of  iron,  called  basic  prussian 
Hue,  was  noticed  at  page  450. 

Although  there  is  no  carbonate  of  the  sesquioxide  of  iron,  the  hydrated  sesqui- 
oxide  is  dissolved  by  alkaline  bicarbonates,  under  certain  conditions  which  are  not 
well  understood,  and  a  red  solution  is  formed. 

Ferric  sulphates.  —  The  neutral  sulphate,  Fe203.3S03,  is  formed  by  adding  to  a 
solution  of  the  protosulphate,  half  as  much  sulphuric  acid  as  it  already  contains, 
and  oxidizing  by  nitric  acid.  It  gives  a  syrupy  liquid,  without  crystallizing. 
This  salt  is  found  native  in  Chili,  forming  a  bed  of  considerable  thickness.  It  is 
generally  massive,  but  forms  also  six-sided  prisms,  with  right  summits,  which  are 
colourless,  and  contain  9HO  (Rose).  Ferric  sulphate  is  soluble  in  alcohol.  It 
may  be  rendered  anhydrous  by  a  low  red  heat ;  but  after  ignition,  it  dissolves  in 
water  with  extreme  slowness,  like  calcined  alum. 

When  hydrated  ferric  oxide  is  digested  in  the  neutral  sulphate,  a  red  solution 
is  formed,  which,  according  to  Maus,  is  the  compound  Fe203 .  2S03.  The  rusty 
precipitate  which  is  formed  in  a  solution  of  the  protosulphate  from  absorption  of 
oxygen,  is  another  subsulphate,  of  which  the  empirical  formula  is  2Fe203.  S03. 
The  decomposition  may  be  represented  by  the  following  equation :  — 

10(FeO.S03)  +  50  =  2Fe203.S03  +  3(Fe203.3S03). 

The  neutral  ferric  sulphate  remains  in  solution. 

A  potass io-ferric  sulphate,  or  iron  alum,  is  formed  by  evaporating  a  solution  of 
the  mixed  salts  to  their  point  of  crystallization.  It  is  colourless  and  exactly 
analogous  in  composition  to  ordinary  alum  (p.  422.).  Its  formula  is  KO  •  S03  + 
Fe203.3S03  +  24HO. 

Another  double  sulphate  is  formed,  which  crystallizes  in  large  six-sided  tables, 
and  of  which  the  formula  is  2(KO  •  SO3)  +  Fe203  •  2S03  +  6HO  (Maus),  when 
potash  is  added  gradually  to  a  concentrated  solution  of  ferric  sulphate,  till  the 
precipitate  formed  ceases  to  redissolve,  and  the  solution  is  evaporated  in  vacuo. 

Berzelius  designates  asferroso-ferric  sulphate  a  combination  containing  FeO  • 
S03  4-  Fe203 '  3S03.  It  is  the  salt  produced  when  a  solution  of  the  neutral  pro- 
tosulphate of  iron  is  exposed  to  the  air,  till  no  more  ochre  is  precipitated.  The 
solution,  which  is  yellowish  red,  does  not  crystallize,  but  gives  the  black  oxide  of 
iron  when  precipitated  by  an  alkali.  A  salt  of  the  same  constituents,  but  in 
different  proportions,  forms  large  stalactites,  composed  of  little  transparent  crystals, 
in  the  copper  mine  of  Fahlun.  This  last  is  represented  by  3FeO  •  2S03  -f 
3(Fe203  •  2S03)  +  36HO  (Berzelius). 

Ferric  nitrate.  —  By  dissolving  iron  in  nitric  acid,  without  heat,  as  in  Schosn- 
bein's  experiments  (page  447),  a  salt  is  obtained  in  large,  transparent,  colourless 
crystals.  From  more  than  one  analysis,  Pelouze  found  the  constituents  of  this 
salt  to  be  in  the  proportion  of  2Fe203.3N05  -\-  l^HO.  Its  solution  is  decomposed 
by  heat,  with  deposition  of  ferric  oxide.  Ordway*,  by  digesting  metallic  iron  in 
nitric  acid  of  sp.  gr.  1-20,  obtained,  first  a  greenish  solution,  then  a  red,  and  ulti- 
mately a  rusty  brown  precipitate ;  and  on  adding  an  equal  volume  of  nitric  acid 
of  sp.  gr.  1-43  as  soon  as  the  last  precipitate  began  to  form,  and  cooling  the  liquid 
below  60°, — or  by  evaporating  the  greenish  solution,  adding  a  large  excess  of 
nitric  acid  and  cooling, — colourless,  oblique,  rhombic  prisms,  were  formed  con  tain- 
ing  Fe203  •  3N05  4-  18HO ;  they  were  deliquescent,  sparingly  soluble  in  nitric 
acid,  melted  at  about  116°  to  a  red  liquid,  and  gave  off  their  acid  partly  at  212°, 
completely  at  a  red  heat.  Two  ounces  of  these  crystals  pounded  and  mixed  with 
an  equal  weight  of  pulverized  bicarbonate  of  ammonia,  produced  a  fall  of  tempe- 

*  Sill.  Am.  J.  [2],  ix.  30. 


456 


IRON. 


rature  from  -f-  58°  to  —  5°.  By  adding  this  compound  to  recently  precipitated 
ferric  hydrate,  Ordway  obtained  basic  salts  containing  from  1  to  8  eq.  oxide  to  1 
eq.  acid.  The  solutions  of  these  salts  were  of  a  deep  red  colour ;  were  not  decom- 
posed by  boiling  or  dilution ;  but  when  they  contained  a  large  excess  of  oxide, 
were  decomposed  by  the  addition  of  chloride  of  sodium  and  other  salts.  Haus- 
mann,*  by  evaporating  the  solution  of  iron  in  nitric  acid  to  a  syrup,  adding  half 
the  volume  of  strong  nitric  acid,  and  leaving  the  solution  to  crystallize,  obtained 
colourless  prisms  containing  Fe203.3N05  +  12HO.  By  mixing  a  very  concen- 
trated solution  of  this  neutral  salt  with  water  till  the  colour  became  reddish  yellow, 
then  boiling,  and  adding  nitric  acid  after  cooling,  an  ochre-coloured  precipitate 
was  formed,  containing  8Fe203  •  2N05  -+-  3 HO.  By  adding  a  very  large  quantity 
of  water  to  a  highly  concentrated  and  slightly  acid  solution  of  the  nitrate,  an  ochre- 
coloured  precipitate  was  sometimes  formed,  containing  36Fe203.N05  +  48HO. 
By  treating  iron  in  excess  with  nitric  acid,  a  precipitate  was  obtained  having  the 
composition  8Fe203.N05  -f-  12HO. 

Ferric,  oxalate  is  very  soluble  and  does  not  crystallize.  It  forms  a  double  salt 
with  oxalate  of  potash,  of  a  rich  green  colour,  of  which  the  formula  is  3(KO.C203) 
+  Fe203.3C203  -f  6HO.  The  crystals  effloresce  in  dry  air.  In  this  double  salt, 
the  ferric  oxide  may  be  replaced  by  alumina  or  oxide  of  chromium.  This  salt  is 
formed  by  dissolving  hydrated  ferric  oxide  to  saturation  in  bioxalate  of  potash 
(salt  of  sorrel),  and  crystallizes  readily  from  a  concentrated  solution.  The  circum- 
stance of  its  being  the  salt  of  sesquioxide  of  iron  most  easily  obtained  and  pre- 
served in  a  dry  state,  should  recommend  it  as  a  pharmaceutical  preparation. 

The  beiizoate  and  vaccinate  of  ferric  oxide  are  insoluble  precipitates.  Hence 
the  benzoate  and  succinate  of  ammonia  are  employed  to  separate  iron  from  man- 
ganese. As  both  these  precipitates  are  dissolved  bya-cids,the  iron  solution  should 
be  made  as  neutral  as  possible.  The  formula  of  the  succinate  is,  Fe203.S. 

Ferric  acid,  Fe03.  —  This  compound,  which  is  analogous  to  manganic  acid,  is 
obtained  in  the  form  of  a  potash-salt  by  exposing  metallic  iron  or  ferric  oxide  to 
the  action  of  powerful  oxidizing  agents.  1.  A  mixture  of  1  part  iron-filings  and 
2  parts  nitre  is  projected  into  a  capacious  crucible  kept  at  a  dull  red  heat,  and  the 
crucible  removed  from  the  fire  as  soon  as  the  mixture  begins  to  deflagrate  and 
form  a  white  cloud ;  if  the  heat  is  too  strong,  the  compound  decomposes  as  fast 
as  it  is  formed.  The  soft,  somewhat  friable  mass  of  ferrate  of  potash  thus  ob- 
tained, may  be  taken  out  with  an  iron  spoon,  and  preserved  in  well  stoppered 
bottles;  or  the  ferrate  of  potash  may  be  obtained  in  solution  by  treating  the  fused 
mass  with  ice-cold  water,  leaving  the  liquid  to  stand  to  allow  the  undissolved 
ferric  oxide  to  settle  down,  and  then  decanting •  the  solution  must  not  be  filtered, 
as  it  is  immediately  decomposed  by  contact  with  organic  matter.  2.  Ferrate  of 
potash  is  also  formed  by  igniting  ferric  oxide  with  hydrate  of  potash  in  an  open 
crucible,  or  with  a  mixture  of  hydrate  of  potash  and  nitre.  3.  Chlorine  gas  is 
passed  through  a  very  strong  solution  of  caustic  potash  containing  hydrated  ferric 
oxide  in  suspension,  fragments  of  solid  potash  being  continually  added  in  order  to 
maintain  a  large  excess  of  alkali  in  the  liquid.  The  ferrate  of  potash,  being 
almost  insoluble  in  the  strong  alkaline  liquid,  is  deposited  in  the  form  of  a  black 
powder,  which  may  be  freed  from  the  greater  part  of  the  mother-liquor  by  drying 
it  on  a  plate  of  porous  earthenware.  Ferrate  of  potash  is  a  very  unstable  com- 
pound, and  has  not  been  obtained  in  the  crystalline  form.  Its  solution  is  of  a 
deep  red  colour,  like  that  of  permanganate  of  potash.  The  acid  has  not  been  ob- 
tained in  the  free  state;  it  appears  indeed  to  be  scarcely  capable  of  existing  in 
that  state,  decomposing,  as  soon  as  liberated,  into  oxygen  and  ferric  oxide.  Fer- 
rate of  baryta  is  formed  by  adding  a  solution  of  ferrate  of  potash  to  a  dilute  solu- 
tion of  a  baryta-salt ;  it  then  falls  down  as  a  deep  carmine-coloured  precipitate, 

*  Aim.  Ch.  Pharm.  Ixxxix.  100. 


QUANTITATIVE    ESTIMATION    OF    IRON.  457 

which  may  be  washed  and  dried  without  changing  colour.  It  gives  off  oxygen 
when  heated,  and  is  readily  decomposed  by  acids. 

Nitroprussic  acid;  Fe2Cy5(N02).H2.  This  acid  and  its  salts  were  discovered 
by  Dr.  Lyon  Playfair.*  It  is  formed  by  the  action  of  nitric  acid  (or  rather  of 
nitric  oxide)  on  hydroferrocyanic  acid  or  a  ferrocyanide.  The  hydroferrocyanic 
acid  is  first  converted  into  hydroferricyanic  acid  : 

4H2FeCy3  +  N02  =  2H3Fe2Cy6  +  2HO  +  N; 

and  afterwards,  by  the  further  action  of  the  nitric  oxide,  into  nitroprussic  acid  : 
H3Fe2Cy6  +  N02  =  Fe2Cy5(N02).H2  +  HCy. 

Cyanogen  is  also  evolved  and  oxamide  deposited ;  but  these  products  are  due  to  a 
secondary  action. 

To  prepare  the  potassium  or  sodium  salt,  ferrocyanide  of  potassium  (2  eq.)  is 
digested  in  the  cold  with  ordinary  nitric  acid  (5  eq.)  diluted  with  an  equal  bulk 
of  water,  till  it  is  completely  dissolved ;  the  solution  boiled  till  it  forms  with  fer- 
rous salts  no  longer  a  dark  blue,  but  a  green  or  slate-coloured  precipitate,  and  then 
left  to  crystallize,  whereupon  it  deposits  a  large  quantity  of  nitre,  together  with 
oxamide.  The  strongly  coloured  mother-liquor  is  neutralized  with  carbonate  of 
potash  or  soda;  boiled;  filtered  to  separate  a  green  or  brown  precipitate;  and 
again  left  to  crystallize.  Nitrate  of  potash  or  soda  then  crystallizes  out  first ;  and 
afterwards,  by  further  evaporation,  the  nitroprussiate.  The  sodium-salt  crystal- 
lizes most  readily,  forming  large  ruby-coloured  prisms,  which  dissolve  in  2?  parts 
of  water  at  60°,  and  in  a  smaller  quantity  of  hot  water.  From  the  solution  of 
this  salt,  the  silver-salt  may  be  obtained  by  double  decomposition ;  and  this,  when 
decomposed  by  hydrochloric  acid,  yields  nitroprussic  acid.  This  acid  crystallizes 
in  dark  red,  very  deliquescent,  oblique  prisms,  which  dissolve  very  readily  in 
water,  alcohol,  and  ether.  The  aqueous  solution  is  very  prone  to  decomposition. 

The  general  formula  of  the  nitroprussiates  or  nitroprussides  is  Fe2Cy5(N02).M2  :")* 
the  radical  (which  might  be  called  nitroferrocyanogen)  may  be  regarded  as  2  eq. 
of  ferrocyauogen,  or  1  eq.  of  ferri cyanogen,  Fe2Cy6,  in  which  1  eq.  of  cyanogen  is 
replaced  by  nitric  oxide,  N02.  Most  of  them  are  strongly  coloured ;  the  ammo- 
nium, potassium,  sodium,  barium,  strontium,  calcium,  and  lead  salts,  dissolve 
readily  in  water,  forming  deep  red  solutions  from  which  the  salts  are  not  precipi- 
tated by  alcohol.  The  other  nitroprussiates  are  insoluble,  or  sparingly  soluble.  A 
solution  of  a  nitroprussiate  forms,  with  the  solution  of  an  alkaline  sulphide,  a 
splendid  blue  or  purple  colour,  which  affords  an  extremely  delicate  test  of  the 
presence,  either  of  a  nitroprussiate,  or  of  an  alkaline  sulphide. 

QUANTITATIVE   ESTIMATION   OP   IRON. 

Iron  is  always  estimated  in  the  form  of  sesquioxide.  If  the  solution  contains 
protoxide,  either  alone  or  mixed  with  sesquioxide,  it  is  first  boiled  with  a  sufficient 
quantity  of  nitric  acid  to  convert  the  whole  of  the  protoxide  into  sesquioxide,  and 
then  treated  with  ammonia  in  excess  to  precipitate  the  latter.  The  precipitate  is 
collected  on  a  filter,  washed,  dried,  and  ignited  at  a  moderate  red  heat;  too  high  a 
temperature  expels  a  portion  of  the  oxygen.  Every  10  parts  of  pure  sesquioxide 
corresponds  to  7  parts  of  metallic  iron.  In  some  cases,  however,  it  is  necessary  to 

*  Phil.  Trans.  1849,  ii.  477. 

f  This  formula  was  proposed  by  Gerhardt.  Playfnir  originally  gave  the  formula 
2(^)3- Ms?  and  subsequently  (Phil.  Mag.  [3.] 'xxxvi.  360)  suggested  the  simpler 
formula,  Fp2Cy5(NO).M2.  Gerhardt's  formula,  however,  agrees  quite  as  well  with  the 
analyses  of  the  best  defined  nitroprussiates  as  either  of  these,  and  is  more  in  accordance  with 
certain  reactions;  viz.,  that  nitroprussiate  of  sodium,  exposed  to  sunshine,  actually  gives  off 
nitric  oxide ;  and  that  when  a  solution  of  the  barium  salt  is  treated  with  red  oxide  of  iner« 
cury,  part  of  the  nitrogen  is  converted  into  nitric  acid. 


458  IRON. 

use  potash  as  the  precipitant.  In  that  case,  the  precipitated  ferric  oxide  is  very 
apt  to  carry  down  with  it  a  portion  of  the  potash,  which  is  exceedingly  difficult  to 
remove  by  washing.  It  is  best  therefore,  after  having  washed  it  two  or  three 
times  with  hot  water,  to  re-dissolve  it  in  acid  and  precipitate  by  ammonia.  In 
other  cases,  as  when  the  solution  contains  organic  matter,  the  iron  must  be  pre- 
cipitated by  sulphide  of  ammonium,  because  such  substances  prevent  the  precipi- 
tation of  the  oxide.  The  precipitated  sulphide,  after  being  washed,  is  then 
dissolved  in  nitric  acid,  and  the  iron  precipitated  by  ammonia  as  before. 

Volumetric  method. — The  quantity  of  iron  in  a  solution  may  also  be  estimated 
by  reducing  it  all  to  the  state  of  protoxide,  either  by  sulphurous  acid  or  by  metallic 
zinc  (in  the  former  case  the  excess  of  sulphurous  acid  must  be  expelled  by  boiling), 
and  then  adding,  from  a  graduated  burette,  a  quantity  of  solution  of  permanganate 
of  potash,  sufficient  to  convert  all  the  protoxide  of  iron  into  sesquioxde : 

KO  •  Mn207  -f  lOFeO  =  2MnO  -f  KG  +  5Fe203- 

The  liquid  must  contain  an  excess  of  acid,  to  hold  the  oxide  of  manganese  in 
solution.  The  first  portions  of  permanganate  added  produce  no  visible  effect ;  but 
as  soon  as  all  the  protoxide  of  iron  is  converted  into  sesquioxide,  the  addition  of 
another  drop  of  the  permanganate  imparts  a  rose  tint  to  the  liquid.  The  value 
of  the  solution  of  the  permanganate  must  be  previously  ascertained  by  dissolving 
1  gramme  of  iron  (harpsichord  wire)  in  hydrochloric  acid,  and  determining  the 
number  of  divisions  of  the  burette  occupied  by  the  quantity  of  the  solution  required 
to  convert  that  quantity  of  iron  into  sesquioxide.  (Margueritte,  Ann.  Gh.  Phys. 
[3],  18,  244.) 

The  preceding  method  may  also  be  applied  to  determine  the  quantities  of  pro- 
toxide and  sesquioxide  of  iron  in  a  solution  when  they  occur  together,  —  viz.,  by 
first  treating  a  portion  of  the  solution,  as  it  is,  in  the  manner  just  described ;  then 
taking  another  equal  portion,  reducing  all  the  iron  in  it  to  protoxide  by  sulphu- 
rous acid,  and  applying  the  same  method  to  the  solution  thus  reduced.  The  first 
determination  gives  the  quantity  of  iron  in  the  state  of  protoxide ;  the  second,  the 
total  quantity  present :  the  difference  is  therefore  the  quantity  in  the  form  of 
sesquioxide. 

Separation  of  iron  from  the  metals  previously  described.  —  From  the  alkalies 
and  alkaline  earths,  iron  is  separated  by  ammonia,  after  having  been  brought  to 
the  state  of  sesquioxide.  In  the  case  of  the  alkaline  earths,  care  must  be  taken 
to  add  but  a  slight  excess  of  ammonia,  to  filter  quickly,  and  exclude  the  air  as 
completely  as  possible  during  the  filtration )  otherwise  the  free  ammonia  will 
absorb  carbonic  acid  from  the  air,  and  then  throw  down  the  earths  in  the  form  of 
carbonates,  together  with  the  ferric  oxide.  Should  such  precipitation  occur,  — 
which  may  generally  be  known  by  the  colour  of  the  oxide,  —  the  precipitate  must 
be  re-dissolved  and  the  treatment  with  ammonia  repeated.  If  the  solution  con- 
tains fixed  organic  substances,  such  as  sugar,  tartaric  acid,  &c.,  the  iron  must  be 
precipitated  by  sulphide  of  ammonium,  and  the  precipitate  treated  in  the  manner 
already  described  (p.  457). 

From  alumina  and  glucina,  iron  is  separated  by  potash,  which  precipitates  the 
iron,  but  holds  the  alumina  or  glucina  in  solution.  The  precipitate,  which  always 
contains  potash,  must  then  be  re-dissolved  in  acid,  and  the  iron  re-precipitated  by 
ammonia. 

The  separation  of  iron  from  zircenia,  yttria,  and  ihorina,  is  effected  by  adding 
a  sufficient  quantity  of  tartaric  acid  to  prevent  the  earths  from  being  precipitated 
when  the  solution  is  rendered  alkaline,  and  throwing  down  the  iron  by  sulphide  of 
ammonium. 

From  magnesia  and  from  manganous  oxide,  iron  is  most  effectually  separated  by 
succinaie  or  benzoate  of  ammonia.  The  solution,  after  all  the  iron  has  been 
brought  to  the  state  of  sesquioxide,  is  mixed  with  a  sufficient  quantity  of  sal-aui- 


COBALT.  459 

moniac  to  hold  the  magnesia  or  manganous  oxide  in  solution,  and  very  carefully 
neutralized  with  ammonia;  it  is  then  treated  with  benzoate  or  suceinate  of  ammo- 
nia, which  throws  down  the  iron  as  ferric  benzoate  or  suceinate,  leaving  the 
magnesia  or  manganous  oxide  in  solution.  The  precipitate  is  washed  and  dried, 
and  ignited  in  an  open  platinum  crucible,  so  that  the  air  may  have  sufficient  access  to 
it  to  prevent  any  reduction  of  the  iron  by  the  carbon  of  the  organic  acid.  Should 
such  reduction  take  place,  the  iron  must  be  re-oxidized  by  nitric  acid.  The  suc- 
cess of  this  mode  of  separation  depends  entirely  on  the  care  with  which  the  acid 
in  the  solution  is  neutralized  with  ammonia  before  adding  the  benzoate  or  sucei- 
nate. If  too  much  ammonia  has  been  added,  manganese  or  magnesia  goes  down 
with  the  iron ;  if  too  little,  a  portion  of  iron  remains  in  solution.  The  addition 
of  ammonia  should  be  continued  till  a  small  quantity  of  ferric  oxide  is  precipitated, 
and  does  not  re-dissolve  on  agitation.  The  supernatant  liquid  has  then  a  deep 
brown  colour,  the  greater  part  of  the  iron  being  still  in  the  solution.  The  separa- 
tion of  ferric  oxide  from  manganous  oxide  may  also  be  effected  by  agitating  the 
solution  with  excess  of  carbonate  of  lime  or  baryta,  which  precipitates  the  iron 
but  not  the  manganese.  According  to  J.  Schiel,*  manganese  may  be  separated 
fioin  iron  by  mixing  the  solution  with  acetate  of  soda  and  passing  chlorine  through 
it ;  bioxide  of  manganese  is  then  alone  precipitated.  The  methods  of  separation 
given  at  page  434,  serve  very  well  for  preparing  a  pure  salt  of  manganese  from  a 
solution  containing  that  metal  together  with  iron,  but  are  not  adapted  for  quanti- 
tative analysis. 


Aridlum  f  This  name  was  given  by  Ullgren  to  a  metal  which  he  believed  to 
exist  in  the  chrome-iron  ores  of  Roros  in  Sweden,  and  in  the  iron  ores  of  Oerns- 
tolso.  Its  characters  very  much  resemble  those  of  iron.  It  forms  two  oxides 
analogous  to  those  of  iron,  and  presenting,  both  with  liquid  reagents  and  with  the 
blowpipe,  characters  which  might  be  exhibited  by  oxides  of  iron  containing  a  little 
chromium  (vid.  Ghem.  Gaz.  1854,  289);  Bahr  (Ann.  Ch.  Pliarm.  Ixxxvii.  264), 
endeavoured  to  prepare  the  supposed  new  metal  by  Ullgren's  process,  and  came  to 
the  conclusion  that  it  was  merely  iron  containing  a  little  phosphorus,  and  perhaps 
also  chromium. 

SECTION    III. 

•_.  •  '.i; 

COBALT. 

Ep.  29-52,  or  369;  Co. 

Cobalt  occurs  in  the  mineral  kingdom  chiefly  in  combination  with  arsenic,  as 
arsenical  cobalt,  CoAs ;  or  with  sulphur  and  arsenic,  as  grey  cobalt  ore,  CoAs. 
CoS2,  but  .contaminated  with  iron,  nickel,  and  other  metals.  Its  name  is  that  of 
the  Kobolds  or  evil  spirits  of  mines,  and  was  applied  to  it  by  the  superstition 
miners  of  the  middle  ages,  who  were  often  deceived  by  the  favourable  appearance 
of  its  ores.  These  remained  without  value,  till  the  middle  of  the  sixteenth  cen- 
tury, when  they  were  first  applied  to  colour  glass  blue.  They  are  now  consumed 
in  great  quantity  for  the  blue  colours  of  porcelain  and  stoneware.  Cobalt  is  like- 
wise found  in  almost  all  meteoric  stones. 

To  obtain  metallic  cobalt,  the  native  arsenide  is  repeatedly  roasted,  by  which 
the  greater  part  of  the  arsenic  is  converted  into  arsenious  acid,  and  carried  off  in 
vapour,  while  the  impure  oxide  of  cobalt,  known  as  za/re,  remains.  This  is  dis- 
solved in  hydrochloric  acid,  and  the  remaining  arsenic  precipitated  as  sulphide, 
by  passing  a  stream  of  sulphuretted  hydrogen  through  the  solution.  To  get  rid 

*Sell.  Am.  J.  [2],  xv.  275. 


460  COBALT. 

of  the  iron  present,  the  last  solution,  after  filtration,  is  boiled  with  a  little  nitric 
acid,  to  peroxidize  that  metal ;  and  carbonate  of  potash  is  added  in  excess,  which 
throws  down  carbonate  of  cobalt  and  sesquioxide  of  iron.  The  precipitate  is 
treated  with  oxalic  acid,  which  forms  an  insoluble  oxalate  of  cobalt  and  soluble 
ferric  oxalate.  The  oxalate  of  cobalt  is  dried  and  decomposed  by  ignition  in  a 
covered  crucible,  when  the  oxide  is  reduced  by  the  carbon  of  the  acid,  which 
goes  off  as  carbonic  acid,  while  the  metallic  cobalt  remains  as  a  black  powder.  To 
separate  cobalt  from  nickel,  with  which  it  is  almost  always  associated,  the  mixed 
oxalates  of  cobalt  and  nickel,  obtained  by  the  preceding  process,  are  dissolved  in 
ammonia,  after  which  the  liquid  is  diluted  and  exposed  to  the  air  in  a  shallow 
basin  for  several  days.  The  ammonia  evaporates,  and  the  salt  of  nickel  precipi- 
tates as  a  green  powder,  while  the  salt  of  cobalt  remains  in  solution.  The  liquid 
is  then  decanted,  and  if  no  additional  precipitate  subsides  from  it  in  twenty-four 
hours,  it  is  free  from  nickel,  and  may  be  evaporated  to  dryness.  The  precipitate 
of  nickel  contains  a  little  cobalt.* 

Cobalt  is  a  brittle  metal,  of  a  reddish  grey  colour,  somewhat  more  fusible  than 
iron,  and  of  the  density  8-5131  (Berzelius).  Rammelsberg,  in  five  experiments 
with  cobalt  reduced  by  hydrogen,  found  the  specific  gravity  to  vary  from  8-132 
to  9495;  the  mean  is  8-957.  Pure  cobalt  is  magnetic,  but  a  minute  quantity  of 
arsenic  causes  it  to  lose  that  property. 

Cobalt  is  less  oxidable  in  the  air  or  by  acids  than  iron,  dissolving  slowly  in 
diluted  hydrochloric  or  sulphuric  acid,  when  heated,  with  evolution  of  hydrogen  ; 
but  it  is  readily  oxidized  by  nitric  acid.  This  metal  forms  a  protoxide  and  sesqui- 
oxide, CoO,  and  Co2()3,  corresponding  with  the  oxides  of  iron,  and  three  inter- 
mediate oxides,  viz.,  Co304  =  CoO.Co203;  Co607  —  4CoO.Co203;  and  Cog09  = 
6CoO.Co203.  According  to  Fremy,  the  first  of  these,  viz.,  Co304  is  a  salifiable 
base  combining  directly  with  acetic  acid,  and  existing  in  several  ammonio-salts  of 
cobalt.  Fremy  has  also  obtained  compound  salts  of  this  nature  containing  a 
bioxide  of  cobalt  Co02. 

Protoxide  of  cobalt,  Cobaltous  oxide,  CoO,  37-52  or  469.  —  Prepared  by  the 
ignition  of  the  carbonate.  This  oxide  is  a  powder  of  an  ash-grey  colour.  It 
colours  glass  blue,  even  when  in  minute  quantity,  no  other  colouring  matter 
having  so  much  intensity.  Smalt  blue  is  a  pounded  potash-glass  containing 
cobalt.  All  compounds  of  cobalt,  when  heated  with  borax  or  phosphorous-salt, 
either  in  the  inner  or  in  the  outer  blow-pipe  flame,  impart  a  splendid  blue  colour 
to  the  bead.  This  coloration  affords  an  extremely  delicate  test  for  cobalt. 

The  salts  of  protoxide  of  cobalt  have  a  reddish  colour  in  solution.  Potash  or 
soda  added  to  these  solutions  forms  a  blue  precipitate  of  the  hydrated  oxide,  in- 
soluble in  excess  of  the  reagent.  Ammonia  also  forms  a  blue  precipitate,  which 
dissolves  in  excess  of  ammonia,  yielding  a  red-brown  solution.  If  the  cobalt  solu- 
tion contains  a  large  quantity  of  free  acid  or  of  an  ammonical  salt,  no  precipitate 
is  formed  by  ammonia.  Alkaline  carbonates  precipitate  a  pink  carbonate  of 
cobalt,  soluble  in  carbonate  of  ammonia.  Hydrosulphuric  acid  does  not  precipi- 
tate a  solution  of  cobalt  containing  either  of  the  stronger  acids;  but  in  a  solution 
of  acetate  of  cobalt,  or  of  any  cobalt-salt  mixed  with  acetate  of  ammonia,  it  forms 
a  black  precipitate  of  protosulphide  of  cobalt.  Alkaline  sulphides  throw  down 
the  same  precipitate  from  all  solutions  of  protoxide  of  cobalt. 

Oxide  of  cobalt  appears  to  combine  with  alkalies  and  earths  as  well  as  with 
acids.  It  dissolves  in  fused  potash,  and  imparts  a  blue  colour  to  the  compound. 
Magnesia  mixed  with  a  drop  of  nitrate  of  cobalt,  and  then  dried  and  ignited, 
assumes  a  feeble  but  characteristic  rose  tint.  A  compound  of  oxide  of  cobalt 
with  alumina  is  obtained  by  mixing  the  solution  of  a  salt  of  cobalt,  which  must 
be  perfectly  free  from  iron  or  nickel,  with  a  solution  of  equally  pure  alum,  preci- 
pitating the  liquor  by  an  alkaline  carbonate,  washing  the  precipitate  with  care, 

*  For  other  methods  of  separating  nickel  and  cobalt,  see  Nickel. 


SALTS    OF    COBALT.  461 

then  drying  and  igniting  it  strongly.  It  forms  a  beautiful  blue  pigment,  known 
as  cobalt-blue,  which  may  be  compared  in  purity  of  tint  with  ultramarine.  A 
compound  of  oxide  of  cobalt  with  oxide  of  zinc  of  a  fine  green  colour  may  be 
prepared  in  a  similar  manner.  These  coloured  compounds  often  afford  useful  con- 
firmatory tests  of  the  presence  of  zinc,  alumina,  or  magnesia.  The  substance  to 
be  examined  is  placed  on  platinum  foil,  moistened  with  nitrate  of  cobalt,  then 
dried,  and  strongly  heated  in  the  blow-pipe  flame. 

Chloride  of  cobalt,  CoCl,  is  obtained  by  dissolving  zaffre  or  the  oxide  in  hydro- 
chloric acid.  Its  solution  is  pink-red,  and  affords  hydrated  crystals  of  the  same 
colour;  but  when  highly  concentrated,  assumes  an  intense  blue  colour,  and  then 
affords  blue  crystals  of  chloride  ot  cobalt,  which  are  anhydrous  (Proust).  The 
red  solution  is  used  as  a  sympathetic  ink ;  characters  written  with  it  on  paper  are 
colourless  and  invisible,  or  nearly  so,  but  when  the  paper  is  warmed  by  holding  it 
near  a  fire  or  against  a  stove,  the  writing  becomes  visible  and  appears  of  a  beauti- 
ful blue.  After  a  while,  as  the  salt  absorbs  moisture,  the  colour  again  disappears, 
but  may  be  reproduced  by  the  action  of  heat.  If  the  paper  be  exposed  to  too 
high  a  temperature,  the  writing  becomes  black,  and  does  not  afterwards  disappear. 
The  addition  of  a  salt  of  nickel  to  the  sympathetic  ink  gives  a  green  instead  of 
blue. 

The  neutral  carbonate  of  cobalt  is  unknown,  oxide  of  cobalt,  like  magnesia, 
being  thrown  down  from  its  solutions  by  alkaline  carbonates,  as  a  carbonate  with 
excess  of  oxide.  The  sub-carbonate  of  cobalt  is  a  pale  red  powder,  which  con- 
tains, according  to  Setterberger,  2  eq.  of  carbonic  acid,  5  eq.  of  oxide  of  cobalt, 
and  4  eq.  of  water. 

Besides  the  sulphate  of  cobalt  corresponding  with  green  vitriol,  another  salt 
was  crystallized  by  Mitscherlich  between  68°  and  86°,  containing  6  eq.  of  water, 
CoO.S03-f  6HO,  isomorphous  with  a  corresponding  sulphate  of  magnesia.  Sul- 
phate of  cobalt  forms  the  usual  double  salts  with  the  sulphates  of  potash  and  am- 
inouia,  containing  6HO. 

Nitrate  of  cobalt,  CoO.N05  —  is  obtained  by  dissolving  the  metal,  the  prot- 
oxide, or  the  carbonate  in  dilute  nitric  acid.  Its  solution  is  carmine-coloured,  and 
on  evaporation  yields  red  crystals  containing  6  eq.  of  water ;  they  deliquesce  in 
the  air,  fuse  below  100°,  and  at  a  higher  temperature  give  off  water  and  melt  into 
a  violet-red  liquid,  which  afterwards  becomes  green  and  thick,  and  is  ultimately 
converted,  with  violent  intumescence  and  evolution  of  nitrous  fumes,  into  black 
sesquioxide  of  cobalt.  Characters  written  on  paper  with  a  solution  of  this  salt 
assume  a  peach-blossom  colour  when  heated. 

A  sexbasic  nitrate,  6CoO.N05-f-5Aq,  is  obtained  on  adding  excess  of  ammonia 
to  a  well  boiled  solution  of  the  neutral  nitrate,  carefully  protected  from  the  air. 
It  then  falls  down  as  a  blue  precipitate,  but  on  the  slightest  access  of  air  quickly 
assumes  a  grass-green  colour  and  partly  redissolves  in  the  liquid. 

Cobalt-yellow,  CoO.KO.N208. — This  compound  is  formed  by  adding  a  solution 
of  nitrite  of  potash  (obtained  by  passing  the  nitrous  fumes  evolved  from  a  heated 
mixture  of  nitric  acid  and  starch  into  caustic  potash)  to  an  acid  solution  of  nitrate 
of  cobalt;  nitric  oxide  and  nitrate  of  potash  are  then  formed,  and  the  cobalt- 
compound  separates  in  the  form  of  a  beautiful  yellow  crystalline  powder : 

CoO.NOs  +  2N05  +  4(KO.N03)  =  3(KO.N06)  +  2N02  +  N208-CoO.KO. 

It  is  likewise  obtained  by  adding  potash,  not  in  excess,  to  solution  of  nitrate  of 
cobalt,  so  as  to  precipitate  a  blue  basic  salt,  treating  this  with  a  slight  excess  of 
nitrite  of  potash,  and  adding  nitric  acid  in  a  thin  stream,  by  means  of  a  pipette. 
Also  by  treating  nitrate  of  cobalt  with  a  slight  excess  of  potash,  so  as  to  throw 
down  the  rose-coloured  hydrated  oxide,  and  passing  nitric  oxide  gas  into  the  mix- 
ture. This  last  reaction  is  so  rapid  that  it  may  be  exhibited  as  a  lecture-experi- 
ment. ^  The  compound  crystallizes  in  microscopic  four-sided  prisms  with  pyramidal 
summits.  It  is  insoluble  in  cold  water,  also  in  alcohol  and  ether,  but  when  boiled 


462  COBALT. 

•with  water  gradually  dissolves  with  evolution  of  acid  vapours  ;  the  solution  yields 
on  evaporation  a  lemon-yellow  salt  of  different  composition.  Nitric  acid  and  hy- 
drochloric acid  do  not  act  upon  it  in  the  cold,  but  decompose  it  at  a  boiling  heat, 
with  evolution  of  nitrous  fumes.  Hydrosulphuric  acid  decomposes  it  very  slowly, 
sulphide  of  ammonium  immediately,  forming  black  sulphide  of  cobalt.  When 
heated,  it  assumes  an  orange-yellow  colour,  gives  off  water  and  afterwards  fumes 
of  nitric  and  hyponitric  acids,  and  leaves  sesquioxide  of  cobalt  mixed  with  nitrite 
of  potash.  Its  beautiful  colour,  its  permanence,  and  the  facility  with  which  it 
mixes  with  other  colours,  render  it  well  adapted  for  artistic  purposes.* 

According  to  A.  Stromeyer,f  this  salt  is  a  nitrite  of  cobaltic  oxide  and  potash, 
Co203.2NOs+  3(KO.N03),  and  its  formation  may  be  represented  by  the  equation, 


When  a  solution  of  lead  is  mixed  with  nitrite  of  potash  and  acetic  acid,  the  liquid 
assumes  a  yellow  colour,  but  no  precipitation  takes  place  ;  but  on  adding  a  cobalt- 
salt,  a  yellowish  green  precipitate  (or  brownish  black  and  crystalline  from  dilute 
solutions)  is  formed,  whose  composition  is  that  of  the  yellow  cobalt-compound  with 
half  the  potash  replaced  by  oxide  of  lead  (Stromeyer). 

Phosphate  of  cobalt,  2CoO.HO.P05,  is  an  insoluble  precipitate  of  a  deep  violet 
colour.  When  2  parts  of  this  phosphate  or  1  part  of  the  arseniate  of  cobalt  are 
carefully  mixed  with  16  parts  of  alumina  and  strongly  ignited  for  a  considerable 
time,  a  beautiful  blue  pigment  is  obtained,  resembling  ultramarine  ;  it  was  disco- 
vered by  Thenard. 

Arseniate  of  cobalt,  3CoO.  As05  +  8HO,  exists  as  a  crystalline  mineral  called 
cobalt-bloom. 

Sesquioxide  of  cobalt,  Cobaltic  oxide,  Co203,  is  formed  when  chlorine  is  trans- 
mitted through  water  in  which  the  hydrated  protoxide  is  suspended,  or  when  a  salt 
of  the  protoxide  is  precipitated  by  a  solution  of  chloride  of  lime.  In  the  former 
case,  water  is  decomposed  by  the  chlorine,  and  hydrochloric  acid  produced,  while 
the  oxygen  of  the  water  peroxidizes  the  cobalt  j 

2CoO  +  HO  +  01=  Co203  +  HOI. 

* 

The  sesquioxide  of  cobalt  is  precipitated  as  a  black  hydrate,  containing  2HO. 
This  hydrate,  when  cautiously  heated  to  600°  or  700°,  yields  the  black  anhydrous 
oxide.  When  sesquioxide  of  cobalt  is  digested  in  hydrochloric  acid,  chlorine  is 
evolved,  and  the  protochloride  formed.  Exposed  to  a  low  red  heat,  the  sesqui- 
oxide loses  oxygen,  and  the  compound  oxide,  CoO.Co203,  is  produced.  (Hess.) 
When  protoxide  of  cobalt  is  calcined  with  a  borax  glass,  at  a  moderate  heat,  it 
absorbs  oxygen,  and  a  black  mass  is  obtained,  which,  mixed  with  manganic  oxide, 
serves  as  a  black  colour  in  enamel  painting. 

Sesquioxide  of  cobalt  acts  as  a  weak  base.  Phosphoric,  sulphuric,  nitric,  and 
hydrochloric  acids  dissolve  its  hydrate  in  the  cold,  without  decomposition  at  first, 
but  the  resulting  salts  are  afterwards  reduced  to  salts  of  the  protoxide.  A  proto- 
salt  of  cobalt  containing  a  small  quantity  of  a  sesquisalt  is  somewhat  deepened  in 
colour.  The  most  permanent  of  the  sesquisalts  is  the  acetate;  the  hydrated 
sesquioxide  while  yet  moist  dissolves  in  acetic  acid,  slowly  but  completely.  The 
solution,  which  has  an  intense  brown  colour,  forms  a  brown  precipitate  with  alka- 
lies and  alkaline  carbonates.  With  ferrocyanide  of  potassium  it  forms  a  dark 
precipitate,  which,  if  the  precipitant  is  in  excess,  gives  up  cyanogen  to  it,  con- 
verting it  into  ferricyanide  of  potassium  and  being  itself  converted  into  green 
ferrocyanide  of  cobalt.  Alkaline  oxalates  colour  the  solution  yellow,  forming  an 
oxalate  of  the  oxide  Co304. 

According  to  Fremy,  the  oxide  Co304  combines  also  with  other  acids.     The 

*  St.  Evre,  Ann.  Ch.  Phys.  [3],  xxxviii.  177. 
t  Ann.  Ch.  Pharm.  xcvi.  218. 


SALTS    OF    COBALT.  463 

acetate  of  this  oxide  is  obtained  by  digesting  in  dilute  acetic  acid  the  hydrated 
oxide  obtained  by  continued  action  of  oxygen  on  the  blue  precipitate  thrown  down 
from  ordinary  cobalt-salts  by  potash  not  in  excess.  Freuny  also  states  that  when 
chlorine  is  passed  into  the  solution  of  ordinary  acetate  of  cobalt,  a  brownish  yellow 
salt  is  formed  containing  the  base  Co3C103,  or  Co304  in  which  1  eq.  of  0  is  re- 
placed by  Cl.  This  chlorine  base  exists  also  in  some  of  the  ammonio  compounds 
of  cobalt  (pp.  463-66).  The  oxide  Co304  is  obtained  in  the  free  state  by  heating 
the  nitrate  or  oxalate  of  cobalt,  or  the  hydrated  sesquioxide  to  redness  in  contact 
with  the  air  (Hess,  Rammelsberg) ;  but  according  to  Beetz  and  Winkelblech,  the 
oxide  thus  obtained  is  Co607.  When  the  residue  obtained  by  gently  igniting  the 
oxalate  in  contact  with  the  air  is  digested  in  strong  boiling  hydrochloric  acid,  the 
oxide  Co304  remains  in  hard,  brittle,"  greyish-black  microscopic  octohedrons,  having 
a  metallic  lustre.  The  same  crystalline  compound  is  obtained  by  igniting  dry  pro- 
tochloride  of  cobalt,  alone  or  mixed  with  sal-ammoniac,  in  dry  air  or  oxygen  gas 
(Schwarzenberg). 

A  cobaltic  acid,  Co305,  is  obtained  in  combination  with  potash  by  strongly 
igniting  the  oxide  Co304,  or  the  protoxide,  or  the  carbonate,  with  pure  hydrate  of 
potash."  A  crystalline  salt  is  then  formed  which,  when  dried  at  100°  C.,  contains 
K0.3Co305+ 3HO,  and  gives  of  1  eq.  of  water  at  130°  (Schwarzenberg). 

Bloxide  of  cobalt,  Co02,  has  not  been  obtained  in  the  free  state,  but  exists,  ac- 
cording to  Fremy,  in  the  oxycobaltiac  salts. 

There  exist  three  sulphides  of  cobalt,  a  protosulphide,  sesquisulphide,  and  bisul- 
phide. 

Sesquwyanide  of  cobalt  has  not  been  obtained  in  the  separate  state,  but  it  exists 
in  a  class  of  double  cyanides,  of  which  the  radical  is  cobalticyanogen,  Cy6Co2,  ana- 
logous to  ferricyanogen.  The  cobalticyanide  of  potassium,  corresponding  with  the 
red  prussiate  of  potash,  is  formed  when  protoxide  of  cobalt  or  its  carbonate  is 
dissolved  in  caustic  potash  which  has  been  treated  with  an  excess  of  hydrocyanic 
acid.  It  is  an  anhydrous  salt,  pale  yellow  and  nearly  colourless  when  pure,  and 
of  the  same  form  as  the  ferricyanide  of  potassium.  Its  solution  does  not  affect 
the  salts  of  iron,  but  forms  a  rose-coloured  precipitate  with  those  of  the  protoxide 
of  cobalt.* 

A  phosphide  of  cobalt,  Co3P,  was  obtained  by  Rose,  as  a  grey  powder,  on  passing 
hydrogen  over  the  subphosphate  of  cobalt  ignited  in  a  porcelain  tube.  It  is  also 
produced  by  the  action  of  phosphuretted  hydrogen  on  the  chloride  of  cobalt,  and 
may  be  looked  upon  as  analogous  in  composition  to  the  former  compound,  H3P. 

Ammoniacal  salts  of  cobalt. — Cobalt-salts  treated  with  excess  of  ammonia  in  a 
vessel  from  which  the  air  is  excluded,  unite  with  the  ammonia,  forming  compounds 
to  which  Fremy  gives  the  name  of  ammonio- cobalt  salts.  Most  of  them  contain 
3  eq.  ammonia  to  1  eq.  of  the  cobalt-salt;  thus  the  chloride  contains  CoC1.3NH3-f- 
HO  :  the  nitrate  CoO.No5.3NH3+2HO.  They  are  mostly  crystallizable  and  of  a 
rose-colour,  soluble  without  decomposition  in  ammonia,  but  decomposed  by  water 
with  separation  of  a  basic  salt.  (Fremy.)  H.  Rose,  by  treating  dry  chloride  of 
cobalt  with  ammoniacal  gas,  obtained  the  compound  CoC1.2NH3;  and  similarly  an 
anhydrous  sulphate  containing  CoO.S03.3NH3. 

When  an  ammoniacal  solution  of  a  cobalt  salt  is  exposed  to  the  air,  oxygen  is 
absorbed,  the  liquid  turns  brown,  and  new  salts  are  formed  containing  a  higher 
oxide  of  cobalt  (Co203  or  C02),  and  therefore  designated  generally  as  peroxidized 
ammonio-cobalt  salts.  Several  of  these  salts  containing  different  bases  are  often 
formed  at  the  same  time.  Fremyf  distinguishes  four  classes  of  these  compounds, 
viz.,  salts  of  oxycobaltia,  luteocobaltia,  fuscocobaltia,  and  roseocobaltia. 

The  oxycobaltia-salts  are  formed  by  the  action  of  the  air  on  concentrated  solu- 

*  For  further  details  on  the  cobalticyanides.  vide  Gmelin's  Handbook  (translation),  vii. 
492-497. 

f  Ann.  Ch.  Phys.,  [3],  xxxv.  257;  Chem.  Gaz.  1853,  201. 


464  COBALT. 

tions  of  ammonio-cobalt  salts.  They  have  generally  an  olive  colour,  are  sparingly 
soluble  in  the  ammoniacal  liquid,  and  are  decomposed  by  water,  especially  when 
hot,  with  evolution  of  pure  oxygen,  liberation  of  ammonia,  and  separation  of  a 
green  basic  salt  containing  cobaltoso-cobaltic  oxide,  C0304.  They  contain  5  eq. 
of  ammonia  associated  with  2  eq.  of  a  monobasic  salt  of  bi-oxide  of  cobalt,  Co02; 
thus  the  nitrate  is  composed  of  2(Co02.N05).5NH3.  The  nitrate  and  sulphate 
crystallize  in  small  prisms  containing  water  of  crystallization  (Fremy). 

The  luteocobaltia-salts  are  formed:  1.  By  the  action  of  the  air  on  dilute  solu- 
tions of  ammonio-cobalt  salts;  2.  By  the  action  of  a  small  quantity  of  water  on 
crystallized  oxycobaltia-salts ;  3.  By  treating  the  brown  solution,  formed  by  the 
action  of  oxygen  in  excess  on  ammonio-cobalt  salts,  with  dilute  acids ;  4.  By  treat- 
ing roseocobaltia-salts  with  excess  of  ammonia.  These  salts  are  of  a  fine  yellow 
colour,  crystallize  readily,  are  tolerably  permanent,  and  resist  for  some  time  the 
action  of  boiling  water.  They  give  no  precipitates  with  alkaline  phosphates  or 
carbonates  at  ordinary  temperatures,  but  are  decomposed  by  boiling  potash,  with 
evolution  of  ammonia  and  separation  of  Co203HO.  Dilute  acids  precipitate  them 
from  their  aqueous  solution  in  the  crystalline  state.  They  contain  1  eq.  of  a 
sesquisalt  of  cobalt,  associated  with  6  eq.  of  ammonia  ;  thus,  the  sulphate  = 
(Co203.3S03).6NH3;  the  chloride  =  Co2Cl3.6NH3.  (Fremy.)  This  last  salt  was 
previously  obtained  by  Rogojski,*  who  regarded  it  as  the  JiydrocJilorate  of  dico- 
baltinamine  ClH.N2H5co  [co  =  f  Co].  He  likewise  obtained  the  other  salts  of  the 
same  base  by  double  decomposition. 

Fuscocobaltia-salts  are  formed  when  an  ammoniacal  solution  of  a  protosalt  of 
cobalt  is  exposed  to  the  air,  and  by  the  action  of  water  on  the  oxycobaltia-salts. 
They  are  all  uncrystallizable,  but  may  be  obtained  in  the  solid  state  by  precipita- 
tion with  alcohol  or  excess  of  ammonia.  They  are  slowly  decomposed  by  boiling 
with  water,  but  quickly  on  the  addition  of  an  alkali,  with  evolution  of  ammonia, 
and  precipitation  of  hydrated  sesquioxide  of  cobalt.  They  are  of  a  brown  colour, 
and  appear  to  contain  basic  salts  of  sesquioxide  of  cobalt,  united  with  4  or  5  eq. 
of  ammonia.  The  nitrate  contains  Co203.2N05.4NH3.3HO. 

Ammonio-chloride  of  cobalt,  after  exposure  to  the  air,  yields  by  evaporation  in 
vacuo,  an  uncrystallizable  residue  having  the  characters  of  the  fuscocobaltia-salts, 
but  containing  a  chlorine-base;  its  formula  is  Co2Cl20.4NH3.3HO.  By  exposing 
the  solution  of  the  ammonio-chloride  to  the  air  for  two  or  three  weeks,  and  then 
boiling  with  sal-ammoniac,  roseocobaltiacal  chloride  separates  out  first,  and  after- 
wards a  black  crystalline  compound  containing  Co3C103.NH3  +  5HO. 

The  roseocobaltia-salts  are  obtained  :  1.  By  slightly  acidulating  the  solution  of  an 
ammonio-cobalt  salt,  which  has  been  exposed  to  the  air ;  2.  By  boiling  the  solution 
of  an  ammonio-cobalt  salt,  which  has  been  exposed  to  the  air  for  two  or  three  days, 
and  contains  a  fuscocobaltia  salt,  with  a  salt  of  ammonia ;  3.  By  mixing  oxyco- 
baltia-salts with  boiling  solutions  of  ammoniacal  salts.  They  have  a  fine  red  or 
rose  colour,  and  some  of  them  crystallize  readily.  Their  reactions  are  similar  to 
those  of  the  luteocobaltia-salts.  The  nitrate  and  the  neutral  sulphate  contain  3  eq. 
of  Co203.3N05,  or  Co203.3S03,  with  5  eq.  ammonia.  There  is  also  an  acid  sulphate 
containing  (Co203.5S04)  5NH3-f  5HO,  obtained  by  adding  sulphuric  acid  in  excess 
to  an  ammoniacal  solution  of  sulphate  of  cobalt  which  has  stood  for  some  days  in 
contact  with  the  air.  Baryta-water  added  to  the  solution  of  the  sulphate,  throws 
down  roseocobaltiacal  oxide,  which  is  rose-coloured,  has  a  strong  alkaline  reaction, 
and  decomposes  on  boiling,  giving  off  ammonia  and  depositing  Co203.  The  chlo- 
ride, Co2Cl3.5NH3.HO,  is  obtained  by  boiling  the  ammonio-chloride  of  cobalt,  or 
the  chlorine-compound  Co2Cl20  4NH3  (p. 464),  or  a  salt  of  oxycobaltia,  with  chlo- 
ride of  ammonium  (Fremy). 

Genthf  and  F.  Claudet|  have  also  described  a  compound  which  appears  to  be 

*  J.  pr.  Chern.  Ivi.  491. 

f  Ann.  Ch.  Pharm.  Ixxx.  275;  Chem.  GTaz.  1851.  2G6. 

JPhil.  Mag.  [4],  ii.  253;  Chein.  Soc.  Qu.  J.  iv.  355. 


SALTS    OF    COBALT.  465 

the  same  as  Fremy's  hydrochlorate  of  roseocobaltia,  although  each  assigns  to  it  a 
different  formula.  When  sulphate  or  chloride  of  cobalt  is.  mixed  with  a  large 
quantity  of  chloride  of  ammonium  and  an  excess  of  ammonia,  exposed  for  some 
time  to  the  air,  and  then  boiled  with  excess  of  hydrochloric  acid,  a  crimson  pow- 
der gradually  separates,  oxygen  is  evolved,  and  the  liquid  becomes  colourless. 
This  compound  dissolves  in  244  parts  of  cold  water,  and  in  a  smaller  quantity  of 
boiling  water,  but  is  decomposed  by  continued  boiling,  unless  hydrochloric  acid  be 
added ;  in  that  case  a  solution  is  obtained,  from  which  the  compound  crystallizes 
on  cooling  in  ruby-coloured  regular  octohedrons.  Genth  assigns  to  this  compound 
the  formula  Co203.3NH4Cl,  regarding  it  as  the  chloride  of  a  conjugated  radical 
Co203.3NH4.  Claudet  finds  it  to  contain  3Cl,2Co,  5N  and  16H,  and  expresses  its 
composition  by  one  of  the  following  formulae  :  — 

fNH2Co2  ~)  f  TT    ^  r 

3NH4Cl  +  2NH2Co;         CU  NH3NH4  tj         GIN  \  p2  \  +2C1N  \ 

(NHNH4  )  l 

According  to  the  two  latter  formulae,  the  compound  is  supposed  to  contain 
ammonium  in  which  part  of  the  hydrogen  is  replaced  by  NH4.  It  might  also  be 
regarded  as  the  hydrochlorate  of  pentacobaltosamine  N5H13Co2.3HCl,  the  base 
being  formed  of  5  eq.  of  ammonia  in  which  2  eq.  of  hydrogen  are  replaced  by 
cobalt.  Gregory*  assigns  to  it  the  formula  Co2Cl3.5NH3,  making  it  identical  with 
Fremy's  roseocobaltiacal  chloride. 

The  compound  heated  in  a  glass  tube  gives  off  ammonia  and  sal-ammoniac,  and 
leaves  CoCl.  When  the  aqueous  solution  is  boiled,  ammonia  is  evolved,  and  a 
precipitate  formed  probably  consisting  of  Co304.3HO,  combined  with  nitride  of 
cobalt.  The  chlorine  compound  treated  with  recently  precipitated  oxide  of  silver, 
yields  the  oxygen-compound  of  the  same  radical;  and  by  double  decomposition 
with  various  silver-salts,  the  other  salts  of  the  base. 

The  ammonia  in  all  these  compounds  is  in  a  peculiar  state,  not  exhibiting  its 
usual  basic  properties,  or  being  recognisable  by  the  usual  reagents  or  replaceable 
by  other  bases.  Claus  attributes  this  circumstance  to  the  ammonia  being  in  a 
passive  state,  which  is  merely  another  way  of  expressing  the  fact,  but  affords  no 
explanation.  Weltzien  supposes  the  compounds  in  question  to  contain  compound 
ammonium-molecules,  in  which  1  or  2  at.  hydrogen  are  replaced  by  ammonium 
itself  (an  idea  first  suggested  by  Mr.  Graham),  viz.,  ammo-cobaltammonium 

NH2AmCo,  and  biammo-cobaltammonium  NHArn2Co  [the  symbol  Am  standing 
for  NH4].  Thus  the  ammoniocobalt  salfs,  containing  2NH3,  may  be  regarded  as 
neutral  salts  of  ammo-cobaltaminonium,  and  those  which  contain  3NH3  as  neutral 
salts  of  biammo-cobaltammonium  :  thus  — 

CoC1.2NH3  =  NH2AmCo.Cl;  and 
CoBr.3NH3  =  NHAm2Co.Br. 


The  fuscocobaltia-salts  may  be  regarded  as  basic  salts  of  the  sesquioxluc  u* 
ammo-cobaltammonium,  e.  g.  — 


Co203.2N05.4NH3=  (NH2AmCo)203.2NOs. 


The  luteocobaltia-aalts,  as  neutral  salts  of  the  sesquioxide  of  biammo-cobaltam 
monium,  e.  y.  — 

Co2O3.3N05.6NH3  =  (NHAin2Co)203.3N05; 
*  Ann.  Ch.  Pharm.  Ixxxvii.  125. 

30 


466  NICKEL. 

The  roseocolaltia  -salts  as  neutral  sesquisalts  containing  1  at.  of  each  of  the 
above-mentioned  ammoniums,  thus  — 


Co2CI3.5NH3- 

NHAm2Co 

And  the  oxycobaltia-salts  as  basic  salts  of  the  same  two  ammonium-molecules, 
e.g.— 

NH2AmCol 

2Co02.2S03.5NH3  =    <-±*  -  •  Y- 
NHAm2Co) 

ESTIMATION    OF    COBALT,    AND    METHODS    OF    SEPARATING   IT    FROM   THE 
PRECEDING    METALS. 

Cobalt  is  generally  precipitated  from  its  solutions  by  caustic  potash.  The  pre- 
cipitate is  bluish,  and  consists  of  ,a  basic  salt,  which,  however,  when  heated,  is 
converted  into  the  hydrated  protoxide  of  a  dingy  rose  colour.  It  must  then  be 
washed  in  hot  water,  dried  and  ignited  in  an  atmosphere  of  hydrogen,  by  which 
it  is  reduced  to  the  metallic  state,  after  which  it  is  weighed.  According  to'Beetz,* 
the  reduction  to  the  metallic  state  may  be  dispensed  with,  an  accurate  result  being 
obtained  by  igniting  the  precipitated  oxide  till  it  no  longer  varies  in  weight,  its 
composition  being  then  4Co.Co203  or  Co607;  but  the  reduction  by  hydrogen  is 
perhaps  the  surer  method. 

Cobalt  is  separated  from  the  alkalies  and  alkaline  earths  by  sulphide  of  ammo- 
nium, the  black  sulphide  of  cobalt  being  then  dissolved  in  nitro-hydrochloric  acid, 
and  the  oxide  precipitated  by  potash  as  above. 

From  magnesia  it  may  also  be  separated  by  sulphide  of  ammonium,  sufficient 
chloride  of  ammonium  being  added  to  hold  the  magnesia  in  solution. 

From  alumina  and  glucina  it  is  separated  by  potash. 

The  separation  of  cobalt  from  manganese  is  difficult.  It  is  best  effected  by 
heating  the  mixed  oxides  in  hydrochloric  acid  gas,  which  converts  them  into 
chlorides,  and  then  heating  the  chlorides  in  a  stream  of  hydrogen,  which  reduces 
the  cobalt  to  the  metallic  state,  but  leaves  the  chloride  of  manganese  undecom- 
posed  ;  the  latter  is  then  dissolved  out  by  water.  Another  mode  of  separation  is 
to  digest  the  mixed  oxides  in  a  solution  of  pentasulphide  of  calcium,  which  dis- 
solves the  sulphide  of  cobalt,  but  leaves  the  sulphide  of  manganese  undissolved."}" 

Cobalt  is  separated  from  iron  in  the  same  manner  as  manganese  (p.  458),  viz., 
by  bringing  the  iron  to  the  state  of  sesquioxide,  then  adding  chloride  of  ammonium, 
neutralizing  with  ammonia,  and  precipitating  the  iron  by  succinate  of  ammonia. 


SECTION  IV. 

NICKEL. 

Eq.  29-57  or  369-6. 

This  metal  resembles  iron  and  cobalt  more  than  any  others,  and  is  associated 
with  these  metals  in  meteorites,  and  in  most  of  the  terrestrial  minerals  which  eon- 
*ain  it.  The  principal  ore  of  nickel  is  arsenical  nickel,  a  mineral  having  the 
colour  of  metallic  copper,  to  which  the  German  miners,  having  attempted  in  vain 


*  Pogg.  Ann.  Ixi.  472.  t  Clocz»  J  Pkarm.  [3,]  vii.  15 


NICKEL.  467 

to  extract  copper  from  it,  gave  the  name  kupfer-nickel,  or  false  copper.  This 
mineral  was  found  by  Cronstedt  of  Sweden,  in  1751,  to  contain  a  particular  metal, 
which  he  called  nickel.  Nickel  imparts  a  remarkable  whiteness  to  the  metallic 
alloys  which  contain  it,  on  which  account  it  has  come  of  late  to  be  valued  in  the 
arts,  being  added  to  brass  to  form  the  well-known  imitations  of  silver. 

The  metal  is  prepared  from  the  native  arsenide,  or  from  an  artificial  arsenide 
called  speiss,  which  contains  about  54  per  cent,  of  nickel,  and  has  been  observed 
by  Wohler  to  occur  in  octohedrons  with  a  square  base,  having  the  composition 
Ni3As.  Speiss  is  a  metallic  substance  which  collects  at  the  bottom  of  the  crucibles 
in  which  smalt  or  cobalt-blue  is  prepared.  In  that  operation,  a  mixture  of  quartzy 
sand,  potashes,  and  the  roasted  ore  of  cobalt  is  fused.  The  previous  roasting  never 
being  perfect,  a  part  of  the  metals  escapes  oxidation;  and  hence  when  the  mixture 
described  is  fused,  the  cobalt,  which  is  more  oxidable  than  nickel  and  copper, 
reacts  upon  the  oxides  of  these  metals,  and  reduces  them,  while  it  is  itself 
oxidated :  the  nickel  and  copper  concentrate  in  the  speiss,  while  the  smalt  contains 
scarcely  any  of  them.  A  salt  of  nickel  may  be  obtained  by  treating  speiss  in  fine 
powder  with  an  equal  weight  of  sulphuric  acid,  diluted  with  four  or  five  times  its 
bulk  of  water,  and  gradually  adding  an  equal  weight  of  nitric  acid,  which  occa- 
sions the  oxidation  of  both  the  nickel  and  the  arsenic.  The  green  solution  thus 
obtained,  when  cooled  and  allowed  to  stand  for  twenty-four  hours,  deposits  much 
nrseriious  acid,  from  which  it  may  be  separated  by  filtration.  A  quantity  of  car- 
bonate of  potash,  equal  to  half  the  weight  of  the  speiss,  is  then  added  to  the 
solution,  which  is  concentrated  and  set  aside  to  crystallize.  The  double  sulphate 
of  nickel  and  potosh,  NiO.S03  -f  KO.S03  +  6HO,  forms  easily,  and  may  be 
obtained  free  from  arsenic  by  a  second  crystallization.  (Dr.  Thomson.)  The  perfect 
separation  of  small  quantities  of  cobalt  and  copper,  which  these  crystals  may  still 
contain,  requires  additional  processes.*  With  the  view  of  obtaining  the  metal,  the 
insoluble  oxalate  of  nickel  may  be  precipitated  from  the  preceding  salt  by  oxalate 
of  ammonia,  washed,  dried,  and  ignited  gently  in  a  covered  crucible.  The  oxalic 
acid  reduces  the  oxide  of  nickel,  and  the  metal  remains  in  a  spongy  state.  It  is 
pyrophoric,  like  manganese  and  iron  prepared  in  the  same  manner,  if  the  tempera- 
ture of  reduction  has  been  low.  To  obtain  the  metal  in  a  solid  mass,  it  should  be 
fused  in  a  crucible  covered  with  pounded  glass.  The  oxide  of  nickel  is  very  easily 
reduced  both  by  carbonic  oxide  and  by  hydrogen. 

Nickel,  when  free  from  cobalt,  is  silver-white,  unalterable  in  air,  and  highly 
ductile.  Its  density,  according  to  Bichter,  is  8-279,  and  after  being  forged  8-666. 
Nickel  is  magnetic  nearly  to  the  same  extent  as  iron.  Magnets  composed  of  this 
metal  lose  their  polarity  at  630°  (Faraday).  It  is  somewhat  more  fusible  than 
iron.  Nickel  forms  two  oxides  corresponding  with  the  protoxide  and  sesquioxide 
of  iron;  but  the  double  compound  of  the  two  oxides  of  nickel,  corresponding  with 
the  black  oxide  of  iron,  has  not  been  observed. 

Protoxide  of  nickel,  NiO,  37 '57,  or  469-6,  may  be  obtained  by  the  ignition  of 
the  carbonate  or  nitrate  of  nickel,  or  by  precipitation  from  its  salts  by  an  alkali, 
as  a  dark  ash-coloured  powder,  or  as  a  bulky  hydrate  of  an  apple-green  colour, 
NiOHO.  Oxide  of  nickel  is  very  soluble  in  acids,  but  not  in  potash  or  soda. 
Ammonia  dissolves  it,  and  forms  an  azure-blue  solution,  from  which  oxide  of 
nickel  is  precipitated  by  potash,  baryta,  and  strontia,  having  a  considerable  tendency 
to  combine  with  salifiable  bases.  The  solutions  of  its  salts  have  all  a  green  colour, 
much  more  intense  than  that  of  the  ferrous  salts.  They  are  not  precipitated  by 
hydrosulphuric  acid  when  a  strong  acid  is  present,  but  afford  a  black  sulphide  with 
alkaline  sulphides.  Carbonate  of  nickel  is  of  a  pale  green  colour  and  soluble  in 
carbonate  of  ammonia. 

Peroxide  or  sesquioxide  of  nickel,  Ni203,  is  obtained  as  a  black  powder,  by  ex- 
posing the  hydrated  protoxide  suspended  in  water  to  a  stream  of  chlorine  gas.  It 

*  Berzelius,  Traite',  torn.  i.f  p.  486 ;  see  also  pp.  469-470,  of  this  volume. 


468  NICKEL. 

does  not  combine  with  acids,  and  in  other  respects  resembles  sesquioxide  of 
cobalt. 

Besides  a  protosulphide,  NiS,  a  subsulphide  of  nickel,  Ni2S,  is  formed,  like  that 
of  manganese,  by  decomposing  the  ignited  sulphate  of  nickel  with  hydrogen.  A 
bisulphide  of  nickel  also  exists  in  combination  as  a  constituent  of  the  mineral 
nickel-glance,  NiS2.NiAs. 

Chloride  of  nickel  NiCl,  forms  a  solution  of  an  emerald-gfeen  colour,  and  yields 
by  evaporation  a  hydrated  salt  of  the  same  colour,  which  becomes  yellow  when 
deprived  of  its  water  of  crystallization.  Chloride  of  nickel,  sublimed  at  a  high 
temperature  without  access  of  air,  forms  golden  scales  which  dissolve  with 
difficulty. 

Sulphate  of  nickel,  crystallizes  from  a  strong  solution  in  slender  green  prisms, 
isomorphous  with  Epsom  salt,  of  which  the  composition  is  NiO.S03  -f  7 HO.  At 
a  higher  temperature,  it  crystallizes  with  6  eq.  of  water  NiO.S03  +  6HO,  like  the 
magnesia  and  cobalt  salts,  and  in  the  same  form.  Mitscherlich  made  the  singular 
observation,  that  when  the  crystals  containing  7  eq.  of  water  are  exposed,  in  a 
close  glass  vessel,  to  a  day  of  sunshine,  or  kept  for  some  time  in  a  temperate  place, 
they  change  their  form,  becoming  a  mass  of  small  crystals,  of  which  the  form  is 
the  regular  octohedron.  The  original  crystals  become  opaque  from  this  change, 
but  lose  none  of  their  combined  water.  Sulphate  of  nickel  forms  the  usual  double 
salts  with  the  sulphates  of  potash  and  ammonia. 

Nickel  also  forms  ammonio-compounds  analogous  to  the  ammonio-cobalt  salts ; 

e.g.  the  ammonio-chloride  —  3NH3.NiCl  =  NH  Am2Ni.Cl  j  ammonio-sulphate  = 

5NH3.NiSO4  =  NH  Am2Ni.S04,  &c. 

The  useful  white  alloy  of  nickel,  German  silver  or  packfong,  is  formed  by 
fusing  together  100  parts  of  copper,  60  of  zinc,  and  40  of  nickel. 

ESTIMATION  OP  NICKEL,  AND  METHODS  OF  SEPARATING  IT  FROM  THE  PRECEDING 

METALS. 

Nickel  is  best  precipitated  from  its  solutions  by  caustic  potash,  which  throws 
down  an  apple-green  precipitate  of  the  hydrated  protoxide,  and  if  the  liquid  be 
heated,  leaves  not  a  trace  of  nickel  in  the  solution.  The  precipitate  must  be 
washed  with  hot  water,  dried,  ignited,  and  weighed;  it  then  consists  of  pure 
protoxide  of  nickel,  containing  78-57  per  cent,  of  the  metal. 

In  separating  nickel  from  other  metals,  it  is  often  necessary  to  precipitate  it  by  sul- 
phide of  ammonium ;  this  precipitation  is  attended  with  difficulties,  because  the  sul- 
phide of  nickel  is  somewhat  soluble  in  the  alkaline  sulphide.  To  make  the  precipitation 
as  complete  as  possible,  Rose  directs  that  the  solution  be  diluted  with  a  considerable 
quantity  of  water,  and  then  treated  with  sulphide  of  ammonium,  as  nearly  colour- 
less as  it  can  be  obtained,  avoiding  a  large  excess  of  the  precipitant  and  likewise 
an  excess  of  ammonia ;  the  glass  is  then  to  be  covered  up  with  filtering  paper, 
and  left  in  a  warm  place.  Under  these  circumstances,  the  excess  of  sulphide  of 
ammonium  is  decomposed  by  the  oxygen  and  carbonic  acid  of  the  air,  without  risk 
of  the  sulphide  of  nickel  being  oxidized.  As  soon  as  the  supernatant  liquid  has 
lost  its  brown  colour,  the  precipitate  is  collected  on  a  filter  and  washed,  as  quickly 
as  possible,  with  water  containing  a  little  sulphide  of  ammonium.  It  must  then 
be  dissolved  in  nitro-hydrochloric  acid,  and  the  nickel  precipitated  by  potash  as 
above. 

The  methods  of  separating  nickel  from  all  the  preceding  metals  except  cobalt, 
are  the  same  as  those  given  for  cobalt  (p.  466). 

The  separation  of  nickel  from  cobalt  itself  is  difficult.  The  best  method  is 
perhaps  that  given  by  H.  Rose,*  depending  on  the  fact  that  protoxide  of  cobalt  in 

*  Handbuch  der  Analytischen  Chemie  (Berlin,  1851),  ii.  164. 


SEPARATION    OF    NICKEL    FROM    COBALT.  469 

solution  is  converted  by  chlorine  into  sesquioxide,  whereas  with  nickel  this  change 
does  not  take  place.  The  metals  or  their  oxides  being  dissolved  in  excess  of 
hydrochloric  acid,  the  solution  is  diluted  with  a  large  quantity  of  water,  about  a 
pound  of  water  to  a  gramme  of  the  metals  or  their  oxides.  Chlorine  gas  is  then 
passed  through  the  solution  for  several  hours,  till  in  fact  the  space  above  the  liquid 
becomes  permanently  filled  with  the  gas;  carbonate  of  baryta  is  then  added  in 
excess,  the  whole  left  to  stand  for  12  or  18  hours,  and  shaken  up  from  time  to 
time.  The  precipitate,  consisting  of  sesquioxide  of  cobalt  and  carbonate  of  baryta, 
is  then  collected  on  a  filter,  and  washed  with  cold  water.  The  filtered  liquid, 
which  has  a  pure  green  colour,  contains  all  the  nickel  without  a  trace  of  cobalt 
The  precipitate  is  boiled  with  hydrochloric  acid  to  convert  the  sesquioxide  of 
cobalt  into  protoxide,  and  dissolve  it  together  with  the  baryta;  the  latter  is  then 
precipitated  by  sulphuric  acid,  and  the  cobalt  from  the  filtrate  by  potash.  The 
nickel  is  also  precipitated  by  potash  after  the  removal  of  any  baryta  that  the  solu- 
tion may  contain  by  sulphuric  acid.  This  method,  if  properly  executed,  gives 
very  exact  results.  The  chief  precautions  to  be  attended  to,  are  to  add  a  large 
excess  of  chlorine,  and  not  to  filter  too  soon,  because  the  precipitation  of  sesqui- 
oxide of  cobalt  by  carbonate  of  baryta  takes  a  long  time. 

Liebig  has  given  several  methods  of  separating  these  two  metals,  founded  on 
the  difference  of  their  reactions  with  cyanide  of  potassium.  1.  The  oxides  of  the 
two  metals  are  treated  with  hydrocyanic  acid  and  then  with  potash,  and  the  liquid 
warmed  till  the  whole  is  dissolved  (pure  cyanide  of  potassium,  free  from  cyanate 
may  also  be  used  as  the  solvent).  The  reddish-yellow  solution  is  boiled  to  expel 
free  hydrocyanic  acid,  whereupon  the  cobaltocyanide  of  potassium  (K2CoCy3), 
formed  in  the  cold,  is  converted  into  cobalticyanide  (K3Co2Cy6),  while  the  nickel 
remains  in  the  form  of  cyanide  of  nickel  and  potassium  (KNiCy2).  Pure  and 
finely-divided  red  oxide  of  mercury  is  then  added  to  the  solution  while  yet  warm, 
whereby  the  whole  of  the  nickel  is  precipitated  partly  as  oxide,  partly  as  cyanide, 
the  mercury  taking  its  place  in  the  solution.  The  precipitate  contains  all  the 
nickel,  together  with  excess  of  mercuric  oxide;  after  washing  and  ignition,  it 
yields  pure  oxide  of  nickel.  The  filtered  solution  contains  all  the  cobalt  in  tho 
form  of  cobalticyanide  of  potassium.  It  is  supersaturated  with  acetic  acid,  boiled 
with  sulphate  of  copper,  which  precipitates  the  cobalt  in  the  form  of  cobalticyanide 
of  copper  (Cu3Co2Cy6.7HO),  and  the  precipitate  retained  in  the  liquid  at  a  boiling- 
heat  till  it  has  lost  its  glutinous  character.  It  is  then  washed,  dried,  and  ignited, 
dissolved  in  hydrochloric  acid  mixed  with  a  little  nitric  acid,  the  copper  precipi- 
tated by  hydrosulphuric  acid,  and  the  filtrate,  after  boiling  for  a  minute  to  expe- 
the  excess  of  that  gas,  mixed  with  boiling  caustic  potash  to  precipitate  the  cobalt.* 
—  2.  Instead  of  adding  the  oxide  of  mercury,  the  solution  containing  the  mixed 
cyanides  may,  after  cooling,  be  supersaturated  with  chlorine,  the  precipitate  of 
cyanide  of  nickel  thereby  produced  being  continually  redissolved  by  caustic  potash 
or  soda.  The  chlorine  produces  no  change  on  the  cobalticyanide  of  potassium, 
but  decomposes  the  nickel-compound,  the  whole  of  the  nickel  being  ultimately 
precipitated  in  the  form  of  black  sesquioxide. •)• 

Liebig's  first  method  J  which  consisted  in  treating  the  solution  of  the  mixed 
cyanides  with  excess  of  hydrochloric  or  sulphuric  acid,  whereby  the  nickel  was 
precipitated  as  cobalticyanide  of  nickel,  leaving  a  solution  of  pure  cobalticyanide 
of  potassium,  has  been  found,  both  by  himself  and  others,  not  to  give  perfectly 
satisfactory  results.  The  method  by  oxalic  acid  (p.  466),  and  the  precipitation 
of  nickel  from  an  ammoniacal  solution  of  the  two  metals  by  potash  (p.  467)  are 
not  sufficiently  accurate  for  quantitative  analysis. 

F.  Claudet  proposes  to  separate  cobalt  from  nickel  and  other  metals  in  the  form 
of  the  ammonio-compound  described  on  page  465,  that  compound  being  very 

*  Ann.  Ch.  Pharm.  Ixv.  244.          f  Ann.  Ch.  Pharm.  Ixxxvii.  128.         J  Ibid.  xli.  291. 


470  ZINC. 

insoluble,  while  corresponding  compounds  of  the  other  metals  do  not  appear  to  be 
formed  under  the  same  circumstances. 

The  separation  of  cobalt  from  nickel  (also  from  zinc  and  the  previously  described 
metals)  may  likewise  be  effected  by  means  of  St.  Evre's  yellow  compound,  which 
is  regarded  by  A.  Stromeyer  as  a  nitrite  of  cobaltic  oxide  and  potash  (p.  462). 
The  solution  containing  the  mixed  metals  is  diluted  with  water  till  about  oOO  parts 
of  water  are  present  to  1  part  of  protoxide  of  cobalt;  a  somewhat  concentrated 
solution  of  nitrite  of  potash*  then  added,  and  a  sufficient  quantity  of  acetic  acid  to 
redissolve  any  precipitated  carbonates ;  and  the  solution  left  to  stand  for  12  to  24 
hours  in  a  covered  vessel,  then  filtered  and  washed,  first  with  acetate  of  potash, 
afterwards  with  alcohol.  The  precipitate  contains  all  the  cobalt  in  the  form  of  the 
above-mentioned  salts,  and  none  of  the  other  metals. 


SECTION  V. 

ZINC. 

32-52;  Zn.  or  Eq.  406-6. 

The  principal  ores  of  zinc  are  calamine,  or  the  carbonate,  a  pulverulent  mineral 
generally  of  a  reddish  or  flesh  colour,  and  zinc-blende,  a  massive  mineral  of  an 
adamantine  lustre,  and  often  black.  The  oxide,  from  the  carbonate  or  from  the 
calcined  sulphide,  is  mixed  with  about  f  of  its  weight,  of  carbonaceous  matter, 
and  heated  to  a  low  white  heat  in  retorts,  or  similar  vessels  of  earthenware  or 
iron.  The  zinc  is  then  reduced  and  volatilized,  and  condenses  in  the  colder  part 
of  the  apparatus. 

In  Silesia,  the  mixture  of  zinc-oxide  and  charcoal,  or  coke,  is  heated  in  muffles, 
(fig.  189)  3  feet  long  and  18  inches  high,  six  of  which  are  laid  in  one  furnace 

FIG.  189. 


(fig.  190),  three  side  by  side.  The  evolved  mixture  of  carbonic  oxide  and  zinc- 
vapour  passes  from  the  upper  and  fore  part  of  the  muffles  M,  through  a  knee- 
shaped  channel,  bed,  and  the  zinc  condenses  therein  and  drops  down  from  the 
lower  aperture  <7  into  the  reservoirs  t  (fig.  190)  placed  beneath. 

Part  of  the  zinc-vapour,  and  likewise  some  cadmium-vapour,  escapes  uncon- 
densed,  together  with  the  carbonic  oxide  gas,  and  burns  in  the  air,  producing  the 
substance  called  Silesian  zinc-flowers.  Silesia  furnishes  the  greater  part  of  the 
zinc  used  in  the  arts. 

.  In  Belgium,  the  reduction  is  performed  in  earthenware  tubes,  laid  side  by  side ; 
and  the  zinc  as  it  condenses  in  the  fore  part  of  these  tubes,  is  scraped  out  from 
time  to  time  in  the  liquid  state. 

*  The  nitrite  of  potash  is  prepared  by  fusing  1  part  of  nitre  in  contact  with  2  parts  of 
metallic  lead,  first  at  a  low  and  then  at  a  bright-red  heat,  exhausting  the  cooled  mass  with 
water,  precipitating  a  small  quantity  of  lead  by  carbonic  acid,  and  then  by  sulphide  of  am- 
monium, evaporating  to  dryness,  and  heating  to  the  melting-point  to  decompose  any  hypo- 
sulphite of  potash  that  may  have  been  formed. 

f  A.  Stromeyer,  Ann.  Ch.  Pharm.  xcvi.  p.  218;  see  also  Liebig  and  Kopp's  Jahresbericht, 
1854,  p.  357. 


471 


FIG. 


In  England,  a  number  of  cast-iron  pots  are  arranged  in  a  circle  in  the  furnace 
fig.  191.).  Through  the  bottom  of  each  of  these  pots,  there  passes  an  iron  tube 
t,  which  is  continued  downwards  through  an  aperture  in  the  bottom  of  the  fur- 
nace. The  upper  end  of  the  tube  is  stopped  with 
a  plug  of  wood,  which  is  charred  during  the  opera- 
tion, and  becomes  sufficiently  porous  to  allow  the 
passage  of  the  zinc-vapour,  but  at  the  same  time 
prevents  the  solid  matter  from  falling  through. 
Each  pot  is  fitted  with  a  cover  well  luted  with  clay. 
The  fire-place  F,  is  in  the  middle.  The  distilled 
zinc  condenses  in  the  tubes  t  f',  and  falls  in  drops 
into  a  receiver  u,  placed  beneath.  This  process  is 
called  (JestUlatio  per  de seen  sum. 

Zinc  may  be  purified  by  a  second  distillation  in 
a  porcelain  retort ;  but  the  first  portions  of  that 
metal  which  come  over  should  be  rejected,  as  they 
generally  contain  cadmium  and  arsenic. 

Zinc  is  a  white  metal,  with  a  shade  of  blue, 
capable  of  being  polished  and  then  assuming  a 
bright  metallic  lustre.  It  is  usually  brittle,  and 
its  fracture  exhibits  a  crystalline  structure.  But 
zinc,  if  pure,  may  be  hammered  into  thin  leaves, 
at  the  usual  temperature;  and  commercial  zinc, 

which  is  impure  and  brittle  at  a  low  temperature,  acquires  the  same  malleability 
between  210°  and  300°:  it  may  then  be  laminated;  and  the  metal  is  now 
consumed  in  the  form  of  sheet  zinc  for  a  variety  of  useful  purposes.  At 
400°  it  again  becomes  brittle,  and  may  be  reduced  to  powder  in  a  mortar  of 
that  temperature.  The  density  of  cast  zinc  is  6-862,  but  it  may  be  in- 
creased by  forging  to  7'21.  Its  point  of  fusion  is  773°  (Daniell).  At  a  red 
heat,  zinc  rises  in  vapour  and  takes  fire  in  the  air,  burning  with  a  white  flame 
like  that  of  phosphorus;  the  white  oxide  produced  is  carried  up  mechani- 
cally in  the  air,  although  itself  a  fixed  substance.  Laminated  zinc  is  a  valuable 
substance,  from  its  little  disposition  to  undergo  oxidation.  When  exposed  to  air 
or  placed  in  water,  its  surface  becomes  covered  with  a  grey  film  of  suboxide, 
which  does  not  increase;  this  film  is  better  calculated  to  resist  both  the  mechanical 
and  chemical  effects  of  other  bodies  than  the  metal  itself,  and  preserves  it.  Zinc 
dissolves  with  facility  in  dilute  hydrochloric,  sulphuric  and  other  hydrated  acids, 
by  substitution  for  hydrogen.  In  contact  with  iron,  it  protects  the  latter  from 
oxidation  in  any  saline  fluid. 

Zinc  appears  to  form  three  oxides,  the  suboxide  above  referred  to,  the  protoxide, 
and  a  peroxide,  which  last  is  produced  when  the  hydrated  protoxide  is  acted  upon 


472  ZINC. 

by  a  solution  of  peroxide  of  hydrogen ;  but  of  these,  the  first  and  last  have  not 
been  studied,  and  the  protoxide  is,  therefore,  the  only  well  known  oxide  of  zinc. 

Protoxide  of  zinc  ;  ZnO ;  40-52  or  506'6. — This  oxide  maybe  obtained,  in 
the  form  of  an  anhydrous  white  powder,  by  the  combustion  of  the  metal  in  a 
stoneware  crucible,  or  as  a  white  hydrate,  by  precipitation  from  its  salts  by  an 
alkali.  It  is  of  a  yellow  colour  at  high  temperatures,  but  becomes  colourless  again 
on  cooling.  By  the  oxidation  of  zinc  in  air  and  water,  without  access  of  carbonic 
acid,  a  hydrate.  3ZnO  +  HO,  has  been  obtained  in  crystalline  needles  (Mitscher- 
lich). 

Oxide  of  zinc  combines  with  acids  and  forms  salts,  which  are  colourless,  like 
those  of  magnesia.  Caustic  alkalies  form  with  zinc-salts  a  white  gelatinous  pre- 
cipitate of  the  hydrated  oxide,  soluble  in  excess  of  the  alkali.  Carbonate  of 
potash  or  soda  throws  down  white  carbonate  of  zinc,  insoluble  in  excess ;  carbo- 
nate of  ammonia,  the  same  precipitate,  soluble  in  excess.  Ferrocyanide  of  potas- 
sium, and  the  alkaline  phosphates  and  arseniates,  also  form  white  precipitates. 
Zinc-salts  containing  a  strong  acid  in  excess,  are  not  affected  by  hydrosulphuric 
acid,  but  give  a  white  hydrated  sulphide  with  alkaline  sulphides.  A  solution  of 
acetate  of  zinc  is  readily  decomposed  by  hydrosulphuric  acid. 

The  native  sulphide  of  zinc,  or  zinc-blende,  ZnS,  crystallizes  in  octohedrons. 
Its  colour  is  variable,  being  sometimes  yellow,  red,  brown,  or  black. 

Chloride  of  zinc,  ZnCl,  is  produced  by  the  combustion  of  zinc  in  chlorine,  and 
by  dissolving  the  metal  in  hydrochloric  acid.  It  is  fusible  at  212°,  volatile  at  a 
red  heat,  and  perhaps  the  most  deliquescent  of  salts.  Chloride  of  zinc-ammo- 
nium, NH3Zn.Cl,  is  obtained,  according  to  Ritthausen,  in  white  prismatic  crystals, 
when  zinc  and  copper,  or  zinc  and  silver,  are  placed  in  contact  in  a  solution  of 
sal-ammoniac,  or  by  the  action  of  zinc  on  a  solution  of  sal-ammoniac  containing 
chloride  of  copper. 

Iodide  of  zinc  is  formed  by  digesting  iodine,  zinc,  and  water  together,  and 

resembles  the  chloride.  The  compound  ZnI.2NH3,  or  NH2(NH4)Zn.I,  forms 
crystals  belonging  to  the  rhombic  system  (Rammelsberg). 

The  neutral  carbonate  of  zinc  forms  the  ore  called  calamine.  When  precipi- 
tated by  an  alkaline  carbonate,  the  salts  of  zinc,  like  those  of  magnesia,  yield  the 
neutral  carbonate  in  combination  with  hydrated  oxide,  2(ZnO.C02)-|-3(ZuO.HO). 
The  mineral  substance,  zinc-bloom,  is  of  the  same  composition.  Precipitated  in 
the  cold,  the  carbonate  is  ZnO.C02+2(ZnO.HO),  but  is  contaminated  with  sul- 
phate of  soda  (Mitscherlich). 

Sulphate  of  zinc,  White  vitriol,  ZnO.S03  +  7HO. —  This  salt  is  formed  by  the 
oxidation  of  the  native  sulphide  at  high  temperatures,  or  by  dissolving  the  metal 
in  dilute  sulphuric  acid.  It  crystallizes  in  colourless  prismatic  crystals,  containing 
7  eq.  of  water,  the  form  of  which  is  a  right  rhombic  prism.  This,  like  all  the 
other  magnesian  sulphates,  gives  up  6  eq.  of  its  water  at  about  212°,  while  the 
seventh  or  constitutional  equivalent  requires  a  heat  of  400°  to  expel  it.  The 
crystals  are  soluble  in  2^-  times  their  weight  of  water,  at  the  usual  temperature, 
and  fuse  in  their  water  of  crystallization  when  heated.  The  salt  also  crystallizes 
above  86°,  with  6  eq.  of  water,  in  oblique  rhombic  prisms  (Mitscherlich.) 
According  to  Kiihn,  another  hydrate  is  formed  ,aud  precipitated  as  a  white  powder 
containing  2  eq.  of  water,  when  a  concentrated  solution  of  sulphate  of  zinc  is 
mixed  with  ojl  of  vitriol.  Sulphate  of  zinc  forms  the  usual  double  salt  with  sul- 
phate of  potash,  ZnO.S03-fKO.S03  +  6HO.  The  double  sulphate  of  zinc  and 
so^a  contains '4  atoms  of  water,  ZnO.S03-f  NaO.S03  +  4HO.  It  is  formed  by  a 
singular  decomposition  (p.  183).  When  a  solution  of  the  sulphate  is  mixed  with 
a  quantity  of  alkali  less  than  sufficient  for  complete  precipitation,  a  subsulphate 
of  zinc  precipitates,  which,  according  to  the  analyses  of  several  chemists,  contains 
4  eq.  of  oxide  of  zinc  to  1  eq.  of  sulphuric  acid,  besides  water.  A  concentrated 
bolution  of  sulphate  of  zinc  dissolves  the  preceding  subsalt,  and,  wfien  saturated, 


ESTIMATION    OF    ZINC.  473 

contains  a  compound  of  1  eq.  of  acid  and  2  eq.  of  base,  according  to  Schindler, 
and  does  not  crystallize.  From  this  solution,  Schindler  obtained  the  former  inso- 
luble subsalt  with  two  different  proportions  of  water,  in  long  crystalline  needles, 
containing  10HO,  by  spontaneous  evaporation  of  the  solution,  and  in  brilliant 
crystalline  plates  containing  2HO,  which  were  deposited  on  boiling  the  solution. 
By  diluting  the  same  solution  with  a  large  quantity  of  water,  he  also  obtained 
another  subsalt,  as  a  light  bulky  precipitate,  which  contained  1  eq,  of  acid,  8  eq. 
of  oxide  of  zinc,  and  2  eq.  of  water.  The  insoluble  matter,  which  precipitates 
when  sulphate  of  zinc-ammonium  (NHgZn^O.SOa  is  thrown  into  water,  is  con- 
sidered by  Kane  as  a  third  subsulphate  of  zinc,  containing  1  eq.  of  acid,  6  eq.  of 
oxide  of  zinc,  and  10  eq.  of  water.  All  these  subsulphates  afford  neutral  sulphate 
of  zinc  to  water,  after  being  heated  to  redness  j  so  that,  whatever  their  constitu- 
tion may  be  when  hydrated,  it  is  certainly  different  from  what  it  is  in  their  anhy- 
drous condition. 

Nitrate  of  zinc,  ZnO.N05-f-(5HO,  is  very  soluble  in  water,  and  moderately 
deliquescent. 

Phosphate  of  zinc,  Zn02.HO.P05  +  2HO,  is  obtained  in  minute  silvery  plates, 
which  are  nearly  insoluble,  on  mixing  dilute  solutions  of  phosphate  of  soda  and 
sulphate  of  zinc. 

Silicate  of  zinc  is  found  as  a  crystalline  mineral,  which  has  received  the  name 
of  the  electrical  oxide  of  zinc,  because  it  acquires,  like  the  tourmalin,  a  high 
degree  of  electrical  polarity  when  heated.  It  contains  water,  and  may  be  repre- 
sented by  the  formula  2(3ZnO.Si03)  +  3HO. 

The  most  important  alloys  of  zinc  are  those  with  copper,  which  form  the  varie- 
ties of  brass.  Zinc  also  combines  readily  with  iron,  and  is  contaminated  by  that 
metal,  when  fused  in  an  iron  crucible. 

ESTIMATION  OF  ZINC,  AND  METHODS  OP  SEPARATING  IT  FROM  OTHER  METALS. 

Zinc  is  precipitated  from  its  solutions  by  carbonate  of  soda,  which,  when  added 
in  excess  and  boiled  with  the  solution,  throws  down  carbonate  of  zinc.  It  is  best, 
however,  to  pour  the  zinc-solution  into  the  hot  solution  of  the  alkaline  carbonate, 
because,  in  that  case,  we  may  be  sure  of  not  forming  a  basic  salt.  If  the  zinc- 
solution  contains  ammoniacal  salts,  it  must  be  boiled  with  a  quantity  of  carbonate 
of  soda  sufficient  to  decompose  those  salts ;  then  evaporated  to  dryness ;  the  resi- 
due treated  with  a  large  quantity  of  water  to  dissolve  out  the  soluble  salts ;  and  the 
carbonate  of  zinc  collected  on  a  filter  and  well  washed  with  hot  water.  The  eva- 
poration should  be  conducted  as  quickly  as  possible.  The  carbonate  of  zinc,  when 
dried  and  ignited,  yields  oxide  of  zinc  containing  80-26  percent,  of  the  metal. 

In  separating  zinc  from  other  metals,  it  is  often  necessary  to  precipitate  by 
sulphide  of  ammonium.  If  the  solution  is  acid,  it  must  be  previously  neutralized 
by  ammonia.  The  precipitate  must  not  be  thrown  on  the  filter  immediately,  but 
left  to  settle  down  completely,  after  which  the  clear  liquid  must  first  be  passed 
through  the  filter,  and  then  the  precipitate  thrown  on  it.  If  this  precaution  be 
neglected,  the  sulphide  of  zinc  will  stop  up  the  pores  of  the  filter.  The  precipi- 
tate is  washed  with  water  containing  a  little  sulphide  of  ammonium ;  then  dissolved 
in  hydrochloric  acid ;  the  solution  boiled  to  drive  off  the  hydrosulphuric  acid ;  ,and 
the  zinc  precipitated  by  carbonate  of  soda  as  above. 

Zinc  is  separated  from  the  alkalies  and  alkaline  earths  (baryta,  strontia,  and 
lime)  by  means  of  sulphide  of  ammonium.  In  the  case  of  the  alkaline  earths, 
however,  great  care  must  be  taken  to  prevent  the  ammoniacal  liquid  from  absorbing 
carbonic  acid  from  the  air,  as  that  would  occasion  a  precipitation  of  the  earth  in  the 
form  of  carbonate.  For  this  purpose,  the  filtration  must  be  effected  as  quickly  as 
possible,  and  the  liquid  well  protected  from  the  air.  The  separation  of  zinc  from 
baryta  may  also  be  effected  by  sulphuric  acid,  and  from  lime  by  oxalate  of 
ammonia. 


474  CADMIUM. 

From  magnesia,  zinc  may  be  separated  by  sulphide  of  ammonium,  a  sufficient 
quantity  of  chloride  of  ammonium  being  previously  added  to  prevent  the  precipi- 
tation of  the  magnesia.  Or  the  separation  may  be  effected  by  converting  the 
zinc  and  magnesia  into  acetates,  and  precipitating  the  zinc  as  sulphide  by  hydro- 
sulphuric  acid. 

The  separation  of  zinc  from  alumina  and  ylucina  may  also  be  effected  by  con- 
verting the  two  bases  into  acetates  and  precipitating  the  zinc  by  hydrosulphuric 
acid  j  or  by  dissolving  in  potash,  and  precipitating  the  zinc  by  hydrosulphuric 
acid;  but  the  former  method  is  to  be  preferred. 

The  conversion  into  acetates  and  precipitation  by  hydrosulphuric  acid  likewise 
serves  to  separate  zinc  from  zircon  ia,  yttria,  thorina,  and  manganese.  The  sepa- 
ration from  manganese  may  also  be  effected  by  converting  the  two  metals  into 
chlorides,  passing  chlorine  gas  through  the  solution  to  convert  the  manganese  into 
bioxide,  and  completing  the  precipitation  of  the  latter  by  carbonate  of  baryta. 

From  iron^  zinc  may  be  separated  by  ammonia,  or  better  bysuccinate  of  ammo- 
nia, the  same  precautions  being  used  as  in  the  separation  of  iron  from  manganese 
by  the  same  method  (p.  458).  The  iron  (in  the  state  of  sesquioxide)  may  also 
be  precipitated  by  carbonate  of  lime  or  carbonate  of  baryta. 

From  cobalt  and  nickel,  zinc  is  separated  by  dissolving  the  oxides  of  both  metals 
in  excess  of  acetic  acid,  and  precipitating  the  zinc  by  hydrosulphuric  acid.  Nickel 
and  cobalt  are  completely  precipitated  by  hydrosulphuric  acid  from  the  neutral 
solutions  of  their  acetates,  but  not  when  a  considerable  excess  of  acetic  acid  is 
present.  But  in  separating  zinc  from  cobalt  and  nickel  in  this  manner,  a  small 
quantity  of  the  latter  metals  is  generally  precipitated  with  the  zinc  towards  the 
end  of  the  process,  the  precipitate  then  becoming  greyish  black.  In  that  case  it 
must  be  redissolved  in  hydrochloric  acid,  the  chlorides  converted  into  acetates,  and 
the  precipitation  repeated.  Another  method  of  separation  is  to  convert  the 
metals  into  chlorides,  and  ignite  the  dry  chlorides  in  a  stream  of  hydrogen  gas  : 
the  nickel  or  cobalt  is  then  reduced  to  the  metallic  state,  while  the  chloride  of 
zinc  remains  unaltered,  and  may  be  dissolved  out  by  water.  (For  the  separation 
of  cobalt  from  zinc,  see  also  p.  470.) 

In  precipitating  zinc  from  its  acetic  acid  solution  by  hydrosulphuric  acid,  it  is  ne- 
cessary that  the  solution  be  quite  free  from  inorganic  acids,  which  would  interfere 
with  the  precipitation.  This  may  be  effected  either  by  precipitating  the  metals 
with  carbonate  of  soda,  washing  the  precipitate  and  dissolving  it  in  acetic  acid,  or 
by  boiling  the  solution  with  excess  of  sulphuric  acid  to  drive  off  the  inorganic 
acids  (if  volatile)  and  decomposing  the  sulphate  with  acetate  of  baryta. 


SECTION  VI. 

CADMIUM. 

Eq.  55-74  or  696-77;  Cd. 

This  metal  is  frequently  found  in  small  quantity,  associated  with  zinc,  and 
derives  the  name  cadmium,  applied  to  it  by  Stromeyer,  from  cddmia  fossilis,  a 
denomination  by  which  the  common  ore  of  zinc  was  formerly  designated.  In  the 
process  of  reducing  ores  of  zinc,  the  cadmium  which  they  contain  comes  over 
timong  the  first  products  of  distillation,  owing  to  its  greater  volatility.  It  maybe 
separated  from  zinc,  in  an  acid  solution,  by  hydrosulphuric  acid,  which  throws 
down  cadmium  as  a  yellow  sulphide.  This  sulphide  dissolves  in  concentrated 
hydrochloric  acid,  affording  the  chloride  of  cadmium,  from  which  the  carbonate 
may  be  precipitated  by  an  excess  of  carbonate  of  ammonia.  Carbonate  of  cad- 
mium is  converted  by  ignition  into  the  oxide ;  and  the  latter  yields  the  metal 


SALTS    OF     CADMIUM.  475 

when  mixed  with  one-tenth  of  its  weight  of  pounded  coal,  and  distilled  in  a  glass 
or  porcelain  retort,  at  a  low  red  heat. 

Cadmium  is  a  white  metal,  like  tin,  very  ductile  and  malleable.  It  fuses  con- 
siderably under  a  red  heat,  and  is  nearly  as  volatile  as  mercury.  The  density  of 
cadmium,  cast  in  a  mould,  is  8-604,  after  being  hammered,  8-6944.  Cadmium 
may  be  dissolved  in  the  more  powerful  acids,  by  substitution  for  hydrogen,  with 
the  aid  of  heat ;  but  nitric  acid  is  its  proper  solvent. 

Oxide  of  cadmium,  CdO ;  6374  or  796'77. —  The  only  known  oxide  of  cad- 
mium is  obtained  by  the  combustion  of  the  metal,  or  by  the  ignition  of  its  carbo- 
nate, as  a  powder  of  an  orange  colour,  or  as  a  white  hydrate  by  precipitation  from 
its  salts  by  an  alkali.  Its  density,  in  the  anhydrous  condition,  is  8*183  (llera- 
path).  By  igniting  the  nitrate,  the  oxide  is  obtained  in  microscopic  octohedrons, 
which  are  dark  bluish  black  by  reflected,  and  dark  brown  with  a  tinge  of  violet 
by  transmitted  light  (Schiller).  This  oxide  is  soluble  in  ammonia,  but  not  in  its 
carbonate  (differing  in  the  last  property  from  zinc  and  copper)  nor  in  the  fixed 
alkalies.  Its  salts  are  white,  and  greatly  resemble  those  of  zinc.  They  are  pre- 
cipitated of  a  fine  yellow  colour  by  hydrosulphuric  acid. 

Sulphide  of  cadmium  is  distinguished  from  sulphide  of  arsenic,  which  it  re- 
sembles in  colour,  by  being  insoluble  in  potash  and  in  sulphide  of  ammonium,  and 
by  sustaining  a  red  heat  without  subliming.  A  crystalline  sulphide  is  obtained 
by  fusing  1  part  of  the  precipitated  sulphide  with  5  parts  of  carbonate  of  potash 
and  5  parts  of  sulphur ;  or  by  passing  dry  hydrosulphuric  acid  gas  over  strongly- 
heated  chloride  of  cadmium. 

Chloride  of  cadmium  forms  a  crystalline  hydrate,  containing  CdCl  +  2HO. 
It  also  forms  crystalline  compounds  with  the  chlorides  of  ammonium,  potassium, 
sodium,  barium,  strontium,  calcium,  magnesium,  manganese,  iron,  cobalt,  nickel, 
and  copper.  A  solution  of  chloride  of  cadmium,  mixed  with  excess  of  ammonia, 
yields  by  spontaneous  evaporation  the  compound  NH2CdCl  (C.  v.  Hauer). 

The  same  ammoniacal  solution  treated  with  excess  of  hydrochloric  acid  de- 
posits crystalline  crusts,  which,  according  to  Schiller,  contain  CdC1.3NH3  or 

NH(NH4)2Cd.Cl.  Sulphurous  acid  gas  passed  through  the  ammoniacal  solution 
throws  down  a  white  crystalline  precipitate  containing  CdO.S02  +  NH4O.S02 
(Schiller.) 

Iodide  of  cadmium  forms  a  crystalline  compound  with  water. 

Bromide  of  cadmium  mixed  in  equivalent  quantity  with  bromide  of  potassium 
in  solution,  yields  crystals,  first  of  2CdBr.KBr-f  2HO,  afterwards  of  CdBr.2KBr 
(C.  v.  Hauer). 

Sulphate  of  cadmium  forms  efflorescent  crystals  containing  CdO.S03  -f-  4HO 
(Stromeyer).  According  to  Kiihn  and  Von  Hauer,  an  acid  solution  of  the  salt 
concentrated  at  the  boiling  heat,  deposits  nodular  crystals,  which  contain  CdO  S03 
4-HO,  and  give  off  their  water  at  212°.  The  crystals  obtained  by  evaporation  at 
ordinary  temperatures  contain  3(CdO.S03)  -f  8HO,  give  off  nearly  3  eq.  water  at 
212°,  and  the  rest  at  a  low  red  heat  (C.  v.  Hauer).  Sulphate  of  cadmium  forms 
with  sulphate  of  potash  the  compound  CdO.S03-f  KO.S03  -f  6HO,  and  similar 
double  salts  with  the  sulphates  of  soda  and  ammonia. 

Several  definite  alloys  of  cadmium  have  been  formed.  At  a  red  heat,  100 
parts  of  platinum  retain  117'3  parts  of  cadmium,  giving  a  compound  =  Cd2Pt : 
100  parts  of  copper  retain,  at  a  red  heat,  82  2  of  cadmium,  which  approaches 
nearly  to  the  proportion  of  CdCu2.  Cadmium  forms  an  amalgam  with  mercury, 
which  crystallizes  in  octohedrons,  and  consists  of  21-74  parts  of  cadmium,  and 
78-26  of  mercury,  CdHg2. 

Estimation  of  cadmium,  and  method  of  separating  it  from  the  preceding 
metals. — Cadmium  is  best  precipitated  from  its  solutions  by  carbonate  of  soda ;  it 


476  COPPER. 

Is  thereby  obtained  as  a  carbonate,  which,  by  ignition  yields  the  brown  oxide  con- 
taining 8745  per  cent,  of  the  metal. 

From  all  the  preceding  metals  cadmium  may  be  separated  by  hydrosulphuric 
acid ;  the  sulphide  of  cadmium  being  then  dissolved  by  nitric  acid,  and  the  metal 
precipitated  by  carbonate  of  soda  as  above. 


SECTION    VII. 

COPPER. 

Eq.  31-66  or  395-7;  Cu  (cuprum). 

Copper,  if  not  the  most  abundant,  is  certainly  one  of  the  most  generally  diffused 
of  the  metals.  *Its  ores  are  often  accompanied  by  metallic  copper,  crystallized  in 
cubes  or  octohedrons.  Very  large  masses  of  native  copper  have  been  found  near 
Lake  Superior  in  North  America,  one  of  which  weighed  2200  pounds;  in  the 
Cliff  mine,  on  the  Eagle  river,  a  mass  has  been  found  weighing  50  tons.  Native 
copper  is  also  found  in  considerable  quantities  in  the  decomposed  basalt  of  Rhein- 
breitenbach,  near  Recsk  in  Hungary,  and  near  Harlech,  North  Wales.  The 
richest  mines  of  Britain  are  those  in  Cornwall  and  Anglesea.  The  common 
ore  of  this  metal  is  copper  pyrites,  a  compound  of  subsulphide  of  copper  and  ses- 
quisulphide  of  iron,  or  a  sulphur-salt,  CuS-f  Fe2S3,  but  in  which  the  two  sulphides 
are  also  found  in  other  proportions,  and  which  also  contains  an  admixture  of  the 
bisulphide  of  iron.  Few  metallurgic  processes  require  more  skill  and  attention 
than  the  extraction  of  copper  from  this  ore.  The  ore  is  first  roasted  at  a  high 
temperature  in  a  reverberatory  or  flame-furnace,  (fig.  192),  whereby  the  sulphide 

FIG.  192. 


of  iron  is  in  great  part  converted  into  oxide,  while  the  sulphide  of  copper  remains 
unaltered.  The  product  of  this  operation  is  then  strongly  heated  with  silicious 
eand,  which  combines  with  the  oxide  of  iron,  forming  a  fusible  slag,  and  separates 
from  the  heavier  copper  compound.  This  operation  is  performed  in  a  reverbera- 
tory furnace  similar  to  the  former,  but  of  smaller  dimensions.  These  processes 
are  several  times  repeated,  whereby  the  quantity  of  iron  is  continually  diminished, 
and  the  sulphide  of  copper  begins  to- decompose,  giving  it  up  its  sulphur  and  ab- 
sorbing oxygen ;  the  temperature  is  then  raised*  high  enough  to  reduce  the  re- 
sulting oxide  by  the  aid  of  carbonaceous  matter.  The  coarse  copper  thus  ob- 
tained, containing  from  80  to  90  per  cent,  of  copper,  is  then  melted  under  the 
action  of  a  strong  blast  of  air,  to  complete  the  expulsion  of  volatile  matter,  and 
the  copper  is  partially  oxidized.  Lastly,  to  free  it  from  oxide,  which  renders  it 
brittle,  it  is  again  melted  with  its  surface  well  covered  with  charcoal,  and  a  pole 
of  birchwood  is  thrust  into  it ;  this  causes  considerable  ebullition,  the  oxide  being 
reduced  by  the  carbonaceous  matter,  and  carbonic  acid  escaping.  Samples  of  the 


CUPROUS    OXIDE.  4*  I 

metal  are  taken  out  from  time  to  time,  and  tested  by  the  hammer,  the  process 
being  discontinued  as  soon  as  the  right  degree  of  toughness  is  attained.  If  the 
poling  is  continued  too  long,  the  copper  takes  up  carbon,  and  then  becomes  even 
more  brittle  than  in  its  former  oxidized  state  :  it  is  then  said  to  be  over-poled,  and 
must  be  again  melted  in  contact  with  the  air  to  burn  away  the  carbon.* 

Copper  is  the  only  metal  of  a  red  colour.  The  crystals  of  native  copper,  and  of 
that  obtained  in  the  humid  way  by  precipitation  with  iron,  belong  to  the  regular 
system ;  but  the  crystals  which  form  in  the  cooling  of  melted  copper  were  found 
by  Seebeck  to  be  rhomboiidal,  and  to  have  a  different  place  in  the  thermo-electric 
series  from  the  other  crystals.  The  density  of  copper  when  cast  is  about  8 '83, 
and  when  laminated  or  forged  8-95  (Berzelius).  It  is  less  fusible  than  silver,  but 
more  so  than  gold,  its  point  of  fusion  being  1996°  (Daniell).  It  is  one  of  the 
most  highly  malleable  metals,  and  in  tenacity  is  inferior  only  to  iron.  It  has  much 
less  affinity  for  oxygen  than  iron,  and  decomposes  water  only  at  a  bright  red  heat, 
and  to  a  small  extent.  In  damp  air,  it  acquires  a  green  coating  of  subcarbonate 
of  copper,  and  its  oxidation  is  remarkably  promoted  by  the  presence  of  acids.  The 
weaker  acids,  such  as  acetic,  have  no  effect  upon  copper,  unless  with  the  concur- 
rence of  the  oxygen  of  the  air,  when  the  copper  rapidly  combines  with  that 
oxygen,  and  a  salt  of  the  acid  is  formed.  Copper  scarcely  decomposes  the  hy- 
drated  acids  by  displacing  hydrogen ;  when  boiled  in  hydrochloric  acid,  it  disen- 
gages only  the  smallest  traces  of  that  gas.  But  hydrogen  does  not  precipitate 
metallic  copper  from  solution.  Copper  acts  violently  on  nitric  acid,  occasioning 
its  decomposition,  with  evolution  of  nitric  oxide,  and  dissolving  as  a  nitrate. 

Dioxide  of  copper,  Red  oxide  of  copper,  Cuprous  oxide,  Cu20;  71 '32  or 
8914.  —  This  degree  of  oxidation  is  better  marked  in  copper  than  in  any  other 
metal  of  the  magnesian  class.  The  dioxide  of  copper  is  found  native  in  octohe- 
dral  crystals,  and  may  be  prepared  artificially  by  heating  to  redness,  in  a  covered 
crucible,  a  mixture  of  5  parts  of  the  black  oxide  of  copper  with  4  parts  of  copper- 
filings.  It  is  a  reddish-brown  powder,  which  undergoes  no  change  in  the  air.  The 
surface  of  vessels  of  polished  copper  is  often  converted  into  red  oxide,  or  bronzed, 
to  enable  them  to  resist  the  action  of  air  and  moisture :  this  is  done  by  covering 
them  with  a  paste  of  sesquioxide  of  iron,  heating  to  a  certain  point,  and  afterwards 
cleaning  them,  to  remove  the  oxide  of  iron;  or  otherwise,  by  means  of  a  boiling 
solution  of  acetate  of  copper. 

Dilute  acids  decompose  red  oxide  of  copper,  dissolving  the  protoxide,  and  leaving 
metallic  copper.  Undiluted  hydrochloric  acid  dissolves  the  red  oxide,  without  de- 
composition, or  rather  forms  a  corresponding  chloride  of  copper,  Cu2Cl,  which  is 
soluble  in  hydrochloric  acid.  The  hydrated  alkalies  precipitate  hydrated  cuprous 
oxide  from  that  solution,  of  a  lively  yellow  colour,  which  changes  rapidly  in  air 
from  absorption  of  oxygen. 

Cuprous  oxide  is  also  formed  when  copper  is  placed  in  a  dilute  solution  of  am- 
monia containing  air,  and  is  dissolved  by  the  alkali.  If  the  ammonia  has  been 
corked  up  in  a  bottle  with  copper  for  some  time,  the  liquid  is  colourless  j  but  on 
pouring  it  out  in  a  thin  stream,  it  immediately  becomes  blue,  by  absorbing  oxygen. 
The  liquid  may  be  again  deprived  of  colour  by  returning  it  to  the  bottle,  and 
closing  it  up,  in  contact  with  the  metal.  Cuprous  oxide  is  also  readily  obtained 
by  the  reducing  action  of  glucose  (grape-sugar)  on  the  protoxide  or  its  salts. 
When  a  solution  of  1  part  of  common  sulphate  of  copper  and  1  part  of  glucose  is 
mixed  with  a  sufficient  quantity  of  caustic  potash  or  soda  to  redissolve  the  preci- 
pitate first  formed,  and  the  liquid  gently  warmed,  cuprous  oxide  is  abundantly 
precipitated  in  the  form  of  a  yellowish-red  crystalline  powder.  Cane-sugar  pro- 
duces the  same  effects,  but  more  slowly,  apparently  because  it  must  first  be  con- 
verted into  glucose. 

*  A  minute  account  of  the  process  of  copper-smelting  as  practised  at  Swansea,  has  lately 
been  gfven  bv  Mr.  Napier  in  the  "  Philosophical  Magazine,"  4th  Series,  vols.  iv.  and  v. 


478  COPPER. 

Compounds  have  been  obtained  of  cuprous-oxide  with  several  acids,  particularly 
with  sulphurous  acid,  the  sulphite  forming  a  double  salt  with  sulphite  of  potash, 
Cu2O.S02+2(KO.S02)  (Muspratt);  also  with  hyposulphurous,  sulphuric,  car- 
bonic and  acetic  acids.  When  fused  with  vitreous  matter,  cuprous  oxide  gives  a 
beautiful  ruby-red  glass;  but  it  is  difficult  to  prevent  the  cuprous  oxide  from 
absorbing  oxygen,  in  which  case  the  glass  becomes  green. 

Hydride  of  copper,  Cuprous  hydride,  Cu2H. — When  a  solution  of  cupricsulphate 
and  hypophosphorous  acid  is  heated  not  above  158°,  this  compound  is  deposited 
as  a  yellow  precipitate,  which  soon  turns  red-brown.  It  gives  off  hydrogen  when 
heated,  takes  fire  in  chlorine  gas,  and  when  treated  with  hydrochloric  acid,  is  con- 
verted into  dichloride  of  copper,  with  evolution  of  a  double  quantity  of  hydrogen, 
the  acid  in  fact  giving  up  its  hydrogen  as  well  as  the  copper  compound  (Wurtz)  : 

Cu2H  +  HC1  =  Cu2Cl  +  HH. 

This  action  is  very  remarkable,  inasmuch  as  metallic  copper  is  scarcely  acted  upon 
by  hydrochloric  acid.  It  appears  to  arise  from  the  two  atoms  of  hydrogen  con- 
tained in  the  acid  and  the  hydride  being  in  opposite  states,  the  former  being  basy- 
lous  or  positive,  the  latter  chlorous  or  negative,  and  so  disposed  to  combine  together, 
just  as  the  hydrogen  of  the  hydrochloric  acid  combines  under  similar  circum- 
stances with  the  oxygen  of  the  compound  Cu20.  The  reduction  of  certain  metallic 
oxides  by  peroxide  of  hydrogen  affords  another  example  of  the  same  kind  of 
action. 

Bisulphide  of  copper,  Cuprous  sulphide,  Cu2S,  forms  the  mineral  copper-glance, 
and  is  also  a  constituent  of  copper  pyrites.  It  is  a  powerful  sulphur-base.  Copper- 
filings,  mixed  with  half  their  weight  of  sulphur,  unite,  when  heated,  with  intense 
ignition,  and  form  this  disulphide. 

Dichloride  of  Copper,  Cuprous  chloride,  Cu2Cl,  may  be  prepared  by  heating 
copper-filings  with  twice  their  weight  of  corrosive  sublimate.  It  was  obtained  by 
Mitscherlich  in  tetrahedrons,  by  dissolving  in  hydrochloric  acid  the  dichloride  of 
copper  formed  on  mixing  solutions  of  the  protochlorides  of  copper  arid  tin,  and 
allowing  the  concentrated  solution  to  cool.  Dichloride  of  copper  so  prepared  is 
white,  insoluble  in  water,  soluble  in  hydrochloric  acid,  but  precipitated  by  dilution. 
It  L  dissolved  by  a  boiling  solution  of  chloride  of  potassium,  and  the  resulting 
solution,  if  allowed  to  cool  in  a  close  vessel,  yields  large  octohedral  crystals  of  a 
double  chloride:  Cu2C1.2KCl;  they  are  anhydrous.  It  is  remarkable  that  the 
forms  of  this  double  salt,  and  of  both  its  constituents,  all  belong  to  the  regular 
system.*  , 

When  finely-divided  metallic  copper  is  boiled  in  a  saturated  solution  of  sal- 
ammoniac,  ammonia  is  evolved  and  a  white  salt  formed,  which  crystallizes  in 
rhombic  dodecahedrons  :  it  contains  NH3.Cu2Cl,  and  may  be  regarded  as  a  dichloride 

of  copper  and  cuprammonium         3p     >  Cl.     A  solution  of  this  salt  exposed  to 

the  air  yields  blue  crystals  of  the  compound  NH3.Cu2Cl  +  NH3CuCl  +  HO;  and 
the  mother-liquor,  after  further  exposure  to  the  air,  contains  the  salt  NH3 .  CuCl  -f- 
NH4C1,  which  at  a  lower  temperature  crystallizes  in  large  cubes  (Ritthausen). 

D'niodide  of  Copper,  Cuprous  iodide,  Cu2I,  is  a  white  insoluble  precipitate, 
obtained  on  mixing  a  solution  of  1  part  of  sulphate  of  copper  and  21  parts  of 
protosulphate  of  iron,  with  a  solution  of  iodide  of  potassium. 

D > cyanide  of  copper,  Cuprous  cyanide,  Cu2Cy.  —  Obtained  as  a  white  curdy 
precipitate  on  adding  hydrocyanic  acid  or  cyanide  of  potassium  to  a  solution  of 
dichlorido  of  copper  in  hydrochloric  acid,  or  to  a  solution  of  protochloride  of 
copper  mixed  with  sulphurous  acid.  It  forms  a  colourless  solution  with  ammonia, 
and  a  yellow  solution  with  strong  hydrochloric  acid,  from  which  it  is  precipitated 
by  potash 

*  Mitscherlich  in  Poggendorff' s  Annalen,  xlix.  401,  1840. 


CUPRIC    OXIDE.  479 

Dicyanide  of  copper  unites  with  the  cyanides  of  the  alkali  and  earth -metals, 
and  with  the  cyanides  of  manganese,  iron,  zinc,  cadmium,  lead,  tin,  uranium,  and 
silver,  forming  double  salts,  some  of  which  have  the  composition  MCy.Cu2Cy, 
others  3MCy.Cu2Cy  (the  symbol  M  denoting  a  metal). 

Cuproso-cvpric  cyanide,  Cu2Cy  .  CuCy,  is  obtained  as  a  green  hydrate  by  adding 
hydrocvanic  acid  or  cuproso-potassic  cyanide,  KCy.Cu2Cy,  to  sulphate  of  copper. 
It  forms  three  compounds  with  ammonia,  viz.,  NH3.Cu3Cy8.HO,  obtained  by 
adding  cyanide  of  ammonium  to  a  protosalt  of  copper,  and  the  compounds 
2NH3.CusCy2  and  3NH3.Cu3Cy2,  formed  by  the  action  of  ammonia  on  the  first 
compound. 

Cuprous  hyposulphite,  Cu20.3S202  +  2HO,  separates  in  microscopic  needles, 
having  a  golden  lustre,  on  adding  a  saturated  solution  of  hyposulphite  of  soda  to 
a  concentrated  solution  of  cupric  sulphite,  till  a  deep  yellow  colour  is  produced. 
It  dissolves  in  aqueous  sal-ammoniac,  and  the  solution  deposits  the  compound 
Cu20.3S202  +  NH3CuCl  +  HO.  (C.  v.  Hauer). 

Cuprous  sulphite  is  said  by  some  chemists  to  be  obtained  in  a  definite  state  by 
the  action  of  sulphurous  acid  on  cupric  oxide ;  but  according  to  Rainmelsberg 
and  Pean  de  St.  Grilles,  it  exists  only  in  combination  with  cupric  sulphite,  forming 
the  compound  Cu2O.S02-|-  CuO.S02,  which  crystallizes  with  3  and  5  eq.  of  water, 
—  and  with  the  sulphites  of  the  alkalies.  By  treating  dichloride  of  copper  with 
excess  of  sulphite  of  ammonia,  prismatic  crystals  are  formed  containing  Cu2O.S02 
-f  7(NII4O.S02)  4-  10  Aq  ;  and  by  saturating  the  solution  of  this  salt  with 
sulphurous  acid,  the  salt  Cu2O.S202  +  NH4O.S03  is  obtained.  A  concentrated 
solution  of  sulphite  of  ammonia  and  cupric  sulphate  saturated  with  sulphurous 
acid  gas,  yields  light  green  crystals  containing  (Cu2O.S02  +  NH40  .  S02)  + 
(Cu20  .  S02  -f-  CuO  .  S02)  +  5  aq.  Corresponding  double  salts  are  formed  by 
the  sulphites  of  potash  and  soda,  but  they  are  very  unstable. 

Protoxide  of  copper,  Black  oxide  of  Copper,  Cuprie  oxide,  CuO;  495*7  or 
39-66.  —  The  base  of  the  ordinary  salts  of  copper,  or  cupric  salts.  It  is  formed 
by  the  oxidation  of  copper  at  a  red  heat,  but  is  generally  prepared  by  igniting  the 
nitrate  of  copper.  It  is  black  like  charcoal,  and  fuses  at  a  high  temperature. 
This  oxide  is  remarkable  for  the  facility  with  which  it  is  reduced,  at  a  low  red 
heat,  by  hydrogen  and  carbon,  which  it  converts  into  water  and  carbonic  acid.  It 
is  this  property  which  recommends  oxide  of  copper  for  the  combustion  of  organic 
substances,  in  close  vessels,  by  which  their  ultimate  analysis  is  effected. 

Oxide  of  copper  is  a  powerful  base.  Its  salts,  the  cupric  salts,  are  generally 
blue  or  green,  when  hydrated,  but  white  when  anhydrous.  Although  neutral  in 
composition,  they  have  a  strong  acid  reaction.  They  are  poisonous;  but  their 
effect  upon  the  animal  system  is  counteracted  in  some  degree  by  sugar.  Liquid 
albumen  forms  insoluble  compounds  with  these  salts,  and  is  an  antidote  to  their 
poisonous  action.  Copper  is  separated  in  the  metallic  state  from  its  salts  by  zinc, 
iron,  lead,  and  the  more  oxidable  metals,  which  are  dissolved,  and  take  the  place 
of  the  former  metal. 

Potash,  or  soda,  added  to  the  solution  of  a  cupric  salt,  throws  down  at  first  a  blue 
precipitate  of  hydrated  cupric  oxide,  which,  however,  on  agitation,  takes  up  a 
portion  of  the  undecomposed  salt,  and  forms  with  it  a  green  basic  salt.  An  excess 
of  the  alkali  throws  down  the  hydrated  oxide  in  bulky  blue  flakes,  which,  on 
boiling  the  mixture,  collect  together  in  the  form  of  a  black  powder,  consisting  of 
the  anhydrous  oxide.  This  reaction  is  greatly  modified  by  the  presence  of  fixed 
organic  substances,  such  as  sugar,  tartaric  acid,  &c:  In  a  solution  of  sulphate  of 
copper,  containing  such  substances  in  sufficient  quantity,  potash  either  produces 
no  precipitate,  or  one  which  is  quickly  re-dissolved,  forming  a  blue  solution  •  and 
from  this  solution,  when  boiled,  the  copper  is  sometimes  wholly  precipitated  as  red 
or  yellow  cuprous  oxide,  as  when  grape-sugar  is  present,  —  or  partially,  as  with 
cane-sugar,  or  not  at  all,  as  with  tartaric  acid.  Ammonia,  added  by  degrees,  and 


480  COPPER. 

with  constant  agitation,  to  the  solution  of  a  cupric  salt,  first  throws  down  a  screen 
basic  salt,  and  afterwards  the  blue  hydrate:  an  excess  of  ammonia  dissolves  the 
precipitate,  forming  a  deep  blue  solution.  A  copper  solution,  diluted  so  far  as  to 
be  colourless,  becomes  distinctly  blue  on  the  addition  of  ammonia.  The  blue 
colour  thus  produced  is  still  visible,  according  to  Lassaigne,  in  a  solution  contain- 
ing 1  part  of  copper  in  100,000  parts  of  liquid.  Carbonate  of  potash  or  soda 
throws  down,  with  evolution  of  carbonic  acid,  a  greenish  blue  precipitate  of  a 
basic  carbonate  of  copper,  which  on  boiling  is  converted  into  the  black  oxide. 
Carbonate  of  ammonia  produces  the  same  precipitate,  but  when  added  in  excess, 
dissolves  it  abundantly,  forming  a  blue  solution.  Hydrosulphuric  acid  and  solutions 
of  alkaline  sulphides  throw  down  a  brownish  black  precipitate  of  protosulphide  of 
copper,  insoluble  in  sulphide  of  potassium  or  sodium,  slightly  soluble  in  sulphide 
of  ammonium.  Frrrocyanide  of  potassium  forms  with  cupric  salts  a  deep  choco- 
late-coloured precipitate  of  ferrocyanide  of  copper.  To  very  dilute  solutions  it 
imparts  a  reddish  colour,  which  is  even  more  delicate  in  its  indications  than  the 
ammonia  reaction,  being  still  visible  in  a  solution  containing  1  part  of  copper  in 
400,000  parts  of  liquid,  according  to  Lassaigne,  and  in  1,000,000  parts,  according 
to  Sarzeau.  Ferrocyanide  of  copper  dissolves  in  aqueous  ammonia,  and  reappears 
when  the  ammonia  is  evaporated.  This  reaction  serves  to  detect  extremely  small 
quantities  of  copper,  even  when  associated  with  other  metals.  Thus,  if  a  solution 
containing  copper  and  iron  be  treated  with  excess  of  ammonia,  a  few  drops  of 
ferrocyanide  of  potassium  added,  the  liquid  filtered,  and  the  filtrate  left  to  evapo- 
rate in  a  small  white  porcelain  capsule,  ferrocyanide  of  copper  will  be  left  behind, 
exhibiting  its  characteristic  red  colour  (Warington).  Salts  of  copper  impart  a 
green  colour  to  flame.  The  black  oxide  of  copper  dissolves  by  fusion  in  a  vitreous 
flux,  and  produces  a  green  glass.  Any  compound  of  copper  fused  with  borax  in 
the  oxidizing  flame  of  the  blowpipe  forms  a  transparent  glass,  which  is  green  while 
hot,  but  assumes  a  beautiful  blue  colour  when  cold.  In  the  reducing  flame,  the 
glass  becomes  opaque,  add  covered  on  the  surface  with  liver-coloured  streaks  of 
cuprous  oxide,  or  metallic  copper.  This  last  reaction  is  somewhat  difficult  to 
obtain,  especially  when  the  quantity  of  copper  is  small,  but  it  may  always  be 
ensured  by  fusing  a  small  piece  of  metallic  tin  in  the  bead.  Copper  salts  mixed 
with  carbonate  of  soda  or  cyanide  of  potassium,  and  heated  on  charcoal  before  the 
blowpipe,  yield  metallic  copper. 

Thenard  obtained  a  higher  oxide  of  copper,  Cu02,  by  the  action  of  diluted 
bioxide  of  hydrogen  on  the  hydrated  protoxide  of  copper. 

Chloride  of  copper,  cupric  chloride,  CuCl,  is  obtained  by  dissolving  the  black 
oxide  in  hydrochloric  acid.  Its  solution  is  green  when  concentrated,  but  blue 
when  more  dilute,  and  the  salt  forms  blue  prismatic  crystals,  containing  two  atoms 
of  water.  It  combines  with  chloride  of  potassium,  and  more  readily  with  chloride 
of  ammonium,  forming  the  double  salts  KCl.CuCl  -f  2HO,  NH4Cl.CuGl  -f  2HO. 
Another  chloride  of  copper  and  ammonium,  containing  NH4C1  2CuCl  +  4HO,  is 
obtained  in  fine  bluish-green  crystals,  by  mixing  the  solution  of  1  eq.  sal-ammoniac 
and  2  eq.  chloride  of  copper. 

Chloride  of  copper  likewise  combines  with  ammonia,  forming  the  three  following 
compounds: — a.  3NH3.CuCl.  This  compound  is  obtained  by  saturating  dry  pro- 
tochloride  of  copper  with  ammoniacal  gas:  it  forms  a  blue  powder.  —  b.  2NH3. 
CuCl.  Formed  by  passing  ammoniacal  gas  through  a  hot  saturated  solution  of 
protochloride  of  copper,  till  the  precipitate  first  formed  is  completely  redissolved. 
During  this  process,  the  liquid  is  kept  almost  boiling  by  the  heat  developed  by  the 
absorption  of  the  gas;  and  the  resulting  solution  yields,  on  cooling,  small  dark 
blue  octahedrons  and  square  prisms  with  four-sided  summits. — c.  NH3.CuCl. 
Obtained  by  heating  a  or  b  to  300°,  or  by  saturating  dry  chloride  of  copper,  at  a 
high  temperature,  with  ammoniacal  gas.  Forms  a  green  powder.  The  compound 
c  may  also  be  regarded  as  chloride  of  cuprammonium,  NH3Cu.Cl,  or  hydrochlorate 
of  cupramine,  NH2Cu.HCl>  the  base  being  ammonium  or  ammonia  in  which  1H 


CUPRIC    SALTS.  481 

is  replaced  by  Cu.  Similarly,  b  may  be  regarded  as  a  basic  hydrochlorate  ofdicu- 
pramtne,  N2H5Cu.HCl,  the  base  being  formed  by  the  union  of  two  atoms  of  am- 
monia into  one,  and  the  substitution  therein  of  ICu  for  1H.  Lastly,  a  may  be 
regarded  as  basic  hydrochlorate  of  tricupramine,  N3H8Cu.HCl;  or  again,  a  may 

be  regarded  as  NHAm2Cu.Cl,  and  b  as  NH2AmCu.Cl. 

Carbonates  of  copper.  —  When  a  salt  of  copper  is  precipitated  by  an  alkaline 
carbonate,  a  hydrated  subcarbonate  is  produced  containing  2  eq.  of  oxide  of  copper 
to  1  eq.  carbonic  acid.  It  is  a  pale  blue  bulky  precipitate,  which  becomes  denser 
and  green  when  treated  with  boiling  water.  It  is  used  as  a  pigment,  and  known 
as  mineral  green.  The  beautiful  native  green  carbonate  of  copper,  malachite,  is 
of  the  same  composition,  CuO.Co2  +  CuO.HO.  The  finely  crystallized  blue  copper 
ore  is  another  subcarbonate.  It  may  be  represented  as  the  neutral  hydrated  car- 
bonate of  copper,  in  combination  with  a  similar  carbonate  of  copper,  in  which  the 
constitutional  water  is  replaced  by  oxide  of  copper : 

(CuO.C02-fHO. 
jCuO.COa-r-CuO. 

In  the  green  carbonate,  the  constitutional  water  of  the  neutral  carbonate  of  copper 
is  replaced  by  hydrate  of  copper.  The  neutral  carbonate  of  copper  itself,  of  which 
the  formula  would  be  CuO.C02-f  HO,  is  unknown.  According  to  Thomson,* 
the  anhydrous  subcarbonate  2CuO .  C02,  occurs  in  the  form  of  vnysorine,  which 
contains  also  ferric  oxide  and  silica. 

Sulphate  of  copper,  Cupric  sulphate,  Blue  vitriol,  CuO.S03.HO -f  4HO  J 
79-66  or  995-74-562  5.  —  This  salt  may  be  formed  by  dissolving  copper  in  sul- 
phuric acid  diluted  with  half  its  bulk  of  water,  with  ebullition ;  the  metal  is  then 
oxidated  with  formation  of  sulphurous  acid.  But  the  sulphate  of  copper  is  more 
generally  prepared,  on  the  large  scale,  by  the  roasting  and  oxidation  of  sulphide 
of  copper ;  or  by  dissolving  in  sulphuric  acid  the  oxide  formed  by  exposing  sheets 
of  metallic  copper  to  air  at  a  red  heat.  It  forms  large  rhomboidal  crystals  of  a 
sapphire-blue  colour,  containing  5  eq.  of  water,  which  lose  their  transparency  in 
dry  air  :  they  are  soluble  in  four  times  their  weight  of  cold,  and  twice  their  weight 
of  boiling  water.  Like  the  other  soluble  salts  of  copper,  the  sulphate  has  an  acid 
reaction ;  it  is  used  as  an  escharotic.  The  water  in  this  salt  may  be  reduced  to  1 
eq.  at  212°;  above  400°  the  salt  is  anhydrous  and  white.  Although  sulphate  of 
copper  does  not  crystallize  alone  with  7HO,  yet,  when  mixed  with  the  sulphates 
of  magnesia,  zinc,  nickel,  and  iron,  it  crystallizes  along  with  these  isomorphous 
salts  in  the  form  of  sulphate  of  iron.  At  a  strong  red  heat  it  melts  and  loses  acid. 

The  anhydrous  sulphate  absorbs  2£  eq.  of  ammonia,  and  forms  a  light  powder  of 
a  deep  blue  colour  (H.  Rose.)  When  ammonia  is  added  to  a  solution  of  sulphate 
of  copper,  an  insoluble  subsulphate  is  first  thrown  down,  which  is  redissolved  as 
the  addition  of  ammonia  is  continued,  and  the  usual  deep  azure-blue  ammoniacal 
solution  formed.  The  ammoniacal  sulphate  may  be  obtained  in  beautiful  indigo- 
blue  crystajs,  by  passing  a  stream  of  ammoniacal  gas  into  a  saturated  hot  solution 
of  the  sulphate  :  it  is  CuO  S03.HO-}-2NH3  (Berzelius).  These  crystals  lose  1  eq. 
ammonia  and  1  eq.  water  at  390°  (Kane),  and  are  converted  into  a  green  powder, 
CuO.S03  +  NH3,  or  (NH3CuO).S03;  by  the  cautious  application  of  a  heat  not 
exceeding  500°,  the  whole  of  the  ammonia  may  be  got  rid  of,  and  sulphate  of 
copper  quite  pure  remains  behind.  Sulphate  of  copper  forms  the  usual  double 
salts  with  sulphate  of  potash  and  with  sulphate  of  ammonia.  A  saturated  hot 
solution  of  the  double  sulphate  of  copper  and  potash  allows  a  remarkable  double 
subsalt  to  precipitate  in  crystalline  grains,  KO.  S03  +  3(<JuO.  S03)  -f-  CuO. 
HO-f3HO.  A  corresponding  seleniate  is  deposited,  below  the  boiling  point,  and 
always  in  crystals.  The  ammoniacal  and  double  salts  of  sulphate  of  copper  may 
be  represented  thus  :  — 

*  Outlines  of  Mineralogy. 

31 


482  COPPER. 

Sulphate  of  copper  (blue  vitriol)  ...........  CuO.S03,HO  f  4HO 

Sulphate  of  copper  and  potash  .............  CuO.S03,(KO.S03)+6HO 

Hydrated  aminoniacal  sulphate  of  copper,  CuO.S03,HO  -f  2NH 
Preceding  salt  dried  at  300°  ...............  (NH3.CuO).S03 

Rose's  ammoniacal  sulphate  ..............  CuO.S03  +  (NH3CuO)S03+4NH3 

Do.  heated  to  350°  ........................  CuO.S03+(NH3CuO)S03 

The  hydrated  ammoniacal  sulphate  may  also  be  regarded  as  NH!2(NH4)Cu.S04 
and  Rose's  ammoniacal  sulphate  as 


Several  subsulphates  of  copper  have  been  formed.  By  digesting  hydrated  oxide 
of  copper  in  a  solution  of  sulphate  of  copper,  a  green  powder  is  obtained,  of  which 
the  constituents  are,  according  to  Berzelius,  3CuO.S03  +  3HO.  The  bluish-green 
precipitate  which  falls  when  ammonia  is  added  to  sulphate  of  copper,  or  potash 
added  in  moderate  quantity  to  the  same  salt,  contains,  according  to  Kane's  and 
Graham's  analyses,  4CuO.S03  +  4HO.  By  a  larger  quantity  of  potash,  Kane  pre- 
cipitated a  clear  grass-green  subsulphate,  containing  8CuO.S03-}-12HO.  The 
last  subsulphate  loses  exactly  half  its  water  at  300°.* 

Nitrate  of  copper,  CuO.N05  -f-  3HO,  is  formed  by  dissolving  copper  in  nitric 
acid.  It  crystallizes  from  a  strong  solution  in  blue  prisms  which  contain  3  atoms 
of  water,  or  in  rhomboidal  plates  which  contain  6  atoms  of  water.  This  salt  acts 
upon  granulated  tin,  with  nearly  as  much  energy  as  hydrated  nitric  acid.  A 
crystallized  ammoniacal  nitrate  of  copper  is  obtained  by  conducting  a  stream  of 
;ammoniacal  gas  into  a  saturated  solution  of  nitrate  of  copper.  It  is  anhydrous,  and 

contains  N05.CuO  -f  2NH3  (Kane).     It  may  be  regarded  as  NH^(NH^)Cu.N06. 

Subnitrate  of  copper,  CuO  N05  -f-  3(CuO  .  HO),  according  to  the  analyses  of 
Gerhardt,  Gladstone,"}"  and  Kuhn,|  is  a  green  powder,  produced  by  the  action  of 
heat  upon  the  neutral  nitrate,  at  any  temperature  between  160°  and  600°  ;  or  by 
adding  to  that  salt  a  quantity  of  alkali  insufficient  for  complete  precipitation. 
When  oxide  of  copper  is  drenched  with  the  most  concentrated  nitric  acid 
(HO.N05),  it  is  this  subsalt,  singular  as  it  may  appear,  which  is  formed,  even 
when  the  acid  is  in  great  excess. 

Oxalate  of  copper  and  potash  is  obtained  by  dissolving  oxide  of  copper  in 
binoxalate  of  potash  ;  it  crystallizes  with  2  and  with  4  eq.  of  water. 

Acetates  of  copper.  —  The  neutral  acetate,  CuO.(C4H303)  -f-  HO,  or  C4H3Cu04  -f 
HO,  is  ^obtained  by  dissolving  oxide  of  copper  in  acetic  acid.  It  forms  fine  crys- 
tals of  a  deep  green  colour,  containing  1  eq.  of  water,  which  lose  their  trans- 
parency in  air,  and  are  soluble  in  5  times  their  weight  of  boiling  water.  This 
salt,  when  it  separates  from  an  acid  solution  below  40°,  also  forms  blue  crystals 
containing  5HO  (Wohler).  The  green  salt  is  found  in  commerce  under  the  im- 
proper name  of  distilled  verdigris.  The  acetates  of  copper  and  potash  unite  in 
single  equivalents,  and  form  a  double  salt  in  fine  blue  crystals,  containing  8HO. 
Verdigris  is  a  subacetate  of  copper,  formed  by  placing  plates  of  the  metal  in  con- 
tact with  the  fermenting  marc  of  the  grape,  or  with  cloth  dipped  in  vinegar. 
The  bluer  species,  which  consists  of  minute  crystalline  plates,  is  a  definite  coin- 
coHipound  of  1  eq.  acetic  acid,  2  eq.  oxide  of  copper,  and  6  eq.  of  water. 
C4H3Cu04.CuO  +  6HO.  The  ordinary  green  species  is  a  mixture  of  the  sesqui- 
and  tribasic  acetates  of  copper,  with  the  preceding  bibasic  acetate.  Water  dis- 
solves out  from  verdigris  the  sesquibasic  acetate,  which  presents  itself  on  evapo- 

*  Transactions  of  the  Royal  Irish  Academy,  vol.  xix.  p.  1  ;  or  Ann.  Ch.  Phys.  t.  Ixxii.  p. 
^72. 
f  Chem.  Soc.  Mem.  iii.  480.  $  Arch.  Pharm.  [2.],  1.  283. 


ESTIMATION    OF    COPPER.  483 

ratin^  the  solution,  sometimes  as  an  amorphous  mass,  and  sometimes  in  crystalline 
grains  of  a  pale  blue  colour.  The  sesquibasic  acetate  consists  of  2  eq.  of  acetic 
acid,  3  eq.  of  oxide  of  copper,  and  6  eq.  of  water;  it  loses  3  eq.  of  water  at 
212°.  The  tribasic  acetate  is  the  insoluble  residue  which  remains  after  the 
lixiviation  of  verdigris.  It  is  a  clear  green  powder,  which  loses  nothing  at  212°. 
It  contains  2  eq.  of  acetic  acid,  6  eq.  oxide  of  copper,  and  3  eq.  of  water 
(Berzelius). 

Acetate  of  copper  also  combines  with  acetate  of  lime,  and  with  several  other 
salts.  The  double  acetate  and  arsenite  of  copper  is  a  crystalline  powder  of  a 
brilliant  sea-green  colour,  which  is  used  as  a  pigment,  under  the  name  of 
Schweinfurt  green.  It  is  obtained  by  mixing  boiling  solutions  of  equal  parts  of 
arsenious  acid  and  neutral  acetate  of  copper,  adding  to  the  mixture  its  own  volume 
of  cold  water,  and  leaving  the  whole  at  rest  for  several  days.  It  is  a  highly 
poisonous  substance.  From  the  analysis  of  Ehrmann,  its  formula  is  C4H3Cu04  + 
3(CuO.As03). 

The  most  important  alloys  of  copper  are  those  which  it  forms  with  tin  and 
zinc  : 

100  parts  of  copper  with  5  tin  (or  4  tin  -f  1  zinc)  form  the  bronze  used  for 
coin. 

100  parts  copper  with  10  tin,  form  bronze  and  gun-metal. 

100  parts  copper  with  20  to  25  tin,  form  bell-metal. 

100  parts  copper  with  30  to  35  tin,  form  speculum-metal. 

A  little  arsenic  is  generally  added  to  the  last  alloy,  to  increase  its  whiteness. 

The  different  varieties  of  brass  are  prepared,  either  by  fusing  together  the  two 
metals,  copper  and  zinc,  or  by  heating  copper  under  a  mixture  of  charcoal  and 
oalamine  —  an  operation  in  which  zinc  is  reduced  and  its  vapour  absorbed  by  the 
copper.  Two  or  three  parts  of  copper  to  one  of  zinc  form  common  brass.  The 
brass  known  as  Muntz's  white  metal,  which  resists  the  solvent  action  of  sea-water 
much  better  than  pure  copper,  and  is,  in  consequence  largely  used  for  the  sheath- 
ing of  ships,  consists  of  60  parts  copper  to  40  parts  zinc,  and  appears  to  be  the 
atomic  compound  Cu2Zn.  Equal  parts  of  copper  and  zinc,  or  four  of  the  former 
and  one  of  the  latter,  give  an  alloy  of  a  higher  colour,  resembling  gold,  and  on 
that  account  called  similar. 

ESTIMATION     OF     COPPER,     AND     METHODS     OF     SEPARATING     IT     FROM     OTHER 

METALS. 

Copper  is  best  precipitated  by  caustic  potash,  which  when  added  to  a  boiling 
solution  of  a  cupric  salt,  throws  down  the  protoxide  of  copper  in  the  form  of  a 
heavy  black  powder.  From  this  precipitate  every  trace  of  potash  may  be  removed 
by  washing  with  hot  water ;  and  the  washed  precipitate  may  then  be  dried  and 
ignited  in  a  platinum  or  porcelain  crucible.  It  must  be  weighed  immediately 
after  cooling,  with  the  cover  on  the  crucible,  because  it  absorbs  moisture  rapidly 
from  the  air.  It  contains  79*82  per  cent,  of  copper  (H.  Rose). 

Copper  is  often  precipitated  from  its  solutions  by  hydrosulphuric  acid.  In  that 
case  the  precipitated  sulphide  must  be  washed  as  quickly  as  possible  with  water 
containing  hydrosulphuric  acid,  to  prevent  oxidation ;  the  precipitate  may  then  be 
dried,  and  the  filter  burnt  with  the  precipitate  on  it,  in  a  porcelain  basin ;  after 
which  the  precipitate  is  treated  with  concentrated  nitric  acid,  which  dissolves  it, 
with  separation  of  sulphur,  and  the  copper  precipitated  from  the  filtered  solution 
by  potash  as  above.  The  chief  precaution  to  be  attended  to  in  this  process  is  to 
wash  the  precipitated  sulphide  quickly,  and  to  preserve  it  as  completely  as  possible 
from  contact  with  the  air;  otherwise  the  sulphide  becomes  partially  oxidized  and 
converted  into  sulphate,  which  being  soluble,  runs  through  the  filter;  when  this 
takes  place,  the  filtrate  becomes  brown,  because  the  copper  thus  carried  through, 
is  again  precipitated  by  hydrosulphuric  acid 


484  COPPER. 

Volumetric  methods. — Copper  may  be  volumetrically  determined  by  means  of  a 
solution  of  permanganate  of  potash,  by  a  process  founded  on  that  adopted  by 
Margueritte  for  the  determination  of  iron  (p.  458).  The  copper  compound 
having  been  weighed  and  dissolved  in  acid,  is  mixed  in  a  porcelain  basin,  with 
neutral  tartrate  of  potash  and  excess  of  caustic  potash,  and  then  heated  with  a 
quantity  of  milk-sugar,  or  honey,  sufficient  to  precipitate  all  the  copper  as  cuprous 
oxide,  the  completion  of  the  precipitation  being  indicated  by  the  brown  colour 
which  the  liquid  then  acquires.  The  precipitated  cuprous  oxide  is  then  filtered, 
washed  with  hot  water,  and  gently  heated,  together  with  the  filter,  with  a  mixture 
of  pure  sesquichloride  of  iron  and  dilute  hydrochloric  acid.  It  is  thereby  dis- 
solved in  the  form  of  protochloride  of  copper,  the  sesquichloride  of  iron  being  at 
the  same  time  reduced  to  protochloride : 

Cu20  +  Fe2Cl3  -I-  HC1  =  2CuCl  +  2FeCl  +  HO. 

In  the  filtered  liquid,  diluted  to  a  convenient  strength  and  heated  to  about  86°, 
the  quantity  of  iron  in  the  state  of  protochloride  is  determined  by  a  graduated 
solution  of  permanganate  of  potash  in  the  manner  already  described  (p.  458),  and 
thence  the  equivalent  quantity  of  copper  is  readily  determined.  The  presence  of 
lead,  zinc,  bismuth,  manganese,  or  iron,  in  the  alkaline  solution,  does  not  interfere 
with  the  process ;  silver  or  mercury  must  be  separated  before  the  precipitation  of 
the  cuprous  oxide. 

Another  method,  which  appears  to  give  very  exact  results,  is  to  treat  the 
copper-solution  with  iodide  of  potassium,  whereby  diniodide  of  copper  is  precipi- 
tated and  iodine  set  free  : 

2(CuO.N05)  +  2KI  =  Cu2  + I  +  2(KO.N05), 

and  remove  the  free  iodine  by  means  of  a  standard  solution  of  hyposulphite  of 
soda,  whereby  iodide  of  sodium  and  tetrathionate  of  soda  are  produced : 

2(NaO.S202)  +  I  =  Nal  +  NaO.S403. 

The  copper-compound,  if  solid,  an  alloy  for  example,  is  dissolved  in  nitric  acid ; 
carbonate  of  soda  added  till  a  slight  precipitate  is  formed ;  and  this  precipitate  re- 
dissolved  in  acetic  acid  (free  nitric  acid  would  vitiate  the  result  by  decomposing 
the  iodide  of  potassium).  A  quantity  of  iodide  of  potassium  is  next  added,  equal 
to  at  least  six  times  the  weight  of  the  copper  to  be  determined,  and  then  the 
standard  solution  of  hyposulphite  of  soda,  in  sufficient  quantity  to  remove  the 
greater  part  of  the  free  iodine,  which  point  will  be  indicated  by  the  colour  of  the 
liquid  changing  from  brown  to  yellow.  Lastly,  a  clear  solution  of  starch  is  added, 
and  the  addition  of  the  hyposulphite  of  soda  cautiously  continued  till  the  blue 
colour  of  the  iodide  of  starch  is  completely  destroyed.  The  solution  of  hyposul- 
phite of  soda  is  graduated  by  dissolving  a  known  weight  of  pure  electrotype 
copper  in  nitric  acid,  and  proceeding  as  above.  If  the  copper-compound  contains 
a  large  quantity  of  lead  or  iron,  these  metals  must  be  removed  before  commencing 
the  determination,  because  the  yellow  colour  of  the  iodide  of  lead  and  the  red  of 
the  acetate  of  iron  might  interfere  with  the  result  (E.  0.  Brown).* 

Pelouze's  method,  which  consists  in  treating  the  copper  solution  with  excess  of 
ammonia,  and  precipitating  the  copper  as  oxysulphide,  Cu0.5CuS,  by  adding  a 
graduated  solution  of  sulphide  of  sodium  till  the  blue  colour  is  completely  de- 
stroyed, appears,  from  Mr.  Brown's  experiments,  to  be  liable  to  uncertainty  from 
two  causes :  first,  because  the  oxysulphide  of  copper  reduces  a  portion  of  the  prot- 
oxide of  copper  to  dioxide,  thereby  rendering  the  solution  colourless  before  the 
precipitation  is  complete ;  and  secondly,  because  a  portion  of  the  sulphide  of 
sodium  is  oxidized  and  converted  into  hyposulphite  of  soda. 

Copper  is  separated  from  all  the  preceding  metals,  except  cadmium,  by  means 

*  In  a  paper  read  before  the  Chemical  Society,  Nov.  17th,  1856,  and  to  be  published  in 
the  10th  volume  of  the  Society's  Journal. 


LEAD.  485 

of  hydrosulphuric  acid,  the  solution  being  previously  acidulated  with  hydrochloric 
or  sulphuric  acid.  When  zinc,  nickel,  or  cobalt  is  present,  a  considerable  excess 
of  acid  must  be  added,  otherwise  a  portion  of  these  metals  will  be  precipitated 
together  with  the  copper. 

From  cadmium,  copper  may  be  separated  by  carbonate  of  ammonia,  which  dis- 
solves the  cppper  and  leaves  the  cadmium.  The  deposition  of  the  cadmium  is 
not  complete  till  the  liquid  has  been  exposed  for  some  time  to  the  air.  The  sepa- 
ration is,  however,  better  effected  by  adding  to  the  solution  of  the  two  metals  a 
quantity  of  cyanide  of  potassium,  sufficient  to  redissolve  the  precipitate  first 
formed,  and  then  passing  hydrosulphuric  acid  through  the  solution.  Sulphide  of 
cadmium  is  then  precipitated,  and  on  driving  off  the  excess  of  hydrosulphuric 
acid  by  heat,  and  adding  more  cyanide  of  potassium,  the  sulphide  of  copper 
remains  completely  dissolved.  The  copper  may  be  precipitated  as  sulphide  by 
mixing  the  filtrate  with  hydrochloric  acid  :  but  it  is  better  to  boil  the  filtrate  with 
aqua-regia,  till  all  the  hydrocyanic  acid  is  expelled,  and  then  precipitate  the  copper 
by  potash  (Haidlen  and  Fresenius). 


SECTION   VIII. 

LEAD. 

Eq.  103-56  or  1294-5;  Pb  (plumbum). 

Lead  was  one  of  the  earliest  known  of  the  metals.  A  considerable  number  of 
its  compounds  are  found  in  nature,  but  the  sulphide,  or  galena,  is  the  only  one 
which  is  important  as  an  ore  of  lead.  The  reduction  of  the  metal  is  effected  by 
heating  the  sulphide  with  exposure  to  air  (or  roasting),  by  which  much  of  the 
sulphur  is  burned  and  escapes  as  sulphurous  acid,  and  a  fusible  mixture  of  oxide 
of  lead  and  sulphate  of  lead  is  produced.  A  fresh  portion  of  the  ore  is  added, 
which  reacts  upon  the  oxide  of  lead,  the  sulphur  and  oxygen  forming  sulphurous 
acid,  and  the  lead  of  both  oxide  and  sulphide  being  consequently  reduced.  Lime 
also  is  added,  which  decomposes  the  sulphate  of  lead,  and  exposes  the  oxide  to  be 
reduced  by  the  fuel  or  by  sulphide. 

Lead  has  a  bluish  grey  colour  and  strong  metallic  lustre,  is  very  malleable,  and 
so  soft,  when  it  has  not  been  cooled  rapidly,  as  to  produce  a  metallic  streak  upon 
paper.  Its  density  is  11-445,  and  is  not  increased  by  hammering.  Its  tenacity 
is  less  than  that  of  any  other  ductile  metal.  The  melting  point  of  lead  is  612° ; 
on  solidifying,  this  metal  shrinks  considerably,  so  that  bullets  cast  in  a  mould  are 
never  quite  round.  Lead,  like  most  other  metals,  assumes  the  octohedral  form  oil 
crystallizing.  Lead  is  one  of  the  less  oxidable  metals,  at  least  when  massive  \  its 
surface  soon  tarnishes,  and  is  covered  with  a  grey  pellicle,  which  appears  to  defend 
the  metal  from  further  change.  Rain  or  soft  water  cannot  be  preserved  with  safety 
in  leaden  cisterns,  owing  to  the  rapid  formation  of  a  white  hydrated  oxide  at  the 
line  where  the  metal  is  exposed  to  both  air  and  water ;  the  oxide  formed  is  soluble 
in  pure  water,  and  highly  poisonous.  But  a  small  quantity  of  carbonic  acid, 
which  spring  and  well  water  usually  contain,  arrests  the  corrosion  of  the  lead,  by 
converting  the  oxide  of  lead  into  an  insoluble  salt,  and  prevents  the  contamination 
of  the  water.*  Lead  is  not  directly  attacked  by  hydrochloric  and  sulphuric  acids, 
at  the  usual  temperature,  but  they  favour  its  union  with  oxygen  from  the  air.  Its 
best  solvent  is  nitric  acid.  Besides  a  protoxide,  PbO,  which  is  a  powerful  base, 
lead  forms  a  suboxide,  Pb/),  and  a  bioxide,  Pb02,  which  do  not  combine  with 
acids. 

Suboxide  of  lead,  Pb20,  was  discovered  by  Dulong,  and  is  best  obtained  by 

*  Dr.  Christison's  Treatise  on  Poisons. 


486  LEAD. 

heating  the  oxalate  of  lead  to  low  redness  in  a  small  retort.  It  is  dark  grey,  almost 
black,  and  pulverulent,  and  is  not  affected  by  metallic  mercury.  According  to  the 
analysis  of  Boussingault,  it  contains  1  eq.  of  oxygen  to  2  eq.  of  lead.  The  grey 
pellicle  which  forms  upon  lead  exposed  to  the  air  is,  according  to  Berzelius,  the 
same  suboxide. 

Protoxide  of  lead,  PbO,  111-56  or  1894  5. — When  a  stream  of  air  is  thrown 
upon  the  surface  of  melted  lead,  the  metal  is  rapidly  converted  into  the  protoxide, 
of  a  sulphur-yellow  colour.  The  oxidated  skimmings  of  the  metal  are,  in  this 
condition,  termed  massicot,  and  were  at  one  time  used  as  a  yellow  pigment.  This 
preparation  is  fused  at  a  bright  red  heat,  and  the  oxide  is  thus  separated  from 
some  metallic  lead,  with  which  it  is  intermixed  in  massicot.  The  fused  oxide,  on 
solidifying,  forms  a  brick-red  mass,  which  divides  easily  into  crystalline  scales, 
tough  and  not  easily  pulverized ;  they  form  litharge.  The  protoxide  of  lead  can 
be  obtained  distinctly  crystallized  by  various  processes,  but  always  presents  itself 
in  the  same  form,  an  octohedron  with  a  rhombic  base  (Mitscherlich).  By  igniting 
the  subnitrate  of  lead,  the  protoxide  is  obtained  very  pure,  and  of  a  rich  lemon- 
yellow  colour.  Its  density  after  fusion  is  9-4214. 

When  the  acetate,  or  any  other  salt  of  lead,  is  precipitated  by  potash,  the  prot- 
oxide falls  as  a  white  hydrate,  which  may  be  dried  at  212°  without  decomposition. 
It  contains  of  per  cent,  water,  and  is,  therefore,  the  hydrate  2PbO .  HO  (Mits- 
cherlich). Oxide  of  lead  likewise  crystallizes  anhydrous,  from  solution,  at  the 
usual  temperature,  when  precipitated  under  such  circumstances  that  it  cannot  find 
water  to  combine  with.  This  oxide  dissolves  in  above  12,000  times  its  weight  of 
distilled  water,  which  acquires  thereby  an  alkaline  reaction,  but  not  in  water  con- 
taining any  saline  matter.  It  is  soluble  in  potash  or  soda ;  and  the  solutions,  when 
evaporated,  yield  small  crystals  of  an  alkaline  compound.  A  compound  of  lime 
and  oxide  of  lead  is  obtained  in  needles,  when  hydrate  of  lime  and  that  oxide  are 
heated  together,  and  the  solution  allowed  to  evaporate  with  exclusion  of  air.  This 
solution  has  been  employed  to  dye  the  hair  black.  Oxide  of  lead  combines  readily 
with  the  earths  and  metallic  oxides  by  fusion,  and  when  added  to  the  materials  of 
glass,  imparts  brilliancy  to  it  and  increased  fusibility. 

Oxide  of  lead  is  a  powerful  base,  resembling  baryta  and  strontia,  and  affords  a 
class  of  salts  which  often  agree  in  form  and  in  general  properties  with  the  salts  of 
these  earths.  Its  carbonate  occurs  in  plumbocalcite,  in  the  form  of  carbonate  of 
lime,  an  isomorphism  by  which  the  protoxide  of  lead  is  connected  with  the  mag- 
nesian  oxides.  All  its  soluble  salts  are  poisonous,  although  no  salt  of  lead,  with 
the  exception  of  the  insoluble  carbonate,  is  highly  so  (Dr.  A.  T.  Thomson).  In 
a  case  of  accidental  poisoning  by  the  carbonate,  acetic  acid  proved  a  sufficient 
antidote.  • 

Caustic  alkalies  precipitate  lead  from  its  solutions  as  a  white  hydrate,  soluble 
in  potash  and  soda,  insoluble  in  ammonia.  Alkaline  carbonates  throw  down  a 
white  precipitate  of  carbonate  of  lead,  insoluble  in  excess  of  the  reagent.  Hydro- 
chloric acid  and  soluble  chlorides  produce  in  moderately  strong  lead-solutions,  a 
white  crystalline  precipitate  of  chloride  of  lead,  easily  soluble  in  potash,  insoluble 
in  ammonia,  soluble  in  a  considerable  quantity  of  water ;  in  dilute  solutions  (e.  y. 
in  a  solution  of  1  part  of  nitrate  of  lead  in  100  parts  of  water)  no  precipitate  is 
formed.  Sulphuric  acid  and  soluble  sulphates  throw  down,  even  from  very  dilute 
solutions,  a  white,  pulverulent  precipitate  of  sulphate  of  lead,  easily  soluble  in 
potash,  soluble  also,  though  slowly,  in  hydrochloric  and  nitric  acid ;  but  by  adding 
a  considerable  excess  of  sulphuric  acid,  lead  may  be  completely  precipitated  even 
from  solutions  containing  hydrochloric  or  nitric  acid.  According  to  Lassaigne,  1 
part  of  oxide  of  lead  (in  the  form  of  nitrate)  dissolved  in  25,000  parts  of  water, 
gives  an  opalescence  with  sulphate  of  soda,  after  a  quarter  of  an  hour.  Hydro- 
sulphuric  acid  and  alkaline  sulphides  produce  a  black  precipitate  of  sulphide  of 
lead,  insoluble  in  sulphide  of  ammonium.  In  very  dilute  solutions,  only  a  brown 
colouring  is  produced,  the  limit  of  the  reaction  being  attained,  according  to  Las- 


PROTOXIDE    OF    LEAD.  487 

saigne,  with  1  part  of  oxide  of  lead  (in  the  form  of  nitrate)  dissolved  in  350,000 
parts  of  water.  If  the  solution  of  the  lead-salt  contains  free  hydrochloric  acid, 
the  precipitate  is  red  or  yellow,  and  a  large  excess  of  hydrochloric  acid  prevents 
it  altogether.  Iodide  of  potassium  produces  a  bright  yellow  precipitate  of  iodide 
of  lead,  which  dissolves  in  boiling  water  and  separates  ugain  on  cooling  in  crys- 
talline spangles,  exhibiting  a  beautiful  play  of  colours.  Chromate  and  bichromate 
of  potash  throw  down  yellow  chromate  of  lead,  easily  soluble  in  caustic  potash. 
The  limit  of  this  reaction  is  attained  with  1  part  of  oxide  of  lead  (in  the  form  of 
nitrate)  dissolved  in  70,000  parts  of  water  (Harting).  Iron  and  zinc  throw  down 
metallic  lead.  If  a  mass  of  zinc  be  suspended  in  a  solution,  made  by  dissolving 
one  ounce  of  acetate  of  lead  in  two  pounds  of  distilled  water,  the  lead  is  preci- 
pitated in  beautiful  crystalline  plates,  which  are  deposited  not  only  in  metallic  con- 
tact with  the  zinc,  but  extend  from  it  to  a  considerable  distance  in  the  liquid, 
forming  what  is  called  the  lead-tree.  Lead-salts,  mixed  with  carbonate  of  soda  or 
cyanide  of  potassium,  and  ignited  on  charcoal  before  the  blow-pipe,  yield  a  malle- 
able button  of  lead.  The  oxides  of  lead  are  reduced  by  simply  heating  them  with 
the  blow-pipe  flame  on  charcoal. 

Sesquioxide  of  lead,  Pb203.  —  Hypochlorite  of  soda  throws  down  from  lead- 
salts  a  reddish-yellow  mixture  of  sesquioxide  and  chloride  of  lead.  The  sesquioxide 
may  be  obtained  free  from  chloride  by  supersaturating  a  solution  of  nitrate  of  lead 
with  potash,  in  quantity  sufficient  to  redissolve  the  precipitated  hydrate,  and  then 
treating  it  with  hypochlorite  of  soda.  The  sesquioxide  is  converted  by  acids  into 
bioxide  and  an  ordinary  salt  of  lead  (Winkelblech). 

Bioxide  or  peroxide  of  lead,  Pb02,  may  be  obtained  in  the  same  manner  as  the 
peroxides  of  cobalt  and  nickel,  by  exposing  the  protoxide  suspended  in  water  to  a 
stream  of  chlorine ;  also  by  fusing  protoxide  of  lead  with  chlorate  of  potash  at  a  tem- 
perature short  of  redness ;  or  by  digesting  the  following  intermediate  oxide,  minium, 
in  diluted  nitric  acid,  which  dissolves  the  protoxide  of  lead,  decanting  off  the 
nitrate  of  lead,  and  washing  the  powder  which  remains  with  boiling  water. 
Wohler  precipitates  a  solution  of  4  parts  of  acetate  of  lead  with  a  solution  of  3 
parts  or  rather  more  of  crystallized  carbonate  of  soda,  and  passes  chlorine  gas 
through  the  resulting  thin  pulpy  mass,  till  the  whole  of  the  carbonate  of  lead  is 
converted  into  brown  bioxide,  amounting  to  2J  parts,  which  may  then  be  washed. 
No  chloride  of  lead  is  formed  in  this  reaction,  the  whole  of  the  chlorine  combining 
with  the  sodium,  while  acetic  and  carbonic  acid  are  set  free.  Bioxide  of  lead  is 
of  a  dark  earthy-brown  colour.  It  loses  half  its  oxygen  by  ignition;  absorbs 
sulphurous  acid  with  great  avidity,  and  becomes  sulphate  of  lead ;  and  affords 
chlorine  when  digested  in  hydrochloric  acid. 

Minium  or  red  lead  is  formed  by  heating  massicot  or  protoxide  of  lead,  which 
has  not  been  fused,  to  incipient  redness  in  a  flat  furnace,  of  a  particular  construc- 
tion, and  directing  a  current  of  air  upon  its  surface.  Oxygen  is  absorbed,  and  an 
oxide  formed  of  a  fine  red  colour,  with  a  shade  of  yellow.  It  is  not  constant  in 
composition.  The  proportion  of  oxygen,  when  the  absorption  is  least  considerable, 
approaches  that  of  a  compound  containing  3PbO.Pb02;  and  such  was  the  compo- 
sition of  a  crystallized  compound  of  a  fine  red  colour,  formed  by  accident  in  a 
minium  furnace,  and  analyzed  by  Houton-Labillardiere.  But  when  the  absorption 
is  favoured  by  time  and  most  considerable,  it  approaches  but  never  exceeds  2-4 
per  cent,  of  the  original  weight  of  the  protoxide.  This  result  agrees  with  the 
formula  Pb304,  and  accordingly  minium  may  be  regarded  as  a  compound  of  prot- 
oxide and  bioxide  of  lead,  2PbO.PbG2,  or  of  protoxide  and  sesquioxide,  PbO.Pb203. 
A  sample  of  minium  analyzed  by  Longchamps  contained  5PbO'.Pb02.  The  finest 
minium  is  obtained  by  calcining  oxide  of  lead  from  the  carbonate,  at  about  600°. 

Minium  is  not  altered  by  being  heated  in  a  solution  of  acetate  of  lead,  which  is 
capable  of  dissolving  free  protoxide  of  lead.  When  heated  to  redness,  it  loses 
oxygen,  and  leaves  the  protoxide.  It  does  not  combine  with  acids,  but  is  resolved 
by  a  strong  acid  into  bioxide  of  bad  and  protoxide,  the  latter  combining  with  the 


488  LEAD. 

acid.  When  minium  is  treated  with  concentrated  acetic  acid,  it  first  becomes 
white,  and  then  dissolves  entirely  in  a  new  quantity  of  acid  without  colouring  it. 
But  the  solution  gradually  decomposes,  and  bioxide  of  lead  separates  from  it  of  a 
blackish-brown  colour  (Berzelius). 

Protosulphide  of  lead ,  PbS,  is  thrown  down  from  salts  of  lead,  by  hydrosul- 
phuric  acid,  as  a  black  precipitate,  which  is  insoluble  in  diluted  acids  or  in  alkalies. 
It  forms  also  the  ore  galena,  which  crystallizes  in  the  cube  and  other  forms  of  the 
regular  system ;  its  density  is  7-585.  Sulphide  of  lead  is  decomposed  easily  by 
nitric  acid,  and  converted  into  nitrate  and  sulphate  of  lead,  with  separation  of  a 
little  sulphur.  The  more  concentrated  the  nitric  acid,  the  greater  is  the  quantity 
of  sulphate  produced.  Recently  precipitated  sulphide  of  lead  may  be  completely 
dissolved  in  the  form  of  nitrate  by  boiling  with  dilute  nitric  acid.  Concentrated 
and  boiling  hydrochloric  acid  dissolves  sulphide  of  lead,  with  disengagement  of 
hydrosulphuric  acid  gas.  Galena  may  be  united  by  fusion  with  more  le"ad,  and 
gives  the  subsulphides  Pb4S,  and  Pb2S.  When  a  solution  of  persulphide  of  potas- 
sium is  added  to  a  salt  of  lead,  a  blood-red  precipitate  appears,  which  is  a  persul- 
phide of  lead,  but  is  almost  immediately  changed  into  the  black  protosulphide  of 
lead  and  free  sulphur. 

Chloride  of  lead,  PbCl,  139-06  or  1738-25. —  Lead  dissolves  slowly  in  hydro- 
chloric  acid,  by  substitution  for  hydrogen,  forming  the  chloride  of  lead,  but  only 
when  assisted  by  the  action  of  the  air.  The  same  compound  is  obtained  by 
digesting  oxide  of  lead  in  hydrochloric  acid,  and  also  falls  as  a  white  precipitate, 
when  a  salt  of  lead  is  added  to  any  soluble  chloride.  The  chloride  of  lead  is 
soluble  in  135  times  its  weight  of  cold  water,  and  more  so  in  hot  water,  from 
which  it  crystallizes  on  cooling  in  long  flattened  acicular  crystals,  which  are  anhy- 
drous. It  is  very  fusible,  and  may  be  sublimed  at  a  higher  temperature. 

Oxy chloride  of  lead. —  Chloride  of  lead  combines  in  five  different  proportions 
with  the  protoxide,  forming  the  following  compounds:  —  a.  SPbCl.PbO.  Four 
parts  of  chloride  of  lead  ignited  with  1  part  of  litharge  yield  a  fused,  laminar, 
pearl-grey  mixture,  which,  when  triturated  with  water,  swells  up  to  a  bulky  mass 
having  the  above  composition  (Vauquelin).  The  same  substance  is  obtained  by 
Mr.  Pattinson,  by  decomposing  carbonate  of  lead  with  lime-water,  and  used  as  a 
white  pigment.  —  b.  PbCl.PbO.  Formed  by  igniting  chloride  of  lead  in  contact 
with  air  till  it  no  longer  fumes,  or  by  fusing  chloride  and  carbonate  of  lead 
together.  Carbonic  acid  is  then  set  free,  and  a  compound  formed  which  is  of  a 
deep  yellow  colour  while  fused,  but  as  it  cools  assumes  a  lemon-yellow  colour,  and 
becomes  nacreous  and  crystalline  (Dobereiner). — c.  PbCl  2PbO.  This  compound 
forms  the  mineral  Mendipite,  found  at  Mendip,  in  Somersetshire,  where  it  occurs 
in  yellowish-white,  right  rhombic  prisms,  which  are  harder  than  gypsum,  translu- 
cent, and  have  an  adamantine  lustre  (Berzelius).  It  also  occurs,  and  in  a  state 
of  greater  purity,  at  Brilon,  near  Stadtbergen,  in  Westphalia;  the  crystals  there 
found  are  white,  translucent,  and  have  a  mother-of-pearl  lustre  on  the  cleavage 
surfaces.*  —  d.  PbCl.SPbo.  Obtained  by  fusing  1  eq.  chloride  of  lead  with  3  eq. 
of  the  protoxide;  also  in  the  hydrated  state,  PbC1.3PbO  +  HO  or  4PbO.HCl,  by 
decomposing  chloride  of  lead  with  ammonia;  by  precipitating  subacetate  of  lead 
with  common  salt;  and  by  decomposing  a  solution  of  common  salt  with  protoxide 
of  lead.  The  hydrate  is  a  white  flocculent  mass,  and  when  fused  yields  the 
anhydrous  compound,  which  is  a  greenish-yellow  laminated  mass,  forming  a  yellow 
powder.  — e.  PbC1.5PbO.  Obtained  by  fusing  1  eq.  chloride  of  lead  with  5  eq. 
of  the  protoxide.  Orange-yellow  substance,  yielding  a  deep  yellow  powder.  — f. 
PbCUPbO,  is  produced  on  fusing  by  heat  a  mixture  of  10  parts  of  pure  oxide  of 
lead  and  1  part  of  pure  sal-ammoniac,  a  portion  of  the  lead  being  at  the  same  time 
reduced.  The  surbasic  chloride  when  fused  affords  cubic  crystals  on  cooling 
glowly.  It  forms  in  that  state  a  beautiful  yellow  pigment,  known  as  Turner's 

*  Rhodius,  Ann.  Ch.  Pharm.  Ixii.  373. 


CARBONATE    OF    LEAD.  489 

yellow  in  this  country,  and  Cassel  yellow  in  Germany.  It  was  prepared  in  Eng- 
land by  digesting  litharge  with  half  its  weight  of  common  salt,  a  portion  of  which 
is,  converted  into  caustic  soda,  and  afterwards  washing  and  fusing  the  oxychloride 
formed.  But  it  is  sufficient  to  use  1  part  of  salt  to  7  parts  of  oxide  of  lead  in  this 
decomposition. 

Bichloride  of  lead,  Pb012.  —  Bioxide  of  lead  dissolves,  without  evolution  of  gas, 
in  cold  dilute  hydrochloric  acid,  forming  a  rose-coloured  liquid,  from  which  alkalies 
throw  down  the  bioxide  in  its  original  state.  The  rose-coloured  acid  solution, 
evaporated  in  vacuo  over  strong  potash-ley,  yields  crystals  of  chloride  of  lead,  PbCl, 
together  with  crystals  of  a  different  character,  which  appear  to  consist  of  Pb012, 
(Rivot,  Beudant,  and  Daguin). 

Bromide  of  lead,  PbBr,  is  much  less  soluble  in  water  than  the  chloride;  hence, 
in  a  liquid  containing  hydrochloric  and  hydrobromic  acids,  if  the  bromine  be  pre- 
cipitated by  acetate  of  lead,  the  filtered  liquid  will  still  contain  chlorine,  which 
may  then  be  detected  by  adding  nitrate  of  silver  (H.  Rose). 

Iodide  of  lead,  Pbl,  229-92  or  2874.  —  Appears  as  a  beautiful  lemon-yellow 
powder,  when  iodide  of  potassium  is  added  to  a  salt  of  lead.  It  is  soluble  in  194 
parts  of  boiling  water,  and  in  1235  parts  of  water  at  the  usual  temperature,  and 
may  be  obtained  from  solution  in  brilliant  hexagonal  scales  of  a  golden-yellow 
colour.  A  compound  of  a  paler  yellow,  which  appears  in  dilute  solutions  and 
when  the  salt  of  lead  is  in  excess,  is  a  basic  iodide.  M.  Denot  finds  three  oxy- 
iodides  of  lead,  containing  1  eq.  of  iodide  of  lead  to  1  eq.,  2  eq.,  and  5  eq.,  of 
oxide  of  lead,  and  always  1  eq.  of  water,  which  last  they  do  not  lose  below  a  tem- 
perature of  about  400°. 

Neutral  iodide  of  lead,  Pbl,  is  decomposed  by  metallic  chlorides,  yielding,  when 
the  iodide  is  in  excess,  compounds  which  may  be  regarded  as  iodide  of  lead,  in 
which  part  of  the  iodine  is  replaced  by  chlorine.  Sesquichloride  of  iron  and  pro- 
tochloride  of  copper  separate  free  iodine  (A.  Engelhardt). 

Cyanide  of  lead,  PbCy,  is  a  white  insoluble  powder,  obtained  by  precipitation. 

Carbonate-  of  lead,  ceruse,  white  lead;  PbO.C02;  133-56  or  1(569-5. — Occurs 
in  nature  well  crystallized,  in  the  form  of  carbonate  of  baryta.  It  is  precipitated 
as  a  white  powder,  of  which  the  grains,  although  very  minute,  are  crystalline, 
when  an  alkaline  carbonate  is  added  to  the  acetate  or  nitrate  of  lead.  The  pre- 
cipitate is  anhydrous.  When  oxide  of  lead  is  left  covered  with  water  in  an  open 
vessel,  it  absorbs  carbonic  acid,  and  becomes  white,  forming  the  subcarbonate, 
PbO.C02  +  PbOHO. 

Carbonate  of  lead  is  invaluable  as  a  white  pigment,  from  its  great  opacity,  which 
gives  it  that  property  called  body  by  painters,  and  enables  it  to  cover  well.  As 
precipitated  by  an  alkaline  carbonate,  it  is  deficient  in  body,  owing  to  the  trans- 
parency of  the  crystalline  grains  composing  the  precipitate.  It  is  also  a  neutral 
carbonate,  as  thus  prepared,  and  differs  in  composition  from  the  ceruse  of  com- 
merce, which  Mulder  finds  always  to  contain  hydrated  oxide  of  lead  in  combina- 
tion with  the  carbonate  of  lead.  The  result  of  Mulder's  analyses  of  numerous 
specimens  of  white  lead,  is,  that  there  are  three  varieties  of  that  substance,  the 
composition  of  which  is  expressed  by  the  three  following  formulae  :  — 

2(PbO.C02)+ PbO.HO; 
5(PbO.C02)  +3(PbO.HO);  and 
3(PbO.CO,)  + PbO.HO.   ' 

Mr.  J.  A.  Phillips  has  also  examined  several  specimens  of  white  lead  prepared  by 
the  Dutch  process.  Four  samples  gave  by  analysis  the  formula,  2(PbO.C02)-{- 
PbO.HO;  one  gave  3(PbO.C02)-f  PbO.HO;  another,  5(PbO.C02) -j- PbO.HO.* 
,  Dr.  T.  Richardson  also  found  that  varieties  of  white  lead  contain  a  portion  of 
oxide  of  lead,  in  addition  to  the  carbonate,  and  so  far  confirms  the  conclusions  of 
Mulder. 

*  Chem.  Soc.  Qu.  Pt.  iv.  p.  165. 


490  LEAD. 

la  the  old  or  Dutch  mode  of  preparing  white  lead,  which  is  still  extensively 
practised,  thin  sheets  of  the  metal  are  placed  over  gallipots  containing  weak  acetic 
acid  (water  with  about  2£  per  cent,  dry  acid),  themselves  imbedded  in  fermenting 
tan,  the  temperature  of  which  varies  from  140°  to  150°.  The  action  is  often  very 
rapid,  and  the  metal  disappears  in  a  few  weeks  to  the  centre  of  the  sheet.  In 
this  process,  from  2  to  2J  tons  of  lead  (4480  to  5600  pounds)  are  converted  into 
carbonate,  by  a  quantity  of  vinegar  which  does  not  contain  more  than  the  small 
quantity  of  50  pounds  of  dry  acetic  acid.  Hence  the  metal  is  certainly  neither 
oxidized  nor  carbonated  in  this  process,  at  the  expense  of  the  acetic  acid.  The 
oxygen  must  be  derived  from  the  air,  and  the  carbonic  acid  from  the  fermenting 
tan.  In  the  newer  process,  litharge,  without  any  preparation,  is  mixed  with  water 
and  about  1  per  cent,  of  acetate  of  lead,  and  carbonic  acid  gas  passed  over  it ;  the 
oxide  of  lead  is  rapidly  converted  into  excellent  ceruse.  There  can  be  little  doubt 
that  all  the  oxide  of  lead  is  successively  dissolved  by  the  acetate,  and  presented 
to  the  carbonic  acid  as  a  soluble  subacetate :  a  compound  which,  it  is  known, 
absorbs  carbonic  acid  with  the  greatest  avidity,  and  allows  its  excess  of  oxide  to 
precipitate  as  carbonate  of  lead.  The  new  process  supplies  likewise  the  theory  of 
the  old  one,  the  function  of  the  acetic  acid  being  manifestly  the  same  in  both 
processes.  Nitrate  of  lead  has  been  substituted  for  the  acetate,  with  other  things 
the  same  as  in  the  last  process. 

Sulphate  of  lead  ;  PbO,  S03;  151-56  or  1894-5.—  This  salt  is  precipitated 
when  sulphuric  acid  or  a  soluble  sulphate  is  added  to  a  solution  of  acetate  or 
nitrate  of  lead,  as  a  white,  dense,  insoluble  precipitate,  which  appears  by  the 
microscope  to  be  composed  of  minute  crystals.  It  is  also  formed  by  the  action  of 
strong  nitric  acid  on  sulphide  of  lead.  Sulphate  of  lead  contains  in  100  parts, 
26-44  sulphuric  acid  and  73-56  oxide  of  lead,  and  may  be  exposed  to  a  red  heat 
without  decomposition.  Dr.  Richardson  finds  that  this  salt  acquires  considerable 
opacity,  arid  may  be  substituted  for  ceruse,  when  prepared  in  a  mode  analogous  to 
the  new  process  for  that  substance ;  namely,  by  supplying  sulphuric  acid,  in  a 
gradual  manner,  to  a  thick  mixture  of  litharge  and  water  containing  a  small  pro- 
portion of  acetate  of  lead.  In  this  manner  the  sulphate  of  lead  may  be  obtained 
united  with  any  desirable  excess  of  oxide  of  lead. 

Nitrate  of  lead;  PbO.N05;  165-56  or  2069-5.  —  Obtained  by  dissolving 
litharge,  at  the  boiling  point,  in  slightly  diluted  nitric  acid,  which  should  be  free 
from  hydrochloric  and  sulphuric  acids.  The  neutral  nitrate  crystallizes  in  large 
octahedrons,  with  the  secondary  faces  of  the  cube,  sometimes  transparent, 
although  generally  white  and  opaque.  The  crystals  are  anhydrous;  they  are 
soluble  in  7£  times  their  weight  of  cold,  and  in  a  much  smaller  quantity  of  hot, 
water.  Nitrate  of  lead  is  decomposed  by  an  incipient  red  heat,  yielding  a  mixture 
of  oxygen  gas  and  peroxide  of  nitrogen  (which  is  prepared  in  this  way),  and 
leaving  the  yellow  oxide  of  lead.  When  a  small  quantity  of  ammonia  is  added  to 
nitrate  of  lead,  or  when  a  dilute  solution  of  the  neutral  salt  is  boiled  with  oxide 
of  lead  in  fine  powder,  a  soluble  bibasic  nitrate  of  lead  is  formed,  PbO.N05  + 
PbO.  It  crystallizes  during  evaporation  in  fine  scales,  or  in  little  opaque  grains, 
which  are  anhydrous.  The  granular  crystals  decrepitate  when  heated,  with  ex- 
traordinary force.  The  tribasic  nitrate  of  lead  precipitates  when  ammonia  is 
added  in  very  slight  excess  to  a  solution  of  nitrate  of  lead.  Its  constituents  are 
2(3PbO.N05)-j-3jhLO  (Berzelius).  It  is  a  white  powder,  which  is  soluble  to  a 
small  extent  in  pure  water.  When  nitrate  of  lead  is  digested  with  a  considerable 
excess  of  ammonia,  the  decomposition  stops  at  the  point  at  which  6  eq.  of  oxide 
of  lead  are  combined  with  1  eq.  of  nitric  acid.  The  sexbasic  nitrate  of  lead 
contains  2(6PbO.NO:>  -f  3HO  (Berzelius). 

Nitrites  of  lead.  —  When  a  solution  of  100  parts  of  nitrate  of  lead  is  boiled 
with  78  parts  of  metallic  lead  in  thin  turnings,  the  lead  is  dissolved,  and  a  little 
nitric  oxitie  is  evolved,  in  consequence  of  a  partial  decomposition  of  nitrous  acid 
previously  formed.  The  solution  is  alkaline  and  yellow ;  and  gives,  on  cooling . 


SALTS    OF    LEAD.  491 

brilliant  crystalline  plates  of  a  golden  yellow  colour,  which  consists  of  the  libasic 
nitrite  of  lead,  2PbO.N03.  By  dissolving  100  parts  of  this  salt  in  water  at 
167°  (75°C.),  and  then  mixing  with  the  solution  35  parts  of  oil  of  vitriol,  pre- 
viously diluted  with  four  times" its  weight  of  water,  one  half  of  the  oxide  of  lead 
is  precipitated  as  sulphate  of  lead,  and  a  solution  is  obtained  of  a  deep  yellow 
colour,  from  which  the  neutral  nitrite  of  lead,  PbO.N03+HO,  crystallizes.  This 
salt  gives  yellow  crystals,  resembling  the  nitrate  in  form.  Its  solution  absorbs 
oxygen  from  the  air,  and,  like  all  the  nitrites,  gives  off  nitric  oxide  at  176 
(80°C.),  while  a  subnitrite  of  lead  precipitates.  Berzelius,  to  whom  we  are  in- 
debted for  the  preceding  facts,  also  formed  a  quadribazic.  nitrite  of  lead,  con- 
taining N03.4PbO  4- HO,  by  boiling  1  part  of  nitrate  of  lead,  and  1J  parts  or 
more  of  metallic  lead,  in  a  long-necked  flask  for  12  hours,  then  filtering  and  leaving 
the  solution  to  crystallize  by  cooling:  it  thus  yields  pale,  flesh-coloured,  silky 
needles,  or,  if  rapidly  coolod,  a  white  powder. 

The  nitrites  of  lead  have  also  been  examined  by  other  chemists,  who  have 
obtained  results  differing  from  those  of  Berzelius.  Thus,  Peligot  and  others  found 
that  Berzelius's  bibasic  nitrite  contains  the  elements  of  2  eq.  of  oxide  of  lead,  1 
eq.  of  hypouitric  acid,  N04,  and  1  eq.  of  water.  Grerhardt  therefore  regards  it  as 
a  compound  of  bibasic  nitrate  and  bibasic  nitrite  of  lead  :  — 

2(PbO.N04)  =  2PbO.N03  +  2PbO.N05. 
and  expresses  its  formation  by  the  equation  :  — 

2(PbO.N06)  +  2Pb  =  2PbO.N06  +  2PbO.N03. 

If  the  action  of  the  metallic  lead  be  further  continued,  a  fresh  portion  of  nitrate  is 
deoxidized,  and  the  result  is  an  orange-coloured  salt,  containing  7Pb0.2N04  (Peli- 
got), which  Grerhardt  regards  as  a  double  salt  more  basic  than  the  former : 

7Pb0.2N04  =  4PbO.N03+  3PbO.N05. 

Finally,  by  the  continued  action  of  the  lead,  the  subnitrate  contained  in  these  two 
salts  is  likewise  reduced,  and  a  subnitrite  is  formed,  viz.,  either  Berzelius's  quad- 
robasic  salt,  4PbO.N03,  or  a  bibasic  nitrite  2PbO.N03,  obtained  by  Bromeis. 
The  last  salt  crystallizes  in  long  golden-yellow  needles  containing  1  eq.  of  water.* 

Phosphate  of  lead. — On  mixing  nitrate  of  lead  with  ordinary  phosphate  of  soda, 
a  precipitate  is  formed  containing  the  two  salts  3PbO.P05  and  2PO.HO.PO5. 
The  latter  is  obtained  pure  by  precipitating  a  boiling  solution  of  nitrate  of  lead 
with  pure  phosphoric  acid.  This  salt  dissolves  in  nitric  acid  and  fixed  alkalies, 
but  very  sparingly  in  acetic  acid ;  ammonia  converts  it  into  3PbO.P05.  It  fuses 
readily  before  the  blow-pipe,  and  crystallizes  on  cooling  in  well  defined  polyhe- 
drons. When  strongly  ignited  with  charcoal,  it  gives  off  phosphorus  and  carbonic 
oxide,  and  leaves  metallic  lead. 

Chlorite  of  lead,  PbO.C103,  is  obtained  in  sulphur-yellow  crystalline  scales  by 
precipitating  nitrate  of  lead  with  an  excess  of  chlorite  of  baryta  containing  free 
chlorous  acid.  It  decomposes  at  259°  with  a  kind  of  explosion,  and  sets  fire  to 
flowers  of  sulphur  triturated  with  it.  Sulphuric  acid  diluted  with  an  equal  weight 
of  water,  decomposes  it,  especially  between  104°  and  122°,  evolving  pure  chlorous 
acid  gas,  and  leaving  88.75  per  cent,  of  sulphate  of  lead  (Millon). 

Chlorate  of  lead,  PbO.C105  -j-  HO,  is  obtained  by  cooling  a  hot  solution  ol 
oxide  of  lead  in  aqueous  chloric  acid,  in  rhomboiidal  prisms  belonging  to  the 
oblique  prismatic  system,  and  isomorphous  with  the  analogously  constituted  crys- 
tals of  chlorate  of  baryta.  These  crystals,  when  heated,  leave  the  yellow  oxychlo- 
ride,  Pb0.2PbCl  (Vauquelin,  Wachter,  Vogel). 

Perchlorate  of  lead,  PbO.C107 — The  solution  of  oxide  of  lead  in  warm  aqueous 

*  For  a  more  detailed  account  of  the  nitrates  and  nitrites  of  lead,  see  GmeHn's  Handbook, 
Translation,  v.  152—157. 


492  LEAD. 

perchloric  acid,  yields  small  prisms  having  a  sweet  but  highly  astringent  taste, 
soluble  in  their  own  weight  of  water,  but  not  deliquescent  (Serullas).  By  boiling 
a  concentrated  solution  of  this  salt  with  carbonate  of  lead,  a  solution  of  a  basic  salt 
is  obtained,  which  if  the  excess  of  base  is  very  large,  yields  by  evaporation,  dull, 
indistinct  crystals,  which  are  resolved  by  water  into  a  solution  of  bibasic  salt,  and 
a  white  insoluble  residue.  When  the  excess  of  base  is  less,  or  when  the  solution 
of  the  bibasic  salt  is  left  to  evaporate,  crystals  of  two  different  forms  are  obtained  j 
both,  however,  containing  2PbO.C10,  +  2HO  (Marignac). 

Ohlorophosphate  of  lead,  PbCl  +  3(3PbO.P05,  occurs  as  pyromorpJiite  and 
green  and  brown  lead-ore.  The  crystals  belong  to  the  hexagonal  system,  and 
have  the  hardness  of  apatite.  It  fuses  readily,  and  on  cooling  solidifies  with  vivid 
incandescence  into  an  angular  crystalline  mass.  In  some  of  these  ores,  the  chlo- 
ride of  lead  is  partly  replaced  by  fluoride  of  calcium,  and  the  triphosphate  of  lead 
by  the  triphosphate  of  calcium  or  trisarseniate  of  lead.  The  calcareous  ores  may 
be  regarded  as  mixtures  of  apatite  and  pyromorphite.  The  same  compound  con- 
taining, however,  an  atom  of  water,  is  formed  artificially  on  pouring  a  boiling  solu- 
tion of  chloride  of  lead  into  a  boiling  solution  of  phosphate  of  soda,  the  latter 
being  in  excess  (Heintz).  When,  on  the  contrary,  a  boiling  solution  of  phos- 
phate of  soda  is  poured  into  an  excess  of  chloride  of  lead,  a  precipitate  is  formed, 
which,  according  to  Heintz,  is  2(3PbO.P05)  -f  PbCl,  but,  according  to  Gerhardt, 
2PbO.HO.POs  +  PbCl. 

Acetate  of  lead,  PbO.(C4H303)  -f  3 HO. —This  salt  is  met  with  well  crystallized, 
and  in  a  state  of  great  purity,  in  commerce.  It  is  generally  prepared  by  dissolv- 
ing litharge  in  the  acetic  acid  procured  by  the  distillation  of  wood.  It  crystal- 
lizes in  flattened  four-sided  prisms;  has  a  taste  which  is  first  sweet  and  then 
astringent ;  is  very  soluble  in  water,  100  parts  of  water  dissolving  59  of  the  salt 
at  60°  ;  and  dissolves  in  8  parts  of  alcohol.  It  effloresces  in  air,  and  is  apt  to  be 
partially  decomposed  by  the  carbonic  acid  of  the  air,  and  thus  to  become  partially 
insoluble.  It  loses  the  whole  of  its  water  when  dried  at  the  usual  temperature  in 
vacuo.  M.  Payen  crystallized  the  anhydrous  acetate  from  solution  in  absolute 
alcohol. 

Tribasic  subacetate  of  lead,  PbO.(C4H303) +2PbO,  is  formed  by  digesting 
oxide  of  lead  in  a  solution  of  the  neutral  salt,  till  it  is  strongly  alkaline.  This 
salt  does  not  crystallize  when  so  prepared,  but  may  be  dried,  and  then  contains  no 
water.  It  is  very  soluble,  but  must  be  dissolved  in  distilled  water,  as  the  car- 
bonic, hydrochloric  and  other  acids  in  well  water  precipitate  its  oxide  of  lead.  M. 
Payen  has  observed  that  the  tribasic  subacetate  crystallizes  readily,  in  fine  pris- 
matic needles,  when  formed  by  adding  ammonia  to  a  moderately  strong  solution 
of  the  neutral  acetate.  The  crystals  contain  1  eq.  of  water,  which  they  lose  at 
212°.  The  acetate  of  ammonia,  formed  at  the  same  time,  appears  to  give  stability 
to  the  subacetate  of  lead  in  solution,  and  prevents  an  excess  of  a  whole  equivalent 
of  ammonia  from  throwing  down  any  oxide  of  lead  from  the  solution.  This  ammo- 
niacal  solution  of  the  subacetate  of  lead,  prepared  without  an  excess  of  ammonia,  is 
a  convenient  form  in  which  to  apply  that  salt  as  a  reagent.* 

Sesquibasic  acetate  of  lead,  3Pb0.2(C4H3O3)  +  HO. — This  salt  was  obtained 
by  Payen  by  adding  1  eq.  of  the  neutral  acetate  to  a  concentrated  and  boiling 
solution  of  1  eq.  of  the  tribasic  acetate.  It  is  also  produced  when  the  neutral  and 
anhydrous  acetate  of  lead  is  heated  in  a  retort  or  porcelain  capsule,  till  the  whole, 
after  being  liquid,  becomes  a  white  and  porous  mass.  The  sesquibasic  acetate  is 
then  formed  by  the  decomposition  of  3  eq.  of  neutral  acetate  of  lead,  from  which 
there  separate  the  elements  of  1  eq.  of  acetic  acid,  in  the  form  of  carbonic  acid  and 
acetone  (Matteucci  and  Wohler).  This  basic  salt  is  very  soluble,  and  crystallizes 
in  plates  of  a  pearly  lustre.  Another  method  of  obtaining  it  is  to  digest  an  aqueous 

*  M^moires  sur  les  Acetates  et  le  Protoxide  de  Plomb,  par  M.  Tayen,  An.  de  Chim.  et  de 
t.  Ixvi.  p.  37. 


SALTS    OF    LEAD.  493 

solution  of  2  eq.  of  the  neutral  acetate  with  1  eq.  of  protoxide  of  lead  free  from 
carbonate,  till  it  dissolves,  and  evaporate  the  filtrate  in  vacuo  over  oil  of  vitriol. 

A  sexbasic  acetate  of  lead,  6PbO.(C4H303),  is  formed  on  dropping  a  solution 
of  the  neutral,  or  of  tribasic  acetate  of  lead,  into  excess  of  ammonia.  It  is  a  white 
precipitate,  which  when  examined  by  the  microscope,  has  a  crystalline  aspect.  It 
contains  a  little  water,  which  it  loses  when  dried  in  vacuo. 

A  bibasic  acetate  of  lead,  2PbO.(C4H303),  is  also  formed,  according  to  Dobe- 
reiner  and  Schindler,  by  boiling  1  eq.  of  neutral  acetate  of  lead  with  1  eq.  of  the 
protoxide. 

The  common  extractum  Saturni  of  the  pharmacopoeias  appears  to  consist  chiefly 
of  bibasic  acetate,  containing  more  or  less  of  the  tribasic  and  sesquibasic  salts. 

Alloys  of  lead. — Lead  and  tin  may  be  fused  together  in  all  proportions.  M. 
Rudberg  finds  that  these  metals  combine  in  certain  definite  proportions,  having 
fixed  points  of  congelation  :  — 

1  atom  of  lead  and  3  atoms  of  tin,  congeal  at  368.6°. 

1  atom  of  lead  and  1  atom  of  tin,  at  464°. 

2  atoms  of  lead  and  1  atom  of  tin,  at  518°. 

3  atoms  of  lead  and  1  atom  of  tin,  at  536°. 

A  thermometer  placed  in  a  fluid  alloy  of  1  atom  of  lead  and  2  atoms  of  tin, 
becomes  stationary  when  the  temperature  falls  to  392° ;  a  portion  then  solidifies, 
and  a  more  fusible  alloy  separates ;  the  temperature  again  falls,  and  afterwards 
becomes  stationary  at  368*6°,  the  crystallizing  point  of  the  alloy  composed  of  1 
atom  of  lead  and  3  atom  of  tin.  If  the  alloy  contains  so  much  tin  that  its  point 
of  complete  congelation  is  below  368-6°,  the  last  compound  always  separates  from 
it  at  that  point,  and  the  thermometer  remains  stationary  for  a  time,  whatever  may 
be  the  proportion  of  the  metals  in  the  alloy.*  Fine  solder  is  an  alloy  of  2  parts 
of  tin  and  1  of  lead;  it  fuses  at  about  360°,  and  is  much  employed  in  tinning 
copper.  Coarse  solder  contains  one-fourth  of  tin,  and  fuses  at  about  500°;  it  is 
the  substance  employed  for  soldering  by  plumbers. 

Lead,  as  reduced  from  the  native  sulphide,  always  contains  a  little  silver.  The 
latter  is  separated  by  allowing  two  or  three  tons  of  the  melted  metal  to  cool  slowly  in 
a  hemispherical  iron  pot,  when  the  lead,  as  it  solidifies,  separates  in  crystals,  which 
can  be  raked  out.  The  silver  remains  almost  wholly  in  the  more  fusible  portion, 
or  what  may  be  looked  upon  as  the  mother-liquor  of  these  crystals ;  so  that  by  this 
operation  the  argentiferous  alloy  is  greatly  concentrated.  This  mode  of  separation 
was  discovered  by  Mr.  Pattinson  of  Newcastle.  To  separate  the  remaining  lead, 
much  of  it  is  converted  into  massicot,  by  the  action  of  air  upon  its  surface,  in  the 
shallow  furnace  used  for  that  preparation ;  and  the  last  portions  of  lead  are  removed 
by  continuing  the  oxidation  upon  a  porous  bason  or  cupel  of  bone-earth,  which 
imbibes  the  fused  oxide  of  lead,  while  the  melted  silver  is  found  in  a  state  of 
purity  upon  the  surface  of  the  cupel,  not  being  oxidable  at  a  high  temperature. 

ESTIMATION   OF   LEAD,   AND    METHODS   OF   SEPARATING   IT   FROM   THE  PRE- 
CEDING   METALS. 

Lead  may  be  estimated  either  as  protoxide  or  as  sulphate.  For  the  former 
mode  of  estimation,  it  is  best  to  precipitate  by  oxalate  of  ammonia,  the  solution 
being  neutral  or  rendered  very  slightly  alkaline  by  ammonia.  The  oxalate  of  lead, 
after  being  washed  and  dried,  is  then  to  be  ignited  in  an  open  procelaiu  crucible, 
whereby  it  is  converted  into  protoxide.  As  lead  is  very  easily  reduced  by  carbo- 
naceous matter  at  a  red  heat,  the  precipitate  must  not  be  ignited  in  contact  with 
the  filter;  but  the  filter,  after  the  greater  part  of  the  precipitate  has  been  removed 
from  it,  must  be  held  on  the  point  of  a  fine  platinum  wire  above  the  crucible,  and 
set  on  fire,  so  that  the  ashes  may  drop  in ;  the  precipitate  may  then  be  added,  and 

*  Rudberg,  An.  Cli.  Phys.  [2],  xlviii.  363. 


494  TIN. 

the  ignition  completed.  The  protoxide  contains  92-83  per  cent,  of  metallic  lead. 
Lead  may  also  be  precipitated  by  carbonate  of  ammonia,  to  which  a  little  free 
ammonia  has  been  added,  and  the  carbonate  of  lead  treated  as  above. 

In^  precipitating  lead  as  sulphate,  if  the  solution  be  neutral,  the  precipitation  is 
best  effected  by  sulphate  of  soda ;  the  sulphate  of  lead  may  then  be  washed  on  a 
filter,  dried  and  ignited;  but  if  the  solution  contains  free  nitric  acid,  it  is  best  to 
precipitate  by  excess  of  sulphuric  acid,  then  evaporate  to  dryness,  and  ignite  till 
all  excess  of  acid  is  driven  off;  treat  the  residue  with  water  to  dissolve  out  any 
soluble  salts  that  may  be  present ;  wash  the  sulphate  of  lead  on  a  filter,  and  then 
dry  and  ignite  it,  burning  the  filter  separately  as  above.  The  sulphate  contains 
68-32  pe/cent.  of  lead. 

From  the  alkalies  and  earths,  and  from  manganese,  iron,  cobalt,  nickel  and 
zinc,  lead  is  easily  separated  by  hydrosulphuric  acid,  the  solution  being  previously 
acidulated  with  nitric  acid.  The  precipitated  sulphide  is  washed  and  dried,  then 
placed,  together  with  the  filter  (which  should  be  as  small  as  possible),  in  a  porce- 
lain dish,  covered  over  with  a  glass  plate  or  a  funnel,  and  treated  with  fuming 
nitric  acid,  added  cautiously  and  by  small  portions  at  a  time.  Violent  action  takes 
place,  and  the  sulphide  of  lead  is  converted  into  sulphate.  A  portion  may,  how- 
ever, be  converted  into  nitrate,  with  separation  of  sulphur :  hence,  to  insure  com- 
plete conversion  into  sulphate,  it  is  necessary  to  add  a  few  drops  of  strong  sul- 
phuric acid.  The  product  must  then  be  strongly  ignited  to  drive  off  the  excess 
of  sulphuric  acid,  and  burn  away  the  remaining  organic  matter  of  the  filter. 

From  cadmium  and  copper,  lead  is  easily  separated  by  sulphuric  acid. 


ORDER  Y. 

OTHER    METALS   PROPER    HAVING   ISOMORPHOUS   RELATIONS   WITH   THE 
MAGNESIAN   FAMILY. 

SECTION  I. 

TIN. 

Eq.  58-82  or  785-25;  Sn  (stannum). 

TIN  does  not  occur  native,  but  its  common  ore  is  reduced  by  a  simple  process, 
and  mankind  appear  to  have  been  in  possession  of  this  metal  from  the  earliest 
ages.  The  most  productive  mines  of  tin  are  those  of  Cornwall,  from  which  the 
ancients  appear  to  have  derived  their  principal  supply  of  this  metal,  and  those 
of  the  peninsula  of  Malacca,  and  island  of  Banca,  in  India. 

The  only  important  ore  of  tin  is  the  bioxide,  which  is  found  in  Cornwall,  both 
in  veins  traversing  the  primary  rocks,  and  in  alluvial  deposits  in  their  neighbour- 
hood. In  the  latter  case,  the  ore  presents  itself  in  rounded  grains  of  greater  or 
less  size,  which  form  together  a  bed  covered  by  clay  and  gravel.  This  ore  has 
evidently  been  removed  from  its  original  situation,  and  the  grains  rounded  by  the 
action  of  water,  which  has  at  the  same  time  divested  it  of  the  other  metallic  ores 
with  which  it  is  accompanied  in  the  vein ;  these  being  softer  are  more  easily 
reduced  to  powder,  and  have  been  carried  away  by  the  stream.  This  ore,  called 
stream  tin,  is  easily  reduced  by  coal,  and  gives  the  purest  tin.  The  metal  from 
the  ore  of  the  veins  is  contaminated  with  iron,  copper,  arsenic,  and  antimony, 
from  which  a  portion  of  it  is  partially  purified  by  liquation.  Bars  of  the  impure 
metal  are  exposed  to  a  moderate  heat,  by  which  the  pure  tin  is  first  melted,  and 


PROTOXIDE    OF    TIN.  495 

separates  it  from  a  less  fusible  alloy  containing  the  foreign  metals.  The  purer 
portion  is  called  yrain  tin,  and  the  other,  ordinary  tin  or  block  tin.  The  mass 
of  grain  tin  is  heated  till  it  becomes  brittle,  and  then  let  fall  from  a  height.  By 
this  it  splits  into  irregular  prisms,  somewhat  resembling  basaltic  columns.  This 
splitting  is  a  mark  of  the  purity  of  the  tin,  for  it  does  not  happen  when  the  tin  is 
contaminated  by  other  metals. 

Pure  tin  is  white,  with  a  bluish  tinge,  very  soft,  and  so  malleable,  that  it  may 
be  beaten  into  thin  leaves,  tinfoil  not  being  more  than  l-1000th  of  an  inch  in 
thickness.  When  a  bar  of  tin  is  bent,  it  emits  a  grating  sound,  which  is  charac- 
teristic ;  and  when  bent  backwards  and  forwards  rapidly,  several  times  in  succession, 
becomes  so  hot  that  it  cannot  be  held  in  the  hand.  At  the  temperature  of  boiling 
water,  tin  can  be  drawn  out  into  wire,  which  is  very  soft  and  flexible,  but  deficient 
in  tenacity.  The  density  of  pure  tin  is  7-285,  or  7-293  after  being  laminated ; 
that  of  the  tin  of  commerce  is  said  to  vary  from  7 '56  to  7 '6.  Its  point  of  fusion 
is  442°,  according  to  Crichton  and  Rudberg;  4456°,  according  to  Kupffer.  Tin  is 
volatile  at  a  very  high  temperature.  The  brilliancy  of  the  surface  of  tin  is  but 
slowly  impaired  by  exposure  to  air,  and  even  in  water  it  is  scarcely  acted  upon. 
Hence  the  great  value  of  this  metal  for  culinary  vessels,  and  for  covering  the  more 
oxidable  metals,  such  as  iron  and  copper,  when  employed  as  such.  Three  oxides 
of  tin  are  known,  the  protoxide,  SnO,  sesquioxide,  Sn203,  and  biuoxide,  Sn02. 

Protoxide  of  tin,  Stannous  oxide;  SnO,  66-82  or  83525.  Tin  dissolves  in 
undiluted  hydrochloric  acid,  at  the  boiling  temperature,  by  substitution  for  hydro- 
gen, and  forms  the  protochloride  of  tin.  From  this  the  protoxide  is  precipitated 
by  an  alkaline  carbonate,  as  a  white  hydrate,  which  may  be  washed  with  tepid 
water  and  dried  at  a  temperature  not  exceeding  176°.  It  does  not  contain  a  trace 
of  carbonic  acid.  This  white  powder  dried  more  strongly  in  a  retort  filled  with 
carbonic  acid,  and  heated  to  redness,  gives  the  anhydrous  oxide  as  a  black  powder, 
the  density  of  which  is  6-666.  In  this  state,  the  oxide  is  permanent;  but  if  a 
body  at  a  red  heat  is  brought  in  contact  with  it  in  open  air,  it  takes  fire  and  burns, 
and  is  entirely  converted  into  bioxide.  If  hydrated  stannous  oxide  be  boiled  with 
a  quantity  of  potash  not  sufficient  to  dissolve  it  entirely,  the  undissolved  portion  is 
converted  into  small,  hard,  shining,  black  crystals  of  anhydrous  stannous  oxide, 
which,  when  heated  to  392°,  decrepitate,  swell  up,  fall  to  pieces,  and  are  converted 
into  an  olive-green  powder,  consisting  also  of  the  anhydrous  protoxide.  Again, 
on  evaporating  a  very  dilute  solution  of  sal-ammoniac,  in  which  hydrated  stannous 
oxide  is  diffused,  that  compound  is  converted,  as  soon  as  the  sal-amrnoniac  crystal- 
lizes, into  anhydrous  stannous  oxide,  having  the  form  of  a  cinnabar-coloured 
powder.  There  are,  therefore,  three  modifications  of  stannous  oxide,  black,  olive- 
green,  and  red  (Fremy).  The  red  modification  is  also  obtained  by  digesting 
thoroughly  washed  hydrated  stannous  oxide  at  a  temperature  of  133°,  in  a  slightly 
acid  solution  of  stannous  acetate,  having  a  density  of  1-06  (Roth). 

Protoxide  of  tin  dissolves  in  acids,  and  with  more  facility  when  hydrated  than 
after  being  ignited.  This  oxide  is  also  dissolved  by  potash  and  soda,  but  the  solu- 
tion after  a  time  undergoes  decomposition;  metallic  tin  is  deposited,  and  the 
bioxide  is  found  in  solution.  The  solution  of  a  stannous  salt,  and  of  a  stannic 
salt  also,  is  apt  to  undergo  decomposition,  when  largely  diluted  with  water,  and  to 
deposit  a  subsalt.  Stannous  salts  absorb  oxygen  from  the  air,  and  have  a  great 
affinity  for  that  element ;  they  convert  the  sesquioxide  of  iron  into  protoxide,  and 
throw  down  mercury,  silver  and  platinum  in  the  metallic  state  from  their  solutions, 
Chloride  of  gold  produces  a  purple  precipitate  in  a  stannous  salt,  consisting,  it  is 
believed,  of  the  bioxide  of  tin  in  combination  with  protoxide  of  gold,  a  test  by 
which  the  protoxide  of  tin  may  always  be  distinguished.  Hydrosvlphuric  acid 
produces  in  neutral  or  acid  solutions  of  stannous  salts,  a  brown-black  precipitate 
of  protosulphide  of  tin,  which,  when  gently  heated  with  a  considerable  quantity 
of  sulphide  of  ammonium  containing  excess  of  sulphur,  is  converted  into  the 
bisulphide  and  dissolved;  acids  added  in  excess  to  this  solution  precipitate  the 


496  TIN. 

yellow  bisulphide.  Caustic  alkalies  and  alkaline  carbonates,  added  to  stannous 
salts,  throw  down  a  white  precipitate  of  hydrated  stannous  oxide,  soluble  in  caustic 
potash  or  soda,  but  not  in  ammonia.  Ferrocyanidc  of  potassium  produces  a  white 
precipitate,  soluble  in  hydrochloric  acid. 

Protosu/phide  of  tin,  SnS,  is  formed  when  sulphur  is  mixed  with  tin  heated 
above  its  melting  point;  it  is  also  obtained  in  small  dark  grey  crystalline  laminae, 
of  sp.  gr.  4-973,  by  adding  the  hydrated  sulphide  precipitated  from  a  stannous 
salt  by  hydrosulphuric  acid,  to  anhydrous  protochloride  of  tin  in  the  melted  state, 
and  removing  the  excess  of  the  protochloride  with  dilute  hydrochloric  acid.  It  is 
decomposed  by  dilute  hydrochloric  acid,  with  evolution  of  hydrosulphuric  acid. 

Protochloride  of  tin.  Salt  of  tin;  SnCl — This  salt  may  be  obtained  in  the 
anhydrous  state  by  gradually  heating  a  mixture  of  equal  weights  of  calomel  and 
tin,  and  finally  distilling  the  protochloride  at  a  strong  red  heat.  The  fused  mass 
on  cooling  forms  a  grey  solid,  of  considerable  lustre,  and  having  a  vitreous  frac- 
ture. The  hydrated  chloride,  known  in  commerce  as  salt  of  tin,  is  procured  by 
evaporating  the  solution  of  tin  in  concentrated  hydrochloric  acid  to  the  point  of 
crystallization.  It  is  thus  obtained  in  needles,  or  in  larger  four-sided  prismatic 
crystals  containing  2  eq.  of  water.  They  fuse  between  100°  and  105°.  The 
specific  gravity  of  the  crystals  is  2-710  at  60°;  that  of  the  fused  mass  at  100°,  is 
2'588  (Penny).  The  salt  parts  with  the  greater  portion,  if  not  the  whole  of  its 
water  at  212°,  but  if  distilled  at  a  higher  temperature,  loses  hydrochloric  acid 
also,  and  leaves  an  oxychloride  of  tin.  It  dissolves  completely  in  a  small  quantity 
of  water  j  but  when  treated  with  a  large  quantity,  is  partly  decomposed,  hydro- 
chloric acid  being  dissolved,  and  a  light  milk-white  powder  separating,  which  is  a 
basic  chloride,  or  oxychloride,  SnCl.SnO  +  2HO.  Both  the  crystals  and  the 
solution  absorb  oxygen  from  the  air,  and  then  a  basic  salt  of  the  sesquioxide  is 
formed 'which  is  also  insoluble  in  water.  From  both  these  causes,  a  complete  and 
clear  solution  of  the  salt  of  tin  is  rarely  obtained,  unless  the  water  is  previously 
acidulated  with  hydrochloric  acid.  This  salt  is  entirely  soluble  in  caustic  alkali, 
but  the  solution  is  liable  to  an  ulterior  change  already  mentioned.  One  part  of 
crystallized  protochloride  of  tin  dissolved,  together  with  8  parts  of  tartaric  acid,  in 
a  sufficient  quantity  of  hot  water,  and  carefully  neutralized  with  potash,  forms  a 
clear  solution,  which  may  be  boiled  and  mixed  with  any  quantity  of  water  without 
becoming  turbid  :  the  white  precipitate  which  forms  in  it  on  the  addition  of  a  little 
more  potash,  especially  on  heating,  is  re-dissolved  by  a  larger  quantity  of  potash. 
(R.  Schneider). 

When  protochloride  of  tin  is  heated  with  a  mixture  of  hydrochloric  and  sul- 
phurous acids,  a  yellow  precipitate  of  bisulphide  of  tin  is  formed  :  GSnOl  -t-2S02-f- 
4HC1  =  SnS2  +  5Sn012T~4HO.  This  reaction  serves  as  a  test  for  sulphurous 
acid. 

The  protochloride  of  tin  is  used  in  calico-printing,  not  only  as  a  mordant,  but 
also  as  a  deoxidizing  agent,  particularly  to  deoxidize  indigo,  and  to  reduce  to  a 
lower  state  of  oxidation  and  discharge  the  sesquioxides  of  iron  and  manganese 
fixed  upon  cloth. 

Protochloride  of  tin  and  potassium  ;  SnCl.KCl.  —  Protochloride  of  tin  forms 
a  double  salt  with  chloride  of  potassium,  and  also  with  chloride  of  ammonium, 
which  compounds  crystallize  in  the  anhydrous  state,  and  also  with  3  eq.  of  water, 
or,  according  to  ilammelsberg,  with  only  1  equivalent. 

Anhydrous  protochloride  of  tin  fused  in  ammoniacal  gas,  absorbs  half  an  equi- 
valent of  that  gas,  according  to  Persoz,  forming  2SnCl.NH3,  or  rather  perhaps 
SnCl.(NH3Sn)Cl. 

Proiiodide  of  tin,  SnI,  is  formed  by  heating  a  mixture  of  granulated  tin  and 
iodine  It  is  obtained  in  beautiful  shining  yellowish  red  prisms  by  gently  boiling 
concentrated  hydriodic  acid  with  strips  of  tinfoil  in  a  long  glass  tube  for  a  day,  or 
more  readily  by  heating  the  acid  with  the  tin  in  a  sealed  glass  tube  to  a  tempera- 
ture of  248°,  or  at  most  302°  for  an  hour;  after  cooling,  the  remaining  portion 


BIOXIDE    OF     TIN.  497 

of  tin  is  found  to  be  covered  with  crystals.  When  tinfoil  and  iodide  of  amyl 
were  heated  together  in  a  sealed  tube  for  a  day  to  356°,  the  tinfoil  became  covered 
with  yellowish-red  quadratic  octohedrons  at  the  part  where  the  tube  cooled  most 
quickly;  but  at  the  part  which  was  immersed  in  the  oil-bath,  and  therefore  cooled 
more  slowly,  the  metal  was  covered  with  sulphur-yellow  prisms,  which  became 
yellowish-red  when  taken  out  (Wb'hler).  Stannous  iodide  was  found  by  Boullay, 
jun.,  to  form  double  salts  with  other  iodides,  particularly  with  the  iodides  of  the 
alkaline  and  earthy  metals,  in  which  two  atoms  of  the  stannous  iodide  are  com- 
bined with  one  of  the  other  iodide. 

Carbonic  acid  does  not  combine  with  either  of  the  oxides  of  tin. 

Protosulphate  of  tin,  SNO.S03. — Tin  dissolves  in  sulphuric  acid,  concentrated 
or  a  little  diluted,  yielding  a  saline  mass,  which  forms  a  brown  solution  in  water 
and  deposits  small  crystalline  needles  on  cooling. 

Protonitrate  of  tin,  SNO.N05,  is  obtained  by  dissolving  hydrated  protoxide  of 
tin  in  nitric  acid  ',  the  solution  cannot  be  concentrated  and  is  easily  altered. 

Tartrate  of  potash  and  tin,  KO.SnO.(C8H40IO)  or  C8H4(KSn)0,2.  —  Bitartrate 
of  potash  dissolves  protoxide  of  tin,  and  forms  a  very  soluble  salt  of  potash  and 
tin,  which,  like  most  of  the  tartrates,  is  not  precipitated  either  by  caustic  alkalies 
or  by  alkaline  carbonates.  An  addition  of  bitartrate  of  potash  is  occasionally 
made  to  the  solution  of  tin  used  in  dyeing. 

Sesquioxide  of  tin,  Sn203. — Was  obtained  by  M.  Fuchs,  by  diffusing  recently 
precipitated  sesquioxide  of  iron  in  a  solution  of  protochloride  of  tin  containing  no 
excess  of  acid,  and  afterwards  boiling  the  mixture.  A  double  decomposition 
occurs,  in  which  sesquioxide  of  tin  precipitates,  and  protochloride  of  iron  is  re- 
tained in  solution  : 

2SnCl  +  Fe203  =  Sn203  +  2FeCl. 

The  sesquioxide  thus  obtained  is  a  slimy  grey  matter,  and  usually  yellow  from 
adhering  oxide  of  iron.  Ammonia  dissolves  it  easily,  and  without  residue,  a  cha- 
racter which  distinguishes  this  oxide  from  the  protoxide  of  tin,  the  latter  being 
insoluble,  or  nearly  so,  in  that  menstruum.  Sesquioxide  of  tin  is  dissolved  by 
concentrated  hydrochloric  acid }  the  taste  of  the  solution  is  not  metallic.  It  is 
distinguished  from  a  salt  of  the  bioxide  of  tin,  by  producing  the  purple  precipi- 
tate with  chloride  of  gold.  A  sesquisulphide  exists,  corresponding  with  this 
oxide.  The  salts  of  sesquioxide  of  tin  have  not  been  examined. 

Bioxide  of  tin,  Stannic  oxide,  Sn02,  74-82  or  935-25.  — This  constitutes  the 
common  ore  of  tin,  which  is  generally  crystallized.  The  crystals  of  tin-stone  &YQ 
sometimes  brownish-yellow  and  translucent,  at  other  times  dark  brown  and  almost 
black,  and  contain  small  quantities  of  the  protoxides  of  iron  and  manganese. 
Their  primitive  form  is  an  obtuse  octohedron  with  a  square  base ;  their  density 
from  6  92  to  6  96.  Bioxide  of  tin  in  this  state  does  not  dissolve  in  acids,  unless 
previously  ignited  with  an  alkali.  Anhydrous  stannic  oxide  may  be  obtained  in 
colourless  crystals  derived  from  a  right  rhomboidal  prism,  which  scratch  glass,  and 
have  a  density  of  5*72,  by  decomposing  vapour  of  bichloride  of  tin  with  water  at 
a  red  heat.  These  crystals  are  isomorphous  with  one  of  the  native  varieties  of 
titanic  acid  (brookite),  whereas  the  crystals  of  native  tin-stone  are  isomorphous 
with  another  variety  of  titanic  acid  (rutile). 

Bioxide  of  tin  is  susceptible  of  two  modifications  called  stannic  and  metastan- 
nic  acid,  distinguished  from  one  another  by  the  proportions  of  water  and  metallic 
oxide  with  which  they  combine. 

Stannic  acid,  or  Hydrated  stannic  oxide,  Sn02.HO,  is  obtained  by  decom- 
posing bichloride  of  tin  with  water,  or  by  precipitating  a  soluble  stannate  with  an 
acid.  It  is  white,  gelatinous,  insoluble  in  water,  but  dissolves  readily  in  dilute 
acids.  A  moderate  heat  converts  it  into  metastannic  acid.  At  a  red  heat,  it 
gives  off  all  its  water,  and  becomes  very  hard. 

Solutions  of  stannic  oxide  in  acids  (the  hydrated  bichloride  for  example),  are 
32 


498  TIN. 

decomposed  by  zinc  and  cadmium,  the  tin  being  precipitated  in  an  arborescent 
form.  Hydrosulphuric  acid  and  sulphide  of  ammonium  throw  down  the  yellow 
bisulphide  soluble  in  alkalies  and  in  sulphide  of  ammonium.  Ammonia  throws 
down  a  white  bulky  hydrate,  soluble  with  some  turbidity  in  a  large  excess  of  am- 
monia. The  presence  of  tartaric  acid  prevents  the  precipitation.  Potash  throws 
down  a  white  bulky  hydrate  (probably  containing  potash),  easily  soluble  in  excess. 
Carbonate  of  potash  gives  a  white  precipitate,  consisting,  according  to  Fremy,  of 
stannate  of  potash,  which  dissolves  in  excess  of  the  reagent,  but  separates  com- 
pletely after  a  while.  Bicarbonate  of  potash  and  sesquicarbonate  of  ammonia 
throw  down  the  hydrated  oxides,  insoluble  in  excess  of  the  reagent.  Chloride  of 
gold  gives  no  precipitate  with  stannic  salts. 

All  salts  of  tin  are  easily  reduced  to  the  metallic  state  when  heated  on  charcoal 
before  the  blowpipe  with  carbonate  of  soda  or  cyanide  of  potassium. 

The  compounds  of  stannic  acid  with  bases  are  represented  by  the  general  for- 
mula, MO.Sn02.  The  stannates  of  the  alkalies  crystallize  readily,  and  may  be  ob- 
tained in  the  anhydrous  state.  They  are  prepared  by  dissolving  stannic  acid  in 
alkalies,  or  by  calcining  metastannic  acid  or  the  metastannates  in  contact  with  an 
excess  of  base.  Stannate  of  potash,  KO.Sn02  +  4HO,  is  white,  very  soluble  in 
water,  insoluble  in  alcohol ;  it  crystallizes  in  oblique  rhomboidal  prisms,  which 
•are  transparent,  sometimes  very  large,  and  slowly  absorb  moisture  from  the  air. 
Tt  has  a  caustic  taste  and  strong  alkaline  reaction.  Water  appears  to  decompose 
it  after  a  while  into  potash  and  metastannate  of  potash.  It  is  precipitated  from 
its  solution  by  nearly  all  soluble  salts,  even  by  those  of  potash,  soda  and  ammonia. 
Stannafe  of  soda,  NaO.Sn02  +  4HO,  resembles  the  potash-salt,  and  is  obtained  in 
a  similar  manner.  It  crystallizes  in  hexagonal  tables,  dissolves  in  cold  more  readily 
than  in  hot  water,  is  insoluble  in  alcohol,  and  has  a  strong  alkaline  reaction 
(Fremy). 

The  stannates  of  all  other  bases  are  insoluble  in  water,  and  may  be  formed  by 
double  decomposition.  The  sesquioxide  of  tin  may  be  regarded  as  a  stannate  of 
stannous  oxide.,  SnO.Sn02  (Fremy). 

Metastannic  acid,  SN50,0. — Tin  treated  with  strong  nitric  acid  is  completely 
transformed  into  a  white  powder,  which,  when  dried  in  the  air  at  ordinary  tempe- 
ratures, contains  Sn50,0.10HO;  after  being  heated  for  some  time  to  212°,  it  is 
reduced  to  Sn5O,0.5HO.  It  is  white,  crystalline,  insoluble  in  water,  and  in  dilute 
nitric  acid  and  sulphuric  acid.  Monohydrated  sulphuric  acid  dissolves  it  in  consider- 
able quantity,  forming  a  compound  which  is  not  decomposed  by  water  or  alcohol. 
It  cfissolves  in  dilute  hydrochloric  acid,  forming  a  liquid,  which,  when  treated  with 
excess  of  acid,  yields  a  white  amorphous  precipitate,  differing  considerably  from 
hydrated  bichloride  of  tin.  Metastannic  acid  also  combines  with  certain  organic 
acids.  The  acid  prepared  with  nitric  acid  is  completely  insoluble  in  ammonia, 
but  when  dissolved  in  potash  and  precipitated  by  an  acid,  it  becomes  gelatinous 
and  soluble  in  ammonia;  in  that  state,  it  contains  more  water  than  in  the  crystal- 
line state;  but  by  the  slightest  desiccation,  or  even  by  boiling  for  a  few  minutes,  it 
gives  up  part  of  its  water,  and  is  reconverted  into  the  modification  insoluble  in 
ammonia.  Other  hydrates  of  metastannic  acid  appear  also  to  exist,  possessing 
different  properties. 

The  metastannates  are  represented  by  the  general  formula  (M0.4HO.)Sn5Olo. 
They  can  only  exist  in  the  hydrated  state,  being  decomposed  when  deprived  of 
their  basic  water.  The  potash  and  soda-salts,  heated  with  excess  of  base,  are 
transformed  into  stannates.  They  are  soluble  in  basic  water.  The  other  rneta- 
Btannates  are  insoluble,  and  are  obtained  by  double  decomposition.  Metastannate 
of  potash,  (K0.4HO).Sn50,0,  is  prepared  by  dissolving  metastannic  acid  in  cold 
potash ;  it  may  be  precipitated  in  the  solid  state  by  adding  pieces  of  potash  to  the 
liquid.  It  is  gummy,  uncrystallizable,  arid  strongly  alkaline.  At  a  red  heat,  it 
gives  off  its  water  and  is  decomposed;  the  calcined  mass,  digested  in  water,  yields 
up  all  its  alkali  and  leaves  insoluble  metastannic  acid.  The  soda-salt,  (Na0.4HO). 


ALLOYS    OF    TIN.  499 

Sn50IO,  closely  resembles  the  potash-salt,  but  is  crystalline,  dissolves  slowly  in 
water,  and  is  decomposed  by  boiling  water.  Metastannafe  of  stannous  oxide, 
(Sn0.4HO).Sn50,0,  is  obtained  by  placing  metastannic  acid  in  contact  with  pro- 
tochloride  of  tin.  It  is  yellow,  and  insoluble  in  water;  when  heated  in  contact 
with  the  air,  it  is  transformed  into  anhydrous  stannic  acid  (Fremy). 

Oxide  of  tin  is  employed  in  the  preparation  of  the  white  glass  known  as 
enamel;  and  the  ignited  and  finely  levigated  oxide  forms  jeweller's  putty,  which  is 
used  in  polishing  hard  objects.  The  hydrated  oxide  resembles  alumina  in  forming 
insoluble  compounds  with  the  organic  colouring  matters;  hence  its  salts  are  much 
prized  as  mordants. 

Bisulphide  of  tin,  Stannic  sulphide,  SnS2,  is  precipitated  from  stannic  salts,  of 
a  dull  yellow  colour,  by  hydrosulphuric  acid  gas.  Prepared  in  the  dry  way,  by 
igniting  a  mixture  of  stannic  oxide,  sulphur,  and  sal-ammoniac  in  a  covered  cru- 
cible, it  forms  the  aurum  musivum  or  mosaic  gold  of  the  alchemists.  In  this 
operation,  the  sal-ammoniac  is  indispensable,  although  it  seems  to  serve  no  other 
purpose  than  to  prevent  the  elevation  of  temperature  which  results  from  the  sul- 
phuration.  Mosaic  gold  when  well  prepared  has  the  yellow  colour  of  gold,  and 
consists  of  brilliant  translucent  scales,  which  are  soft  to  the  touch.  No  acid  dis- 
solves it,  except  aqua-regia.  It  is  decomposed  by  dry  chlorine,  yielding  the  com- 
pound, SnCl2.SCl2. 

Bichloride  of  tin,  Permuriate  of  tin,  Stannic  chloride,  SnCl2;  129 '82  or 
1622-75. — The  anhydrous  bichloride  of  tin,  known  as  the  fuming  liquor  of  Liba- 
vius,  is  procured  by  distilling,  at  a  gentle  heat,  a  mixture  of  4  parts  of  corrosive 
sublimate  and  1  part  of  tin  in  filings,  or  tin  amalgamated  with  a  little  mercury, 
and  then  reduced  to  powder.  A  colourless,  highly  limpid  liquid  is  found  in  the 
condenser,  which  fumes  strongly  in  humid  air.  The  bichloride  boils  at  248° ;  the 
density  of  its  vapour,  observed  by  Dumas,  is  9 '1997.  It  forms  a  solid  saline  mass 
with  one  third  of  its  weight  of  water,  and  dissolves  in  a  larger  quantity  of  water. 
The  same  salt  is  obtained  in  solution,  by  conducting  a  stream  of  chlorine  gas  into 
a  strong  solution  of  the  protochloride  of  tin,  till  the  latter  is  saturated,  which  is 
shown  by  the  solution  ceasing  to  precipitate  mercury  from  a  solution  of  corrosive 
sublimate.  A  solution  of  this  salt  extensively  used  in  dyeing,  and  known  as  the 
nitromuriate  of  tin,  is  generally  prepared  by  oxidizing  crystallized  protochloride 
of  tin  with  nitric  acid;  or  by  dissolving  tin  in  a  mixture  of  hydrochloric  and 
nitric  acids,  avoiding  any  considerable  elevation  of  temperature. 

Ammonio-bichloride  of  tin,  Sn012.NH3  or  (NH3Sn)Cl2. — Anhydrous  bichloride 
of  tin  absorbs  ammoniacal  gas,  and  forms  a  white  powder,  which  may  be  sublimed 
without  decomposition ;  after  sublimation  it  is  entirely  soluble  in  water  (Rose). 

Chlorosulphide  of  tin,  SnS2.2SnCl2.  —  Hydrosulphuric  acid  gas  is  rapidly  ab- 
sorbed by  bichloride  of  tin,  with  formation  of  hydrochloric  acid  gas  : 

8SnCla  +  2HS  =  SnS2.2SnCl2+ 2HC1. 

The  compound  obtained  by  perfect  saturation  with  hydrosulphuric  acid  is  a 
yellowish  or  reddish  liquid,  heavier  than  water.  When  heated,  it  gives  off  bichlo- 
ride of  tin,  and  leaves  the  bisulphide  (Dumas). 

Bichloride  of  tin  and  sulphur,  SnCl2.2S012. — Formed  by  the  action  of  chlorine 
gas  on  bisulphide  of  tin  at  ordinary  temperatures : 

SnS2  -f  6C1  =  SnCl2.2S012. 

Large  yellow  crystals,  which  fuse  when  heated,  and  sublime  without  decomposi- 
tion ;  they  furne  in  the  air  more  strongly  than  the  bichloride. 

I  Bichloride  of  tin  with  Pentachloride  of  phosphorus,  2Sn012.PCl5.  —  When  a 
mixture  of  the  last-described  compound  with  terchloride  of  phosphorus  is  mode- 
rately heated  in  a  stream  of  hydrochloric  acid  gas,  a  rapid  action  takes  place,  and 
this  compound  is  formed,  together  with  other  products  : 

2(SnCl,.2SCla)  +  3PC13  =  2SnCl2.PCl5  +  2PC15  +  28,01. 


500  TIN. 

If  the  retort  in  which  the  action  takes  place  is  connected  with  a  receiver  sur- 
rounded with  ice,  a  pasty,  yellowish  mass  collects  in  the  receiver,  and  an  amor- 
phous white  body  remains  in  the  retort.  On  heating  the  yellowish  mass  to 
between  212°  and  250°,  dichloride  of  sulphur  escapes,  and  there  remains  a  mixture 
of  pentachloride  of  phosphorus  with  the  double  chloride,  identical,  in  fact,  with 
the  amorphous  white  mass  in  the  retort.  On  heating  this  mixture  to  a  tempera- 
ture between  284°  and  320°,  the  pentachloride  of  phosphorus  is  also  driven  off, 
leaving  the  double  chloride,  which  sublimes  between  392°  and  428°,  in  highly 
lustrous  colourless  needles,  which,  however,  soon  crumble  to  an  amorphous 
powder,  even  when  kept  in  close  vessels.  The  compound  fumes  strongly  in  the 
air,  and  rapidly  absorbs  water,  being  thereby  converted  into  transparent  colourless 
crystals  containing  water  of  crystallization.* 

Bichloride  of  tin  with  Oxy chloride  of  phosphorus,  2SnCl2  +  P02C13. —  Ob- 
tained by  the  action  of  oxychloride  of  phosphorus  on  bichloride  of  tin  j  if  an  ex- 
cess of  either  substance  is  present,  the  compound  separates  in  large  isolated  crys- 
tals. It  has  a  peculiar  odour,  melts  at  131°,  and  boils  at  356°,  and  distils  with- 
out alteration  if  kept  from  contact  with  moist  air.  It  fumes  in  the  air  and  is 
decomposed  by  water.  When  oxychloride  of  phosphorus  comes  in  contact  in  a 
close  vessel  with  the  compound,  SnCl2.2SCl2,  the  whole  dissolves,  forming  a 
yellowish  liquid,  from  which,  after  a  while,  the  compound  2SnCl2.P02Cl3  crystal- 
lizes; and  above  the  crystals  there  remains  a  yellow  liquid,  probably  SC12  (Cassel- 
niaiin). 

Bichloride  of  tin  with  Phosphuretted  hydrogen,  3SnCl2.PH3. — These  two 
bodies  unite  without  production  of  hydrochloric  acid;  the  compound  is  solid 
(Rose). 

Bichloride  of  tin  with  potassium,  SnCl2.KCl. — The  solution  of  bichloride  of 
tin,  when  mixed  with  an  equivalent  quantity  of  chloride  of  potassium  and  evapo- 
rated, yields  this  double  salt  in  anhydrous  regular  octohedrons  having  a  vitreous 
lustre.  A  similar  double  salt  is  formed  with  chloride  of  ammonium. 

A  sulphate  and  nitrate  of  bioxide  of  tin,  have  been  crystallized;  this  base 
forms  no  carbonate. 

Both  the  sulphide  and  bisulphide  of  tin  act  as  sulphur-acids,  combining  with 
alkaline  sulphides.  The  bisulphide  of  tin  dissolves  with  digestion  in  sulphide  of 
sodium,  and  the  concentrated  solution  yields  fine  crystals  of  the  salt,  2NaS.SnS8 
-f  12HO.  By  gradually  adding  tin  to  melted  pentasulphide  of  sodium,  treating 
the  resulting  mass  with  water,  and  then  filtering  and  evaporating,  yellowish  octo- 
hedral  crystals  are  obtained,  containing  NaS.SnS2  -f-  2110."}"  The  bisulphide  of 
tin  is  found  combined  with  the  subsulphides  of  copper  and  iron,  forming  tin 
pyrites,  a  rare  mineral,  2Fe2S.SnS2  -f  2Cu.S.SnS2. 

Alloys  of  tin. — Tin  alloyed  with  small  quantities  of  antimony,  copper,  and  bis- 
muth, forms  the  best  kind  of  pewter,  possessing  the  peculiar  whiteness  of  metallic 
tin.  The  most  fusible  compound  of  tin  and  bismuth  is  that  of  an  atom  of  each 
metal,  Bi.Sn;  it  melts  at  289-4°  (Kudberg).  When  the  metals  are  mixed  in 
other  ratios,  a  portion  first  congeals  at  a  higher  temperature,  separating  from  the 
compound  mentioned,  which  remains  liquid  till  the  temperature  falls  to  289-4°. 
Although  tin  precipitates  copper  from  its  solutions  in  acids,  yet  it  is  possible  to 
precipitate  tin  upon  copper,  and  to  cover  the  latter  with  tin,  as  is  proved  by  the 
tinning  of  pins.  Tin  is  dissolved  in  a  mixture  of  1  part  of  bitartrate  of  potash, 
2  of  alum,  2  of  common  salt,  and  a  certain  quantity  of  water,  and  the  pins,  which 
consist  of  brass  wire,  are  introduced  at  the  boiling  temperature.  The  pins  undergo 
no  change  in  this  liquor,  supposing  it  to  contain  no  undissolved  tin,  but  the 
moment  a  fragment  of  tin  touches  the  pins,  all  those  in  contact  with  each  other 
are  tinned.  Dr.  Odling  finds  that  pure  copper  boiled  in  a  moderately  dilute  and 
rather  acid  solution  of  stannous  chloride,  also  becomes  coated  with  tin.J 

*  Casselmann.  Ann.  Ch.  Pharm.  Ixxxiii.  257. 

f  Kiihn,  Pogg.  Ann.  Ixxxv.  293.  J  Chem.  Soc.  Qu.  J.  ix.  291. 


TITANIUM.  501 


ESTIMATION   OP   TIN,  AND  METHODS    OF    SEPARATING   IT   FROM    THE   PRECEDING 

METALS. 

Tin  is  estimated  in  the  state  of  bioxide,  a  compound  which  contains  78*62  per 
cent,  of  the  metal.  If  the  tin  is  united  with  other  metals  in  the  form  of  an  alloy, 
the  alloy  must  be  treated  with  nitric  acid  of  sp.  gr.  about  1-3.  The  tin  is  then 
converted  into  bioxide,  while  the  other  metals  (with  the  exception  of  antimony) 
are  dissolved  by  the  acid.  The  oxide  of  tin  must  then  be  thoroughly  washed, 
afterwards  dried,  ignited,  and  weighed.  To  insure  complete  oxidation,  the  alloy 
should  be  finely  divided. 

When  the  tin  is  in  solution  in  hydrochloric  acid  (which  is  its  usual  solvent)  it 
must  first  be  precipitated  as  a  sulphide  by  hydrosulphuric  acid,  and  the  sulphide 
then  converted  into  bioxide  by  roasting  in  an  open  porcelain  crucible,  a  small 
quantity  of  nitric  acid  being  added  to  insure  complete  oxidation. 

Precipitation  by  hydrosulphuric  acid  serves  also  to  separate  tin  from  all  metals 
which  are  not  thrown  down  by  that  reagent  from  their  acid  solutions. 

From  cadmium,  copper,  and  lead,  tin  may  be  separated  by  treating  the  solution 
with  a  slight  excess  of  ammonia,  and  then  adding  sulphide  of  ammonium  con- 
taining excess  of  sulphur.  All  the  metals  are  thereby  converted  into  sulphides; 
but  the  sulphide  of  tin  dissolves,  while  the  others  are  left  undissolved. 

Volumetric  estimation  of  tin. — The  following  method  of  estimating  the  amount 
of  tin  in  the  commercial  protochloride  is  given  by  Dr.  Penny  :*  it  is  based  on  the 
conversion  of  protochloride  of  tin  into  bichloride  by  the  action  of  chromic  acid  in 
presence  of  free  hydrochloric  acid : 

3SnCl  +  K0.2Cr03  +  7HC1  =  3SnCl2H  KC1  -f  Cr2Cl3  +  7HO. 

The  solution  of  the  tin-salt  is  mixed  with  a  sufficient  quantity  of  hydrochloric 
acid  and  gently  heated,  and  a  solution  of  bichromate  of  potash  gradually  added, 
till  a  drop  of  the  liquid  added  to  acetate  of  lead  (a  solution  of  1  part  of  that  salt 
in  8  parts  of  water  being  scattered  in  large  drops  on  a  porcelain  plate)  produces  a 
faint  yellow  colour ;  or  till  the  liquid  produces  a  dark  brown  or  red  colouring  in 
an  acidulated  mixture  of  sulphocyanide  of  potassium  and  a  pure  protosalt  of  iron. 
"With  the  commercial  solution  of  the  protochloride  of  tin,  the  contrary  method  is 
adopted ;  that  is  to  say,  the  tin  solution,  diluted  and  reduced  to  a  definite  volume, 
is  poured  into  a  solution  of  bichromate  of  potash  containing  a  known  weight  of 
that  salt.  Penny  finds,  by  direct  experiments,  that  83-2  parts  of  pure  bichromate 
of  potash  correspond  to  100  parts  of  tin. 


SECTION    II. 

TITANIUM. 

JEfc.  24-33  or  303-7;  Ti. 

This  metal  was  discovered  in  1791,  by  Mr.  G-regor  of  Cornwall,  and  afterwards 
by  Klaproth,  who  gave  it  the  name  titanium.  In  the  form  of  titanic  acid  it  con- 
stitutes several  minerals,  as  rutile,  anatase,  menachanite,  &c. ;  and  as  titanate  of 
protoxide  of  iron,  it  forms  ilmenite  and  other  species. 

When  titaniferous  iron-ores  are  smelted  in  the  blast  furnace,  small  cubic  crystals 
of  a  bright  copper  colour  are  found  on  the  slag  which  adheres  to  the  lower  part  of 
the  furnace.  These  crystals  were  long  supposed  to  be  metallic  titanium;  but 
Wb'hlerf  has  shown  that  they  also  contain  carbon  and  nitrogen,  being,  in  fact,  a 

*  Chem.  Soc.  Qu.  J.  iv.  249. 

f  Ann.  Ch.  Pharm.  Ixxiii.  34 ;  Chem.  Soc.  Qu.  J.  ii.  352. 


502  TITANIUM. 

compound  of  cyanide  of  titanium  with  nitride  of  titanium,  CyTi.3NTi3.  Pure 
titanium  is  obtained  by  heating  the  double  fluoride  of  potassium  and  titanium 
with  potassium  in  a  covered  crucible.  The  metal  is  then  set  freg  with  vivid  in- 
candescence, and  the  fluoride  of  potassium  may  be  removed  by  washing  with 
water.  Titanium  thus  obtained  is  a  dark  green,  heavy,  amorphous  powder,  which 
does  not  exhibit  any  shade  of  copper  colour,  even  after  pressure ;  under  the  micro- 
Bcope  it  appears  as  a  cemented  mass,  having  the  colour  and  lustre  of  iron.  Me- 
tallic titanium  is  also  obtained  by  mixing  titanic  acid  with  one-sixth  of  its  weight 
of  charcoal  and  exposing  it  to  the  strongest  heat  of  a  wind-furnace.  It  was  thus 
obtained  in  the  form  of  a  copper-coloured  or  gold-coloured  powder  by  Vauquelin, 
Lampadius,  and  others ;  but  possibly  the  charcoal  which  they  used  may  have  con- 
tained nitrogen,  and  that  element  united  with  the  reduced  metal. 

Pure  titanium  (prepared  from  the  double  fluoride)  burns  with  great  splendour 
when  heated  in  the  air,  and,  if  sprinkled  into  a  flame,  is  consumed,  with  brilliant 
scintillations,  at  a  considerable  distance  above  the  point  of  the  flame.  When 
heated  to  redness  in  oxygen-gas,  it  burns  with  a  splendour  resembling  a  discharge 
of  electricity.  In  chlorine-gas  it  exhibits  similar  phenomena,  requiring  also  the 
aid  of  heat  to  set  it  on  fire.  Mixed  with  red  lead  and  heated,  it  burns  with  such 
violence  that  the  mass  is  thrown  out  of  the  vessel,  with  loud  detonation.  Titanium 
does  not  decompose  water  at  ordinary  temperatures,  but  on  heating  the  water  to 
the  boiling  point,  hydrogen  begins  to  escape.  Warm  hydrochloric  acid  dissolves 
titanium  with  brisk  evolution  of  hydrogen.  Ammonia  added  to  the  solution 
throws  down  a  black  oxide;  and,  on  heating  the  liquid,  hydrogen  is  evolved,  and 
the  precipitate  first  turns  blue,  and  is  afterwards  converted  into  white  titanic  acid. 

Titanium  forms  three  compounds  with  oxygen :  viz.,  the  protoxide,  TiO,  whose 
composition  is,  however,  doubtful ;  the  sesquioxide,  Ti203 ;  and  titanic  acid,  Ti02. 

Protoxide  of  titanium.  TiO,  32  33  or  403-7  —  is  formed  when  titanic  acid  is 
exposed  in  a  charcoal  crucible,  to  the  highest  temperature  of  a  wind-furnace. 
W'here  the  acid  was  in  contact  with  the  charcoal,  a  thin  coating  of  metallic  tita- 
nium is  formed;  but  within,  it  is  changed  into  a  black  mass,  which  is  insoluble  in 
all  acids,  and  not  otherwise  aifected  by  them,  and  is  oxidated  with  difficulty  when 
heated  in  contact  with  air,  or  by  fusion  with  nitre.  Protoxide  of  titanium  is  also 
obtained  by  the  moist  way,  in  the  form  of  a  deep  purple  powder,  when  a  fragment 
of  zinc  or  iron  is  introduced  into  a  solution  of  titanic  acid  in  hydrochloric  acid ; 
but  it  alters  so  quickly  by  absorption  of  oxygen,  that  no  opportunity  has  yet  been 
obtained  of  studying  its  properties.  The  composition  assigned  to  it  above  is, 
therefore,  hypothetical.  The  blue  powder  is,  perhaps,  a  compound  of  protoxide 
of  titanium  with  oxide  of  zinc  or  iron. 

Sesquioxide  of  titanium,  Ti203. — When  anhydrous  titanic  acid  is  strongly 
ignited  in  a  current  of  hydrogen  gas,  it  becomes  black  and  loses  considerably  in 
weight.  From  a  determination  of  the  actutil  loss  of  weight,  Ebelmen  concludes 
that  sesquioxide  of  titanium  is  produced.  The  residue  is  not  acted  upon  by  nitric 
or  hydrochloric  acid,  but  dissolves  in  sulphuric  acid,  forming  a  violet  solution.* 

Titanic  acid,  Ti02,  40-33  or  503-7. — In  the  mineral  rutile,  titanic  acid  is  crys- 
tallized in  the  form  of  tinstone,  the  link  by  which  tin  is  connected  with  titanium. 
Again,  ilnienite  and  other  varieties  of  titanate  of  iron,  FeO.Ti02  are  isomorphous 
with  sesquioxide  of  iron ;  and  thus  tin  comes  to  be  connected  through  titanium 
with  the  last  order  of  metals.  But  titanic  acid  is  dimorphous,  and  crystallizes,  in 
anatase,  in  an  unconnected  form.  The  best  method  of  obtaining  pure  titanic  acid 
is  to  fuse  titanate  of  iron,  reduced  to  powder  and  levigated  with  sulphur.  The 
sulphur  has  no  action  upou  the  titanic  acid,  but  converts  the  protoxide  of  iron 
into  a  sulphide  of  iron,  which  is  dissolved  by  hydrochloric  acid.  If  iron  is  still 
retained  by  the  titanic  acid,  the  latter  is  heated  in  a  stream  of  hydrosulphuric  acid 

*Ann.  Ch.  Phys.  [3.]  xx.  385. 


NITRIDES    OF    TITANIUM.  503 

gas,  by  which  every  particle  of  iron  is  converted  into  sulphide,  and  then  removed 
by  hydrochloric  acid. 

Titanic  acid  is  a  white  powder,  which  acquires  a  yellow  tint  by  exposure  to  a 
high  temperature;  it  is  infusible  and  insoluble  in  water.  Titanic  acid  is  consi- 
derably analogous  in  properties  to  silica;  like  that  acid  it  has  a  soluble  modifica- 
tion, formed  by  igniting  titanic  acid  with  an  alkaline  carbonate,  which  is  soluble 
in  dilute  hydrochloric  acid.  The  acid  solution  of  titanic  acid  gives  an  orange-red 
precipitate  with  an  infusion  of  gall-nuts,  which  is  characteristic  of  titanic  acid. 
On  neutralizing  the  acid  solution  with  ammonia,  the  soluble  modification  of  titanic 
acid  is  thrown  down  as  a  white  gelatinous  precipitate.  When  this  precipitate  is 
dried  and  heated,  it  glows,  and  the  titanic  acid  is  then  no  longer  soluble  in  acids. 
When  a  solution  of  bichloride  of  titanium,  or  of  the  sulphate  of  titanic  acid  in 
water,  is  boiled  for  some  time,  titanic  acid  precipitates  in  the  insoluble  modifi- 
cation. 

Titanic  acid  mixed  with  borax,  or  better  with  phosphorus-salt,  forms  in  the  outer 
blowpipe-flame  a  colourless  glass,  but  in  the  inner  flame,  a  glass  which  is  yellow 
while  hot,  but  assumes  a  violet  colour  on  cooling.  The  same  character  is  exhibited 
by  those  salts  of  titanic  acid  whose  bases  do  not  themselves  impart  any  colour  to 
the  bead.  If  the  titanic  acid  contains  iron,  the  colour  of  the  bead  is  brown-red 
or  blood-red  instead  of  violet.  Many  titanates  yield  the  blue  colour  only  with 
phosphorus-salt,  not  with  borax.  The  colour  is  produced  more  readily  by  heating 
the  substance  on  charcoal  than  on  platinum  wire.  The  above  characters  suffice  to 
distinguish  titanic  acid  from  all  other  substances. 

Bisulphide  of  titanium,  TiS2,  was  discovered  by  Rose,  who  formed  it  by  passing 
the  vapour  of  bisulphide  of  carbon  over  titanic  acid,  in  a  porcelain  tube  main- 
tained at  a  bright  red  heat. 

Bichloride  of  titanium,  TiCl2,  was  formed  by  Mr.  George,  of  Leeds,  by  trans- 
mitting chlorine  over  metallic  titanium  at  a  red  heat.  It  is  a  transparent  colour- 
less liquid,  resembling  bichloride  of  tin,  and  boiling  a  little  above  212°.  The 
density  of  its  vapour  is  6-615  (Dumas).  Bichloride  of  titanium  combines  with 
ammonia,  and  forms  a  white  saline  mass,  TiCl2-2NH3.  Metallic  titanium  is  most 
easily  obtained  by  heating  this  compound  to  redness.  Bichloride  of  titanium  also 
absorbs  phosphuretted  hydrogen,  and  forms  a  dry  brown  powder.  From  this 
compound  when  heated,  a  lemon-yellow  sublimate  rises,  which  Rose  found  to  con- 
tain 3  atoms  of  bichloride  of  titanium,  combined  with  1  atom  of  a  compound  of 
phosphuretted  hydrogen  and  hydrochloric  acid,  analogous  to  sal-ammoniac,  but 
which  could  not  be  isolated.  Bichloride  of  titanium  combines  with  the  alkaline 
chlorides,  forming  double  salts,  which  are  colourless  and  capable  of  crystallizing. 
It  also  combines  with  chloride  of  cyanogen,  forming  a  yellow  crystalline  compound 
containing  CyC1.2TiCl2,  and  with  anhydrous  hydrocyanic  acid,  forming  the  com- 
pound HCy.TiCl2,  a  yellow  pulverulent  substance  which  sublimes  below  212°,  in 
transparent,  shining,  lemon-yellow  crystals. 

Bromide  of  titanium,  TiBr2,  is  obtained  by  passing  bromine  vapour  over  an 
intimate  mixture  of  titanic  acid  and  carbon,  heated  to  bright  redness,  and  distilling 
the  resulting  brown  liquid  with  excess  of  mercury  to  remove  free  bromine.  It  is 
an  amber-yellow  crystalline  body  of  specific  gravity  2-6.  It  melts  at  102°,  and 
boils  at  356°.  It  attracts  moisture  with  the  greatest  avidity,  and  is  converted  into 
titanic  and  hydrobromic  acids  (F.  B.  Duppa). 

A  volatile  bifluoride  of  titanium,  TiF2,  was  obtained  by  Unverdorben,  by  dis- 
tilling titanic  acid  in  a  platinum  apparatus  with  fluor  spar  in  powder  and  fuming 
sulphuric  acid. 

A  definite  sulphate  of  titanic  acid,  Ti02  .  S03,  is  obtained  by  dissolving  titanic 
acid  iu  sulphuric  acid,  and  evaporating  to  dryness  at  a  heat  below  redncss° 

Nitrides  of  titanium.  —  H.  Rose,  by  heating  the  double  chloride  of  titanium 
and  ammonium  in  ammoniacal  gas,  or  by  heating  the  ammonio-chloride  of  titanium, 
2NH3 .  TiCl2,  with  sodium,  obtained  a  copper-coloured  substance  which  he  supposed 


504  TITANIUM. 

to  be  metallic  titanium,  but  which  Wohler  has  shown  to  consist  of  nitride  of 
titanium,  Ti3N2,  or  more  probably  Ti6N4  =  STiN  .  Ti3N ;  it  contains  28  per  cent, 
of  nitrogen.  This  compound  is  redder  than  the  cubic  crystals  of  the  blast- 
furnaces, which  have  a  tinge  of  yellow.  Another  nitride  of  titanium,  TiN,  is 
produced  when  titanic  acid  is  strongly  heated  in  a  stream  of  ammoniacal  gas.  Its 
powder  is  dark  violet,  with  a  tinge  of  copper-colour ;  in  small  pieces  it  exhibits  a 
violet  copper-colour  and  metallic  lustre.  A  third  nitride,  Ti5N3,  or  more  probably 
2TiN  .  Ti3N,  is  formed  when  Rose's  titanium  is  subjected  to  the  action  of  a  stream 
of  hydrogen  at  a  strong  red  heat.  It  has  a  brassy  or  almost  gold-yellow  colour 
and  a  metallic  lustre.  It  is  also  obtained  (mixed  however  with  carbon)  when 
titanic  acid  is  heated  to  redness  in  a  stream  of  cyanogen  gas  or  hydrocyanic  acid 
vapour;  no  cyanide  of  titanium  is  formed  in  this  reaction.  All  these  three 
nitrides  of  titanium  sustain,  without  decomposition,  a  temperature  at  least  equal  to 
that  of  melting  silver.  Mixed  in  the  state  of  powder  with  the  oxides  of  copper, 
lead,  or  mercury,  and  heated,  they  emit  a  lively  sparkling  flame,  and  reduce  the 
oxides  to  the  metallic  state.  When  fused  with  hydrate  of  potash,  they  give  off 
ammoniacal  gas  (Wohler). 

Nitrocyanide  of  titanium,  C2NTi  .  3Ti3N.  —  This  is  the  copper-coloured  com- 
pound already  spoken  of  as  occurring  in  the  iron  furnaces,  and  formerly  mistaken 
for  metallic  titanium.  Its  formation  appears  to  be  connected  with  that  of  cyanide 
of  potassium,  so  constantly  observed  in  the  blast-furnaces.  It  sometimes  occurs 
in  very  large  masses;  in  a  furnace  at  Ru'beland  in  the  Hartz,  a  mass  of  it  was 
found,  weighing  80  pounds.  This  compound  forms  cubic  crystals  harder  than 
quartz,  and  of  specific  gravity  5-3.  It  contains  18  per  cent,  of  nitrogen  and  4  of 
carbon.  In  its  chemical  characters,  it  resembles  the  nitrides  just  described,  giving 
off  ammonia  when  heated  with  potash,  and  reducing  the  oxides  of  lead,  copper, 
and  mercury,  when  heated  with  them.  A  similar  product  may  be  formed  by 
placing  a  mixture  of  titanic  acid  and  ferrocyanide  of  potassium  in  a  well  closed 
crucible,  and  exposing  it  for  an  hour  to  a  heat  sufficient  to  melt  nickel  (Wohler). 

ESTIMATION   OF   TITANIUM,  AND    METHODS   OF   SEPARATING   IT   FROM   THE   PRE- 
CEDING  METALS. 

Titanium  is  always  estimated  in  the  form  of  titanic  acid.  This  compound  is 
best  precipitated  from  its  solutions  in  acids  by  ammonia,  which  throws  it  down  in 
the  form  of  a  very  bulky  precipitate,  resembling  hydrate  of  alumina.  A  great 
excess  of  ammonia  must  be  avoided,  as  it  would  re-dissolve  a  small  portion  of  the 
titanic  acid.  The  precipitate  after  ignition  contains  60  per  cent,  of  titanium. 

If  the  titanic  acid,  after  precipitation  by  ammonia,  is  to  be  redissolved  in  acids, 
which  is  sometimes  necessary  in  order  to  separate  it  from  other  metals,  great  care 
must  be  taken  in  the  precipitation  to  avoid  all  rise  of  temperature,  and  the  pre- 
cipitate must  be  washed  with  cold  water,  because  heat  has  the  effect  of  rendering 
titanic  acid  more  or  less  insoluble  in  acids. 

.  Titanic  acid  may  also  in  some  cases  be  separated  from  its  acid  solutions  by 
boiling;  from  the  solution  in  sulphuric  acid,  complete  precipitation  is  effected  by 
this  method ;  but  when  hydrochloric  acid  is  the  solvent,  a  small  portion  of  titanic 
acid  always  remains  in  solution  after  boiling. 

Protoxide  of  titanium  is  precipitated  from  its  solutions  by  ammonia,  and  the 
precipitate,  after  standing  from  24  to  36  hours,  is  converted,  with  evolution  'of 
hydrogen,  into  titanic  acid,  in  which  form  it  may  be  estimated. 

From  the  alkalies  and  alkaline  earths,  titanic  acid  may  be  separated  by  ammonia, 
the  solution  in  the  latter  case  being  carefully  excluded  from  the  air.  Baryta  may 
also  be  separated  by  sulphuric  acid. 

Titanic  acid  is  separated  from  magnesia  by  boiling,  if  the  two  are  dissolved  in 
sulphuric  acid,  and  by  precipitation  with  carbonate  of  baryta,  when  hydrochloric 
acid  is  the  solvent. 


CHROMIUM.  505 

The  separation  from  alumina  and  glucina  is  also  effected  by  boiling  the  sulphuric 
acid  solution. 

From  the  metals  which  are  precipitated  as  sulphides  by  sulphide  of  ammonium, 
viz.,  manyanese,  iron,  cobalt,  nickel,  and  zinc,  titanic  acid  is  separated  by  mixing 
the  acid  solution  with  tartaric  acid  and  excess  of  ammonia  (which  then  forms  no 
precipitate),  and  adding  sulphide  of  ammonium,  which  precipitates  everything  but 
the  titanic  acid.  The  filtered  solution  is  then  evaporated  to  dryness,  and  the 
residue  ignited  in  a  platinum  crucible  to  expel  ammoniacal  salts  and  burn  away  the 
carbon  of  the  tartaric  acid.  As  this  carbonaceous  matter  is  very  difficult  to  burn, 
the  ignition  should  either  be  performed  in  a  muffle  furnace,  or  a  stream  of  oxygen 
should  be  very  gently  directed  into  the  crucible.  The  residue  consists  of  titanic 
acid,  which  may  then  be  weighed. 

From  cadmium,  copper,  lead,  and  tin,  titanium  is  easily  separated  by  hydro- 
sulphuric  acid. 

SECTION  III. 

CHROMIUM. 

Eq.  26-8  or  335;  Cr. 

This  metal,  so  remarkable  for  the  variety  and  beauty  of  its  coloured  preparations, 
was  discovered  by  Vauquelin  in  1797,  in  the  red  mineral  now  known  as  chromate 
of  lead.  It  has  since  been  found  in  other  minerals,  more  particularly  chrome-iron 
(FeO  .  Cr203),  a  mineral  which  many  countries  possess  in  considerable  quantity. 
It  is  from  this  ore  that  the  compounds  of  chromium,  used  in  the  arts,  are  actually 
derived.  The  metal  may  be  procured  by  the  reduction  of  its  oxide,  in  the  usual 
way;  but  the  reduction  is  as  difficult  as  that  of  manganese.  Chromium  is  a 
greyish-white  metal,  of  density  5-9,  very  difficult  to  fuse,  and  not  magnetic.  It 
does  not  undergo  oxidation  in  the  air.  It  dissolves  in  hydrofluoric  acid  with 
evolution  of  hydrogen.  Chromium  is  also  obtained  as  a  brown  powder,  when 
sesquichloride  of  chromium  is  heated  in  ammoniacal  gas  (Liebig). 

Chromium  forms  several  compounds  with  oxygen;  viz.  protoxide  of  chromium, 
or  chromous  oxide,  CrO,  isomorphous  with  ferrous  oxide,  &c. ;  sesquioxide  of 
chromium,  or  chromic  oxide,  Cr203,  isomorphous  with  ferric  oxide  and  alumina ; 
and  chromic  acid,  Cr03,  isomorphous  with  sulphuric  acid  ;  also  a  chromoso-chromic 
oxide,  Cr304,  or  CrO.Cr203,  and  four  oxides  intermediate  between  chromic  oxide 
and  chromic  acid,  which  may,  in  fact,  be  regarded  as  chromates  of  chromic  oxide ; 
viz.  monochromate  of  chromic  oxide,  or  Cr2O3.Cr03  =  Cr306;  the  bichromate, 
Cr203.2Cr03  =  Cr4O9;  the  neutral  chromate,  Cr203.3Cr03  =  Cr5012,  and  the  acid 
chromate,  Cr203.4Cr03  =  Cr6015. 

Protoxide  of  chromium,  Chromous  oxide,  CrO;  34-8  or  435.  —  This  oxide 
probably  exists  in  chrome-iron,  and  in  pyrope.  It  is  precipitated  in  the  form  of  a 
hydrate  by  the  action  of  potash  on  a  solution  of  the  protochloride.  The  anhy- 
drous protoxide  has  not  yet  been  obtained.  The  hydrate  is  very  unstable,  decom- 
poses water,  even  at  ordinary  temperatures,  and  if  the  air  be  not  excluded  by  fill- 
ing the  apparatus  with  hydrogen  is  converted,  almost  as  soon  as  formed,  into 
chromoso-chromic  oxide,  Cr304,  with  evolution  of  hydrogen  (Peligot).  It  is  yellow 
when^recently  precipitated,  brown  when  dry,  and  may  be  preserved  unaltered  in 
dry  air.  When  ignited  it  gives  off  hydrogen,  and  the  oxygen  thereby  liberated 
converts  the  remaining  protoxide  into  sesquioxide  (Moberg). 

Hydrated  chromous  oxide  is  insoluble  in  dilute  acids,  but  dissolves  slowly  in 
strong  acids.  The  chromous  salts  are  best  prepared  by  mixing  a  solution  of  the 
protochloride  with  the  corresponding  potash  or  soda  salts,  access  of  air  being  care- 
iully  prevented.  They  are  generally  of  a  red  colour,  sometimes  inclining  to"  blue; 


506  CHROMIUM. 

dissolve  but  sparingly  in  cold  water,  but  more  readily  in  hot  water.  Like  ferrous 
salts,  they  dissolve  large  quantities  of  nitric  oxide,  forming  dark  brown  solutions. 

Protochloride  of  chromium,  chromous  chloride,  CrCl ;  62*3  or  778  75.  —  Ob- 
tained by  passing  hydrogen  gas  over  perfectly  anhydrous  sesquichloride  of  chro- 
mium very  gently  heated,  as  long  as  hydrochloric  acid  gas  continues  to  escape. 
The  hydrogen  must  be  previously  freed  from  all  traces  of  oxygen  by  passing  it 
through  a  solution  of  protochloride  of  tin  in  caustic  potash,  then  through  tubes 
containing  sulphuric  acid  and  chloride  of  calcium,  and  lastly  over  red-hot  metallic 
copper.  The  protochloride  is  also  formed  by  passing  dry  chlorine  gas  over  a  red- 
hot  mixture  of  charcoal  and  chromic  oxide.  The  first  method  yields  the  proto- 
chloride in  the  form  of  a  white,  velvety  substance,  retaining  the  form  of  the  ses- 
quichloride from  which  it  has  been  formed  \  the  second  method  yields  it  in  fine 
white  crystals,  usually  mixed,  however,  with  chromic  oxide,  chromic  chloride,  and 
charcoal. 

Protochloride  of  chromium  dissolves  in  water,  with  evolution  of  heat,  forming  a 
blue  solution,  which  rapidly  turns  green  when  exposed  to  the  air  or  to  chlorine  gas. 
With  potash  it  forms  a  dark  brown  precipitate  (yellow,  according  to  Moberg,  if 
the  air  be  completely  excluded)  of  hydrated  chromous  oxide,  which,  however, 
quickly  changes  to  light  brown  chromoso-chromic  oxide,  with  evolution  of  hydro- 
gen. Ammonia  forms  a  greenish  white  precipitate,  without  evolution  of  hydro- 
gen.' With  ammonia  and  sal-ammoniac,  a  blue  liquid  is  formed  which  turns  red 
on  exposure  to  the  air.  Sulphide  of  ammonium  or  potassium  forms  a  black  pre- 
cipitate of  chromous  sulphide.  The  solution  of  protochloride  of  chromium  is  one 
of  the  most  powerful  deoxidizing  agents  known.  With  a  solution  of  monochromate 
of  potash,  it  forms  a  dark  brown  precipitate  of  chromoso-chromic  oxide,  which, 
however,  disappears  on  the  addition  of  an  excess  of  the  protochloride,  and  forms  a 
green  solution.  It  precipitates  calomel  from  a  solution  of  corrosive  sublimate. 
With  cupric  salts,  it  forms  at  first  a  white  precipitate  of  cuprous  chloride ;  but 
when  added  in  ^excess  throws  down  red  cuprous  oxide.  It  instantly  converts 
tuny stw  acid  into  blue  oxide  of  tungsten,  and  precipitates  gold  from  the  solution 
of  the  chloride. 

Chromous  carbonate  is  formed  by  adding  a  solution  of  the  chloride  to  carbonate 
of  potash  •  its  precipitate  is  red  or  red-brown,  if  the  alkaline  solution  is  hot,  but 
in  the  form  of  dense  yellow  or  bluish  green  flakes,  if  it  is  cold ;  the  precipitate 
appears,  however,  to  have  the  same  composition  in  all  cases  (Moberg). 

Chromous  sulphite  is  obtained  by  double  decomposition  in  the  form  of  a  brick- 
red  precipitate,  which  becomes  bluish  green  on  exposure  to  the  air  (Moberg). 

Chromous  sulphate.  —  When  the  metallic  powder  obtained  by  treating  sesqui- 
chloride of  chromium  with  potassium  is  treated  with  dilute  sulphuric  acid,  hydro- 
gen is  evolved,  and  a  solution  obtained  which  exhibits  the  characters  of  a  chro- 
uious  salt  (Peligot). 

Chromoso-chromic  oxide,  Cr304  =  CrO.Cr203.  — Formed  when  the  protoxide 
comes  in  contact  with  water,  and  consequently  at  the  moment  of  its  precipitation 
by  potash,  from  a  solution  of  the  protochloride.  After  washing  with  water  and 
drying  in  vacuo,  it  has  the  colour  of  Spanish  tobacco.  It  is  but  feebly  attacked 
by  acids.  The  hydrate  is  composed  of  Cr304.HO;  when  heated,  it  is  converted 
into  chromic  oxide  with  evolution  of  hydrogen. 

Sesquioxide  of  chromium,  Chromic  oxide,  77'6  or  970.  —  This  oxide  exists  in 
chrome-iron,  but  is  not  immediately  derived  from  that  mineral.  When  chromate 
of  mercury,  the  orange  precipitate  obtained  on  mixing  nitrate  of  mercury  and 
chromate  of  potash,  is  strongly  ignited,  chromic  oxide  remains  as  a  powder  of  a 
good  green  colour.  Chromic  oxide  is  also  obtained,  by  deoxidizing  the  chromic 
acid  of  bichromate  of  potash  in  various  ways;  by  ignition  with  sulphur,  for 
instance,  or  by  igniting  together  1  part  of  bichromate  of  potash  with  1|  parts  of 
sal-ammoniac  and  1  part  of  carbonate  of  potash,  whereby  chloride  of  potassium 
and  sesquioxide  of  chromium  are  formed,  the  chromic  acid  losing  half  its  oxygen, 


CHROMIC    SALTS.  507 

which  is  converted  into  water  by  the  hydrogen  of  the  ammonia.  Another  pro- 
cess, interesting  from  affording  the  oxide  in  the  state  of  crystals,  is  to  pass  the 
vapour  of  chlorochromic  acid  (Cr02Cl)  through  a  tube  heated  to  whiteness,  when 
oxygen  and  chlorine  gases  are  disengaged,  and  chromic  oxide  attaches  itself  to  the 
surface  of  the  tube.  The  crystals  have  a  metallic  lustre,  and  are  of  so  deep  a  green 
as  to  appear  black ;  they  have  the  same  form  as  specular  iron  ore,  a  density  of  5 '21, 
and  are  as  hard  as  corundum  ( Wohler).  The  ignited  oxide  is  not  soluble  in  acids  ; 
heated  with  access  of  air,  and  in  contact  with  an  alkali,  it  absorbs  oxygen,  and  is 
converted  into  chromic  acid.  Fused  with  borax  or  other  vitreous  substances,  ses- 
quioxide  of  chromium  produces  a  beautiful  green  colour ;  it  is  the  colouring  matter 
of  the  emerald,  and  is  employed  to  produce  a  green  colour  upon  earthenware. 
Sesquioxide  of  chromium  (and  not  chromic  acid)  is  also  the  colouring  matter  of 
pink  colour  applied  to  stoneware.  This  substance  is  formed  by  strongly  igniting 
a  mixture  of  100  parts  of  bioxide  of  tin,  33  parts  of  chalk,  and  not  more  than  one 
part  of  sesquioxide  of  chromium.* 

To  obtain  the  same  oxide  in  the  hydrated  state,  a  solution  of  bichromate  of  pot- 
ash is  brought  to  the  boiling  point,  and  hydrochloric  acid  and  alcohol  added  alter- 
nately in  small  quantities,  till  the  solution  passes  from  a  red  to  a  deep  green  colour, 
and  no  longer  effervesces  from  escape  of  carbonic  acid  gas,  on  addition  of  either 
the  acid  or  alcohol.  In  this  experiment,  the  chromic  acid  liberated  by  the  hydro- 
chloric acid,  is  deprived  of  half  its  oxygen  by  the  hydrogen  and  carbon  of  the 
alcohol,  and  the  resulting  sesquioxide  of  chromium  is  dissolved  by  the  excess  of 
hydrochloric  acid  present,  and  in  fact  converted  into  the  corresponding  sesquichlo- 
ride  of  chromium.  Many  other  organic  substances  may  be  used  in  place  of  alco- 
hol in-  this  experiment,  such  as  sugar,  oxalic  acid,  &c.  The  reduction  may  also  be 
effected  by  hydro-sulphuric  acid  or  even  by  hydrochloric  acid  alone,  if  added  in 
sufficient  excess ;  in  this  last  case,  sesquichloride  of  chromium  and  chloride  of 
potassium  are  then  formed,  and  part  of  the  chlorine  escapes  as  gas ;  thus  : 

K0.2Cr03  +  7HC1  =  KC1  +  Cr2Cl3  +  7HO  +  30L 

The  oxide  of  chromium  is  precipitated  from  the  green  solution  by  ammonia,  and 
falls  as  a  pale  bluish-green  hydrate.  The  same  oxide  is  obtained  more  directly, 
when  to  a  boiling  solution  of  bichromate  of  potash  a  hot  solution  of  pentasulphide 
of  potassium  is  added,  the  chromic  acid  then  giving  half  its  oxygen  to  the  sulphur. 

Hydrated  chromic  oxide  is  soluble  in  acids,  and  forms  salts.  It  is  also  dis- 
solved by  potash  and  soda,  but  not  to  a  great  extent  by  ammonia.  Its  salts  have 
a  sweet  taste,  and  are  poisonous.  The  oxide  itself  becomes  of  a  greener  colour 
when  dried,  and  loses  water.  A  moderate  heat  affects  its  relations  to  acids,  the 
sulphate  of  the  heated  (or  green)  oxide  not  forming  a  double  salt,  for  instance, 
with  sulphate  of  potash.  When  heated  to  redness,  it  glows,  or  undergoes  the 
same  change  as  zirconia,  bioxide  of  tin,  and  many  other  hydrated  oxides  when 
made  anhydrous;  becomes  denser,  assumes  a  pure  green  colour,  and  ceases  to  be 
soluble  in  acids. 

The  salts  of  chromic  oxide  exhibit  two  different  modifications,  green  and  violet; 
some  acids,  e.g.,  sulphuric  and  hydrochloric,  produce  both  modifications;  others 
only  one.  Ammonia  produces,  in  solutions  of  green  salts,  a  bluish-grey  precipi- 
tate, but  in  solutions  of  the  violet  salts,  a  greenish-grey  precipitate,  both  of 
which,  however,  yield  green  solutions  when  dissolved  in  sulphuric  or  hydrochloric 
acid  (Regnault) ;  according  to  H.  Rose,  however,  the  precipitate  is  bluish-grey  in 
both  cases.  The  liquid  above  the  precipitate  has  a  reddish  colour,  and  contains 
a  small  quantity  of  chromic  acid.  Potash  and  soda  form  similar  precipitates, 
which  dissolve  in  excess  of  the  alkali,  forming  green  solutions  from  which  the 
chromic  oxide  is  precipitated  by  boiling.  The  alkaline  carbonates  form  greenish 

*  Malaguti,  Ann.  Ch.  Phys.  [3.]  Ixi.  p.  433.  Mr.  0.  Sims  finds  that  sesquioxide  of  iron 
and  bioxide  of  manganese  may  be  substituted  for  oxide  of  chromium  in  pink  colour,  so  that 
the  coloration  of  that  substance  is  of  a  very  peculiar  character. 


508  CHROMIUM. 

precipitates  (violet  by  candle-light),  which  dissolve  to  a  considerable  extent  in 
excess  of  the  reagent.  Uydrosulphuric  acid  forms  no  precipitate ;  sulphide  of 
ammonium  throws  down  the  hydrated  sesquioxide. 

Zinc,  immersed  in  a  solution  of  chrome-alum  or  sesquichloride  of  chromium 
excluded  from  the  air,  gradually  reduces  the  chromic  salt  to  a  chromous  salt,  the 
liquid  after  a  few  hours  acquiring  a  fine  blue  colour,  and  hydrogen  being  evolved 
by  decomposition  of  water.  If  the  zinc  be  left  in  the  liquid  after  the  change  of 
colour  from  green  to  blue  is  complete,  hydrogen  continues  to  escape  slowly,  and 
the  liquid  after  some  weeks  or  months,  is  found  no  longer  to  contain  chromium, 
the  whole  of  that  metal  being  precipitated  in  the  form  of  a  basic  salt,  and  its  place 
taken  by  zinc.  Tin,  at  a  boiling  heat,  likewise  reduces  the  chromic  salt  to  a  chro- 
mous salt,  but  only  to  a  limited  extent ;  and  on  leaving  the  liquid  to  cool  after  the 
action  has  ceased,  a  contrary  action  takes  place,  the  protochloride  of  chromium 
decomposing  the  protochloride  of  tin  previously  formed,  reducing  the  tin  to  the 
metallic  state,  and  being  itself  reconverted  into  sesquichloride.  Iron  does  not 
reduce  chromic  salts  to  chromous  salts,  but  merely  precipitates  a  basic  sulphate 
of  chromic  oxide,  or  an  oxy chloride,  as  the  case  may  be.* 

Sesquioxide  (and  also  the  protoxide)  of  chromium,  ignited  with  an  alkaline  car- 
bonate, or  better  with  a  mixture  of  the  carbonate  and  nitre,  is  converted  into 
chromic  acid,  which  unites  with  the  alkali ;  and  on  dissolving  the  fused  product 
in  water,  filtering  if  necessary,  and  neutralizing  with  acetic  acid,  the  characteristic 
reactions  of  chromic  acid  (p.  511)  may  be  obtained  with  lead  and  silver-salts.  An 
oxide  of  chromium  fused  with  borax,  in  either  blowpipe  flame,  yields  an  emerald- 
green  glass.  The  same  character  is  exhibited  by  those  salts  of  chromic  acid  whose 
bases  do  not  of  themselves  impart  decided  colours  to  the  bead. 

A  sesquisulphide  of  chromium,  Cr2S3,  corresponding  with  the  oxide,  is  obtained 
by  exposing  the  latter,  in  a  porcelain  tube,  to  the  vapour  of  bisulphide  of  carbon,  at 
a  bright  red  heat.  It  is  a  substance  of  a  dark  grey  colour,  which  is  dissolved  by 
nitric  acid. 

Sesquichloride  of  chromium,  Chromic  chloride,  Cr2Cl3;  160-1  or  2001.2. — This 
salt  is  obtained  as  a  sublimate  of  a  peach-purple  colour,  when  chlorine  is  passed 
over  a  mixture  of  oxide  of  chromium  and  charcoal,  ignited  in  a  porcelain  tube  :  or 
in  the  hydrated  state  by  evaporating  the  solution  of  sesquichloride  of  chromium 
to  dryness.  The  salt  obtained  by  the  latter  process  is  a  green  powder  containing 
Cr2Cl3-f  9HO.  When  heated,  it  gives  off  water  and  hydrochloric  acid,  and  leaves 
a  residue  o£  oxychloride  of  chromium.  Heated  in  a  current  of  hydrochloric  acid 
gas,  it  likewise  parts  with  its  water,  and  is  converted  into  the  violet  anhydrous 
sesquichloride.  The  solution,  evaporated  in  vacuo,  leaves  an  amorphous  mass 
which  dissolves  in  water  with  evolution  of  heat,  and  consists  of  Cr2Cl3-f6HO 
(Peligot).  Anhydrous  sesquichloride  of  chromium  is  perfectly  insoluble  in  cold 
water,  and  dissolves  but  very  slowly  in  boiling  water;  but  if  to  cold  water  in  which 
the  sesquichloride  is  immersed,  there  be  added  a  very  small  quantity,  even  y^p^? 
of  protochloride  of  chromium,  a  green  solution  is  formed  identical  with  that  which 
is  obtained  by  dissolving  chromic  oxide  in  hydrochloric  acid  (Peligot). 

Chromic  sulphate,  Cr203.3S03;  197-6  or  247-0.  — Chromic  oxide  is  dissolved 
by  sulphuric  acid,  but  the  salt  does  not  crystallize.  Chromic  sulphate  exhibits  a 
violet  and  a  green  modification.  The  violet  sulphate  is  obtained  by  leaving  8 
parts  of  hydrated  chromic  oxide,  dried  at  212°,  and  8  or  10  parts  of  strong  sul- 
phuric acid  in  a  loosely  stoppered  bottle  for  several  weeks.  The  solution,  which 
is  green  at  first,  gradually  becomes  blue,  and  deposits  a  greenish  blue  crystalline 
mass.  On  dissolving  this  substance  in  water,  and  adding  alcohol,  a  violet-blue 
crystalline  precipitate  is  formed;  and  by  dissolving  this  precipitate  in  very  weak 
alcohol,  and  leaving  the  solution  to  itself  for  some  time,  small  regular  octohedrons 
are  deposited,  containing  Cr203.3S03  +  15HO.  The  green  sulphate  is  prepared 

*  H.  Loewel,  Ann.  Ch.  Phys.  [3],  xl.  42. 


CHROME-ALUM.  509 

by  dissolving  chromic  oxide  in  strong;  sulphuric  acid  at  a  temperature  between 
122°  and  140°;  also  by  boiling  a  solution  of  the  violet  sulphate.  The  liquid,  when 
quickly  evaporated,  yields  a  green  crystalline  salt,  having  the  same  composition  as 
the  violet  sulphate.  The  green  sulphate  dissolves  readily  in  alcohol,  forming  a  blue 
solution,  but  the  violet  salt  is  insoluble  in  alcohol.  The  solution  of  the  green  sul- 
phate is  not  completely  decomposed  by  soluble  baryta-salts  at  ordinary  temperatures, 
a  boiling  heat  being  required  to  complete  it;  the  violet  sulphate,  on  the  contrary,  is 
deprived  of  all  its  sulphuric  acid  by  baryta-salts  at  ordinary  temperatures.  When 
either  the  green  or  the  violet  sulphate  is  heated  to  390°,  with  excess  of  sulphuric 
acid,  a  light  yellow  mass  is  obtained,  which,  when  further  heated,  leaves  a  residue 
of  anhydrous  chromic  sulphate,  having  a  red  colour.  This  anhydrous  salt  is  com- 
pletely insoluble  in  water,  and  dissolves  with  difficulty  even  in  acid  liquids.* 

Chromic  sulphate  forms  a  crystallizable  double  salt  with  sulphate  of  potash,  viz., 
chrome-alum,  KO.S03-|-Cr203.3S03  +  24HO.  This  salt  is  produced  when  a  mix- 
ture of  its  constituent  salts,  with  a  little  free  sulphuric  acid,  is  left  to  spontaneous 
evaporation.  The  best  mode  of  preparing  it  is  to  mix  three  parts  of  a  saturated 
solution  of  neutral  chromate  of  potash,  first  with  one  part  of  oil  of  vitriol,  and  then 
with  two  parts  of  alcohol,  which  is  to  be  added  by  small  portions  to  the  mixture 
of  acid  and  chromate,  and  not  to  apply  artificial  heat.  The  chromic  acid  is  thus 
deoxidized  in  a  gradual  manner,  and  large  crystals  of  the  double  sulphate  are 
slowly  deposited, (Fischer).  The  octohedral  crystals  of  chrome-alum  are  of  a  dark 
purple  colour,  and  of  a  beautiful  ruby-red,  when  so  small  as  to  be  transparent. 
The  solution  is  bluish-purple,  but  when  heated  to  140°  or  180°  becomes  green, 
and,  according  to  Fischer,  either  deposits  on  evaporation  a  bright-green  amorphous, 
difficultly  soluble  mass,  or  yields  crystals  of  sulphate  of  potash,  while  green  chromic 
sulphate  remains  in  solution.  According  to  Loewel,f  on  the  contrary,  the  change 
of  the  purple  into  the  green  salt  does  not  arise  from  a  separation  of  the  two  simple 
salts,  but  merely  from  loss  of  water  of  crystallization.  A  solution  of  chrome-alum, 
which  has  become  green  and  un crystallizable  by  heating,  does  not  deposit  any 
sulphate  of  potash  even  when  concentrated ;  neither  does  that  salt  separate  when 
the  crystals  are  melted  in  a  sealed  tube ;  but  the  green  liquid  obtained  by  either 
of  these  processes  yields,  when  heated  to  77°  and  86°  in  a  dry  atmosphere,  a  dark 
green  mass  containing  Cr203.3S03+KO.S03,  with  scarcely  6  eq.  water  (Loewel). 
The  violet  crystals  containing  24  Aq.,  when  left  for  several  days  in  dry  air  at  a 
temperature  between  77°  and  86°,  give  off  12  Aq.,  and  assume  a"  lilac  colour.  At 
212°,  another  quantity  of  water  goes  off,  and  the  crystals  become  green;  and,  by 
gradually  raising  the  temperature  to  about  660°,  the  whole  of  the  water  may  be 
expelled  without  causing  the  salt  to  melt.  The  anhydrous  crystals  are  green,  and 
dissolve  without  residue  in  boiling  water,  but  at  a  temperature  somewhat  above  660°, 
they  suddenly  become  greenish-yellow,  without  perceptible  loss  of  weight,  and  are 
afterwards  perfectly  insoluble  in  water. 

Oxalate  of  chromium  and  potash,  3(KO.C203)  -f  Cr203.3CA  +  6HO. — This 
is  another  beautiful  double  salt  of  chromium.  It  is  easily  prepared  by  the  follow- 
ing process  of  Dr.  Gregory :  —  One  part  of  bichromate  of  potash,  two  parts  of 
binoxalate  of  potash,  and  two  parts  of  crystallized  oxalic  acid  are  dissolved  to- 
gether in  hot  water.  A  copious  evolution  of  carbonic  acid  gas  takes  place,  arising 
from  the  deoxidation  of  the  chromic  acid,  at  the  expense  of  a  portion  of  the  oxalic 
acid ;  and  nothing  fixed  remains,  except  the  salt  in  question,  of  which  a  pretty 
concentrated  solution  crystallizes  upon  cooling  in  prismatic  crystals,  which  are 
black  by  reflected  light,  but  of  a  splendid  blue  by  transmitted  light,  when  suf- 
ficiently thin  to  be  translucent.  The  oxide  of  chromium  is  not  completely  pre- 
cipitated from  this  salt  by  an  alkaline  carbonate;  and  it  is  remarkable  that  only  a 
small  portion  of  the  oxalic  acid  is  thrown  down  from  it  by  chloride  of  calcium. 
When  fully  dried  and  then  carefully  ignited,  this  salt  is  completely  decomposed, 

*  Regnault,  Cours  de  Chimie.  f  Ann.  Ch.  Phys.  [3],  xliv.  313. 


510  CHROMIUM. 

and  leaves  a  mixture  of  chromate  and  carbonate  of  potash.  The  corresponding 
double  oxalate  of  chromium  and  soda  contains  9HO,  according  to  Mitscherlich. 
In  the  analogous  oxalate  of  ferric  oxide  and  soda,  the  proportion  of  water  appeared 
to  the  author  to  be  10HO. 

The  mineral  chrome-iron,  FeO.Cr203,  crystallizes  in  octohedrons,  and  cor- 
responds with  the  magnetic  oxide  of  iron,  having  the  sesquioxide  of  iron  replaced 
by  sesquioxide  of  chromium.  Its  density  is  4-5 ;  it  is  about  as  soft  as  felspar, 
and  infusible.  When  exposed  to  long-continued  calcination,  in  contact  with 
carbonate  of  potash,  in  a  reverberatory  furnace,  the  oxide  of  chromium  of  this 
compound  absorbs  oxygen,  and  combines  as  chromic  acid  with  the  potash,  while 
the  protoxide  of  iron  becomes  sesquioxide.  The  addition  of  nitre  increases  the 
rapidity  of  oxidation,  but  is  not  absolutely  required  in  the  process.  A  yellow 
alkaline  solution  of  carbonate  and  chromate  of  potash  is  obtained  by  lixiviating 
the  calcined  matter,  which  is  generally  converted  into  the  red  chromate  or  bichro^- 
mate  of  potash,  by  the  addition  of  the  proper  quantity  of  sulphuric  acid,  the 
latter  salt  being  more  easily  purified  by  crystallization  than  the  neutral  chromate. 

Chromic  acid,  Cr03,  52-19  or  651-8.  —  This  acid  is  not  liberated  from  the 
chromates  in  a  state  of  purity  by  any  acid  except  the  fluosilicic;  it  is  also  easily 
altered.  Fluosilicic  acid  gas  is  conducted  into  a  warm  solution  of  bichromate  of 
potash,  till  the  potash  is  completely  separated  as  the  insoluble  fluoride  of  silicon 
and  potassium,  which  may  be  ascertained  by  testing  a  few  drops  of  the  solution 
with  tartaric  acid  or  chloride  of  platinum.  The  solution  is  evaporated  to  dryness 
by  a  steam  heat,  and  the  chromic  acid  redissolved  by  water ;  it  gives  an  opaque, 
dull  red  solution.  Chromic  acid  may  also  be  obtained  anhydrous  and  in  acicular 
crystals,  by  distilling,  in  a  platinum  retort,  a  mixture  of  4  parts  of  chromate  of 
lead,  3  parts  of  finely  pulverized  fluor  spar,  and  7  parts  of  Nordhausen  sulphuric 
acid^  sulphate  of  lime  is  formed,  together  with  perfluoride  of  chromium,  the 
vapour  of  which  is  received  in  a  large  platinum  crucible,  covered  with  wet  paper 
and  used  as  a  condenser.  The  perfluoride  is  decomposed  by  the  aqueous  vapour 
from  the  paper,  being  resolved  into  hydrofluoric  acid  and  beautiful  orange-red 
acicular  crystals  of  chromic  acid,  which  fill  the  crucible.  A  third  and  easier 
method  of  preparing  chromic  acid  is  to  mix  a  solution  of  bichromate  of  potash, 
saturated  between  122°  and  140°,  with  1^  times  its  volume  of  strong  sulphuric 
acid,  adding  the  acid  by  successive  small  portions.  Bisulphate  of  potash  is  then 
formed,  which  remains  in  solution,  and  the  liquid,  as  it  cools,  deposits  the  chromic 
acid  in  long  red  needles.  These  may  be  drained,  first  in  a  funnel,  afterwards  on 
a  brick;  then  dissolved  in  water;  the  solution  treated  with  a  small  quantity  of 
chromate  of  baryta  to  remove  the  last  portion  of  sulphuric  acid ;  and  the  filtered 
liquid  evaporated  in  vacuo.  Chromic  acid  differs  remarkably  from  sulphuric  acid, 
in  having  but  little  aflinity  for  basic  water,  so  that  it  may  be  obtained  anhydrous 
by  evaporating  its  solution  to  dryness.  Indeed,  the  chromate  of  water  is  not 
known  to  exist,  even  in  combination,  both  the  bichromate  and  terchromate  of 
potash  being  anhydrous  salts.  The  free  acid  is  a  powerful  oxidizing  agent,  and 
bleaches  organic  colouring  matters :  chromic  acid  then  loses  half  its  oxygen,  and 
becomes  oxide  of  chromium.  It  is  also  converted  into  sesquichloride  of  chromium 
by  hydrochloric  acid,  with  evolution  of  chlorine : 

2Cr03  +  6HC1  =  CrBCl,  +  6HO  +  3d; 

and  into  sesquioxide  by  hydrosulphuric  acid,  with  precipitation  of  sulphur : 
2Cr03  +  3HS  =  Cr203  +  3HO  +  38. 

Sulphurous  acid  passed  through  a  solution  of  chromic  acid,  or  its  salts,  throws 
down  a  brown  precipitate,  consisting  of  monocbromate  of  chromic  oxide,  or 
bioxide  of  chromium;  Cr203.Cr03  =  8Cr02.  The  other  intermediate  oxides,  or 
chromates  of  chromic  oxide  mentioned  on  page  505,  are  formed  by  other  imper- 
fect reductions'  of  chromic  acid,  or  by  the  imperfect  oxidation  of  chromic  oxide. 


CHROMATES.  511 

They  are  all  brown  substances,  soluble  in  potash  and  in  nitric  acid.  One  of  them, 
t'he  bichromate,  dissolves  also  without  decomposition  in  hydrochloric  and  sulphuric 
acid ;  the  others  are  reduced  by  hydrochloric  acid  to  sesquichloride,  with  evolution 
of  chlorine,  and  resolved  by  sulphuric  acid  into  chromic  acid  and  sulphate  of 
chromic  oxide.* 

Chromic  acid  forms  bibasic,  monobasic,  biacid,  and  a  few  tri-acid  salts.  The 
monochromates  of  the  alkalies  are  yellow,  the  bichromates  red ;  the  chromates  of 
the  metals  proper  are  bright  yellow,  red,  or  occasionally  of  some  other  colour. 
All  chromates  heated  with  oil  of  vitriol  give  off  oxygen,  and  form  sulphate  of 
chromic  oxide,  together  with  another  sulphate.  When  heated  with  hydrochloric 
acid,  they  give  off  chlorine  and  form  sesquichloride  of  chromium,  together  with 
another  metallic  chloride.  Heated  in  the  anhydrous  state  with  common  salt  and 
sulphuric  acid,  they  give  off  red  vapours  of  chlorochromic  acid,  which  condense 
to  a  brownish  red  liquid.  Similarly,  when  heated  with  fluor  spar  and  sulphuric 
.acid,  they  give  off  red  vapours  of  terfluoride  of  chromium.  A  few  only  of  the 
chromates,  more  particularly  those  of  the  alkalies,  are  soluble  in  water,  but  they 
all  dissolve  in  nitric  acid.  Solutions  of  the  alkaline  chromates  form  a  pale  yellow 
precipitate  with  baryta  salts;  bright  yellow  with  lead-salts;  brick  red  with  mer- 
curous  salts ;  and  crimson  with  silver  salts. 

Chromate  of  potash,  Yellow  chromate  of  potash,  KO.Cr03;  97*8  or  1222-5. — 
This  salt  is  produced  in  the  treatment  of  the  chrome  ore,  but  is  seldom  crystal- 
lized. It  may  be  formed  from  the  bichromate,  by  fusing  that  salt  with  an  equi- 
valent quantity  of  carbonate  of  potash ;  or  by  adding  caustic  potash  to  a  red  solu- 
tion of  the  bichromate,  till  its  colour  becomes  a  pure  golden  yellow.  The  solution 
of  chromate  of  potash  has  a  great  tendency  to  effloresce  upon  the  sides  of  the 
basin  when  evaporated.  Its  crystals  are  of  a  yellow  colour,  anhydrous,  and  iso- 
morphous  with  sulphate  of  potash.  One  hundred  parts  of  water  at  10°  dissolve 
48 J  parts  of  this  salt;  the  solution  preserves  its  yellow  colour,  even  when  diluted 
to  a  great  degree. 

Bichromate  of  potash,  Red  chromate  of  potash,  K0.2O03;  148'6  or!857'5. — 
This  beautiful  salt,  of  which  a  large  quantity  is  consumed  in  the  arts,  crystallizes 
in  prisms  or  in  large  four-sided  tables,  of  a  fine  orange-red  colour.  It  fuses  below 
a  red  heat,  and  forms  on  cooling  a  crystalline  mass,  the  crystals  of  which  have, 
according  to  Mitscherlich,  the  same  form  as  those  obtained  from  an  aqueous  solu- 
tion; but  this  mass  falls  to  powder  as  it  cools,  from  the  unequal  contraction  of  the 
crystals  in  different  directions.  At  60°,  water  dissolves  yL  of  its  weight  of  this 
salt,  and  at  the  boiling  point  a  considerably  greater  quantity. 

Bichromate  of 'chloride  of  potassium,  Peliyot's  salt,  KC1.2Cr03. — This  salt, 
which  we  are  obliged  to  designate  as  if  it  contained  chloride  of  potassium  com- 
bined as  a  base  with  chromic  acid,  is  formed  by  dissolving  together,  with  the  aid 
of  heat,  about  three  parts  of  bichromate  of  potash  and  four  of  concentrated  hydro- 
chloric acid,  with  a  small  quantity  of  water,  avoiding  the  evolution  of  chlorine.  It 
crystallizes  in  flat  red  quadrangular  prisms,  and  is  decomposed  by  solution  in  pure 
water. 

Tcrchromate  of  potash,  K0.3Cr03,  is  obtained  crystallized  when  a  solution  of 
the  bichromate  is  mixed  with  nitric  acid,  and  evaporated.  Bichromates  of  soda 
and  silver  exist  which  are  anhydrous,  like  the  bichromate  of  potash  (Warington). 

Chromate  of  soda ,  NaO.O03  -f-  10HO. —  By  the  evaporation  of  a  concentrated 
solution  of  this  salt,  it  is  obtained  in  large  fine  crystals,  having  the  form  of  glauber 
salt.  The  bichromate  crystallizes  in  thin,  hyacinth-red,  six-sided  prisms,  bevelled 
at  the  ends. 

Chromate  of  ammonia,  NH4O.Cr03  is  prepared  by  evaporating  a  mixture  of 
chromic  acid  with  a  slight  excess  of  ammonia.  It  crystallizes  in  lemon-yellow 

*  For  a  full  account  of  these  brown  oxides,  see  the  translation  of  Gtnelin's  Handbook,  iv. 
113. 


512  CHROMIUM. 

needles,  very  soluble  in  water,  and  having  an  alkaline  reaction  and  pungent  saline 
taste.  When  heated,  they  give  off  ammonia,  water,  and  oxygen,  and  leave  sesqui- 
oxide  of  chromium.  The  bichromate,  NH40.2Cr03,  forms  orange-yellow  or  reddish 
brown  rhombic  tables,  which  at  a  heat  below  redness  are  decomposed,  with  emis- 
sion of  light  and  feeble  detonation,  leaving  the  sesquioxide.  It  combines  with 
chloride  of  mercury,  forming  crystalline  compounds,  containing  NH40.2Cr03.H^C) 
-f  HO,  and  3(NH40  2Cr03).HgCl  (Richmond  and  Abel).*  Rammelsberg  has 
obtained  an  acid  salt  composed  of  NH40.6Cr03  -f  IOHO. 

Chromate  of  baryta,  BaO  Cr03  is  a  lemon-yellow  powder  obtained  by  precipi- 
tating a  baryta-salt  with  an  alkaline  chromate.  It  is  insoluble  in  water,  but  dis- 
solves easily  in  nitric,  hydrochloric,  or  chromic  acid.  When  a  baryta-salt  is  pre- 
cipitated with  neutral  chromate  of  potash,  and  sulphuric  acid  added,  the  precipi- 
tate dissolves  with  partial  decomposition,  and  on  diluting  with  water,  mixing  the 
filtered  solution  with  chromic  acid,  and  evaporating  in  vacuo,  neutral  chromate  of 
baryta  first  separates,  then  crystals  of  a  bichromate,  Ba0.2O03  -f  2HO,  and  after- 
wards a  double  salt  containing  2(Ba0.3O03.HO)  +  (K0.3Cr03.HO).  (Bahr.)f 

Neutral  chromate  of  lime,  CaO.Cr03,  is  obtained  by  treating  carbonate  of  lime 
with  aqueous  chromic  acid;  and  by  treating  the  neutral  salt  with  excess  of  chro- 
mic acid  and  evaporating,  a  bichromate,  Cr0.2Cr03  -f  2HO,  is  obtained.  Chlo- 
ride of  calcium  mixed  with  monochromate  of  potash,  yields  a  double  salt  contain- 
ing 5(CaO.Cr03)  +  KO.O03.  (Bahr.) 

Chromate  of  magnesia  forms,  according  to  the  author's  observations,  yellow 
crystals  which  are  very  soluble,  and  contain  5HO.  It  does  not  form  a  double  salt 
with  chromate  of  potash,  as  sulphate  of  magnesia  does  with  sulphate  of  potash. 
It  is  remarked  that  the  insoluble  metallic  chromates  generally  carry  down  por- 
tions of  the  neutral  precipitating  salts,  or  of  subsalts,  and  their  analysis  is  often 
unsatisfactory  from  that  cause.  When  the  magnesian  chromates  are  compared 
with  the  sulphates  of  the  same  family,  the  former  are  found  to  have  their  water 
readily  replaced  by  metallic  oxides,  but  not  by  salts ;  so  that  subchrornates  with 
excess  of  oxide  are  numerous,  while  few  or  no  double  chromates  exist. 

Chromate  of  lead,  PbO.Cr03;  1624  or  2030.— This  compound,  so  well  known 
as  chrome-yellow,  is  obtained  by  mixing  nitrate  or  acetate  of  lead  with  chromate  or 
bichromate  of  potash.  The  precipitate  is  of  a  lighter  shade  from  dilute  than  from 
concentrated  solutions.  It  is  entirely  soluble  in  potash  or  soda,  but  not  in  dilute 
acids. 

Subchromate  of  lead,  2PbO.Cr03,  is  of  a  red  colour.  It  is  formed  when  a  solu- 
tion of  neutral  chromate  of  potash,  mixed  with  as  much  free  alkali  as  it  already 
contains,  is  added  to  a  solution  of  nitrate  of  lead.  But  the  finest  vermilion-red 
subchromate  is  formed  when  one  part  of  the  neutral  chromate  of  lead  is  thrown 
into  five  parts  of  nitre  in  a  state  of  fusion  by  heat.  Water  dissolves  the  chromate 
and  nitrate  of  potash  in  the  fused  mass,  and  leaves  the  subchromate  of  lead  as  a 
crystalline  powder,  (Liebig  and  Wohler).  An  orange  pigment  may  be  obtained 
very  economically,  by  boiling  the  sulphate  of  lead,  which  is  a  waste  product  in 
making  acetate  of  alumina  from  alum  by  means  of  acetate  of  lead,  with  a  solution 
of  chromate  of  potash.  The  subchromate  of  lead  forms  a  beautiful  orange  upon 
cloth,  which  is  even  more  stable  than  the  yellow  chromate,  not  being  acted  upon 
by  either  alkalies  or  acids.  One  method  of  dyeing  chrome-orange,  is  to  fix  the 
yellow  chromate  of  lead  first  in  the  calico,  by  dipping  it  successively  in  acetate  of 
lead  and  bichromate  of  potash,  and  then  washing  it.  This  should  be  repeated,  in 
order  to  precipitate  a  considerable  quantity  of  the  chromate  in  the  calico.  A  milk 
of  lime  is  then  heated  in  an  open  pan;  and  when  it  is  at  the  point  of  ebullition, 
the  yellow  calico  is  immersed  in  it,  and  instantly  becomes  orange,  being  deprived 
of  a  portion  of  its  chromic  acid  by  the  lime,  which  forms  a  soluble  chromate  of 

*  Chem.  Soc.  Qu.  J.  iii.  139.  f  J.  pr.  Chem.  Ix.  60. 


ESTIMATION     OF     CHROMIUM.  513 

lime.  At  a  lower  temperature,  lime-water  dissolves  the  eliminate  of  lead  entirely, 
and  leaves  the  cloth  white. 

Chromate  of  silver  falls  as  a  reddish  brown  precipitate  when  nitrate  of  silver  ia 
added  to  neutral  chromate  of  potash.  Dissolved  in  hot  and  concentrated  solution 
of  ammonia,  it  yields,  on  cooling,  large  well  formed  crystals,  AgO.Cr03  +  2NH3, 
isomorphous  with  the  analogous  ammoniacal  sulphate  and  selcniate  of  silver. 

Ghlorochromic  acid,  Cr02Cl,  or  2Cr03.CrCl3. — This  is  a  volatile  liquid,  obtained 
by  distilling,  in  a  glass  retort,  at  a  gentle  heat,  3  parts  of  bichromate  of  potash 
and  3^-  parts  of  common  salt,  previously  reduced  to  powder  and  mixed  together, 
with  5  parts  by  water-measure  of  pil  of  vitriol,  discontinuing  the  distillation  when 
the  vapours,  from  being  of  a  deep  orange-red,  become  pale  —  that  change  arising 
from  watery  vapour.  The  compound  is  a  heavy  red  liquid,  decomposed  by  water. 
The  density  of  its  vapour  is  5-9. 

Terfluoride  of  chromium,  CrF3,  is  obtained  in  the  manner  already  mentioned 
under  the  preparation  of  chromic  acid.  It  is  a  blood-red  liquid.  No  correspond- 
ing terchloride  of  chromium  has  been  obtained  in  an  isolated  state. 

Perchromic  acid,  Cr207.  —  When  peroxide  of  hydrogen  dissolved  in  water  is 
mixed  with  a  solution  of  chromic  acid,  the  liquid  assumes  a  deep  indigo-blue 
colour,  but  often  loses  this  colour  very  rapidly,  giving  off  oxygen  at  the  same  time. 
The  same  blue  colour  is  formed  by  adding  a  mixture  of  aqueous  peroxide  of 
hydrogen  and  sulphuric  or  hydrochloric  acid  to  bichromate  of  potash ;  but,  in  a 
very  short  time,  oxygen  is  evolved,  and  a  potash-salt,  together  with  a  chromic  salt, 
left  in  solution.  For  each  atom  of  KO .  2Cr03,  four  atoms  of  oxygen  are  evolved, 
provided  an  excess  of  H02  be  present :  t 

KO .  2Cr03  +  0  +  4S03  =  KO .  S03  +  Cr203 .  3S03  +  40. 

The  peroxide  of  hydrogen  first  gives  up  1  at.  0  to  the  2  at.  of  Cr03,  and  forms 
Cr207;  and  this  compound  is  subsequently  resolved  into  Cr203  and  40.  With 
ether,  perchromic  acid  forms  a  more  stable  blue  mixture  than  with  water,  and  in 
this  state  may  be  made  to  unite  with  ammonia  and  with  certain  organic  bases," 
forming  very  stable  compounds,  from  which  stronger  acids  separate  the  blue  acid. 


ESTIMATION    OF    CHROMIUM,    AND    METHODS    OP    SEPARATING   IT    FROM   THE 

PRECEDING   METALS. 

Chromium  is  usually  estimated  in  the  state  of  sesquioxide.  When  it  exists  in 
solution  in  that  state,  it  may  be  precipitated  by  ammonia,  care  being  taken  to  avoid 
a  large  excess  of  that  reagent  (which  would  dissolve  a  portion),  and  to  heat  the 
liquid  for  some  time.  The  chromic  oxide  is  then  completely  precipitated,  and  the 
precipitate,  after  washing  and  drying,  is  reduced  by  ignition  to  the  state  of  anhy- 
drous sesquioxide,  containing  70-1  per  cent,  of  the  metal. 

When  chromium  exists-in  solution  in  the  state  of  chromic  acid,  it  is  best  to 
precipitate  it  by  a  solution  of  mercurous  nitrate;  the  mercurous  chromate 
thereby  thrown  down  yields  by  ignition  the  anhydrous  sesquioxide.  The  chromic 
acid  might  also  be  precipitated  and  estimated  in  the  form  of  a  baryta  or  lead  salt. 

Chromic  acid  may  also  be  estimated  by  means  of  oxalic  acid,  which  reduces  it 
to  sesquioxide,  being  itself  converted  into  carbonic  acid.  The  quantity  of  carbonic 
acid  evolved  determines  the  quantity  of  chromic  acid  present,  3  eq.  C02  corre- 
sponding to  1  eq.  Cr03,  as  shown  by  the  equation  : 

2Cr03  +  3C203  =  Cr203  +  6CO2. 

The  mode  of  proceeding  is  the  same  as  that  adopted  for  the  valuation  of  black 
oxide  of  manganese  (p.  438).     If  the  object  be  merely  to  determine  the  quantity 
of  chromium  present,  any  salt  of  oxalic  acid  may  be  used ;  but  if  the  alkalies  are 
33 


514  CHROMIUM. 

also  to  be  estimated  in  the  remaining  liquid,  tlie  ammonia  or  baryta  salt  must  be 
used. 

Chromic  oxide,  in  the  state  of  neutral  or  acid  solution,  is  easily  separated  from 
the  alkalies  or  alkaline  earths,  by  precipitation  with  ammonia,  care  being  taken 
in  the  latter  case  to  protect  the  liquid  and  precipitate  from  the  air.  The  same 
method,  with  addition  of  sal-ammoniac,  serves  to  separate  chromic  oxide  from 
magnesia.  The  separation  from  the  alkaline  earths  and  from  magnesia  may  also 
be  effected  by  precipitating  the  whole  with  an  alkaline  carbonate,  and  igniting  the 
precipitate  with  a  mixture  of  carbonate  of  soda  and  nitre.  The  chromium  is  then 
converted  into  chromate  of  soda,  which  may  be  dissolved  out,  and  the  solution, 
after  neutralization  with  nitric  or  acetic  acid,  treated  with  mercurous  nitrate  as 
above. 

From  alumina,  and  glucina,  chromic  oxide  may  be  separated  by  treating  the 
solution  with  excess  of  potash,  and  boiling  the  liquid  to  precipitate  the 'chromic 
oxide.  The  separation  is,  however,  more  completely  effected  by  fusing  with  nitre 
and  carbonate  of  soda,  treating  the  fused  mass  with  water,  adding  an  excess  of 
nitric  acid  to  dissolve  anything  that  may  be  insoluble  in  water,  and  precipitating 
the  alumina  or  glucina  by  ammonia. 

Another  method  of  converting  chromic  oxide  into  chromic  acid,  and  thereby 
effecting  its  separation  from  the  abovementioned  oxides,  is  to  treat  the  mixture 
with  excess  of  potash,  and  heat,  the  solution  gently  with  bioxide  of  lead.  The 
whole  of  the  chromium  is  then  converted  into  chromic  acid,  and  remains  dissolved 
•as  chromate  of  lead  in  the  alkaline  liquid;  and  on  filtering  from  the  excess  of 
bioxide  of  lead,  and  any  other  insoluble  matter  that  may  be  present,  and  super- 
saturating the  filtrate  with  acetic  acid,  the  chromate  of  lead  is  precipitated 
{Chancel).* 

Chromic  acid  may  be  separated  from  the  alkalies  in  neutral  solutions  by  pre- 
cipitation with  mercurous  nitrate;  also  by  reducing  it  to  chromic  oxide  with 
hydrochloric  acid  and  alcohol,  and  precipitating  by  ammonia.  From  the  earths  it 
•may  also  -be  separated  by  this  latter  method,  or,  again,  by  fusing  with  carbonate  of 
soda,  dissolving  out  with  water,  &c. 

From  manganese,  iron  (in  the  state  of  protoxide),  cobalt,  nicJcel,  and  zinc, 
chromium  in  the  state  of  sesquioxide  may  be  separated  by  agitation  with  carbonate 
of  baryta,  which  precipitates  the  chromic  oxide,  leaving  the  protoxides  in  solution. 
The  precipitate  is  then  treated  with  dilute  sulphuric  acid,  which  dissolves  the 
chromic  oxide  and  leaves  the  baryta,  and  the  filtrate  treated  with  ammonia  to  pre- 
cipitate the  chromic  oxide.  Chromium  may  also  be  separated  from  all  these 
metals,  except  manganese,  by  fusion  with  nitre  and  carbonate  of  soda,  or  with  the 
carbonate  alone  if  it  is  already  in  the  form  of  chromic  acid ;  or  again,  the  separa- 
tion may  be  effected  by  means  of  potash  and  bioxide  of  lead,  according  to  Chancel's 
method  above  described. 

From  cadmium,  copper,  lead,  and  tin,  chromium  is  easily  separated  by  hydro- 
sulphuric  acid. 

When  sesquioxide  of  chromium  and  chromic  acid  occur  together  in  a  solution, 
the  chromic  acid  may  be  precipitated  by  mercurous  nitrate,  the  solution  being 
first  completely  neutralized,  and  the  sesquioxide  precipitated  from  the  filtrate  by 
ammonia,  which  at  the  same  time  throws  down  a  mercury-compound,  to  be  after- 
wards separated  from  the  chromic  acid  by  ignition. 

*  Compt.  rend,  xliii.,  927. 


VANADIUM.  515 

SECTION   IY. 

VANADIUM. 

Eq.  68-55  or  856-9;  V. 

Vanadium,  so  named  from  Vanadis,  a  Scandinavian  deity,  was  discovered  by 
Sefstrcem  in  1830,  in  the  iron  prepared  from  the  iron  ore  of  Taberg,  in  Sweden, 
and  procured  afterwards  in  larger  quantity  from  the  slag  of  that  ore.  It  was 
found  afterwards  by  Mr.  Johnston,  in  a  new  mineral  discovered  by  him,  the  vana- 
diate  of  lead,  from  Wanlockhead.  It  is  one  of  the  rarest  of  the  elements.  The 
metal  itself  has  considerable  resemblance  in  properties  to  chromium.  It  combines 
with  oxygen  in  three  proportions,  forming  the  protoxide  of  vanadium,  VO,  bioxide, 
V02,  and  vanadic  acid,  V03. 

Protoxide  of  vanadium,  VO,  76*55  or  95*69,  is  produced  by  the  action  of 
charcoal  or  hydrogen  upon  vanadic  acid.  It  is  a  black  powder  of  semi-metallic 
lustre,  and  when  made  coherent  by  pressure,  conducts  electricity  like  a  metal. 
It  does  not  combine  with  acids,  and  exhibits  none  of  the  characters  of  an  alkaline 
base.  It  is  readily  oxidized  when  heated  in  the  open  air,  and  passes  into  the 
following  compound. 

Bioxide  of  vanadium,  Vanadic  oxide,  V02,  84-55  or  1056-9,  is  produced  by 
the  action  of  hydrosulphuric  acid  and  other  deoxidating  substances  upon  vanadic 
acid.  When  pure,  it  is  a  black  pulverulent  substance,  quite  free  from  any  acid 
or  alkaline  reaction.  It  dissolves  in  acids,  and  forms  salts,  most  of  which  are  of  a 
blue  colour.  Vanadic  salts  form,  with  the  hydrates  and  monocarbonates  of  the 
fixed  alkalies,  a  greyish-white  precipitate  of  hydrated  vanadic  oxide,  which  dis- 
solves in  a  moderate  excess  of  the  reagent,  but  is  precipitated  by  a  large  excess  in 
the  form  of  a  vanadite  of  the  alkali.  Ammonia  in  excess  produces  a  brown  pre- 
cipitate, soluble  in  pure  water,  but  insoluble  in  water  containing  ammonia.  Fer- 
rocyanide  of  potassium  forms  a  yellow  precipitate,  which  turns  green  on  exposure 
to  the  air.  Hydrosulphuric  acid  produces  no  precipitate.  Sulphide  of  ammo- 
nium forms  a  black-brown  precipitate,  soluble  in  excess.  Tincture  of  galls  forms 
a  finely-divided  black  precipitate,  which  gives  to  the  liquid  the  appearance  of  ink. 

Bioxide  of  vanadium  is  also  capable  of  acting  as  an  acid,  and  forms  compounds 
with  alkaline  bases,  some  of  which  are  crystallizable.  It 'is  hence  called  vanadous 
acid,  and  its  salts  vanadites.  These  salts  in  the  dry  state  are  brown  or  black  j 
they  are  all  insoluble  in  water,  excepting  those  of  the  alkalies.  The  solutions  of 
the  alkaline  vanadites  are  brown,  but  when  treated  with  hydrosulphuric  acid,  they 
acquire  a  splendid  red-purple  colour,  arising  from  the  formation  of  a  sulphur-salt. 
Acids  colour  them  blue,  by  forming  a  double  salt  of  vanadic  oxide  and  the  alkali. 
Tincture  of  galls  colour  them  blackish-blue.  The  insoluble  vanadites,  when 
moistened  or  covered  with  water,  become  green,  and  are  converted  into  salts  of 
vanadic  acid. 

Vanadic  acid,  V03'  92-55  or  1156-9.  —  It  is  in  this  state  that  vanadium 
occurs  in  the  slag  of  the  iron-ore  of  Taberg,  and  in  the  vanadiate  of  lead.  It  is 
obtained  by  dissolving  the  latter  mineral  in  nitric  acid,  and  precipitating  the  lead 
and  arsenic,  with  which  the  vanadium  is  accompanied,  by  hydrosulphuric  acid. 
A  blue  solution  of  bioxide  of  vanadium  remains,  which  becomes  vanadic  acid  when 
evaporated  to  dryness.  Vanadic  acid  fuses,  but  retains  its  oxygen  at  a  strong  red 
heat.  It  is  very  sparingly  soluble,  water  taking  up  only  1 '100th  of  its  weight  of 
this  compound,  thereby  acquiring  a  yellow  colour  and  an  acid  reaction.  It  acts 
the  part  of  a  base  to  stronger  acids.  An  interesting  double  phosphate  of  silica 
and  vanadic  acid  was  observed  in  crystalline  scales,  of  which  the  formula  is 


516       „  VANADIUM. 

2Si03.P05  +  2V03.P05  +  6HO.  Vanadic  acid  forms,  with  bases,  neutral  and 
acid  salts,  the  first  of  which  admit  of  an  isomeric  modification,  being  both 
white  and  yellow,  while  the  acid  salts  are  of  a  fine  orange-red.  Vanadic 
and  chromic  acids  are  the  only  acids  of  which  the  solution  is  red,  while  they  are 
distinguished  from  each  other  by  the  vanadic  acid  becoming  blue,  and  the  chromic 
acid  green,  when  they  are  deoxidized.  All  the  vanadiates  are,  more  or  less, 
soluble  in  water;  some  of  them,  however,  as  the  baryta  and  lead  salts,  are  very 
sparingly  soluble.  The  vanadiates  of  the  alkalies  are  sparingly  soluble  in  cold 
water,  especially  if  it  contains  a  free  alkali  or  another  alkaline  salt;  e.  g.,  vanadiate 
of  ammonia  is  nearly  insoluble  in  water  containing  sal-ammoniac ;  hence  on  treat- 
ing a  solution  of  vanadiate  of  potash  with  excess  of  sal-ammoniac,  a  precipitate  of 
vanadiate  of  ammonia  is  produced.  The  aqueous  solutions  of  the  vanadiates  are 
coloured  red  by  the  stronger  acids,  but  the  mixture  often  becomes  colourless  again 
after  a  while.  They  give  orange-red  precipitates  with  the  salts  of  teroxide  of 
antimony,  protoxide  of  lead,  protoxide,  of  copper,  and  protoxide  of  mercury. 
Hydrosulphuric  acid  produces  in  neutral  solutions  of  the  vanadiates  a  mixed 
precipitate  of  sulphur  and  hydrated  vanadic  oxide ;  in  acid  solutions,  it  merely 
throws  down  sulphur  and  reduces  the  vanadic  acid  to  vanadic  oxide.  Sulphide 
of  ammonium  imparts  to  solutions  of  the  vanadiates  a  brown-red  colour,  and,  on 
adding  an  acid  to  the  solution,  a  light  brown  precipitate  is  formed,  consisting  of 
vanadic  sulphide  mixed  with  sulphur;  the  liquid  at  the  same  time  generally 
acquires  a  blue  colour. 

All  compounds  of  vanadium  heated  with  borax  or  phosphorus  salt  in  the  outer 
blowpipe  flame,  produce  a  clear  bead,  which  is  colourless  if  the  quantity  of 
vanadium  be  small,  yellow  if  it  be  large ;  in  the  inner  flame,  the  bead  acquires  a 
beautiful  green  colour. 

Sulphides  and  chlorides  of  vanadium,  corresponding  with  the  bioxide  and 
vanadic  acid,  have  likewise  been  formed.* 

ESTIMATION    OF    VANADIUM,    AND     METHODS    OF     SEPARATING    IT    FROM    THE 

PRECEDING    METALS. 

Vanadium,  in  the  state  of  vanadic  oxide  or  vanadic  acid,  is  estimated  by  re- 
ducing it  to  the  state  of  protoxide  by  ignition  in  a  stream  of  hydrogen ;  100  parts 
of  the  protoxide  contain  90-54  of  the  metal. 

In  solutions  of  vanadous  salts,  the  vanadium  is  precipitated  by  mixing  the 
solution  with  excess  of  mercuric  chloride  (corrosive  sublimate),  and  then  with 
ammonia.  The  precipitate,  consisting  of  mercuric  vanadiate,  and  amido-chloride 
of  mercury,  is  ignited,  whereupon  vanadic  acid  remains  mixed  only  with  a  small 
quantity  of  mercuric  oxide,  from  which  it  is  separated  by  solution  in  carbonate  of 
ammonia. 

When  vanadic  acid  is  dissolved  in  a  liquid,  it  may  be  obtained  by  evaporating 
the  liquid,  and  if  volatile  acids  or  ammonia  are  also  present,  by  igniting  the  residue. 

Vanadic  acid  may  be  separated  from  many  acids  and  other  substances,  by 
causing  it  to  unite  with  ammonia,  expelling  the  excess  of  ammonia  by  evaporation, 
and  then  adding  a  saturated  solution  of  sal-ammoniac,  in  which  vanadiate  of 
ammonia  is  insoluble.  The  precipitate  is  then  washed  on  a  filter,  first  with  solu- 
lution  of  sal-ammoniac,  then  with  alcohol,  and  the  ammonia  driven  of  by  ignition. 
This  method  serves  to  separate  vanadic  acid  from  the  fixed  alkalies. 

Vanadium  may  be  separated  from  many  of  the  preceding  metals  by  the  solubility 
of  its  sulphide  in  sulphide  of  ammonium;  and  from  others,  which  are  precipitated 
from  their  acid  solutions  by  hydrosulphuric  acid,  by  acidulating  the  liquid,  and 
passing  hydrosulphuric  acid  gas  through  it;  the  vanadium  then  remains  dissolved 
in  the  form  of  vanadic  oxide. 

*  Berzelius,  Ann.  Ch.  Phys.  [2.]  xlvii.  337. 


TUNGSTEN.  517 

From  lead,  baryta,  and  strontia,  vanadic  acid  may  be  separated  by  fusion  with 
bisulphate  of  potash ;  on  treating  the  fused  mass  with  water,  sulphate  of  lead, 
baryta,  or  strontia  remains,  while  vanadiate  of  potash  is  dissolved.  Sulphuric  acid 
cannot  be  used  to  effect  this  separation,  because  the  precipitated  sulphate  always 
carries  down  with  it  a  portion  of  the  vanadium. 


SECTION   V. 

TUNGSTEN. 

Syn.  WOLFRAM.     Eq.  94-64,  or  1183;  W. 

This  element  exists  in  the  form  of  tungstic  acid  in  several  minerals,  the  most 
important  of  which  are  the  native  tungstate  of  lime,  CaO.W03,  and  wolfram,  or 
the  tungstate  of  manganese  and  iron,  MnO.W03  4-  3(FeO.W03).  Its  name 
tungsten  means  in  Swedish,  heavy  stone,  and  is  expressive  of  the  great  density  of 
its  compounds. 

Tungstic  acid  parts  with  oxygen  easily,  and  may  be  reduced  in  a  glass  tube,  by 
means  of  dry  hydrogen  gas,  at  a  red  heat.  The  metal  is  thus  obtained  in  the 
state  of  a  dense,  dark  grey  powder,  which  it  is  necessary  to  expose  to  a  very  vio- 
lent heat  to  fuse  into  globules,  for  tungsten  is  even  less  fusible  than  manganese. 
The  metal,  when  fused,  has  the  colour  and  lustre  of  iron,  and  is  not  altered  in 
air :  it  is  one  of  the  densest  of  the  metals,  its  specific  gravity  being  from  17'22  to 
17*6.  By  passing  the  vapour  of  chloride  or  oxychloride  of  tungsten  mixed  with 
hydrogen,  through  a  red-hot  glass  tube,  the  metal  is  obtained  in  the  form  of  a 
dense  specular  film  of  steel-grey  colour,  and  sp.  gr.  16-54  (Wohler).  When 
heated  to  redness  in  the  pulverulent  form,  it  takes  fire,  burns,  and  is  converted 
into  tungstic  acid.  Tungsten  forms  two  compounds  with  oxygen,  viz.,  tungstic 
oxide,  W02,  and  tungstic  acid,  W03. 

Tungstic  oxide,  W02,  110-64  or  1383.  —  This  oxide  is  obtained  as  a  brown 
powder  when  tungstic  acid  is  reduced  by  hydrogen  at  a  temperature  not  exceeding 
low  redness.  Tungstic  acid  may  also  be  deprived  of  oxygen  in  the  humid  way, 
by  pouring  diluted  hydrochloric  acid  over  it,  and  placing  zinc  in  the  liquor ;  the 
tungstic  acid  then  gradually  changes  into  tungstic  oxide,  in  the  form  of  brilliant 
crystalline  plates  of  a  copper-red  colour.  No  saline  compounds  of  this  oxide  with 
acids  are  known.  When  digested  in  a  strong  solution  of  hydrate  of  potash,  it 
dissolves,  with  disengagement  of  hydrogen  gas  and  formation  of  tungstate  of 
potash. 

A  compound  of  tungstic  oxide  and  soda,  Na0.2W02,  of  a  very  singular  nature, 
was  discovered  by  Wohler.  It  is  obtained  by  adding  to  fused  tungstate  of  soda 
as  much  tungstic  acid  as  it  will  take  up,  and  exposing  the  mass  at  a  red  heat  to 
hydrogen  gas.  After  dissolving  out  the  neutral  undecomposed  tungstate  by  water, 
the  new  compound  remains  in  golden  yellow  scales  and  regular  cubes,  possessing 
the  metallic  lustre  of,  and  a  striking  resemblance  to  gold.  This  compound  is  not 
decomposed  by  aqua  regia,  sulphuric  or  nitric  acid,  or  by  alkaline  solutions,  but 
yields  to  hydrofluoric  acid.  It  cannot  be  prepared  by  uniting  soda  directly  with 
tungstic  oxide. 

Tungstic  acid,  W03;  118-64  or  1483,  is  most  conveniently  obtained  by  decom- 
posing the  native  tungstate  of  lime,  finely  pulverized,  by  hydrochloric  acid ;  chlo- 
ride of  calcium  is  dissolved,  and  tungstic  acid  precipitates.  It  is  also  obtained 
from  wolfram  by  digesting  that  mineral  in  nitro-hydrochloric  acid,  which  dissolves 
the  oxides  of  iron  and  manganese,  and  leaves  the  tungstic  acid  in  the  form  of  a 
yellow  powder  —  or  by  fusing  the  mineral  with  four  times  its  weight  of  nitre; 
treating  the  fused  mass  with  water  to  dissolve  out  the  tungstate  of  potash  thereby 
produced ;  adding  chloride  of  calcium  to  the  filtrate  to  throw  down  the  tungstio 


518  TUNGSTEN. 

acid  as  tungstate  of  lime ;  and  decomposing;  the  washed  lime-salt  with  nitric  acid. 
Dissolved  in  ammonia  and  reprecipitated  by  acids,  tungstic  acid  always  forms  a 
compound  with  the  acid  employed.  It  may  be  obtained  in  the  separate  state  by 
heating  the  tungstate  of  ammonia  to  redness.  It  is  an  orange-yellow  powder, 
which  becomes  dull  green  when  strongly  heated.  Its  density  is  6 "12.  It  is  quite 
insoluble  in  water  and  in  acids,  but  dissolves  in  alkaline  solutions. 

Tungstic  acid  forms  both  neutral  and  acid  salts  with  the  alkalies.  Neutral 
tungstate  of  potash,  KO.W03,  is  a  very  soluble  salt,  which  may  be  obtained  in 
-small  crystals  by  evaporating  its  solution.  When  a  little  acid  is  added  to  the 
solution,  an  acid  salt  precipitates,  which  is  very  slightly  soluble  in  water.  The 
neutral  tungstate  of  soda  is  also  very  soluble,  but  may  be  obtained  in  good  crys- 
tals, which  contain  a  large  quantity  of  water  of  crystallization.  The  acid  tung- 
state of  soda,  Na0.2W03,  is  very  crystallizable,  and  soluble  in  eight  parts  of  water. 
A  combination  of  tungstic  acid  with  tungstic  oxide,  Wr02.W03,  is  obtained  as  a 
fine  blue  powder  when  tungstate  of  ammonia  is  heated  to  redness  in  a  retort,  and 
is  also  produced  under  other  circumstances.  Malaguti  is  disposed  to  consider  this 
compound  as  a  distinct  acid  of  tungsten,  W205.* 

All  the  salts  of  tungstic  acid  have  a  very  high  specific  gravity.  The  alkaline 
and  earthy  tungstates  are  colourless.  The  only  soluble  tungstates  are  those  of  the 
alkalies  and  magnesia.  Solutions  of  the  alkaline  tungstates  give,  with  hydro- 
chloric, nitric,  sulphuric,  and  phosphoric  acid,  white  precipitates  consisting  of 
compounds  of  tungstic  acid  with  the  other  acid.  The  precipitate  formed  by  phos- 
phoric acid  dissolves  in  excess  of  that  reagent ;  the  precipitates  formed  by  the 
other  three  acids  turn  yellow  on  boiling.  A  solution  of  an  alkaline  tungstate  su- 
persaturated with  sulphuric,  hydrochloric,  phosphoric,  oxalic  or  acetic  acid,  yields, 
on  the  introduction  of  a  piece  of  zinc,  a  beautiful  blue  colour  arising  from  the 
formation  of  blue  oxide  of  tungsten ;  this  effect  is  not  produced  with  nitric,  tar- 
taric,  or  citric  acid.  Solutions  of  alkaline  tungstates  form  with  lime-water  and 
with  salts  of  baryta,  lime,  zinc,  lead,  mercury,  and  silver,  white  precipitates  con- 
sisting of  tungstates  of  those  bases.  A  soluble  tungstate  mixed  with  sulphide  of 
ammonium  and  then  with  an  acid  in  excess,  yields  a  light  brown  precipitate  of 
sulphide  of  tungsten,  soluble  in  sulphide  of  ammonium. 

With  borax  and  phosphorus-salt  in  the  outer  blow-pipe  flame,  tungstic  acid 
forms  a  colourless  bead ;  in  the  inner  flame  it  forms  with  borax,  a  yellow  glass,  if 
the  quantity  of  tungsten  present  be  somewhat  considerable,  but  colourless  with  a 
smaller  quantity.  With  phosphorus-salt  in  the  inner  flame  it  forms  a  glass  of  a 
pure  blue  colour,  unless  iron  is  also  present,  in  which  case  the  colour  is  blood-red ; 
the  addition  of  tin,  however,  renders  it  blue. 

The  above  mentioned  characters  of  tuugstic  acid,  though  general,  are  not  in- 
variable. Tungstic  acid  appears  to  be  susceptible  of  certain  modifications  analo- 
gous to  those  of  phosphoric  acid,  and  depending  upon  the  proportions  in  which  it 
unites  with  water  and  other  bases.  In  some  of  these  modifications  it  is  much 
more  soluble  than  in  others,  and  is  not  precipitated  by  nitric  or  hydrochloric  acid. 

Laurent  distinguished  five  or  six  classes  of  tungstates,  viz., 

1.  Ordinary  tungstates,  W03MO,  with  or  without  water  (M  denoting  a  metal 
or  hydrogen).  To  this  class  belong  the  neutral  potash,  soda,  and  baryta-salts,  and 
most  of  the  insoluble  salts  of  tungstic  acid.  No  acid  salts  of  this  class  appear  10 
exist.  The  solution  of  an  ordinary  tungstate  dropped  into  excess  of  dilute  nitric 
acid  produces  a  gelatinous  precipitate.  The  hydrated  tungstic  acid  obtained  by 
the  action  of  aqua  regia  on  wolfram  belongs  to  this  variety,  its  formula  being 
W03.HO.  2.  Paratungstates,  W40I2.2MO,  with  or  without  water.  To  this  class 
belong  the  salts  commonly  called  bitungstates  of  potash,  soda,  ammonia,  baryta, 
&c.  They  all,  excepting  the  soda-salt,  dissolve  but  sparingly  in  water.  The  so- 
lutions give  no  precipitate  on  the  addition  of  very  small  quantities  of  nitric  acid. 

*  Ann.  Ch.  Pbys.  [2],  Ix.  271. 


SULPHIDES    OF    TUNGSTEN.  519 

or  of  very  weak  hydrochloric  acid.  They  give  precipitates  with  the  ammoniacal 
solutions  of  nitrate  of  magnesia,  zinc,  and  silver,  which  the  ordinary  tungstates 
do  not.  3.  Metafwngstates,  W309.MO,  with  or  without  water.  The  ammonia-salt 
of  this  variety  is  formed  by  boiling  a  solution  of  the  paratungstate  for  several 
hours ;  the  solution  filtered  when  cold  and  then  evaporated  to  a  syrup,  yields  very 
soluble  octohedrons.  The  solution  is  not  precipitated  by  concentrated  hydro- 
chloric acid. — 4.  Isotungstates,  W206.MO,  with  or  without  water.  The  ammonia- 
salt  is  formed  by  boiling  metatungstate  of  ammonia  with  excess  of  ammonia ;  it 
is  but  slightly  soluble  in  water.  The  acid,  which  may  be  separated  from  it  by 
means  of  another  acid,  is  principally  characterized  by  reproducing  the  isotungstate 
when  treated  with  ammonia.  5.  PoJy  tun  g  states,  W6Oi8.3MO.  When  the  yellow 
acid  obtained  from  wolfram  is  treated  with  ammonia,  and  the  solution  slowly  eva- 
porated, paratungstate  of  ammonia  is  first  deposited  and  afterwards  the  isotung- 
gtate.  The  mother-liquor  separates  into  two  layers,  one  of  which  is  brown  and 
syrupy,  and  changes  on  drying  to  an  easily  soluble  crystalline  mass,  probably  a 
double  salt  of  ammonia  and  iron.  Boiled  with  strong  nitric  acid,  it  yields  a  pre- 
cipitate which  is  not  gelatinous,  and  does  not  turn  yellow  when  boiled.  Poly- 
tungstic  acid  is  further  characterized  by  forming  with  ammonia  a  very  soluble 
salt,  which  becomes  gummy  on  evaporation.  6.  Laurent  also,  mentioned  another 
class  of  tungstates,  viz.,  Homotungstates,  containing  W60,5.MO.  According  to 
Margueritte*  also  there  exist  acid  tungstates  containing  3,  4,  5  and  6  eq.  of  acid 
to  1  eq.  of  base. 

The  composition  of  the  tungstates  has  also  been  recently  examined  by  W. 
Lotz,f  whose  results  differ  in  many  points  from  the  preceding.  According  to 
Lotz,  crude  tungstic  acid,  obtained  from  wolfram  by  the  action  of  hydrochloric 
and  a  small  quantity  of  nitric  acid,  yields  by  digestion  with  ammonia  and  evapo- 
ration at  a  very  genile  heat,  yellow  needles  of  an  ammonia-salt,  containing 
3NH40.7W03+6HO,  or  2(NH40.  2W03)+NH40.  3W08  +  6HO.  By  mixing 
warm  concentrated  solutions  of  1  eq.  of  monotungstate  of  soda,  and  rather  more 
than  1  eq.  chloride  of  ammonium,  a  double  salt  is  obtained,  composed  of 
(2NH4O.WO3)  +  NaO.W03+3HO;  and  by  adding  1  eq.  metatungstate  of  soda 
to  a  boiling  solution  of  2  eq.  chloride  of  ammonium,  another  double  salt  is  formed 
containing  3Na0.7W03-f4(3NH40  7W03)+ 14HO.  The  needle-shaped  ammo- 
nia-salt mixed  with  solutions  of  the  neutral  salts  of  barium,  strontium,  manganese, 
nickel,  and  lead,  yields  precipitates  of  the  general  formula,  3M0.7W03.  With 
alumina  a  white  curdy  precipitate  is  formed  containing  A1203.7W03  + 9HO.  Ses- 
quioxide  of  chromium  forms  a  salt  of  a  similar  constitution.  With  magnesia,  a 
sparingly  soluble  crystalline  double  salt  is  formed,  containing  2(Mg0.2W03)-f 
NH40.3W03-|-10HO;  a  similar  double  salt  with  zinc.  Cadmium  also  forms  a 
double  salt  containing  3NH40.7W03+4(3Cd0.7WaO)+35HO.  To  the  octo- 
hedral  tungstate  of  ammonia,  which  was  regarded  by  Margueritte  as  NH40.3WO3 
-I-5HO,  and  by  Laurent  as  a  metastungstate  containing  (NH4)|H^W80,0+  5HO, 

or  5NIgQ  j  18WO-H-30HO.     Lotz  assigns  the  formula,  2(NH40.4W03)+15eq. 

The  solution  of  this  salt  is  not  precipitated  by  nitric  or  hydrochloric  acid  at 
ordinary  temperatures,  but  after  continued  boiling  yields  a  yellow  precipitate ;  but 
if  it  be  previously  mixed  with  potash,  the  addition  of  an  acid  produces  an  irnme- 
mediate  white  precipitate,  which  turns  yellow  on  boiling ;  the  needle-shaped  salt 
gives  an  immediate  precipitate  with  acids,  without  previous  addition  of  alkali. 
The  octohedral  salt  differs  from  the  needle-shaped  salt  also,  in  not  forming  pre- 
cipitates with  solutions  of  the  earths  and  other  metallic  oxides,  except  when 
previously  mixed  with  ammonia,  by  which,  indeed,  it  is  converted  into  the  salt, 
3NH40.7W03. 

Sulphides  of  tungsten.  —  The  bisulphide  is  prepared  by  mixing  one  part  of 

*  Ann.  Ch.  Phys.  [3],  xvii.  475.  f  Ann.  Ch.  Pharm.  xci.  49. 


520  TUNGSTEN. 

tungsten  with  six  parts  of  cinnabar,  and  exposing  the  mixture,  covered  with  char- 
coal, in  a  crucible,  to  a  white  heat ;  or,  according  to  Roche,  by  fusing  bitungstate 
of  potash  with  an  equal  weight  of  sulphur,  and  washing  the  fused  mass  with 
water.  The  tersulphide  is  formed  by  dissolving  tungstic  acid  in  an  alkaline  sul- 
phide, and  precipitating  by  an  acid.  It  is  of  a  liver-brown  colour,  and  becomes 
black  on  drying.  The  tersulphide  of  tungsten  has  a  certain  degree  of  solubility 
*n  water  containing  no  saline  matter,  and  is  a  strong  sulphur-acid.  The  salt 
KS.WS3  forms  pale  red  crystals.  Two  parts  of  this  sulphur-salt  dissolved  in  water 
with  one  part  of  nitre,  give  large. and  beautiful  ruby-red  crystals  of  a  double  salt, 
KS.WS,+  KO.N05. 

Phosphides  of  tungsten. — Phosphorus  and  tungsten  combine  directly,  but  with- 
out emission  of  light  and  heat,  when  finely  pounded  metallic  tungsten  contained 
in  a  glass  tube  is  heated  to  redness  in  phosphorus  vapour.  The  resulting  com- 
pound is  a  dull,  dark  grey  powder,  very  difficult  to  oxidize,  and  containing  W3P2. 
Another  compound,  W4P,  is  obtained  in  magnificent  crystalline  groups,  having 
exactly  the  appearance  of  natural  geodes,  by  reducing  a  mixture  of  2  eq.  phos- 
phoric and  1  eq.  tungstic  acids  at  a  very  high  temperature  in  a  crucible  lined  with 
charcoal.  The  crystals  are  six-sided  prisms,  sometimes  an  inch  long,  of  a  steel- 
grey  colour,  and  strong  lustre;  their  specific  gravity  is  5-207.  This  compound  is 
a  perfect  conductor  of  electricity;  undergoes  no  change  when  heated  to  the 
melting  point  of  manganese  in  a  close  vessel,  and  remains  nearly  unaltered  when 
heated  to  redness  in  the  air;  but  burns  with  great  splendour  on  charcoal  in  a 
stream  of  oxygen,  or  on  fused  chlorate  of  potash ;  it  is  not  attacked  by  any  acid, 
not  even  by  aqua-regia  (Wohler).* 

Bichloride  of  tungsten,  WC12,  is  formed  when  metallic  tungsten  is  heated  in 
chlorine  gas.  It  condenses  in  dark  red  needles,  which  are  very  fusible  and  vola- 
tile. This  chloride  is  decomposed  by  water,  and  tungstic  oxide  with  hydrochloric 
acid  formed. 

Terchloride  of  tungsten,  WC13,  is  produced  at  the  same  time  as  the  last  com- 
pound, and  also  when  the  sulphide  of  tungsten  is  heated  in  chlorine  gas.  It  forms 
a  sublimate  of  beautiful  red  crystals,  which  are  resolved  by  water  into  tungstic 
and  hydrochloric  acids.  A  chlorotungstic  acid,  or  double  compound  of  terchloride 
of  tungsten  and  tungstic  acid,  W02C1,  or  WC13.2W03,  is  prepared  by  heating 
tungstic  oxide  in  chlorine  gas.  It  condenses  in  yellow  crystalline  scales:  when 
suddenly  heated,  it  is  resolved  into  tungstic  acid,  bichloride  of  tungsten,  and 
chlorine.  Another  compound  is  known,  containing  2WC13.W03  (Bonnet). 

According  to  A.  Riche,f  the  terchloride  of  tungsten  is  the  only  product  ob- 
tained when  tungsten  is  heated  in  pure  dry  chlorine  gas  :  it  crystallizes  in  needles, 
not  of  a  red  but  of  a  steel-grey  colour.  The  bichloride  is  formed  in  small  quan- 
tity, as  a  blackish-brown  mass,  by  heating  the  terchloride  in  dry  hydrogen  ;  and 
the  red  oxychloride,  WC120,  by  passing  chlorine  gas  over  a  mixture  of  tungstic 
acid  and  charcoal,  and  distilling  the  product  in  an  atmosphere  of  hydrogen. 

ESTIMATION  OF  TUNGSTEN,  AND    METHODS    OF   SEPARATING   IT   FROM   THE   PRE- 
CEDING   METALS. 

Tungsten  is  always  estimated  in  the  form  of  tungstic  acid.  When  this  acid 
exists  in  a  solution  not  containing  any  other  fixed  substance,  it  is  sufficient  to 
evaporate  to  dryness  and  ignite  the  residue.  The  tungstic  acid  is  then  obtained 
in  a  state  of  purity,  and  contains  79-76  per  cent,  of  the  metal.  Tungstic  oxide 
is  easily  converted  into  tungstic  acid  by  fusion  with  carbonate  of  soda. 

The  best  method  of  separating  tungstic  acid  from  the  fixed  alkalies  is  to  treat 
the  solution,  after  exact  neutralization  with  nitric  acid,  with  a  solution  of  niercu- 
rous  nitrate.  Mercurous  tungstate  is  then  precipitated,  and  the  mercury  may  be 
expelled  from  the  dried  precipitate  by  careful  ignition  in  a  good  draught. 

*  Chein.  Soc.  Qu.  J.  v.  91. t  Compt.  rend.  xlii.  203. 


MOLYBDENUM.  521 

The  separation  of  tungstic  acid  from  the  earths  may  be  effected  by  decomposing 
the  compound  with  nitric  acid,  and  treating  the  decomposed  mass  with  carbonate 
of  ammonia,  which  dissolves  the  tungstic  acid. 

Tungstic  acid  may  be  readily  separated  from  many  metallic  oxides,  such  as  the 
oxides  of  iron,  manganese,  nickel,  cobalt,  lead,  &c.,  by  fusing  the  whole  with  car- 
bonate of  soda,  and  digesting  the  fused  mass  with  water,  which  dissolves  tho 
tungstic  acid  and  leaves  the  oxides  undissolved. 

*  From  titanic  acid,  tungstic  acid  is  separated  by  ammonia,  which  dissolves  only 
the  latter. 

The  best  mode  of  separating  tungstic  acid  from  chromic  acid,  is  to  treat  the 
concentrated  solution  with  excess  of  hydrochloric  acid,  which  precipitates  the 
greater  part  of  the  tungstic  acid ;  then  boil  with  alcohol  to  reduce  the  chromic  acid 
to  chromic  oxide;  and  dissolve  the  tungstic  acid  by  ammonia. 


SECTION  VI. 

MOLYBDENUM. 

Eq.  47-88  or598-5;  Mo. 

This  metal  is  closely  allied  to  tungsten.  Its  native  sulphide  was  first  dis 
tinguished  from  plumbago  by  Scheele,  in  1778 ;  and  a  few  years  afterwards, 
molybdic  acid,  which  he  had  formed,  was  reduced,  and  molybdenum  obtained 
from  it,  by  another  Swedish  chemist,  Hjelm.  The  name  molybdenum  is  derived 
from  the  Greek  term  for  plumbago. 

The  oxides  of  molybdenum  are  easily  reduced,  when  exposed  to  a  strong  heat 
in  a  crucible  lined  with  charcoal,  but  the  metal  itself  is  very  refractory.  Bucholz, 
who  obtained  it  in  rounded  buttons,  found  it  to  be  a  white  metal,  of  density  be- 
tween 8*615  and  8¥636.  It  may  be  reduced  from  its  chlorides  by  hydrogen,  like 
tungsten  (p.  177),  and  then  forms  a  light  steel-grey  specular  deposit,  adhering  to 
the  glass  (Wohler).  It  is  not  acted  upon  by  hydrochloric,  hydrofluoric,  or  diluted 
sulphuric  acid ;  but  is  dissolved  by  concentrated  sulphuric  acid,  by  nitric  acid, 
and  by  aqua-regia.  Hydrate  of  potash  does  not  dissolve  this  metal  in  the  humid 
way.  Molybdenum  combines  in  three  proportions  with  oxygen,  forming  molyb- 
dous  oxide,  MoO,  molybdic  oxide,  Mo02,  and  molybdic  acid,  Mo03. 

Molt/bdous  oxide,  MoO,  55-88  or  698-5.  — This  oxide  is  obtained  by  adding  to 
the  concentrated  solution  of  any  molybdate,  so  much  hydrochloric  acid  as  to  re- 
dissolve  the  molybdic  acid  which  is  at  first  thrown  down,  and  placing  zinc  in  the 
liquid;  this  becomes  first  blue,  then  reddish-brown,  and  finally  black,  and  contains 
the  chloride  of  zinc  and  protochloride  of  molybdenum.  To  separate  the  oxide  of 
molybdenum  from  the  oxide  of  zinc,  ammonia  is  added  to  the  liquid  in  quantity 
no  more  than  sufficient  to  precipitate  the  former,  while  the  latter  remains  in 
solution.  The  molybdous  oxide  carries  down  with  it  a  portion  of  oxide  of  zinc, 
from  which  it  may  be  freed  by  washing  with  ammonia :  it  is  thus  obtained  as  a 
hydrate  of  a  black  colour.  The  hydrate  of  molybdous  oxide  dissolves  with  dif- 
ficulty in  acids,  forming  solutions  which  are  almost  black  and  opaque,  and  which 
do  not  yield  crystallizable  salts.  These  solutions  yield  with  the  alkalies  and  their 
carbonates  a  brownish-black  precipitate  of  the  hydrated  oxide,  insoluble  in  the 
caustic  alkalies,  slightly  soluble  in  the  neutral  carbonates,  but  readily  soluble  in 
bicarbonate  of  potash  or  carbonate  of  ammonia.  Hydrosulphuric  acid  throws 
down  a  brown-black  precipitate,  and  tulphide  of  ammonium  a  yellowish-brown 
precipitate  of  sulphide  of  molybdenum,  easily  soluble  in  sulphide  of  ammonium. 
Ferrocyanide  or  ferricyanide  of  potassium  forms  a  dark-brown  precipitate,  in- 


522  MOLYBDENUM. 

soluble  in  excess.  Phosphate  of  soda  forms  a  brownish-white  precipitate.  Molyb- 
dous  oxide  resists,  after  ignition,  the  action  of  all  acids. 

Molybdic  oxide,  Mo02;  63-88  or  798-5.  —  This  oxide  may  be  obtained  by 
igniting  molybdate  of  ammonia  in  a  covered  crucible,  but  mixed  with  a  little 
molybdic  acid.  It  is  better  procured  by  igniting  rapidly,  in  a  covered  crucible,  a 
mixture  of  anhydrous  molybdate  of  soda  (which  may  contain  an  excess  of  soda) 
with  sal-ammoniac.  Water  poured  upon  the  fused  mass  dissolves  common  salt, 
and  leaves  a  brown  powder,  almost  black.  But  molybdic  oxide  prepared  in  this 
way  is  insoluble  in  acids.  The  hydrated  oxide  may  be  obtained  in  various  ways, 
one  of  which  consists  in  digesting  molybdic  acid  with  hydrochloric  acid  and 
copper,  till  all  the  molybdic  acid  is  dissolved.  From  the  solution,  which  is  of  a 
deep-red  colour,  molybdic  oxide  is  precipitated,  in  appearance  exactly  similar  to 
the  hydrated  sesquioxide  of  iron,  by  ammonia  added  in  sufficient  excess  to  retain 
all  the  oxide  of  copper  in  solution.  The  hydrate  has  a  certain  degree  of  solu- 
bility in  pure  water,  and  should,  therefore,  be  washed  with  solution  of  sal-am- 
inoniac,  and  lastly  with  alcohol.  This  hydrate  reddens  litmus  paper,  but  pos- 
sesses no  other  property  of  an  acid.  It  is  not  dissolved  by  the  hydrated  alkalies, 
but  is  soluble  in  their  carbonates,  like  several  earths  and  metallic  oxides.  It  dis- 
solves in  acids  and  forms  salts,  which  are  red  when  they  contain  water  of  crystal- 
lization, and  black  when  anhydrous.  The  aqueous  solutions  of  these  salts  have  a 
reddish-brown  colour,  and  a  rough,  somewhat  acid  and  subsequently  metallic 
taste.  When  heated  in  the  air,  they  have  a  tendency  to  become  blue  by  oxida- 
tion. With  zinc,  they  first  blacken,  and  then  yield  a  black  precipitate  of  hydrated 
molybdous  oxide.  Their  behaviour  with  alkalies,  hydrosulphuric  acid,  &c.,  is 
similar  to  that  of  the  molybdous  salts,  excepting  that  the  precipitates  are  lighter 
in  colour.  The  oxalate  of  molybdic  oxide  may  be  obtained  in  crystals  by  spon- 
taneous evaporation. 

Molybdic  acid,  Mo03;  71*88  or  898 '5. — The  native  sulphide  of  molybdenum, 
in  fine  powder,  is  roasted  in  an  open  crucible,  with  constant  stirring,  at  a  heat  not 
exceeding  low  redness,  so  long  as  sulphurous  acid  goes  off.  It  leaves  a  dull 
yellow  powder,  which  is  impure  molybdic  acid.  This  is  dissolved  in  ammonia, 
and  the  molybdate  of  ammonia  purified  by  evaporation,  during  which  some  foreign 
matters  are  deposited,  and  crystallized.  The  crystallized  salt,  exposed  to  a  mode- 
rate heat,  so  as  to  avoid  fusion,  gives  off  its  ammonia,  and  leaves  molybdic  acid  in 
a  state  of  purity.  The  acid  thus  prepared  is  a  white  and  light  porous  mass,  which 
may  be  diffused  in  water,  and  divides  into  little  crystalline  scales  of  a  silky  lustre. 
It  fuses  at  a  red  heat,  and  forms  on  cooling  a  straw-coloured  crystalline  mass,  the 
density  of  which  is  349.  This  acid  forms  no  hydrate.  It  requires  570  times  its 
weight  of  water  to  dissolve  it.  Before  being  ignited,  it  is  soluble  in  acids,  and 
forms  a  class  of  compounds,  in  which  it  appears  to  play  the  part  of  base,  but  of 
which  not  much  is  known.  When  boiled  with  bitartrate  of  potash,  molybdic  acid 
dissolves,  even  after  being  fused  by  heat. 

When  a  solution  of  bichloride  of  molybdenum  is  poured  into  a  saturated  or 
nearly  saturated  solution  of  molybdate  of  ammonia,  a  blue  precipitate  falls,  which 
is  a  molybdate  of  molybdic  oxide,  M02.2M03.  This  compound  is  likewise  readily 
formed  in  a  variety  of  other  circumstances. 

The  salts  of  molybdic  acid  are  colourless,  when  their  base  is  not  coloured. 
When  they  are  treated  with  other  acids,  molybdic  acid  is  precipitated,  but  dis- 
solves in  an  excess  of  the  acid.  It  forms  both  neutral  and  acid  salts  with  the 
alkalies.  These  alkaline  molybdates  are  the  only  ones  that  are  easily  soluble  in 
water;  of  the  rest,  some  dissolve  sparingly,  and  others  are  completely  insoluble. 
Solutions  of  the  alkaline  molybdates  are  coloured  yellow  by  hydrosul^huric  acid 
from  formation  of  a  sulphomolybdate  of  the  alkali-metal  (MS,MOS3),  and  then 
yield  with  acids  a  brown  precipitate  of  tersulphide  of  molybdenum.  This  is  an 
extremely  delicate  test  for  molybdic  acid.  They  form  white  precipitates  with  salts  of 
the  earths,  and  precipitates  of  various  colours  with  salts  of  the  heavy  metals ;  e.  y 


MOLYBDATES.  523 

white  with  lead  and  silver  salts ;  yellow  with  ferric  salts ;  and  yellowish-white 
with  mercurous  salts. — Protochloride  of  tin  produces  immediately  a  greenish  blue 
precipitate,  soluble  in  hydrochloric  acid  forming  a  green  solution ;  which  turns 
blue  on  the  addition  of  a  very  small  quantity  of  the  tin-solution. — When  tribasw 
phosphoric  acid,  or  a  liquid  containing  it,  is  added  to  the  solution  of  molybdate 
of  ammonia,  together  with  an  excess  of  hydrochloric  acid,  the  liquid  turns  yellow, 
and  after  a  while  deposits  a  yellow  precipitate  of  molybdic  acid  combined  with 
small  quantities  of  phosphoric  acid  and  ammonia.  This  precipitate  is  soluble  in 
ammonia  and  likewise  in  excess  of  the  phosphate.  The  reaction  is  therefore  es- 
pecially adapted  for  the  detection  of  small  quantities  of  phosphoric  acid.  The 
bibasic  and  monobasic  phosphates  do  not  produce  the  yellow  precipitate.  Arsenic 
acid  gives  a  similar  reaction.  According  to  Seligsohn,*  the  yellow  precipitate  is 
a  phoKphomoh/bdate  of  ammonia,  2(3NH4O.P06)  +  15(H0.4Mo03.)  By  digest- 
ing it  in  a  dilute  solution  of  acetate  of  potash  or  soda,  crystalline  double  salts  are 

formed,  containing  2(3NH4O.P05)  +  15(Qr  -^J  j  .4Mo03).     With  acetate  of 

baryta,  a  double  salt  is  formed,  containing  3NH4O.P05-f  30(BaO.Mo03) ;  and 
similarly  with  acetate  of  lead. 

Molybdic  acid  and  other  compounds  of  molybdenum  form  a  colourless  bead  with 
lorax  and  phosphorus-salt  in  the  outer  blowpipe  flame.  In  the  inner  flame,  they 
form  a  brown  bead  with  borax  and  a  green  bead  with  phosphorus-salt. 

Molybdates  of  potash. — The  monomolybdate,  KO.Mo03,  is  obtained  by  agita- 
ting the  termolybdate  with  an  alcoholic  solution  of  potash :  it  then  separates  as 
an  oily  mass,  which,  when  dried  over  lime  and  sulphuric  acid,  crystallizes  in  four- 
sided  prisms  containing  2(KO.Mo03)  +  HO.  It  is  also  obtained  by  mixing  a  so- 
lution of  molybdate  of  ammonia  with  excess  of  carbonate  of  potash,  and  evapo- 
rating to  a  syrup.  Bimolybdate  of  potash  does  not  appear  to  exist.  When  a 
solution  of  molybdic  acid  in  carbonate  of  potash  is  mixed  with  strong  nitric  or 
hydrochloric  acid  till  a  slight  permanent  precipitate  is  produced,  the  liquid  after  a 
while  yields  crystals  of  a  salt  containing  4K0.9Mo03  -f  6HO ;  and  this  salt  is 
decomposed  by  water  into  monomolybdate,  which  dissolves  readily,  and  termo- 
lybdate, which  is  sparingly  soluble  : 

2(4K0.9MoO3)  =  3(KO.Mo03)  -f  5(K0.3Mo03). 

The  termolybdate  dissolves  easily  in  boiling  water,  and  separates  as  a  bulky  white 
precipitate  when  the  solution  is  quickly  cooled ;  but  by  slow  cooling  it  is  obtained 
in  needles,  having  a  beautiful  silky  lustre  and  containing  KO.3Mo03  +  3HO. 
Nitric  acid  added  in  excess  to  a  solution  of  molybdic  acid  in  carbonate  of  potash 
throws  down  a  white  precipitate  consisting  sometimes  of  quadromoJybJate  and 
sometimes  of  pentamolybdate  of  potash,  both  anhydrous  (Svanberg  arid  Struve).f 

Monomolybdate  of  soda,  NaO.Mo03  -f  2  HO,  is  obtained  by  fusing  molybdic 
acid  with  an  equivalent  quantity  of  carbonate  of  soda.  It  is  easily  soluble  in 
water,  and  crystallizes  in  small  rhombohedrons,  which  melt  easily  and  give  off 
their  water.  The  bimolybdate,  Na0.2Mo03  +  HO,  is  obtained  in  a  similar 
manner.  It  crystallizes  in  needles,  and  dissolves  sparingly  in  cold,  readily  in  boil- 
ing water.  The  termolybdate  is  obtained  by  adding  nitric  acid  to  a  solution  of 
molybdic  acid  in  carbonate  of  soda,  as  a  bulky  white  precipitate,  more  soluble 
than  the  corresponding  potash-salt.  The  solution  yields  crystals  containing 
NaO.3Mo03-f-  7HO.  Nitric  acid  added  in  excess  to  a  solution  of  molybdate  of 
soda  throws  down  nothing  but  molybdic  acid  (Svanberg  and  Struve).^ 

Monomolybdate  of  ammonia,  NH4O.Mo03,  obtained  by  treating  molybdic  acid 
in  excess  with  strong  solution  of  ammonia  in  a  closed  vessel,  then  precipitating 
with  alcohol,  and  drying  over  quicklime,  forms  microscopic  four-sided  prisms, 

*  J.  pr.  Chera.  Ixvii.  474.  f  Ann.  Ch.  Pharm.  Ixviii.  494. 

Ann.  Ch.  Pharm.  Ixviii.  404. 


524  MOLYBDENUM. 

which  are  anhydrous.  The  bimolybdate,  NH40.2Mo03,  Ls  deposited  as  a  white 
crystalline  powder  when  a  solution  of  molybdic  acid  in  excess  of  ammonia  is 
quickly  evaporated.  A  solution  of  molybdic  acid  in  ammonia,  evaporated  by  heat 
to  the  crystallizing  point,  or  left  to  evaporate  in  the  air,  deposits  large  transparent 
six-sided  prisms,  containing  NII40.2Mo03  -f  NH40.3Mo03  +  3HO  (Svanberg  and 
Struve). 

Monomolybdate  of  baryta,  BaO.Mo03,  is  precipitated  as  a  sparingly  soluble 
crystalline  powder,  on  adding  chloride  of  barium  to  a  solution  of  molybdic  acid  in 
excess  of  ammonia.  Baryta-salts,  containing  Ba0.3Mo03  +  3HO  and  Ba0.2Mo03 
-f  Ba023Mo03  +  6HO,  are  obtained  by  precipitating  the  corresponding  potash 
and  ammonia-salts  with  chloride  of  barium.  By  decomposing  monomolybdate  of 
baryta  with  dilute  nitric  acid,  an  acid  salt  is  formed  containing  Ba0.9Mo03  -f- 
4HO;  it  crystallizes  in  small  six-sided  prisms,  fusible  and  insoluble  in  water 
(Svanberg  and  Struve). 

Monomolybdate  of  magnesia,  MgO.Mo03-|-5HO,  is  obtained  in  distinct  crystals 
by  boiling  molybdic  acid  and  magnesia  alba  with  water,  and  evaporating  the 
filtrate;  it  gives  off  3  eq.  water  at  212°  (Struve).* 

Molybdate  of  manganous  oxide,  MnO.Mo03  +  HO,  is  obtained  as  a  heavy 
white  powder,  by  treating  carbonate  of  manganese  with  termolybdate  of  potash  or 
soda. 

Protosulphate  of  iron  added  to  a  solution  of  molybdate  of  potash,  reduces  the 
molybdic  acid  to  a  lower  state  of  oxidation ;  but  if  chlorine  gas  be  passed  through 
the  solution  at  the  same  time,  a  bulky  precipitate  is  formed,  which,  when  dried  in 
the  air,  forms  a  light  yellow  powder,  consisting  of  pentamolybdate  of  ferric  oxide, 
Fe203-5Mo03  +  16HO. 

By  boiling  the  solution  of  termolybdate  of  potash  or  soda,  or  acid  molybdate  of 
ammonia,  with  hydrate  of  alumina,  manganic  oxide,  ferric  oxide,  or  chromic 
oxide,  and  evaporating  to  the  crystallizing  point,  double  salts  are  obtained.  The 
composition  of  the  double  salts  containing  alumina,  ferric  oxide,  or  chromic  oxide, 
with  potash  or  oxide  of  ammonium,  may  be  represented  by  that  of  the  alumina 
and  potash-salt,  viz.,  Al2Os.6Mo03  -f  3(K0.2Mo03)  +  20HO.  The  potassio-man- 
yanic  salt  contains  Mn203.6Mo03  -f  5(K0.2Mo03)  +  12HO.  The  ammonio- 
manganic  salt  is  similarly  constituted.  The  sodio-chromic  salt  contains  O203.6Mo03 
+  3(Na0.2Mo03)  -f  21HO  (Struve). 

Acid  molybdate  of  ammonia,  added  to  a  boiling  solution  of  sulphate  of  copper, 
throws  down  a  heavy  green  amorphous  powder,  consisting  of  basic  molybdate  of 
copper,  4Cu0.3Mo03  -f-  5HO.  By  adding  molybdate  of  ammonia  in  excess  to  a 
cold  solution  of  sulphate  of  copper,  a  double  salt  is  formed,  consisting  of 
Cu0.2Mo03  +  NH40.3Mo03  -f  9HO.  It  is  a  white-blue  crystalline  powder, 
which  gives  off  4  eq.  of  water  at  212°  and  4  eq.  more  at  266°  (Struve). 

Molybdate  of  lead,  PbO.Mo03,  is  formed  by  precipitating  nitrate  of  lead  with 
termolybdate  of  potash.  It  is  a  heavy  white  powder,  which  melts  only  at  a  high 
temperature.  It  occurs  finely  crystallized  as  a  mineral.  Chromate  of  lead  is 
dimorphous,  and  corresponds  in  the  least  usual  of  its  forms  with  molybdate  of 
lead :  hence  molybdenum  is  connected  with  the  magnesian  metals,  and  tungsten 
also  with  the  same  class,  from  the  isomorphism  of  the  tungstates  and  molybdates. 

Sulphides  of  molybdenum.  —  The  bisulphide  is  the  ore  from  which  the  com- 
pounds of  this  metal  are  derived.  It  occurs  in  many  parts  of  Sweden,  and  might 
be  procured  in  quantity  if  any  useful  application  of  the  metal  were  discovered. 
It  is  a  lead-grey  mineral,  having  the  metallic  lustre,  composed  of  flexible  laminae, 
soft  to  the  touch,  and  making  a  streak  upon  paper  like  plumbago.  Nitric  acid 
oxidates  it  easily,  without  dissolving  it.  Its  density  is  from  4-138  to  4*569.  A 
tersulphide  of  molybdenum  is  obtained  in  the  same  way  as  the  corresponding 
compound  of  tungsten,  and  affords  crystallizable  sulphur-salts  which  are  red.  The 

*  Ann.  Ch.  Pharm.  xcvi.,  266. 


TELLURIUM.  525 

milphomolybdate  of  potassium  combines  likewise  with  nitrate  of  potash.  When  a 
solution  of  the  former  salt  is  boiled  with  tersulphide  of  molybdenum  in  excess, 
the  latter  is  converted  into  bisulphide  of  molybdenum,  and  a  quadrisulphide  of 
molybdenum  dissolves  in  combination  with  the  sulphide  of  potassium.  The  quad- 
risulphide may  be  precipitated  by  hydrochloric  acid,  and  when  dried  is  a  cinnamon- 
brown  powder. 

Chlorides  of  molybdenum.  —  A  protochloride  is  formed  when  molybdous  oxide 
is  dissolved  in  hydrochloric  acid;  the  bichloride  when  molybdenum  is  heated  dry- 
in  chlorine  gas,  as  a  dark-red  gas  which  condenses  in  crystals,  like  those  of  iodine. 
It  forms  a  crystallizable  double  salt  with  sal-ammoniac.  Chloromolybdic  acid,  or 
a  compound  of  terchloride  of  molybdenum  and  molybdic  acid,  Mo02Cl,  or  MoCLj  -f- 
2Mo03,  is  formed  with  (molybdic  acid),  when  molybdic  oxide  is  exposed  to  chlorine 
gas  at  a  red  heat.  It  sublimes  below  a  red  heat,  and  condenses  in  crystalline 
scales,  which  are  white  with  a  shade  of  yellow. 

ESTIMATION    OF    MOLYBDENUM,    AND    METHODS    OF    SEPARATING   IT   FROM   THE 

PRECEDING    METALS. 

The  determination  of  molybdic  acid  is  more  difficult  than  that  of  tungstic  acid, 
on  account  of  its  partial  volatility.  The  best  mode  of  estimating  it  is  to  convert 
it  into  molybdic  oxide  by  ignition  in  an  atmosphere  of  hydrogen ;  the  oxide  which 
is  perfectly  fixed  may  then  be  weighed ;  it  contains  74-95  per  cent,  of  the  metal. 
When  molybdic  acid  exists  in  solution  in  ammonia  or  in  other  acids,  the  solution 
must  be  carefully  evaporated  to  dryness,  and  the  residue  treated  as  above. 

Molybdic  acid  is  separated  from  most  metallic  oxides  by  its  solubility  in  sulphide 
of  ammonium.  The  filtered  solution  is  then  treated  with  an  excess  of  very  dilute 
nitric  acid,  to  precipitate  the  tersulphide  of  molybdenum ;  the  precipitate  collected 
on  a  weighed  filter,  and  its  quantity  determined ;  after  which,  a  weighed  quantity 
of  it  is  ignited  in  an  atmosphere  of  hydrogen,  to  convert  it  into  the  bisulphide, 
MoS2,  from  the  weight  of  which  the  amount  of  molybdenum  is  calculated. 

Molybdic  acid  is  separated  from  the  earths  by  fusing  with  carbonate  of  soda, 
and  digesting  the  fused  mass  in  water,  which  dissolves  molybdate  of  soda,  and 
leaves  the  earth  in  the  form  of  carbonate. 

From  the  fixed  alkalies,  molybdic  acid  may  be  separated  by  precipitation  with 
mercurous  nitrate,  and  its  quantity  estimated  from  the  weight  of  the  precipitate. 


SECTION  VII 

TELLURIUM. 

JEq.  64-14  or  801-8;  Te. 

Tellurium  is  a  metal  of  rare  occurrence,  and  appeared  at  one  time  to  be  almost 
confined  to  certain  gold  mines  in  Transylvania ;  but  it  has  been  found  lately  in 
considerable  abundance,  at  Schemnitz,  in  Hungary,  combined  with  bismuth ;  and 
in  the  silver  mine  of  Sadovinski  in  the  Altai,  united  with  silver  and  with  lead. 
It  was  first  described  as  a  new  metal  by  Klaproth,  who  gave  it  the  name  of  tellu- 
rium, from  tellus,  the  earth. 

Tellurium  is  chiefly  obtained  from  telluride  of  bismuth.  The  ore,  after  being 
freed  from  the  matrix  by  pounding  and  washing,  is  mixed  with  an  equal  weight 
of  carbonate  of  potash  or  soda,  the  mixture  made  up  into  a  paste  with  olive  oil, 
arid  heated  in  a  well-closed  crucible,  carefully  at  first  to  prevent  frothing,  and 
afterwards  to  a  full  white  heat.  The  fused  mass  is  then  digested  in  water ;  which 
leaves  the  bismuth  and  the  excess  of  charcoal  undissolved,  and  dissolves  the 


526  TELLURIUM. 

tellurium  in  the  form  of  telluride  of  potassium  or  sodium*,  which  imparts  a  port- 
wine  colour  to  the  liquid.  The  solution  deposits  metallic  tellurium  when  exposed 
to  the  air,  or  more  quickly  when  air  is  blown  through  it;  and  the  precipitated 
metal  is  purified  by  washing  with  acidulated  water,  and  subsequent  distillation  in 
an  atmosphere  of  hydrogen  (Berzelius).  The  metal  is  also  obtained  from  the 
ore  called  foliated  tellurium,  which  contains  13  per  cent  of  tellurium,  and  63  per 
cent,  of  lead,  together  with  copper,  gold,  antimony,  and  sulphur.  The  finely 
pounded  mineral  is  freed  from  the  sulphide  of  lead  and  antimony  by  repeated 
boiling  with  strong  hydrochloric  acid  and  washing  with  water;  the  residual  tellu- 
ride of  gold  treated  with  strong  nitric  acid ;  the  tellurium-solution  poured  off  from 
the  gold  and  evaporated  to  dry  ness;  the  residue  dissolved  in  hydrochloric  acid; 
and  the  tellurium  precipitated  from  the  solution  by  sulphurous  acid  (Berthier).* 

In  a  state  of  purity,  tellurium  is  silver-white  and  very  brilliant.  It  is  very 
crystallizable,  assuming  a  rhombohedral  form,  in  which  it  is  isomorphous  with 
arsenic  and  antimony.  It  is  brittle  for  a  metal,  and  an  indifferent  conductor  of 
heat  and  electricity.  Its  density  is  from  6-2324  to  6-2578,  according  to  Berze- 
lius. Tellurium  is  about  as  fusible  as  antimony,  and  may  be  distilled  at  a  high 
temperature.  It  burns  in  air,  at  a  high  temperature,  with  a  lively  blue  flame, 
green  at  the  borders,  and  diffuses  a  dense  white  smoke,  which  generally  has  the 
odour  of  decaying  horse-radish,  from  the  presence  of  a  little  selenium.  Tellurium 
belongs  to  the  sulphur-class  of  elements.  Like  selenium  and  sulphur,  it  dissolves 
to  a  small  extent  in  concentrated  sulphuric  acid,  and  communicates  to  it  a  fine 
purple-red  colour.  In  this  solution,  the  metal  is  not  oxidated,  for  it  is  precipi- 
tated again,  in  the  metallic  state,  by  water.  This  metal  has  also  considerable 
analogy  with  antimony,  and  may  probably  connect  together  the  sulphur  and  phos- 
phorus families.  Tellurium  combines  in  two  proportions  with  oxygen,  forming 
tellurous  acid,  Te02,  and  telluric  acid,  TeG3. 

Tellurous  acid,  TeOa;  80-14  or  1001-8.  — This  acid  differs  remarkably  in 
properties  according  as  it  is  anhydrous  or  hydrated. f  Hydrated  tellurous  acid  is 
obtained  by  precipitating  bichloride  of  tellurium  with  cold  water;  or  by  fusing 
anhydrous  tellurous  acid  with  an  equal  weight  of  carbonate  of  potash,  as  long  as 
carbonic  acid  is  disengaged,  dissolving  the  tellurite  of  potash  in  water,  and  adding 
nitric  acid  to  it  till  the  liquor  distinctly  reddens  litmus  paper.  A  white  and 
bulky  precipitate  is  produced,  which  is  washed  with  ice-cold  water,  and  after- 
wards dried  without  artificial  heat.  Tellurium  likewise  dissolves-  with  violence  in 
pure  nitric  acid  of  density  1-25,  and  if  after  the  first  five  minutes,  the  clear  liquid 
be  poured  into  water,  tellurous  acid  is  precipitated  in  white  flocks.  But  if  not 
immediately  precipitated,  the  nitric  acid  solution  undergoes  a  change. 

The  hydrated  acid  obtained  by  these  processes  forms  a  light,  white,  earthy 
mass,  of  a  bitter  and  metallic  taste.  It  instantly  reddens  litmus  paper,  and  while 
still  moist,  dissolves  to  a  sensible  extent  in  water.  It  is  very  soluble  in  acids,  and 
the  solutions  are  not  subject  to  change,  except  that  which  is  formed  by  nitric  acid. 
Ammonia  and  the  alkaline  carbonates  also  dissolve  hydrated  tellurous  acid  with 
facility,  the  latter  becoming  bicarbonates. 

Anhydrous  tellurous  acid When  the  solution  of  tellurous  acid  in  water  is 

heated  to  140°,  it  deposits  the  anhydrous  acid  in  grains,  and  loses  its  acid  reac- 
tion. The  same  change  occurs  when  an  attempt  is  made  to  dry  the  hydrated  tel- 
lurous acid  by  heat :  it  parts  with  combined  water,  and  becomes  granular.  The 
solution  of  tellurous  acid  in  nitric  acid  changes  spontaneously  in  a  few  hours,  and 

*  For  further  details  respecting  the  extraction  of  tellurium,  vide  Berzelius,  Traite  de 
Chimie,  i.  344 ;  and  the  translation  of  Gmelin's  Handbook,  iv.  393.  Wohler  states,  in  a  note 
to  his  paper  on  telluride  of  ethyl  (Ann.  Ch.  Pharm.  Ixxxiv.  70),  that  tellurium  may  be  obtained 
in  considerable  quantities  from  the  residues  of  the  Transylvanian  gold-extraction,  which  have 
hitherto  been  thrown  away  as  worthless. 

f  Berzelius  regarded  the  hydrated  and  anhydrous  acids  as  containing  different  modifica- 
tions of  the  same  compound,  and  distinguished  them  as  a-tellurous  and  /?-tellurous  acid. 


TELLURIC    ACID.  527 

in  a  quarter  of  an  hour  when  heat  is  applied  to  it,  and  allows  the  anhydrous  acid 
to  precipitate.  When  the  deposition  of  the  acid  is  slow,  it  forms  a  crystalline 
mass  of  fine  grains,  among  which  octohedral  crystals  may  be  perceived  by  the 
microscope.  The  acid  is  then  anhydrous.  In  this  state  it  does  not  redden  litmus, 
or  not  till  after  a  time.  It  is  but  very  slightly  soluble  in  water,  and  the  solution 
has  no  acid  reaction.  At  a  low  red  heat,  it  fuses  into  a  clear  transparent  liquid 
of  a  deep  yellow  colour,  which  6n  cooling  becomes  a  white  and  highly  crystalline 
mass,  easily  detached  from  a  crucible.  Tellurous  acid  is  volatile,  although  less  so 
than  the  metal  itself. 

The  solutions  of  hydrated  tellurous  acid  in  the  stronger  acids  yield  a  black  pre- 
cipitate of  metallic  tellurium,  when  treated  with  powerful  deoxidizing  agents,  such 
as  zinc,  phosphorus,  protochloride  of  tin,  sulphurous  acid,  and  the  alkaline  bisul- 
phates.  Hydrosulphuric  acid  and  sulphide  of  ammonium  throw  down  black-brown 
sulphide  of  tellurium,  easily  soluble  in  excess  of  sulphide  of  ammonium. 

The  tellurites,  or  compounds  of  tellurous  acid  with  salifiable  bases,  contain  1 
atom  of  base  united  with  1,  2,  or  4  atoms  of  acid.  They  are  fusible,  and  gene- 
rally solidify  in  the  crystalline  form  on  cooling ;  the  quadrotellurites,  however, 
form  a  glass.  Tellurites  are  colourless  unless  they  contain  a  coloured  base ;  those 
which  are  soluble  have  a  metallic  taste.  Most  of  them,  when  heated  to  redness 
with  charcoal,  yield  metallic  tellurium,  sometimes  with  slight  detonation ;  and  the 
reduced  metal  volatilizes  readily,  being  at  the  same  time  reoxidized  and  forming  a 
white  deposit  on  the  charcoal;  it  likewise  imparts  a  green  colour  to  the  flame ; 
the  tellurites,  when  ignited  with  potassium,  or  with  charcoal  and  carbonate  of  pot- 
ash, yield  telluride  of  potassium  which  dissolves  in  water,  forming  a  port-wine 
coloured  solution ;  with  the  zinc  and  silver-salts,  however,  and  a  few  others,  this 
reduction  does  not  take  place.  The  tellurites  of  ammonia,  potash  and  soda  are 
easily  soluble  in  water ;  those  of  baryta,  strontia,  and  lime  are  sparingly  soluble ; 
the  rest,  insoluble.  An  aqueous  solution  of  a  tellurite  is  decomposed  by  the  car- 
bonic acid  of  the  air.  Nearly  all  tellurites  dissolve  in  strong  hydrochloric  acid 
without  evolving  chlorine  when  heated ;  the  solution  exhibits  the  above-mentioned 
characters  of  a  solution  of  tellurous  acid  in  the  stronger  acids,  except  in  so  far  as 
it  may  be  interfered  with  by  the  presence  of  another  base.  The  solution  when 
diluted  in  water  yields  a  white  precipitate  of  tellurous  acid,  provided  the  excess  of 
hydrochloric  acid  present  is  not  too  great. 

Monotellurite  of  potash,  KO.Te02,  is  obtained  by  heating  1  eq.  tellurous  acid 
with  eq.  of  carbonate  of  potash.  The  fused  mass  on  cooling  forms  crystals  of  large 
size.  The  salt  dissolves  slowly  in  cold,  more  quickly  in  warm  water.  Bitellurite 
of  potash,  KO.Te204,  is  obtained  by  fusing  two  atoms  of  tellurous  acid  with  one 
atom  of  carbonate  of  potash.  It  appears  to  be  capable  of  existing  in  a  hot  solu- 
tion, and  of  crystallizing  in  certain  circumstances;  but  it  is  decomposed  by  cold 
water,  which  resolves  it  into  the  neutral  salt,  which  dissolves,  and  a  quadritellu- 
rite  of  potash,  KO.Te408  4-  4HO.  The  latter  salt  cannot  be  redissolved  in  water, 
without  decomposition.  In  losing  its  water  when  heated,  it  swells  up  like  borax. 

Telluric  acid,  Te03;  88-14  or  1101-8.  —  This  acid  is  obtained  in  combination 
with  potash,  by  fusing  tellurous  acid  with  nitre.  It  may  then  be  transferred  to 
baryta,  and  the  insoluble  tellurate  of  baryta  decomposed  by  sulphuric  acid.  The 
solution  of  telluric  acid  gives  bulky,  hexagonal,  prismatic  crystals.  Its  taste  is 
not  acid,  but  metallic,  resembling  that  of  nitrate  of  silver.  Indeed,  it  appears  to 
be  but  a  feeble  acid,  reddening  litmus  but  slightly,  when  the  solution  is  diluted. 
The  crystallized  acid  contains  3HO,  of  which  it  loses  2HO  by  efflorescence,  a 
little  above  212°.  It  then  appears  insoluble  in  cold  water,  but  may  be  com- 
pletely redissolved  by  long  digestion,  particularly  with  ebullition,  and  is  not  per- 
manently altered. 

Anhydrous  telluric  acid.  —  The  crystals  of  hydrated  telluric  acid  give  off  all 
their  water  at  a  heat  below  redness,  and  are  converted  into  a  mass  of  a  fine  orange- 
yellow  colour,  without  changing  their  form.  This  yellow  matter,  which  is  distin- 


528  TELLURIUM. 

guished,  as  alpha-telluric  acid  by  Berzelius,  is  remarkable  for  its  indifference  to 
chemical  reagents,  being  completely  insoluble  in  cold  or  boiling  water,  in  hot 
hydrochloric  and  nitric  a^ids,  and  in  potash-ley.  At  a  high  temperature,  it  is  de- 
composed, evolving  oxygen,  and  leaving  tellurous  acid  white  and  pulverulent. 

Telluric  acid  has  but  slight  affinity  for  bases.  The  hydrated  acid  withdraws 
from  alkaline  carbonates,  only  so  much  alkali  as  to  form  a  biacid  salt.  Telluric 
acid  forms  bibasic,  sesquibasic,  monobasic,  biacid,  and  quadracid  salts.  The  tel- 
lurates  are  colourless,  unless  they  contain  a  coloured  base.  At  a  red  heat,  they 
give  off  oxygen  and  are  converted  into  tellurites.  Before  the  blowpipe,  they 
behave  like  the  tellurites;  also  with  reducing  agents,  such  as  protochloride  of  tin, 
and  sulphurous  acid,  excepting  that  the  reduction  does  not  take  place  so  quickly, 
and  in  some  cases  requires  the  application  of  heat.  Hydrosulphuric  acid,  added 
to  the  solution  of  a  tellurate,  produces  no  change  at  first;  but  if  the  liquid  be 
placed  in  a  stoppered  bottle  and  left  for  a  while  in  a  warm  place,  a  brown  precipi- 
tate of  sulphide  of  tellurium  is  formed.  Tellurates  dissolve  in  cold  strong  hydro- 
chloric acid  without  decomposition.  The  solutions  are  not  yellow,  like  those  of 
the  tellurites  in  hydrochloric  acid,  and  may  be  diluted  with  water  without  becoming 
milky,  even  though  the  excess  of  hydrochloric  acid  be  but  small.  But  on  boiling 
the  solution,  chlorine  is  evolved,  and  the  liquid,  if  subsequently  mixed  with 
water,  gives  a  precipitate  of  tellurous  acid,  provided  the  excess  of  hydrochloric 
acid  is  not  too  great. 

Neutral  tellurate  of  potash  is  KO.Te03-f  5110 ;  the  bitellurate  of  potash, 
KO.Te206+4HO;  the  quadritellurate  of  potash,  KO.Te4012  +  4HO.  All  these 
salts  may  be  obtained  directly,  in  the  humid  way,  by  dissolving  the  proper  pro- 
portions of  hydrated  acid  and  carbonate  of  potash  together,  in  hot  water.  A  por- 
tion of  the  combined  water  in  the  last  two  salts  is  unquestionably  basic,  but  how 
much  of  it  is  so  has  not  been  determined.  They  cannot  be  made  anhydrous  by 
heat  without  being  essentially  altered  in  properties. 

The  neutral  tellurate  of  potash  undergoes  no  change  in  constitution  under  the 
influence  of  heat,  resembling  in  that  respect  those  tribasic  phosphates  of  which 
the  whole  three  atoms  of  base  are  fixed.  The  bitellurate  of  potash  loses  its  water 
and  becomes  yellow  at  a  temperature  below  redness,  and  is  changed  into  a  quadri- 
tellurate, which  is  insoluble  both  in  water  and  in  dilute  acids.  Water  dissolves 
out  neutral  tellurate  from  the  yellow  mass.  The  insoluble  salt  is  named,  by  Ber- 
zelius, the  alpha-quadritellurate  of  potash.  The  elements  of  this  compound  are 
united  by  a  powerful  affinity.  It  is  formed  when  hydrated  telluric  acid  is  intima- 
tely mixed  with  a  potash-salt,  such  as  nitre  or  chloride  of  potassium,  and  the 
mixture  calcined  at  a  temperature  which  should  be  much  below  a  red  heat;  also 
when  tellurous  acid  is  ignited  with  chlorate  of  potash,  and  in  other  circumstances. 
Hydrate  of  potash  dissolves  the  alpha-quadri tellurate  by  fusion,  and  nitric  acid  by 
a  long  continued  ebullition ;  but,  in  both  cases,  the  acid  set  free  in  the  solution 
exhibits  the  properties  of  ordinary  telluric  acid. 

TeUuretted  hydrogen,  Hydrotelluric  acid,  TeH,  is  a  gaseous  compound  of  tel- 
lurium and  hydrogen,  analogous  in  constitution  and  properties  to  sulphuretted 
hydrogen.  It  is  obtained  by  fusing  tellurium  with  zinc  or  with  tin,  and  acting  on 
the  mixture  with  hydrochloric  acid. 

Definite  sulphides  of  tellurium  have  been  obtained,  corresponding  with  tellurous 
and  telluric  acids.  They  are  sulphur-acids. 

Two  chlorides  of  tellurium  have  been  formed,  a  protochloride,  TeCl,  to  which 
there  is  no  corresponding  oxide,  and  a  bichloride,  Te012-  No  higher  chloride, 
corresponding  with  telluric  acid,  has  been  obtained. 

Tellurium  forms  alloys  with  several  metals,  e.  g.,  with  potassium,  sodium, 
.aluminum,  bismuth,  zinc,  tin,  lead,  iron,  copper,  mercury,  silver,  and  gold.  Some 
of  these  alloys,  as  those  of  bismuth,  silver,  and  gold,  are  found  native. 

Telluride  of  potassium  is  prepared  by  mixing  1  part  of  tellurium  powder  with 
10  parts  of  burnt  tartar;  introducing  the  mixture  into  a  porcelain  retort  fitted 


ESTIMATION     OF     TELLURIUM.  529 

with  a  glass  tube  bent  downwards  at  right  angles ;  heating  the  retort  to  redness 
for  three  or  four  hours,  as  long,  indeed,  as  carbonic  oxide  continues  to  escape ; 
and  then  introducing  the  end  of  the  bent  tube  into  a  flask  kept  full  of  carbonic 
acid  gas,  to  prevent  access  of  air;  this  latter  precaution  is  necessary  on  account 
of  the  highly  pyrophoric  character  of  the  product  (Wbhler).  The  compound 
may  also  be  obtained  by  heating  tellurium  with  potassium,  in  a  retort  rilled  with 
hydrogen  ;  combination  then  takes  place  attended  with  vivid  combustion.  Tellu- 
ride  of  potassium  dissolves  in  water,  forming  a  port-wine  coloured  solution,  which 
on  exposure  to  the  air  becomes  decolorized,  and  deposits  tellurium  in  shining 
scales ;  with  acids  it  evolves  telluretted  hydrogen  gas.  Telluride  of  sodium  is 
prepared  by  similar  methods,  and  possesses  similar  properties. 

ESTIMATION   OF  TELLURIUM,  AND  METHODS    OF   SEPARATING  IT  FROM   THE  PRE- 
CEDING  METALS. 

When  tellurium  exists  in  solution  in  the  form  of  tellurous  acid  it  is  reduced  to 
the  metallic  state  by  sulphurous  acid  or  an  alkaline  bisulphite.  The  reduced  tel- 
lurium is  then  collected  on  a  weighed  filter,  and  carefully  dried  at  gentle  heat.  If 
the  solution  is  alkaline,  it  must  be  previously  acidulated  with  hydrochloric  acid ; 
if  it  contains  nitric  acid,  which  might  redissolve  a  portion  of  the  precipitated  tel- 
lurium, it  must  be  boiled  with  hydrochloric  acid  till  all  the  nitric  acid  is  decom- 
posed, then  diluted  with  water,  and  treated  with  sulphurous  acid  as  above.  If 
the  tellurium  is  in  the  state  of  telluric  acid,  that  compound  must  first  be  reduced 
to  tellurous  acid  by  boiling  with  hydrochloric  acid,  and  the  tellurium  then  reduced 
by  sulphurous  acid. 

Tellurium  may  be  separated  from  the  alkalies  and  earths,  and  from  manganese, 
iron,  cobalt,  nickel,  zinc,  and  chromium,  by  means  of  hydrosulphuric  acid.  If 
the  precipitated  sulphide  of  tellurium  is  quite  pure  and  definite,  it  may  be  col- 
lected on  a  weighed  filter,  dried  and  weighed,  and  the  amount  of  tellurium  calcu- 
lated from  it.  But  if  it  contains  excess  of  sulphur,  which  is  often  the  case,  it 
must  be  boiled  with  aqua-regia  till  it  is  completely  decomposed;  the  solution 
filtered  from  the  separated  sulphur;  freed  from  nitric  acid  in  the  manner  above 
described ;  and  the  tellurium  precipitated  by  sulphurous  acid. 

The  separation  of  tellurium  from  cadmium,  copper,  and  lead,  may  be  effected 
by  means  of  sulphide  of  ammonium,  in  which  the  sulphide  of  tellurium  is  easily 
soluble.  The  filtered  solution  is  then  treated  with  excess  of  hydrochloric  acid  to 
precipitate  the  sulphide  of  tellurium,  which  is  then  decomposed  by  aqua-regia  as 
just  described.  Tellurium  may  be  separated  from  tin  in  solution  by  means  of 
sulphurous  acid. 

The  quantity  of  metallic  tellurium  in  an  alloy  may  be  estimated  by  heating  the 
alloy  in  a  current  of  chlorine  gas;  passing  the  volatile  chloride  of  tellurium  into 
water  acidulated  with  hydrochloric  acid,  which  dissolves  it;  and  reducing  the  tel- 
lurium by  sulphurous  acid. 

34 


530  ARSENIC. 


ORDER  VI. 

METALS    ISOMORPHOUS   WITH   PHOSPHORUS. 

SECTION  I. 

ARSENIC. 

%  75  or  937-5. 

THIS  metal  is  found  native,  but  more  generally  in  combination  with  other  metals, 
particularly  cobalt  and  nickel,  and  is  largely  condensed,  during  the  roasting  of 
their  ores,  in  the  state  of  arsenious  acid.  The  metal  may  be  easily  obtained,  in  a 
state  of  purity,  by  subliming  a  portion  of  native  arsenic  in  a  glass  tube  or  retort, 
by  the  heat  of  a  lamp,  or  by  reducing  a  mixture  of  one  part  of  arsenious  acid  and 
three  parts  of  black  flux,  in  the  same  apparatus.  The  metal  in  condensing  forms 
a  crust,  of  a  steel-grey  colour  and  bright  metallic  lustre.  It  has  been  observed  to 
crystallize  by  sublimation  in  rhombohedral  crystals,  and  is  isomorphous  with  tellu- 
rium and  antimony.  It  is  a  brittle  metal,  and  very  easily  pulverized.  The  density 
of  arsenic  is  from  5  to  5-96.  It  rises  in  vapour  at  356°  (180°  Cent.)  without  first 
undergoing  fusion.  Arsenic  vapour  is  colourless  ;  its  density  is  10-370;  and,  like 
phosphorus  and  oxygen,  its  combining  measure  is  one  volume.  It  has  as  strong 
an  effect  upon  the  organ  of  smell  as  selenium ;  its  odour  resembles  that  of  garlic. 
Arsenic  combines  in  three  proportions  with  oxygen,  forming  by  spontaneous  oxida- 
tion in  air  a  grey  sub-oxide,  the  composition  of  which  is  undetermined ;  it  also 
forms  arsenious  and  arsenic  acids,  As03  and  As05. 

Arsenious  acid,  99  or  1237 '5.  —  This  compound  is  formed  when  metallic 
arsenic  is  volatilized  in  contact  with  the  air.  It  is  obtained  in  large  quantity,  as 
an  accessary  product,  in  the  roasting  of  arsenical  ores  of  tin,  cobalt,  and  nickel, 
and  as  principal  product  in  the  roasting  of  arsenical  pyrites.  These  operations  are 
performed  in  reverberatory  furnaces,  communicating  with  chambers  in  which  the 
.arsenious  acid  condenses.  The  product  is  purified  by  a  second  sublimation  in 
vessels  of  cast-iron,  or,  on  a  small  scale,  in  glass  or  earthen  retorts. 

Arsenious  acid  heated  in  a  tube  closed  at  both  ends  melts  into  a  colourless 
liquid;  but  under  the  ordinary  atmospheric  pressure,  it  volatilizes  at  about  380° 
(at  444°  according  to  Mitchell),  without  previous  fusion,  producing  a  colourless 
vapour,  which  has  a  density  of  13-850,  and  is  therefore  composed  of  1  volume  of 
arsenic  vapour  and  3  volumes  of  oxygen,  condensed  into  1  volume.  The  vapour 
is  inodorous  when  pure,  but  if  the  acid  be  volatilized  in  contact  with  any  easily 
oxidizable  substance,  as  when  it  is  thrown  on  red-hot  coals  or  iron,  the  garlic 
odour  of  metallic  arsenic  becomes  perceptible. 

In  the  solid  state,  arsenious  acid  exhibits  three  modifications,  one  amorphous, 
;and  two  crystalline.  (1.)  When  the  sides  of  the  vessel  in  which  the  acid  is  dis- 
tilled become  strongly  heated,  the  vapour  condenses,  at  a  temperature  near  the 
melting  point  of  the  acid,  into  a  transparent  vitreous  mass,  having  a  conchoidal 
fracture.  (2.)  When  arsenious  acid  is  sublimed  in  a  glass  tube,  or  under  any 
circumstances  which  allow  the  vapour  to  condense  suddenly,  and  solidify  at  once, 
without  passing  through  the  semi-fused  state,  it  assumes  the  form  of  regular  octo- 
hedrons,  which,  if  the  sublimation  be  slowly  conducted,  are  distinct,  and  have 
an  adamantine  lustre.  Similar  octohedral  crystals  are  obtained  when  arsenious 
acid  separates  from  its  solution  in  water  or  in  ammonia.  (3  )  In  the  roasting  of 


ARSENIOUS    ACID.  531 

arsenical  cobalt  ores,  arsenious  acid  is  sometimes  obtained  in  the  form  of  thin 
transparent  flexible  plates,  derived  from  a  right  rhombic  prism  (Wb'hler).  Crystals 
of  similar  form  are  obtained  by  saturating  a  boiling  solution  of  caustic  potash  with 
arsenious  acid,  and  then  leaving  it  to  cool,  or  mixing  it  with  water  (Pasteur). 
Vitreous  arsenious  acid,  even  when  completely  protected  from  air  and  moisture, 
gradually  loses  its  transparency,  and  becomes  an  opaque  white  mass,  passing  in 
fact  into  the  octohedral  variety. 

The  specific  gravity  of  transparent  vitreous  arsenious  acid  is  3-7385,  that  of  the 
octohedral  variety  3-699  (Guibourt).  The  vitreous  acid  dissolves  in  water  more 
quickly  and  more  abundantly  than  the  opaque  crystalline  acid ;  the  same  quantity 
of  water  which  at  54°  or  55°  will  take  up  36  or  38  parts  of  the  former,  will  not  take 
up  more  than  12  or  14  of  the  latter  (Bussy).  According  to  Guibourt,  on  the  con- 
trary, 100  parts  of  boiling  water  dissolve  9-68  parts  of  the  vitreous,  and  11-47  of 
the  opaque  acid ;  and  when  the  solutions  are  left  to  cool  to  60°,  the  first  retains 
1-78  parts,  and  the  latter  2-9  parts  of  the  acid.  The  discrepancy  of  these  state- 
ments and  of  various  others  respecting  the  solubility  of  arsenious  acid,  may  per- 
haps be  reconciled  by  the  great  facility  with  which  the  amorphous  variety  passes 
into  the  crystalline,  and  vice  versa.  It  appears  indeed  that  heat  tends  'to  trans- 
form the  opaque  into  the  vitreous  acid,  and  cold  to  produce  the  contrary  change, 
and  this  tendency  is  manifested  even  in  presence  of  water.  Thus  the  opaque  acid 
is  converted  into  the  vitreous  by  long  boiling  with  water,  the  contrary  change 
taking  place  gradually  in  the  solution  when  cold. 

The  aqueous  solution  of  arsenious  acid  is  transparent  and  colourless,  and  red- 
dens litmus  slightly.  Hydrosulphuric  acid  colours  it  yellow,  and  on  the  addition 
of  hydrochloric  acid  throws  down  a  yellow  precipitate  of  AsS3.  On  the  addition 
of  a  small  quantity  of  ammonia,  it  gives  a  yellow  precipitate  with  nitrate  of  silver, 
and  a  peculiar  light  green  (Scheele's  green)  with  sulphate  of  copper ;  these  pre- 
cipitates are  easily  soluble  in  excess  of  ammonia.  Mixed  with  hydrochloric  acid 
it  produces  a  grey  metallic  deposit  on  copper.  With  zinc  and  sulphuric  or  hydro- 
chloric acid,  it  evolves  arseniuretted  hydrogen  gas  (p.  533). 

Arsenious  acid  dissolves  in  many  acids,  in  hydrochloric  acid  for  example,  with 
much  greater  facility  than  in  water,  but  without  forming  any  definite  compounds. 
It  is  dissolved,  however,  by  bitartrate  of  potash,  with  formation  of  a  crystallizable 
salt  analogous  to  the  potash-tartrate  of  antimony.  The  vitreous  acid  dissolved  in 
boiling  dilute  hydrochloric  acid  crystallizes  on  cooling  in  regular  octohedrons,  the 
deposition  of  each  crystal  being  accompanied  by  a  flash  of  light.  Agitation 
increases  the  number  of  crystals  produced,  and  the  intensity  of  the  light.  The 
opaque  acid  dissolved  in  hydrochloric  acid  does  not  emit  any  light  on  crystallizing ; 
the  same  is  the  case  with  the  crystals  obtained  by  cooling  a  solution  of  the  vitre- 
ous acid  in  hydrochloric  acid,  when  these  crystals  are  redissolved  in  hydrochloric 
acid.  Hence  it  appears  that  the  vitreous  acid  dissolves  as  such  in  hydrochloric 
acid,  and  that  the  emission  of  light  at  the  moment  of  crystallization  is  due  to  the 
change  from  ,the  amorphous  to  the  crystalline  state. 

Arsenious  acid  is  dissolved  by  potash,  soda,  and  ammonia,  also  by  alkaline 
carbonates,  but  from  these  latter  solutions  it  is  sometimes  deposited  in  the  free 
state,  so  that  it  is  doubtful  whether  arsenious  acid  displaces  carbonic  acid  in  the 
humid  way.  The  arsenites  of  the  earths  and  metallic  oxides  are  insoluble  in  water, 
but  soluble  in  acids. 

With  potash,  arsenious  acid  forms  the  salts  2KO .  As03,  KO  .  As03,  and  KO . 
H0.2As03;  similar  salts  with  soda.  With  baryta,  it  forms  2BaO .  As03,  and 
BaO .  As03 ;  and  with  lime,  2CaO .  As03.  With  nickel,  cobalt,  and  silver,  it 
forms  bibasic  and  sesquibasic  salts. 

The  neutral  solutions  of  the  alkaline  arsenites  give  a  yellow  precipitate  with 
nitrate  of  silver,  and  Scheele's  green  with  copper  salts.  Acidulated  with  hydro- 
chloric acid,  they  give  with  hydrosulphuric  acid,  &c.,  the  same  reactions  as 
aqueous  arsenious  acid. 


532  ARSENIC. 

Nitric  acid  and  aqua  regia  transform  arsenious  into  arsenic  acid.  Hydrogen, 
charcoal,  and  other  reducing  agents  easily  reduce  it  to  the  metallic  state. 

Arsenious  acid  has  a  rough  taste,  slightly  metallic,  and  afterwards  sweetish.  It 
is  one  of  the  most  violent  among  acrid  poisons. 

The  principal  industrial  use  of  arsenious  acid  is  in  calico-printing;  it  is  also 
used  in  glass-making,  serving  to  transform  the  protoxide  of  iron  into  sesquioxide, 
which  produces  glasses  less  highly  coloured  than  the  protoxide. 

Arsenic  acid,  As05,  115  or  1437'5. — This  acid  is  obtained  by  heating  powdered 
arsenious  acid  in  a  basin  with  an  equal  quantity  of  water,  and  adding  nitric  acid 
in  small  quantities  to  the  mixture  at  the  boiling  point,  so  long  as  ruddy  fumes 
escape.  An  addition  of  hydrochloric  acid  to  the  water  is  generally  made,  to 
increase  the  solubility  of  the  arsenious  acid,  but  it  is  not  absolutely  necessary. 
The  solution  of  arsenic  acid  is  then  evaporated  to  dryness,  to  expel  the  remaining 
nitric  and  hydrochloric  acids ;  but  the  dry  mass  must  not  be  heated  above  the 
melting  point  of  lead,  otherwise  oxygen  gas  is  emitted  and  arseuious  acid  repro- 
duced. Arsenic  acid  thus  obtained  is  milk-white,  and  contains  no  water.  Ex- 
posed to  air,  it  slowly  deliquesces,  and  runs  into  a  liquid.  But  notwithstanding 
this,  when  strongly  dried,  it  does  not  dissolve  completely  in  water  at  once,  and  a 
portion  of  it  appears  to  be  insoluble;  but  the  whole  is  dissolved  by  continued 
digestion.  Arsenic  acid,  in  absorbing  moisture  from  the  air,  sometimes  forms 
hydrated  crystals,  which  are  highly  deliquescent;  but  this  acid  is  easily  made 
anhydrous,  and  does  not  retain  basic  water  with  force,  like  phosphoric  acid.  Its 
solution  has  a  sour  taste,  and  reddens  vegetable  blues.  Arsenic  acid,  indeed,  is  a 
strong  acid,  and  with  the  aid  of  heat  expels  all  the  volatile  acids  from  their  com- 
binations. Arsenic  acid  undergoes  fusion  at  a  red  heat,  and  at  a  higher  tempera- 
ture is  completely  dissipated  in  the  form  of  arsenious  acid  and  oxygen. 

When  an  equivalent  of  arsenic  acid  is  ignited  with  an  excess  of  carbonate  of 
soda,  three  equivalents  of  carbonic  acid  are  expelled,  and  a  tribasic  arseniate  of 
soda  formed,  which  when  dissolved  in  water,  crystallizes  with  24  equivalents  of 
water,  forming  the  salt  3NaO.  As05  -f  24HO,  isomorphous  with  the  subphosphate 
of  soda.  The  same  salt  is  obtained  by  treating  arsenic  acid  in  solution  with  an 
excess  of  caustic  soda.  When  carbonate  of  soda  is  added  to  a  hot  solution  of 
arsenic  acid,  so  long  as  there  is  effervescence,  a  salt  is  obtained  by  evaporation  cor- 
responding with  the  common  phosphate  of  soda,  containing  2  eq.  of  soda  and  1 
eq.  of  water  as  bases.  This  salt  affects  the  same  two  multiples,  in  its  water  of 
crystallization,  as  phosphate  of  soda,  namely,  24HO  and  14HO,  but  most  fre- 
quently assumes  the  smaller  proportion,  forming  the  salt  2NaO .  HO .  As05  +  14HO. 
This  arseniate  is  more  soluble  than  the  phosphate,  and  slightly  deliquescent  in 
damp  air.  When  to  the  last  salt  a  quantity  of  arsenic  acid  is  added  equal  to  that 
which  it  already  contains,  and  the  solution  is  highly  concentrated,  the  salt  named 
biarseniate  of  soda  crystallizes  at  a  low  temperature.  This  salt  contains  1  eq.  of 
soda  and  2  eq.  of  water  as  bases,  with  2  eq.  of  water  of  crystallization,  and  corres- 
ponds with  the  biphospbate  of  soda.  Its  formula  is  Na0.2HO.As05  +  2HO. 
The  biarseniate  of  potash,  which  is  analogous  in  composition,  is  a  highly  crystal- 
lizable  salt.  It  is  sometimes  prepared  by  deflagrating  arseuious  acid  with  an  equal 
weight  of  nitrate  of  potash.  These  arseniates  of  the  alkalies,  which  contain  water 
as  base,  all  lose  that  element  at  a  red  heat ;  but,  unlike  the  phosphates,  they  recover 
it  when  redissolved  in  water.  Arsenic  acid,  therefore,  forms  only  one,  and  that  a 
tribasic  class  of  salts.  The  arseniates  of  the  earths  and  other  metallic  oxides  are 
insoluble  in  water,  but  soluble  in  acids.  Arseniate  of  silver  (3AgO.  As05)  falls 
as  a  precipitate  of  a  chocolate-brown  colour,  when  nitrate  of  silver  is  added  to  the 
solution  of  an  arseniate,  and  affords  an  indication  of  the  presence  of  arsenic  acid. 
On  treating  a  solution  of  arsenic  acid  with  ammonia  in  excess,  chloride  of  ammo • 
nium,  and  sulphate  of  magnesia,  a  white  crystalline  precipitate  is  formed,  consist- 
ing of  arseniate  of  magnesia  and  ammonia,  2MgO.NH40.  As05  -\-  12Aq.,  similar 
in  appearance  and  analogous  in  constitution  to  the  ammonio-magnesian  phosphate. 


ARSENIC    AND    HYDROGEN.  533 

Hydrosulphuric  acid  produces  a  yellow  precipitate  of  AsS5  after  a  considerable 
time  j  but  if  the  solution  be  previously  mixed  with  sulphurous  acid,  which  reduces 
the  arsenic  acid  to  arsenious  acid,  a  precipitate  of  AsS3  is  immediately  produced. 

Sulphides  of  arsenic.  —  When  the  bisulphide,  realgar,  is  digested  in  caustic 
potash,  it  gives  off  sulphur  and  leaves  a  brownish  black  powder,  having  some 
resemblance  to  bioxide  of  lead,  which,  according  to  Berzelius,  is  the  sulphide  As6S. 
Bisulphide  of  arsenic,  AsS2,  is  obtained  by  fusing  sulphur  with  an  excess  of 
arsenic  or  arsenious  acid.  It  is  transparent  and  of  a  fine  ruby  colour  after  cooling, 
and  may  be  distilled  without  decomposition.  It  forms  the  crystalline  mineral 
realgar.  Sulpharsenious  acid,  or  orpiment,  AsS3,  also  occurs  native.  It  may  be 
prepared  by  decomposing  a  solution  of  arsenious  acid  in  hydrochloric  acid, 
hydrosulphuric  acid,  or  by  an  alkaline  sulphide.  This  sulphide  has  a  rich 
yellow  colour,  and  is  the  basis  of  the  pigment  called  kiny's  yellow.  It  is 
insoluble  in  acids,  but  soluble  to  a  small  extent  in  water  containing  hydrosul- 
phuric acid,  and  also  in  pure  water,  but  is  precipitated  by  ebullition  with 
a  little  hydrochloric  acid.  When  heated,  it  fuses  readily  and  becomes  crystalline 
on  cooling.  It  is  readily  dissolved  by  ammonia  and  solutions  of  the  fixed  alkalies, 
and  is  indeed  a  powerful  sulphur-acid.  Sulpharsenic  acid,  AsS5,  falls  as  a  yellow 
precipitate,  having  much  the  appearance  of  orpiment,  when  a  solution  of  arsenic 
acid  somewhat  concentrated  is  decomposed  by  hydrosulphuric  acid.  It  may  be 
sublimed  without  change,  and  after  cooling  forms  a  non-crystalline  mass.  It  is 
also  a  powerful  sulphur-acid,  forming  salts  called  sulpharseniates.  Persulphide 
of  arsenic,  AsS18,  is  obtained  by  precipitating  neutral  solution  of  sulpharseniate  of 
potassium  with  alcohol,  filtering  the  liquid,  and  evaporating  off  two-thirds  of  the 
alcohol ;  the  concentrated  solution,  when  left  to  cool,  deposits  the  persulphide  of 
arsenic  in  shining  yellow  crystalline  laminae. 

Chlorides  of  a.rsenic. — A  terchloride,  AsCl3,  corresponding  with  arsenious  acid, 
is  formed  when  arsenic  is  introduced  into  chlorine  gas,  in  which  it  takes  fire  and 
burns  spontaneously.  The  same  compound  is  obtained  by  distilling  a  mixture  of 
1  part  of  arsenic  with  6  parts  of  corrosive  sublimate ;  also  by  distilling  arsenious 
acid  with  excess  of  hydrochloric  acid,  or  of  common  salt  and  sulphuric  acid.  It 
is  a  colourless,  oily,  and  very  dense  liquid,  which  is  resolved  by  water  into  arsenious 
and  hydrochloric  acids.  When  a  mixture  of  arsenic  and  calomel  is  distilled,  a 
dark  brown  sublimate  is  formed,  consisting  partly  of  Hg2ClAs,  partly  of  Hg4ClAs. 
No  chloride  corresponding  with  arsenic  acid  is  known.  Bromide  of  arsenic, 
AsBr3,  is  formed  by  the  direct  combination  of  its  elements.  Iodide  of  arsenic, 
AsI3,  is  formed,  according  to  Plisson,  by  digesting  3  parts  of  arsenic  with  10  of 
iodine  and  100  of  water,  as  long  as  the  odour  of  iodine  is  perceived.  The  liquid 
yields  by  evaporation  red  crystals  of  the  iodide.  Fluoride  of  arsenic,  AsF3,  is 
obtained  by  distilling  a  mixture  of  fluor  spar  and  arsenious  acid  with  sulphuric 
acid.  It  is  a  fuming,  colourless  liquid ;  the  density  of  its  vapour  is  2730  (Un- 
Terdorben). 

Arsenic  and  hydrogen.  —  A  solid  arsenide  of  hydrogen  was  obtained  by  Davy, 
by  using  metallic  arsenic  as  the  negative  pole  (the  chloroid)  in  decomposing 
water.  Gay-Lussac  and  Thenard  have  also  shown  that  the  same  compound  pre- 
cipitates when  arsenide  of  potassium  is  dissolved  in  water.  It  is  a  chestnut-brown 
powder,  which  may  be  dried  without  change.  Its  composition  has  not  been 
determined  with  accuracy.  Arseniuretted  hydrogen,  AsH3,  a  gas  analogous  in 
constitution  to  ammonia,  is  obtained  by  dissolving  arseniate  of  potassium  or  sodium 
in  water,  or  an  alloy  of  equal  parts  of  zinc  and  arsenic  in  sulphuric  acid  diluted 
with  three  times  its  weight  of  water;  or  again,  when  zinc  dissolves  in  hydro- 
chloric or  dilute  sulphuric  acid,  with  which  arsenious  acid  is  mixed : 

6Zn  +  3HO  +  As03  +  6S03  =  6(ZnO.S03)  +  AsH3. 
It  is  a  dangerous  poison,  when  inhaled  even  in  the  most  minute  quantity,  and 


534  ARSENIC. 

should,  therefore,  be  prepared  with  the  greatest  caution.  The  density  of  this  gas 
is  2695  (Dumas).  It  is  liquefied  by  a  cold  of  — 40°.  When  passed  through  a 
glass  tube  heated  to  redness  by  a  spirit  lamp,  it  is  decomposed  and  deposits  me- 
tallic arsenic.  The  flame  of  this  gas,  when  burned  in  air,  also  deposits  metallic 
arsenic  upon  a  cold  object  exposed  to  it.  No  combination  of  arseniuretted  hy- 
drogen is  known  with  either  acids  or  bases.  It  precipitates  many  of  the  metallic 
solutions  which  are  precipitated  by  hydrosulphuric  acid,  but  not  oxide  of  lead,  its 
hydrogen  alone  being  oxidated,  and  the  arsenic  being  precipitated  in  combination 
with  the  metal.  From  the  salts  of  silver,  gold,  platinum,  and  rhadium,  it  precipi- 
tates the  metals,  while  arsenious  acid  remains  in  solution.  This  gas,  when  pure,  is 
completely  absorbed  by  a  solution  of  sulphate  of  copper,  and  AsCu3  precipitated. 

TESTING   FOR   ARSENIC. 

Poisoning  from  arsenious  acid  is  much  more  frequent  than  from  any  other  sub- 
stance. Hence,  a  more  than  usual  degree  of  importance  is  attached  to  the  modes 
of  detecting  the  presence  of  arsenic  in  minute  quantity.  Of  the  different  prepa- 
rations of  the  metal,  arsenic  acid,  and  after  it  arsenious  acid,  are  the  most  poison- 
ous j  the  salts  and  sulphides  are  so  in  a  much  less  degree.  Arsenious  acid  in  the 
solid  form  and  unmixed  with  foreign  matters,  is  easily  recognized  as  a  white  heavy 
powder,  which  is  tasteless  or  nearly  so,  is  entirely  volatilized  by  heat,  and  diffuses 
a  garlic  odour  in  the  reducing  flame  of  a  lamp.  When  dissolved  in  water,  arse- 
nious acid  may  be  detected  by  the  fluid  tests,  already  mentioned  (p.  531).  The 
silver  and  copper  tests  are  most  conveniently  applied  in  the  following  forms. 

1.  Ammonio-nitrate  of  silver. — This  is  an  exceedingly  delicate  test  of  arsenious 
acid,  whether  free,  or  in  combination  with  an  alkali.     It  is  prepared  by  adding 
diluted  ammonia  to  a  solution  of  nitrate  of  silver,  till  the  oxide  of  silver,  which  is 
first  thrown  down,  is  redissolved.     When  the  ammonia  has  been  added  in  proper 
quantity  and  not  in  excess,  the  odour  of  that  substance  is  scarcely  perceptible, 
and  the  liquid  contains  in  solution  the  crystallizable  ammonio-nitrate  of  silver, 
AgO.N05.2NH3.     This  test-liquid  throws  down  from  arsenious  acid,  the  yellow 
arsenite  of  silver,  which  is  redissolved  both  by  acids  and  by  ammonia.     A  solu- 
tion of  nitrate  of  silver  gives  the  same  indication  as  the  prepared  ammonio-nitrate 
in  an  alkaline  but  not  in  an  acid  solution  of  arsenious  acid.     Nitrate  of  silver 
produces,  in  phosphate  of  soda  or  any  other  soluble  phosphate,  a  yellow  precipi- 
tate of  phosphate  of  silver  of  the  same  colour  as  the  arsenite  of  silver,  and  which 
might,  therefore,  be  mistaken  for  the  latter  j    but  the  action  of  the  ammonio- 
nitrate  is  not  liable  to  that  ambiguity,  as  it  does  not  produce  a  yellow  precipitate 
in  an  alkaline  solution  of  phosphoric  acid,  the  phosphate  of  silver  being  then  re- 
tained in  solution  by  the  ammonia  of  the  reagent,  although  arseniate  of  silver  is 
precipitated  in  the  same  circumstances.     Both  phosphate  and  arseniate  of  silver 
are  indeed  considerably  more  soluble  in  ammonia  than  the  arsenite  of  the  same 
metal. 

2.  Ammonio-sulphate  of  copper  gives  a  beautiful  green  precipitate,  the  arsenite 
of  copper,  in  both  alkaline  and  acid  solutions  of  arsenious  acid;    sulphate  of 
copper  gives  the  same  precipitate  in  the  former,  but  not  in  the  latter. 

But  in  solutions  containing  organic  matter,  the  indications  of  these  tests  are 
sometimes  delusive,  and  often  doubtful.  Recourse  is  then  had  to  the  proper 
means  of  obtaining  arsenic  in  the  metallic  form,  from  the  liquid  suspected  to  con- 
tain arsenious  acid.  Indeed,  even  where  the  indications  of  the  fluid  tests  are 
clear,  the  reduction  test  should  never  be  omitted,  the  evidence  which  it  affords 
being  of  a  superior  and  completely  demonstrative  character.  The  reduction  test 
of  arsenic  is  practised  in  two  different  ways  :  (1)  by  the  reduction  of  the  sulphide 
of  arsenic  by  means  of  charcoal  and  carbonate  of  potash,  and  (2)  by  the  produc- 
tion, and  subsequent  decomposition  of  the  gaseous  compound  of  arsenic  and  hy- 
drogen. The  following  operations  are  necessary  in  the  practice  of  the  first 
method : — 


TESTING    FOR    ARSENIC.  535 

REDUCTION   TEST  OF  ARSENIC. 

I.  Preparation  of  the  fluid  : 

1.  Heat  the  mass  with  about  one-fourth  of  its  weight  of  strong  sulphuric 
acid  in  a  retort,  to  which  is  adapted  a  receiver  having  its  inner  surface 
wetted,  till  the  organic  matter  is  carbonized. 

2.  Pulverize  the  residue,  and  treat  it  with  nitric  acid  mixed  with  a  little 
hydrochloric  acid,  in  order  to  bring  the  arsenic  to  the  state  of  arsenic 
acid,  which  is  easily  soluble. 

3.  Boil  with  water;  filter;  and  mix  the  filtrate  with  the  liquid  in  the  re- 
ceiver.* 

II.  Precipitation  of  the  sulphide  of  arsenic  : 

1.  Transmit  a  stream  of  hydrosulphuric  acid  gas  through  the  liquid  for 
half  an  hour.f 

2.  Heat  the  liquid  in  an  open  vessel  for  a  few  minutes,  to  cause  the  pre- 
cipitate to  separate. 

3.  Wash  the  precipitate  by  affusion  of  water  acidulated  with  hydrochloric 
acid,  and  subsidence. 

4.  Dry  the  precipitate  at  a  temperature  not  exceeding  300°. 

III.  "deduction  of  the  sulphide  of  arsenic  : 

1.  Mix  the  dried  precipitate  intimately  with  twice  its  bulk  of  dry  black 
flux  (carbonate  of  potash  and  charcoal),  or  with  a  mixture  of  pounded 
charcoal  and  dry  carbonate  of  soda,  or  with  cyanide  of  potassium,  and 
heat  to  redness  in  a  glass  tube,  of  the  form  and  size  of  a  or  6,  exhibited 
below. 

2.  Heat   slowly  a  particle  of  the  metallic   crust  in  a  glass  tube  c,  and 
observe  the  formation  of  a  white  crystalline  sublimate  of  arsenious  acid. 

3.  Dissolve  the  sublimate  in  a  small  quantity  of  boiling  water,  and  test 
with  ammonio-nitrate  of  silver,  &c.,  as  above 


Fm.  193. 


( 


O 


Marsh's  test.  —  Hydrogen  cannot  be  evolved  in  contact  with  any  preparation  of 
arsenic,  soluble  or  insoluble,  without  combining  with  the  metal,  which  is  thus 
removed  from  the  liquor,  in  the  form  of  arseniuretted  hydrogen  gas.  Mr.  Marsh 
has  founded,  upon  this  fact,  a  simple  and  elegant  mode  of  obtaining  metallic 
arsenic  from  arsenical  liquors.  The  stopcock  being  removed  from  the  bulb- 
apparatus  represented  in  the  figure,  a  fragment  of  zinc  is  placed  in  the  lower  bulb, 

*  This  is  the  mode  of  preparation  most  generally  adopted,  and  it  is  applicable  to  all  cases 
of  searching  for  mineral  poisons.  Another  method,  which  is  especially  applicable  when  tho 
matter  to  be  examined  contains  a  large  quantity  of  fat,  is  to  heat  the  mass  with  strong  hy- 
drochloric acid,  or  aqua-regia,  in  a  large  retort;  the  greater  part  of  the  arsenic  is  then  con- 
verted into  chloride,  and  may  be  collected  in  a  receiver  containing  water. 

f  As  the  arsenic  is  in  the  state  of  arsenic  acid,  it  is  best  to  mix  the  liquid  with  sulphu- 
rous acid  before  passing  the  hydrosulphuric  acid  gas  through  it. 


536 


ARSENIC. 


and  diluted  sulphuric  acid  poured  upon  it.     The  stopcock  being  replaced  and 
closed,  the  lower  bulb  is  soon  filled  with  hydrogen  gas,  and  the  acid  liquid  forced 
into  the  upper  bulb.     It  is  necessary  to  test  this  hydrogen  for 
FIG.  194.  arsenic,  which  will  be  found  in  it,  if  the  zinc  itself  contains 

that  metal.  The  gas  for  this  purpose  is  kindled  at  the  stop- 
cock and  allowed  to  burn  with  a  small  flame.  If  a  stoneware 
plate  be  depressed  upon  the  flame,  a  black  spot  of  steel-grey 
colour  and  bright  metallic  lustre,  is  formed,  in  a  few  seconds, 
upon  the  surface  of  the  plate,  supposing  the  gas  to  contain 
arsenic;  or  if  a  cold  piece  of  glass  be  held  over  the  flame,  at 
a  small  height  above  it,  a  white  sublimate  of  arsenious  acid 
condenses  upon  the  glass.  But  if  the  zinc  employed  contains 
no  arsenic,  neither  of  these  effects  is  produced.  The  zinc 
being  proved  to  be  free  from  arsenic,  a  portion  of  the  liquor 
to  be  tested  is  introduced  into  the  lower  bulb,  in  addition  to 
the  acid  and  zinc  already  there  ]  and  when  the  bulb  is  again 
filled  with  hydrogen  gas,  the  latter  is  burned  and  examined 
precisely  as  before.  If  the  liquor  is  loaded  with  organic 
matter,  as  generally  happens  with  the  liquids  submitted  to 
examination  in  actual  cases  of  poisoning,  the  gas  may  be  filled 
with  froth,  and  the  evolution  of  it  very  slow.  But  in  the  course  of  a  night,  the 
gas  is  generally  obtained  in  sufficient  quantity,  and  in  a  proper  state,  to  permit  of 
examination.  It  is  much  better,  however,  first  to  remove  the  organic  matter  by 
one  of  the  methods  above  given ;  the  gas  is  then  evolved  freely  and  without 

frothing,  and  a  plain  bottle  with  a  cork  and 
FIG.  195.  glass  jet  will  be  sufficient  for  this  reduction 

experiment.     Then    also,  instead    of  burning 

'  the  gas  at  the  jet,  it  may  be  allowed  to  escape 
by  a  horizontal  tube,  such  as  that  in  figure  195, 
a  portion  of  which  is  heated  to  redness  by  a 
spirit  lamp.  The  arsenic  condenses  within  the 
tube,  beyond  the  flame  and  nearer  the  aperture, 
and  forms  a  metallic  crust,  which  may  be  con- 
verted by  sublimation  into  arsenious  acid ;  the 
sublimate  may  then  be  dissolved  in  a  small 
quantity  of  boiling  water,  and  the  solution 
tested  with  ammonio-nitrate  of  silver,  &c.,  as 
before. 

When    the   liquid   examined  contains  anti- 
mony, that  metal  combines  with  the  nascent 

hydrogen,  and  comes  off  as  antimoniuretted  hydrogen,  a  gas  which,  when 
burned,  or  heated  in  a  glass  tube,  gives  the  metal  and  a  white  sublimate,  in  the 
same  circumstances  as  arsenic  (L.  Thompson).  Antimony,  however,  may  be 
recognised  by  a  peculiarity  of  its  reduction  in  the  ignited  tube.  This  metal  is 
deposited  in  the  tube,  on  both  sides  of  the  heated  portion  of  it,  and  closer  to  the 
flame  than  arsenic,  owing  to  the  inferior  volatility  of  antimony.  The  white  sub- 
limate also,  if  dissolved  in  water  containing  a  drop  of  ammonia,  will  not  give  the 
proper  indications  with  the  fluid  tests  of  arsenic,  if  the  metal  be  antimony. 
Another  distinction  is,  that  the  arsenical  deposit  is  soluble  in  hypochlorite  of  soda, 
whereas  the  antimonial  deposit  is  not. 

Antidotes  to  arsenious  acid. — When  hydrated  sesquioxide  of  iron  is  mixed 
with  a  solution  of  arsenious  acid  to  the  consistence  of  a  thin  paste,  a  reaction  occurs 
by  which  the  arsenious  acid  disappears  in  a  few  minutes,  and  the  mass  ceases  to 
be  poisonous.  The  arsenious  acid  takes  oxygen  from  the  sesquioxide  of  iron,  and 
becomes  arsenic  acid,  while  the  sesquioxide  of  iron  is  reduced  to  protoxide,  a  prot- 
arseniate  of  iron  being  the  result,  which  is  insoluble  and  inert : 


ESTIMATION    OF    ARSENIC.  537 

2Fe203  +  As03  =  4FeO  .  As05. 

The  constitution  of  this  arseniate  of  iron  is  probably  2FeO .  HO .  AsO  4-  2FeO. 
Sesquioxide  of  iron,  when  used  as  an  antidote  to  arsenious  acid,  should  be  in  a 
gelatinous  state,  as  it  is  obtained  by  precipitation,  without  drying.  It  may  bo 
prepared  extemporaneously,  by  adding  bicarbonate  of  soda  in  excess  to  any  tincture 
or  red  solution  of  iron.  Calcined  magnesia  may  likewise  be  used  as  an  antidote 
to  arsenic.  Care  should  be  taken  in  preparing  the  latter  not  to  employ  too  great 
a  heat,  which  would  render  it  very  dense,  and  cause  it  to  combine  but  slowly  with 
the  arsenious  acid. 

ESTIMATION   OF  ARSENIC,    AND    METHODS    OF    SEPARATING  IT   FROM   THE 
PRECEDING    METALS. 

When  arsenic  is  contained  in  a  solution  entirely  in  the  form  of  arsenic  acid,  the 
best  mode  of  estimating  it  is  to  precipitate  it  in  the  form  of  anmionio-maguesian 
arseniate,  2MgO  .  NH40  .  As05  +  12HO.  The  solution  is  mixed  with  excess  of 
ammonia,  and  then  with  sulphate  of  magnesia,  to  which  a  quantity  of  chloride  of 
ammonium  has  been  added,  sufficient  to  prevent  the  precipitation  of  the  magnesia 
by  ammonia.  The  liquid  is  then  left  to  stand  for  about  twelve  hours ;  the  precipi- 
tate collected  on  a  weighed  filter;  washed  with  water  containing  ammonia;  and 
dried  over  sulphuric  acid  in  vacuo  at  ordinary  temperatures ;  it  has  then  the  com- 
position expressed  by  the  above  formula.  It  may  also  be  dried,  and  more  expe- 
ditiously,  by  exposing  it  to  a  temperature  of  exactly  212°  F.,  whereby  it  loses 
11  eq.  of  water,  and  is  reduced  to  2MgO.NH4O.As05  +  HO.  Exposure  to  a 
higher  temperature  occasions  loss  of  arsenic. 

If  the  liquid  contains  arsenious  acid,  that  compound  may  be  converted  into 
arsenic  acid  by  mixing  the  solution  with  hydrochloric  acid,  and  adding  chlorate 
of  potash  by  small  quantities.  The  vessel  must  be  left  in  a  moderately  warm  place 
till  the  odour  of  free  chlorine  has  entirely  disappeared.  Aqua  regia  may  also  be 
used  to  effect  the  oxidation,  but  it  is  less  convenient.  In  either  case,  the  liquid 
must  be  considerably  diluted  with  water,  otherwise  part  of  the  arsenic  will  be  con- 
verted into  chloride,  and  volatilized.  It  is  best,  perhaps,  to  perform  the  oxidation 
in  a  capacious  retort  having  a  receiver  adapted  to  it. 

Arsenious  acid  may  also  be  estimated  by  its  action  on  terchloride  of  gold.  The 
arsenious  acid  is  thereby  converted  into  arsenic  acid,  and  gold  is  precipitated 
in  the  metallic  state.  The  quantity  of  gold  thus  reduced  gives  the  quantity  of 
arsenious  acid  present : 

2AuCl3  +  6HO  -f  3As03  =  2Au  -f  6HC1  +  3As05. 

The  gold  solution  used  for  the  purpose  is  the  sodio-chloride,  or  amrnoiiio-chloride 
of  gold.  It  must  be  free  from  nitric  acid ;  but  the  presence  of  hydrochloric  acid, 
even  in  large  excess,  does  not  interfere  with  the  action.  The  liquid,  after  the 
addition  of  the  arsenic  solution,  must  be  left  to  itself  for  a  considerable  time  to 
enable  the  gold  to  settle  down  completely. 

When  arsenic  and  arsenious  acids  exist  together  in  solution  the  former  may  be 
precipitated  as  ammonio-magnesian  arseniate  (a  considerable  quantity  of  sal- 
ammoniac  being  added  to  prevent  the  simultaneous  precipitation  of  the  arsenious 
acid) ;  the  arsenious  acid  converted  into  arsenic  acid  by  oxidation  with  chlorate  of 
potash  and  hydrochloric  acid,  and  then  precipitated  in  a  similar  manner;  or  th« 
arsenious  acid  may  be  estimated  by  chloride  of  gold,  as  last  described. 

The  separation  of  arsenic  in  solution  from  the  alkalies,  earths,  and  those  metals 
which  are  not  precipitated  from  their  acid  solutions  by  hydrosulphuric  acid,  is 
effected  by  passing  a  stream  of  that  gas  through  the  acid  liquid  for  a  considerable 
time,  then  leaving  it  to  stand,  and  heating  it  gently  to  ensure  the  complete  pre- 
cipitation of  the  sulphide  of  arsenic.  If  the  arsenic  is  in  the  form  of  arsenic 


538  ARSENIC. 

acid,  that  compound  must  be  previously  reduced  to  arsenious  acid  by  means  of 
sulphurous  acid.  The  tersulphide  of  arsenic  is  collected  on  a  weighed  filter, 
thoroughly  washed,  and  dried  at  a  moderate  heat.  If  quite  pure,  it  may  be 
weighed  with  the  filter,  and  the  quantity  of  arsenic  thereby  directly  determined. 
But  as  it  almost  always  contains  an  excess  of  sulphur,  it  is  better  to  take  a  weighed 
quantity  of  it  from  the  filter,  oxidize  it  in  a  capacious  flask  by  means  of  dilute 
hydrochloric  acid  and  chlorate  of  potash,  continuing  the  operation  till  the  greater 
part  of  the  sulphur  is  converted  into  sulphuric  acid,  and  the  remainder  collects  at 
the  bottom  of  the  liquid  in  a  compact  yellow  globule ;  then  decant  the  liquid, 
wash  the  globule  of  sulphur,  and  weigh  it ;  and,  finally,  estimate  the  quantity  of 
sulphur  in  the  solution  by  precipitation  with  chloride  of  barium,  adding  the 
quantity  thus  found  to  the  weight  of  the  globule.  The  proportion  of  sulphur  in 
the  precipitated  sulphide  of  arsenic  being  thus  ascertained,  the  amount  of  arsenic 
is  easily  calculated. 

From  cadmium,  copper,  and  lead,  arsenic  may  be  separated  by  means  of  sul- 
phide of  ammonium.  The  filtered  aimnoniacal  solution  is  then  treated  with  excess 
of  hydrochloric  or  acetic  acid  to  throw  down  the  sulphide  of  arsenic,  and  the  pre- 
cipitate treated  in  the  manner  just  described. 

The  separation  of  arsenic  from  tin  is  attended  with  considerable  difficulty. 
One  of  the  best  methods  is  to  convert  the  two  metals  into  sulphides,  and  separate 
them,  after  drying  and  weighing  the  whole,  by  ignition  in  a  stream  of  hydro- 
sulphuric  acid  gas.  The  mixed  sulphides  are  introduced  into  a  weighed  glass 
bulb,  having  a  tube  attached  to  it  on  each  side.  One  of  these  tubes,  the  exit- 
tube,  must  be  at  least  a  quarter  of  an  inch  in  diameter,  to  prevent  stoppage,  and 
bent  downwards  so  as  to  dip  into  a  flask  containing  ammonia.  The  whole  is  then 
weighed,  hydrosulphuric  acid  gas  passed  through  the  apparatus,  and  the  bulb 
heated  till  the  whale  of  the  sulphide  of  arsenic  is  sublimed.  Part  of  the  sulphide 
of  arsenic  passes  into  the  ammoniacal  liquid,  by  which  it  is  dissolved,  and  the 
rest  sublimes  in  the  wide  tube.  When  the  operation  is  ended,  and  the  apparatus 
has  cooled,  the  wide  tube  is  cut  off  at  a  short  distance  from  the  bulb,  then  broken, 
and  the  pieces  digested  in  caustic  potash  to  dissolve  out  the  sulphide  of  arsenic. 
The  solution  thus  obtained  is  added  to  the  ammoniacal  liquid  in  the  flask ;  the 
sulphide  of  arsenic  precipitated  by  hydrochloric  acid,  oxidized  without  previous 
filtration  with  hydrochloric  acid  and  chlorate  of  potash ;  and  the  resulting  arsenic 
acid  precipitated  by  ammonia  and  sulphate  of  magnesia.  The  sulphide  of  tin  re- 
maining in  the  bulb  is  converted  into  stannic  oxide  by  treating  it  with  strong 
nitric  acid. 

When  arsenic  is  combined  with  other  metals  in  the  form  of  an  alloy,  the  whole 
may  be  dissolved  or  oxidized  by  means  of  aqua  regia,  or,  better,  with  hydrochloric 
acid  and  chlorate  of  potash,  and  the  arsenic  separated  by  one  of  the  preceding 
methods.  In  the  case  of.  tin,  however,  it  is  best  to  fuse  the  alloy  in  thin  laminae 
with  five  times  its  weight  of  carbonate  of  soda  and  an  equal  quantity  of  sulphur, 
whereby  a  mixture  of  sulpharseniate  and  sulphostannate  of  soda  is  obtained,  which 
dissolves  completely  in  hot  water.  The  sulphides  of  tin  and  arsenic  may  then  be 
precipitated  by  hydrochloric  acid,  and  separated  as  above.* 

*  For  a  full  account  of  the  methods  of  estimating  arsenic  and  separating  it  from  other 
metals,  vide  H.  Rose,  "  Handbuch  der  analytischen  Chemie,"  1851,  ii.  381. 


ANTIMONY.  539 

i 
SECTION    II- 

ANTIMONY. 

Eq.  120-24  or  1503*;  Sb  (stibium). 

This  metal  was  well  known  to  the  alchemists,  and  is  one  of  the  metals  the  pre- 
parations of  which  were  first  introduced  into  medicine.  Its  sulphide  is  not  an  un- 
common mineral,  and  is  the  source  from  which  the  metal  and  its  compounds  are 
always  derived. 

The  sulphide  of  antimony  is  easily  reduced  to  the  metallic  state  by  mixing 
together  4  parts  of  that  substance,  3  parts  of  crude  tarter,  and  1^  parts  of  nitre, 
and  projecting  the  mixture  by  small  quantities  at  a  time  into  a  red  hot  crucible. 
The  sulphide  is  also  sometimes  reduced  by  fusion  with  small  iron  nails,  which 
combine  with  the  sulphur,  and  disengage  the  antimony.  Or  it  may  be  obtained  in 
a  state  of  greater  purity  by  strongly  igniting  in  a  crucible  a  quantity  of  the  pot- 
ash-tartrate  of  antimony,  and  placing  the  resulting  metallic  mass  in  water  to  remove 
any  potassium  it  may  have  acquired. 

Antimony  is  a  white  and  brilliant  metal,  generally  possessing  a  highly  lamel- 
lated  structure.  It  is  easily  obtained  in  rhombohedral  crystals  of  the  same  form 
as  arsenic  and  tellurium.  Its  density  is  from  6-702  to  6-86.  It  undergoes  no 
change  in  the  air.  The  point  of  fusion  of  antimony  is  estimated  at  797°;  it  may 
be  distilled  at  a  white  heat.  This  metal  burns  in  air  at  a  red  heat,  and  produces 
copious  fumes  of  oxide  of  antimony. 

Antimony  combines  in  three  proportions  with  oxygen,  forming  oxide  of  anti- 
mony and  antimonic  acid,  Sb03  and  Sb06,  which  correspond  respectively  with 
arsenious  and  arsenic  acids ;  and  antimonious  acid,  Sb04,  which  is  probably  an 
intermediate  or  compound  oxide,  analogous  to  the  black  oxide  of  iron. 

Teroxide  of  antimony,  Antimonic  oxide,  Antimonious  acid,  Sb03,  144-24  or 
1803.  —  This  oxide  may  be  obtained  by  dissolving  the  sulphide,  finely  pounded 
and  in  the  condition  in  which  it  is  known  as  prepared  sulphide  of  antimony,  in 
four  times  its  weight  of  concentrated  hydrochloric  acid.  Pure  hydrosulphuric  acid 
goes  off,  and  the  antimony  is  converted  into  terchloride : 

SbS3  +  3HC1  =  SbCl3  =  3HS. 

The  clear  solution  may  be  poured  off,  and  precipitated  at  the  boiling  heat  by  a 
solution  of  carbonate  of  potash  added  in  excess  j  the  carbonic  acid,  which  does  not 
combine  with  oxide  of  antimony,  escaping  as  gas.  Teroxide  of  antimony,  so  pre- 
pared, is  anhydrous,  but  is  slightly  soluble  in  water :  it  is  white,  but  assumes  a 
yellow  tint  when  heated.  It  is  fusible  at  a  red  heat,  and  sublimes  at  a  high  tem- 
perature in  a  close  vessel,  where  it  cannot  pass  into  a  higher  state  of  oxidation. 
The  brilliant  crystalline  needles  which  condense  about  antimony  in  a  state  of  com- 
bustion likewise  consist  of  this  oxide.  They  possess  the  unusual  prismatic  form 
of  arsenious  acid  observed  by  Wohler.  Oxide  of  antimony  also  crystallizes  as  fre- 
quently in  regular  octohedrons,  the  other  form  of  arsenious  acid.  It  occurs  in  the 
prismatic  form  as  a  rare  mineral,  whose  density  is  5  '227. 

When  a  solution  of  potash  is  poured  upon  the  bulky  hydrate  of  teroxide  of  anti- 
mony, which  is  precipitated  from  the  chloride  by  water,  a  portion  of  the  oxide  is 

*  The  number  129,  given  by  Berzelius  for  the  equivalent  of  antimony,  and  hitherto  gene- 
rally adopted,  appears  from  recent  experiments  by  Schneider  (Fogg.  Ann.  xcviii.  293)  and 
by  H.  Rose  (Berl.  Akad.  Ber.  1856,  p.  229)  to  be  much  too  high.  Schneider,  by  reducing 
the  tersulphide  of  antimony  with  hydrogen,  finds  the  equivalent  to  be  120-24 ;  and  Rose,  by 
decomposing  the  terchloride  with  hydrosulphuric  acid,  and  precipitating  the  chlorine  with 
nitrate  of  silver,  finds  the  number  120-69. 


540  ANTIMONY. 

dissolved,  but  the  greater  part  loses  its  water,  and  is  reduced  in  a  few  seconds  to 
a  fine  greyish,  crystalline  powder,  which  is  a  neutral  combination  of  teroxide  of 
antimony  with  potash.  Teroxide  of  antimony  also  combines  with  acids,  forming 
the  salts  of  antimony  or  antimonic  salts. 

The  solution  of  these  salts  give  with  hydrosit/phuric  acid  a  brick-red  precipitate 
of  tersulphide  of  antimony,  easily  soluble  in  sulphide  of  ammonium,  and  reprecipi- 
tated  by  acids.  This  precipitate  dissolves  in  strong  boiling  hydrochloric  acid,  forming 
the  terchloride,  which  when  thrown  into  water  yields  a  precipitate  of  the  oxychlo- 
ride.  This  reaction  with  hydrosulphuric  acid  distinguishes  antimony  from  all  other 
metals.*  Zinc  or  iron  precipitates  antimony  from  its  solutions  in  the  form  of  a 
black  powder,  which,  when  fused  on  charcoal  before  the  blow-pipe,  yields  a  brittle 
button  of  the  metal.  According  to  Dr.  Odling,f  antimony  is  also  precipitated  by 
copper,  in  the  form  of  a  brilliant  metallic  film,  which  may  be  dissolved  off  the 
copper  by  a  solution  of  permanganate  of  potash,  yielding  a  solution  which  will  give 
the  characteristic  red  precipitate  with  hydrosulphuric  acid.  This  reaction  affords 
a  ready  method  of  separating  antimony  from  liquids  containing  organic  matter,  — 
as  in  medico-legal  inquiries.  All  compounds  of  antimony  fused  upon  charcoal 
with  carbonate  of  soda  or  cyanide  of  potassium,  yield  a  brittle  globule  of  anti- 
mony, a  thick  white  fume  being  at  the  same  time  given  off,  and  the  charcoal 
covered  to  some  distance  around  with  a  white  deposit  of  antimonic  oxide.  The 
reduction  with  cyanide  of  potassium  may  also  be  performed  in  a  porcelain  crucible, 
without  charcoal.  A  solution  of  terchloride  of  gold  added  to  the  solution  of  a  salt 
of  teroxide  of  antimony,  forms  a  yellow  precipitate  of  metallic  gold,  the  oxide  of 
antimony  being  at  the  same  time  converted  into  antimonic  acid,  which  compound 
is  precipitated  as  a  white  powder,  together  with  the  gold,  unless  the  solution  con- 
tains a  very  large  excess  of  hydrochloric  acid.  In  a  solution  of  oxide  of  antimony 
in  potash,  terchloride  of  gold  produces  a  black  precipitate,  which  is  not  altered  by 
heating.  This  reaction  is  extremely  delicate. 

Tersulphide  of  antimony,  SbS3,  168-24  or  2103. — The  common  ore  of  antimony 
is  a  tersulphide,  SbS3,  corresponding  with  the  preceding  oxide  of  antimony.  It  is 
rarely  free  from  sulphide  of  arsenic,  which  thus  often  enters  into  the  antimonial 
preparations  derived  from  the  sulphide  of  antimony,  but  into  tartar-emetic  less 
frequently  than  the  others.  The  same  sulphide  is  formed  when  salts  of  the  oxide 
of  antimony,  such  as  tartar-emetic,  are  precipitated  by  hydrosulphuric  acid ;  but 
it  is  then  of  an  orange-red  colour.  When  the  precipitated  sulphide  is  dried,  it 
loses  water  and  becomes  anhydrous,  still  remaining  of  a  dull  orange  colour ;  but 
when  heated  more  strongly,  it  shrinks  at  a  particular  temperature,  and  assumes 
the  black  colour  and  metallic  lustre  of  the  native  sulphide.  This  sulphide  is  also 
obtained  of  a  dark  brown  colour  by  boiling  the  prepared  sulphide  of  antimony  in  a 
solution  of  carbonate  of  potash,  and  allowing  the  solution  to  cool ;  by  fusing  2| 
parts  of  the  prepared  sulphide  with  1  part  of  carbonate  of  potash ;  or  dissolving  it 
in  a  boiling  solution  of  caustic  potash,  and  afterwards  adding  an  acid.  The  last 
preparation  is- known  as  Kermes  mineral.  It  has  a  much  duller  colour  than  the 
precipitated  sulphide,  but  differs  from  it  only  in  containing  small  quantities  of 
oxide  and  pentasulphide  of  antimony,  together  with  an  alkaline  sulphide  which 
cannot  be  removed  by  washing  (Berzelius).  When  the  cooled  mother-liquor  from 
which  kermes  is  deposited  is  mixed  with  hydrochloric  acid,  a  precipitate  is  ob- 
tained, consisting,  like  the  kermes,  of  SbS3  mixed  with  Sb03  and  SbS5,  but  of  a 
redder  colour.  It  is  sometimes  called  the  golden  mlphuret  of  antimony. 

When  the  sulphide  of  antimony  is  oxidated  at  a  red  heat,  much  sulphur  is 
burned  off,  and  an  impure  oxide  of  antimony  remains.  This  matter  forms,  when 
fused,  the  glass  of  antimony,  which  contains  a  considerable  quantity  of  undecom- 

*  For  the  reactions  of  antimonic  salts  with  alkalies,  see  terchloride  of  antimony  and  tartar 
tmetic. 

f  Guy's  Hospital  Reports,  [3.]  ii.  249. 


SULPHATE    OF    ANTIMONY.  541 

posed  sulphide.  The  glass,  reduced  to  powder,  is  boiled  with  bitartrate  of  potash 
as  a  source  of  oxide  of  antimony,  in  the  pharmaceutical  preparation  of  tartar- 
emetic.  The  oxide  of  antimony  is  dissolved  out  from  the  glass  by  acids,  and  a 
substance  is  left  which  is  called  sajfron  of  antimony.  This  last  is  a  definite  com- 
pound of  oxide  and  sulphide  of  antimony,  Sb03.2SbS3,  which  also  occurs  as  a 
mineral — namely,  red  antimony  ore. 

Terchloride  of  antimony,  SbCl3,  is  obtained  by  distilling  either  metallic  anti- 
mony or  the  tersulphide  of  antimony  with  corrosive  sublimate.  When  heated  it 
flows  like  an  oil,  and  becomes  a  crystalline  mass  on  cooling.  It  is  a  powerful 
cautery.  This  salt  deliquesces  in  air,  and  becomes  turbid,  owing  to  the  deposition 
of  a  subsalt.  A  concentrated  solution  of  chloride  of  antimony  is  also  obtained  by 
dissolving  the  sulphide  of  antimony  in  hydrochloric  acid.  When  this  solution  is 
thrown  into  water,  it  gives  a  white  bulky  precipitate,  which  after  a  time  resolves 
itself  into  groups  of  small  crystals,  having  usually  a  fawn  colour;  it  wa&  formerly 
called  the  powder  of  Algaroth.  These  small  crystals  are  an  oxychloride  of  anti- 
mony, which,  according  to  the  analyses  of  Johnston  and  Malaguti,  contains 
2SbCl3.9Sb03. 

A  solution  of  terchloride  of  antimony,  to  which  water  is  added,  and  then  a 
sufficient  quantity  of  hydrochloric  acid  to  redissolve  the  precipitate  thereby  pro- 
duced, gives  with  potash  a  white  precipitate  of  the  hydrated  teroxide,  soluble  in  a 
very  large  excess  of  the  alkali.  Ammonia  forms  the  same  precipitate  insoluble 
in  excess.  Carbonate  of  potash,  or  soda,  produces  also  a  white  precipitate  of  the 
hydrated  teroxide,  which  is  soluble  in  excess,  especially  of  the  potash-salt,  but  re- 
appears after  a  while.  These  reactions  are  greatly  modified  by  the  presence  of 
fixed  organic  acids,  especially  of  tartaric  acid.  In  such  a  case,  water  forms  DO 
precipitate,  ammonia  but  a  slight  one  and  after  some  time  only,  and  the  precipi- 
tate formed  by  potash  dissolves  easily  in  excess  of  the  alkali.  (See  Tartar-emetic.} 

Terfluoride  of  antimony,  SbF3,  is  obtained,  by  treating  the  teroxide  with 
strong  hydrofluoric  acid,  in  colourless  crystals  which  dissolve  in  water  without  de- 
composition. It  unites  with  fluoride  of  potassium,  forming  the  compound  3KF. 
SbF3,  and  similarly  with  fluoride  of  sodium  and  fluoride  of  ammonium. 

Sulphate  of  antimony,  Sb03.3S03,  is  obtained,  by  boiling  metallic  antimony  with 
concentrated  sulphuric  acid,  as  a  white  saline  mass,  which  is  decomposed  by  water. 

Oxalate  of  potash  and  antimony,  KO.C203-f-Sb03.3C203. — This  is  a  double 
crystallizable  salt  of  antimony,  which,  like  the  tartrate  of  potash  and  antimony, 
may  be  dissolved  in  water  without  decomposition.  It  is  prepared  by  saturating 
binoxalate  of  potash  with  oxide  of  antimony.  It  is  soluble  at  48°  in  ten  times  its 
weight  of  water  (Lassaigne).  According  to  Bussy,  when  binoxalate  of  potash  is 
digested  upon  oxide  of  antimony  in  excess,  two  salts  are  formed,  one  in  oblique 
prisms,  and  another  less  soluble,  in  intricate  small  crystals ;  but  neither  is  very 
stable.  The  former  is  decomposed  by  a  large  quantity  of  water :  its  analysis  gave 
3(KO.C203)  +  Sb03.3C203+6HO.* 

Tartrate  of  potash  and  antimony,  KO.Sb03  +  C8H40,0.2HO.  —  This  salt,  the 
tartar-emetic,  or  potash  tartrate  of  antimony  of  pharmacy,  is  prepared  by  neutral- 
izing bitartrate  of  potash  with  oxide  of  antimony :  the  oxide  obtained  by  decom- 
posing the  chloride  or  sulphate  of  antimony  with  water  answers  best  for  the  pur- 
pose. A  quantity  of  oxide  of  antimony  may  be  boiled  with  three  or  four  times 
its  weight  of  water,  and  bitartrate  of  potash  added  in  small  quantities  till  the 
oxide  is  entirely  dissolved.  The  filtered  solution  yields  the  salt,  on  cooling,  iu 
large  transparent  crystals,  the  form  of  which  is  an  octohedron  with  a  rhombic 
base ;  they  become  white  in  the  air,  and  lose  their  water  of  crystallization.  They 
are  soluble  in  14  times  their  weight  of  cold  water,  and  in  1-88  parts  of  boiling 
water,  but  not  in  alcohol.  The  mother-liquor  of  these  crystals  becomes  a  syrupy 
liquid,  and  dries  up  into  a  gummy  mass  without  crystallizing,  when  oxide  of  anti- 

*J.  Pharm.  1838.  p.  509. 


542  ANTIMONY. 

mony  has  been  dissolved  in  excess  by  the  acid  tartrate  in  preparing  the  salt. 
Potash  added  to  a  solution  of  the  salt  throws  down  the  teroxide  of  antimony,  but 
the  precipitate  is  easily  soluble  in  excess  of  potash.  -A mraorua  forms  no  precipi- 
tate at  first,  and  but  a  slight  one  after  standing.  Alkaline  carbonates  form  a  pre- 
cipitate of  the  teroxide  insoluble  in  excess  of  the  reagent.  With  hydrosulphuric 
acid,  the  reaction  is  the  same  as  with  other  salts  of  antimony.  (See  p.  540.) 
Salts  of  the  earths  and  basic  metallic  oxides,  such  as  baryta  and  oxide  of  silver, 
throw  down  from  its  solution  a  compound  of  the  tartrate  of  antimony  with  tartrate 
of  baryta,  tartrate  of  silver,  &c.  (Wallquist.)  Strong  acids  decompose  the  salt, 
and  produce  a  precipitate  which  is  a  mixture  of  bitartrate  of  potash  with  oxide 
of  antimony,  or  with  a  subsalt  of  that  oxide. 

This  salt  was  formerly  described  as  a  double  tartrate  of  potash  and  antimony, 
or,  abstracting  its  water  of  crystallization,  which  is  differently  stated  at  2 
and  3  equivalents,  as  KO.(C4H205)  -f  Sb03.(C4H205).  When  the  atomic 
weight  of  tartaric  acid  is  doubled,  and  it  is  represented  as  a  bibasic  acid,  the 
formula  for  dry  tartar-emetic  becomes  KO.Sb03.(C8H4010).  In  comparing  the 
last  formula  with  that  of  bitartrate  of  potash,  represented  also  as  a  bibasic 
salt,  KO.HO.(C8H4Oi0),  it  is  observed  that  1  eq.  of  oxide  of  antimony  takes 
the  place  of  1  eq.  'of  water  as  base,  although  the  former  contains  3  eq.  of 
oxygen,  and  the  latter  only  one.  Tartrate  of  potash  and  antimony  is,  in  this 
respect,  an  anomalous  salt.  Another  equally  remarkable  fact  respecting  this  salt 
has  been  observed  by  M  Dumas,  namely,  that  2  eq.  of  water  are  separated  from 
the  anhydrous  salt  at  428°,  leaving  a  substance  of  which  the  elements  are 
C8H2Ou.SbK.  The  first  part  of  this  formula,  C8H20,2,  M.  Dumas  looks  upon  as  a 
quadribasic  salt-radical,  existing  in  the  tartrates,  which  in  hydrated  tartaric  acid 
is  united  with  4H,  in  bitartrate  of  potash  with  3H  +  K,  and  in  tartrate  of  anti- 
mony and  potash  with  Sb-f-K.  Here  Sb  is  found  equivalent  to  and  capable  of  re- 
placing 3H.  Tartrate  of  antimony  and  potash  might,  therefore,  be  represented 
by  KSb(C8H2012)  +  2HO+  water  of  crystallization.  If  Sb02  be  regarded  as  a 
radical  capable  of  replacing  1  eq.  of  hydrogen  (similar  to  uranyl,  U202,  the  hypo- 
thetical radical  of  the  uranic  salts),  the  formula  of  tartar-emetic  dried  at  212°  may 
be  written  as  C8H4K(Sb02)012,  and  that  of  the  salt  dried  between  392°  and  428°, 
as  C8H2K(Sb02)010. 

Antimonic  acid,  Sb05,  160-24  or  2003.  — This  compound  is  obtained  in  the 
hydrated  state :  1.  By  treating  antimony  with  nitric  acid,  or  with  aqua-regia  con- 
taining excess  of  nitric  acid.  2.  By  decomposing  pentachloride  of  antimony  with 
water.  3.  By  precipitating  a  solution  of  antimoniate  of  potash  with  an  acid. 

The  hydrated  acid  obtained  by  either  of  these  methods  gives  off  its  water  at  a 
moderate  heat,  and  yields  anhydrous  antimonic  acid  in  the  form  of  a  yellowish 
powder,  which  is  tasteless,  insoluble  in  water,  decomposes  alkaline  carbonates, 
and,  when  heated  to  redness,  gives  off  oxygen,  and  is  converted  into  antimoniate 
of  antimonic  oxide,  Sb03.SbG5. 

The  hydrates  obtained  by  the  three  methods  above  described  are  by  no  means 
identical.  The  acid  in  the  first  is  monobasic,  whereas  in  the  other  two  it  is 
bibasic.  The  bibasic  acid  is  distinguished  by  the  name  of  metantimonic  acid, 
while  the  monobasic  acid  is  called  simply  antimonic  acid  (Fremy).% 

Antimonic  acid  forms  neutral  or  normal  salts,  containing  MO.Sb05,  and  acid  salts 
whose  formula  is  MO  .  (Sb05)2.  Metantimonic  acid  forms  neutral  salts  containing 
(M0)2 .  Sb05,  and  acid  salts  containing  (MO)2.(Sb05)2,  or  MO  .  Sb06,  so  that  the 
acid  metantimoniates  are  isomeric  or  polymeric  with  the  neutral  antimoniates.  An 
acid  metantimoniate  easily  changes  into  a  neutral  antimoniate.  The  mctantimor 
niates  of  potash,  soda,  and  ammonia  are  crystalline ;  the  antimoniates  of  the  same 
bases  are  gelatinous  and  uncrystallizable.  The  soluble  acid  metantimoniates  form 
a  crystalline  precipitate  with  salts  of  soda ;  the  soluble  antimoniates  do  not  form 
any  such  precipitate  (Fremy). 

Antimoniates  of  potash. — The  neutral  salt,  KO.Sb05.5HO,  is  obtained  by 


ANTIMONIATES.  543 

fusing  1  part  of  antimony  with.  4  parts  of  nitre,  digesting  the  fused  mass  in  tepid 
water  to  remove  nitrate  and  nitrite  of  potash,  and  boiling  the  residue  for  an  hour 
or  two  with  water.  The  white  insoluble  mass  of  anhydrous  antimoniate  is  thereby 
transformed  into  a  hydrate  containing  5  eq.  water,  which  is  soluble.  The  solu- 
tion when  evaporated  leaves  this  hydrate  in  the  form  of  a  gummy  uncrystal- 
Hzable  mass,  which  gives  off  2  eq.  of  water  at  320°,  and  the  whole  at  a  higher 
temperature. 

Acid  antimoniate  of  potash,  KO  .  (Sb05)2  is  obtained  by  passing  carbonic  acid 
gas  through  a  solution  of  the  neutral  antimoniate.  It  is  white,  crystalline,  per- 
fectly insoluble  in  water,  and  is  converted  into  the  neutral  salt  when  heated  with 
excess  of  potash.  This  salt  is  the  antimonium  diaphoreticum  lavatum  of  the 
pharmacopoeias  (Fremy). 

Neutral  metantimoniate  of  potash,  2KO.Sb05,  is  prepared  by  fusing  antimonic 
acid  or  neutral  antimoniate  of  potash  with  a  large  excess  of  potash.  The  fused 
mass  dissolves  in  a  small  quantity  of  water,  and  the  solution  evaporated  in  vacuo 
yields  crystals  of  the  neutral  metantimoniate.  This  salt  dissolves  freely  and  with- 
out decomposition  in  warm  water  containing  excess  of  potash ;  but  cold  water  or 
alcohol  decomposes  it  into  potash  and  the  acid  metantimoniate.  Hence  the  aque- 
ous solution  of  this  salt  gives  a  precipitate,  after  a  while,  with  salts  of  soda 
(Fremy). 

Acid  metantimoniate  of  potash,  KO  .  Sb05+7HO,  sometimes  called  granular 
antimoniate  of  potash. — This  salt  is  used  as  a  test  for  soda.  To  obtain  it,  the 
neutral  antimoniate  is  first  prepared  and  dissolved  in  the  manner  above  described; 
the  solution  filtered  to  separate  any  acid  antimoniate  that  may  remain  undissolved; 
then  evaporated  to  a  syrup  in  a  silver  vessel ;  and  hydrate  of  potash  added  in  lumps 
to  convert  the  antimoniate  into  metantimoniate.  The  evaporation  is  continued  till 
the  liquid  begins  to  crystallize,  which  is  ascertained  by  taking  out  a  drop  now  and 
then  upon  a  glass  rod,  and  the  liquid  is  left  to  cool.  A  crystalline  mass  is  thus 
obtained,  consisting  of  neutral  and  acid  metantimoniate  of  potash ;  the  alkaline 
liquor  is  then  decanted,  and  the  salt  dried  upon  filtering  paper  or  unglazed  porce- 
lain (Fremy).  This  salt  may  also  be  prepared  by  treating  terchloride  of  anti- 
mony with  an  excess  of  potash  sufficient  to  redissolve  the  precipitate  first  formed, 
and  adding  permanganate  of  potash  till  the  solution  acquires  a  faint  rose  colour. 
The  liquid,  filtered  and  evaporated,  yields  crystals  of  the  granular  metantimoniate 
(Reynoso).  This  salt  is  sparingly  soluble  in  cold  water,  but  dissolves  readily  in 
water  between  113°  and  122°.  When  boiled  with  water  for  a  few  minutes,  or 
kept  in  contact  with  water  for  some  time,  it  is  converted  into  the  neutral  antimo- 
niate. It  must  therefore  be  preserved  in  the  soli^  state,  and  dissolved  just  before 
it  is  required  for  use.  A  small  quantity  of  it  is  then  treated  with  about  twice  its 
weight  of  cold  water  to  remove  excess  of  potash,  and  convert  any  neutral  metanti- 
moniate into  the  acid  salt;  the  liquid  decanted;  the  remaining  salt  rapidly  washed 
three  or  four  times  with  cold  water;  then  left  in  contact  with  water  for  a  few 
minutes,  and  the  liquid  filtered.  ,  On  adding  to  the  solution  thus  obtained,  a  small 
quantity  of  any  soda-salt,  a  crystalline  precipitate  is  formed,  consisting  of  acid 
metantimoniate  of  soda,  NaO  .  Sb05  +  7HO.  This  reaction  is  apparent  in  a  solu- 
tion containing  only  1  part  of  soda  in  300.  In  strong  solutions  of  soda,  the  pre 
cipitate  appears  immediately,  but  in  dilute  solutions  only  after  a  while,  the  crystals 
being  deposited  on  the  sides  of  the  vessel.  An  excess  of  potash  in  the  reagent 
also  retards  the  precipitation  (Fremy*). 

*  TraitS  de  Chimie  G6ne>ale,  par  Pelouze  et  Fremy,  2me.  ed.  t.  3,  pp.  151,  157.  Accord- 
ing to  Heffter  (Pogg.  Ann.  Ixxxvi.  418),  the  granular  antimoniate  of  potash  is  KO .  HO-f- 
12(KO.  Sb05-f-7HO);  the  precipitated  soda-salt  is  similarly  constituted  ;  and  by  treating 
the  solution  of  this  salt  in  boiling  water  with  salts  of  the  earths  and  metallic  oxides,  precipi- 
tates are  obtained,  also  of  similar  composition,  or  differing  only  in  the  water  which  they 
contain.  Heffter's  formulte  were  calculated  according  to  the  old  equivalent  of  antimony, 
129;  but  Schneider  has  shown  that,  on  re-calculating  the  analyses  with  the  lower  equivalent 
120-24,  the  numbers  of  the  equivalents  of  base  and  acid  come  out  equal. 


544  ANTIMONY. 

Antlmoniates  of  ammonia. — When  the  metantimonic  acid,  obtained  by  decom- 
posing pentachloride  of  antimony  with  water,  is  treated  with  ammonia,  part  of  it 
dissolves,  and  a  solution  is  formed  containing  neutral  metantimoniate  of  ammonia. 
A  few  drops  of  alcohol  added  to  the  solution,  throw  down  a  precipitate  consisting 
of  acid  metantimoniate  of  ammonia,  NH40  .  Sb05  +  6HO.  This  salt  is  slightly 
soluble,  and  its  solution  precipitates  soda-salts.  It  changes  spontaneously  in  a 
few  days,  even  when  kept  in  a  close  vessel,  into  neutral  antimoniate  of  ammonia, 
which  is  completely  insoluble  in  water.  The  same  change  is  instantly  produced 
in  it  by  heat  (Fremy). 

Antimoniate  of  lead,  PbO  .  Sb05,  may  be  obtained  as  a  yellow  powder  by  fusing 
autimonic  acid  with  oxide  of  lead,  or  as  a  white  hydrate  by  precipitation :  the 
hydrate  gives  off  its  water  when  heated,  and  turns  yellow.  This  salt  is  used  as  a 
pigment  under  the  denomination  of  Naples  yellow. 

Antimoniate  of  antimony,  Sb03 .  Sb05 .  or  Sb04,  is  obtained  by  the  action  of 
heat  upon  antimonic  acid,  by  roasting  the  teroxide  or  tersulphide,  or  by  treating 
powdered  antimony  with  excess  of  nitric  acid.  It  is  white,  infusible,  and  unalter- 
able by  heat;  slightly  soluble  in  water.  It  was  formerly  regarded  as  a  distinct 
acid,  Sb04,  and  called  antimonious  acid j  but  it  does  not  form  salts;  and,  when 
boiled  with  bitartrate  of  potash,  it  is  resolved  into  cream  of  tartar,  which  dissolves, 
and  a  residue  of  antimonic  acid. 

Pentasulphide  of  antimony,  Sulpha  ntimonic  acid,  Sb05,  is  obtained  by  passing 
hydrosulphuric  acid  gas  into  an  acid  solution  of  pentachloride  of  antimony,  or  into 
the  solution  of  an  alkaline  antimoniate.  It  has  an  orange-colour  much  less  red 
than  the  tersulphide;  it  is  the  golden  sulphuret  of  antimony  of  several  pharmaco- 
poeias. It  combines  with  basic  metallic  sulphides,  forming  the  sulpha  ntimoniates. 
The  sodium-salt,  3NaS  .  SbS5,  which  is  sometimes  used  in  medicine,  is  obtained  by 
mixing  18  parts  of  finely-pounded  tersulphide  of  antimony,  12  parts  of  dry  car- 
bonate of  soda,  13  parts  of  lime,  and  31  parts  of  sulphur;  triturating  the  mixture 
for  about  half  an  hour ;  leaving  it  for  two  or  three  days  in  a  flask  filled  with  water, 
and  shaking  it  from  time  to  time ;  then  filtering  and  evaporating,  first  over  the 
open  fire,  afterwards  in  vacuo.  The  salt  is  thus  obtained  in  large  regular  tetra- 
hedrons of  a  pale  yellow  calour.  It  is  very  soluble  in  water,  and  is  decomposed 
by  acids,  which  throw  down  hydrated  pentasulphide  of  antimony. 

Pentachloride  of  antimony,  Sb015,  is  obtained  by  heating  metallic  antimony  in 
a  current  of  dry  chlorine,  and  distilling  the  product  in  a  dry  retort,  rejecting  the 
first  portions  of  the  distillate,  which  contain  excess  of  chlorine.  It  is  a  yellowish, 
very  volatile  liquid,  which  emits  suffocating  vapours.  Water  first  converts  it  into 
a  crystalline  hydrate,  and  then  decomposes  it,  forming  antimonic  acid :  SbCl5  + 
5HO=Sb05-|-5HCl.  It  absorbs  ammonia  and  phosphuretted  hydrogen,  forming 
red-brown  solid  compounds.  It  absorbs  defiant  gas  as  readily  as  chlorine,  and 
forms  Dutch  liquid.  It  likewise  absorbs  hydrosulphuric  acid  gas  at  ordinary 
temperatures,  forming  a  white  crystalline  mass,  consisting  of  chlorosulphide  of 
antimony,  SbCl3S2,  exactly  analogous  to  chlorosulphide  of  phosphorus,  PC13S2. 
Pentasulphide  of  antimony,  treated  with  dry  chlorine  aided  by  heat,  forms  a  white 
pulverulent  compound,  containing  SbCl8S3,  or  Sb016.3SCl;  this  compound  is 
decomposed  at  572°  (300°  C.)  into  chlorine,  chloride  of  sulphur,  and  terchloride 
of  antimony.  Pentachloride  of"  antimony  combines  with  hydrocyanic  acid,  forming 
a  white,  crystalline,  volatile  compound,  composed  of  SbCl6.3HCy.  It  also  com- 
bines with  chloride  of  cyanogen. 

Antimoniuretted  hydrogen.  —  This  compound  is  obtained  by  dissolving  an  alloy 
of  zinc  and  antimony  in  hydrochloric  or  dilute  sulphuric  acid,  or  by  dissolving 
zinc  in  either  of  these  dilute  acids  containing  oxide  or  chloride  of  antimony, 
tartar  emetic,  &c.  The  gas,  however,  always  contains  more  or  less  free  hydrogen. 
Its  comparative  purity  may  be  tested  by  means  of  a  solution  of  nitrate  of  silver, 
Thich  absorbs  the  antirnoniuretted  hydrogen,  and  leaves  the  free  hydrogen.  An 
alloy  of  2  parts  zinc  and  1  part  antimony  yields  the  purest  gas;  an  alloy  contain- 


ESTIMATION    OF    ANTIMONY.  545 

ing  a  larger  proportion  of  antimony  gives  more  free  hydrogen  ;  and  an  alloy  of 
equal  parts  of  the  two  metals  yields  scarcely  anything  but  free  hydrogen.  As  the 
compound  has  never  been  obtained  in  a  state  of  purity,  its  composition  has  not 
been  correctly  ascertained,  but  it  is  probably  SbH3. 

Antimoniuretted  hydrogen  is  a  colourless  gas,  and  when  free  from  arsenic,  quite 
inodorous.  It  is  insoluble  in  water,  and  in  alkaline  liquids;  with  solutions  of 
silver  or  mercury  it  forms  precipitates  containing  silver  or  mercury,  together  with 
antimony.  When  burned  from  a  jet,  it  deposits,  on  a  plate  of  porcelain,  metallic 
spots,  greatly  resembling  those  of  arsenic,  but  differing  from  the  latter  in  posses- 
sing less  lustre  and  in  not  being  soluble  in  hypochlorite  of  soda.  They  may  also 
be  dissolved  in  aqua-regia  or  in  permanganate  of  potash  (p.  540),  and  the  solution 
will  give  the  characteristic  orange  precipitate  with  hydrosulphuric  acid.  A  me- 
tallic deposit  may  also  be  obtained  by  heating  a  glass  tube  through  which  the  gas 
is  passed;  and  this  deposit,  when  sublimed,  will  not  exhibit  the  characters  of 
arsenic  (p.  536). 

Alloys  of  antimony  with  potassium  or  sodium  may  be  obtained  by  igniting  me- 
tallic antimony,  or  its  oxide  or  sulphide,  with  an  organic  salt  of  potash  or  soda. 
Thus,  when  5  parts  of  crude  tartar  and  4  parts  of  antimony  are  slowly  heated  in 
a  covered  crucible  till  the  mixture  becomes  charred,  then  heated  to  whiteness  for 
an  hour,  and  left  to  cool,  a  crystalline  regulus  is  obtained  containing  12  per  cent, 
of  potassium.  This  alloy  decomposes  water  rapidly,  and  oxidizes  slowly  in  the 
air  when  in  the  compact  state,  but  becomes  heated  and  takes  fire  when  rubbed  to 
powder. 

A  mixture  of  7  parts  of  antimony  and  3  parts  of  iron,  heated  to  whiteness  in 
a  crucible  lined  with  charcoal,  forms  a  white,  very  hard,  slightly  magnetic  alloy, 
which  gives  sparks  when  filed.  It  is  always  formed  when  sulphide  of  antimony 
is  reduced  by  iron  in  excess. 

With  zinc,  antimony  forms  alloys  of  definite  crystalline  character.  A  fused 
mixture  of  the  two  metals,  containing  from  43  to  70  per  cent,  of  zinc,  deposits 
by  partial  cooling,  silver-white  rhombic  prisms,  containing  from  43  to  64  per  cent, 
of  zinc.  The  alloy  containing  exactly  43  per  cent,  of  zinc,  appears  to  be  a 
definite  compound,  stibiotrizincyl,  SbZn3.  Mixtures  containing  from  33  to  20 
per  cent,  of  zinc  deposit  rhombic  crystals  containing  from  35  to  21  per  cent,  of 
zinc.  The  alloy  containing  exactly  33  per  cent,  is  stibiobizincyl,  SbZna.  These 
alloys,  especially  SbZn3,  decompose  water  with  evolution  of  hydrogen  at  the  boil- 
ing heat,  and  very  rapidly  under  the  influence  of  acids  (J.  P.  Cooke*). 

Type-metal,  is  an  alloy  of  antimony  and  lead,  usually  containing  76  per  cent, 
of  lead,  which  corresponds  nearly  with  the  formula  Pb2Sb. 


ESTIMATION    OF    ANTIMONY,    AND    METHODS    OF    SEPARATING    IT    FROM    THE 

PRECEDING    METALS. 

Antimony  cannot  be  estimated  in  the  form  of  antimonious  or  antimonic  acid, 
because  we  can  never  be  sure  of  the  purity  of  those  bodies.  The  best  mode  of 
proceeding  is  to  precipitate  it  by  hydrosulphuric  acid,  collect  the  sulphide  of  anti- 
mony on  a  weighed  filter,  and,  after  ascertaining  the  total  quantity  of  the  precipi- 
tate, estimate  the  proportion  of  sulphur  in  it  in  the  manner  already  described  with 
reference  to  sulphide  of  arsenic  (p.  538).  Or  the  sulphide  of  antimony  may  be 
decomposed  by  heating  it  in  a  current  of  hydrogen  gas,  whereupon  hydrosulphuric 
acid  and  sulphur-vapour  escape,  and  metallic  antimony  remains  behind.  For 
this  purpose,  a  weighed  portion  of  the  sulphide  is  placed  in  a  small  porcelain  cru- 
cible having  a  hole  in  its  cover,  through  which  a  tube  passes  to  convey  the  hydro- 
gen. The  temperature  is  gradually  raised,  and  the  process  continued  till  the 

*  Sill.  Am.  J.  [2.]  xviii.  229;  xx.  222. 
35 


546  ANTIMONY. 

weight  of  the  crucible  no  longer  varies.     The  reduction  may  also  be  performed  in 
a  bulb-tube. 

When  antimonious  and  antimonic  acids  occur  together  in  solution,  the  total 
quantity  of  antimony  may  be  ascertained  by  treating  one  portion  of  the  liquid  in 
the  manner  just  described,  and  the  quantity  existing  as  antimonious  acid  may  be 
determined  in  another  portion  by  means  of  terchloride  of  gold,  2  eq.  of  precipi- 
tated gold  corresponding  to  3  eq.  of  antimonious  acid : 

2AuCl3-h  6HO  +  3Sb03  =  2Au  +  6HC1  +  3Sb05. 

The  separation  of  antimony  from  the  alkalies  and  earths,  and  from  those  metals 
which  are  not  precipitated  from  their  acid  solutions  by  hydrosulphuric  acid;  is 
effected  by  means  of  that  reagent. 

To  separate  antimony  from  cadmium,  copper,  and  lead,  the  solution,  after  being 
neutralized  with  ammonia,  is  mixed  with  sulphide  of  ammonium  containing 
excess  of  sulphur.  The  sulphide  of  antimony  then  dissolves,  the  other  sulphides 
remaining  undissolved  j  and  on  mixing  the  filtrate  with  acetic  acid  (hydrochloric 
acid  might  redissolve  a  portion  of  the  precipitate,  especially  as  the  liquid  becomes 
heated),  the  sulphide  of  antimony  is  reprecipitated,  and  may  be  treated  as  above. 

When  antimony  is  combined  with  any  of  the  preceding  metals  in  the  form  of 
an  alloy,  it  may  be  separated  by  treating  the  alloy  with  nitric  acid,  whereby  the 
other  metals  are  dissolved,  and  the  antimony  converted  into  insoluble  antimonic 
.acid.  This  method  is,  however,  not  rigidly  exact;  for  the  nitric  acid  dissolves  a 
small  portion  of  the  antimony. 

Separation  of  antimony  from  arsenic  and  fin. — The  separation  of  these  metals 
>is  attended  with  considerable  difficulty.  The  best  mode  of  effecting  it  is  to  con- 
cert them  into  arseniate,  stannate,  and  antimoniate  of  soda,  and  treat  the  mixture 
with  dilute  alcohol,  which  dissolves  the  arseniate  and  stannate  of  soda,  and  leaves 
the  antimoniate  undissolved. 

If  the  three  metals  exist  together  in  solution,  they  must  be  precipitated  as  sul- 
phides by  hydrosulphuric  acid,  and  the  precipitate  treated  by  one  of  the  following 
methods : — 

(1.)  The  precipitated  sulphides  are  fused  in  a  silver  crucible  with  a  mixture  of 
hydrate  of  soda  and  nitre  :  or,  better,  they  are  oxidized  by  heating  them  with 
strong  nitric  acid;  the  solution,  together  with  the  insoluble  stannic  and  antimonic 
acids,  mixed  with  excess  of  caustic  soda,  and  evaporated  to  a  small  bulk ;  then 
transferred  to  a  silver  crucible,  evaporated  to  dryness,  and  kept  for  some  time  in  a 
state  of  red  hot  fusion.  The  fused  mass,  consisting  of  arseniate,  stannate,  and 
antimoniate  of  soda,  is  disintegrated  by  digestion  in  warm  water;  the  contents  of 
the  crucible  transferred  to  a  beaker-glass ;  and  the  crucible  well  rinsed  out  with  a 
measured  quantity  of  water.  The  greater  part  of  the  arseniate  and  stannate  of 
soda  Alien  dissolves,  while  the  antimoniate  remains  undissolved.  But  to  effect 
complete  separation,  a  quantity  of  alcohol  of  sp.  gr.  0-833  is  added,  equal 
in  bulk  to  one-third  of  the  water  used ;  the  mixture  left  to  stand  for  24 
hours  and  frequently  stirred;  and  the  antimoniate  of  soda,twhich  has  then  com- 
pletely settled  down,  is  collected  on  a  filter  and  washed,  first,  with  a  mixture  of  1 
volume  of  the  same  alcohol  to  3  vols.  of  water,  then  with  1  vol.  alcohol  to  2  vols. 
water;  next,  with  a  mixture  of  equal  measures  of  water  and  alcohol;  and,  lastly, 
with  3  vols.  alcohol  to  1  vol.  water  (EL  Rose).* 

(2.)  The  precipitated  sulphides  of  the  three  metals  are  dissolved  in  a  mixture 
of  sulphide  of  sodium  and  caustic  soda,  and  the  liquid  mixed  with  a  solution  of 
hypochlorite  of  soda.  The  sulphides  are  thereby  oxidized  and  converted  into 
arsenic,  stannic,  and  antimonic  acids,  which  combine  with  the  soda,  and  may  be 
separated  by  treatment  with  dilute  alcohol,  and  washing,  as  in  Rose's  process. 
This  method  is  due  to  Dr.  Williamson ;  it  is  easier  of  execution  than  the  former, 

*  Handb.  d.  anal.  Chcm.  1851,  ii.  429. 


SEPARATION    OF    ANTIMONY    FROM    ARSENIC.         547 

as  the  fused  mixture  of  the  soda-salts  is  very  hard,  and  difficult  to  disintegrate  hy 
water. 

The  antimoniate  of  soda,  separated  by  either  of  these  processes,  is  digested  in 
a  mixture  of  hydrochloric  and  tartaric  acids,  which  dissolves  it  completely;  the 
antimony  then  precipitated  by  hydrosulphuric  acid;  and  its  quantity  estimated  in 
the  manner  already  described  (p.  545). 

The  filtrate  containing  the  arseniate  and  stannate  of  soda  is  supersaturated  with 
hydrochloric  acid,  which  throws  down  a  bulky  precipitate  of  arseniate  of  stannic 
oxide ;  hydrosulphuric  acid  gas  passed  through  the  liquid  till  the  white  precipi- 
tate is  completely  converted  into  a  brown  mixture  of  the  sulphides  of  tin  and 
arsenic ;  the  whole  left  to  stand  till  the  odour  of  hydrosulphuric  acid  is  no  longer 
perceptible ;  the  precipitate  collected  on  a  weighed  filter ;  and  the  filtrate  heated 
for  some  time  to  expel  the  greater  part  of  the  alcohol ;  then  mixed  with  sulphur- 
ous acid,  and  again  treated  with  hydrosulphuric  acid,  whereby  a  small  quantity  of 
sulphide  of  arsenic  is  generally  precipitated.  This  quantity  of  sulphide  of  arse- 
nic being  quite  free  from  tin,  need  not  be  added  to  the  mixed  sulphides  on  the 
filter. 

These  mixed  sulphides  are  dried  at  212°,  their  total  weight  determined,  and  a 
known  quantity  heated  in  a  stream  of  hydrosulphuric  acid  gas  in  the  manner 
described  at  page  538.  The  residual  sulphide  of  tin  is  then  converted  into  stat- 
nic  oxide,  and  the  sublimed  sulphide  of  arsenic,  together  with  the  small  quantity 
separately  precipitated,  is  converted  into  arsenic  acid  by  treatment  with  hydro- 
chloric acid  and  chlorate  of  potash,  and  the  arsenic  precipitated  as  ammonio-mag- 
nesian  arseniate  (H.  Rose). 

If  the  three  metals  are  in  the  state  of  solid  oxides,  the  mixture  may  be  dis- 
solved in  hydrochloric  acid,  with  addition  of  tartaric  acid,  and  the  metals  precipi- 
tated as  sulphides  as  before.  If  the  metals  are  mixed  in  the  form  of  an  alloy, 
they  may  be  dissolved  in  aqua-regia,  the  solution  mixed  with  tartaric  acid,  then 
diluted,  and  precipitated  in  the  same  manner. 

The  method  just  described  may,  of  course,  be  applied  to  the  separation  of  anti- 
mony from  tin  or  from  arsenic  alone.  In  these  cases,  however,  simpler  methods 
may  often  be  advantageously  adopted. 

Separation  of  antimony  from  tin.  —  When  these  two  metals  exist  together  in 
solution,  and  the  sum  of  their  weights  is  known,  the  separation  may  be  effected, 
and  the  weights  of  the  two  determined,  by  immersing  in  the  solution  a  piece  of 
pure  tin,  which  precipitates  the  antimony  in  the  form  of  a  black  powder.  To 
render  the  precipitation  complete,  a  gentle  heat  must  be  applied,  and  the  solution 
must  contain  excess  of  acid.  The  antimony  is  collected  on  a  weighed  filter,  dried 
at  a  gentle  heat,  and  weighed.  If  the  sum  of  the  weights  is  not  previously 
known,  the  metals  must  be  precipitated  together  by  zinc  from  a  known  quantity 
of  the  solution,  and  the  antimony  precipitated  by  tin  from  another  portion.  When 
the  two  metals  exist  together  in  an  alloy,  a  portion  of  the  alloy  must  be  weighed, 
then  dissolved  in  aqua-regia,  and  the  solution  mixed  with  tartaric  acid,  diluted 
with  water,  and  treated  as  above. 

Another  method  of  separation  is  to  precipitate  the  two  metals  with  zinc,  and 
treat  the  precipitate  with  strong  hydrochloric  acid  without  previously  decanting 
the  solution  of  chloride  of  zinc.  The  tin  then  dissolves,  while  the  antimony 
remains  undissolved,  the  presence  of  the  chloride  of  zinc  diminishing  its  tendency 
to  dissolve  in  the  acid.  The  tin  may  afterwards  be  precipitated  by  hydrosulphuric 
acid,  and  the  sulphide  converted  into  stannic  oxide,  by  treating  it  with  strong 
nitric  acid  (Levol).* 

Separation  of  antimony  from  arsenic.  —  When  these  two  metals  are  associated 
in  the  metallic  state,  they  may  be  completely  separated  by  heating  the  alloy  in  a 
stream  of  carbonic  acid,  the  arsenic  then  volatilizing,  and  the  antimony  remaining 

*  Ann.  Ch.  Phys.  [3.]  xiii.  125. 


548 


BISMUTH. 


Antimony  is,  however,  the  only  metal  from  which  arsenic  can  be  completely  sepa- 
rated in  this  manner*  hence,  if  the  alloy  contains  any  other  metal,  some  of  the 
arsenic  will  be  retained,  and  the  method  is  no  longer  applicable. 

When  this  is  the  case,  the  alloy  may  be  dissolved  in  aqua  regia,  or  in  hydro- 
chloric acid  to  which  chlorate  of  potash  is  gradually  added ;  the  solution  diluted 
with  water  after  addition  of  tartaric  acid ;  then  mixed  with  a  considerable  quantity 
of  chloride  of  ammonium  and  excess  of  ammonia ;  and  the  arsenic  precipitated  as 
ammonio-magnesian  arseniate  by  addition  of  sulphate  of  magnesia.  The  antimony 
may  then  be  precipitated  from  the  filtrate  by  hydrosulphuric  acid. 


SECTION  III. 

BISMUTH. 

Eq.  213,or2662-5;  Bi. 

Bismuth  is  generally  found  in  the  metallic  state,  disseminated  in  quartz-rock  ; 
but  occurs  also  as  an  oxide,  carbonate,  and  sulphide,  either  alone  or  associated 

with  other  metals ;  also  in  combina- 

FIG.  196.  tion  with  tellurium.   Native  bismuth 

is,  however,  the  only  mineral  which 
occurs  in  sufficient  abundance  for 
the  economical  extraction  of  the 
metal.  The  process  of  extraction 
as  performed  in  Saxony,  whence  all 
the  bismuth  of  commerce  is  obtained, 
is  very  simple,  the  mineral  being 
merely  heated  in  close  vessels,  so  as 
to  melt  the  bismuth,  and  thereby 
separate  it  from  the  gangue  or  ac- 
companying rock.  The  fusion  is 
performed  in  iron  tubes,  laid  in  an 
inclined  position,  in  a  furnace.  (Fig.  196.)  The  ore  is  introduced  at  the  upper 
end,  o?,  which  is  then  plugged.  The  other  end,  b,  is  closed  with  an  iron  plate 
having  an  aperture,  o,  through  which  the  melted  metal  runs  into  earthen  pots,  a, 
heated  by  a  few  coals  placed  in  the  space,  A"  below,  so  as  to  keep  the  metal  in 
the  melted  state.  It  is  then  ladled  out  and  run  into  moulds.  The  crude  metal 
thus  obtained  is  afterwards  fused  with  1-1  Oth  of  its  weight  of  nitre,  to  free  it  from 
sulphur,  arsenic,  and  certain  foreign  metals. 

Commercial  bismuth,  however,  is  still  somewhat  impure.  To  free  it  completely 
from  other  metals,  it  is  dissolved  in  nitric  acid,  the  clear  liquid  decanted  and 
mixed  with  water,  which  throws  down  a  subnitrate  of  bismuth ;  and  this  compound 
is  reduced  at  a  moderate  heat,  either  with  black  flux,  or  in  a  crucible  lined  with 
charcoal. 

Bismuth  crystallizes  in  octohedrons  and  cubes.  It  may  be  obtained  in  very 
beautiful  crystals,  by  fusing  several  pounds  of  the  ordinary  metal  in  a  crucible  or 
iron  ladle,  adding  nitre  from  time  to  time,  and  stirring,  till  a  portion  of  the  fused 
metal,  taken  out  and  exposed  to  the  air,  no  longer  assumes  an  indigo  colour, 
changing  to  violet  or  rose  and  disappearing  on  cooling,  but  a  fine  green  or  golden 
tint,  which  it  retains  on  cooling;  then  leaving  the  metal  to  cool  slowly,  on  a  hot 
sand-bath,  for  instance,  till  a  crust  forms  on  the  surface ;  piercing  this  crust  with 
a  hot  coal;  and  pouring  out  the  portion  which  still  remains  liquid.  On  subse- 
quently detaching  the  crust,  the  inner  surface  of  the  metal  is  found  to  be  covered 
vrith  beautiful  fretted  cubes,  like  those  of  common  salt. 

Bismuth  is  moderately  hard,  slightly  sonorous,  and  brittle,  but  may  be  some- 


OXIDES    OF    BISMUTH.  549 

what  extended  by  careful  hammering.  Its  colour  is  reddish  tin-white,  with 
moderate  lustre.  The  specific  gravity  of  pure  bismuth  is  9-6542  (Karsten),  9-799 
(Marchand  and  Scherer) ;  of  commercial  bismuth,  9'822  (Brisson),  9-833  (Hera- 
path),  9-861  (Bergman).  Strong  pressure  rather  diminishes  than  increases  the 
density.  Bismuth  melts  at  480°  (Crichton) ;  at  507°  (Rudberg);  at  509° 
(Hermann);  and  expands  in  solidifying.  It  boils  at  an  incipient  white  heat,  and 
if  the  air  be  excluded,  sublimes  in  laminae. 

Bismuth  forms  four  compounds  with  oxygen,  viz.,  the  bioxide,  Bi02j  the 
teroxide,  Bi03;  the  quadroxide,  Bi04;  and  bismuthic  acid,  Bi05. 

Bioxide  or  suboxide  of  bismuth. — Bismuth  oxidizes  slowly  when  exposed  to  the 
air  at  ordinary  temperatures,  becoming  covered  with  a  brownish  film  of  suboxide. 
When  heated  in  the  air  till  it  fuses,  it  oxidates  more  rapidly,  becoming  covered 
with  the  same  brown  oxide,  which  is  renewed  as  often  as  it  is  removed,  till  the 
whole  of  the  metal  is  oxidized.  This  suboxide  is  also  formed  when  subnitrate  of 
bismuth  is  heated  with  protochloride  of  tin.  By  pouring  a  hydrochloric  acid 
solution  of  equivalent  quantities  of  teroxide  of  bismuth  and  protochloride  of  tin 
into  excess  of  moderately  strong  potash,  a  black-brown  precipitate  is  formed, 
consisting  of  a  lower  oxide  of  bismuth  combined  with  stannic  acid ;  and  on  treat- 
ing this  compound  with  stronger  potash,  the  stannic  acid  dissolves  and  an  oxide 
of  bismuth  remains,  which,  when  dried  in  vacuo,  or  at  100°,  out  of  contact  with 
the  air,  forms  a  blackish-grey  crystalline  powder,  consisting  of  Bi02,  retaining, 
however,  a  small  quantity  of  water.  It  shows  but  little  disposition  to  absorb 
oxygen  at  ordinary  temperatures,  but  when  heated,  it  is  instantly  converted,  with 
a  glimmering  light,  into  teroxide.  Acids  decompose  it  into  metallic  bismuth  and 
teroxide.  When  ignited  in  an  atmosphere  of  carbonic  acid,  it  becomes  perfectly 
anhydrous,  and  in  that  state  does  not  undergo  any  perceptible  alteration  by  ex- 
posure to  the  air  at  ordinary  temperatures,  and  oxidizes  but  slowly  even  at  a  red 
heat  (R.  Schneider).* 

Teroxide  of  Bismuth,  Bi03;  237  or  3662-5.— Bismuth  heated  in  the  air  till  it 
boils,  takes  fire  and  burns  with  a  faint  bluish  white  flame,  forming  teroxide  of 
bismuth,  the  vapour  of  which  condenses  on  the  surface  of  cold  bodies  in  the  form 
of  flowers  of  bismuth.  The  same  oxide  is  obtained  in  solution  by  acting  on  bis- 
muth with  nitric  acid,  the  metal  being  then  dissolved  with  evolution  of  nitrous 
fumes.  Strong  sulphuric  acid  likewise  dissolves  it  at  a  boiling  heat,  with  evolu- 
tion of  sulphurous  acid.  Hydrochloric  acid  acts  but  slightly  on  it,  even  with  the 
aid  of  heat.  When  the  solution  of  the  nitrate  is  mixed  with  water,  a  white  pre- 
cipitate of  subnitrate  is  produced;  and  this,  when  gently  ignited,  yields  the 
teroxide  in  the  form  of  a  lemon-yellow  powder.  By  fusing  the  hydrated  oxide 
with  hydrate  of  potash,  or  boiling  it  with  potash-ley,  the  anhydrous  oxide  may  be 
obtained  in  yellow  shining  needles.  Teroxide  of  bismuth  fuses  at  a  strong  red 
heat,  and  solidifies  in  a  crystalline  mass  on  cooling.  It  is  easily  reduced  to  the 
metallic  state  by  potassium  or  sodium  at  a  gentle  heat,  and  by  charcoal  before  the 
blowpipe. 

Teroxide  of  bismuth  combines  with  acids,  forming  salts  which  are  very  heavy, 
colourless,  unless  the  acid  itself  is  coloured,  and  exert  a  poisonous  action.  Heated 
on  charcoal  with  carbonate  of  soda,  they  yield  a  button  of  metal.  Zinc,  tin,  cad- 
mium, iron,  and  lead,  precipitate  the  metal  from  the  solutions  of  these  salts. 
Water  decomposes  most  bismuth-salts  —  provided  they  do  not  contain  too  large  an 
excess  of  acid,  throwing  down  a  sparingly  soluble  basic  salt,  while  the  acid 
remains  in  solution,  together  with  a  small  quantity  of  oxide.  Hydrosulphuric 
acid  produces  a  brown-black  precipitate  of  tersulphide  of  bismuth,  insoluble  in 
sulphide  of  ammonium.  Caustic  alkalies,  at  ordinary  temperatures,  throw  down 
the  white  hydrated  oxide,  but  at  a  boiling  heat,  especially  if  they  are  concen- 
trated, they  produce  a  yellow  precipitate  of  the  anhydrous  oxide :  these  precipi- 

*  Pogg.  Ann.  Ixxxviii.  45. 


550  BISMUTH. 

tates  are  insoluble  in  excess  of  the  alkali.  Alkaline  carbonates  throw  down  a 
white  precipitate  of  carbonate  of  bismuth,  slightly  soluble  in  excess,  but  precipi- 
tated from  the  solution  by  a  caustic  alkali.  Chroma te  or  bichromate  of  potash 
throws  down  a  yellow  chromate  of  bismuth,  insoluble  in  caustic  potash,  whereby  it 
is  distinguished  from  chromate  of  lead.  Sulphuric  acid  produces  no  precipitate. 

Quadroxide  of  bismuth,  Bi04,  —  When  a  bismuth-salt  contains  free  chlorine, 
caustic  potash  produces  in  it,  not  a  white  but  a  yellow  precipitate,  which  consists 
of  the  hydrate  of  a  higher  oxide,  but  cannot  be  obtained  free  from  chlorine.  When 
this  yellow  hydrate  is  boiled  with  an  alkaline  chlorite  having  a  strong  alkaline 
reaction,  it  turns  brown,  like  peroxide  of  lead,  and  is  converted  into  the  quadroxide 
of  bismuth  (Arppe).  This  oxide  is  completely  dissolved  by  boiling  nitric  acid ; 
any  yellow  or  green  residue  that  may  be  left,  consists  of  bismuth ic  acid.  It  is 
perhaps  a  compound  of  teroxide  of  bismuth  with  bismuthic  acid;  Bi03.Bi05. 

Bismuthic  acid,  Bi05.  —  Prepared  by  passing  chlorine  through  a  strong  solu- 
tion of  potash  in  which  finely  divided  teroxide  of  bismuth  is  suspended ;  also,  by 
heating  a  mixture  of  potash  and  teroxide  of  bismuth  for  a  long  time  in  contact 
with  the  air,  —  or  better,  by  calcining  a  mixture  of  teroxide  of  bismuth,  caustic 
potash,  and  chlorate  of  potash.  Bismuthic  acid,  prepared  by  any  of  these  methods, 
is  always  more  or  less  mixed  with  teroxide  of  bismuth,  which,  however,  may  be 
dissolved  out  of  weak  nitric  acid.  Bismuthic  acid  is  a  light  red  powder,  which, 
at  a  temperature  a  little  above  212°,  gives  off  part  of  its  oxygen,  and  is  converted 
into  quadroxide  of  bismuth.  Strong  acids  also  decompose  it,  reducing  it  to  the 
state  of  teroxide  of  bismuth,  which  then  unites  with  the  acid.  Bismuthic  acid 
combines  with  potash,  and  forms  a  few  double  salts,  whose  bases  are  the  alkali  and 
teroxide  of  bismuth. 

Bisulphide  of  bismuth,  BiS2,  separates  in  crystals  from  a  fused  mixture  of 
metallic  bismuth  and  the  tersulphide,  and  may  also  be  obtained  by  fusing  10  parts 
of  bismuth  with  3  parts  of  sulphur,  melting  the  resulting  mixture  three  times  with 
fresh  sulphur,  and  cooling  quickly.  Hydrochloric  acid  decomposes  this  com- 
pound, yielding  metallic  bismuth  and  the  terchloride.  Hence,  and  from  the  fact 
that  its  crystalline  form  is  the  same  as  that  of  the  tersulphide,  and  that  by  fusing 
the  tersulphide  with  metallic  bismuth,  in  certain  proportions,  crystals  may  be 
obtained  of  the  same  form  but  containing  less  sulphur,  Schneider  concludes  that 
the  supposed  bisulphide  is  merely  a  mixture  of  the  tersulphide  with  metallic 
bismuth. 

Tersulphide  of  bismuth,  BiS3,  occurs  native  as  bismuth-glance,  and  may  be 
formed  artificially  by  fusing  bismuth  with  sulphur,  and  by  decomposing  bismuth- 
salts  with  hydrosulphuric  acid.  The  native  variety  forms  right  rhombic  prisms, 
isomorphous  with  sulphide  of  antimony :  its  colour  is  light  lead-grey ;  specific 
gravity  from  64  to  6-5.  Tersulphide  of  bismuth  is  decomposed  by  heat;  the 
native  sulphide,  heated  in  a  tube,  yields  sublimed  sulphur;  and  the  artificial 
sulphide,  when  fused  and  left  to  cool,  yields  globules  of  metallic  bismuth  as  it 
solidifies. 

Selenide  of  bismuth,  BiSe3,  is  obtained  by  melting  together  1  eq.  of  bismuth 
and  3  eq.  of  selenium,  and  re-melting  the  product  with  fresh  selenium  out  of  con- 
tact with  the  air.  On  a  recently  fractured  surface,  it  exhibits  a  steel-grey  colour, 
metallic  lustre,  and  a  distinct  crystalline  laminated  texture.  Its  density  is  6-82  ; 
hardness  equal  to  that  of  galena;  it  may  be  readily  pulverized.  It  is  scarcely 
attacked  by  hydrochloric  acid,  but  nitric  acid  and  aqua  regia  decompose  it  readily 
(Schneider). 

Bichloride  of  bismuth,  BiCl2,  is  formed  by  the  action  of  dry  hydrogen  on  the 
terchloride  of  bismuth  and  ammonium,  2NH4Cl.BiCl3,  at  about  570°,  or  by  heat- 
ing 1  part  of  pulverized  bismuth  with  2  parts  of  subchloride  of  mercury  in  a  sealed 
tube,  at  about  460°,  and  purifying  the  product  by  repeated  fusion  in  sealed  tubes. 
It  is  a  black  hygroscopic  mass,  which,  by  heating  in  the  air,  and  by  the  action  of 
acids,  is  resolved  into  metallic  bismuth  and  the  terchloride. 


SALTS    OF    BISMUTH.  551 

Tercliloride  of  bismuth,  BiCl3.  —  Pulverized  bismuth  thrown  into  chlorine  gas 
takes  fire  and  burns  with  a  pale  blue  light,  forming  the  terchloride.  This  com- 
pound may  also  be  obtained  by  heating  1  part  of  bismuth  with  2  parts  of  proto- 
chloride  of  mercury,  or  by  evaporating  to  dryness  the  solution  of  teroxide  of  bis- 
muth in  hydrochloric  acid,  and  distilling  the  residue  out  of  contact  with  the  air. 
It  is  a  white  opaque  solid,  with  a  slight  tinge  of  brown  or  grey,  and  a  granular 
fracture  ;  melts  very  readily,  forming  an  oily  liquid.  The  hydrated  terclilori.de  is 
obtained  in  crystals  by  dissolving  the  teroxide  in  hydrochloric  acid,  and  evapora- 
ting. The  anhydrous  chloride,  the  crystals,  and  the  solution  are  decomposed  by 
water,  yielding  oxy chloride  of  bismuth,  BiCl3.2Bi03,  in  the  form  of  an  insoluble 
white  powder,  commonly  known  as  pearl-white,  —  and  hydrochloric  acid  holding  a 
small  quantity  of  bismuth  in  solution.  A  sulphochloride,  of  analogous  composi- 
tion, Bi013.2BiS3,  is  obtained  by  heating  chloride  of  bismuth  and  ammonium  with 
sulphur  or  tersulphide  of  bismuth,  or  by  passing  hydrosulphuric  acid  gas  over  the 
same  compound,  heated  to  a  temperature  between  485°  and  572°,  and  afterwards 
heating  the  product  to  its  melting  point  in  the  same  gas :  — 

3BiCl3  +  6HS  =  BiCl3.2BiS3  +  6HC1. 

The  product  of  either  of  these  operations,  after  being  washed,  first  with  water  con- 
taining so  much  hydrochloric  acid  as  not  to  give  a  precipitate  with  the  terchloride, 
then  with  water  slightly  acidulated,  and  lastly  with  pure  water,  forms  small,  dark 
grey,  crystalline  needles,  which,  when  heated  in  the  air,  give  off,  first,  chloride  of 
bismuth,  then  sulphurous  acid,  and  leave  a  mixture  of  oxychloride  and  basic  sul- 
phate of  bismuth  (Schneider).  A  seleniochloride,  BiCl3.2BiSe  ,  is  obtained  by 
adding  terselenide  of  bismuth  to  fused  chloride  of  bismuth  and  ammonium.  It 
forms  small  needle-shaped  crystals,  having  a  dark  steel-grey  colour  and  metallic 
lustre  (Schneider). 

Terchloride  of  bismuth  and  ammonium. — A  solution  of  1  eq.  of  terchloride  of 
bismuth  and  2  eq.  of  sal-ammoniac,  yields,  by  evaporation,  double  six-sided  pyra- 
mids containing  2NH4Cl.BiCl3,  isomorphous  with  the  corresponding  terchloride  of 
antimony  and  ammonium  (Jacquelain).  A  solution  of  1  eq.  terchloride  of  bis- 
muth and  6  eq.  sal-ammoniac  yields  rhombic  crystals,  containing  8NH4Cl.BiCl3 
(Arppe). 

Bismuth  dissolves  in  a  boiling  solution  of  protochloride  of  copper,  the  liquid 
being  decolorized,  and  appearing  to  contain  the  compound,  3Cu2Cl .  BiCl3.  Bis- 
muth dissolves  in  a  similar  manner  in  other  cupric  salts  (Schneider). 

Teriodide  of  bismuth,  BiT3  —  Obtained  as  a  crystalline  sublimate  by  heating 
1  eq.  (32  parts)  of  tersulphide  of  bismuth  with  3  eq.  (475  parts)  of  iodine. 
Large,  thin,  crystalline  laminae,  having  the  form  of  regular  six-sided  prisms,  of  a 
blackish  grey  colour,  with  a  tinge  of  brown  and  a  strong  lustre.  The  compound, 
heated  in  the  air,  volatilizes  for  the  most  part,  leaving  a  small  quantity  of  basic 
oxide  of  bismuth  of  a  red-brown  colour.  Boiling  water  converts  it  into  the  same 
compound.  Aqueous  potash  decomposes  it,  forming  iodate  of  bismuth,  Bi03.  3I03: 
the  same  change  is  more  slowly  produced  by  alkaline  carbonates.  Alkaline  sul- 
phides decompose  it,  forming  tersulphide  of  bismuth.  Hydrochloric  acid  dissolves 
it  without  decomposition ;  nitric  acid,  with  separation  of  iodine. 

Sulphates  of  bismuth. — When  bismuth  is  heated  with  strong  sulphuric  acid, 
sulphurous  acid  is  evolved,  and  the  metal  is  converted  into  a  white  insoluble 
powder,  consisting  of  tersufphate  of  bismuth,  Bi03 .  3S03,  which  is  decomposed 
by  water,  yielding  a  very  acid  salt  which  dissolves,  and  a  monobasic  sulphate, 
Bi03 .  S03  -f  HO,  which  remains.  There  is  also  a  bisulphite  of  bismuth,  which 
is  obtained  in  small  delicate  needles  when  an  acid  solution  of  nitrate  of  bismuth  is 
mixed  with  sulphuric  acid  (Heintz). 

Carbonate  of  bismufh,  Bio3  .  C02,  is  obtained  by  adding  nitrate  of  bismuth  to 
the  solution  of  an  alkaline  carbonate  :  this  salt  is  used  in  medicine. 

Nitrates   of  bismuth.  —  The  neutral   or    tertiitrate,   Bi03 .  3N06  +  10HO,  is 


552  BISMUTH. 

obtained  by  dissolving  bismuth  in  hot  nitric  acid,  evaporating  the  solution,  and 
leaving  it  to  cool.  The  salt  then  separates  in  transparent  oblique  prisms  of  six  or 
eight  sides,  and  terminated  with  several  faces.  At  212°  they  separate  into  a  solid 
and  a  liquid  portion,  the  latter  solidifying  as  it  cools.  At  302°,  they  are  reduced 
to  the  mononitrate,  Bi03 .  N05  +  HO ;  which,  when  further  heated  to  500°,  gives 
up  all  its  acid  and  water,  and  leaves  oxide  of  bismuth. 

Subnitrates  of  bismuth.  —  a.  Ternitrate  of  bismuth  dissolves  without  decompo- 
sition in  a  small  quantity  of  water,  especially  if  a  few  drops  of  nitric  acid  are 
added.  But  a  larger  quantity  of  water  decomposes  it,  forming  a  white  precipitate 
of  a  subsalt,  commonly  called  mayistery  of  bismuth.  This  substance  is  generally 
regarded  as  a  mononitrate  containing  one  atom  of  water,  Bi03 .  N05  4-  HO ;  but, 
according  to  Becker,*  the  basic  nitrate  obtained  directly  by  treating  the  ternitrate 
with  cold  water,  consists  of  Bi03 .  N05  -f  2  HO.  This  precipitate,  when  recently 
formed,  dissolves  somewhat  freely  in  water,  especially  if  the  water  contains  nitric 
acid.  Hence,  if,  after  the  precipitation  of  the  basic  salt,  the  supernatant  liquid 
be  mixed  with  a  large  quantity  of  water,  the  precipitate  is  completely  redissolved ; 
but  after  a  while,  a  basic  salt  separates,  containing  5Bi03 .  4N05  4-  9Aq ;  this, 
according  to  Becker,  is  the  true  magistery  of  bismuth,  inasmuch  as,  in  the  usual 
mode  of  preparing  that  substance,  the  same  change  takes  place  in  washing  the 
precipitate.  Boiling  water  decomposes  this  salt,  extracting  all  the  nitric  acid, 
excepting  about  1  per  cent. — b.  A  salt  containing  5Bi03 .  4N05  +  12HO,  is 
obtained  by  evaporating  a  solution  of  the  ternitrate  at  a  strong  heat.  When  the 
precipitate  first  obtained  by  the  action  of  cold  water  on  a  solution  of  the  ternitrate 
is  heated  in  contact  with  a  free  acid,  or  when  the  same  acid  solution  is  poured  into 
hot  water,  a  white,  very  loose  powder  is  precipitated,  containing  6Bi03.  5N05  + 
OHO.  This  salt  is  decomposed  by  water  more  readily  than  the  preceding.  If  it 
be  washed  with  water  as  long  as  the  filtrate  continues  to  exhibit  a  strong  acid 
reaction,  a  crystalline  residue  is  left  on  the  filter,  containing  4Bi03 .  3N05 .  9Aq. 
Duflos  obtained  a  magistery  of  bismuth  having  the  same  composition,  by  treating 
the  crystals  of  the  neutral  nitrate  with  24  times  their  weight  of  water.  Lastly, 
if  the  mononitrate,  completely  freed  from  the  adhering  acid  liquid,  be  treated  with 
water  likewise  free  from  acid,  it  dissolves  completely ;  but  the  liquid  after  a  while 
becomes  milky,  and  after  long  standing  deposits  a  white  amorphous  powder,  con- 
taining 5Bi03  .  3N05  4-  8HO.  This  salt  may  be  formed,  in  addition  to  the  true 
magistery  of  bismuth,  if,  in  the  preparation  of  that  substance,  too  large  a  quantity 
of  water  be  used,  and  the  greater  part  of  the  acid  liquid  removed  (Becker). 
Magistery  of  bismuth  is  used  as  a  cosmetic,  but  has  the  serious  disadvantage  of 
being  blackened  by  hydrosulphuric  acid. 

Bichromate  of  bismuth,  Bi03  .  20r03.  —  When  a  solution  of  ternitrate  of  bis- 
muth, containing  as  little  free  acid  as  possible,  is  poured  into  a  moderately  con- 
centrated solution  of  bichromate  of  potash,  bichromate  of  bismuth  is  obtained  in 
the  form  of  a  yellow  flocculent  precipitate,  which  becomes  dense  and  crystalline 
after  a  while,  or  immediately  if  heated.  It  may  be  dried  without  decomposition 
between  212°  and  257°,  but  becomes  blackish-green  at  a  red  heat.  It  contains 
69-48  per  cent,  of  teroxide  of  bismuth  (J.  Lowe). 

The  alloys  of  bismuth  are  remarkable  for  their  fusibility.  The  amalgam  of  this 
metal  is  liquid.  An  alloy  of  8  parts  bismuth,  5  lead,  and  3  tin,  melts  at  202° ; 
another  mixture  of  2  bismuth,  1  lead,  and  1  tin,  at  200-75°  :  these  mixtures  are 
known  by  the  name  of  fusible  metal.  Bismuth  is  also  added  to  the  alloy  of  tin 
and  lead  used  for  casting  stereotype  plates.  Besides  increased  fusibility,  bismuth 
communicates  to  this  alloy  the  property  of  expanding  on  becoming  solid,  by  which 
it  is  rendered  capable  of  taking  an  accurate  impression. 

*  Arcliiv.  Pharm.  lv.,  31  and  129. 


URANIUM.  553 


ESTIMATION    OF    BISMUTH,    AND    METHODS     OF    SEPARATING    IT    FROM    THE 

PRECEDING    METALS. 

The  best  reagent  for  precipitating  bismuth  from  its  solutions  is  carbonate  of 
ammonia ;  which,  when  added  in  excess,  throws  down  the  bismuth  completely : 
the  liquid  must,  however,  be  left  to  stand  for  some  hours  in  a  warm  place,  other- 
wise a  considerable  quantity  of  the  bismuth  will  remain  in  solution.  The  precipi- 
tate, after  being  washed  and  dried,  must  be  separated  from  the  filter  as  completely 
as  possible,  the  filter  separately  burned,  and  the  precipitate  ignited  in  a  porcelain 
crucible  :  a  platinum  crucible  would  be  attacked  by  it :  after  ignition,  it  consists 
of  teroxide  of  bismuth  containing  89-66  per  cent,  of  the  metal. 

If  the  solution  contains  hydrochloric  acid,  the  bismuth  cannot  be  estimated  by 
precipitation  with  carbonate  of  ammonia,  or  any  other  alkali,  because  the  precipi- 
tate so  produced  would  contain  oxychloride  of  bismuth  (p.  555).  In  this  case, 
therefore,  the  bismuth  must  be  precipitated  by  hydrosulphuric  acid ;  the  sulphide 
of  bismuth  oxidized  and  dissolved  by  nitric  acid ;  and  the  diluted  solution  treated 
with  carbonate  of  ammonia,  as  above. 

Bismuth  is  separated  from  the  alkalies  and  earths,  and  from  iron,  cobalt,  nickel, 
zinc,  and  chromium,  by  hydrosulphuric  acid  ;  from  tin,  arsenic,  and  antimony,  by 
sulphide  of  ammonium;  from  lead,  by  sulphuric  acid;  and  from  copper  and 
cadmium,  by  ammonia.  The  separation  of  bismuth  from  cadmium  may  also  be 
effected  by  cyanide  of  potassium,  which  dissolves  the  latter  as  cyanide  of  cadmium 
and  potassium,  and  precipitates  the  bismuth.  The  precipitated  bismuth,  however, 
always  contains  potash,  and  must  therefore  be  dissolved  in  nitric  acid  and  pre- 
cipitated by  carbonate  of  ammonia.  These  two  metals  may  also  be  separated  by 
means  of  bichromate  of  potash,  which  throws  down  the  bismuth  as  Bi03  .  2Cr03, 
and  retains  the  cadmium  in  solution. 


OEDER  VII. 


METALS  NOT  INCLUDED  IN  THE  FOREGOING  CLASSES,  WHOSE  OXIDES  ARE  NOT 
REDUCED  BY  HEAT  ALONE. 

SECTION    I. 
URANIUM. 

^.60  or  750;  U. 

THIS  metal  is  obtained  from  pitchblende,  a  mineral  containing  from  40  to  95 
per  cent,  of  uranoso-uranic  oxide,  U304,  associated  with  sulphur,  arsenic,  lead, 
iron,  and  several  other  metals.  The  mineral  is  finely  pounded ;  freed  by  elutria- 
tion  from  the  finer  earthy  impurities;  roasted  for  a  short  time,  to  remove  part  of 
the  sulphur  and  arsenic ;  then  dissolved  in  nitric  acid,  and  the  solution  evaporated 
to  dry  ness.  The  residue  is  exhausted  with  water;  the  solution  filtered  from  the 
brick-red  residue  of  ferric  oxide,  ferric  arseniate,  and  lead-sulphate;  the  greenish 
yellow  filtrate  slightly  concentrated  by  evaporation,  and  left  to  cool,  whereupon  it 
deposits  crystals;  and  the  resulting  radiated  mass  of  crystallized  uranic  nitrate 
drained  on  a  funnel,  and  then  washed  with  a  small  quantity  of  cold  water.  As 
the  water  dissolves  a  portion  of  the  crystals,  it  is  used  in  a  subsequent  operation 


554  URANIUM. 

to  redissolve  the  residue  obtained  by  evaporating  the  solution  of  pitchblende  in 
nitric  acid.  The  uranic  nitrate,  after  being  dried  in  the  air,  is  introduced  into  a 
wide-mouthed  bottle  containing  ether,  in  which  it  immediately  dissolves;  the 
yellow  solution  is  left  to  evaporate  in  the  air ;  and  the  resulting  crystals  are  puri- 
fied by  solution  in  hot  water  and  recrystallization.  The  mixed  mother-liquids, 
after  dilution  with  water,  are  treated  with  hydrosulphuric  acid  to  precipitate  arse- 
nic, lead,  and  copper,  and  the  filtrate  is  freed  from  oxide  of  iron  by  evaporating 
to  dryness  and  digesting  the  residue  in  water.  The  solution  thus  obtained  yields 
a  fresh  crop  of  crystals  of  uranic  nitrate.  This  salt  is  converted  by  ignition  into 
uranoso-uranic  oxide,  U304,  and  from  this  the  protoxide  is  obtained  by  ignition 
with  reducing  agents  (Peligot). 

Metallic  uranium  is  obtained  by  decomposing  the  protochloride  with  potassium 
or  sodium.  If  the  mixture  be  heated  in  a  platinum  crucible  over  a  spirit-lamp, 
and  the  soluble  alkaline  chloride  washed  out  by  water,  the  uranium  is  obtained  in 
the  form  of  a  black  powder,  or  sometimes  aggregated  on  the  sides  of  the  crucible 
in  small  plates,  having  a  silvery  lustre  and  a  certain  degree  of  malleability.  But, 
by  introducing  into  a  porcelain  crucible,  first,  a  layer  of  sodium,  then  chloride  of 
potassium,  and  then  a  mixture  of  chloride  of  potassium  and  protochloride  of  ura- 
nium (the  use  of  the  chloride  of  potassium  being  to  moderate  the  action,  which  is 
otherwise  very  violent),  placing  the  porcelain  crucible  within  a  closed  earthen 
crucible  lined  with  charcoal,  and  heating  it,  first  moderately,  till  the  reduction 
takes  place,  and  then  strongly  in  a  blast-furnace  for  15  or  20  minutes,  the  metal 
is  obtained  in  fused  globules  (Peligot). 

Uranium,  in  its  compact  state,  is  somewhat  malleable  and  hard,  but  is  scratched 
by  steel.  Its  specific  gravity  is  18-4;  its  colour  is  like  that  of  nickel  or  iron. 
When  exposed  to  the  air,  it  soon  tarnishes  and  assumes  a  yellowish  colour.  At  a 
red  heat  it  oxidizes  with  vivid  incandescence,  and  becomes  covered  with  a  bulky 
layer  of  black  oxide,  which  protects  the  interior  from  oxidation.  In  the  pulve- 
rulent state,  it  takes  fire  at  about  402°,  burning  with  great  splendour,  and  forming 
a  dark-green  oxide.  It  is  permanent  in  the  air  at  ordinary  temperatures,  and 
does  not  decompose  cold  water.  It  dissolves  with  evolution  of  hydrogen  in  dilute 
acids,  forming  green  solutions.  It  combines  directly  with  chlorine,  giving  out 
great  light  and  heat,  and  forming  a  green  volatile  chloride.  It  unites  directly 
with  sulphur  at  a  slightly  elevated  temperature  (Peligot). 

Uranium  forms  four  compounds  with  oxygen,  viz.,  the  protoxide,  UO  ;  the  ses- 
quioxide,  U203;  and  two  intermediate  oxides,  U405,  and,  U304,  which  may  be  re- 
garded as  compounds  of  the  other  two,  viz.,  2UO.U203  and  UO.U203. 

Protoxide  of  uranium  ;  Uranous  oxide,  UO,  68,  or  850.  —  This  oxide  is  ob- 
tained by  exposing  uranoso-uranic  oxide,  mixed  with  charcoal  powder,  bullock's 
blood,  or  oil,  to  the  strongest  heat  of  a  blast-furnace ;  by  heating  the  same  oxide 
to  redness  in  a  current  of  dry  hydrogen ;  by  igniting  uranic  oxalate  out  of  con- 
tact of  air,  or  better,  iu  a  current  of  hydrogen ;  or  by  igniting  the  chloride  of 
uranyl  and  potassium  (p.  556),  either  alone  or  in  a  current  of  hydrogen.  Prot- 
oxide of  uranium  has  sometimes  the  form  of  an  earthy  powder  of  a  grey  or  brown 
colour  j  sometimes  of  crystalline  scales  having  the  metallic  lustre.  It  was  for  a 
long  time  regarded  as  metallic  uranium,*  titf  Peligot  f  pointed  out  its  true  nature, 
and  obtained  the  real  metal  in  the  manner  above  mentioned. 

Uranous  oxide,  after  ignition,  is  insoluble  in  boiling  dilute  hydrochloric  or  sul- 
phuric acid,  but  dissolves  in  strong  sulphuric  acid.  The  hydrated  oxide  dissolves 
readily  in  acids.  Solutions  of  uranous  salts  are  green,  and,  when  treated  with 
alkalies  or  alkaline  carbonates,  or  with  carbonate  of  lime,  yield  a  reddish-brown 
gelatinous  hydrate  of  uranous  oxide,  which  dissolves  in  alkaline  carbonates,  espe- 
cially in  carbonate  of 'ammonia,  forming  a  green  solution.  Alkaline  hydrosulphates 

*  See  the  first  edition  of  this  work,  page  643. 
f  Ann.  Ch.  Phys.  [3],  v.  5 ;  and  xii.  258. 


URANIC    SALTS.  555 

yield  a  LTar-k  precipitate  of  uranous  sulphide.  Uranous  salts  are  converted  into 
uram'c  suits  by  exposure  to  the  air,  by  the  action  of  nitric  acid,  and  by  gold  and 
silver  salts;  the  action  in  the  last  case  being  accompanied  by  precipitation  of  me- 
tallic gold  or  silver. 

Pro/octiloi-ide  of  uranium  ;  Uranous  chloride,  UC1,  is  obtained  by  burning 
uranium  in  chlorine  gas,  or  by  passing  that  gas  over  an  intimate  mixture  of  char- 
eual  and  either  of  the  oxides  of  uranium,  strongly  heated  in  a  tube  of  very  re- 
fractory glass.  It  crystallizes  in  dark-green  regular  octohedrons,  which  have  a 
metallic  lustre,  and,  when  heated  to  redness,  volatilize  in  red  vapours  and  form  a 
sublimate.  It  fumes  strongly  on  exposure  to  the  air,  and  dissolves  very  readily  in 
water,  forming  a  green  solution. 

Uranous  sulphate,  UO.S03,  is  found  native  as  uranium-vitriol,  and  may  be 
formed  artificially  by  dissolving  uranoso-uranic  oxide  in  boiling  oil  of  vitriol ;  or 
hyd rated  uranous  oxide  in  dilute  sulphuric  acid ;  or  by  decomposing  a  concen- 
trated solution  of  uranous  chloride  with  sulphuric  acid.  Crystallizes  with  two 
and  with  four  atoms  of  water.  A  bibasic  uranous  sulphate  is  obtained  by  treating 
the  normal  salt  with  a  large  quantity  of  water;  by  exposing  the  alcoholic  solution 
of  that  salt  to  the  sun's  rays ;  by  careful  addition  of  ammonia  to  its  aqueous  solu- 
tion ;  and  by  boiling  that  solution  with  green  uranoso-uranic  oxide.  It  forms  a 
light-green  powder  having  a  silky  lustre. 

Uranoso-uranic  oxide,  U304,  or  UO.U203. — This  oxide  forms  the  principal  con- 
stituent of  pitchblende.  It  is  obtained  artificially  by  burning  the  metal  or  the 
protoxide  in  the  air ;  by  heating  the  protoxide  to  redness  in  an  atmosphere  of 
aqueous  vapour ;  and  by  gentle  ignition  of  uranic  oxide  or  uranic  nitrate.  It  is 
a  dark-green  powder  which  dissolves  in  acids,  forming  green  solutions,  exhibiting 
characters  intermediate  between  those  of  uranous  and  uranic  salts,  and  probably 
consisting  of  mere  mixtures  of  the  two. 

Another  intermediate  oxide,  U405,  or  2UO.U203,  is  said  to  be  formed  by 
strongly  igniting  the  last  oxide  or  the  sesquioxide.  It  is  black,  and  dissolves  in 
acids,  like  the  last;  but  it  is  probably  a  mere  mixture  of  U304,  with  the  prot- 
oxide. 

Sesquioxide  of  uranium  ;  Uranic  oxide,  U203;  144,  or  1800. — Uranium  and 
its  lower  oxides  dissolve  in  nitric  acid,  with  evolution  of  nitric  oxide  and  forma- 
tion of  uranic  nitrate.  When  a  solution  of  this  salt  in  absolute  alcohol  is  evapo- 
rated at  a  gentle  heat,  till  nitrous  ether  begins  to  escape,  an  orange-yellow  spongy 
mass  is  obtained,  consisting  of  hydrated  uranic  oxide  mixed  with  undecornposed 
nitrate :  the  nitrate  may  be  dissolved  out  by  water,  and  the  hydrated  oxide  then 
remains,  exhibiting  a  lemon-yellow  or  orange-yellow  colour.  This  hydrate  is  per- 
manent in  the  air,  and  does  not  absorb  carbonic  acid. .  At  572°,  it  yields  anhy- 
drous uranic  oxide,  which  is  also  yellow;  and  at  a  low  red  heat,  it  is  converted 
into  green  uranoso-uranic  oxide. 

The  uranic  salts  arc  obtained  by  oxidizing  uranous  or  uranoso-uranic  salts  with 
nitric  acid,  or  by  exposing  them  to  the  air.  Most  of  them  contain  one  equivalent 
of  uranic  oxide  combined  with  one  equivalent  of  an  acid.  Now,  as  this  is  con- 
trary to  the  usual  analogy  of  the  normal  salts  of  sesquioxides,  most  of  which  con- 
tain three  equivalents  of  acid  to  one  equivalent  of  base,  e.  y.,  ferric  sulphate 
=  Fe203.3S03;  sulphate  of  alumina  =  A1203.3S03, —  Peligot  is  of  opinion  that 
the  base  of  these  salts  is  not  really  a  sesquioxide,  but  the  protoxide  of  a  compound 
radical,  uranyl,  U202,  made  up  of  the  elements  of  2  equivalents  of  uranous  oxide  : 
U203— (U202)0.  To  abbreviate  the  formulae,  we  shall  denote  the  compound  radi- 
cal, uranyl,  by  the  symbol  U' ;  we  have  then  for  the  formula  of  uranic  sulphate ; 
U203.S03  =  (U202)  O.S03  =  U'O.S03. 

Urauic  salts  are  yellow;  they  are  mostly  soluble  in  water,  and,  in  solution,  have 
a  very  rough  taste,  without  any  metallic  after-taste.  They  are  reduced  to  uranous 
salts  by  hydrosulphuric  acid ;  also  by  alcohol  or  ether,  in  sunshine.  Caustic 
alkalies  added  to  urauic  solutions  throw  down  a  yellow  precipitate,  consisting  of  a 


556  URANIUM. 

uranate  of  the  alkali,  which  is  insoluble  in  excess  of  the  reagent.  Alkaline  car- 
bonates produce  a  yellow  precipitate,  consisting  of  a  carbonate  of  uranic  oxide  and 
the  alkali,  soluble  in  excess,  especially  in  bicarbonate  of  potash  or  sesquicarbonate 
of  ammonia.  Potash  added  to  these  solutions  throws  down  all  the  urauic  oxide. 
From  the  solution  in  carbonate  of  ammonia,  the  uranic  oxide  is  likewise  precipi- 
tated by  boiling.  Carbonate  of  baryta  precipitates  uranic  oxide  completely  from 
its  solutions  at  ordinary  temperatures.  Phosphate  of  soda,  added  to  uranic  salts 
not  containing  too  much  free  acid,  produces  a  white  precipitate  of  uranic  phos- 
phate, having  a  slight  tinge  of  yellow.  Sulphide  of  ammonium  produces  a 
black  precipitate  of  uranic  sulphide,  which  remains  for  a  long  time  suspended  in 
the  liquid.  Ilydrosulphuric  acid  produces  no  precipitate.  Ferrocyanide  of 
potassium  produces  a  dark  red-brown  precipitate  ;  ferricyanide  of  potassium, 
none.  Metallic  zinc  does  not  precipitate  uranium  in  the  metallic  state  from  uranic 
solutions,  but,  after  a  long  time,  produces  a  yellow  precipitate  of  uranic  oxide. 

Uranic  oxide  and  its  salts,  fused  with  phosphorus-salt  in  the  outer  blowpipe 
flame,  produce  a  clear  yellow  glass  which  becomes  greenish  on  cooling.  In  the 
inner  flame,  the  glass  assumes  a  green  colour,  becoming  still  greener  when  cold. 
Similar  colours  with  borax.  The  oxides  of  uranium  are  not  reduced  to  the 
metallic  state  by  fusion  with  carbonate  of  soda  on  charcoal.  Uranic  oxide  is  used 
for  imparting  a  delicate  yellow  tint  to  glass  ;  the  glass  thus  coloured  is  called 
canary  glass. 

Chloride  of  uranyl,  U303C1  =  U'Cl)  —  When  dry  chlorine  gas  is  passed  over 
uranous  oxide  at  a  red  heat,  the  tube  becomes  filled  with  an  orange-yellow  vapour 
of  this  compound,  which  solidifies  in  a  yellow  crystalline  mass,  easily  fusible,  but 
not  very  volatile.  Dissolved  in  water,  it  forms  hydrated  chloride  of  uranyl,  or 
hydrochlorate  of  uranic  oxide  : 

U202C1  +  HO  =  UA-HC1. 

Chloride  of  uranyl  and  potassium,  KCl.UCl-f  2Aq.,  is  formed  by  evaporating 
an  aqueous  mixture  of  uranic  chloride  and  chloride  of  potassium.  By  heating 
the  hydrated  crystals  to  212°,  the  anyhdrous  compound  is  obtained. 

Uranic  sulphate;  sulphate  of  uranyl.  —  The  monosulphate  V'O.S03-j-3Aq.  is 
obtained  by  dissolving  uranoso-uranic  oxide  in  strong  sulphuric  acid,  diluting  the 
solution  with  water,  and  oxidizing  with  nitric  acid;  also  by  decomposing  a  solution 
of  uranic  nitrate  with  sulphuric  acid,  expelling  the  excess  of  acid  by  heat,  dis- 
solving the  residue  in  water,  evaporating  the  solution  to  a  syrup,  and  leaving  it  to 
crystallize.  Forms  small  lemon-yellow  prisms.  According  to  Berzelius,  a  bfsul- 
phate  and  a  tersulphate  are  obtained  by  dissolving  the  monosulphate  in  sulphuric 
acid  ;  but  PeUigot  denies  their  existence.  A  basic  sulphate  is  found  native  in  the 
form  of  a  yellow  powder.  The  monosulphate  forms,  with  sulphate  of  potash,  a 
crystalline  double  salt,  whose  formula  is  : 

KO.S03  +  U203.S03-f  2HO  =     /    2S04+2HO. 


Uranic  nitrate  ;  nitrate  of  uranyl  ;  U203.N05=U'O.N05,  is  formed  by  treating 
the  metal  or  either  of  its  oxides  with  nitric  acid.  It  crystallizes  in  lemon-yellow 
prisms.  The  solution  of  this  salt  possesses  the  power  of  lowering  the  refrangi- 
bility  of  rays  of  light  which  fall  upon  it,  producing  the  peculiar  phenomenon 
called  fluorescence.  This  property  is  likewise  exhibited  by  other  compounds  of 
uranium,  especially  by  canary-glass.  A  basic  nitrate  is  formed  by  gently  igniting 
the  normal  salt. 

Uranic  -phosphates  ;  phosphates  of  uranyl.  —  Three  of  these  salts  are  known, 
all  containing  3  atoms  of  base  to  1  atom  of  acid.  When  uranic  oxide  is  digested 
in  a  small  quantity  of  aqueous  phosphoric  acid,  a  yellow  saline  mass  is  produced, 
part  of  which  dissolves  in  boiling  water,  leaving  a  light  yellow  powder,  which  is 
th^  neutral  phosphate  (2U'O.HO).P05.  The  aqueous  solution  concentrated  by 


ESTIMATION    OF    URANIUM.  557 

heat,  and  then  left  to  evaporate  in  vacuo  over  oil  of  vitriol,  deposits  a  lemon- 
yellow  crystalline  salt,  consisting  of  the  acid  phosphate,  (U'0.2HO).P05.  The 
basic  phosphate  has  not  been  obtained  in  the  separate  state;  but  when  uranic 
nitrate  is  mixed  with  a  moderate  excess  of  basic  phosphate  of  soda  (3NaO.P05), 
a  dark  yellow  precipitate  is  formed,  containing  (Na0.2U'0).P05+8U'O.P05 
(Wertheim).*  When  uranic  acetate  is  added  to  a  solution  of  any  soluble  phos- 
phate containing  an  abundance  of  ammonia  and  free  acetic  acid,  a  yellow  precipi- 
tate is  formed  consisting  of  ammonio-uranic  phosphate,  2U'O.NH4O.P05,  which, 
when  ignited,  leaves  uranic  pyrophosphate,  2U'O.P05.  This  reaction  affords  a 
ready  and  exact  method  of  estimating  phosphoric  acid.  The  insoluble  phos- 
phates, even  those  of  alumina  and  sesquioxide  of  iron,  are  also  decomposed  by 
boiling  with  uranic  acetate  in  presence  of  a  large  excess  of  acetate  of  ammonia 
and  free  acetic  acid,  the  bases  dissolving,  while  the  phosphoric  remains  undissolved 
in  the  form  of  the  ammonio-uranic  phosphate  above  described.  To  separate  phos- 
phoric acid  from  iron  in  this  manner  requires,  however,  a  very  large  excess  of  the 
uranium  salt  (W.  Knop).f 

A  neutral  and  an  acid  arseniate  of  uranyl,  analogous  in  composition  to  the 
phosphates,  have  also  been  obtained  by  similar  means.  The  composition  of  these 
phosphates  and  arseniates  affords  a  strong  argument  in  favour  of  the  uranyl 
theory. 

Compounds  of  uranic  oxide  with  bases.  —  Uranic  oxide  combines  as  an  acid 
with  the  alkalies,  earths,  and  other  metallic  oxides,  forming  salts  which  may  be 
called  uranates.  The  uranates  of  the  alkalies  are  obtained  by  precipitating  a 
solution  of  uranic  oxide  in  an  acid  with  an  alkali ;  the  uranates  of  the  earths  and 
heavy  metallic  oxides,  by  adding  ammonia  to  a  solution  of  an  uranic  salt  mixed 
with  one  of  these  bases.  The  uranates  are  for  the  most  part  yellow,  and  after 
ignition  orange-yellow.  The^  soda-compound,  Na0.2U203-}-6HO,  is  used  for 
colouring  glass,  and  is  prepared  on  the  large  scale  by  roasting  pitchblende  with 
limestone  in  a  reverberatory  furnace;  treating  the  resulting  uranate  of  lime  with 
dilute  sulphuric  acid,  by  which  the  uranic  oxide  is  almost  completely  dissolved ; 
mixing  the  green  solution  with  crude  carbonate  of  soda,  by  which  the  uranium  is 
precipitated  together  with  other  metals,  but  redissolved  tolerably  free  from  im- 
purities by  excess  of  the  alkali ;  and  treating  the  liquid  with  dilute  sulphuric  acid 
as  long  as  effervescence  is  produced.  The  uranate  of  soda  is  then  precipitated  in 
a  form  well  adapted  for  the  manufacture  of  yellow  glass. 

ESTIMATION    OF    URANIUM,     AND     METHODS    OP    SEPARATING    IT    FROM    THE 

PRECEDING    METALS. 

Uranium  is  completely  precipitated  from  uranic  solutions  by  ammonia.  The 
precipitate,  which  consists  of  hydrated  uranic  oxide  containing  ammonia,  must  be 
washed  with  water  containing  sal-ammoniac,  as  it  runs  through  the  filter  when 
washed  with  pure  water.  It  is  then  dried  and  ignited  in  an  open  crucible, 
whereby  it  is  converted  into  uranoso-uranic  oxide,  U304 ;  but  to  obtain  a  perfectly 
definite  result,  and  prevent  further  oxidation  during  cooling,  it  is  necessary  to  put 
the  cover  on  the  crucible  while  the  substance  is  still  red-hot,  and  keep  it  there  till 
the  crucible  is  quite  cold.  The  oxide  thus  obtained  contains  84-90  per  cent,  of 
uranium.  An  accurate  result  is  likewise  obtained  by  igniting  the  sesquioxide  in 
an  atmosphere  of  hydrogen,  whereby  it  is  reduced  to  protoxide  containing  88-24 
per  cent,  of  the  metal. 

If  the  uranic  solution  contains  a  considerable  quantity  of  an  earth  or  a  fixed 
alkali,  the  precipitate  formed  by  ammonia  carries  down  with  it  a  certain  portion 
of  the  earth  or  alkali ;  to  free  it  from  which  it  must,  before  ignition,  be  redis- 
solved in  hydrochloric  acid  and  reprecipitated  by  ammonia. 

*  J.  pr.  Chem.  xliii.  321.  f  Chem.  Gaz.  1856,  467. 


558  CERIUM. 

From  the  fixed  alkalies,  uranium,  in  the  state  of  sesquioxide,  is  separated  by 
ammonia,  attention  being  paid  to  the  precaution  just  mentioned. 

From  baryta  it  is  separated  by  sulphuric  acid ;  from  strontia  and  lime,  also  by 
sulphuric  acid  with  addition  of  alcohol. 

From  magnesia,  manganese,  cobalt,  nickel,  and  zinc,  these  metals  being  in  the 
state  of  protoxide,  and  the  uranium  in  the  state  of  sesquioxide,  it  is  separated  by 
precipitation  with  carbonate  of  baryta. 

From  iron  it  is  separated  by  carbonate  of  ammonia,  both  metals  being  in  the 
state  of  sesquioxide ;  the  uranic  oxide  then  dissolves,  while  the  ferric  oxide  re- 
mains undissolved.  Care  must,  however,  be  taken  that  the  carbonate  of  ammonia 
be  really  monocarbonate,  quite  free  from  excess  of  carbonic  acid,  otherwise  the 
iron  will  also  be  dissolved.  To  ensure  this  condition,  the  carbonate  of  ammonia 
must  be  previously  boiled,  and  the  solution  of  the  oxides,  if  acid,  must  be  neu- 
tralized with  ammonia  till  a  slight  permanent  precipitate  begins  to  form :  the 
solution  should  then  be  diluted  with  water.  The  uranic  oxide  is  separated  from 
the  filtrate  either  by  boiling,  or  by  supersaturation  with  hydrochloric  acid  and 
precipitation  by  ammonia. 

From  alumina,  uranium  is  also  separated  by  carbonate  of  ammonia,  and  with 
greater  facility. 

From  cadmium,  copper,  lead,  tin,  arsenic,  antimony,  ani  bismuth,  uranium  is 
separated  by  hydrosulphuric  acid  ]  from  titanium  and  chromium  in  the  same 
manner  as  iron  is  separated  from  those  metals  (pp.  505,  514)  ;  and  from  vanadium, 
tungsten,  molybdenum,  and  tellurium,  by  sulphide  of  ammonium,  in  which  the 
sulphides  of  the  last  named  metals  are  soluble. 


SECTION  II. 

CERIUM. 

Eq.  47-26,  or  590-87.    Ce. 

This  metal,  which  was  discovered  in  1803,  simultaneously  by  Klaproth,  and  by 
Hisinger  and  Berzelius,  exists,  together  with  lanthanum  and  didymiuin,  in  cerite, 
allanite,  orthite,  yttro-cerite,  and  a  few  other  minerals,  all  of  somewhat  rare  oc- 
currence. The  most  abundant  of  them  is  cerite,  which  is  a  compound  of  silicic 
acid  with  the  oxides  of  cerium,  lanthanum,  and  didymium,  together  with  small 
quantities  of  lime  and  oxide  of  iron.  To  extract  the  oxides  of  the  three  metals, 
the  cerite  is  finely  pounded  and  boiled  for  some  hours  with  strong  hydrochloric 
acid,  or  aqua-regia,  which  dissolves  the  metallic  oxides,  leaving  nothing  but  silica. 
The  filtered  solution  is  then^treated  with  a  slight  excess  of  ammonia,  which  pre- 
cipitates everything  but  the  lime ;  the  precipitate  is  redissolved  in  hydrochloric 
acid,  and  the  solution  treated  with  excess  of  oxalic  acid.  A  white  or  faintly  rose- 
coloured  precipitate  is  then  obtained,  consisting  of  the  oxalates  of  cerium,  lan- 
thanum, and  didymium  :  it  is  curdy  at  first,  but  in  a  few  minutes  becomes  crys- 
talline, and  easily  settles  down.  When  dried  and  ignited,  it  yields  a  red-brown 
powder,  containing  the  three  metals  in  the  state  of  oxide.  The  finely  pounded 
cerite  may  also  be  mixed  with  strong  sulphuric  acid  to  the  consistence  of  a  thick 
paste,  the  mixture  gently  heated  till  it  is  converted  into  a  dry  white  powder,  and 
this  powder  heated  somewhat  below  redness  in  an  earthen  crucible.  The  three 
metals  are  thus  brought  to  the  state  of  basic  sulphates,  which  dissolve  completely 
when  very  gradually  added  to  cold  water;  and  the  solution  treated  with  oxalic 
acid  yields  a  precipitate  of  the  mixed  oxalates,  which  may  be  ignited  as  before. 

From  the  red-brown  mixture  of  the  oxides  of  cerium,  lanthanum,  and  didy- 
mium thus  obtained,  a  pure  oxide  of  cerium  may  be  prepared  by  either  of  the 


CEROUS    OXIDE.  559 

following  processes:  —  1.  The  mixed  oxides  are  heated  with  strong  hydrochloric 
acid,  wliich  dissolves  the  whole,  with  evolution  of  chlorine;  the  solution  precipi- 
tated with  excess  of  caustic  potash  :  and  chlorine  gas  passed  through  the  liquid 
with  the  precipitate  suspended  in  it.  The  cerium  is  thereby  brought  to  the  state 
of  sesquioxide,  which  is  left  undissolved  in  the  form  of  a  bright  yellow  precipi- 
tate, while  the  lanthanum  and  didymium  remain  in  the  state  of  protoxides,  and 
dissolve.  To  ensure  complete  separation,  the  passage  of  the  chlorine  must  be  con- 
tinued till  the  liquid  is  completely  saturated  with  it,  and  the  solution,  together 
with  the  precipitate,  left  for  several  hours  in  a  stoppered  bottle,  and  agitated  now 
and  then.  The  liquid  is  then  filtered,  the  washed  precipitate  treated  with  strong 
boiling  hydrochloric  acid,  which  dissolves  it  with  evolution  of  chlorine,  and  forms 
a  colourless  solution  of  protochloride  of  cerium;  and  this,  when  treated  with 
oxalic  acid  or  oxalate  of  ammonia,  yields  a  perfectly  white  precipitate  of  oxalate 
of  cerium,  which  may  be  converted  into  oxide  by  ignition  (Mosander).  2.  The 
red-brown  mixture  of  the  three  oxides  is  treated  with  very  dilute  nitric  acid  (1 
part  of  nitric  acid  of  ordinary  strength  to  between  50  and  100  parts  of  water), 
which  dissolves  the  greater  part  of  the  oxides  of  lanthanum  and  didymium,  and 
leaves  the  oxide  of  cerium ;  and  by  treating  the  residue  with  very  strong  nitric 
acid,  the  last  traces  of  lanthanum  and  didymium  may  be  extracted  (Mosander, 
Marignac).  3.  The  red-brown  mixture  of  the  three  oxides  is  boiled  for  several 
hours  in  a  strong  solution  of  chloride  of  ammonium.  The  oxides  of  lanthanum 
and  didymium  then  dissolve,  with  evolution  of  ammonia,  and  eerie  or  ceroso-ceiic 
oxide  is  left  in  a  state  of  purity.  It  must  be  collected  on  a  filter  and  washed  with 
a  solution  of  sal-ammoniac,  because,  when  washed  with  pure  water,  it  first  runs 
through  the  filter,  and  then  stops  it  up  (Watts).* 

Metallic  cerium  is  obtained  by  heating  the  pure  anhydrous  protochloride  with 
potassium  or  sodium.  It  is  a  grey  powder  which  acquires  the  metallic  lustre  by 
pressure.  It  oxidizes  readily,  decomposes  water  slowly  at  ordinary  temperatures, 
quickly  at  the  boiling  heat,  and  dissolves  rapidly  in  dilute  acids,  with  evolution 
of  hydrogen,  forming  a  solution  of  a  cerous  salt. 

Protoxide  of  cerium  ;  Cerous  oxide,  CeO ;  55-26  or  690.8.  —  This  oxide  is 
scarcely  known  in  the  anhydrous  state.  The  sesquioxide,  exposed  to  the  strongest 
heat  of  a  wind-furnace,  in  a  crucible  lined  with  charcoal,  yields  a  residue  chiefly 
consisting  of  protoxide,  but  the  reduction  is  never  complete.  The  hydrated  prot- 
oxide is  easily  obtained  by  precipitating  the  chloride  with  a  caustic  alkali.  It  dis- 
solves readily  in  acids,  forming  the  protosnlts  of  cerium  or  cerous  salts,  the  solu- 
tions of  which  are  distinguished  by  the  following  characters :  Caustic  potash  or 
soda  produces  a  white  precipitate  of  the  hydrated  protoxide,  which  is  insoluble 
in  excess,  and  is  converted  into  the  yellow  sesquioxide  by  the  action  of  chlorine  or 
hypochlorous  acid.  Ammonia  precipitates  a  basic  salt.  Alkaline  carbonates 
form  a  white  precipitate  of  cerous  carbonate  insoluble  in  excess.  Oxalic  acid  or 
oxnlale  of  ammonia  produces  a  white  precipitate  of  cerous  oxalate,  gelatinous  at 
first,  but  quickly  assuming  the  crystalline  character,  and  converted  by  ignition  in 
an  open  vessel  into  a  salmon-coloured  powder,  consisting  of  sesquioxide  of  cerium 
mixed  with  protoxide.  Hydrosulphuric  acid  produces  no  precipitate.  Sulphide 
of  ammonium  throws  down  the  hydrated  protoxide.  Ferrocycntide  of  potassium 
produces  a  white  pulverulent  precipitate ;  ferricyanide  of  potassium,  none.  Sul- 
phate of  potash  produces  a  white  crystalline  precipitate  of  potassio-cerous  sulphate, 
nearly  insoluble  in  pure  water,  and  quite  insoluble  in  excess  of  sulphate  of  potash. 
With  dilute  solutions  the  precipitate  takes  some  time  to  form.  This  character, 
together  with  the  behaviour  of  the  oxalate,  and  the  yellow  coloration  of  the 
hydrated  protoxide  by  chlorine,  serves  to  distinguish  cerium  from  all  other  metals. 
Cerous  salts  in  solution  have  a  sweet  astringent  taste,  and  redden  litmus,  even 
when  the  acid  is  perfectly  saturated.  All  compounds  of  cerium,  ignited  with 

*  Chem.  Soc.  Qu.  J.  ii.  147. 


560  CERIUM. 

Lorax  or  phosphorus-salt  in  the  outer  blowpipe-flame,  yield  a  glass  which  is  deep 
red  while  hot,  but  becomes  colourless  on  cooling.  In  the  inner  flame  a  colourless 
bead  is  formed,  but  when  ignited  with  excess  of  oxide  of  cerium,  it  forms  a  yellow 
enamel. 

Sesquioxide  of  cerium  ;  Cc.ric  oxide,  Ce203. — It  is  doubtful  whether  this  oxide 
has  been  obtained  in  the  separate  state.  The  hydrated  protoxide,  the  nitrate, 
and  the  oxalate,  yield,  when  ignited  in  the  acid,  a  salmon-coloured  powder,  which 
is  generally  regarded  as  eerie  oxide;  but,  according  to  Marignac,  it  is  a  mixture 
or  compound  of  the  sesquioxide  and  protoxide  of  cerium,  not  quite  constant  in 
composition,  but  containing  on  the  average  82-15  per  cent  of  metal,  and  therefore 
nearly  agreeing  with  the  formula  Ce709or3Ce0.2Ce,03.  When  mixed  with  oxide 
of  didymium,  its  colour  is  red-brown.  This  oxide  is  nearly  insoluble  in  strong 
nitric  and  hydrochloric  acids,  even  at  the  boiling  heat,  but  strong  boiling  sulphuric 
acid  dissolves  it.  Hydrochloric  acid,  with  the  aid  of  reducing  agents,  such  as 
alcohol,  dissolves  it  slowly  at  the  boiling  heat,  forming  a  solution  of  cerous  chloride. 
If  mixed  with  the  oxide  of  lanthanum  or  didymium,  it  dissolves  readily  in  strong 
boiling  hydrochloric  acid,  with  evolution  of  chlorine.  The  solution  of  this  oxide 
in  strong  sulphuric  acid  has  a  bright  yellow  colour,  and  deposits  yellow  prismatic 
crystals,  which,  according  to  Marignac,  consist  of  a  ceroso-cericsulphate,  contain- 
ing Ce709.4S03  +  7HO.  Potash,  added  to  the  solution  of  this  salt,  throws  down 
a  yellow  hydrate,  which  dissolves  readily  in  acids.  The  solutions  are  yellow,  and, 
when  boiled  with  hydrochloric  acid,  are  converted  into  cerous  salts. 

Protosulphide  of  cerium,  CeS,  is  obtained  by  igniting  the  carbonate  in  vapour 
of  bisulphide  of  carbon,  or  by  heating  an  oxide  of  cerium  with  sulphide  of  potas- 
sium. The  first  process  yields  a  light  powder  of  the  colour  of  red  lead ;  the  second, 
a  product  resembling  mosaic  gold.  The  sesqui sulphide  of  cerium  is  not  known  in 
the  free  state,  but  exists  in  certain  sulphur-salts. 

Protochloride  of  cerium,  CeCl. — Cerium  burns  vividly  when  heated  in  chlorine 
gas,  and  forms  this  compound.  The  anhydrous  chloride  may  be  prepared  by 
igniting  the  sulphide,  or  the  residue  obtained  by  evaporating  to  dryness  a  solution 
of  the  chloride  mixed  with  sal-ammoniac,  in  a  current  of  chlorine  gas.  If  the  air 
is  not  completely  excluded,  an  oxychloride  is  also  produced.  The  anhydrous 
chloride  is  a  white  porous  mass,  fusible  at  a  red  heat,  and  perfectly  soluble  in 
water.  A  hydrated  chloride  is  obtained  in  colourless  four-sided  prisms,  by  dis- 
solving the  hydrated  oxide  or  the  carbonate  in  hydrochloric  acid,  and  evaporating 
to  a  syrup.  The  solution,  when  exposed  to  the  air,  turns  yellow,  from  formation 
of  a  eerie  salt.. 

Sesquichloride  of  cerium.  —  The  hydrated  sesquioxide  dissolves  in  cold  hydro- 
chloric acid,  forming  a  red  solution,  which,  however,  soon  gives  off  chlorine,  and 
is  reduced,  more  or  less  completely,  to  protochloride. 

Protofluoride  of  cerium  is  formed  by  precipitating  the  protochloride  with  an 
alkaline  fluoride.  The  sesqiri fluoride  occurs  native  in  six-sided  prisms,  mixed 
with  half  its  weight  of  protofluoride ;  also  with  the  fluorides  of  yttrium  and  calcium, 
in  yttrocerite.  An  oxyfluoride  of  cerium,  Ce4F303  +  3HO,  is  also  found  native. 

Cerous  carbonate,  CeO .  C02-f-3HO,  is  formed  by  exposing  the  hydrated  prot- 
oxide to  the  air,  or  by  precipitation. 

Cerous  oxalate,  C4Ce208,  is  precipitated  from  cerous  salts  by  oxalic  acid  or 
oxalate  of  ammonia  added  in  excess,  even  when  the  solution  contains  a  consider- 
able quantity  of  free  nitric  or  hydrochloric  acid.  It  is  at  first  curdy,  but  soon 
becomes  very  dense  and  crystalline.  When  ignited  with  free  access  of  air,  it 
yields  ceroso-ceric  oxide. 

Cerous  sulphate,  CeO .  S03. — The  anhydrous  salt  is  a  white  powder,  which, 
when  sprinkled  with  a  small  quantity  of  water,  becomes  very  hot,  and  condenses 
into  a  solid  mass,  very  difficult  to  dissolve.  It  forms  two  crystalline  hydrates, 
viz.,  2(CeO.S03)-f3HO  and  (CeO .  S03)  +  3HO.  The  anhydrous  salt,  heated 
i?i  a  close  vessel,  leaves  a  basic  cerous  sulphate;  but,  with  free  contact  of  air,  it 


ESTIMATION    OF    CERIUM.  561 

leaves  a  basic  eerie  or  eeroso-ceric  sulphate.  Cerous  sulphate  forms  with  sulphate 
of  potash  a  crystalline  double  salt,  containing  CeO  .  S03+K0  .  S03,  which  is 
nearly  insoluble  in  water. 

Cerous  phosphate.  — Obtained  by  precipitating  a  cerous  salt  with  phosphate  of 
soda.  It  also  occurs  native  (associated  with  the  phosphates  of  lanthanum  and 
didymium),  in  several  forms.  In  Monazite  and  Edwardsite,  it  occurs  in  oblique 
rhombic  prisms ;  in  the  former  it  is  associated  with  thorina,  and  small  quantities 
of  lime,  manganese,  and  tin;  in  the  latter,  with  alumina,  zirconia,  and  silica. 
Gryptolite  is  a  tribasic  phosphate  of  cerium,  occurring  in  rose-coloured  apatite  of 
Arendal  in  Norway,  and  is  separated  by  dissolving  the  apatite  in  nitric  acid.  It 
then  remains  in  the  form  of  a  crystalline  powder,  appearing  under  the  microscope 
to  consist  of  hexagonal  prisms.  Sp.  gr.  4-6  (Wb'hler).*  Phosphocerite  is  a  mine- 
ral similar  in  composition  to  cryptolite.  It  was  discovered  by  Mr.  0.  Sims  in  the 
cobalt-ore  of  Johannisberg  in  Sweden,  of  which  it  forms  about  one-thousandth 
part.  It  remains  as  a  residual  product  when  the  ore  after  calcination  is  treated 
with  hydrochloric  acid  for  the  purpose  of  extracting  the  cobalt.  It  is  a  greyish 
yellow  crystalline  powder,  mixed  with  a  small  quantity  of  minute  dark  purple 
crystals,  which  are  strongly  attracted  by  the  magnet,  and  consist  chiefly  of  mag- 
netic oxide  of  iron.  The  crystals  of  phosphocerite,  when  examined  by  the  micro- 
scope, exhibits  two  forms,  one  an  octohedron,  the  other,  a  four-sided  prism  with 
quadrilateral  summits,  both  forms  apparently  belonging  to  the  right  prismatic 
system.  Sp.  gr.  4 '78.  The  mineral  contains  64-68  per  cent,  protoxide  of  cerium, 
&c.,  2846  phosphoric  acid,  2-83  oxide  of  iron,  and  341  oxide  of  cobalt,  silica, 
&c.  It  is  very  rich  in  didymium.  Strong  sulphuric  acid,  aided  by  gentle  heat, 
decomposes  it,  forming  a  pasty  mass,  which  dissolves  in  cold  water  with  the 
exception  of  a  small  quantity  of  silica  (Watts). f 

ESTIMATION    OP   CERIUM,  AND    METHODS   OP   SEPARATING    IT    FROM    THE  PRECE- 
DING  METALS. 

Cerium  is  precipitated  from  neutral  solutions  of  cerous  salts  by  potash,  as  cerous 
hydrate ;  or  by  oxalate  of  ammonia,  as  cerous  oxalate ;  and  either  of  these  com- 
pounds is  converted  by  ignition  in  an  open  vessel  into  ceroso-ceric  oxide.  This 
oxide,  as  already  observed,  is  not  perfectly  definite  in  constitution ;  it  may  be 
stated  approximately  to  contain  96-5  per  cent,  of  cerous  oxide,  or  82-5  per  cent, 
of  the  metal,  and  this  estimate  may  be  adopted  where  great  accuracy  is  not 
required.  A  more  exact  method,  however,  is  to  dissolve  the  hydrate  precipitated 
by  potash  in  dilute  sulphuric  acid,  then  evaporate,  and  heat  the  residue  to  com- 
mencing redness,  whereby  it  is  converted  into  the  anhydrous  sulphate  CeO.S03, 
•containing  57 -6  per  cent,  of  the  protoxide  of  cerium,  or  49*6  per  cent,  of  the 
metal. 

Hydrosulphuric  acid  serves  to  separate  cerium  from  all  metals  which  are  pre- 
cipitated by  that  reagent  from  their  acid  solutions. 

From  manganese,  iron,  cobalt,  nickel,  zinc,  titanium,  chromium,  vanadium,  and 
tvgsten,  cerium  maybe  separated  by  means  of  a  saturated  solution  of  sulphate  of  potash. 

From  alumina  it  may  be  separated  by  carbonate  of  baryta,  which  precipitates 
alumina  and  not  cerous  oxide ;  from  glud.ua  by  sulphate  of  potash. 

From  yttria,  with  which  it  is  often  associated  in  minerals,  it  is  separated  by  a 
saturated  solution  of  sulphate  of  potash  added  in  excess,  the  sulphate  of  yttria  and 
potash  being  soluble  in  excess  of  sulphate  of  potash,  while  the  cerous  double  salt 
remains  uudissolved. 

From  zirconia,  cerium  is  separated  by  treating  the  boiling  acid  solution  with 
sulphate  of  potash,  whereby  the  greater  part  of  the  zirconia  is  precipitated  as 
basic  sulphate,  while  the  cerium  remains  dissolved;  to  complete  the  precipitation, 

*  Ann.  Ch.  Pharm.  Ivii.,  268.  f  Chcm.  Soc.  Qu.  J.  ii.  131. 


562  LANTHANUM. 

a  small  quantity  of  ammonia  must  be  added,  but  not  sufficient  to  saturate  the  acid 
(H.  Rose). 

From  magnesia  also  cerium  may  be  separated  by  sulphate  of  potash ;  from 
"baryta,  strontia,  and  lime,  it  is  separated  by  ammonia  added  in  slight  excess ;  or 
from  baryta  by  sulphuric  acid,  and  from  strontia  and  lime  by  sulphuric  acid  and 
alcohol;  and  from  the  fixed  alkalies  by  precipitation  with  oxalate  of  ammonia. 


SECTION    VI. 

LANTHANUM. 

Eq.  27  or  588 ;  La. 

The  red-brown  oxide  obtained  from  cerite  by  the  methods  already  described 
(p.  558),  and  originally  regarded  as  the  oxide  of  a  single  metal,  cerium,  was  shown 
by  Mosander,*  in  1839,  to  contain  the  oxide  of  another  metal,  to  which  he  gave 
the  name  lanthanum.  Subsequently,  in  1841, f  Mosander  discovered  that  even  this 
supposed  simple  oxide  contained  two.distinct  metals,  for  one  of  which  the  name  of  lan- 
thanum was  retained,  while  the  other  was  called  didymium.  These  two  metals  appear 
to  be  constantly  associated  with  cerium,  though  not  always  in  the  same  proportion. 

The  separation  of  lanthanum  and  didymium  from  cerium  may  be  effected  by 
either  of  the  methods  already  described  (p.  559) ;  the  second  and  third  are  easier 
and  more  expeditious  than  the  first.  If  the  solution  obtained  by  treating  the 
crude  red-brown  oxide  with  dilute  nitric  acid  be  evaporated  to  dryness,  and  the 
residue  treated  with  nitric  acid  diluted  with  at  least  200  parts  of  water,  a  solu- 
tion will  be  obtained  quite  free  from  cerium  (Marignac).  Boiling  the  red-brown 
oxide  with  chloride  of  ammonium  also  yields  a  solution  of  lanthanum  and  didy- 
mium free  from  cerium.  In  both  cases,  however,  it  is  best  to  test  a  portion  of 
the  solution  for  cerium  by  precipitating  with  excess  of  caustic  potash,  and  passing 
chlorine  through  the  solution.  The  presence  of  cerium,  even  in  very  small  quan- 
tity, will  be  indicated  by  the  formation  of  a  yellow  precipitate,  after  the  liquid, 
supersaturated  with  chlorine,  has  been  left  in  a  close  vessel  for  several  hours. 

A  solution  free  from  cerium  having  been  obtained,  the  separation  of  the  lantha- 
num and  didymium  is  effected  by  the  different  solubilities  of  their  sulphates.  To 
convert  them  into  sulphates,  the  solution  is  treated  with  excess  of  a  caustic  alkali, 
and  the  washed  precipitate  dissolved  in  dilute  sulphuric  acid.  The  mode  of  pro- 
ceeding varies  according  as  the  lanthanum  or  the  didymium  is  in  excess. 

1.  When  the  lanthanum  is  in  excess,  in  which  case  the  solution  has  but  a  faint 
amethyst  tinge,  the  liquid  is  evaporated  to  dryness,  and  the  residue  heated  in  a 
platinum-dish  to  a  temperature  just  below  redness,  to  drive  off  the  excess  of  acid, 
and  render  the  sulphates  perfectly  anhydrous.  The  residue  is  then  dissolved  in 
rather  less  than  six  times  its  weight  of  water,  at  about  36°  Fah.  (2°  or  3°  C.), 
the  salt  being  reduced  to  powder  and  added  in  successive  small  portions,  and  the 
vessel  containing  the  liquid  being  immersed  in  ice-cold  water.  Without  these 
precautions,  the  temperature  of  the  liquid  may  be  raised  several  degrees,  in  con- 
sequence of  the  heat  evolved  by  the  combination  of  the  anhydrous  sulphates  with 
water;  and,  in  that  case,  crystallization  will  commence,  and  rapidly  extend  through 
the  whole  mass  of  liquid,  as  these  sulphates  are  much  less  soluble  in  warm  than  in 
cold  water;  but  if  the  liquid  be  properly  cooled,  the  whole  dissolves  completely. 
The  solution  is  next  to  be  heated  in  the  water-bath  to  about  104°  F.  (40°  C.) ; 
the  sulphate  of  lanthanum  then  crystallizes  out,  accompanied  by  only  a  small  quan- 
tity of  sulphate  of  didymium.  To  purify  it  completely,  it  is  again  rendered  anhy- 
drous, re-dissolved  in  ice-cold  water,  &c.,  and  the  entire  process  repeated  ten  or 

*  Pogg.  Ann.  xlvi.  648 ;  xlvii.  207.  f  Ibid.  Ivi.  504. 


LANTHANUM.  563 

twelve  times.     The  test  of  purity  is  perfect  whiteness,  the  smallest  quantity  of 
didymium  imparting  an  amethyst  tinge  (Mosander). 

2.  When  the  didymium-salt  is  in  excess,  in  which  case  the  liquid  has  a  decided 
rose-colour,  separation  may  be  effected  by  leaving  the  solution  containing  excess 
of  acid,  in  a  warm  place  for  a  day  or  two.  The  sulphate  of  didymium  then  sepa- 
rates in  large  rhombohedral  crystals  modified  with  numerous  secondary  faces; 
and,  at  the  same  time,  slender,  needle-shaped,  violet-coloured  crystals  are  formed, 
containing  the  two  sulphates  mixed.  The  rhombohedral  crystals,  which  are  nearly 
free  from  lanthanum,  are  removed,  and  the  needles,  together  with  the  mother- 
liquid,  treated  as  in  the  first  method,  to  obtain  sulphate  of  lanthanum  (Mosander). 

In  both  cases,  the  separation  may  be  greatly  facilitated  by  first  dissolving  the 
mixed  oxides  of  the  two  metals  in  a  large  excess  of  nitric  acid,  and  precipitating 
in  successive  portions  by  oxalic  acid :  the  first  precipitates  thus  formed  have  a 
much  deeper  rose-colour,  and  are  much  richer  in  didymium  than  the  latter.  The 
separation  thus  effected  is  very  imperfect  in  itself,  but  it  greatly  facilitates  the  sub- 
sequent separation  of  the  sulphates,  which  is  much  more  rapid,  when  one  of  the 
sulphates  is  in  great  excess  with  regard  to  the  other  (Marignac). 

Metallic  lanthanum  is  obtained  by  decomposing  the  anhydrous  chloride  with 
sodium,  and  dissolving  out  the  chloride  of  sodium  with  alcohol  of  sp.  gr.  0-833. 
It  is  a  dark,  lead-grey  powder,  soft  to  the  touch,  and  adhering  when  pressed. 

Protoxide  of  lanthanum,  LaO,  55  or  688,  is  obtained  in  the  anhydrous  state 
by  igniting  the  precipitated  hydrate  or  carbonate  in  a  covered  crucible.  It  is  a 
white  powder,  which  turns  brown  when  heated  in  the  air,  probably  from  partial 
conversion  into  a  higher  oxide.  The  hydrated  oxide  is  formed  when  the  metal  or 
the  anhydrous  oxide  is  immersed  in  warm  water,  or  when  a  salt  of  lanthanum  is 
precipitated  by  caustic  potash.  It  is  a  white  substance,  viscid  while  moist,  and 
slightly  alkaline  to  test-paper.  It  absorbs  carbonic  acid  from  the  air  with  great 
rapidity. 

Oxide  of  lanthanum,  even  after  strong  ignition,  dissolves  very  easily  in  acids. 
When  boiled  with  a  solution  of  chloride  of  ammonium,  it  dissolves  and  expels  the 
ammonia.  The  salts  of  lanthanum  are  perfectly  colourless  when  free  from  didy- 
mium. The  soluble  salts  have  an  astringent  taste.  Potash  and  soda,  added  to 
the  solutions,  throw  down  the  hydrated  oxide,  which  dissolves  completely  in 
chlorine-water,  without  forming  any  yellow  deposit.  Ammonia  throws  down  a 
basic  salt.  Oxalic  acid  or  oxalate  of  ammonia,  throws  down  a  white  flocculent 
precipitate,  which  does  not  become  crystalline.  In  other  respects,  the  solutions 
resemble  those  of  cerous  salts.  Compounds  of  lanthanum  do  not  impart  any  colour 
to  borax  or  phosphorus  salt. 

Chloride  of  lanthanum  is  obtained  in  the  anhydrous  state  by  igniting  the  oxide 
in  a  current  of  hydrochloric  acid  gas,  and  as  a  hydrate  by  evaporating  a  solution 
of  the  oxide  in  hydrochloric  acid.  It  dissolves  very  readily  in  water. 

Carbonate  of  lanthanum  is  found  native  in  small  crystalline  scales,  containing 
traces  of  protoxide  of  cerium.  When  obtained  by  precipitation,  it  forms  a  gela- 
tinous mass,  which  gradually  changes  into  shining  crystalline  scales  (Mosander). 

Sulphate  of  lanthanum,  LaO  .  S03,  is  obtained  by  spontaneous  evaporation  in 
small  prismatic  crystals,  containing  3  eq.  of  water  of  crystallization.  It  parts  with 
its  water  at  a  low  red  heat,  and  with  half  its  acid  at  a  strong  red  heat.  It  is  much 
less  soluble  in  hot  than  in  cold  water  (p.  559).  It  forms  with  sulphate  of  potash 
a  very  sparingly  soluble  double  salt,  similar  to  the  sulphate  of  cerium  and 
potassium. 

Nitrate  of  lanthanum  crystallizes  in  deliquescent  colourless  prisms,  very  easily 
soluble  in  water  and  in  alcohol.  When  carefully  heated,  so  as  not  to  expel  any  of 
the  acid,  it  fuses,  and  solidifies  into  a  colourless  glass  on  cooling.  If  the  heat  is 
raised,  so  as  to  drive  off  a  portion  of  the  acid,  a  fused  mass  remains  which,  on 
coolinpr,  forms  a  kind  of  enamel,  but  almost  immediately  afterwards  crumbles  to  a 
bulky  white  powder,  and  with  such  force  that  the  particles  are  scattered  about  to 
a  considerable  distance  (Mosander). 


564  DIDYMIUM. 


ESTIMATION   OP   LANTHANUM. 


Lanthanum  is  precipitated  from  its  solutions  by  potash,  or  by  oxalate  of  ammo- 
nia, and  the  precipitate  converted  by  ignition  in  a  covered  platinum  crucible  into 
the  anhydrous  oxide,  containing  85*7  per  cent,  of  the  metal. 

The  methods  of  separating  lanthanum  from  other  metals  are  the  same  as  those 
adopted  for  cerium.  The  separation  of  lanthanum  from  cerium  itself  may  be 
effected  by  boiling  the  mixed  oxides  in  a  solution  of  chloride  of  ammonium  (p.  559). 


SECTION  VII. 

DIDYMIUM. 

Eq.  48  or  600 ;  Di. 

Didymium  was  discovered  by  Mosander  in  1841  ;*  and  its  compounds  have  since 
been  more  minutely  examined  by  Marignac.f 

A  pure  salt  of  didymium  is  obtained  by  recrystallizing  the  rose-coloured  rhom- 
bohedrons  which  separate  from  an  acid  solution  of  the  mixed  sulphates  of  lanthanum 
and  didymium  by  spontaneous  evaporation ;  and  from  the  pure  sulphate  thus 
prepared,  the  other  compounds  of  the  metal  may  be  formed. 

Metallic  didymium  is  obtained  by  heating  potassium  with  an  excess  of  chloride 
of  didymium,  and  washing  out  the  soluble  chlorides  with  cold  water.  It  is  thus 
obtained,  for  the  most  part,  as  a  grey  metallic  powder ;  but  partly,  also,  in  fused 
globules.  The  powder,  thrown  into  the  flame  of  a  spirit-lamp,  burns  with  bright 
sparks  like  iron-filings.  The  powder  decomposes  water  at  ordinary  temperatures  ; 
the  fused  granules  do  not :  in  either  form,  however,  the  metal  dissolves  rapidly  in 
dilute  acids,  with  evolution  of  hydrogen. 

Protoxide  o/  didymium,  DiO,  56  or  700.  —  Obtained  in  the  anhydrous  state 
by  strongly  igniting  the  nitrate,  oxalate,  or  the  precipitated  hydrate  in  a  covered 
crucible,  It  is  perfectly  white  j  is  slowly  converted  into  a  hydrate  by  immersion 
in  warm  water ;  dissolves  readily  in  the  weakest  acids ;  and  expels  ammonia  from 
ammoniacal  salts  when  boiled  with  them.  The  hydrate,  DiO. HO,  is  a  gelatinous 
mass  resembling  alumina,  but  having  a  very  pale  rose-colour.  It  contracts  much 
by  desiccation. 

The  salts  of  didymium  have  either  a  pure  rose-colour,  like  the  sulphate,  or 
slightly  inclining  to  violet,  like  the  nitrate  in  the  state  of  strong  solution.  Potash, 
soda,  and  ammonia  precipitate  the  hydrate;  so  does  sulphide  of  ammonium. 
Carbonate  of  baryta  also  throws  down  the  hydrated  oxide  slowly,  but  completely. 
Oxalate  of  ammonia  precipitates  didymium  completely  from  neutral  solutions ; 
and  oxalic  acid  almost  completely,  unless  the  solution  contains  a  large  excess  of 
acid.  The  sulphates  of  potash,  soda,  and  ammonia  form,  immediately  in  strong, 
and  gradually  in  weak  solutions,  rose-white  precipitates  of  double  sulphates, 
slightly  soluble  in  water,  less  soluble  in  excess  of  the  reagent ;  the  soda-salt  is  the 
least  soluble  of  the  three.  Phosphoric  and  arsenic  acids,  at  a  boiling  heat,  form 
precipitates  sparingly  soluble  in  acids.  All  compounds  of  didymium  impart  to 
borax  and  phosphorus-salt  a  very  pale  rose-colour.  They  do  not  colour  carbonate 
of  soda  before  the  blowpipe. 

Peroxide  of  didymium.  —  When  the  oxalate,  nitrate,  carbonate,  or  hydrate  of 
didymium  is  ignited  in  contact  with  the  air,  and  not  very  strongly,  a  dark  brown 

*  Pogg.  Ann.  Ivi.  504. 

f  Ann.  Ch.  Phys.  [3],  xxxviii.  148;  Chem.  Soc.  Qu.  J.,  vi.  260. 


DIDTMIUM.  565 

oxide  is  obtained,  containing  from  0-32  to  0-88  per  cent,  of  oxygen  more  than  the 
protoxide.  When  treated  with  acids  it  dissolves  readily,  giving  off  the  excess  of 
oxygen,  and  forming  a  solution  containing  the  protoxide.  It  is  probably  a  mixture 
of  the  protoxide  with  a  small  quantity  of  a  higher  oxide  of  definite  composition. 
By  strong  ignition  in  a  close  vessel,  it  is  converted  into  the  white  protoxide. 

Sulphide  of  didymium,  DiS,  is  obtained  by  igniting  the  oxide  in  the  vapour 
of  bisulphide  of  carbon.  It  is  a  light,  brownish  green  powder,  which  dissolves  in 
acids,  with  evolution  of  hydrosulphuric  acid.  A  greyish-white  oxysulphide, 
2DiO .  DiS,  is  obtained  by  igniting  the  oxide  with  carbonate  of  soda  and  excess  of 
sulphur,  and  digesting  the  fused  mass  in  water  (Marignac). 

Chloride  of  didymium  is  obtained  as  a  hydrate  in  rose-coloured  crystals  of 
considerable  size,  by  evaporating  a  solution  of  the  oxide  in  hydrochloric  acid. 
The  crystals,  which  are  very  soluble  in  water  and  alcohol,  contain  DiC1.4HO. 
The  solution,  when  evaporated,  gives  off  hydrochloric  acid,  and  leaves  an  oxy- 
chloride,  not  however  of  constant  composition  (Marignac). 

Carbonate  of  didymium,  DiO.C02. —  Precipitated  as  a  white,  bulky  hydrate, 
tinged  with  rose-colour,  on  adding  an  alkaline  carbonate  or  bicarbonate  to  a  salt  of 
didymium.  The  precipitate  formed  in  the  cold  with  nitrate  of  didymium  and 
bicarbonate  of  ammonia,  contains,  after  drying  in  vacuo,  DiO.Cl2  +  2HO.  At 
212°,  it  gives  off  1 J  eq.  water  and  a  small  quantity  of  carbonic  acid  (Marignac). 

Oxalate  of  didymium,  C4Di208,  is  precipitated  from  neutral  solutions  as  a  rose- 
white  powder,  which  dissolves  in  warm  nitric  or  hydrochloric  acid,  and  separates, 
on  cooling,  in  the  form  of  a  granular  crystalline  powder,  sometimes  even  in  small 
rose-coloured  prismatic  crystals.  After  drying  in  the  air,  it  contains  8  eq.  water, 
6  eq.  of  which  go  off  at  212°  (Marignac). 

Sulphate  of  didymium,  DiO.S03.  —  Formed  by  dissolving  the  oxide  or  carbo- 
nate in  dilute  sulphuric  acid.  The  solution  is  rose-coloured,  and  deposits,  by 
spontaneous  evaporation,  dark  rose-coloured,  shining  crystals,  having  the  form  of 
an  oblique  rhomboidal  prism  (Mosander),  and  cleaving  readily  and  distinctly  in  a 
direction  parallel  to  the  base.  They  contain  3(DiO.S03)  +  8Aq.,  and  give  off 
the  whole  of  their  water  at  392°  F.  (200°  C.),  leaving  an  anhydrous  powder, 
which  may  be  heated  to  redness  without  further  alteration.  A  solution  of  the 
sulphate,  when  heated,  especially  to  the  boiling  point,  deposits  a  crystalline  pre- 
cipitate containing  DiO.S03  -f  2HO.  The  following  table  exhibits  the  solubility 
of  the  anhydrous  salt,  and  of  the  two  crystalline  hydrates  in  water  at  different 
temperatures : — 

TemnpratnrP  Anhydrous  Sulphate  with        Sulphate  crystallized 

Sulphate.  2  eq.  water.  in  the  cold. 

12°  0  43-1  —  — 

14  39-3  —  — 

18  25-8  16-4  — 

19  —  —  H-7 
.    25                        20-6                       —  — 

38  13-0  —  — 

40  —  _  8-8 

50  11-0  —  6-5 

100  1-7 

The  anhydrous  sulphate,  exposed  to  the  heat  of  an  intense  charcoal  fire,  gives 
off  two-thirds  of  its  sulphuric  acid,  and  leaves  a  tribasic  sulphate,  3DiO.S03 
(Marignac). 

Sulphate  of  didymium,  mixed  in  solution  with  sulphate  of  potash,  forms  a  crys- 
talline double. salt,  which  appears  to  contain  KO.S034-  3(DiO.S03)  -f  2HO;  it 
dissolves  in  sixty-three  times  its  weight  of  cold  water.  With  sulphate  of  soda  it 
forms  the^  anhydrous  double  salt,  NaO.S03  +  3(DiO.S03),  which  requires  two 
hundred  times  its  weight  of  water  to  dissolve  it,  and  is  still  less  soluble  in  a  solu- 


566  TANTALUM. 

tion  of  sulphate  of  soda.  With  sulphate  of  ammonia,  it  forms  the  salt 
NH4O.S03  +  3(DiO.S03)  -f  8HO  soluble  in  eighteen  times  its  weight  of  water 
(Marignac). 

Sulphite  of  didymium,,  DiO.S02  -p-  2HO.  —  Oxide  of  didymium  suspended  in 
water,  is  readily  dissolved  by  a  stream  of  sulphurous  acid  gas,  forming  a  rose- 
coloured  solution  which  becomes  turbid  when  heated,  forming  a  light  bulky  pre- 
cipitate, which  redissolves  as  the  liquid  cools,  unless  the  temperature  has  been 
raised  to  the  boiling  point,  in  which  case  it  remains  undissolved  (Marignac). 

Nitrate  of  didymium,  DiO.N05.  —  This  salt  is  very  soluble  in  water  and  in 
alcohol  of  the  strength  of  96  per  cent.  The  aqueous  solution  has  a  pure  rose 
colour  when  dilute,  but  appears  violet  by  reflected  light  when  strong.  A  syrupy  so- 
lution solidifies  on  cooling  into  a  deliquescent  crystalline  mass,  which,  when  carefully 
heated  to  300°  C.,  melts,  becomes  perfectly  anhydrous,  and  exhibits  the  compo- 
sition of  the  neutral  nitrate.  At  a  higher  temperature,  it  is  decomposed,  giving 
off  nitrous  fumes,  and  leaving  a  residue  from  which  water  extracts  a  portion  of 
neutral  nitrate,  and  leaves  a  basic  salt  containing  4DiO.N05  -f-  5HO.  (Marignac). 

Phosphate  of  didymium,  3DiO.P05-f  2HO.  — Precipitated,  after  a  few  hours, 
as  a  white  powder,  on  adding  a  strong  solution  of  phosphoric  acid  to  a  strong  so- 
lution of  nitrate  of  didymium.  It  is  insoluble  in  water,  very  sparingly  soluble  in 
dilute  acids ;  but  dissolves  readily  in  the  stronger  acids  when  concentrated ;  gives 
off  its  water  when  ignited  (Marignac). 

Arseniate  of  didymium,  5Di0.2As05  +  2HO. — Obtained  as  a  pulverulent  pre- 
cipitate by  the  action  of  arsenic  acid  on  solutions  of  didymium  at  the  boiling  heat, 
or  as  a  gelatinous  precipitate  by  the  action  of  neutral  arseniate  of  potash  at  ordi- 
nary temperatures.  It  is  but  slightly  soluble  in  dilute  acids  (Marignac). 

The  quantitative  estimation  of  didymium  is  effected  in  the  same  manner  as 
that  of  lanthanum.  The  anhydrous  protoxide  contains  85-7  per  cent,  of  the 
metal.  * 

The  methods  of  separating  didymium  from  the  preceding  metals  are  also  the 
same  as  for  lanthanum.  For  separating  it  from  lanthanum  itself,  no  method  has 
yet  been  devised  sufficiently  exact  for  quantitative  analysis. 


SECTION  VIII. 

TANTALUM. 

Eq.  68-82  or  860-3;  Ta. 

This  metal  was  discovered  by  Ekeberg  in  1802.  It  is  a  rare  metal,  occuring 
only  in  a  few  minerals,  the  principal  of  which  are  Swedish  tantalite  and  yttro- 
tantalite. 

Tantalum  is  obtained,  in  the  metallic  state,  by  heating  the  fluoride  of  tantalum 
and  potassium,  or  fluoride  of  tantalum  and  sodium,  with  sodium,  in  a  well  covered 
iron  crucible,  and  afterwards  washing  out  the  soluble  salts  by  water.  The  reduced 
metal  thus  obtained  is  not  quite  pure,  being  more  or  less  contaminated  with  acid 
tantalate  of  soda,  the  quantity  of  which  may,  however,  be  diminished  by  covering 
the  mixture  in  the  crucible  with  chloride  of  potassium. 

Tantalum  is  a  black  powder,  which,  according  to  H.  Rose,  is  a  good  conductor 
of  electricity.  When  heated  in  the  air,  it  burns  with  a  bright  light,  and  is  con- 
verted, though  with  difficulty,  into  tantalic  acid.  It  is  not  attacked  by  sulphuric, 
hydrochloric,  or  nitric  acid,  or  even  by  aqua  regia.  It  dissolves  slowly  in  warm 
aqueous  hydrofluoric  acid,  with  evolution  of  hydrogen,  and  very  rapidly  in  a  mix- 
ture of  hydrofluoric  and  nitric  acids. 


HYDRATED    TANTALIC    ACID.  567 

Tantalum  forms  two  compounds  with  oxygen,  viz.,  tantalous  acid,  probably 
TaO,  and  tantah'c  acid,  Ta02. 

Tantalous  acid  is  obtained  by  placing  tantalic  acid  in  a  small  cavity  in  a  cru- 
cible filled  with  charcoal,  and  exposing  it  to  the  strongest  heat  of  a  blast-furnace; 
a  thin  film  on  the  outside  is  at  the  same  time  reduced  to  the  state  of  metal.  It  is 
a  dark  grey  mass  which  scratches  glass,  and  acquires  metallic  lustre  by  bur- 
nishing. 

Tantalic  acid,  Ta02;  84-82  or  1060-3.*— This  compound  is  formed  when  tan- 
talum burns  in  the  air;  also  by  the  action  of  water  on  chloride  of  tantalum ;  and, 
in  the  form  of  a  potash-salt,  by  fusing  metallic  tantalum  or  tantalous  acid  with 
hydrate,  carbonate,  or  bisulphate  of  potash.  It  exists,  in  combination  with  various 
bases,  in  the  minerals  above  mentioned,  and  is  usually  extracted  from  tantalite, 
which  contains  the  oxides  of  iron  and  manganese,  together  with  small  quantities 
of  stannic  and  tungstic  acids,  by  one  of  the  following  processes:  —  1.  The  mine- 
ral, after  being  pulverized  and  levigated,  is  fused  with  twice  its  weight  of  hydrate 
of  potash ;  the  fused  mass  digested  in  hot  water;  and  the  filtered  solution  super- 
saturated with  hydrochloric  or  nitric  acid :  hydrated  tantalic  acid  is  then  precipi- 
tated in  white  flakes,  which  may  be  purified  by  washing  with  water  (Berzelius). 
2.  A  better  method,  however,  is  to  fuse  the  levigated  tantalite  in  a  platinum  cru- 
cible with  six  or  eight  times  its  weight  of  bisulphate  of  potash ;  pulverize  the 
mass  when  cold ;  and  boil  it  repeatedly  with  fresh  quantities  of  water  till  no  more 
sulphate  of  potash,  iron,  or  manganese  is  dissolved  out  of  it.  The  residue,  which 
consists  of  hydrated  tantalic  acid  mixed  with  ferric  oxide,  stannic  acid,  and  tungs- 
tic acid,  is  then  digested  in  sulphide  of  ammonium  containing  excess  of  sulphur, 
which  removes  the  stannic  and  tungstic  acids,  and  converts  the  iron  into  sul- 
phide; the  liquid  is  filtered,  and  the  tantalic  acid  washed  with  water  containing 
sulphide  of  ammonia,  then  boiled  with  strong  hydrochloric  acid  to  remove  the 
iron,  and  finally  washed  with  boiling  water.  The  hydrated  tantalic  acid  thus 
prepared  is  converted  into  the  anhydrous  acid  by  ignition.  It  may  still,  however, 
contain  silica,  to  remove  which,  it  is  dissolved  in  aqueous  hydrofluoric  acid,  the 
filtered  solution  mixed  with  sulphuric  acid  and  evaporated  to  dryness,  and  the 
residue  ignited  as  long  as  its  weight  continues  to  diminish  :  the  silica  is  then  ex- 
pelled as  gaseous  fluoride  of  silicon  (Berzelius). 

Anhydrous  tantalic  acid  is  a  white  powder,  which  remains  white  when  heated, 
or  acquires  but  a  very  faint  tinge  of  yellow.  Its  specific  gravity  varies  from 
7-022  to  8-264,  increasing-  with  the  temperature  to  which  the  acid  has  been 
exposed  (H.  Rose).  It  neither  melts  nor  volatilizes  when  heated,  and  is  destitute 
of  taste  and  smell.  It  is  reduced  to  the  metallic  state  in  the  circuit  of  a  very 
powerful  voltaic  battery;  partially  also  by  very  strong  ignition  in  contact  with 
charcoal.  When  ignited  in  the  vapour  of  bisulphide  of  carbon,  it  yields  sulphide 
of  tantalum : 

2Ta02  +  4CS2  =  Ta2S3  +  4CO  -f  5S. 

It  is  insoluble  in  all  acids,  and  can  only  be  rendered  soluble  by  fusion  with  hydrate 
or  carbonate  of  potash. 

Hydrated  tantalic  acid,  obtained  by  precipitating  an  aqueous  solution  of  tanta- 
late  of  potash  with  hydrochloric  acid,  or  by  decomposing  chloride  of  tantalum  with 
water  containing  a  small  quantity  of  ammonia,  is  a  snow-white  bulky  powder, 
which  reddens  litmus-paper  while  moist,  and  dissolves  in  hydrochloric  and  hydro- 

*  The  composition  of  tantalic  acid  is  usually  represented  by  the  formula  Ta03,  which,  ac- 
cording to  the  original  analysis  of  that  compound  by  Berzelius  (88-5  per  cent,  tantalum  -f- 
11-5  per  cent,  oxygen),  gives  for  tantalum  the  equivalent  number  185.  But  according  to 
the  recent  experiments  of  H.  Rose  (Berl.  Akad.  Ber.,  1856,  885),  the  tantalum-compounds 
appear  to  contain  '2  eq.  of  the  chlorous  element,  viz.,  the  chloride,  TaCl2,  tantalic  acid,  Ta02, 
&c. :  he  also  finds  the  chloride  to  contain  49-25  per  cent,  of  tantalum,  making  the  equiva- 
lent of  tantalum  68-82. 


568  TANTALUM. 

fluoric  acids.  When  strongly  heated  it  gives  off  its  water  and  becomes  incandes- 
cent. The  hydrate,  obtained  by  fusing  tantalite  with  bisulphate  of  potasli  in  the 
manner  above  described,  is  of  a  denser  and  more  crystalline  character,  is  insoluble 
in  all  acids  excepting  strong  sulphuric  acid,  and  is  precipitated  from  the  solution 
by  water.  When  heated,  it  becomes  anhydrous,  but  does  not  emit  light. 

Tantalic  acid  combines  with  bases  much  more  readily  than  with  acids.  When 
fused  with  hydrate  of  potash  in  a  silver  crucible,  it  forms  a  transparent  mass  of 
tantalate  of  potash,  which,  after  cooling,  dissolves  completely  in  water.  With 
hydrate  of  soda  it  fuses  into  an  opaque  turbid  mass,  and  ultimately  deposits  a 
sediment,  which  is  not  taken  up  by  fusion  with  any  excess  of  the  alkali.  Water 
poured  upon  the  fused  mass  when  cold  dissolves  out  the  excess  of  soda,  but  not 
a  trace  of  tantalic  acid ;  and  the  residue,  when  treated  with  fresh  water,  dissolves 
and  forms  an  opalescent  solution  of  acid  tantalate  of  soda,  which  salt  is  completely 
insoluble  in  a  strong  solution  of  caustic  soda,  and  is  therefore  precipitated  on 
mixing  the  liquid  with  the  solution  of  soda  previously  obtained  by  treating  the 
fused  mass  with  water.  When  tantalic  acid  is  fused  with  carbonate  of  potash  or 
Kodn,  the  fused  mass  is  not  completely  soluble  in  water. 

Hydrochloric  acid,  added  in  excess  to  the  solution  of  an  alkaline  tantalate,  first 
precipitates  the  tantalic  acid,  and  then  redissolves  it,  forming  a  slightly  opalescent 
liquid.  Sulphuric  acid  also  precipitates  the  tantalic  acid,  but  does  not  redissolve 
it  when  added  in  excess.  Carbonic  acid  gas,  passed  through  the  solution  of  an 
alkaline  tantalate,  precipitates  the  whole  of  the  tantalic  acid  in  the  form  of  an 
acid  salt.  Chloride  or  sulphate  of  ammonium  also  precipitates  the  tantalic  acid 
from  these  solutions  in  the  form  of  hydrate,  mixed  with  small  quantities  of  ammo- 
nia and  the  fixed  alkali.  The  presence  of  carbonate  of  potash  or  soda  prevents 
the  formation  of  this  precipitate  at  ordinary  temperatures;  but  it  then  appears 
ifter  boiling  for  some  time.  Sulphide  of  ammonium  produces  no  precipitate. 
Chloride  of  barium  or  calcium  forms  a  precipitate  of  tantalate  of  baryta  or  lime, 
insoluble  in  water  and  in  ammoniacal  salts.  Nitrate  of  silver  forms,  in  the  solu- 
tion of  a  neutral  alkaline  tantalate,  a  white  precipitate,  which  is  turned  brown  by 
a  small  quantity  of  ammonia,  and  dissolves  in  a  larger  quantity.  A  solution  of 
basic  mercurous  nitrate  forms  a  yellowish  white  precipitate,  which  turns  black 
when  heated.  Ferrocyanide  of  potassium,  added  to  a  very  slightly  acidulated 
solution  of  an  alkaline  tantalate,  forms  a  yellow  precipitate ;  ferricyanide  of  po- 
tassium a  white  precipitate.  Infusion  of  aalls,  added  to  a  solution  of  an  alkaline 
tantalate  acidulated  with  sulphuric  or  hydrochloric  acid,  forms  a  light  yellow  pre- 
cipitate soluble  in  alkalies.  Zinc,  immersed  in  the  solution  of  an  alkaline  tanta- 
late acidulated  with  hydrochloric  acid,  does  not  produce  any  blue  colour ;  neither 
is  that  colour  produced,  or  but  very  faintly,  on  addition  of  sulphuric  acid.  But 
if  chloride  of  tantalum  be  dissolved  in  strong  sulphuric  acid,  and  then  water  and 
metallic  zinc  added,  a  fine  blue  colour  is  produced,  which  does  not  change  to 
brown,  but  soon  disappears.  The  blue  colour  is  also  produced  on  placing  zinc  in 
a  solution  of  chloride  of  tantalum  in  hydrochloric  acid,  to  which  a  small  quantity 
of  water  has  been  added ;  too  much  water,  however,  prevents  its  formation. 

Before  the  blowpipe  tantalic  acid  dissolves  abundantly  in  phosphorus-salt, 
forming  a  clear,  colourless  glass,  which  undergoes  no  alteration  when  heated  in 
the  inner  flame,  and  does  not  turn  red  on  addition  of  protosulphate  of  iron.  With 
borax  also  it  forms  a  transparent  glass,  which,  however,  if  the  quantity  of  tantalic 
acid  is  somewhat  large,  may  be  rendered .  opaque  by  interrupted  blowing,  or 
flaming,  as  it  is  technically  called,  but  recovers  its  transparency  by  long  exposure 
to  a  continued  blast.  A  very  large  quantity  of  tantalic  acid  renders  the  glass 
opaque.  No  alteration  takes  place  in  the  inner  flame.  With  carbonate  of  soda 
on  charcoal,  tantalic  acid  produces  effervescence,  but  does  not  fuse  into  a  bead  or 
undergo  reduction. 

The  above-described  characters  are  sufficient  to  distinguish  tantalic  acid  from 
all  the  substances  previously  described.  From  titanic  acid,  which  it  most 


ESTIMATION    OF    TANTALUM.  569 

resembles,  it  is  distinguished,  first,  by  its  behaviour  before  the  blowpipe;  secondly, 
by  its  perfect  insolubility  in  strong  sulphuric  acid  after  ignition,  ignited  titanic 
acid,  when  finely  pulveriz^l,  being  soluble  in  that  acid;  and,  thirdly,  by  the  fact 
that,  when  it  is  fused  with  bisulphate  of  potash,  and  the  fused  mass  treated  with 
cold  water,  the  tautalic  acid  remains  undissolved  in  combination  with  sulphuric 
acid;  whereas  titanic  acid,  similarly  treated,  yields  a  fused  mass,  which  dissolves 
completely  in  a  considerable  quantity  of  cold  water,  provided  the  fusion  has  been 
continued  long  enough.  From  silica,  tantalic  acid  is  distinguished  by  its  behaviour 
before  the  blowpipe ;  silica  being  insoluble  in  phosphorus-salt,  and  fusing  to  a 
transparent  bead  when  heated  on  charcoal  with  a  small  quantity  of  carbonate  of 
soda.  The  behaviour  of  tantalic  acid  with  zinc,  with  tincture  of  galls,  and  with 
hydrofluoric  acid,  also  distinguishes  it  from  silica. 

Sulphide  of  tantalum,  Ta2S3. — Obtained  by  igniting  tantalic  acid  in  the  vapour 
of  bisulphide  of  carbon,  or  by  exposing  chloride  of  tantalum  to  the  action  of 
hydrosulphuric  acid  gas.  The  product  is  not  perfectly  definite  in  either  case. 
The  second  process  yields  a  sulphide  containing  24-08  per  cent,  sulphur,  whereas 
the  formula  Ta2S3,  requires  25.86  per  cent.  The  former  process  gives  a  product 
containing  28 -5  per  cent,  sulphur.  Sulphide  of  tantalum  is  a  black  substance, 
which  acquires  a  brass-yellow  colour  by  trituration  in  an  agate  mortar.  Heated  in 
an  atmosphere  of  chlorine  gas,  it  is  converted  into  chloride  of  tantalum  and  chlo- 
ride of  sulphur  (H.  Rose). 

Chloride  of  tantalum,  TaCl2.  — Prepared  by  passing  chlorine  gas  over  a  heated 
mixture  of  tantalic  acid  and  charcoal.  Tantalic  acid  is  mixed  with  starch  or  sugar, 
and  the  mixture  completely  charred  by  ignition  in  a  covered  crucible.  It  is  then 
introduced  in  small  pieces  into  a  glass  tube  which  is  strongly  heated  by  a  charcoal 
fire,  while  a  stream  of  dry  carbonic  acid  is  passed  through  it.  As  soon  as  all  the 
moisture  is  expelled,  the  tube  is  left  to  cool,  the  flow  of  carbonic  acid  being  still 
kept  up ;  the  carbonic  acid  apparatus  is  then  replaced  by  a  chlorine  apparatus, 
and  the  tube  again  heated  after  the  carbonic  acid  and  atmospheric  air  have  been 
completely  expelled  by  the  chlorine.  Chloride  of  tantalum  is  then  obtained  in 
the  form  of  a  sublimate  of  a  pure  yellow  colour.  If,  however,  the  tantalic  acid 
contains  tungstic  acid,  the  colour  of  the  sublimate  is  red;  and  if  stannic  or  titanic 
acid  is  present,  yellow  drops  of  liquid  chloride  are  also  produced.  Chloride  of  tan- 
talum melts  at  430°,  and  volatilizes  at  291°.  "Water  decomposes  it,  forming 
hydrochloric  and  tantalic  acids ;  but  the  decomposition  is  not  complete  even  at  the 
boiling  heat :  water  containing  a  small  quantity  of  ammonia  decomposes  the  chlo- 
ride perfectly  even  at  ordinary  temperatures.  According  to  the  recent  experiments 
of  H.  Rose,  chloride  of  tantalum  contains  81-14  per  cent,  of  tantalum. 

Bromide  of  tantalum  is  prepared  in  the  same  manner  as  the  chloride;  when 
freed  from  excess  of  bromine,  it  has  a  yellowish  colour. 

Fluoride  of  tantalum,  TaF2. — Ignited  tautalic  acid  does  not  dissolve  in  aqueous 
hydrochloric  acid ;  but  the  hydrate  dissolves,  forming  a  clear  solution,  which, 
when  evaporated,  partly  gives  off  the  tantalum  as  fluoride,  but  also  leaves  a  white 
residue  of  oxyfluoride.  Fluoride  of  tantalum  forms  with  fluoride  of  potassium  a 
crystalline  double  salt,  containing  KF.2TaF2;  and  with  fluoride  of  sodium  the 
salt,  NaF.TaF2  (H.  Rose). 

ESTIMATION   AND    SEPARATION    OF   TANTALUM. 

Tantalum  is  estimated  in  the  form  of  anhydrous  tantalic  acid,  containing  81-13 
per  cent,  of  the  metal.  It  occurs  in  nature  associated  with  lime,  magnesia,  yttria, 
and  the  oxides  of  iron  and  manganese,  and  occasionally  with  zirconia^  titanic  acid, 
and  a  few  other  substances.  From  these  it  is  separated  by  fusion  with  hydrate  of 
potash,  or,  better,  with  bisulphate  of  potash,  in  the  manner  already  described 
(567).  Some  compounds  of  tantalic  acid  may  be  decomposed  by  sulphuric  acid, 


570  COLUMBIUM. 

the  tantalic  acid  being  separated  in  the  insoluble  state,  and  all  the  bases  passing 
into  the  solution. 

Tantalate  of  zirconia  may  be  decomposed  in  this  Banner.  On  treating  that 
compound  with  strong  sulphuric  acid,  and  digesting  the  cooled  mass  for  some  time 
with  a  large  quantity  of  water,  sulphate  of  zirconia  dissolves,  and  tantalic  acid 
remains  behind  in  combination  with  sulphuric  acid,  from  which  it  may  be  purified 
by  repeated  boiling  with  water. 

From  titanic  acid,  with  which  it  sometimes  occurs  in  nature,  tantalic  acid  is 
separated  by  fusing  the  mineral  with  bisulphate  of  potash,  and  treating  the  fused 
mass  with  a  large  quantity  of  water.  Titanic  acid  then  dissolves,  especially  if  the 
water  is  slightly  acidulated  with  hydrochloric  acid,  while  sulphate  of  tantalic  acid 
remains  undissolved.  The  titanic  acid  is  precipitated  from  the  solution  by  boil- 
ing :  the  separation  is,  however,  not  very  complete.  In  some  cases,  the  decompo- 
sition may  be  effected  by  sulphuric  acid. 

From  the  alkalies,  tantalic  acid  may  be  completely  separated  by  sulphuric  acid, 
provided  the  compound  is  soluble  in  water.  In  the  contrary  case,  it  must  first  be 
fused  with  carbonate  or  hydrate  of  potash.  If,  however,  the  quantity  of  alkali  is 
to  be  likewise  estimated,  the  compound  must  be  rendered  soluble  by  fusion  with 
sulphate  of  ammonia.* 


SECTION  IX. 

COLUMBIUM. 

Synonyme.     Niobium;  Cb. 

This  metal  was  discovered  byHatchett  in  1801,  in  a  black  mineral  (columbite), 
from  Massachusetts,  in  North  America ;  it  was  thence  named  Columbium.  Wol- 
laston,  in  1809,  examined  it  further,  and  pronounced  it  to  be  identical  with  the 
tantalum  discovered  by  Ekeberg,  in  Swedish  tantalite.  This  idea  of  the  identity 
of  the  two  metals  remained  current  till  1846,  when  II.  Rose,")"  by  a  more  careful 
investigation  of  the  matter,  was  led  to  conclude  that  the  American  columbite,  and 
the  tantalite  from  Bodenmais,  in  Bavaria,  contained  two  acids  bearing  a  very  close 
resemblance  to  tantalic  acid,  but  nevertheless,  distinct  from  it  and  from  each  other. 
To  the  metals  supposed  to  exist  in  these  acids  he  assigned  the  names  Niobium 
and  Pelopium.  But  by  a  later  investigation^  he  finds  that  these  two  acids  really 
contain  the  same  metal,  associated  with  different  quantities  of  oxygen ;  he  there- 
fore discards  the  name  pelopium,  and  proposes  to  designate  by  niobium  the  metal 
contained  in  American  columbite  and  Bavarian  tantalite.  As,  however,  this  metal 
is  clearly  the  one  discovered  fifty  years  ago  by  Hatchett,  we  cannot  do  better  than 
retain  for  it  the  name  originally  proposed  by  its  discoverer,  viz.,  COLUMBIUM. § 

Columbium  likewise  occurs,  associated  with  yttrium,  uranium,  iron,  and  small 
quantities  of  other  metals,  in  a  Siberian  mineral  called  urano-tantalite,  yttro-ilme- 
nite,  or  samarskite;  also  in  pyrochlore,  eukolite  or  wohlerite,  euxenite,  and  in  a 
variety  of  pitchblende  from  Satersdalen 

Metallic  columbium  is  obtained  by  passing  dry  ammoniacal  gas  over  the  chlo- 
ride. It  is  a  black  powder,  which  oxidizes  when  heated  in  the  air.  Nitric  acid 
and  aqua-regia  have  no  effect  upon  it;  but  a  mixture  of  hydrofluoric  and  nitric 
acids  attacks  it  at  ordinary  temperatures.  It  combines  with  oxygen  in  two  pro- 
portions, forming  columbous  and  columbic  acids,  formerly  supposed  by  Rose  to 

*  H.  Rose,  Handb.  d.  Anal.  Chem.  1851,  ii.  326-335. 
f  Pogg.  Ann.  Ixiii.  317;  MX.  115. 
J  Pogg.  Ann.  xc.  456;  Ann.  Ch.  Pharm.  Ixxxviii.  245. 

|  See  a  paper  "  On  the  Nomenclature  of  the  Metals  contained  in  Columbite  and  Tanta- 
lite," by  Prof.  Connell,  Phil.  Mag.  [4]. 


CHLORIDES    OF    COLUMBIUM.  571 

contain  different  metals,  and  called  respectively  niobic  and  pelopic  acids.     The 
composition  of  these  acids  has  not  yet  been  determined. 

Columbous  acid,  or  a  mixture  of  that  acid  with  columbic  acid,  is  separated  from 
the  minerals  containing  it  by  processes  similar  to  those  already  described  for  the 
preparation  of  tantalic  acid  (p.  567) ;  and  when  the  acid,  or  mixture  of  acids,  thus 
obtained,  is  mixed  with  charcoal  and  heated  in  a  stream  of  chlorine  gas,  with  the 
precautions  already  detailed  for  the  preparation  of  chloride  of  tantalum  (p  570),  it 
is  generally  converted  into  two  chlorides,  —  the  one  white,  volatile,  but  not  fusi- 
ble ;  the  other  yellow,  likewise  volatile,  and  easily  fusible ;  the  latter  contains  the 
larger  proportion  of  chlorine.  It  was  the  formation  of  these  two  chlorides  which 
led  Rose  to  conclude  that  certain  varieties  of  tantalite  contained  two  distinct 
metals,  niobium  and  pelopium ;  he  now  finds,  however,  that  the  substance  which 
he  regarded  as  perfectly  pure  niobic  acid,  obtained  by  the  action  of  water  on  the 
white  chloride,  may,  by  mixing  it  with  a  large  excess  of  charcoal,  and  gently 
igniting  the  mixture  in  a  stream  of  chlorine  gas,  with  strict  attention  to  all  the 
precautions  above  alluded  to,  be  completely  converted  into  the  yellow  chloride,  — 
the  so-called  chloride  of  pelopium.  But  if  a  smaller  quantity  of  charcoal  be  used, 
or  if  the  mixture  be  too  strongly  ignited  during  the  action  of  the  chlorine,  espe- 
cially at  the  commencement,  the  white  and  less  volatile  chloride  (chloride  of 
niobium),  is  obtained,  as  well  as  the  yellow  compound. 

Columbium  appears,  then,  to  be  capable  of  uniting  with  chlorine  in  two  propor- 
tions ;  and  the  chlorides  thus  formed  yield,  when  treated  with  water,  two  acids  of 
corresponding  constitution,  viz.,  Columbous  and  Columbic  acids,  the  latter,  which 
contains  the  larger  proportion  of  oxygen,  being  formed  from  the  yellow  chloride. 

Columbous  acid  (Rose's  niobic  acid)  may,  like  tantalic  acid,  be  obtained  in  the 
amorphous  and  the  crystalline  state,  viz.,  by  the  rapid  or  gradual  action  of  water 
on  the  chloride.  Its  specific  gravity  is  lower  than  that  of  tantalic  acid,  and  is 
subject  to  similar  variations.  Samples  of  the  acid,  prepared  from  various  sources, 
exhibited,  after  ignition  over  a  spirit-lamp  to  the  point  of  incandescence,  specific 
gravities  ranging  from  4-66  to  5'26;  by  stronger  ignition,  the  density  was  dimin- 
ished. The  mean  density  of  the  amorphous  acid  was  found  to  be  greater  than 
that  of  the  crystalline  in  the  ratio  of  1  to  0-875.  The  acid  is  colourless  both  in 
the  anhydrous  and  hydrated  states,  but  when  heated  assumes  a  yellow  colour, 
much  deeper  than  that  of  heated  tantalic  acid.  The  hydrated  acid  becomes 
incandescent  during  its  transition  to  the  anhydrous  state. 

Columbous  acid  is  decomposed  by  ignition  in  a  stream  of  hydrosulphuric  acid, 
and  converted  into  sulphide  of  columbium.  When  ignited  in  ammoniacal  gas,  it 
turns  black,  and  yields  a  large  quantity  of  water. 

Columbous  acid,  after  ignition,  is  insoluble  in  all  acids.  The  hydrated  acid  is 
but  very  sparingly  soluble  in  hydrochloric  acid ;  so  that  when  an  alkaline  colum- 
bite  is  precipitated  by  excess  of  hydrochloric  acid,  the  filtrate  retains  only  a  trace 
of  columbous  acid  in  solution.  The  hydrated  acid  dissolves,  to  a  certain  extent, 
in  oxalic  and  in  hydrofluoric  acid. 

The  alkaline  columbites  are  soluble  in  water,  in  solutions  of  potash  and  carbo- 
nate of  potash,  but  dissolve  with  great  difficulty  in  excess  of  soda  and  carbonate 
of  soda,  more  sparingly  even  than  tantalate  of  soda.  Columbous  acid  is  precipi- 
tated from  Its  alkaline  solutions  by  acids,  especially  by  sulphuric  acid,  even  at 
ordinary  temperatures ;  whereas  the  precipitation  of  tantalic  acid  requires  the  aid 
of  heat.  Oxalic  acid  does  not  affect  alkaline  columbites ;  but  carbonic  acid  gas 
precipitates  an  acid  salt  soluble  in  a  large  quantity  of  water ;  acetic  acid  and  sal- 
ammoniac  also  form  precipitates.  A  solution  of  an  alkaline  columbite,  acidulated 
with  sulphuric  or  hydrochloric  acid,  forms  a  red  precipitate  with  ferrocyamde  of 
potassium,  bright  yellow  with  the  ferricyanide,  and  orange-red  with  infusion  of 
galls.  A  piece  of  zinc,  immersed  in  the  acidulated  solution,  forms  a  beautiful 
blue  precipitate,  which  after  a  while  changes  to  brown. 

Before  the  blowpipe,  especially  in  the  inner  flame,  columbous  acid  assumes  a 


572  COLUMBIUM. 

greenish  yellow  colour  while  hot,  but  becomes  colourless  on  cooling.  With  borax 
it  forms  in  the  outer  flame  a  colourless  bead,  which,  if  the  acid  is  in  sufficient 
quantity,  becomes  opaque  by  flaming.  In  the  inner  flame,  the  bead  assumes  a 
greyish  blue  colour,  provided  it  contains  a  sufficient  quantity  of  acid  to  produce 
opacity  on  cooling.  In  phosphorus-salt,  the  acid  dissolves  in  large  quantity, 
forming  a  colourless  bead  in  the  outer  flame,  and  in  the  inner,  a  violet-coloured, 
or,  if  the  bead  be  saturated  with  the  acid,  a  beautiful  blue  bead,  the  colour  disap- 
pearing in  the  outer  flame.  The  addition  of  protosulphate  of  iron  changes  the 
colour  to  blood-red.  These  characters,  together  with  the  above-mentioned  precipi- 
tates, sufficiently  distinguish  columbous  from  tantalic  acid. 

Columbic  acid  (Rose's  pelopic  acid)  bears  a  very  strong  resemblance  to  tantalic 
acid,  and  is  intermediate  in  its  properties  between  that  acid  and  columbic  acid. 
Its  specific  gravity  ranges  from  5*5  to  6-7.  It  appears  to  be  susceptible  of  three 
modifications;  viz.,  amorphous,  crystalline  before  ignition,  and  crystalline  after 
ignition  at  the  heat  of  a  porcelain-furnace.  It  is  insoluble  in  all  acids  after  igni- 
tion. It  is  precipitated  from  its  alkaline  solutions  by  the  same  reagents  as  colum- 
bous acid.  The  precipitate  formed  by  hydrochloric  acid  redissolves  in  excess, 
forming  an  opalescent  solution  from  which  the  acid  is  completely  precipitated  by 
sulphuric  acid  at  a  boiling  heat.  The  acidulated  solutions  yield  a  brownish-red 
precipitate  with  ferrocyanide  of  potassium,  white  with  ferricyanide,  and  orange- 
yellow  with  infusion  of  galls.  Zinc  behaves  with  these  solutions  in  the  same 
manner  as  with  solutions  of  tantalic  acid.  A  fine  blue  colour  is  obtained  by  treat- 
ing the  yellow  chloride  of  columbium  with  hydrochloric  acid,  diluting  with  water, 
and  adding  a  piece  of  zinc. 

With  borax  before  the  blowpipe,  columbic  acid  behaves  like  tantalic  acid.  In 
phosphorus-salt  it  dissolves  in  large  quantity,  forming  a  colourless  bead  in  the 
outer  flame.  In  the  inner  flame,  the  bead  assumes  a  light-brown  colour,  tinged 
with  violet,  the  colour  disappearing  again  after  a  while  in  the  outer  flame.  The 
addition  of  protosulphate  of  iron  changes  the  brown  colour  to  crimson. 

It  is  remarkable  that  columbic  acid  cannot  be  formed  directly  from  columbous 
acid,  even  by  the  most  powerful  oxidizing  agents.  It  appears,  however,  to  be 
deprived  of  a  portion  of  its  oxygen  by  certain  reducing  agents. 

The  methods  of  estimating  columbium  and  separating  it  from  other  metals  are 
the  same  as  for  tantalum.  No  method  is  known  of  separating  columbium  from 
tantalum ;  but  these  metals  have  not  hitherto  been  found  occurring  together. 


Rmenium.(p) — According  to  the  observations  of  R.  Hermann,*  it  would  appear 
that  Siberian  yttrotantalite  or  yttroilmenite  contains  a  peculiar  metal,  ilmenium, 
which  forms  an  acid,  ilmenic  acid,  very  closely  resembling  columbous  acid,  but 
nevertheless  distinct  from  it ;  the  chief  points  of  difference  being  the  lower  specific 
gravity,  viz.,  4-1  to  4-2;  the  insolubility  of  the  hydrate  in  hydrochloric  acid;  and 
the  formation  of  a  compound  with  sulphuric  acid  which  is  decomposed  by  a  large 
quantity  of  water,  leaving  a  residue  of  hydrated  ilmenic  acid.  H.  Rose,f  however, 
is  of  opinion  that  the  supposed  ilmenic  acid  is  merely  columbous  [niobic]  acid, 
more  or  less  impure.  The  question  must,  for  the  present,  be  regarded  as  unde- 
cided. Rose  likewise  regards  yttroilmenite  as  identical  with  urano-tantalite  or 
.sainarskite. 

*  J..pr.  Chem.  xxxviii.  91,  119;  xl.  475;  Ixv.  54.  f  Pogg.  Ann.  Ixxi.  157. 


MERCURY. 


573 


ORDER  VIII. 

METALS  WHOSE  OXIDES  ARE  REDUCED  TO  THE  METALLIC  STATE  BY  HEAT, 

(NOBLE  METALS). 

SECTION  I. 

MERCURY. 

Eq.  100  or  1250;  Hg. 

Mercury,  or  quicksilver,  as  it  is  named  from  its  fluidity,  has  been  known  from 
all  antiquity.  It  is  found  to  a  small  extent  in  the  metallic  state,  but  its  principal 
ore  is  the  native  sulphide,  cinnabar.  The  most  valuable  European  mines  of  mer- 
cury are,  those  of  Almaden  in  Spain,  and  of  Idria  in  Illyria.  At  Almaden  the 
cinnabar  is  found  in  veins,  often  nearly  fifty  feet  thick,  traversing  micaceous 
schists  of  the  older  transition  period :  in  Illyria  it  is  disseminated  in  beds  of  grit, 
bituminous  schist,  or  compact  limestone  of  more  recent  date.  The  mode  of  ex- 
traction in  both  these  localities,  consists  in  simply  roasting  the  ore  in  a  distillatory 
apparatus,  whereby  the  sulphur  is  burned  and  converted  into  sulphurous  acid, 
while  the  mercury  is  set  free  in  the  form  of  vapour,  and  condenses  in  chambers 
or  vessels  provided  for  it. 

The  arrangement  adopted  in  Illyria  is  represented  in  figures  197, 198, 199.  A  is 
a  large  furnace  (figs.  197  and  199),  on  each  side  of  which  is  a  series  of  condensing 

.  FIG.  197. 


Fro.  198. 


d' 


574 


MERCURY. 
Fia.  199. 


chambers,  C  C  C  C  C  D.  The  space  Y,  separated  from  the  fire-place  by  tbe  perforated 
arch  n  n',  is  filled  with  the  ore  in  large  lumps  ;  smaller  pieces  are  introduced  into 
the  next  compartment  above  the  archpp';  and  on  the  uppermost  arch,  r  /,  are 
laid  a  number  of  earthen  capsules,  containing  the  pulverized  ore  and  the  mer- 
curial residues  of  preceding  operations.  The  fire  being  lighted,  and  the  heat 
gradually  raised,  the  sulphur  is  burned  by  the  air  which  enters  through  channels 
opening  into  the  spaces  G,  H  j  and  the  mixture  of  mercurial  vapour,  sulphurous 
acid,  and  smoke  from  the  fire,  passes  through  the  horizontal  channel  at  the  top  of 
the  furnace,  then  up  and  down  through  the  condensing  chambers,  C  C  C  C,  and 
finally  escapes  into  the  air. 

The  greater  part  of  the  mercury  condenses  in  the  first  three  chambers,  whence 
it  runs  into  the  channels  a  b  c  d,  a'  br  cr  df,  which  conduct  it  into  a  reservoir.  To 
facilitate  the  condensation  of  the  last  portions  of  mercury  in  the  chambers  D  D, 
the  vapours  are  made  to  pass  between  a  series  of  boards  placed  from  side  to  side 
of  these  chambers  in  an  inclined  position,  and  having  a  stream  of  water  con- 
tinually running  over  them.  As  the  mercury  which  condenses  in  these  last 
chambers  is  mixed  with  a  considerable  quantity  of  dust,  it  is  collected  in  separate 
channels,  then  filtered,  and  the  residues  returned  to  the  furnace  as  already 
described. 

The  mercury  obtained  by  this  process  is  purified  by  filtratation  through  coarse 
linen  cloth,  and  sent  into  the  market  in  wrought-iron  bottles,  each  containing 
about  fifty  pounds. 

At  Almaden,  the  mercury  is  also  extracted  from  the  cinnabar  by  roasting,  the 
operation  being  conducted  in  furnaces  called  buytrones.  (Figs.  200  and  201.) 


FIG.  200. 


PURIFICATION    OF    MERCURY. 
FIG.  201. 


575 


Fm.  203. 


The  fire  is  made  at  A,  and  the  space  B,  above  it,  is  filled  with  the  ore,  the 
largest  pieces  being  laid  on  the  perforated  arch  at  the  bottom,  smaller  pieces 
above,  and  the  whole  covered  with  lumps  of  a  mixture  of  clay,  powdered  ore,  arid 
the  residues  of  preceding  operations.  The  vapours  pass  through  an  aperture  p, 
in  the  upper  part  of  the  furnace,  into  a  series  of  tubular  vessels  called  aludeh, 
open  at  both  ends  and  fitting  one  into  the  other.  These  are  laid  on  a  surface 
<•,  6,  a,  called  the  aludel-bath,  first  descending  a 
little,  then  ascending,  and  finally  opening  into  pIG  202 

the  chimney.  The  form  and  disposition  of  the 
aludels  is  shown  in  figure  202.  The  condensed 
mercury  escapes  at  the  joints  of  the  aludels,  and 
runs  into  the  channel  b  b,  by  which  it  is  con- 
veyed into  the  reservoirs  m,  n  n.  The  uncondensed  mercurial  vapour  passes  into 
the  chamber  E,  where  it  deposits  a  mercurial  dust,  which  yields  by  filtration  an 
additional  quantity  of  liquid  mercury,  and  a 
residue  which  is  mixed  with  clay  and 
pounded  ore,  and  returned  to  the  furnace  in 
the  manner  above  mentioned.  The  heating 
of  the  furnace  is  continued  for  twelve  or 
thirteen  hours:  it  is  then  left  to  cool  for 
three  or  four  days,  after  which  it  is  cleared 
out  and  arranged  for  another  operation. 

In  the  duchy  of  Deux  Fonts,  a  mixture 
of  cinnabar  and  limestone  is  heated  to  red- 
ness in  retorts  of  earthenware  or  cast-iron, 
placed  side  by  side  in  an  oblong  furnace 
(fig.  203),  and  provided  with  receivers  con- 
taining a  certain  quantity  of  water.  Sul- 
phide of  calcium  and  sulphate  of  lime  are 
then  formed,  and  the  mercury  is  evolved  in 
vapour,  which  condenses  in  the  receivers. 

At  Horzowitz,  in  Bohemia,  a  mixture  of  cinnabar  and  smithy-scales  is  placed 
in  iron  dishes,  which  are  attached  one  above  the  other  by  the  centres  of  their 
bases  to  a  vertical  iron  axis,  and  covered  with  an  iron  receiver,  closed  at  top  and 
dipping  into  water  at  the  bottom.  The  upper  part  of  the  receiver  is  surrounded 
by  the  furnace,  and  imparts  its  heat  to  the  dishes,  from  which  the  mercury  rises 
in  vapour  and  collects  in  the  water  below. 

The  mercury  of  commerce  is  generally  very  pure ;  it  is  sometimes,  however, 
contaminated  with  foreign  metals,  and  in  that  case  its  fluidity  is  remarkably 
impaired. 

Mercury  may  be  purified  by  distilling  it  from  half  its  weight  of  iron-turnings, 
or  by  digesting  it  with  a  small  quantity  of  nitric  acid,  or  with  a  solution  of  corro- 
sive sublimate,  which  rids  it  of  metals  more  oxidable  than  itself.  The  purification 
may  also  be  effected  by  agitating  the  mercury  with  a  small  quantity  of  solution 
of  sesquichloride  of  iron.  Pure  mercury  should  leave  no  residue  when  dissolved 


576  MERCURY. 

in  nitric  acH,  evaporated,  and  ignited;  when  made  to  run  down  a  slightly  inclined 
surface,  it  should  retain  its  round  form,  and  not  drag  a.  tail;  and  when  agitated 
in  a  bottle  with  dry  air,  it  should  not  yield  any  black  powder. 

Mercury  is  liquid  at  ordinary  temperatures.  Its  colour  is  white,  with  a  shade 
of  blue  when  compared  with  that  of  silver,  and  it  has  a  high  metallic  lustre.  At 
39°  or  40°  below  zero,  it  becomes  solid,  and  crystallizes  in  regular  octahedrons. 
According  to  M.  Kupffer,  the  density  of  mercury  at  39-2°  is  13.5886;  at  62.6°, 
13-5569;  and  at  78-8°,  13-535  (according  to  Kopp,  it  is  13-595  at  39-2°).  In 
the  solid  state,  its  density  is  about  14-0.  Mercury  boils  at  662°,  forming  a 
colourless  vapour,  the  density  of  which  was  observed,  by  Durnas,  to  be  6976 ;  the 
theoretical  density  is  6930.  Mercury  emits  a  sensible  vapour  between  68°  and 
80°,  but  not  under  20°  (Faraday).  When  heated  near  its  boiling  point,  mercury 
absorbs  oxygen  from  the  air,  and  forms  crystalline  scales  of  the  red  oxide.  It  is 
not  affected  by  boiling  hydrochloric  or  dilute  sulphuric  acid,  but  is  readily  dis- 
solved by  dilute  nitric  acid.  This  metal  never  dissolves  in  hydrated  acids  by  sub- 
stitution for  hydrogen.  Mercury  combines  with  oxygen  in  two  proportions, 
forming  the  black  oxide,  Hg20,  and  the  red  oxide,  composed  of  single  equivalents, 
HgO,  both  of  which  are  bases.  According  to  these  formulae,  the  equivalent  of 
mercury  is  assumed  to  be  100 ;  but  whether  it  should  be  this  number  or  a  multiple 
of  it  by  2,  no  certain  means  exist  of  deciding,  while  we  are  in  ignorance  of  any 
isomorphous  relation  of  mercury  with  the  magnesian  metals. 

MERCUROUS   COMPOUNDS. 

Dioxide  of  mercury  (black  oxide),  Mercurous  oxide,  Hg20,  208  or  2600.  — 
This  oxide  is  obtained  by  the  action  of  a  cold  solution  of  potash,  used  in  excess, 
upon  calomel.  The  substances  should  be  mixed  briskly  together  in  a  mortar,  in 
order  that  the  decomposition  may  be  as  rapid  as  possible,  and  the  oxide  be  left  to 
dry  spontaneously  in  a  dark  place.  Mr.  Donovan  finds  these  precautions  neces- 
sary, from  the  disposition  of  this  oxide  to  resolve  itself  into  metallic  mercury  and 
the  higher  oxide.  The  decomposition  of  mercurous  oxide  is  promoted  by  eleva- 
tion of  temperature,  and  by  exposure  to  light. 

Mercurous  oxide  is  a  black  powder,  whose  density  is  10-69  (J.  Hera  path);  it 
unites  with  acids  and  forms  salts.  Its  soluble  salts  are  all  partially  decomposed 
by  pure  water,  which  combines  with  a  portion  of  their  acid,  and  throws  down  a 
subsalt  containing  an  excess  of  oxide.  They  are  precipitated  black  by  hydrosul- 
phuric  acid  and  alkaline  sulphides.  Caustic  alkalies  throw  down  a  black  pre- 
cipitate of  mercurous  oxide.  The  alkaline  carbonates  precipitate  white  mercurous 
carbonate,  which  soon  turns  black  from  decomposition.  Carbonate  of  baryta  also 
decomposes  mercurous  salts,  forming  a  mercuric  salt,  which  remains  in  solution, 
and  a  precipitate  of  metallic  mercury.  Mercurous  salts  are  decomposed  by  hydro- 
chloric acid  and  soluble  chlorides,  with  precipitation  of  calomel  as  a  white  powder, 
a  property  by  which  they  are  distinguished  from  the  salts  of  the  red  oxide  of 
mercury.  In  very  dilute  solutions,  only  an  opalescence  is  produced.  The  pre- 
cipitate turns  black  when  treated  with  potash  or  ammonia.  Mercurous  salts  form 
with  phosphate  of  soda  a  white  precipitate  of  mercurous  phosphate,  and  with 
alkaline  chromates,  a  brick-red  precipitate  of  mercurous  chromate.  Oxalic  acid 
and  alkaline  oxalates  form  a  white  precipitate  of  mercurous  oxalate.  Ferrocyanide 
of  potassium  produces  a  thick  white  precipitate,  and  ferricyanide  of  potassium  a 
red-brown  precipitate.  Tincture  of  galls  yields  a  brownish-yellow  precipitate. 

The  salts  of  this,  and  also  of  the  red  oxide,  are  reduced  to  the  metallic  state 
by  copper  and  the  more  oxidable  metals,  and  by  the  proto-com pounds  of  tin ;  also  by 
phosphorous  and  sulphurous  acids.  The  precipitated  mercury  often  takes  the  form 
of  a  grey  powder,  in  which  no  metallic  globules  are  perceptible,  and  remains  in 
this  condition  while  moist.  Mercury  in  this  divided  state  possesses  the  medicinal 
qualities  of  the  milder  mercurials,  and  has  often  been  mistaken  for  black  oxide. 


MERCUROUS  COMPOUNDS.  57T 

To  obtain  precipitated  mercury,  equal  weights  of  crystallized  protochloride  of  tin 
(salt  of  tin)  and  corrosive  sublimate  may  be  dissolved,  the  first  in  dilute  hydro- 
chloric acid  and  the  second  in  hot  water,  and  the  solutions  mixed,  with  stirring. 
The  salt  of  tin  takes  up  all  the  chlorine  of  the  corrosive  sublimate,  becoming 
bichloride  of  tin,  which  remains  in  solution,  while  the  mercury  is  liberated,  and 
forms  so  fine  a  precipitate,  that  it  requires  several  hours  to  subside.  It  may  be 
washed  by  aifusion  of  hot  water  and  subsidence,  and  slightly  drained  on  a  filter, 
but  not  allowed  to  dry.  There  can  be  no  doubt  that  it  is  in  this  divided  state, 
and  not  as  the  black  oxide,  that  mercury  is  obtained  by  trituration  with  fat,  tur- 
pentine, syrup,  saliva,  &c.,  in  many  pharmaceutical  preparations. 

Bisulphide  of  mercury,  Hg2S,  is  obtained,  as  a  black  precipitate,  by  the  action 
of  hydrosulphuric  acid  on  a  solution  of  mercurous  nitrate  or  upon  calomel.  This 
sulphide  is  decomposed  by  a  gentle  heat,  and  resolved  into  globules  of  mercury 
and  the  higher  sulphide. 

Dichloride  of  mercury,  Mercurous  chloride,  Calomel,  Hg2Cl,  235f5  or  2943-75. 
—  A  variety  of  processes  are  given  for  the  preparation  of  this  remarkable  sub- 
stance. It  may  be  obtained  in  the  humid  way,  by  digesting  1|  parts  of  mercury 
with  1  part  of  pure  nitric  acid,  of  density  from  1-2  to  1-25,  till  the  metal  ceases 
to  dissolve,  and  the  liquid  has  begun  to  assume  a  yellow  tint.  A  solution  is  also 
prepared  of  1  part  of  chloride  of  sodium  in  32  parts  of  distilled  water,  to  which 
a  certain  quantity  of  hydrochloric  acid  is  added ;  and  this,  when  heated  to  near 
the  boiling  point,  is  mixed  with  the  mercurial  salt.  The  mercury  takes  up  the 
chlorine  of  the  common  salt,  and  the  subchloride  of  mercury  formed  precipitates 
as  a  white  powder,  while  the  nitric  acid  and  oxygen  are  given  up  by  the  mercury 
to  the  sodium,  which  becomes  nitrate  of  soda : 

NaCl-f  Hg2O.N05  =  Hg2Cl  +  NaO.N03. 

The  excess  of  acid  in  this  process  is  intended  to  prevent  the  precipitation  of  any 
subnitrate  of  mercury,  which  the  dilution  of  the  nitrate  of  mercury,  on  mixing 
the  solutions,  might  occasion.  Calomel  is  also  obtained  by  rubbing  together,  in  a 
mortar,  4  parts  of  protochloride  of  mercury  (corrosive  sublimate)  with  3  parts  of 
running  mercury.  The  mixture  is  afterwards  introduced  into  a  glass  balloon,  and 
sublimed  by  a  heat  gradually  increased.  Here  the  protochloride  of  mercury  com- 
bines with  mercury,  and  the  dichloride  is  produced.  The  same  result  is  obtained 
by  mixing  mercuric  sulphate  with  as  much  mercury  as  it  already  contains,  and 
about  one-third  of  its  weight  of  chloride  of  sodium,  and  subliming  the  mixture. 
The  vapour  of  the  dichloride  of  mercury,  in  these  sublimations,  is  advantageously 
condensed  by  conducting  it  into  a  vessel  containing  hot  water;  the  vapour  of  the 
water  then  condenses  the  salt  in  an  extremely  fine  and  beautifully  white  powder. 
The  product  of  this  operation  is  recommended  by  its  purity,  as  well  as  by  its 
minute  division ;  for  the  water  dissolves  out  all  the  protochloride  of  mercury  by 
which  the  dichloride  is  accompanied.  It  appears  that  whenever  the  dichloride  is 
sublimed,  a  small  portion  of  it  is  resolved  into  mercury  and  the  protochloride. 
As  the  calomel  usually  condenses  in  a  solid  cake,  it  must,  to  prepare  it  for  medi- 
cal use,  be  reduced  to  a  fine  powder,  and  washed  with  hot  water  to  remove  the 
soluble  chloride. 

Dichloride  of  mercury  is  obtained  by  sublimation,  in  four-sided  prisms,  termi- 
nated by  summits  of  four  faces.  When  the  solid  cake  is  finely  pounded,  the  salt 
acquires  a  yellow  tinge.  The  density  of  this  salt  in  the  solid  condition  is  6-5;  in 
the  state  of  vapour  8350.  One  volume  of  the  vapour  contains  one  volume  of 
vapour  of  mercury  and  half  a  volume  of  chlorine.  This  salt  is  so  very  sparingly 
soluble  in  water,  that  when  mercurous  nitrate  is  added  to  hydrochloric  acid 
diluted  even  with  250,000  times  its  weight  of  water,  a  sensible  precipitate  of 
dichloride  of  mercury  appears.  When  boiled  for  a  long  time  in  hydrochloric 
acid,  this  salt  is  resolved  into  protochloride  of  mercury  which  dissolves,  and  mer- 
cury which  is  reduced. 
37 


578  MERCURY. 

Action  of  ammonia  on  dichloride  of  mercury.  —  The  dry  dichloride  was  foun.l 
by  Rose  to  absorb  an  equivalent  of  ammonia,  and  to  become  black.  Exposed  to 
air,  the  compound  loses  its  ammonia,  and  the  dichloride  of  mercury  recovers  its 
white  colour.  This  ammoniacal  compound  is  Hg2Cl.NH3,  and  may  be  regarded  as 

as  ^chloride  °f  mercury  in  which  1  eq.  of  mercury  is  re- 
placed by  mercurammonium,  NH3Hg.  Or  again,  if  we  suppose  the  mercurous 
salts  to  contain,  not  two  distinct  atoms,  but  a  double  atom  of  mercury  (Hg'  =  Hs:2)j 
this  double  atom  being  the  equivalent  of  one  atom  of  hydrogen — thus,  calomel  = 
Hg'Cl;  black  oxide  of  mercury  =  Hg'O,  &c.,  —  then  the  ammoniacal  compound, 

Hg2Cl.NH3  may  be  regarded  as  chloride  of  mercurosammonium,  NH3Hg'.Cl,  or 
chloride  of  ammonium  in  which  one  eq.  H  is  replaced  by  a  double  atom  of  mer- 
cury. 

When  calomel  is  digested  in  aqueous  ammonia,  it  turns  black,  and  was  found 
by  Kane  to  be  converted  into  mercurous  amido-chloride,  Hg2Cl.Hg2NH2,  sal-am- 
inoniac  being  formed  at  the  same  time  : 

2Hg2Cl  +  2NH3  =  Hg2Cl.Hg2NH2  +  NH4C1. 
This    compound   may  also   be   regarded   as   chloride  of  bimercurosammonhim, 

NH2Hg'2.Cl.  It  is  not  altered  by  boiling  water;  when  quite  dry,  it  is  of  a  grey 
colour. 

Dibromide  of  mercury,  Mercurous  bromide,  Hg2Br,  is  a  white  insoluble  powder, 
resembling  in  all  respects  the  dichloride,  and  formed  in  similar  circumstances.  A 
boiling  solution  of  bromide  of  strontium  was  found  by  Loewig  to  dissolve  three 
equivalents  of  dibromide  of  mercury,  of  which  one  equivalent  precipitated  during 
the  cooling  of  the  solution.  When  the  filtered  solution  was  evaporated,  it  de- 
posited a  salt  in  small  crystals,  containing  SrBr.2Hg2Br.  These  crystals  were 
decomposed  by  pure  water,  and  resolved  into  the  insoluble  dibromide,  Hg2Br, 
and  a  double  salt,  SrBr.Hg2Br,  which  dissolved  easily,  and  crystallized  by  evapo- 
ration. 

Diniodide  of  mercury,  Mercurous  iodide,  Hg2I,  is  obtained  by  precipitation  as 
a  green  powder,  which  is  red  when  heated.  It  is  also  formed  by  triturating  mer- 
cury and  iodine  together  in  a  mortar,  with  a  few  drops  of  alcohol,  in  the  propor- 
tion of  2  eq.  of  the  former  to  1  eq.  of  the  latter. 

No  dicyanide  of  mercury  exists ;  and  it  is  doubtful  whether  a  di fluoride,  cor- 
responding with  the  dioxide,  has  been  formed. 

Mercurous  carbonate,  Carbonate  of  black  oxide  of  mercury,  Hg02  C02,  pre- 
cipitates as  a  white  powder,  when  an  alkaline  carbonate  is  added  to  the  nitrate  of 
the  same  oxide.  The  precipitate  becomes  grey  when  the  liquid  containing  it  is 
boiled,  and  carbonic  acid  escapes.  This  carbonate  is  soluble  both  in  carbonic  acid 
water,  and,  to  a  slight  extent,  in  an  excess  of  alkaline  carbonate. 

Mercurous  sulphate,  Sulphate  of  black  oxide  of  mercury,  Hg2O.S03;  248  or 
3100. — This  salt  is  obtained  by  digesting  1  part  of  mercury  in  1J  parts  of  sul- 
phuric acid,  avoiding  a  high  temperature,  and  interrupting  the  process  as  soon  as 
all  the  mercury  is  converted  into  a  white  salt.  It  is  also  precipitated  when  sul- 
phuric acid  is  added  to  a  solution  of  mercurous  nitrate.  The  salt  may  be  washed 
with  a  little  cold  water.  It  crystallizes  in  prisms,  and  requires  500  times  its 
weight  of  cold  and  300  of  hot  water  to  dissolve  it.  With  aqueous  ammonia  this 
salt  forms  a  dark  grey  powder,  containing  ammonia  or  its  elements. 

Mercurous  selenia.te.  —  Aqueous  solutions  of  seleniate  of  soda  and  mercurous 
nitrate  form  a  white  precipitate,  probably  consisting  of  the  neutral  salt,  Hg^O.SeOg, 
which,  however,  gradually  turns  yellow'during  washing,  and,  when  dried  at  100°, 
is  found  to  be  reduced  to  6Hg20.5Se03  (Korner). 


MERCURIC    COMPOUNDS.  579 

Mercurous  selenite.  —  The  neutral  salt  Hg2O.SeO2  is  found  native  as  onofrite,  a 
yellow  earthy  mineral,  occurring,  together  with  horn-quicksilver  and  native  mer- 
cury, at  San  Onofrio,  in  Mexico.  It  is  also  obtained  by  double  decomposition  as 
a  white  powder,  which  melts  at  356°,  and  when  heated  above  that  point,  is 
converted  into  a  brick-red,  opaque,  crystalline  mass  of  the  salt,  3Hg20.4SeOz, 
(Kohler).* 

Mercurous  nitrates,  Nitrates  of  black  oxide  of  mercury.  — The  neutral  nitrate 
is  obtained  when  mercury  is  dissolved  in  an  excess  of  cold  nitric  acid :  it  crys- 
tallizes readily  in  transparent  rhombs.  It  is  soluble  with  heat  in  a  small  quantity 
of  water,  but  is  decomposed  by  a  large  quantity  of  water,  and  an  insoluble  sub- 
salt  formed,  unless  nitric  acid  be  added  to  the  water.  The  formula  of  this  salt  is 
Hg2O.N05  +  2HO.  A  subnitrate  is  formed  when  the  black  oxide  is  dissolved  in 
a  solution  of  the  preceding  salt,  or  when  an  excess  of  mercury  is  digested  in 
diluted  nitric  acid  at  the  usual  temperature.  It  crystallizes  readily  in  white, 
opaque  rhombic  prisms,  which  contain,  according  to  both  Gr.  Mitscherlich  and 
Kane,  3Hg20.2N05  +  3HO;  or,  according  to  Marignac,  4Hg20.3N03  -f  HO. 
This  salt  was  observed  by  Gr.  Mitscherlich  to  be  dimorphous.  When  dissolved  by 
dilute  nitric  acid,  it  yields  the  neutral  salt.  The  subnitrate  is  soluble  in  a  little 
water,  but  when  treated  with  a  large  quantity,  it  leaves  undissolved,  like  the  neu- 
tral nitrate,  a  white  powder,  which  retains  its  colour  so  long  as  the  supernatant 
liquid  is  acid,  but  becomes  yellow  when  washed  with  water.  The  yellow  su~b~ 
nitrate  of  mercury  was  found  to  contain  2Hg2O.N05  -f  HO  (Kane).  Another 
subnitrate,  containing,  according  to  Marignac,  5Hg20.3N05  +  2HO,  is  obtained 
by  boiling  the  solution  or  the  mother-liquor  of  the  neutral  or  the  sesquibasic 
nitrate  with  excess  of  mercury  for  several  hours.  This  salt  crystallizes  in  colour- 
less or  slightly  yellow  crystals,  derived  from  an  unsymmetrical  oblique  prism ;  it 
appears  to  be  the  most  stable  of  all  the  mercurous  subnitrates.  When  very  dilute 
ammonia  is  added  to  the  preceding  soluble  nitrates,  without  neutralizing  the  whole 
acid,  a  velvety  black  precipitate  falls,  known  as  Hahnemann's  soluble  mercury. 
This  salt  contains,  according  to  the  analysis  of  C.  Gr.  Mitscherlich,  3Hg2O.N05  + 
NH3.  But  when  pains  were  taken  to  avoid  decomposition  of  the  salt  in  washing 
it,  its  composition  was  found  by  Kane  to  be  2Hg2O.N05  -f  NH3.  Bibasic  mer- 
curous nitrate,  mixed  in  solution  with  nitrate  of  lead,  yields  a  crystalline  double 
salt,  containing  2(PbO.NOs)  +  2Hg2O.N05;  and  similar  double  salts  with  the 
nitrates  of  baryta  and  strontia  (Gr.  Staedeler). 

Mercurous  acetate,  Hg2O.C4H303,  falls  when  acetic  acid,  or  an  acetate,  is  added 
to  the  nitrate,  in  crystalline  scales  of  a  pearly  lustre.  It  is  anhydrous,  and 
sparingly  soluble  in  water. 

MERCURIC   COMPOUNDS. 

Protoxide  of  mercury  (red  oxide},  Mercuric  oxide,  HgO,  108  or  1351. — This 
compound  is  formed,  as  described,  by  the  oxidation  of  mercury  at  a  high  tempera- 
ture, or  by  heating  the  nitrate  of  mercury  till  all  the  nitric  acid  is  expelled,  and 
the  mass,  calcined  almost  to  redness,  no  longer  emits  vapours  of  nitric  oxide.  As 
prepared  by  the  latter  process,  protoxide  of  mercury  forms  a  brilliant  orange-red 
powder,  crystallized  in  plates,  and  having  the  density  11-074.  It  is  very  dark 
red  at  a  high  temperature,  but  becomes  paler  as  it  cools.  When  reduced  to  a  fine 
powder,  it  becomes  yellow,  like  litharge,  without  any  shade  of  red.  It  was  found 
by  Mr.  Donovan  to  be  soluble  to  a  small  extent  in  water,  forming  a  solution  which 
has  a  slight  alkaline  reaction.  If  contaminated  with  nitric  acid,  it  gives  off  nitrous 
fumes  when  heated  in  a  glass  tube,  and  forms  a  yellow  sublimate  of  subnitrate. 
This  oxide  is  known  in  pharmacy  as  red  precipitate.  The  same  compound  is  ob- 
tained by  precipitation,  when  a  solution  of  corrosive  sublimate  is  mixed  with  an 

*  Pogg.  Ann.  Ixxxix.  146. 


580  MERCURY. 

excess  of  caustic  potash ;  it  then  forms  a  dense  powder  of  a  lemon-yellow  colour. 
It  is  necessary  to  use  the  potash  in  excess,  otherwise  a  dark  brown  oxychloride  is 
formed.  The  precipitated  oxide  parts  with  a  little  moisture  when  gently  heated, 
but  does  not  change  in  appearance.  This  yellow  precipitated  oxide  differs  in  some 
respects  from  the  red  oxide ;  it  combines  in  the  cold  with  oxalic  acid,  whereas  the 
red  oxide  does  not ;  it  is  converted  into  black  oxychloride  by  the  action  of  an 
alcoholic  solution  of  mercuric  chloride,  which  has  no  action  on  the  red  oxide,  and 
it  is  attacked  by  chlorine  much  more  readily  than  the  latter.  At  a  red  heat,  the 
oxide  of  mercury  is  entirely  volatilized  in  the  form  of  oxygen  and  metallic  mer- 
cury ;  the  same  decomposition  takes  place  more  slowly  under  the  influence  of 
light.  The  oxide  detonates  when  heated  with  sulphur,  and  converts  chlorine  into 
hypochlorous  acid. 

The  salts  of  mercuric  oxide,  when  they  do  not  contain  a  coloured  acid,  are 
colourless  in  the  neutral,  and  yellow  in  the  basic  state.  They  have  a  disagreeable 
metallic  taste,  and  act  as  violent  acrid  poisons.  Some  of  them,  e.  g.,  the  nitrate 
and  sulphate,  are  resolved  by  water  into  a  soluble  acid  salt,  and  an  insoluble  basic 
salt.  From  their  aqueous  solutions  the  mercury  is,  for  the  most  part,  precipitated 
in  the  metallic  state  by  the  same  substances  as  from  mercurous  salts ;  but  the  com- 
plete reduction  of  the  mercury  is  often  preceded  by  the  formation  of  a  mercurous 
salt :  such,  for  example,  is  the  action  of  phosphorous  acid,  sulphurous  acid,  proto- 
chloride  of  tin,  metallic  copper,  &c.  Gold  does  not  by  itself  reduce  mercury 
from  its  salts ;  but  if  a  drop  of  a  mercuric  solution  be  laid  on  a  piece  of  gold, 
and  a  bar  of  zinc,  tin,  or  iron  be  brought  in  contact  with  the  moistened  surface, 
an  electrolytic  action  is  set  up,  and  the  gold  becomes  amalgamated  at  the  point  of 
contact.  Hydrosulphuric  acid  and  alkaline  sulphides,  added  in  excess  to  mer- 
curic salts,  throw  down  a  black  precipitate  of  mercuric  sulphide,  insoluble  in 
strong  nitric  acid.  If,  however,  the  quantity  of  the  re-agent  added  is  not  suf- 
ficient for  complete  decomposition,  a  white  precipitate  is  formed  consisting  of  a 
compound  of  mercuric  sulphide  with  the  original  salt,  and  often  coloured  yellow 
or  brown  by  excess  of  the  sulphide  :  this  re-action  is  quite  peculiar  to  mercuric 
salts.  Ammonia  and  carbonate  of  ammonia  form  white  precipitates,  generally 
consisting  of  a  compound  of  the  mercuric  salt  with  amide  of  mercury.  The 
fixed  alkalies  throw  down  a  yellow  precipitate  of  mercuric  oxide  (not  hydrated), 
insoluble  in  excess.  If,  however,  the  solution  contains  a  large  quantity  of  free 
acid,  no  red  precipitate  is  formed,  or  only  a  slight  one  after  a  considerable  time. 
Monocarbonate  of  potash  or  soda  throws  down  red-brown  mercuric  carbonate. 
But  if  any  ammoniacal  salt  is  present  in  the  solution,  the  fixed  alkalies  and  their 
carbonates  throw  down  the  white  precipitate  above  mentioned.  Bicarbonate  of 
potash  or  soda  also  gives  a  brown-red  precipitate,  with  mercuric  nitrate  or  sul- 
phate ;  but  with  the  chloride  it  forms  a  white  precipitate  which  afterwards  turns 
red.  The  carbonates  of  baryta,  strontia,  and  lime  precipitate  mercuric  oxide 
from  the  solutions  of  the  sulphate  and  nitrate,  but  not  from  the  chloride.  Phos- 
phate of  soda  throws  down  white  mercuric  phosphate  from  the  sulphate  and 
nitrate,  but  not  from  the  chloride.  Chromate  of  potash  forms  a  yellowish  red 
precipitate.  Ferrocyanide  of  potassium  forms,  in  solutions  not  too  dilute,  a  white 
precipitate  which  gradually  turns  blue.  Tincture  of  galls  forms  an  orange-yellow 
precipitate  with  all  mercuric  solutions  except  the  chloride.  Iodide  of  potassium 
produces  a  scarlet  precipitate  of  mercuric  iodide,  soluble  in  excess  either  of  the 
mercuric  salt  or  of  iodide  of  potassium. 

When  aqueous  ammonia  is  digested  for  several  days  upon  precipitated  oxide  of 
mercury,  the  latter  is  converted  into  a  yellowish  white  powder,  which  Kane  regards 
as  2HgO.HgNH2-f  3HO,  or  as  a  hydrated  compound  of  amide  and  oxide  of  mercury, 
which  may  be  called  oxyamide  of  mercury.  According  to  Millon,*  on  the  other 
hand,  its  composition  is  4HgO.NH3-f  2HO,  or  rather  3HgO  .  HgNH2.HO  +  2HO. 

*  Compt.  rend.  xxi.  826. 


MERCURIC    COMPOUNDS.  581 

This  substance,  when  placed  in  vacuo  over  quicklime,  gives  off  2  eq.  water,  turns 
brown,  and  in  that  state  undergoes  no  further  alteration  by  exposure  to  the  air 
at  ordinary  temperatures;  but  between  100°  and  130°  C.,  it  gives  off  a  third 
atom  of  water,  and  is  reduced  to  the  anhydrous  compound  3HgO.  HgNH2.  The 
yellow  hydrated  compound  rapidly  absorbs  carbonic  acid  from  the  air,  and  turns 
white.  Dilute  potash  has  no  action  upon  it ;  but  very  strong  potash,  at  a  boiling 
heat,  decomposes  it,  with  evolution  of  ammonia.  The  brown  anhydrous  compound 
resists  the  action  of  aqueous  potash  even  at  the  boiling  heat,  but  is  decomposed 
by  fusion  with  hydrate  of  potash.  Oxyamide  of  mercury  is  a  powerful  base,  and 
expels  ammonia  from  its  salts.  One  equivalent  of  this  compound,  represented  by 
the  formula  3HgO .  HgNH2,  saturates  1  eq.  of  sulphuric  acid,  nitric  acid,  &c. ; 
thus  the  sulphate  is  3HgO .  HgNH2 .  S03 ;  the  nitrate,  3HgO.HgNH2.N06-f  HO, 
&c.  &c. 

Nitride  of  mercury,  Mercurammonia,  NHg3.  —  This  compound  is  formed  by 
passing  dry  ammoniacal  gas  over  precipitated  mercuric  oxide  previously  well 
washed  and  dried : 

3HgO  +  NH3  — NHg3+3HO. 

After  removing  the  excess  of  mercuric  oxide  by  dilute  nitric  acid,  the  mercuram- 
monia  is  obtained  in  the  form  of  a  dark  flea-brown  powder,  which  explodes,  by 
heat,  friction,  percussion,  or  by  contact  with  oil  of  vitriol,  almost  as  violently  as 
iodide  of  nitrogen.  When  carefully  heated  with  hydrate  of  potash,  it  is  decom- 
posed without  detonation,  yielding  ammoniacal  gas  and  sublimed  metallic  mer- 
cury. It  is  also  decomposed  by  hydrochloric  acid,  sulphuric,  and  concentrated 
nitric  acid,  yielding  an  ammoniacal  and  a  mercuric  salt.  It  may  be  regarded  as 
ammonia  in  which  the  hydrogen  is  entirely  replaced  by  an  equivalent  quantity  of 
mercury,  (Plantamour).* 

By  the  action  of  various  ammoniacal  salts  at  a  boiling  heat  on  mercuric  oxide, 
compounds  are  obtained  consisting  of  nitride  of  mercury  combined  with  mercuric 
salts:  e.g.  with  nitrate  of  ammonia,  the  compound  NHg3+2(3HgO.  N05)  is 
obtained ;  with  phosphate  of  ammonia,  the  compound  NHg3  +  3HgO  .  P05-f2HO ; 
with  carbonate  of  ammonia,  the  compound  2(NHg3  +  HgO.  C02+2HO)-f-HO; 
with  chromate  of  ammonia,  the  compound  NHg3.  HgO  .  2HO-f  4(HgO.Cr03), 
which  when  treated  with  ammonia  is  converted  into  NHg3+HgO.  Cr63-f  2HO; 
with  acetate  of  ammonia,  the  compound  NHg3+  C4H3IIg04  -f-  4HO,  &c.  &c. 
(Hirzel).f 

Protosulphide  of  mercury,  Mercuric  sulphide,  Cinnabar,  HgSj  116  or  1450. 
—-This  is  the  common  ore  of  mercury,  and  sometimes  occurs  crystallized,  forming 
a  beautiful  vermilion.  It  is  prepared  artificially  by  fusing  one  part  of  sulphur  in 
a  crucible,  and  adding  to  it  by  degrees  six  or  seven  parts  of  mercury,  stirring  it 
after  each  addition,  and  covering  it  to  preserve  it  from  contact  of  air,  when  it 
inflames,  from  the  heat  evolved  in  the  combination.  The  product  is  exposed  to  a 
sand-bath  heat,  to  expel  the  sulphur  uncombined  with  mercury,  and  afterwards 
sublimed  in  a  glass  matrass  at  a  red  heat.  A  brilliant  red  mass  of  a  crystalline 
structure  is  thus  obtained,  which,  when  reduced  to  fine  powder,  forms  the  lively 
red  pigment  vermilion.  This  sulphide  is  black  before  sublimation.  It  is  precipi- 
tated black  also  when  hydrosulphuric  acid  is  passed  through  a  solution  of  corro- 
sive sublimate,  but  is  of  the  same  composition  in  both  states.  The  sulphide  of 
mercury,  however,  may  be  obtained  of  a  red  colour  without  sublimation,  or  in  the 
humid  way,  by  several  methods. 

Liebig  recommends  for  this  purpose  to  moisten  the  preparation  called  white  pre- 
cipitate, recently  prepared,  with  sulphide  of  ammonium,  and  allow  them  to  digest 
together.  The  black  sulphide  is  instantly  produced,  which  in  a  few  minutes 
passes  into  a  fine  red  cinnabar,  the  colour  of  which  is  improved  by  digesting  it  at 

*  Ann.  Ch.  Pharm.  xl.  115.  f  Ann.  Ch.  Pharm.  Ixxxiv.  258. 


582  MERCURY. 

a  gentle  heat  in  a  strong  solution  of  hydrate  of  potash.  The  sulphide  of  ammo- 
nium used  in  this  experiment  is  prepared  by  dissolving;  sulphur  to  saturation  in 
hydrosulphate  of  ammonia.  Cinnabar  is  not  attacked  by  sulphuric,  nitric  or 
hydrochloric  acid,  or  by  solutions  of  the  alkalies,  but  is  dissolved  by  aqua-regia. 

Pt'otochloride  of  mercury,  Mercuric  chloride,  Corrosive  sublimate,  135-5  or 
1693-75. — This  compound  may  be  formed  by  dissolving  red  oxide  of  mercury  in 
hydrochloric  acid,  or  by  adding  hydrochloric  acid  to  any  soluble  salt  of  that  oxide ; 
but  it  is  generally  prepared  in  a  different  manner.  Four  parts  of  mercury  are 
added  to  five  parts  of  sulphuric  acid,  and  the  mixture  boiled  till  it  is  converted 
into  a  dry  saline  mass.  The  mercuric  sulphate  thus  obtained  is  mixed  with  an 
equal  weight  of  common  salt,  and  heated  strongly  in  a  retort  by  a  sand-bath ; 
chloride  of  mercury  sublimes  and  condenses  in  the  upper  part  and  neck  of  the 
retort,  while  sulphate  of  soda  remains  behind  with  the  excess  of  chloride  of  sodium. 
The  mercury  and  sodium  have  exchanged  places  in  the  salts ; 

NaCl  +  HgO  .  S03  =  HgCl  +  NaO  .  S03. 

Mercury,  when  heated  in  a  stream  of  chlorine  gas,  burns  with  a  pale  flame,  and 
is  converted  into  a  white  sublimate  of  chloride.  The  salt  has  been  prepared  on  a 
lanre  scale  in  this  manner,  which  was  suggested  as  a  manufacturing  process  by  Dr. 
A/T.  Thomson. 

The  sublimed  chloride  of  mercury  forms  a  crystalline  mass,  the  density  of  which 
is  6-5 }  it  fuses  at  509°,  and  boils  at  about  563°.  The  vapour  of  chloride  of  mer- 
cury is  colourless,  its  density  9420,  one  volume  of  it  containing  1  volume  of  mer- 
cury vapour  and  1  volume  of  chlorine  gas.  This  salt  is  soluble  in  16  parts  of  cold 
and  in  3  parts  of  boiling  water,  in  2£  parts  of  cold  and  in  H  part  of  boiling  alco- 
hol, and  in  3  parts  of  cold  ether.  It  is  not  decomposed  by  sulphuric  or  nitric 
acid ;  is  largely  dissolved  by  the  latter,  and  also  by  hydrochloric  acid.  It  is 
obtained  by  sublimation  and  from  solution  in  two  different  crystalline  forms.  The 
solutions  of  chloride  of  mercury  exposed  to  the  direct  rays  of  the  sun  evolve 
oxygen,  while  hydrochloric  acid  is  dissolved  and  dichloride  of  mercury  precipi- 
tates. The  decomposition  of  this  salt  by  the  action  of  light  is  much  more 
rapid  when  the  solution  contains  organic  matter.  The  poisonous  action  of  chloride 
of  mercury,  which  is  scarcely  inferior  to  that  of  arsenious  acid,  is  best  counteracted 
by  liquid  albumen,  with  which  chloride  of  mercury  forms  an  insoluble  and  inert 
compound. 

Many  metals,  viz.  arsenic,  antimony,  bismuth,  zinc,  tin,  lead,  iron,  nickel,  and 
copper,  decompose  mercuric  chloride  in  the  dry  way,  withdrawing  the  half  or  the 
whole  of  its  chlorine,  and  separating  calomel  or  metallic  mercury,  which  latter 
forms  an  amalgam  with  the  excess  of  the  other  metal.  Arsenic  forms  terchloride 
of  arsenic  and  a  brown  sublimate.  An  intimate  mixture  of  3  pts.  antimony  and 
1  pt.  corrosive  sublimate,  well  pressed  into  a  glass,  becomes  hot  and  liquid  in  the 
course  of  half  an  hour,  and  on  the  application  of  heat  yields  terchloride  of  anti- 
mony and  metallic  mercury.  Tin  heated  with  corrosive  sublimate  yields  a  distil- 
late of  bichloride  of  tin,  and  a  grey  residue  containing  calomel  and  protochloride 
of  tin.  Many  metals  also  reduce  the  mercury  from  the  aqueous  or  alcoholic  solu- 
tion of  the  chloride  (p.  581).  Most  metals  throw  down  calomel  together  with  the 
mercury;  but  zinc,  cadmium,  and  iron  precipitate  nothing  but  mercury,  zinc 
being  thereby  converted  into  a  semi-fluid  amalgam,  and  cadmium  forming  an 
amalgam  which  crystallizes  in  beautiful  needles.  The  other  reactions  of  mercuric 
chloride  in  solution  have  been  already  described  (p.  581,  582). 

Chloride  of  mercury  with  ammonia.  —  1.  "When  chloride  of  mercury  is  gently 
heated  in  a  stream  of  ammoniacal  gas,  the  latter  is  absorbed,  and  the  compound 
fuses  from  heat  evolved  in  the  combination.  The  product  was  found  by  Rose  to 
contain  2HgCl .  NH3.  This  compound  boils  at  590°,  and  may  be  distilled  without 

loss  of  ammonia ;  it  is  decomposed  by  water 2.  Fusible  white  precipitate. 

When  the  double  chloride  of  mercury  and  ammonium,  called  sal  alernbroth,  is 


NITROCHLORIDE    OF    MERCURY.  583 

precipitated  by  potash  in  the  cold,  a  white  powder  is  obtained,  which  was  first 
distinguished  by  Wohler  from  the  compound  next  described;  its  composition  may 
be  expressed,  according  to  Kane's  analysis,  by  the  formula  HgCl.NH3.  The 
same  compound  is  also  formed  when  ammonia  is  added  to  a  solution  of  sal-ammo- 
niac, the  liquid  brought  to  the  boiling  point,  and  chloride  of  mercury  dropt  into 
it  so  long  as  the  precipitate  which  is  produced  is  redissolved.  The  compound 
appears,  on  the  cooling  of  the  solution,  in  small  crystals,  which  are  garnet  dode- 
cahedrons (Mitscherlich).  The  crystalline  form  of  this  compound  belongs,  there- 
fore, to  the  regular  system,  like  that  of  sal-ammoniac. 

8.  Mercuric  amido-chloride.  — The  compound  known  as  white  precipitate,  and 
sometimes  infusible  white  precipitate,  to  distinguish  it  from  the  preceding,  is 
formed  when  ammonia  is  added  to  a  solution  of  chloride  of  mercury.  When  first 
produced,  it  is  bulky  and  milk-white ;  it  is  decomposed  by  hot  water  or  by  much 
washing  with  cold  water,  and  acquires  a  yellow  tinge.  Kane  has  shown  that 
white  precipitate  is  free  from  oxygen,  and  contains  nothing  but  the  elements  of  a 
double  chloride  and  amide  of  mercury,  and  represents  it  by  the  formula  HgCl. 
HgNH2.  White  precipitate  is  distinguished  from  calomel  by  solution  of  ammo- 
nia, which  does  not  alter  the  former,  but  blackens  the  latter :  it  is  readily  dis- 
solved by  acids. 

4.  Nitrochloride  of  mercury.  —  Mitscherlich    has    observed   that  when  white 
precipitate  is  gradually  heated  in  a  metal  bath,  and  the  heat  continued  for  a  long 
time,  three  atoms  of  it  give  off  two  atoms  of  ammonia  and  one  atom  of  chloride 
of  mercury,  while  a  red  matter  remains  in  crystalline  scales,  having  much  the 
appearance  of  red  oxide  of  mercury  produced  by  the  oxidation  of  the  metal  in  air, 
and  containing  two  atoms  of  chloride  of  mercury,  united  with  a  compound  of  one 
atom  of  nitrogen  and  three  atoms  of  mercury,  2HgCl.NHg3.     He  concludes  that 
the  atom  of  white  precipitate  should  be  multiplied  by  three ;  its  decomposition 
by  the  heat  of  the  metal  bath  will  then  be  represented  by  the  equation : — 

8(HgCl.HgNH2)  =  2HgCl.NHg,+  2NH,  +  HgCl. 

The  red  compound  is  itself  decomposed  by  a  temperature  above  680°,  and 
resolved  into  chloride  of  mercury,  mercury  and  nitrogen.  It  is  insoluble  in  water, 
and  is  not  altered  in  boiling  solutions  of  the  alkalies.  It  may  be  boiled  without 
change  in  diluted  or  concentrated  nitric  acid,  and  in  pretty  concentrated  sulphuric 
acid,  but  is  decomposed  and  dissolved  when  boiled  in  the  most  concentrated  sul- 
phuric acid  or  in  hydrochloric  acid ;  no  gas  is  evolved,  but  ammonia  and  chloride 
of  mercury  are  found  in  the  acid  solution.  The  compound  NHg3  is  not  isolated 
by  passing  ammonia  over  the  heated  red  compound.  Mercury  conducts  itself  in 
these  compounds  in  the  same  way  as  potassium  with  ammonia,  the  olive-coloured 
substance  produced  by  the  action  of  dry  ammonia  upon  potassium  being  the 
amide  of  potassium,  3(K.NH2),  and  the  plumbago-looking  substance  left  on 
heating  the  amide  of  potassium,  when  ammonia  escapes,  a  compound  of  nitrogen 
and  potassium,  NK3.* 

5.  When  white  precipitate  is  boiled  in  water,  it  is  changed  into  a  heavy  canary- 
yellow  powder,  which  Kane  regards  as  a  compound   of  the  amido-chloride  of 
mercury  with  oxide  of  mercury,  HgCl.  HgNH2.2HgO.     Two  atoms  of  water  are 
decomposed  in  its  formation,  yielding  the  two  atoms  of  oxygen  which   are  found 
in  the  yellow  compound,  while  the  two  atoms  of  hydrogen,  added  to  an  atom  of 
chlorine  and  an  atom  of  amidogen,  form  an  atom  of  hydrochlorate  of  ammonia, 
which  is  found  in  solution  : 

2(HgCl.HgNH2)  +  2HO  =  HgCl.HgNH2.2HgO  -f  NH4C1. 

Solutions  of  potash  and  soda  convert  white  precipitate  into  the  same  yellow 
substance,  while  a  metallic  chloride  is  formed  and  ammonia  evolved,  (Kane). 

*  Mitscherlich  in  Poggendorff's  Annalen,  vol.  xxxix.  p.  409. 


584  MERCURY. 

The  five  compounds  just  described  may  be  regarded  as  salts  of  metalloidal 
radicals,  formed  from  ammonium  (NH4)  in  which  the  whole  or  part  of  the  hydrogen 
is  replaced  by  an  equivalent  quantity  of  m  rcury.  Thus,  the  fusible  white  pre- 
cipitate, HgCl .  NH3,  may  be  regarded  as  a  chloride  of  mercur ammonium,  = 

Cl.N  •<  TT3r ;  the  preceding  compound,  2HgCl.NH3,  as  a  double  chloride  consisting 
of  the  same  compound  united  with  chloride  of  mercury,  namely  as  ClHg  -f- 

(  TT 

Cl.N  \  jj^.;  similarly,  infusible  white  precipitate,  HgCl.HgNH2,  is  a  chloride  of 

(H 

bimerciirammonium,  C1N  -I  TTZ   ;    the   yellow   powder  obtained   by  boiling   this 

compound  with  water  is  a  chloride  of  tetramer  cur  ammonium  combined  with  two 
atoms  of  water,  =  ClNHg4  -f  2HO;  and  the  red  compound,  2HgCl.NHg3,  may 
be  regarded  as  a  compound  of  this  same  chloride  with  chloride  of  mercury, 
namely  as  CIHg.ClNHgv 

Oxychloride  of  mercury.  —  When  a  solution  of  corrosive  sublimate  is  precipi- 
tated by  potash  or  soda,  mercuric  oxide  goes  down,  in  combination  with  a  portion 
of  chloride,  as  a  brown  precipitate,  unless  a  considerable  excess  of  alkali  be 
employed.  The  same  oxychloride  is  produced  by  an  alkaline  carbonate ;  but  a 
double  carbonate  is  then  also  formed.  Chloride  of  mercury  is  not  immediately 
precipitated  by  the  bicarbonates  of  potash  and  soda;  and  hence  that  salt  may  be 
employed  to  detect  the  presence  of  a  neutral  alkaline  carbonate  in  these  bicar- 
bonates. This  oxychloride  may  also  be  formed  by  passing  chlorine  through  a 
mixture  of  water  and  oxide  of  mercury.  It  may  be  obtained  crystalline  and  of  a 
very  dark  colour,  almost  black,  by  mixing  corrosive  sublimate  with  chloride  of 
lime,  and  boiling  the  liquid,  or  by  treating  a  solution  of  corrosive  sublimate  with 
bicarbonate  of  potash,  and  allowing  the  solution  to  stand  in  an  open  vessel,  when 
carbonic  acid  gradually  escapes,  and  the  compound  HgC1.4HgO  is  deposited. 
This  oxychloride  is  decomposed  by  a  moderate  heat,  chloride  of  mercury  subliming, 
while  the  red  oxide  remains. 

Sidphochloride  of  mercury,  HgC1.2HgS.  —  When  hydrosulphuric  acid  gas  is 
passed  through  a  solution  of  chloride  of  mercury,  the  precipitate  which  first 
appears,  and  does  not  subside  readily,  is  white;  it  has  been  shown  by  Rose  to  be  a 
compound  of  chloride  and  sulphide  of  mercury.  This  substance  is  changed 
entirely  into  sulphide  of  mercury,  when  left  in  water  containing  hydrosulphuric 
acid.  On  the  other  hand,  precipitated  sulphide  of  mercury  digested  in  a  solution 
of  chloride  of  mercury,  takes  down  that  salt,  and  forms  the  compound  in  question. 
The  same  compound  may  be  formed  in  the  dry  way,  by  fusing  protosulphide  of 
mercury  (either  black  or  red)  with  eight  or  ten  times  its  weight  of  corrosive  sub- 
limate, in  a  sealed  tube,  and  dissolving  out  the  excess  of  chloride  by  boiling 
water ;  the  sulphochloride  then  remains  in  the  form  of  a  dirty-white  powder 
having  a  distinctly  crystalline  structure  (R.  Schneider).  Sulphide  of  mercury 
combines  likewise  with  the  bromide,  iodide,  fluoride,  and  nitrate  of  mercury,  and 
always  in  the  proportion  of  two  atoms  of  the  sulphide  to  one  atom  of  the  other 
salt. 

Double  salts  of  chloride  of  mercury.  —  Chloride  of  mercury  was  found  by  M. 
Bonsdorff  to  combine  with  chloride  of  potassium  in  three  different  proportions, 
forming  a  series  of  salts  in  which  the  chloride  of  potassium  remains  as  one  equi- 
valent, while  the  chloride  of  mercury  goes  on  increasing.  They  are  KCl.HgCl. 
HO,  which  crystallizes  in  large  transparent  rhomboidal  prisms;  KC1.2HgC1.2HO 
crystallizing  in  fine  needle-like  amianths;  and  KCl-t-4HgCl  +  4HO,  which  crys- 
tallizes also  in  fine  needles.  Chloride  of  sodium  forms  only  one  compound, 
NaC1.2HgC1.4HO,  which  crystallizes  in  fine  regular  hexahedral  prisms.  One  of 
the  double  salts  of  chloride  of  ammonium  has  long  been  known  as  sal  alembroth. 
It  crystallizes  in  flattened  rhomboidal  prisms,  NH4Cl.HgCl.HO,  and  is  isomor- 
phous  with  the  corresponding  potassium  salt.  When  exposed  to  dry  air,  it  gives 


PROTIODIDE    OF    MERCURY.  585 

off  its  water  without  change  of  form.  Kane  has  also  obtained  NH4C1.2HgCl, 
and  the  same  with  an  atom  of  water,  NH4C1.2HgCl.HO,  the  first  in  a  rhomboidal 
form,  and  the  second  in  long  silky  needles.  All  these  double  chlorides  are  ob- 
tained by  dissolving  their  constituent  salts  together  in  the  proper  proportions. 
The  chlorides  of  barium  and  strontium  form  well-crystallized  compounds  with 
chloride  of  mercury,  viz.  BaCl.2HgCl.4HQ,  and  SrCl.2HgCl.2HO.  Chloride  of 
calcium  combines  in  two  proportions  with  mercuric  chloride.  When  chloride  of 
mercury  is  dissolved  to  saturation  in  chloride  of  calcium,  tetrahedral  crystals 
separate  from  the  solution,  which  are  tolerably  persistent  in  air,  and  contain 
CaC1.5HgC1.8HO.  After  the  deposition  of  these  crystals,  the  liquid  yields, 
when  evaporated  by  a  gentle  heat,  a  second  crop  of  large  prismatic  crystals, 
CaC1.2HgC1.6HO,  which  are  very  deliquescent.  Chloride  of  magnesium  also 
forms  two  salts,  MgCl.3HgCl.HO,  and  MgCl.HgCl.6HO,  both  deliquescent. 
Chloride  of  nickel  gives  two  compounds,  one  of 'which  crystallizes  in  tetrahedrons, 
like  the  chloride  of  calcium  salt.  Chloride  of  manganese  forms  a  compound  in 
good  crystals,  MnCl.HgCl.4HO.  The  chlorides  of  iron  and  zinc  form  similar 
isomorphous  salts,  FeCl.HgCl.HO,  and  ZnCl.HgCl.HO.  The  double  chlorides 
of  zinc  and  of  manganese  are  remarkable  in  one  respect,  that  chloride  of  mercury 
dissolved  by  them  in  excess  crystallizes  by  evaporation  in  fine  large  crystals,  such 
as  cannot  be  obtained  in  any  other  way.  The  chlorides  of  cobalt,  nickel,  and 
copper  form  similar  crystallizable  salts  ]  but  chloride  of  lead  does  not  appear  to 
form  a  double  salt  with  chloride  of  mercury.  (Bonsdorff.) 

Mercuric  chloride  likewise  forms  definite  compounds  with  alkaline  chromates. 
A  hot  solution  of  equal  parts  of  mercuric  chloride  and  bichromate  of  ammonia 
deposits,  on  cooling,  large  hexagonal  prisms,  of  a  splendid  red  colour,  containing 
NH40.2Cr03+HgCl-f  HO,  and  the  mother-liquor  deposits  a  further  crop  of  red, 
somewhat  needle-shaped  crystals,  containing  3(NH40.2Cr03)-f  HgCl.  (Richmond 
and  Abel.*)  Monochromate  of  potash  forms  with  mercuric  chloride  a  brick-red 
precipitate  of  mercuric  chromate  j  and,  on  evaporating  the  filtered  liquid,  small 
pale  red  crystals  are  obtained  of  a  double  salt,  containing  KO.Cr03-f- HgCl.  A 
solution  of  equivalent  quantities  of  mercuric  chloride  and  bichromate  of  potash 
yields  beautiful  red  pointed  crystals,  containing  K0.2Cr03-f-HgCl.  (Darby.f) 
On  mixing  the  cold  saturated  aqueous  solutions  of  acetate  of  copper  and  mercuric 
chloride,  and  leaving  the  mixture  to  evaporate,  deep  blue,  concentric,  radiated 
hemispheres  are  obtained,  containing  CuO.C4H3Cu04-f  HgCl.  (Wbhler  and 
Htitteroth.)J 

Protobromide  of  mercury,  Mercuric  bromide,  HgBr;  180  or  2250. — This  salt 
is  obtained  by  treating  mercury  with  water  and  bromine.  It  is  colourless,  soluble 
in  water  and  alcohol,  and  when  heated,  fuses  and  sublimes,  exhibiting  a  great 
analogy  to  chloride  of  mercury  in  its  properties.  Its  density  in  the  state  of 
vapour  is  12370.  Bromide  of  mercury  forms  a  similar  compound  with  sulphide 
of  mercury,  HgBr.2HgS,  which  is  yellowish.  It  was  also  combined,  by  Bons- 
dorff, with  a  variety  of  alkaline  and  earthy  bromides.  Bromide  of  mercury  com- 
bines with  half  an  equivalent  of  ammonia,  in  the  dry  way,  and  also  gives,  with 
solution  of  ammonia,  a  white  precipitate,  analogous  to  that  derived  from  chloride 
of  mercury. 

Protiodide  of  mercury,  mercuric,  iodide,  Hgl,  226-36  or  2829 -5. — Falls  as  a 
precipitate  of  a  fine  scarlet  colour,  when  iodide  of  potassium  is  added  to  a  solu- 
tion of  chloride  of  mercury.  It  may  also  be  obtained  by  triturating  its  con- 
stituents together,  in  the  proper  proportion,  with  a  few  drops  of  alcohol.  To  pro- 
cure it  in  crystals,  Mitscherlich  dissolves  iodide  of  mercury  to  saturation,  in  a 
hot  concentrated  solution  of  the  iodide  of  potassium  and  mercury,  and  allows  the 
solution  to  cool  gradually.  When  heated  moderately,  mercuric  iodide  becomes 

*  Chera.  Soc.  Qu.  J.  iii.  202.  f  Chem  Soc.  Qu.  J.  i.  24. 

J  Ann.  Ch.  Pharm.  liii.  142. 


586  MERCURY. 

yellow ;  at  a  higher  temperature,  it  fuses  and  sublimes,  condensing  in  rhomboidal 
plates  of  a  fine  yellow  colour.  The  forms  of  the  red  and  yellow  crystals  are  totally 
different,  so  that  the  change  of  colour  is  due  to  the  dimorphism  of  mercuric 
iodide.  The  yellow  crystals  generally  return  gradually  into  the  red  state  when 
cold ;  and  this  change  may  be  determined  at  once  by  scratching  the  surface  of  a 
crystal,  or  by  crushing  it.  The  density  of  mercuric  iodide  in  the  state  of  vapour 
is  15630;  it  is  the  heaviest  of  gaseous  bodies.  Mercuric  iodide  is  slightly  soluble 
in  water,  but  requires  more  than  6000  times  its  weight  of  water  to  dissolve  it.  It 
is  much  more  soluble  in  alcohol  and  in  acids,  particularly  with  the  assistance  of 
heat.  Mercuric  iodide  is  very  soluble  in  iodide  of  potassium  ;  it  is  also  dissolved 
by  a  solution  of  mercuric  chloride,  especially  when  hot.  Hence,  when  a  few  drops 
of  iodide  of  potassium  solution  are  added  to  a  solution  of  corrosive  sublimate,  a 
precipitate  is  formed,  which  redissolves  on  agitating  the  liquid;  a  somewhat 
larger  quantity  of  iodide  of  potassium  renders  the  precipitate  permanent;  and  a 
still  further  addition  causes  it  to  disappear  entirely. 

When  treated  with  sulphuretted  hydrogen  water,  mercuric  iodide  forms  the 
compound  HgI.2HgS,  which  is  yellow.  Mercuric  iodide  unites  with  other 
iodides,  and  forms  a  class  of  salts  as  extensive  as  the  compounds  of  chloride  of 
mercury.  They  have  been  studied  by  M.  P.  Boullay.*  Mercuric  iodide  also 
combines  with  chlorides;  it  is  dissolved  by  a  hot  solution  of  mercuric  chloride, 
and  two  compounds  have  been  obtained  on  the  cooling  of  the  solution,  viz.,  a 
yellow  powder,  Hgl.HgCl,  and  white  dendritic  crystals,  HgI.2HgCl. 

Mercuric  iodide  treated  with  very  strong  aqueous  ammonia  forms  the  com- 
pound NH3Hg.I;  with  somewhat  less  concentrated  ammonia  it  yields  white  needles 

of  the  compound  NH3.2HgI,  or  NH3HgI-fHgI,  and  a  red-brown  powder  consist- 
ing of  iodide  of  tetramercurammonium  with  2  eq.  water,  NHg4I  -f  2 HO.  The 
formation  of  this  last  compound  is  represented  by  the  equation  : 

4HgI  -f  4NH3  +  2110  =  NHg4I.2HO  +  3NH4I. 

Iodide  of  tetramercurammonium  is  also  formed  by  passing  ammoniacal  gas  over 
mercuric  oxy-iodide : 

HgLSHgO  +  NH,  =  NHg4L2HO  +  HO; 

by  digesting  the  chloride  of  tetramercurammonium  in  aqueous  iodide  of  potassium 
(Rammelsberg) ;  and  by  adding  ammonia  to  a  solution  of  iodide  of  mercury  and 
potassium  mixed  with  caustic  potash  (Nessler)  :*f* 

4(HgLKI)  +  NH3  +  3KO  =  NHg4L2HO  +  7KI  +  HO. 

This  last  reaction  affords  an  extremely  delicate  test  for  ammonia.  A  solution  of 
iodide  of  mercury  and  potassium  is  prepared  by  adding  iodide  of  potassium  to  a 
solution  of  corrosive  sublimate,  till  a  portion  only  of  the  resulting  red  precipitate 
is  re-dissolved,  then  filtering,  and  mixing  the  filtrate  with  caustic  potash.  The 
liquid  thus  obtained  produces  a  brown  precipitate  with  a  very  small  quantity  of 
ammonia,  either  free  or  in  the  form  of  an  ammoniacal  salt.  The  precipitate  is 
soluble  in  excess  of  iodide  of  potassium  (Nessler). 

Mercuroso-mercuric  iodide,  Hg4I3  or  Hg2I.2HgI.  —  This  compound  is  obtained 
by  precipitating  a  solution  of  mercurous  nitrate  with  hydriodic  acid  or  iodide  of 
potassium,  and  collecting  the  precipitate  on  a  filter  after  the  green  colour  has 
changed  to  yellow;  or  by  dissolving  in  aqueous  iodide  of  potassium  half  as  much 
iodine  as  it  already  contains,  and  adding  the  solution  to  a  solution  of  mercurous 
nitrate.  It  is  a  yellow  powder,  which  turns  red  when  heated. 

Cyanide  of  mercury,  HgCy,  126  or  1575. — This  salt  is  most  easily  obtained  by 

*  Ann.  Ch.  Phys.  [2.]  xxxiv.  337.  fChem.  Gaz.  1856,  445,  463. 


CYANIDE    OF    MERCURY.  587 

saturating  hydrocyanic  acid  with  red  oxide  of  mercury.  To  prepare  the  hydro- 
cyanic acid  required,  the  process  of  Wiukler  may  be  followed.  Fifteen  parts  of 
ferrocyanide  of  potassium  are  distilled  with  13  parts  of  oil  of  vitriol  diluted  with 
100  parts  of  water,  and  the  distillation  continued  by  a  moderate  heat  nearly  to 
dryness.  The  vapour  should  be  made  to  pass  through  a  Liebig's  condensing  tube, 
and  be  afterwards  received  in  a  flask  containing  30  parts  of  water.  A  portion 
of  the  condensed  hydrocyanic  acid  is  put  aside,  and  the  remainder  mixed  with  16 
parts  of  oxide  of  mercury  in  fine  powder,  and  well  agitated  till  the  odour  of  hydro- 
cyanic acid  is  no  longer  perceptible.  The  solution  is  drawn  off  from  the  undis- 
solved  oxide  of  mercury,  and  the  reserved  portion  of  hydrocyanic  acid  mixed  with 
it.  The  last  addition  is  necessary  to  saturate  a  portion  of  oxide  of  mercury,  which 
cyanide  of  mercury  dissolves  in  excess.  This  operation  yields  12  parts  of  the  salt 
in  question. 

Cyanide  of  mercury  may  also  be  obtained  by  boiling  1  pt.  of  ferrocyanide  of 
potassium  for  ten  minutes  with  2  pts.  of  neutral  mercuric  sulphate  and  8  pts.  of 
water,  filtering  the  liquid,  and  leaving  it  to  crystallize  by  cooling.  The  reaction 
may  be  represented  by  the  equation : 

K2FeCy3  +  3HgO  =  SHgCy  +  2KO  +  FeO. 

A  third  method  of  preparing  this  compound  is  to  heat  the  red  oxide  of  mercury 
with  about  an  equal  weight  of  pure  and  finely  powdered  Prussian  blue,  and  a  large 
quantity  of  water,  stirring  the  mixture  frequently ;  then  boil  the  filtrate  with  oxide 
of  mercury  to  throw  down  the  last  portions  of  iron ;  and  neutralize  the  excess  of 
mercuric  oxide  in  the  liquid  with  hydrocyanic  acid. 

Cyanide  of  mercury  crystallizes  in  square  prisms,  which  are  anhydrous,  and 
resembles  chloride  of  mercury  in  its  solubility  and  poisonous  qualities.  The  red 
oxide  of  mercury,  even  when  dry,  absorbs  hydrocyanic  acid,  with  formation  of 
water  and  evolution  of  heat.  The  affinity  of  mercury  for  cyanogen  appears  to  be 
particularly  intense,  oxide  of  mercury  decomposing  all  the  cyanides,  even  cyanide 
of  potassium,  and  liberating  potash.  Cyanide  of  mercury  is  consequently  not 
precipitated  by  potash.  Nor  is  it  decomposed  by  any  acid,  with  the  exception  of 
hydrochloric,  hydriodic,  and  hydrosulphuric  acids.  By  a  heat  approaching  to  red- 
ness, cyanide  of  mercury  is  decomposed,  and  resolved  into  mercury  and  cyanogen 
gas.  When  exposed  in  the  moist  state  to  the  action  of  chlorine  in  a  dark  place,  it 
is  converted  into  mercuric  chloride  and  gaseous  chloride  of  cyanogen  : 

HgCy  +  2Cl=HgCl  +  CyCl. 

But  in  strong  sunshine,  a  different  action  takes  place,  attended  with  considerable 
rise  of  temperature,  and  yielding  sal-ammoniac,  mercuric  chloride,  a  peculiar  yellow 
oil,  a  small  quantity  of  gaseous  chloride  of  cyanogen,  and  a  trace  of  carbonic  acid 
(Serullas).  When  hydrocyanic  acid  is  digested  upon  inercurous  oxide,  the  mer- 
curic cyanide  dissolves,  and  metallic  mercury  is  liberated. 

Oxycyanide  of  mercury,  HgCy.HgO,  is  produced  as  a  white  powder  intermixed 
with  the  red  oxide,  when  hydrocyanic  acid  of  considerable  strength  (10  or  20  per 
cent.)  is  agitated  with  red  oxide  of  mercury  in  large  excess.  It  is  sparingly 
soluble  in  cold  water,  but  may  be  dissolved  out  by  hot  water,  and  crystallizes  on 
cooling  in  transparent,  four-sided,  acicular  prisms.  When  heated  gently,  it 
blackens  slightly,  and  then  explodes  (Johnston).* 

Cyanide  of  mercury,  digested  upon  red  oxide  of  mercury,  dissolves  a  large  quan- 
tity of  it,  and  forms,  according  to  Kiihn,  a  tribasic  cyanide  of  mercury,  HgCy. 
3HgO,  which  is  more  soluble  in  water  than  the  neutral  cyanide,  and  crystallizes 
with  less  facility  in  small  acicular  crystals. 

Cyanide  of  mercury  and  potassium,  KyCy.HgCy,  is  formed  on  dissolving  cya- 
nide of  mercury  in  a  solution  of  cyanide  of  potassium,  and  crystallizes  in  regular 

•*  Phil.  Trans.  1839,  p.  113. 


588  MERCURY. 

octohedrons.  Cyanide  of  mercury  also  forms  crystallizable  double  salts  with  other 
cyanides,  such  as  the  cyanides  of  sodium,  barium,  calcium,  magnesium,  &c.  It 
also  combines  with  chlorides,  bromides,  iodides,  and  with  several  oxi-salts,  such  as 
chromate  and  formiate  of  potash,  with  which  it  forms  the  compounds  2(KO.Cr03)  + 
HgCy  and  C2HK04.HgCy. 

Mercuric  sulphate,  HgO.S03  j  148  or  1850.  — This  salt  is  formed  by  boiling  5 
parts  of  sulphuric  acid  upon  4  parts  of  mercury,  till  the  metal  is  converted  into  a 
dry  saline  mass.  Mercuric  sulphate  is  a  white  crystalline  salt,  neutral  in  compo- 
sition, but,  like  most  of  the  neutral  salts  of  mercury,  cannot  exist  in  solution. 
Water  decomposes  it,  forming  a  dense  yellow  subsulphate,  and  a  solution  of  an 
acid  sulphate.  This  subsulphate  is  known  as  turbith  mineral,  a  name  applied  to  it 
by  the  older  chemists,  because  it  was  supposed  to  produce  effects  in  medicine 
analogous  to  those  of  a  root  formerly  employed,  and  known  as  convolvulus  turpe- 
thum.  The  composition  of  turbith  mineral  is  3HO.S03  or  HgO.S03  -f  2HgO 
(Kane).  Solution  of  ammonia  converts  both  the  neutral  sulphate  an-d  turbith 
mineral  into  a  heavy  powder,  which  Kane  names  ammonio-turbith,  and  finds  to  be 
HgO.S03  +  Hg.NH2  +  2HgO.  It  is,  therefore,  analogous  in  composition  to  the 
yellow  powder  produced  by  the  decomposition  of  white  precipitate,  and  may  be 
regarded  as  a  sulphate  of  tetramercurammonium  with  2  eq.  of  water :  NH£4.S04-f 
2HO. 

Mercuric  sulphites.  —  The  neutral  sulphite,  HgO.S02,  may  be  formed  by  preci- 
pitating the  nitrate,  HgO.N05,  with  an  alkaline  sulphate ;  but  it  is  very  unstable, 
and  resolves  itself  spontaneously  into  mercuric  sulphate  and  metallic  mercury. 
The  basic  sulphite,  2HgO.S02,  is  obtained  by  precipitating  a  solution  of  the  basic 
nitrate,  2HgO.S05,  with  an  alkaline  sulphite.  It  is  a  white,  heavy  powder,  inso- 
luble in  water,  and  changing,  when  slightly  heated,  into  mercurous  sulphate; 
2HgO.S02  =  Hg2O.S03.  Iodide  of  potassium  converts  it  into  red  mercuric  iodide 
(P6an  de  St.  G-illes).*  A  bisulphite,  Hg0.2S02  +  HO,  is  obtained  as  a  white 
crystalline  powder  by  pouring  a  saturated  solution  of  bisulphite  of  soda  on  solid 
mercuric  chloride.  It  dissolves  readily  in  water,  and  is  decomposed  by  heat, 
whether  in  solution  or  in  the  solid  state,  with  separation  of  metallic  mercury 
(Wicke).f  By  treating  mercuric  chloride  with  a  solution  of  neutral  sulphite  of 
potash,  a  double  salt,  HgO.S02-fHO,  is  obtained  in  small  needle-shaped  crystals, 
whose  solution  is  neutral  to  test-paper.  Similar  salts  are  formed  with  the  neutral 
sulphites  of  soda  and  ammonia.  By  treating  mercuric  chloride  in  excess  with 
neutral  sulphite  of  soda,  the  salt,  2(HgO.S02)  -f  NaO.S02  +  HO,  is  obtained, 
which  is  alkaline  to  test-paper.  The  solutions  of  these  double  sulphites  are  pre- 
cipitated by  hydrosulphuric  acid  and  soluble  sulphides,  but  not  by  alkalies.  (Pean 
de  St.  Gilles). 

Mercuric  seleniate. — A  hot  aqueous  solution  of  selenic  acid  forms  with  mercuric 
oxide  prepared  by  precipitation,  a  soluble  neutral  seleniate,  HgO.Se034-  HO,  and 
a  red  insoluble  basic  salt,  containing  2(3HgO.Se03)  -f  HO  (Korner).J 

Mercuric  selenite. — Mercuric  oxide  forms  with  aqueous  selenious  acid,  according 
to  Berzelius,  an  insoluble  neutral  and  a  soluble  acid  selenite ;  according  to  Kohler, 
on  the  other  hand,  selenious  acid  does  not  form  any  soluble  salt  with  mercuric 
oxide,  but  only  a  pale  yellow  amorphous  salt,  containing  7Hg0.4Se02. 

Nitrates  of  the  red  oxide  of  mercury,  Mercuric  nitrates.  — The  neutral  nitrate 
cannot  be  crystallized,  but  it  is  formed  in  solution  when  chloride  of  mercury  is 
precipitated  by  nitrate  of  silver.  When  red  oxide  of  mercury  is  dissolved  in 
nitric  acid,  or  when  the  metal  is  dissolved  in  the  same  acid  with  ebullition,  till  a 
drop  of  the  solution  no  longer  occasions  a  precipitate  in  water  containing  a  soluble 
chloride,  a  subnitrate  is  formed,  crystallizing  in  small  prisms,  which  are  deliques- 
cent in  damp  air.  Its  composition  is  expressed  by  the  formula  2HgO.N05  -f  2HO. 

*  Ann.  Ch.  Phys.  [3],  xxxvi.  80.  f  Ann.  Ch.  Pharm.  xcv.  176. 

J  Pogg.  Ann.  Ixxxix.  446. 


ALLOYS    OF    MERCURY.  589 

It  is  the  only  crystallizable  nitrate  of  this  oxide.  Decomposed  by  water,  this  salt 
yields  a  yellow  subnitrate,  which,  after  washing  with  warm,  but  not  boiling  water, 
is  3Hg.N05-f  HO.  When  the  sub-nitrate  is  prepared  by  boiling  water,  it  has  a 
red  colour,  and  probably  consists  of  6HgO.N05,  (Kane). 

Nitrate  of  mercury  yields  several  compounds  when  treated  with  ammonia, 
(a.)  When  a  dilute  and  not  very  acid  solution  of  that  salt  is  treated  in  the  cold, 
with  weak  solution  of  ammonia  not  added  in  excess,  a  pure  milk-white  precipitate 
appears,  which  is  not  granular,  and  remains  suspended  in  the  liquid  for  a  consider- 
able time.  It  was  analyzed  by  C.  G.  Mitscherlich,  and  to  distinguish  it  from 
some  other  salts  containing  the  same  constituents,  may  be  called  Mitscherlich s 
ammonia-subnitrate.  It  contains  2HgO.N05+ HgNH2.  (6.)  The  preceding 
compound  is  altered  in  its  appearance  by  boiling  water,  and  becomes  much  heavier 
and  more  granular,  forming  Soubeiran's  ammonia-subnitrate)  the  composition  of 
which  is  found  by  Kane  to  be  HgO.N05  +  Hg.NH2  -f  2HgO,  or  it  resembles  in 
constitution  the  bodies  already  described  containing  chlorine  and  sulphuric  acid. 
This  compound  is  also  formed  by  decomposing  a  dilute  solution  of  mercuric  nitrate 
with  a  slight  excess  of  ammonia  (Soubeiran).  (V.)  A  third  compound,  the  yellow 
crystalline  ammonia-subnitrate,  was  obtained  by  C.  G.  Mitscherlich  by  boiling 
the  ammonia  subnitrate  (a)  with  excess  of  ammonia,  and  adding  nitrate  of  am- 
monia, by  which  a  portion  of  the  powder  is  dissolved ;  the  solution,  as  it  cools  and 
loses  ammonia,  yields  small  crystalline  plates  of  a  pale  yellow  colour.  The  con- 
stituents of  this  salt  are  2HgO.N05  and  NH3.  Kane  doubles  its  equivalent,  and 
represents  it  as  a  compound  of  Soubeiran's  salt  with  nitrate  of  ammonia,  as  it 
appears  to  be  produced  by  the  solution  of  the  former  salt  in  the  latter,  (HgO.N03 
-f-  Hg.NH2  +  HgO)  -f  NH4O.N05.  (d.)  Soubeiran's  ammonia  subnitrate  (a)  is 
dissolved  in  considerable  quantity,  when  boiled  in  a  strong  solution  of  nitrate  of 
ammonia,  and  the  solution  deposits,  on  cooling,  small  but  very  brilliant  needles, 
which  were  observed  and  analyzed  by  Kane.  This  salt,  which  may  be  called 
Kane  &  ammonia  subnitrate,  is  decomposed  by  water,  nitrate  of  ammonia  dis- 
solving, and  Soubeiran's  subsalt  being  left  undissolved.  It  contains  the  elements 
of  3(NH4O.N05)  and  4HgO.  Kane  believes  that  it  is  most  likely  to  contain 
Soubeiran's  subnitrate  ready  formed,  which  leaves  two  atoms  of  nitrate  of  ammo- 
nia and  two  atoms  of  water  to  be  otherwise  disposed  of.* 

These  ammonia-nitrates,  like  the  corresponding  chlorides  and  sulphates,  may  be 
regarded  as  nitrates  of  mercurammoniums,  containing  one  or  more  atoms  of  mer- 
cury in  place  of  hydrogen.  Thus,  Mitscherlich' s  ammonia-subnitrate  (a)  is 

NHHg3.N06-f  HO  — nitrate  of  trimercurammonium  with  1  eq.  water;  Soubeiran's 
salt  (6)  is  NHg4.N06  -f-  2HO  =  nitrate  of  tetrarnercuraminonium  with  2  eq. 

water;  the  crystalline  salt  (c)  is  NH2Hg2.N06  4-  HO  =  nitrate  of  bimercuram- 
nionium  with  1  eq.  water;  and  (W)  is  a  compound  of  (b~)  with  nitrate  of  ammo- 
nia and  water  =  2(NH4.N06)  +  2HO  +  (NHg4.N06  -f  2HO). 

Nitrate  of  mercury  forms  an  insoluble  compound  with  sulphide  of  mercury 
HgO.N05  +  2HgS,  resembling  the  compounds  of  the  sulphate  and  chloride  with 
sulphide  of  mercury.  It  also  forms  double  salts  with  iodide  and  cyanide  of  mer- 
cury. 

Alloys  of  mercury  or  amalgams.  —  Mercury  combines  with  a  great  number  of 
metals,  forming  compounds  called  amalgams,  which  are  liquid  or  solid  according 
as  the  mercury  or  the  other  metal  predominates.  A  very  small  quantity  of  a 
foreign  metal  suffices  to  impair  the  fluidity  of  mercury  in  a  very  great  degree. 
All  amalgams  are  decomposed  by  heat,  the  mercury  volatilizing  and  the  other 
metal  remaining. 

*  Trans,  of  the  Royal  Irish  Academy,  yol.  xix.  pt.  i. ;  or,  Ann.  Ch.  Phys.  [2],  Ixxxii. 
225. 


590  MERCURY. 

The  union  of  mercury  with  potassium  and  sodium  is  attended  with  considerable 
disengagement  of  heat ;  the  resulting  amalgams  are  of  a  pasty  consistence,  and 
decompose  water.  The  amalgams  of  tin  and  lead,  when  heated  till  they  are  quite 
liquid,  and  then  left  to  cool  slowly,  yield  solid  crystalline  amalgams  of  definite 
constitution.  An  amalgam  of  silver,  Hg2Ag,  is  found  native  in  the  form  of  regu- 
lar dodecahedrons. 

An  amalgam  of  tin  is  used  for  silvering  glass.  For  this  purpose  a  sheet  of  tin- 
foil is  laid  on  a  horizontal  table,  and  mercury  poured  over  the  whole  surface,  so  as 
to  form  a  layer  about  l-5th  or  l~6th  of  an  inch  thick.  The  plate  of  glass  is  then 
slid  along  the  surface  in  such  a  manner  as  to  cut  this  layer  in  halves  horizontally, 
which  prevents  the  introduction  of  air-bubbles.  The  glass  is  then  loaded  with 
weights,  so  as  to  press  out  the  excess  of  mercury;  and  after  a  few  days,  the  sur- 
face is  found  to  be  covered  with  a  closely-adhering  layer  of  an  amalgam  containing 
about  5  parts  of  tin  to  1  of  mercury. 

Mercury  combines  very  readily  with  bismuth.  An  amalgam  obtained  by  heat- 
ing a  mixture  of  497  parts  of  bismuth,  310  lead,  177  tin,  and  100  mercury,  is 
very  well  adapted  for  injecting  anatomical  preparations :  it  is  solid  at  ordinary 
temperatures,  and  has  a  silvery  lustre,  melts  at  171-5  (Fah.),  and  solidifies  at  140°. 
An  amalgam  of  lead  and  tin,  sometimes  also  containing  bismuth,  is  used  for  cover- 
ing the  cushions  of  electrical  machines. 

ESTIMATION    OF    MERCURY,     AND     METHODS    OP    SEPARATING    IT    FROM    THE 

PRECEDING   METALS, 

Mercury  is  generally  estimated  in  the  metallic  state;  sometimes,  however,  as 
sulphide,  HgS,  or  as  dichloride,  Hg2Cl.  To  separate  it  from  its  compounds  in 
the  metallic  state,  it  may  be  distilled  with  quicklime,  in  a  tube  of  hard  glass 
sealed  at  one  end.  Into  this  tube  is  introduced,  first  a  layer  of  carbonate  of  lime, 
about  an  inch  long ;  then  the  mixture  of  the  substance  with  quicklime ;  lastly,  a 
layer  of  quicklime  about  two  inches  long,  and  a  plug  of  asbestos  to  keep  the  lime 
in  its  place.  The  open  end  of  the  tube  is  next  drawn  out  into  a  narrow  neck, 
and  bent  at  an  obtuse  angle.  The  tube  is  laid  in  a  combustion-furnace,  the  same 
as  that  which  is  used  for  organic  analysis  (277),  the  neck  being  turned  down- 
wards and  made  to  pass  into  a  narrow-mouthed  bottle  containing  water,  so  as  to 
terminate  just  above  the  surface  of  the  water.  The  tube  is  then  gradually  heated 
by  laying  pieces  of  red-hot  charcoal  round  it,  beginning  at  the  part  near  the  neck, 
containing  the  pure  quicklime.  This  portion  having  been  brought  to  a  full  red 
heat,  the  heat  is  carefully  extended  towards  the  middle  part,  to  decompose  the 
compound  and  volatilize  the  mercury  :  any  portion  of  the  compound  that  may  vola- 
tilize undecomposed,  will  be  decomposed  in  passing  over  the  red-hot  lime  at  the 
end.  Lastly,  the  back  part  of  the  tube  containing  the  carbonate  is  heated,  so  as 
to  evolve  carbonic  acid  gas  and  sweep  out  all  the  mercury  vapour  contained  in  the 
tube.  The  quantity  of  carbonic  acid  thus  evolved  may  be  increased  by  mixing 
the  carbonate  of  lime  with  bicarbonate  of  soda.  The  mercury  condenses  under 
the  water  in  the  bottle,  which  must  be  kept  cold.  The  water  is  poured  off  as 
completely  as  possible ;  the  mercury  transferred  to  a  weighed  porcelain  crucible ; 
the  greater  part  of  the  water  which  still  adheres  to  it  removed  by  means  of  blot- 
ting-paper; the  drying  completed  over  sulphuric  acid;  and  the  mercury  finally 
weighed. 

Mercury  may  also  be  precipitated  from  its  solutions  in  the  metallic  state  by 
protochloride  of  tin,  or  by  phosphorous  acid;  the  solution  then  decanted;  the 
mercury  washed  with  water;  and  driecbin  the  manner  just  described. 

Mercury  is  also  frequently  precipitated  from  its  solutions,  as  a  sulphide,  by 
hydrosulphuric  acid.  In  that  case,  if  the  precipitate  consists  of  the  pure  proto- 
sulphide,  HgS,  as  when  it  is  thrown  down  from  a  solution  of  corrosive  sublimate, 
the  precipitate  may  be  simply  collected  on  a  weighed  filter,  washed,  dried  over  the 


SILVER.  591 

water-bath,  weighed,  and  the  quantity  of  mercury  thence  determined.  But  if,  as 
is  generally  thtT  case,  the  precipitate  also  contains  free  sulphur,  as  when  it  is 
thrown  down  from  a  solution  containing  a  ferric  salt,  or  a  considerable  excess  of 
nitric  acid, — or  if  it  be  precipitated  in  conjunction  with  the  sulphides  of  other 
metals,  then  the  mercury  must  be  separated  from  it  by  distillation  with  lime,  as 
above  described.  Or  again,  the  mixture  of  sulphides  may  be  converted  into 
chlorides  by  gentle  heating  in  a  stream  of  chlorine  gas,  the  volatile  chloride  of 
mercury  passed  into  water,  and  the  mercury  precipitated  from  the  solution  by 
protochloride  of  tin. 

The  precipitation  of  mercury  in  the  form  of  dichloride  is  best  effected  by  means 
of  hydrochloric  acid  and  formiuate  of  potash  or  soda.  If  the  mercury  is  contained 
in  an  alloy,  the  alloy  must  be  dissolved  in  aqua-regia;  if  it  is  contained  in  solution 
in  the  form  of  mercuric  nitrate,  hydrochloric  acid  must  be  added,  the  solution,  in 
either  case,  nearly  neutralized  with  potash,  forminate  of  potash  or  soda  then  added, 
and  the  whole  exposed  for  some  days  to  a  temperature  between  140°  and  176°  F. 
(at  the  boiling  heat,  the  mercury  would  be  reduced  to  the  metallic  state).  The 
dichloride  then  precipitates,  and  must  be  collected  on  a  weighed  filter,  washed, 
dried  at  a  gentle  heat,  and  weighed. 

The  quantity  of  mercurous  oxide  present  in  a  solution  may  also  be  determined 
by  precipitation  with  hydrochloric  acid.  The  solution  must,  however,  be  very 
dilute,  and  be  kept  cool ;  it  must  also  contain  but  a  very  small  quantity  of  free 
nitric  acid,  as  a  larger  quantity  would  convert  the  dichloride  of  mercury  into  pro- 
tochloride. To  determine  the  proportions  of  mercurous  and  mercuric  oxide,  when, 
they  exist  together  in  solution,  the  mercurous  oxide  is  first  precipitated  with 
hydrochloric  acid,  and  the  remaining  mercury  by  protochloride  of  tin  or  hydro- 
sulphuric  acid. 

Mercury  may  be  separated  from  all  other  metals,  except  arsenic  and  antimony, 
by  its  superior  volatility.  When  it  exists  in  the  form  of  an  amalgam,  the  com- 
pound is  simply  heated,  and  the  quantity  of  mercury  determined  by  the  loss  of 
weight.  If  it  exists  as  an  oxide,  chloride,  &c.,  combined  with  compounds  of 
other  metals,  it  may  be  separated  by  distillation  with  quicklime,  as  above  described. 
Its  separation  from  the  alkalies  and  earths,  and  from  uranium,  manganese,  nickel, 
cobalt,  iron,  zinc,  and  chromium,  may  also  be  effected  by  precipitation  with  hydro- 
sulphuric  acid.  From  bismuth  and  cadmium  it  may  be  separated  by  reduction 
with  protochloride  of  tin ;  from  copper,  by  mixing  the  solution  with  excess  of 
cyanide  of  potassium,  and  passing  hydrosulphuric  acid  through  the  liquid,  whereby 
the  mercury  is  precipitated  as  sulphide,  while  the  copper  remains  dissolved ;  from 
lead,  by  precipitating  that  metal  with  sulphuric  acid ;  also  by  treating  the  solution 
with  excess  of  cyanide  of  potassium,  which  precipitates  the  lead,  but  not  the 
mercury.  From  arsenic,  tin  and  antimony,  mercury  is  separated  by  the  solubility 
of  the  sulphides  of  metals  in  sulphide  of  ammonium. 


SECTION  II. 

SILVER. 

%  108,  or  1350 ;  Ag  (argentum). 

This  metal  is  found  in  various  parts  of  the  world,  and  occurring  often  in  the 
metallic  state,  and  being  easily  melted,  must  have  attracted  the  attention  of  man- 
kind at  an  early  period.  Before  the  discovery  of  America,  the  silver  mines  of 
8axony  were  of  considerable  importance ;  but  the  silver  mines  of  Mexico  and  Peru 
far  exceed  in  value  the  whole  of  the  European  and  Asiatic  mines,  the  former 


592  SILVER. 

having  furnished  during  the  last  three  centuries,  according  to  Hurnboldt,  316 
millions  of  pounds  troy  of  pure  silver. 

A  considerable  quantity  of  silver  is  obtained  from  ores  of  lead  by  cupellatiou,  as 
described  under  that  metal.  From  argentiferous  copper  ores  also  the  silver  is 
extracted  by  a  process  called  liquation,  which  consists  in  fusing  the  coarse  copper 
(p.  476)  with  three  times  its  weight  of  lead;  a  mixture  of  two  alloys  is  then 
obtained,  the  more  fusible  of  which,  containing  the  greater  part  of  the  lead  and 
nearly  all  the  silver,  is  separated  by  the  application  of  a  moderate  heat,  and  yields 
the  silver  by  cupellation. 

Native  silver,  which  is  in  the  form  of  threads  or  thin  leaves,  is  separated  from 
the  gangue  or  accompanying  rock,  by  amalgamation,  a  process  which  is  also 
followed  in  the  treatment  of  the  most  frequent  ore  of  silver,  the  sulphide,  when 
it  is  not  accompanied  by  sulphide  of  lead.  At  Freiburg,  in  Saxony,  the  sulphide 
of  silver,  ground  to  powder,  is  roasted  in  a  reverberatory  furnace  with  10  per  cent. 

of  chloride  of  sodium,  by  which  the  silver  is  con- 
FIG.  204.  verted  into  chloride.     It  is  then  introduced  into 

barrels  (fig.  204),  with  water,  iron,  and  a  quantity 
of  metallic  mercury,  and  the  materials  kept  in  a 
state  of  agitation  for  eighteen  hours  by  the  revo- 
lution of  the  barrels  on  their  axes.  The  chloride 
of  silver,  although  insoluble,  is  reduced  to  the 
metallic  state  by  the  iron,  and  chloride  of  iron  is 
produced,  while  the  silver  forms  a  fluid  com- 
pound with  the  mercury.  By  adding  more  water, 
and  turning  the  barrels  more  slowly,  the  fluid 
amalgam  separates  and  subsides.  It  is  drawn  off 
and  subjected  to  pressure  in  a  chamois  leather 
bag,  the  mercury  passing  through  the  leather, 
while  a  soft  amalgam  of  silver  remains  in  the  bag.  The  mercury  is  afterwards 
separated  from  this  amalgam  by  a  species  of  distillation,  per  desccnsum,  and  the 
silver  remains. 

In  South  America,  where  fuel  is  scarce,  a  different  process  is  adopted.  The 
ore,  in  a  finely  divided  and  moist  condition,  is  exposed  for  a  considerable  time  to 
the  successive  action  of  common  salt,  sulphate  of  copper  (obtained  by  roasting 
copper  pyrites),  and  mercury,  the  materials  being  spread  on  a  paved  floor,  and 
trodden  by  men  or  horses  to  effect  an  intimate  mixture ;  and  the  silver  amalgam 
thus  obtained  is  separated  from  the  exhausted  ore  by  washing  with  water.  In  this 
process,  the  chloride  of  sodium  and  sulphate  of  copper  form  sulphate  of  soda  and 
protochloride  of  copper.  The  latter  gives  up  chlorine,  converting  part  of  the 
silver  into  chloride,  and  separates  the  sulphur,  provided  an  excess  of  chloride  of 
sodium  is  present  to  dissolve  the  dichloride  of  copper  as  it  forms.  The  dichloride 
of  copper  then  acts  upon  another  portion  of  the  sulphide  of  silver,  forming  disul- 
phide  of  copper  and  chloride  of  silver  :  Cu2Cl-f  AgS^Cu2S  +  AgCl.  The  chloride 
of  silver  thus  produced,  dissolves  in  the  chloride  of  sodium,  and  is  decomposed  by 
the  mercury  subsequently  added,  yielding  calomel  and  metallic  silver.  This  pro- 
cess is  always  attended  with  considerable  loss  of  mercury,  which  however  may 
be  diminished  by  the  previous  addition  of  iron.  Mr.  P.  Johnston  proposes  to 
diminish  the  loss  of  mercury,  as  soluble  chloride,  which  occurs  in  this  process,  by 
using  an  amalgam  of  zinc  and  mercury,  instead  of  pure  mercury. 

Silver  is  obtained  free  from  other  metals,  and  in  a  state  of  purity,  for  chemical 
and  other  purposes,  by  the  following  processes:  —  1.  The  metal  is  dissolved  in 
pure  nitric  acid  slightly  diluted,  and  precipitated  by  a  solution  of  chloride  of 
sodium,  the  salts  of  the  other  metals  present  remaining  in  solution.  The  insoluble 
chloride  of  silver,  thus  obtained,  is  thoroughly  washed  upon  a  filter  with  hot 
water  and  dried.  A  quantity  of  carbonate  of  potash,  equal  to  twice  the  weight 
of  the  silver,  is  then  fused  in  a  crucible,  and  the  chloride  of  silver  gradually 


SILVER.  593 

added  to  it,  whereupon  chloride  of  potassium  is  formed,  and  carbonic  acid  and 
oxygen  escape  with  effervescence.  The  crucible  is  then  exposed  to  a  heat  suffi- 
cient to  fuse  the  reduced  silver,  which  subsides  to  the  bottom. — 2.  The  mode  of 
separating  silver  from  the  common  metals,  in  the  ordinary  practice  of  assaying,  is, 
like  many  metallurgic  operations,  an  exceedingly  elegant  and  refined  process.  A 
portion  of  the  silver  alloy,  the  assay,  is  fused  with  several  times  its  weight  of  pure 
lead  (an  alloy  of  1  copper  and  15  silver  with  96  lead,  for  instance)  upon  a  bone- 
earth  cupel,  which  is  supported  in  a  little  oven  or  muffle,  heated  by  a  proper 
furnace.  Air  being  allowed  access  to  the  assay,  the  lead  is  rapidly  oxidated,  and 
its  highly  fusible  oxide  imbibed,  as  it  is  produced,  by  the  porous  cupel.  The  dis- 
position of  copper  and  other  common  metals  to  oxidate  is  increased  by  the  pre- 
sence of  the  lead ;  and  their  oxides,  which  form  fusible  compounds  with  oxide  of 
lead,  are  removed  in  company  with  the  latter.  When  the  foreign  metal  is  almost 
entirely  removed,  the  assay  is  observed  to  become  rounder  and  more  brilliant,  and 
the  last  trace  of  fused  oxide  occasions  a  beautiful  play  of  prismatic  colours  upon 
its  surface,  after  which  the  assay  becomes,  in  an  instant,  much  whiter,  or  flashes, 
an  indication  that  the  cupellation  is  completed. 

Pure  silver  may  also  be  obtained  from  an  alloy  containing  only  silver  and 
copper,  by  precipitating  the  two  metals  with  excess  of  carbonate  of  soda  with  the 
aid  of  heat,  boiling  the  precipitate  for  about  ten  minutes  with  a  solution  of  grape- 
sugar,  whereby  the  copper  is  reduced  to  the  state  of  red  oxide,  and  the  silver  to 
the  metallic  state,  and  treating  the  moist  precipitate  with  a  hot  solution  of  carbo- 
nate of  ammonia :  the  copper  then  dissolves,  and  pure  silver  remains. 

Pure  silver  is  the  whitest  of  the  metals,  and  susceptible  of  the  highest  polish ; 
when  granulated  by  being  poured  from  a  height  of  a  few  feet  into  water,  its  surface 
is  rough,  but  its  aspect  peculiarly  beautiful.  It  crystallizes  in  cubes  and  regular 
octohedrons,  both  from  a  state  of  fusion  and  by  precipitation  from  solution.  Silver 
is  in  the  highest  degree  ductile  and  malleable;  its  density  varies  between  10474 
and  10-542;  it  fuses  at  1873°.  When  in  the  liquid  state,  it  is  capable  of  absorb- 
ing oxygen  gas  from  the  air,  which  is  discharged  again  in  the  solidification  of  the 
metal,  and  gives  rise  to  a  sort  of  vegetation  upon  its  surface,  or  even  occasions  the 
projection  of  small  portions  of  the  silver  to  a  distance,  an  accident  which  is 
known  in  assaying  as  the  spitting  of  the  metal.  G-ay-Lussac  observed,  that  when 
a  little  nitre  was  thrown  upon  the  surface  of  melted  silver  in  a  crucible,  and  the 
whole  kept  in  a  state  of  fusion  for  half  an  hour,  a  very  considerable  absorption  of 
oxygen  took  place.  When  the  crucible  was  removed  from  the  fire  and  quickly 
placed  under  a  bell-jar  filled  with  water,  which  can  be  done  without  danger,  the 
silver  discharged  a  quantity  of  oxygen  equal  to  20  times  its  volume.  This 
property  is  possessed  only  by  pure  silver,  and  does  not  appear  at  all  in  silver  con- 
taining 1  or  2  per  cent,  of  copper.  As  oxide  of  silver  is  reduced  by  a  red  heat, 
the  absorption  of  the  oxygen  by  the  fluid  metal  must  be  a  phenomenon  of  a 
different  nature  from  simple  oxidation. 

Silver  does  not  combine  with  the  oxygen  of  the  air  at  the  usual  temperature, 
nor  even  when  heated  j  the  tarnishing  of  polished  silver  in  air  is  occasioned  by 
the  formation  of  sulphide  of  silver.  Silver  does  not  dissolve  in  any  hydrated 
acid,  by  substitution  for  hydrogen,  but  on  the  contrary  is  displaced  from  solution 
in  an  acid  by  hydrogen,  and  precipitated  in  the  metallic  state.  This  metal  is  also 
precipitated  by  mercury  and  by  all  the  more  oxidable  metals.  Its  salts  are  reduced 
at  the  usual  temperature  by  sulphate  of  iron,  the  protoxide  in  which  is  converted 
into  sesquioxide.  But  if  the  ferric  sulphate  is  boiled  upon  the  precipitated  silver, 
the  latter  is  dissolved  again,  and  oxide  of  silver  and  protoxide  of  iron  reproduced. 
Silver,  however,  is  oxidated  when  fused  or  heated  strongly  in  contact  with  sub- 
stances for  which  oxide  of  silver  has  a  great  affinity,  as  with  a  siliceous  glass,  and 
stains  the  glass  yellow.  It  is  oxidated  by  concentrated  sulphuric  acid,  with  evo- 
lution of  sulphurous  acid.  Silver  is  readily  dissolved  by  nitric  acid,  at  a  gentle 
heat,  and  with  much  violence,  at  a  high  temperature,  nitrate  of  silver  being 


594  SILVER. 

formed,  and  nitric  oxide  escaping.  Silver  combines  in  three  proportions  with 
oxygen,  forming  a  suboxide,  Ag20,  a  protoxide  AgO,  and  a  peroxide,  Ag02. 

Suboxide  of  silver,  Ag20.  —  Pure  protoxide  of  silver  is  completely  reduced 
to  the  state  of  metal  by  hydrogen  gas,  at  212°  ;  but  the  oxide  contained 
in  citrate  of  silver  loses  only  half  its  oxygen  under  the  same  circumstances, 
the  suboxide  being  formed,  and  remaining  in  combination  with  one  half 
of  the  citric  acid  of  the  former  salt.  The  aqueous  solution  of  the  suboxide 
salt  is  dark  brown,  and  the  suboxide  is  precipitated  black  from  it  by  potash. 
When  the  solution  of  the  subsalt  is  heated,  it  becomes  colourless,  and  metallic 
silver  appears  in  it.  The  salt  dissolves  with  a  brown  colour  in  ammonia.  Several 
other  salts  of  silver,  containing  organic  acids,  comport  themselves  in  the  same 
way  as  the  citrate,  when  heated  in  hydrogen.*  A  solution  of  protoxide  of  silver 
In  ammonia  deposits  on  exposure  to  the  air,  a  grey  suboxide,  containing  108  parts 
of  silver  to  54  parts  oxygen.  When  heated,  it  gives  off  oxygen  and  leaves 
metallic  silver  (Faraday). j" 

Protoxide  of  silver,  AgO,  116  or  1450. — This  oxide  is  thrown  down,  when  pot- 
ash or  lime-water  is  added  to  a  solution  of  nitrate  of  silver,  as  a  brown  powder, 
which  becomes  of  a  darker  colour  when  dried.  The  powder  was  found  to  be  anhy- 
drous by  Gay-Lussac  and  Thenard;  its  density  is  7-143,  according  to  J.  Hera- 
path;  7*250,  according  to  P.  Boullay;  8-2558,  according  to  Karsten.  Oxide  of 
silver  is  decomposed  by  light,  or  at  a  red  heat,  into  oxygen  gas  and  metallic  silver. 
Hydrogen  reduces  it  even  at  212°.  It  is  also  reduced  by  an  aqueous  solution  of 
phosphorous  acid.  When  recently  precipitated,  it  is  decomposed  by  aqueous  sul- 
phurous acid,  yielding  metallic  silver  and  sulphate  of  silver;  but  the  decomposition 
is  only  partial,  even  when  aided  by  heat.  When  immersed  in  water,  it  is  reduced 
by  zinc,  cadmium,  tin,  and  copper,  but  not  by  iron  or  mercury.  In  an  aqueous 
solution  of  hypochlorous  acid,  it  is  converted  into  chloride  of  silver,  oxygen  being 
evolved  together  with  a  small  quantity  of  chlorine. 

Oxide  of  silver  is  a  powerful  base,  and  forms  salts,  several  of  which  have  been 
found  isomorphous  with  the  corresponding  salts  of  soda.  Like  oxide  of  lead,  it 
dissolves  to  a  small  extent  in  pure  water  free  from  saline  matter,  and  the  solution 
has  an  alkaline  reaction.  Oxide  of  silver  is  not  dissolved  by  solutions  of  the 
hydrates  of  potash  and  soda.  Its  salts  are  precipitated  black  by  hydrosulphuric 
acid  and  alkaline  sulphides.  When  treated  with  hydrochloric  acid  or  a  soluble  chlo- 
ride, they  yield  a  white  curdy  precipitate,  the  chloride  of  silver,  which  soon 
becomes  purple,  if  exposed,  while  moist,  to  the  direct  rays  of  the  sun.  This  pre- 
cipitate is  not  dissolved  by  nitric  acid,  but  is  dissolved  by  ammonia  in  common 
with  most  of  the  insoluble  salts  of  silver.  This  precipitate  is  visible,  according  to 
Lassaigne,  even  in  solutions  containing  only  1  part  of  silver  in  800,000  parts  of 
liquid.  In  a  solution  containing  1  part  of  silver  in  200,000  parts,  hydrochloric 
acid  or  common  salt  produces  a  slight  turbidity  :  with  1  part  of  silver  in  400,000, 
the  same  reagents  produce  a  scarcely  perceptible  opalescence ;  and  if  the  propor- 
tion of  liquid  amounts  to  800,000  parts,  the  opalescence  does  not  show  itself  fur  a 
quarter  of  an  hour.  Hydrobromic  acid  and  soluble  metallic  bromides,  added  to 
solutions  of  silver  salts,  throw  down  all  the  silver  in  the  form  of  yellowish  white 
bromide,  insoluble  in  nitric  acid,  and  sparingly  soluble  in  ammonia.  Hydriodic 
acid  and  soluble  iodides  form  a  pale  yellow  precipitate  of  iodide  of  silver,  likewise 
insoluble  in  nitric  acid,  and  still  less  soluble  in  ammonia.  Hydrocyanic  acid  and 
soluble  cyanides  throw  down  a  white  precipitate  of  cyanide  of  silver,  easily  soluble 
in  ammonia,  insoluble  in  cold  dilute  nitric  acid,  but  dissolved  by  strong  nitric  acid 
at  a  boiling  heat,  with  evolution  of  nitric  oxide.  Ammonia  added  in  very  small 
quantity  to  perfectly  neutral  silver-salts,  produces  a  slight  brown  precipitate  of 
oxide  of  silver,  easily  soluble  in  excess ;  but  if  the  solution  contains  excess  of  acid, 
ammonia  produces  no  precipitate.  Potash  added  to  the  ammoniacal  solution  pro- 

*  Ann.  Ch.  Pharm.  xxx.  1.  f  Ann.  Ch.  Phys.  [2],  ix.  107, 


PROTOXIDE    OF    SILVER.  595 

duces  a  white  precipitate,  provided  the  excess  of  ammonia  be  but  small.  The 
fixed  alkalies  form,  in  neutral  or  acid  solutions  of  silver-salts,  a  brown  precipitate 
of  oxide  of  silver,  insoluble  in  excess.  Alkaline  carbonates  precipitate  white  car- 
bonate of  silver,  soluble  in  ammonia  and  carbonate  of  ammonia.  Ordinary  tri- 
laxic  phosphate  of  soda  forms  a  yellow  precipitate  ;  pyrophosphate  and  metaphos- 
phafe  of  soda  form  white  precipitates.  Chromate  of  potash  forms  a  dark  crimson 
precipitate  of  chromate  of  silver.  Alkaline  arsenites  form  a  canary-yellow  precipi- 
tate of  arsenite  of  silver.  Oxalic  acid  forms  a  white  pulverulent  precipitate  of 
oxalate  of  silver.  Silver  is  precipitated  from  its  solutions  in  the  metallic  state  by 
phosphorus,  phosphorous  acid,  phosphuretted  hydrogen,  and  sulphurous  acid  (im- 
perfectly) ;  by  various  metals,  viz.,  zinc,  cadmium,  tin,  lead,  iron,  manganese, 
copper,  mercury,  bismuth,  tellurium,  antimony,  and  arsenic  ;  also  by  protoxide  of 
uranium,  hydrated  protoxide  of  manganese,  and  protoxide  of  tin  ;  and  by  various 
organic  substances  at  a  boiling  heat,  e.  g.,  charcoal,  sugar,  aldehyde,  formic  acid, 
tincture  or  infusion  of  galls,  and  volatile  oils.  Many  organic  substances  added  to 
a  solution  of  nitrate  of  silver  mixed  with  excess  of  ammonia,  throw  down  metallic 
silver  in  the  form  of  a  beautiful  specular  film,  lining  the  sides  of  the  vessel.  This 
effect  is  produced  by  aldehyde,  saccharic  acid,  salicylous  acid,  pyrorneconic  acid, 
and  various  essential  oils.  A  mixture  of  oil  of  cinnamon  and  oil  of  cloves  is  found 
to  produce  an  exceedingly  brilliant  speculum,  and  has  indeed  been  used  for  silver- 
ing mirrors  in  place  of  the  ordinary  process  with  tin  and  mercury;  it  is  particu- 
larly adapted  for  silvering  curved  surfaces.  A  very  bright  and  regular  specular 
surface  is  also  produced  by  adding  a  solution  of  milk-sugar  to  an  ammoniacal  solu- 
tion of  nitrate  of  silver  mixed  with  caustic  potash  or  soda;  the  precipitation  then 
takes  place  without  the  application  of  heat  (Liebig).* 

Oxide  of  silver  combines  with  ammonia  and  forms  the  fulminating  ammonmret 
of  silver,  a  substance  of  a  dangerous  character  from  the  violence  with  which  it 
explodes.  The  ammoniuret  may  be  formed  by  digesting  newly  precipitated  oxide 
of  silver  in  strong  ammonia,  or  more  readily  by  dissolving  nitrate  of  silver  in 
ammonia,  and  precipitating  the  liquor  by  potash  in  slight  excess.  If  this  sub- 
stance be  pressed  by  a  hard  body,  while  still  moist,  it  explodes  with  unequalled 
violence  ;  when  dry,  the  touch  of  a  feather  is  often  sufficient  to  cause  it  to  fulmi- 
nate. The  explosion  is  obviously  occasioned  by  the  reduction  of  the  silver  from 
the  combination  of  its  oxygen  with  the  hydrogen  of  the  ammonia,  and  the  evolu- 
tion of  nitrogen  gas. 

Sulphide  of  silver,  AgS,  124  or  1550.  —  Sulphur  and  silver  may  be  combined 
together  by  fusion  ;  the  excess  of  sulphur  escapes,  and  at  a  high  temperature  the 
sulphide  melts  ;  it  forms,  on  cooling,  a  crystalline  mass.  This  compound  has  a 
lead-grey  colour  and  metallic  lustre.  It  is  so  soft  that  it  may  be  cut  with  a  knife, 
and  is  malleable.  The  sulphide  of  silver  is  also  remarkable  for  conducting  elec- 
tricity, like  a  metal,  when  warmed.  The  same  compound  occurs  in  nature,  some- 
times crystallized  in  octohedrons  with  secondary  faces.  This  sulphide  is  particu- 
larly interesting  from  being  isomorphous  with  the  sulphide  of  copper,  AgS  with 
Cu2S  (p.  501).  These  two  sulphides  replace  each  other  in  indeterminate  propor- 
tions in  several  double  sulphides  of  silver  and  other  ffletals,  as  in  polybasite  and 
fahl-ores,  the  composition  of  which  may  be  expressed  by  the  following  formulae, 
the  symbols  placed  above  each  other  representing  constituents,  of  which  either  the 
one  or  the  other  may  be  present  : 


Polybasite     . 

„  ,  ,  /. 

Fabl-ores      ( 

Chloride  of  silver,  AgCl,  143*5  or  1793*75.  —  This  salt  contains,  in  100  parts, 


*  Ann.  Ph.  Pharm.  xcviii.    132. 


596  SILVER. 

24-69  parts  of  chlorine,  and  75-31  parts  of  silver.  It  is  found  native  as  horn-sil- 
ver, in  translucent  cubes  or  octohedrons  of  a  greyish-white  colour,  and  specific 
gravity  5-55.  The  same  compound  is  also  thrown  down  as  a  white  precipitate,  at 
first  very  bulky  and  curdy,  when  hydrochloric  acid  or  a  soluble  chloride  is  added 
to  any  soluble  salt  of  silver,  except  the  hyposulphite.  It  is  wholly  insoluble  in 
water,  and  the  most  minute  quantity  of  hydrochloric  acid  contained  in  water  may 
be  detected  by  adding  to  it  a  drop  of  a  solution  of  nitrate  of  silver.  Hydro- 
chloric acid,  when  concentrated,  dissolves  chloride  of  silver,  which  crystallizes 
from  it  in  octohedrons,  when  the  solution  is  evaporated.  This  salt  dissolves  easily 
in  solution  of  ammonia,  and  crystallizes  also  as  the  ammonia  evaporates.  When 
heated,  it  fuses  at  about  500°,  forming  a  transparent  yellowish  liquid,  which 
becomes,  after  cooling,  a  mass  that  may  be  cut  with  a  knife,  and  has  considerable 
resemblance  to  horn  :  a  property  to  which  it  was  indebted  for  the  name  of  horn- 
silver,  applied  to  it  by  the  older  chemists.  It  is  not  volatile.  Chloride  of  silver 
is  not  affected  by  a  concentrated  solution  of  potash.  It  is  easily  reduced  to  the 
state  of  metal  by  zinc  or  iron  with  water.  Chloride  of  silver  may  be  dissolved  out 
in  this  way  by  means  of  zinc  and  acidulated  water,  from  a  porcelain  crucible  in 
which  it  has  been  fused.  To  obtain  pure  silver  by  this  mode  of  reduction,  it  is 
necessary  to  use  zinc  free  from  lead,  otherwise  that  metal,  not  being  dissolved  by 
the  sulphuric  acid,  remains  mixed  with  the  silver.  A  better  mode  of  reduction 
is  to  boil  the  chloride  of  silver  with  an  equal  weight  of  starch-sugar  and  a  solution 
of  one  part  of  carbonate  of  soda  in  three  parts  of  water  (Bottger).  The  chloride 
and  other  salts  of  silver  acquire  a  dark  colour  when  exposed  to  light ;  chlorine 
escapes,  and  a  portion  of  the  salt  appears  to  be  reduced  to  the  metallic  state,  as 
the  blackened  surface  conducts  electricity.  According  to  Wetzlar,  the  black  sub- 
stance contains  an  inferior  chloride  of  silver,  and  is  not  attacked  by  nitric  acid,  or 
soluble  in  ammonia.  It  has  also  been  supposed  that  the  blackening  is  due,  not  to 
any  chemical  decomposition,  but  merely  to  a  change  in  the  state  of  aggregation  of 
the  particles.  It  appears,  however,  from  some  recent  experiments  by  Dr.  F. 
Guthrie,  that  the  chloride  is  completely  decomposed  and  metallic  silver  separated, 
even  in  presence  of  free  nitric  acid.  Paper  charged  with  chloride  of  silver  is  very 
sensitive  to  the  impression  of  light,  and  is  the  material  used  for  positive  photo- 
graphs, the  unaltered  chloride  being  afterwards  dissolved  out  by  a  solution  of  hypo- 
sulphite of  soda. 

One  hundred  parts  of  chloride  of  silver  absorb  17 '9  parts  of  ammoniacal  gas, 

forming  the  compound,  3NH3.2AgCl,  or  NH(NH4>2Ag  j  ^      This  compound 

gives  off  its  ammonia  in  the  air.  Chloride  of  silver  is  dissolved  by  concentrated 
and  boiling  solutions  of  the  chlorides  of  potassium,  sodium,  and  ammonium,  and, 
on  cooling,  a  double  salt  is  deposited  in  crystals,  generally  cubes.  Chloride  of 
silver  is  also  dissolved  by  cyanide  of  potassium,  and  the  solution  yields  a  double 
salt  by  evaporation  (Liebig). 

Bromide  of  silver,  AgBr,  188  or  2350. — This  salt  consists  in  100  parts,  of 
42-56  bromine  and  57 '44  silver.  It  is  found  native  in  Mexico  and  in  Bretagne; 
sometimes  in  small  amorphous  masses,  sometimes  in  greenish-yellow  octohedral 
crystals.  It  is  insoluble  in  water,  and  falls  as  a  precipitate  which  is  white  at  first, 
but  becomes  pale  yellow  when  collected.  When  fused  and  cooled,  it  yields  a  mass 
of  a  pure  and  intense  yellow  colour.  It  has  most  of  the  properties  of  chloride  of 
silver,  but  dissolves  very  sparingly  in  ammonia. 

Iodide  of  silver,  Agl,  23436  or  2929-5. — This  salt  contains,  in  100  parts, 
53-87  of  iodine  and  46-13  of  silver.  It  is  found  native,  sometimes  in  regular 
hexagonal  prisms.  It  is  insoluble  in  water,  like  the  chloride,  and  is  prepared  in 
a  similar  manner  by  precipitation,  but  is  distinguished  from  that  salt  by  its  colour, 
which  is  pale  yellow,  by  the  difficulty  with  which  it  is  dissolved  in  ammonia, 
being  even  less  soluble  than  the  bromide,  and  by  being  blackened  more  slowlj 


SALTS    OF    SILVER.  597 

by  the  action  of  light.  According  to  Martini,  2500  parts  of  ammonia,  of 
density  0-960,  are  required  to  dissolve  one  part  of  iodide  of  silver.  It  is  soluble 
to  a  large  extent,  at  the  boiling  temperature,  in  concentrated  solutions  of  the 
alkaline  and  earthy  iodides,  and  forms  with  them  double  salts. 

Silver  is  rapidly  dissolved  by  hydriodic  acid,  with  evolution  of  hydrogen.  If 
the  action  is  assisted  by  heat,  the  solution  deposits,  on  cooling,  a  colourless  crys- 
talline salt,  resembling  nitrate  of  silver,  but  decomposing  as  soon  as  it  is  separated 
from  the  liquid :  it  appears  to  consist  of  an  iodide  of  silver  and  hydrogen.  The 
mother-liquor,  when  left  to  itself,  deposits  iodide  of  silver  in  large  regular  six-sided 
prisms,  resembling  the  native  iodide  (H.  Ste. -Claire  Deville).* 

Fluoride  of  silver,  AgF,  is  obtained  by  dissolving  the  oxide  or  carbonate  in 
hydrofluoric  acid.  It  is  very  soluble  in  water,  and  is  partly  decomposed  by  evapo- 
ration. 

Cyanide  of  silver,  AgCy;  134  or  1675. — This  salt  contains,  in  100  parts, 
1941  cyanogen  and  80-59  silver.  It  falls  as  a  white  powder  when  hydrocyanic 
acid  is  added  to  a  solution  of  nitrate  of  silver.  It  is  distinguished  from  chloride 
of  silver  by  dissolving  in  concentrated  nitric  and  sulphuric  acids,  when  heated. 
It  is  readily  decomposed  by  hydrochloric  acid,  and  yields  hydrocyanic  acid,  100 
parts  of  cyanide  of  silver  giving  20-36  parts  of  hydrocyanic  acid.  It  is  decom- 
posed by  a  red  heat,  giving  off  half  its  cyanogen  and  leaving  paracyanide  of  silver, 
Ag6Cy3.  Cyanide  of  silver  is  dissolved  by  cyanide  of  potassium,  and  other  soluble 
cyanides.  The  double  cyanide  of  potassium  and  silver  crystallizes  in  octohedrons, 
KCy.AgCy. 

Carbonate  of  silver,  AgO.C02,  is  a  white  insoluble  powder. 

Sulphate  of  silver,  AgO.S03;  156  or  1950.  —  Obtained  by  dissolving  silver, 
with  heat,  in  concentrated  sulphuric  acid,  or  by  precipitating  a  solution  of  nitrate 
of  silver  with  sulphate  of  potash.  It  is  soluble  in  88  times  its  weight  of  boiling 
water,  and  crystallizes,  on  cooling,  in  the  form  of  anhydrous  sulphate  of  soda. 
This  salt  is  highly  soluble  in  ammonia,  and  gives,  by  evaporation,  an  ammoniacal 
sulphate  of  silver  in  fine  transparent  crystals,  which  are  persistent  in  air; 

AgO.S03  +  2NH3,  or  NH2(NH<)Ag.S04.  Chromate  and  seleniate  of  silver  form 
analogous  compounds  with  ammonia,  which  are  all  isomorphous.  The  bichromate 
of  silver  is  also  isomorphous  with  bichromate  of  soda. 

IJyposulphate  of  silver,  AgO.S205,  is  soluble  in  water,  and  crystallizes  in  the 
same  form  as  hyposulphate  of  soda.  It  crystallizes  also  with  ammonia,  as  AgO.Sjj05 

+  2NH3,  or  NH^NHjA^SA. 

Hyposulphite  of  silver,  AgO.S202.  —  Hyposulphurous  acid  appears  to  have  a 
greater  affinity  for  oxide  of  silver  than  for  any  other  base.  Oxide  of  silver  decom- 
poses the  alkaline  hyposulphites,  liberating  one  half  of  their  alkali,  and  forming  a 
double  hyposulphite  of  the  alkali  and  silver.  These  double  salts  are  best  prepared 
by  adding  chloride  of  silver  in  small  portions  to  the  soluble  hyposulphite  of  pot- 
ash, soda,  ammonia,  or  lime  in  the  cold,  till  the  liquid  is  saturated;  after  which, 
the  solution  is  filtered,  and  mixed  with  a  large  quantity  of  alcohol,  which  precipi- 
tates the  double  salt;  the  potash  and  soda  salts  are  crystallizable.  Herschel 
considers  the  double  salts  obtained  in  this  manner  as  probably  containing  one  eq. 
of  hyposulphite  of  silver  to  two  eq.  of  the  other  hyposulphite.  The  solution  of 
one  of  these  double  salts  dissolves  more  oxide  of  silver,  and  forms  a  double  salt, 
which  is  believed  to  contain  single  equivalents  of  the  salts,  and  precipitates  as  a 
white  crystalline,  pulverulent,  bulky  mass.  The  second  compound  is  sparingly 
soluble  in  water,  but  dissolves  in  ammonia,  and  communicates  to  the  Jiquor  an 
intensely  sweet  taste. 

The  hyposulphite  of  silver  itself  is  an  insoluble  substance ;  it  is  prone  to  undergo 
decomposition,  changing  spontaneously  into  sulphate  and  sulphide  of  silver. 

*  Compt.  rend.  xlii.  894. 


598  SILVER. 

"When  to  a  dilute  solution  of  nitrate  of  silver,  a  dilute  solution  of  hyposulphite  of 
soda  is  added  by  small  quantities,  a  white  precipitate  of  hyposulphite  of  silver  falls, 
which  dissolves  again  in  a  few  seconds,  from  the  formation  of  the  soluble  double 
hyposulphite  of  soda  and  silver.  When  enough  of  hyposulphite  of  soda  has  been 
gradually  added  to  render  the  precipitate  permanent,  without,  however,  decom- 
posing the  whole  silver  salt,  a  flocculent  mass  is  obtained  of  a  dull  grey  colour, 
which  is  permanent.  The  liquor  contains  much  hyposulphite  of  silver,  and  has 
an  intensely  sweet  taste,  not  at  all  metallic ;  the  silver  is  not  precipitated  from  it 
by  hydrochloric  acid  or  the  chlorides.  An  excess  of  hyphosulphate  of  soda 
destroys  the  precipitated  hyposulphite  of  silver,  converting  it  into  sulphide  of 
silver. 

Nitrate  of  silver,  AgO.N06;  170  or  2125.  —  When  a  piece  of  pure  silver  is 
suspended  in  nitric  acid,  it  dissolves  for  a  time  without  effervescence  at  a  low  tem- 
perature, nitrous  acid  being  produced,  which  colours  the  liquid  blue;  but  if  heat 
be  applied  or  the  temperature  allowed  to  rise,  then  the  metal  dissolves  with  violent 
effervescence,  from  the  escape  of  nitric  oxide.  The  nitrate  of  silver  crystallizes 
on  cooling  in  colourless  tables,  which  are  anhydrous.  It  is  soluble  in  1  part  of 
cold,  in  £  part  of  hot  water,  and  in  4  parts  of  boiling  alcohol.  The  solution  of 
this  salt  does  not  redden  litmus  paper,  like  most  metallic  salts,  but  is  exactly  neu- 
tral Nitrate  of  silver  fuses  at  426°,  and  forms  a  crystalline  mass  on  cooling ;  it 
is  cast  into  little  cylinders  for  the  use  of  surgeons.  It  is  sometimes  adulterated 
in  this  state  with  nitrate  of  potash,  which  may  be  detected  by  the  alkaline  residue 
which  the  salt  then  leaves  when  heated  before  the  blowpipe,  —  or  with  nitrate  of 
lead,  in  which  case  the  solution  of  the  salt  is  precipitated  by  iodide  of  potassium, 
of  a  full  yellow  colour.  When  applied  to  the  flesh  of  animals,  it  instantly 
destroys  the  organization  and  vitality  of  the  part.  It  forms  insoluble  compounds 
with  many  kinds  of  animal  matter,  and  is  employed  to  remove  it  from  solution. 
When  organic  substances,  to  which  a  solution  of  nitrate  of  silver  has  been  applied, 
are  exposed  to  light,  they  become  black  from  the  reduction  of  the  oxide  of  silver 
to  the  metallic  state.  A  solution  of  nitrate  of  silver  in  ether  is  employed  to  dye 
the  hair  black.  One  part  of  nitrate  of  silver  and  4  parts  of  gum  arabic  dissolved 
in  4  parts  of  water,  and  blackened  with  a  small  quantity  of  Indian  ink,  form  the 
indelible  marking  ink  used  to  write  upon  linen.  The  part  of  the  linen  to  be 
marked  should  be  first  wetted  with  a  solution  of  carbonate  of  soda  and  dried,  and 
the  writing  should  be  exposed  to  the  light  of  the  sun.  For  this  ink,  which  is 
expensive,  another  liquid  has  been  substituted  by  bleachers,  namely  coal  tar,  made 
sufficiently  thin  with  naphtha  to  write  with,  which  is  found  to  resist  chlorine,  and 
to  answer  well  as  a  marking  ink. 

A  strong  solution  of  nitrate  of  silver  absorbs  two  equivalents  of  ammoniacal 
gas,  and  forms  the  crystallizable  Ammoniacal  nitrate  of  silver,  Ago.N05  +  2NH3 

=  NH2(NH4)Ag.N06.  The  dry  nitrate  in  powder  absorbs  three  atoms  of  ammo- 
nia, AgO.NO.  +  3NH3  =  NH(NH^A^N06. 

Nitrate  of  silver  forms  a  double  salt  with  nitrate  of  the  red  oxide  of  mercury, 
which  crystallizes  in  prisms.  Nitrate  of  silver  and  cyanide  of  mercury  also  form 
a  double  salt,  when  hot  solutions  of  them  are  mixed :  AgO.N05-J-2HgCy-f  8HO. 
Cyanide  of  silver  is  soluble  in  a  boiling  solution  of  nitrate  of  silver,  and  forms  a 
crystalline  compound,  Ago.N05  -f  2AgCy,  which  is  decomposed  by  water. 

Nitrite  of  silver,  AgO.N03;  154  or  1925.  —  Nitrate  of  soda  is  fused  at  a  red 
heat,  till  it  is  wholly  converted  into  nitrite  by  loss  of  oxygen;  the  latter  salt  then 
begins  to  give  off  nitrous  acid,  and  a  small  portion  of  the  salt  dissolved  in  water 
will  be  found  to  precipitate  silver  brown.  The  fusion  is  then  interrupted,  the  salt 
dissolved  in  boiling  water,  precipitated  by  nitrate  of  silver,  and  filtered  while  still 
very  hot.  The  nitrite  of  silver,  which  requires  120  times  its  weight  of  water  at 
60°  to  dissolve  it,  is  precipitated  as  the  solution  cools.  The  other  nitrites  are 
prepared  by  rubbing  this  salt  in  a  mortar  with  chlorides  taken  in  equivalent  quan- 


ESTIMATION    OF    SILVER.  599 

titles.  It  appears  from  experiments  of  Proust,  that  two  subnitrites  of  silver 
exist,  one  soluble  and  the  other  insoluble. 

Acetate  of  silver,  which  is  soluble  in  100  times  its  weight  of  cold  water,  is  pre- 
cipitated when  acetate  of  copper  is  mixed  with  a  concentrated  solution  of  nitrate 
of  silver  It  crystallizes  from  solution  in  boiling  water  in  anhydrous  needles. 

Oxalate  of  silver  is  an  insoluble  powder.  A  double  oxalate  of  potash  and 
silver  is  formed  by  saturating  binoxalate  of  potash  with  carbonate  of  silver.  It  is 
very  soluble,  and  forms  rhomboidal  crystals,  which  are  persistent  in  air. 

Peroxide  of  silver.  —  A  superior  oxide  of  silver  is  deposited  upon  the  positive 
pole  or  zincoid  of  a  voltaic  battery  in  a  weak  solution  of  nitrate  of  silver,  in  the 
form  of  needles  of  3  or  4  lines  in  length,  which  are  black  and  have  a  metallic 
lustre,  while  metallic  silver  is,  at  the  same  time,  deposited  in  crystals  upon  the 
negative  pole  or  chloroid.  The  former  crystals  are  converted  by  sulphuric  acid 
into  oxide  of  silver  and  oxygen,  and  yield  with  hydrochloric  acid,  chloride  of 
silver  and  chlorine.  According  to  Fischer,  whose  observations  are  confirmed  by 
L.  G-melin,  the  peroxide  prepared  as  above  from  nitrate  of  silver  always  retains 
nitric  acid,  and  if  prepared  in  a  similar  manner  from  the  sulphate,  it  always 
retains  sulphuric  acid.* 

Alloys  of  silver. — Silver  may  be  readily  alloyed  with  most  metals.  It  combines 
by  fusion  with  iron,  from  which  it  cannot  be  separated  by  cupellation.  Native 
silver  is  always  associated  with  gold ;  the  two  metals  are  found  crystallized  toge- 
ther in  all  proportions  in  the  same  cubic  or  octohedral  crystals.  Grold  may  be 
detected  in  a  silver  coin,  by  dissolving  the  latter  in  pure  nitric  acid,  when  a  small 
quantity  of  black  powder  remains,  which  after  being  washed  with  water,  will  be 
found  to  dissolve  in  nitro-hydrochloric  acid,  giving  a  yellow  solution,  in  which 
protochloride  of  tin  produces  a  precipitate  of  the  purple  powder  of  Cassius.  Pure 
silver,  being  very  soft,  is  always  alloyed  in  coin  and  plate,  with  a  certain  quantity 
of  copper,  to  make  it  harder.  The  standard  silver  of  England  is  an  alloy  of  222 
pennyweights  of  silver  with  18  pennyweights  of  copper,  or  it  contains  92-5  per 
cent,  of  silver.  The  standard  of  the  Spanish  dollar,  of  the  French  and  most 
other  coinages,  is  90  per  cent,  of  silver.  The  alloy  of  silver  and  copper  of  great- 
est stability  consists  of  71  9  silver,  and  28-1  copper,  and  corresponds  with  the 
formula  AgCu4.f 

ESTIMATION     OF    SILVER,    AND     METHODS    OF    SEPARATING    IT    FROM    OTHER 

METALS. 

Silver,  when  in  the  state  of  solution,  is  always  estimated  as  chloride.  The  so-  . 
lution,  if  not  already  acid,  is  slightly  acidulated  with  nitric  acid ;  the  silver  pre- 
cipitated with  hydrochloric  acid,  and  the  liquid  placed  for  some  hours  in  a  warm 
situation  to  cause  the  precipitated  chloride  of  silver  to  settle  down.  The  precipi- 
tate is  collected  on  a  filter,  which  should  be  as  small  as  possible,  washed  with 
water,  and  dried  at  212°.  It  must  then  be  separated  as  completely  as  possible 
from  the  filter;  introduced  into  a  porcelain  crucible,  previously  weighed;  the  filter 
burnt  to  ashes  outside  the  crucible ;  the  ashes  added  to  the  contents  of  the  cru- 
cible ;  and  the  whole  strongly  heated  over  a  lamp  till  the  chloride  of  silver  is 
brought  to  a  state  of  tranquil  fusion,  after  which  it  is  left  to  cool  and  weighed. 
It  contains  75-26  per  cent,  of  silver.  This  mode  of  estimation  is  aifected  with  an 
error,  arising  from  the  partial  reduction  of  the  chloride  of  silver  by  the  organic 
matter  of  the  filter.  The  error  thus  occasioned  is  but  slight  when  the  process  is 
well  conducted,  and  may  always  be  obviated  by  treating  the  fused  chloride  after 
cooling  with  nitric  acid  to  dissolve  the  reduced  silver;  then  adding  hydrochloric 

*  Gmelin's  Handbook,  Translation,  vi.  145. 
f  Levol,  Ann.  Ch.  Phys.  [3],  xxxvi.  220. 


600  GOLD. 

acid,  evaporating  to  dryness,  and  again  fusing  the  residue.  Another  mode  of  pro- 
ceeding is  to  collect  the  chloride  of  silver  on  a  weighed  filter,  and  dry  it  in  an  oil- 
bath  at  about  300°  F.  The  chloride  may  also  be  washed  by  decantation,  and 
the  use  of  a  filter  avoided  altogether  j  but  the  washing  requires  very  careful  mani- 
pulation. 

The  quantity  of  silver  in  a  solution  may  also  be  determined  by  precipitating  it 
with  a  solution  of  chloride  of  sodium  of  known  strength.  The  solution  of  chloride 
of  sodium  is  made  of  such  a  strength  that  a  cubic  decimetre  of  it  exactly  precipi- 
tates 1  gramme  of  pure  silver.  It  is  added  to  the  silver  solution  from  a  burette, 
divided  into  cubic  centimetres,  the  liquid  being  well  shaken  after  each  addition, 
to  cause  the  precipitate  to  settle  down.  The  number  of  cubic  centimetres  of  solu- 
tion thus  added  determines  the  quantity  of  silver  present. 

As  silver  is  reduced  from  many  of  its  salts  by  the  mere  action  of  heat,  the 
quantity  of  silver  in  such  compounds  may  be  readily  determined  by  simply  ignit- 
ing them  in  a  porcelain  crucible.  This  method  is  applicable  to  nearly  all  salts  of 
silver  which  contain  organic  acids.  It  must  be  observed,  however,  that  in  some 
cases,  a  certain  quantity  of  carbon  remains  combined  with  the  silver,  and  that 
some  organic  silver  compounds  containing  nitrogen  leave  cyanide  of  silver  when 
ignited. 

The  method  of  precipitating  by  hydrochloric  acid  serves  to  separate  silver  from 
all  other  metals.  If  lead  be  present  in  solution  with  silver,  the  liquid  must  be 
diluted  with  a  large  quantity  of  water  before  the  hydrochloric  acid  is  added ; 
because  the  chloride  of  lead  is  but  sparingly  soluble.  The  separation  of  silver 
from  lead  may  also  be  effected  by  precipitating  both  the  metals  as  chlorides,  and 
dissolving  the  chloride  of  silver  in  ammonia.  To  separate  silver  from  mercury, 
the  latter  metal,  if  in  the  state  of  mercurous  oxide,  must  first  be  converted  into 
mercuric  oxide  by  oxidation  with  nitric  acid. 

The  estimation  of  the  quantity  of  silver  in  alloys,  such  as  coins,  is  usually 
effected  either  by  cupellation  in  the  manner  already  described  (p.  593),  or  by  dis- 
solving the  alloy  in  nitric  acid,  and  precipitating  the  silver  with  a  graduated  solu- 
tion of  chloride  of  sodium.* 

The  cupellation  of  silver  is  always  attended  with  a  certain  loss,  arising  partly 
from  a  portion  of  the  melted  silver  being  absorbed  by  the  cupel,  and  partly  by 
volatilization.  The  loss  thus  occasioned  varies  with  the  proportion  of  lead  em- 
ployed in  the  cupellation,  with  the  proportion  of  silver  in  the  alloy,  and  likewise 
with  the  heat  of  the  furnace :  hence  the  results  obtained  require  a  certain  correc- 
tion, the  amount  of  which  must  be  determined  by  special  trials  made  upon  alloys 
of  known  composition  and  with  different  proportions  of  lead. 


SECTION  III. 

GOLD. 

Eq.  98-33  or  1229-16;  Au.  (Aurum). 

Gold  is  found  in  small  quantity  in  most  countries,  sometimes  mixed  with  iron 
pyrites,  copper  pyrites,  and  galena,  but  generally  native,  massive,  and  dissemi- 
nated in  threads  through  crystalline  rocks,  such  as  quartz,  or  in  grains  among  the 
sand  of  rivers,  and  in  alluvial  deposits  formed  by  the  disintegration  of  ancient 
rocks.  In  these  deposits,  some  of  which  are  of  great  extent,  gold  is  occasionally 
found  in  masses  of  considerable  size,  called  nuy<jets.  Formerly,  the  principal  sup- 

*  The  process,  by  Gay-Lussac,  for  this  purpose  is  described,  with  the  requisite  Tables,  in 
the  Parliamentary  Report  upon  the  Royal  Mint,  1837,  Appendix,  p.  145.  See  also  Dr, 
Miller's  Elements  of  Chemistry,  p.  1035. 

37 


GOLD. 


601 


ply  of  this  metal  was  from  the  mines  of  South  America,  Hungary,  and  the  Uralian 
mountains ;  but  of  late  years,  the  largest  quantities  have  been  obtained  from  Cali- 
fornia and  Australia.  Native  gold  is  sometimes  pure,  but  is  more  frequently 
associated  in  various  proportions  with  silver. 

Gold  is  separated  from  the  substances  with  which  it  is  mechanically  associated, 
either  by  washing  with  water,  whereby  the  earthy  matters  are  carried  away  while 
the  heavy  gold  particles  remain  behind,  or  by  amalgamation.  The  small  quantity 
of  gold  which  occurs,  generally  associated  with  silver,  in  certain  lead  and  copper 
ores,  is  extracted  by  liquation  and  cupellation,  in  the  manner  already  described  for 
silver.  By  these  processes,  gold  is  obtained  free  from  all  other  metals  except 
silver,  and  from  this  it  may  be  separated  by  nitric  acid,  which  dissolves  the  silver, 
but  only  when  it  forms  a  large  proportion  of  the  alloy.  When  nitric  acid  does 
not  dissolve  the  silver,  the  alloy  is  submitted  to  an  operation  termed  quartation, 
which  consists  in  fusing  it  with  four  times  its  weight  of  silver,  after  which  the 
whole  of  the  silver  may  be  dissolved  out  by  nitric  acid. 

Pure  gold  may  be  obtained  from  any  alloy  containing  it,  by  dissolving  the  alloy 
in  a  mixture  of  two  measures  of  hydrochloric  and  one  measure  of  nitric  acid ; 
separating  the  solution  from  insoluble  chloride  of  silver  by  nitration ;  evaporating 
it  over  the  water-bath  till  acid  vapours  cease  to  be  exhaled ;  then  dissolving  the 
residue  in  water  acidulated  with  hydrochloric  acid ;  and  adding  protosulphate  of 
iron,  which  completely  precipitates  the  gold  in  the  form  of  a  brown  or  brownish- 
yellow  powder,  the  protosulphate  of  iron  being  at  the  same  time  converted  into 
sesquisulphate  and  sesquichloride : 

6(FeO .  S03)  +  Au2Cl3  =  2(Fe203 .  3S03)  +  Fe2Cl3  +  2Au. 

The  gold  thus  precipitated  is  quite  destitute  of  metallic  lustre,  but  acquires  that 
character  by  burnishing. 

From  alloys  of  gold  and  silver,  or  of  gold,  silver,  and  copper,  the  gold  may  also 
be  separated  by  the  action  of  strong  sulphuric  acid.  The  alloy,  after  being  granu- 
lated by  pouring  it  in  the  melted  state  into  water,  is  heated  in  a  platinum  or  cast- 
iron  vessel  with  2£  times  its  weight  of  sulphuric  acid  of  specific  gravity  1-815 
(66°  Baume),  the  heat  being  continued  as  long  as  sulphurous  acid  is  evolved. 
The  silver  and  copper  are  thereby  converted  into  sulphates,  while  the  gold  remains 
unattacked.  The  solution  is  boiled  for  a  quarter  of  an  hour  with  an  additional 
quantity  of  sulphuric  acid  of  specific  gravity  1-653,  or  58°  Baume  (obtained  by 
concentrating  the  acid  mother-liquors  of  sulphate  of  copper  produced  in  the  opera- 
tion), and  afterwards  left  at  rest.  The  gold  then  settles  down,  and  the  liquid, 
after  being  diluted  with  water,  is  transferred  to  a  leaden  vessel  and  again  boiled 
with  sheets  of  copper  immersed  in  it.  The  silver  is  then  precipitated  in  the 
metallic  state,  while  the  copper  is  converted  into  sulphate,  and  dissolves.  The 
gold  deposited  in  the  manner  above  described  still  retains  a  small  quantity  of 
silver,  from  which  it  is  separated  by  treating  it  a  second  and  a  third  time  with 
strong  sulphuric  acid:  it  then  retains  only  0-005  of  silver.  This  process  is  not 
applicable  to  alloys  containing  more  than  20  per  cent,  of  gold ;  richer  alloys  must 
first  be  fused  with  the  requisite  quantity  of  silver.  It  is  applied  on  the  large 
scale  to  the  extraction  of  gold,  chiefly  from  alloys  which  contain  but  little  of  that 
metal,  such  as  native  silver  and  old  silver  coins,  and,  as  now  practised,  is  economi- 
cally available  even  when  the  amount  of  gold  does  not  exceed  one  part  in  2000. 

Gold  is  the  only  metal  of  a  yellow  colour.  When  pure,  it  is  more  malleable 
than  any  other  metal,  and  nearly  as  soft  as  lead.  Its  ductility  appears  to  have 
scarcely  a  limit.  A  single  grain  of  gold  has  been  drawn  into  a  wire  500  feet  in 
length,  and  this  metal  is  beaten  out  into  leaves  which  have  not  more  than 
1-200,000  of  an  inch  of  thickness.  The  coating  of  gold  on  gilt  silver  wire  is  still 
thinner.  Gold,  when  very  thin,  is  transparent,  thin  gold  leaf  appearing  green  by 
transmitted  light.  The  green  colour  passes  into  a  ruby  red  when  highly  attenuated 
gold  is  heated :  in  the  red  gold-glass,  the  gold  is  in  the  metallic  state  (Faraday). 


602  GOLD. 

The  point  of  fusion  of  this  metal  is  2192°,  according  to  Pouillet;  2518°,  accord- 
ing  to  Guyton-Morveau ;  2590°,  according  to  Daniell :  it  contracts  considerably 
upon  becoming  solid.  The  density  of  gold  varies  from  19-258  to  19 '367,  accord- 
ing as  it  has  been  more  or  less  compressed.  Gold  does  not  oxidate  or  tarnish  in 
air,  at  the  usual  temperature,  nor  when  strongly  ignited.  But  this  and  the  other 
noble  metals  are  dissipated  and  partly  oxidated,  when  a  powerful  electric  charge 
is  sent  through  them  in  thin  leaves.  It  is  not  dissolved  by  nitric,  hydrochloric, 
or  sulphuric  acid,  or  indeed  by  any  single  acid.  It  is  acted  upon  by  chlorine, 
which  converts  it  into  sesquichloride,  and  by  acid-niixtures,  such  as  aqua-regia, 
which  evolve  chlorine.  It  combines  in  two  proportions  with  oxygen,  forming  the 
two  oxides  Au20  and  Au203,  which  show  but  little  tendency  to  combine  with 
acids.  Some  chemists,  however,  double  the  atomic  weight  of  gold,  and  regard 
these  oxides  as  protoxide,  AuO,  and  teroxide,  Au03,  respectively. 

Oxide  of  gold,  Aurous  oxide,  Au20,  204-66  or  2558-25.  —  This  oxide  is  ob- 
tained as  a  green  powder  by  decomposing  the  corresponding  chloride  of  gold  with 
a  cold  solution  of  potash.  It  is  partly  dissolved  by  the  alkali,  and  soon  begins  to 
undergo  decomposition,  being  resolved  into  the  higher  oxide  and  metallic  gold. 
The  latter  forms  upon  the  sides  of  the  vessel  a  thin  film,  which  is  green  by  trans- 
mitted light,  like  gold  leaf. 

Chloride  of  gold,  Aurous  chloride,  Au2Cl,  is  obtained  by  evaporating  a  solution 
of  the  sesquichloride  to  dryness,  and  heating  the  powder  thus  obtained  in  a  sand- 
bath,  retaining  it  at  about  the  temperature  of  melting  tin,  and  constantly  stirring 
it,  so  long  as  chlorine  is  evolved.  It  is  a  white,  saline  mass,  having  a  tinge  of 
yellow,  and  quite  insoluble  in  water.  In  the  dry  state  it  is  permanent,  but  in 
contact  with  water  it  gradually  undergoes  decomposition,  and  is  converted  into 
gold  and  the  sesquichloride.  This  change  takes  place  almost  instantaneously  at 
the  boiling  temperature. 

Aurous  iodide,  Au2I,  is  formed  by  the  action  of  hydriodic  acid  on  auric  oxide, 
water  being  formed  and  two-thirds  of  the  iodine  set  free : 

Au203  +  SHI  =  Au2I  +  3HO  +  21; 

also  by  adding  iodide  of  potassium  in  proper  proportion,  and  in  successive  small 
quantities,  to  an  aqueous  solution  of  auric  chloride : 

Au2Cl3  +  SKI  =  Au2I  -f  3KC1  +  21. 

It  is  a  lemon-yellow,  crystalline  powder,  insoluble  in  cold  water,  and  very  sparingly 
soluble  in  boiling  water. 

Aurous  sulphide  is  formed  when  hydrosulphuric  acid  gas  is  passed  into  a  boiling 
solution  of  the  sesquichloride  of  gold.  It  is  dark-brown,  almost  black.  Aurous 
sulphide  combines  with  the  protosulphides  of  potassium  and  sodium,  forming 
double  salts  containing  1  eq.  of  aurous  sulphide  with  1  eq.  of  the  alkaline  sul- 
phide. The  sodium-salt  is  obtained  by  fusing  together  2  eq.  protosulphide  of 
sodium,  1  eq.  gold,  and  6  eq.  sulphur ;  digesting  the  fused  mass  in  water;  filter- 
ing the  yellow  solution  in  an  atmosphere  of  nitrogen ;  and  concentrating  in  vacuo 
over  sulphuric  acid.  Yellow  crystals  are  then  obtained,  having  the  form  of  ob- 
lique hexagonal  prisms  with  trilateral  or  quadrilateral  summits,  and  containing 
NaS.Au2S  -f-  8Aq.  They  are  soluble  in  water  and  alcohol.  The  potassium-salt, 
which  is  obtained  in  a  similar  manner,  forms  indistinct  crystals  (Col.  Yorke).* 

Sesquwxide  of  gold,  Auric  oxide,  Au203,  220-66  or  2758-25. — This  oxide  has 
many  of  the  properties  of  an  acid.  It  is  obtained  by  digesting  magnesia  in  a 
solution  of  sesquichloride  of  gold,  when  an  insoluble  compound  of  auric  oxide 
and  magnesia  is  formed,  which  is  collected  upon  a  filter  and  well  washed.  The 
compound  is  afterwards  digested  in  nitric  acid,  which  dissolves  the  magnesia,  with 
traces  of  auric  oxide,  but  leaves  the  greater  part  of  the  latter  undissolved.  It  is 

*  Chem.  Soc.  Qu.  J.  i.  236. 


AUROUS    COMPOUNDS.  603 

left  in  the  state  of  a  reddish-yellow  hydrate,  which  when  dried  in  air  becomes 
chestnut-brown.  When  precipitated  by  an  alkali,  auric  oxide  carries  down  a 
portion  of  the  latter,  of  which  it  may  be  deprived  by  nitric  acid.  Dried  at  212°, 
it  abandons  its  water,  becomes  black,  and  is  in  part  reduced.  When  exposed  to 
light,  particularly  to  the  direct  rays  of  the  sun,  its  reduction  is  very  rapid.  It  is 
decomposed  by  an  incipient  red  heat.  Hydrochloric  acid  is  the  only  acid  which 
dissolves  and  retains  this  oxide,  and  then  sesquichloride  of  gold  is  formed.  It  is 
dissolved  by  concentrated  nitric  and  sulphuric  acid,  but  precipitated  from  these 
solutions  by  water.  The  affinity  of  this  oxide  for  alkaline  oxides,  on  the  contrary, 
is  so  great  that,  when  boiled  in  a  solution  of  chloride  of  potassium,  it  is  dissolved, 
the  liquid  becoming  alkaline,  and  aurate  of  potash,  or  a  compound  of  auric  oxide 
and  potash,  being  formed.  The  compounds  of  auric  oxide  with  the  alkalies  and 
alkaline  oxides  are  nearly  colourless,  and  are  not  decomposed  by  water.  They 
appear  to  be  of  two  different  degrees  of  saturation,  aurates  which  are  soluble,  and 
superaurates  which  are  insoluble.  The  only  one  of  these  compounds  which  has 
been  studied  in  some  degree  is  the  aurate  of  ammonia,  or  fulminating  gold  as  it 
is  named,  from  its  violently  explosive  character. 

Aurate  of  ammonia.  —  When  the  solution  of  gold  is  precipitated  by  a  small 
quantity  of  ammonia,  a  powder  of  a  deep  yellow  colour  is  obtained,  which  is  a 
compound  of  aurate  of  ammonia  with  a  portion  of  sesquichloride  of  gold.  This 
compound-explodes  by  heat,  but  the  detonation  is  not  strong.  But  when  the  so- 
lution of  gold  is  treated  with  an  excess  of  ammonia,  and  the  precipitate  well 
washed  by  ebullition  in  a  solution  of  ammonia,  or  better  in  water  containing 
potash,  the  fulminating  gold  has  a  yellowish  brown  colour  with  a  tinge  of  purple. 
When  dry,  it  explodes  very  easily  with  a  loud  report,  accompanied  by  a  feeble 
flame.  It  may  be  exploded  by  a  heat  a  little  above  the  boiling  point  of  water,  or 
by  the  blow  of  a  hammer.  Its  composition  has  not  been  exactly  determined ;  but 
if  the  ammonia  is  present  in  double  the  proportion  that  would  contain  the  hydro- 
gen necessary  to  burn  the  oxygen  of  the  auric  oxide,  which  Berzelius  considers 
probable,  its  constituents  may  be  Au203.2NH3-|  HO.  The  affinity  of  auric  oxide 
for  ammonia  is  so  great,  that  it  takes  that  alkali  from  all  acids.  Thus,  when  auric 
oxide  is  digested  in  sulphate  of  ammonia,  fulminating  gold  is  formed,  and  the  liquid 
becomes  acid. 

Aurate  of  potash,  KO.Au203  +  6HO.  —  Obtained  in  the  crystalline  state  by 
evaporating  a  solution  of  sesquioxide  of  gold  in  a  slight  excess  of  pure  potash, 
first  over  the  open  fire  and  afterwards  in  vacuo :  the  crystals  may  be  freed  from, 
adhering  potash  by  recrystallization  from  water,  then  drained  on  unglazed  porce- 
lain and  dried  in  vacuo.  Aurate  of  potash  is  very  soluble  in  water,  and  forms  a 
yellowish  strongly  alkaline  solution,  which  is  decomposed  by  nearly  all  organic 
bodies,  the  gold  being  precipitated  in  the  metallic  state :  it  is  also  decomposed  by 
heat.  With  most  metallic  salts  it  forms  precipitates  of  aurates,  which  are  inso- 
luble in  water,  but  soluble  in  excess  of  the  precipitant ;  thus,  chloride  of  calcium 
forms  a  precipitate  of  aurate  of  lime,  soluble  in  excess  of  chloride  of  calcium. 
The  solution  of  aurate  of  potash  may  be  used  as  a  bath  for  electro-gilding. 

Aurosulphite  of  potash,  KO.Au203  +  4(K0.2S02)  +  5110;  or  5KO  j 

-f  5HO. — Deposited  in  beautiful  yellow  needles  when  sulphite  of  potash  is  added 
drop  by  drop  to  an  alkaline  solution  of  aurate  of  potash.  It  is  nearly  insoluble 
in  alkaline  solutions,  but  dissolves  with  decomposition  in  pure  water,  especially  if 
hot,  giving  off  sulphurous  acid  and  depositing  metallic  gold.  Acids  decompose  it 
in  a  similar  manner.  After  drying  in  vacuo,  it  may  be  preserved  for  two  or  three 
months,  in  well-closed  bottles,  but  ultimately  decomposes,  giving  off  sulphurous 
acid  and  leaving  metallic  gold  and  sulphate  of  potash.  The  same  decomposition 
takes  place  more  quickly  when  the  salt  is  heated  (Frerny).* 

*  Ann.  Ch.  Pharm.  Ivi.  315. 


604  GOLD. 

Purple  of  Cassius.  —  When  protochloride  of  tin  is  added  to  a  dilute  solution 
of  gold,  a  purple-coloured  powder  falls,  which  has  received  that  name.  It  is  ob- 
tained of  a  finer  tint  when  protochloride  of  tin  is  added  to  a  solution  of  the  ses- 
quichloride  of  iron,  till  the  colour  of  the  liquid  takes  a  shade  of  green,  and  the 
liquid  in  that  state  added,  drop  by  drop,  to  a  solution  of  sesquichloride  of  gold 
free  from  nitric  acid,  and  very  dilute.  After  24  hours,  a  brown  powder  is  de- 
posited, which  is  slightly  transparent,  and  purple-red  by  transmitted  light.  When 
dried  and  rubbed  to  powder,  it  is  of  a  dull  blue  colour.  Heated  to  redness,  it 
loses  a  little  water,  but  no  oxygen,  and  retains  its  former  appearance.  If  washed 
with  ammonia  on  the  filter  while  still  moist,  it  is  dissolved,  and  a  purple  liquid 
passes  through,  which  rivals  the  hypermanganate  of  potash  in  beauty.  From 
this  liquid,  the  colouring  matter  separates  very  gradually,  weeks  elapsing  before 
the  upper  strata  of  the  liquid  become  colourless •  but  it  is  precipitated  more  rapidly 
when  heated  in  a  close  vessel  between  140°  and  180°.  The  powder  of  Cassius  is 
insoluble  in  solutions  of  potash  and  soda.  It  may  also  be  formed  by  fusing  toge- 
.ther  2  parts  of  gold,  8£  parts  of  tin,  and  15  parts  of  silver,  under  borax,  to  pre- 
vent the  oxidation  of  the  tin,  and  treating  the  alloy  with  nitric  acid  to  dissolve  out 
the  silver ;  a  purple  residue  is  left  containing  the  tin  and  gold  that  were  employed. 

The  powder  of  Cassius  is  certainly,  after  ignition,  a  mixture  of  binoxide  of  tin 
and  metallic  gold,  from  which  the  gold  can  be  dissolved  out  by  aqua-regia,  while 
the  binoxide  of  tin  is  left;  and  the  last  mode  of  preparing  it,  favours  the  idea 
that  its  constitution  is  the  same  before  ignition ;  but  the  solubility  of  the  un- 
ignited  powder  in  ammonia,  and  the  fact  that  mercury  does  not  dissolve  out  gold 
from  the  powder  when  properly  prepared,  appear  to  be  conclusive  against  that 
opinion.  The  proportions  of  its  constituents  vary  so  much,  that  there  must  be 
more  than  one  compound ;  or  more  likely  the  colouring  compound  combines  with 
more  than  one  proportion  of  binoxide  of  tin.  Berzelius  proposed  the  theory  that 
the  powder  of  Cassius  may  contain  the  true*  protoxide  of  gold  combined  with  ses- 
quioxide  of  tin,  AuO.Sn203,  a  kind  of  combination  containing  an  association  of 
three  atoms  of  metal,  which  is  exemplified  in  black  oxide  of  iron,  spinell,  gahnite, 
franklinite,  and  other  minerals,  and  which  we  have  repeatedly  observed  to  be 
usually  attended  with  great  stability.  A  glance  at  its  formula  shows  how  readily 
the  powder  of  Cassius,  as  thus  represented,  may  pass  into  gold  and  binoxide  of 
tin;  AuO.Sn203  =  Au  +  2Sn02.  The  existence  of  a  purple  oxide  of  gold,  AuO, 
is  not  established ;  but  it  is  probably  the  substance  formed  when  a  solution  of 
gold  is  applied  to  the  skin  or  nails,  and  which  dyes  them  purple.  Paper,  coloured 
purple  by  a  solution  of  gold,  becomes  gilt  when  placed  in  the  moist  state  in  phos- 
phuretted  hydrogen  gas,  which  reduces  the  gold  to  the  metallic  state. 

Pelletier  gives  the  following  method  of  preparing  a  purple  of  Cassius  of 
constant  composition  :  —  20  grammes  of  gold  are  dissolved  in  100  grammes  of 
aqua-regia  containing  20  parts  nitric  to  80  parts  of  commercial  hydrochloric 
acid;  the  solution  is  evaporated  to  dryness  over  the  water-bath;  the  residue 
dissolved  in  water ;  the  filtered  solution  diluted  with  7  or  8  decilitres  of  water ; 
and  tin  filings  introduced  into  it :  in  a  few  minutes  the  liquid  becomes  brown 
and  turbid,  and  deposits  a  purple  precipitate,  which  merely  requires  to  be 
washed  and  dried  at  a  gentle  heat.  The  purple  thus  prepared  contains  in  100 
parts  :  32-746  stannic  acid,  14-618  protoxide  of  tin,  44-772  aurous  oxide  (Au20) 
and  7*864  water.  The  precipitate  obtained  by  treating  sesquichloride  of  gold  with 
pure  protochloride  of  tin  is  always  brown.  To  obtain  a  fine  purple  precipitate, 
the  chloride  of  gold  should  be  treated  with  a  mixture  of  protochloride  and  bichlo- 
ride of  tin.  The  following  process  gives  a  fine  purple  : — a.  A  neutral  solution  is 
prepared  of  1  part  of  tin  in  hydrochloric  acid ;  b.  A  solution  of  2  parts  tin  in 
cold  aqua-regia  (1  part  hydrochloric  acid  to  8  nitric),  the  liquid  being  merely 
heated  towards  the  end  of  the  process,  that  it  may  not  contain  any  protoxide  of 
tin  ;  c.  Seven  parts  of  gold  are  dissolved  in  aqua-regia  (6  hydrochloric  to  1  nitric), 
and  the  solution,  which  is  nearly  neutral,  diluted  with  3500  parts  of  water.  To 


AURIC     COMPOUNDS.  605 

this  solution  r,  the  solution  b  is  first  added,  and  then  the  solution  a,  drop  by  drop, 
till  the  proper  colour  is  produced.  If  the  quantity  of  a  be  too  small,  the  precipi- 
tate is  violet;  if  too  large,  it  is  brown.  It  must  be  washed  quickly,  so  that  the 
liquid  may  not  act  upon  it  too  long.  It  weighs  6£  parts  (Bouisson).* 

Sesquisulphide  of  gold,  Au2S3,  or  Auric  sulphide,  is  formed  when  a  dilute  solu- 
tion of  gold  is  precipitated  cold  by  hydrosulphuric  acid.  It  is  a  flocculent  matter 
of  a  strong  yellow  colour,  which  becomes  deeper  by  drying ;  it  loses  its  sulphur  at 
a  moderate  heat. 

Scsquichloride  of  gold,  Perchloride  of  gold,  Auric  chloride,  Au2Cls,  303-16  or 
3789-5.  —  This  compound  is  formed  when  gold  is  dissolved  in  aqua-regia.  The 
solution  is  yellow,  and  becomes  paler  with  an  excess  of  acid,  but  is  of  a  deep  red 
when  neutral  in  composition.  It  is  obtained  in  the  last  condition  by  evaporating 
the  solution  of  gold,  till  the  liquid  is  of  a  dark  ruby  colour,  and  begins  to  emit 
chlorine.  It  forms  on  cooling  a  dark  red  crystalline  mass,  which  deliquesces 
quickly  in  air.  But  the  only  method  of  procuring  auric  chloride  perfectly  free 
from  acid  salt,  is  to  decompose  aurous  chloride  with  water.  A  compound  of  chlo- 
ride of  gold  and  hydrochloric  acid  crystallizes  easily  from  an  acid  solution,  in  long 
needles  of  a  pale  yellow  colour,  which  are  permanent  in  dry  air,  but  run  into  a 
liquid  in  damp  air.  The  solution  of  this  salt  deposits  gold  on  its  surface,  and  on 
the  side  of  the  vessel  turned  to  the  light.  The  gold  is  also  precipitated  in  the 
metallic  state  by  phosphorus,  by  most  metals,  by  ferrous  salts,  by  arsenious  and 
antimonious  acids,  and  by  many  vegetable  and  animal  substances,  by  vegetable 
acids,  by  oxalate  of  potash,  &c.,  carbonic  acid  then  escaping.  Hydrosulphuric 
acid  and  sulphide  of  ammonium  throw  down  black  sulphide  of  gold,  soluble  in 
excess  of  the  latter  reagent.  Ammonia  and  carbonate  of  ammonia  produce  a 
yellow  precipitate  of  fulminating  gold.  Potash  added  in  excess  forms  no  preci- 
pitate, unless  it  contains  organic  matter,  in  which  case  a  slight  precipitate  of  au- 
rous oxide  is  produced.  Cyanide  of  potassium  produces  a  yellow  precipitate 
soluble  in  excess.  Tincture  of  galls  throws  down  metallic  gold.  Chloride*  of  gold 
is  soluble  in  ether  and  in  some  essential  oils.  It  forms  double  salts  with  most 
other  chlorides,  which  are  almost  all  orange-coloured  when  crystallized  j  in  efflo- 
rescing, they  acquire  a  lemon-yellow  colour,  but  in  the  anhydrous  state  they  are 
of  an  intense  red.  They  are  obtained  by  evaporating  the  mixed  solutions  of  the 
two  salts. 

Chloride  of  gold  and  potassium,  KC1.  Au2Cl3  -f  5HO.  —  Crystallizes  in  striated 
prisms  with  right  summits,  or  in  thin  hexagonal  tables  which  are  very  efflorescent ; 
becomes  anhydrous  at  212°.  The  anhydrous  salt  fuses  readily  when  heated,  but 
loses  chlorine  and  becomes  a  liquid,  which  is  black  while  hot,  and  yellow  when 
cold.  It  is  then  a  compound  of  aurous  chloride  with  chloride  of  potassium. 
Chloride  of  gold  and  ammonium  crystallizes  in  transparent  prismatic  needles, 
which  become  opaque  in  air;  Mr.  Johnston  found  their  composition  to  be 
NH4Cl.Au2Cl3 +  2HO.  Chloride  of  gold  and  sodium  crystallizes  in  long  four- 
sided  prisms,  and  is  persistent  in  air.  Its  composition  is  NaCl .  Au2Cl3  -f  4HO. 
Bonsdorff  has  prepared  similar  double  salts  with  the  chlorides  of  barium,  strou- 
tium,  calcium,  magnesium,  manganese,  zinc,  cadminm,  cobalt,  and  nickel.  The 
salt  of  lime  contains  six,  and  the  salt  of  magnesia  twelve  equivalents  of  water. 

Sesquibromide  of  gold,  Au2Br3,  is  formed  by  dissolving  gold  in  a  mixture  of 
nitric  and  hydrobromic  acids.  It  greatly  resembles  the  sesquichloride,  and  forms 
also  an  extensive  series  of  double  salts. 

Auric  iodide,  Au2I3,  is  formed  by  gradually  adding  a  neutral  solution  of  auric 
chloride  to  a  solution  of  iodide  of  potassium  :  the  liquid  then  acquires  a  dark- 
green  colour,  and  yields  a  dark-green  precipitate  of  Au2I3,  which  redissolves  on 
agitation ;  but  after  1  eq.  of  the  auric  chloride  has  been  added  to  4  eqs.  of  iodide 
of  potassium,  a  further  addition  of  the  gold-solution  decolourizes  the  liquid  and 

*  J.  Phann.  [2],  xvi.  629. 


606  GOLD. 

forms  a  permanent  precipitate  of  auric  iodide,  because  the  iodide  of  gold  and 
potassium  at  first  produced  is  thereby  decomposed.  The  successive  actions  are 
represented  by  the  following  equations  : 

(1.)  4KI+  Au2Cl3  =  3KC1  +  KI.  Au2I3; 

(2.)  3(KI .  Au2I3)  +  Au2Cl3  ==  3KC1  +  4Au2I3 

Auric  iodide  is  a  very  unstable  compound;  when  exposed  to  the  air  at  ordinary 
temperatures,  it  is  gradually  converted  into  yellow  aurous  iodide,  and  afterwards 
into  metallic  gold.  It  combines  with  hydriodic  acid  and  with  the  more  basic 
metallic  iodides,  forming  a  series  of  very  dark-coloured  salts;  e.  g.  iodo-aurate 
of  potassium,  KI .  Au2I3. 

The  oxides  of  gold  show  but  little  tendency  to  combine  with  oxygen-acids  :  the 
sesquioxide  dissolves  in  strong  nitric  acid,  but  the  solution  is  decomposed  by 
evaporation  or  dilution. 

Hyposulphite  of  aurous  oxide  and  soda : 

Au20 .  S202+3(NaO .  S202)+ 4HO ;  or  **&  1 4S20,  +  4HO. 

This  salt  is  prepared  by  mixing  concentrated  solutions  of  sesquichloride  of  gold 
and  hyposulphite  of  soda,  and  precipitating  with  alcohol.  When  purified  by  re- 
peated solution  in  water  and  precipitation  by  alcohol,  it  forms  delicate,  colourless 
needles.  It  has  a  sweetish  taste,  dissolves  very  easily  in  water,  but  very  sparingly 
in  alcohol.  It  is  decomposed  by  heat  and  by  nitric  acid,  with  deposition  of  me- 
tallic gold.  Its  solution  gives  a  blackish  precipitate  with  hydrosulphuric  acid  and 
soluble  sulphides.  The  presence  of  gold  in  this  solution  is  not  indicated  by  pro- 
tosulphate  of  iron,  protochloride  of  tin,  or  oxalic  acid;  and,  on  the  other  hand, 
sulphuric  acid,  hydrochloric  acid,  and  the  vegetable  acids  neither  precipitate  sul- 
phur nor  expel  sulphurous  acid  from  it.  When  mixed  with  chloride  of  barium, 
it  yields  a  gelatinous  precipitate  of  Hyposulphite  of  aurous  oxide  and  baryta, 

containing  or>Vi  [•  4S202.     Sulphuric  acid  removes  all  the  baryta  from  this  salt, 

and  leaves  hyd 'rated  aurous  hyposulphite,  which  is  uncrystallizable,  strongly  acid, 
and  tolerably  stable  at  ordinary  temperatures.  The  solution  of  the  soda-salt  is 
used  for  fixing  daguerreotype  pictures  (Fordos  and  Gelis).* 

A  hyposulphite  of  auric  oxide  and  soda  appears  also  to  be  formed  by  dropping 
a  neutral  solution  of  chloride  of  gold  into  aqueous  hyposulphite  of  soda  (Fordos 
and  Gelis). 

Alloys  of  gold.  —  Gold  unites  with  nearly  all  metals;  but  its  most  important 
alloys  are  those  which  it  forms  with  silver  and  copper.  Gold  which  is  used  for 
coins,  watches,  articles  of  jewellery,  &c.,  is  always  alloyed  with  copper,  to  increase 
its  hardness,  pure  gold  being  much  too  soft  for  any  of  these  purposes.  The  stand- 
ard for  coin  in  the  United  Kingdom  is  11  gold  with  1  alloy;  in  France  and  the 
United  States  of  America,  9  gold  to  1  alloy.  For  articles  of  jewellery,  gold  is 
also  frequently  alloyed  with  silver,  which  gives  it  a  lighter  colour.  The  alloys  of 
gold,  both  with  silver  and  with  copper,  are  more  fusible  than  gold  itself.  The 
solder  used  for  gold  trinkets  is  composed  of  5  parts  gold  and  1  part  copper,  or  of 
4  parts  gold,  1  part  copper,  and  1  part  silver. 

Amalgam  of  gold.  —  Gold  unites  readily  with  mercury,  forming  a  white  amal- 
gam ;  the  smallest  quantity  of  mercurial  vapour  coming  in  contact  with  gold  is 
sufficient  to  turn  it  white.  Mercury  is  capable  of  dissolving  a  large  quantity  of 
gold  without  losing  its  fluidity,  but,  when  quite  saturated,  it  acquires  a  waxy  con- 
sistence. When  the  liquid  amalgam  is  strained  through  chamois-leather,  mercury 
passes  through  together  with  a  very  small  quantity  of  gold,  and  there  remains  a 

*  Ann.  Ch.  Phys.  [3],  xiii.  394. 


ESTIMATION    OF    GOLD.  607 

white  amalgam,  of  pasty  consistence,  containing  about  2  parts  of  gold  to  1  part 
of  mercury.  By  dissolving  1  part  of  gold  in  1000  parts  of  mercury,  pressing 
through  chamois-leather,  and  treating  the  residue  with  dilute  nitric  acid  at  a 
moderate  heat,  a  solid  amalgam,  AuJIg,  is  obtained,  which  crystallizes  in  shining 
four-sided  prisms,  retains  its  lustre  in  the  air,  is  not  decomposed  by  boiling  nitric 
acid,  and  does  not  melt  even  when  heated  till  the  mercury  volatilizes  (T.  H. 
Henry).* 

.Gliding  and  silvering.  —  The  pasty  amalgam  of  2  parts  gold  and  1  part  mer- 
cury is  used  for  gilding  ornamented  articles  of  copper  and  bronze.  The  surface  of 
the  object  is  first  thoroughly  cleaned  by  heating  it  to  redness,  then  plunging  it 
into  dilute  sulphuric  acid,  and  sometimes  for  an  instant  also  into  strong  nitric 
acid  j  it  is  then  amalgamated  by  washing  it  with  a  solution  of  nitrate  of  mercury, 
arid  afterwards  pressed  upon  the  pasty  amalgam,  a  portion  of  which  adheres  to  it. 
The  mercury  is  then  expelled  by  heat,  and  the  gold-surface  finally  polished.  Silver 
may  be  gilt  by  similar  processes. 

By  substituting  an  amalgam  of  silver  for  the  amalgam  of  gold,  articles  of  copper, 
bronze,  and  brass  may  be  silvered  or  plated. 

Articles  of  copper,  chiefly  copper  trinkets,  are  also  gilt  by  immersion  in  a  boil- 
ing solution  of  chloride  of  gold  in  an  alkaline  carbonate,  after  having  been  cleaned 
by  processes  similar  to  those  just  described. 

But  the  process  now  most  generally  adopted  is  that  of  electro-gilding ,  which  is 
performed  by  immersing  the  objects  to  be  gilt  in  a  solution  of  10  parts  of  cyanide 
of  potassium  and  1  part  of  cyanide  of  gold  in  100  parts  of  distilled  water,  and 
connecting  them  with  the  negative  pole  of  a  voltaic  battery,  while  the  positive 
pole  is  connected  with  a  bar  of  gold  also  immersed  in  the  liquid.  The  solution  is 
then  decomposed  by  the  current,  the  gold  being  deposited  on  the  objects  at  the 
negative  pole,  while  the  gold  connected  with  the  positive  pole  dissolves  and  keeps 
the  solution  at  a  nearly  uniform  strength.  The  cyanide  of  potassium  in  the  solu- 
tion is  sometimes  replaced  by  ferrocyanide  of  potassium,  and  the  cyanide  of  gold 
by  sesquioxide  of  gold,  chloride  of  gold  and  potassium,  or  sulphide  of  gold ;  but 
the  composition  above  given  is  that  which  is  most  generally  adopted.  This  mode 
of  gilding  may  be  at  once  applied  to  copper,  brass,  bronze,  silver,  or  platinum. 
To  gild  iron,  steel,  or  tin,  it  is  necessary  first  to  deposit  a  layer  of  copper  on  the 
surface,  which  is  effected  by  immersion  for  a  few  seconds  in  a  bath  of  cyanide  of 
copper  and  potassium. 

Electro-silvering  or  electro-plating  is  performed  in  a  similar  manner,  with  a 
bath  composed  of  1  part  of  cyanide  of  silver  and  10  parts  of  cyanide  of  potassium 
dissolved  in  100  parts  of  water;  it  is  principally  applied  to  articles  made  of  nickel- 
silver. 

Platinum  may  also  be  deposited  in  a  similar  manner  on  copper  or  silver;  but  it 
does  not  adhere  very  firmly. 

ESTIMATION     OF     GOLD,    AND     METHODS     OF    SEPARATING     IT     FROM     OTHER 

METALS. 

Gold  is  always  estimated  in  the  metallic  state.  It  is  generally  precipitated  from 
its  solution  in  aqua-regia  by  protosulphate  of  iron  or  oxalic  acid.  Protosulphate 
of  iron  precipitates  the  gold  in  the  form  of  a  fine  brown  powder.  If  the  gold 
solution  is  quite  neutral,  it  must  first  be  acidulated  with  hydrochloric  acid,  other- 
wise the  precipitated  gold  will  be  contaminated  with  sesquioxide  of  iron  formed 
by  the  action  of  the  air  on  the  solution  of  the  protosulphate.  If  the  gold  solution 
contains  much  free  nitric  acid,  there  is  a  risk  of  some  of  the  precipitated  gold 
being  re-dissolved  by  the  aqua-regia  present.  To  prevent  this,  the  excess  of  nitric 
acid  must  be  destroyed  by  adding  hydrochloric  acid,  and  boiling  before  the  iron 

*Phil.  Mag.  [4],  ix.  468. 


608  PLATINUM. 

solution  is  added.  Oxalic  acid  reduces  gold  slowly  but  completely;  the  gold 
solution  must  be  digested  with  it  for  24  or  48  hours. 

These  methods  of  precipitation  serve  to  separate  gold  from  most  other  metals. 
In  such  cases,  oxalic  acid  is  mostly  to  be  preferred  as  the  precipitating  agent, 
because,  when  the  quantities  of  the  other  metals  are  also  to  be  determined,  the 
presence  of  a  large  amount  of  iron  in  solution  is  very  inconvenient. 

The  separation  of  gold  in  alloys  may  generally  be  effected  by  dissolving  out  the 
baser  metals  with  nitric,  or  sometimes  with  hydrochloric  or  sulphuric  acid. 
When,  however,  the  proportion  of  gold  is  considerable,  it  may  happen  that  the 
alloy  is  but  very  slowly  attacked  by  nitric  acid,  especially  if  the  other  metal  be 
silver  or  lead.  In  such  a  case,  it  is  best  to  treat  the  alloy  with  aqua-regia,  and 
precipitate  the  gold  with  oxalic  acid.  Or,  again,  the  alloy  may  be  fused  with  a 
known  weight  of  lead  or  silver,  as  in  the  method  of  quartation  (p.  602),  and 
thereby  rendered  decomposable  by  nitric  acid. 

The  analysis  or  assay  of  an  alloy  of  gold  and  copper  is  usually  made  by  cupel- 
lation  with  lead.  The  weight  of  the  button  remaining  on  the  cupel  gives  directly 
the  amount  of  gold  in  the  alloy  after  certain  corrections  similar  to  those  required 
in  the  case  of  silver  (p.  601).  Alloys  containing  both  silver  and  coppe.r  are 
cupelled  with  lead  and  a  quantity  of  silver  sufficient  to  bring  the  proportion  of  gold 
and  silver  in  the  alloy  to  1  part  gold  and  3  parts  silver.  The  button  obtained  by 
cupellation  then  consists  of  an  alloy  of  gold  and  silver,  from  which  the  silver  may 
be  dissolved  out  by  nitric  acid. 

Small  ornamental  articles,  which  would  be  destroyed  if  submitted  to  any  of  the 
preceding  processes,  are  approximately  assayed  by  rubbing  them  on  a  peculiar 
kind  of  black  stone,  called  the  touchstone,  so  as  to  leave  a  streak  of  metal,  the 
appearance  of  which  may  be  compared  with  that  of  similar  streaks  produced  from 
alloys  of  known  composition.  A  further  comparison  is  obtained  by  examining  the 
appearance  which  the  streaks  present  when  treated  with  acids.  This  method  is 
also  sometimes  used  in  the  assaying  of  coins,  to  afford  an  indication  of  the  quantity 
of  silver  required  in  the  cupellation.  The  touchstone,  which  is  a  peculiar  kind 
of  bituminous  quartz,  was  originally  obtained  from  Lydia ;  but  stones  of  similar 
quality  are  now  found  in  Bohemia,  Saxony,  and  Silesia. 


ORDER  IX. 

METALS    IN    NATIVE   PLATINUM. 

SECTION    I. 
PLATINUM. 

^.98-68  or  1233-5;  Pt. 

This  metal  was  discovered  in  the  auriferous  sand  of  certain  rivers  in  America. 
Its  name  is  a  diminutive  of  plata,  silver,  and  was  applied  to  it  on  account  of  its 
whiteness.  It  occurs  in  the  form  of  rounded  or  flattened  grains  of  a  metallic 
lustre.  It  has  been  found  in  Brazil,  Colombia,  Mexico,  St.  Domingo,  and  on  the 
eastern  declivity  of  the  Ural  chain ;  in  small  quantity  also  in  certain  copper-ores 
from  the  Alps ;  it  is  everywhere  associated  with  the  debris  of  a  rock,  easily  re- 
cognised as  belonging  to  one  of  the  earliest  volcanic  formations. 

The  grains  of  native  platinum  contain  from  75  to  87  per  cent,  of  that  metal,  a 
quantity  of  iron  generally  sufficient  to  render  them  magnetic,  from  £  to  1  per 


PLATINUM. 


609 


cent,  of  palladium,  but  sometimes  much  less,  with  small  quantities  of  copper, 
rhodium,  osmium,  iridium,  and  ruthenium.  To  separate  the  platinum  from  these 
bodies,  the  ore  is  digested  in  a  retort  with  hydrochloric  acid,  to  which  additions 
of  nitric  acid  are  made  from  time  to  time.  When  the  hydrochloric  acid  is  nearly 
saturated,  the  liquid  is  evaporated  in  the  retort  to  a  syrup,  then  diluted  with 
water,  and  drawn  off  from  the  insoluble  residue.  If  the  mineral  is  not  com- 
pletely decomposed,  more  aqua-regia  is  added  and  the  distillation  continued.  A 
portion  always  remains  undissolved,  consisting  of  grains  of  a  compound  of  osmium 
and  iridium,  and  little  brilliant  plates  of  the  same  alloy,  besides  foreign  mineral 
substances  which  may  be  mixed  with  the  ore.  The  solution  is  generally  deep  red, 
and  emits  chlorine  from  the  presence  of  perchloride  of  palladium ;  to  decompose 
which  the  liquid  is  boiled,  whereupon  chlorine  escapes,  and  the  palladium  is  re- 
duced to  protochloride.  Chloride  of  potassium  is  then  added,  which  precipitates 
the  platinum  as  a  sparingly  soluble  double  chloride  of  platinum  and  potassium, 
which  has  a  yellow  colour  if  pure,  but  red  if  it  is  accompanied  by  the  double 
chloride  of  iridium  and  potassium.  The  precipitate  is  collected  on  a  filter,  and 
washed  with  a  dilute  solution  of  chloride  of  potassium.  By  igniting  this  double 
salt  with  twice  its  weight  of  carbonate  of  potash  to  the  point  of  fusion,  the 
platinum  is  reduced  to  the  metallic  state,  while  a  portion  of  the  iridium  remains  as 
peroxide.  The  soluble  potash-salts  are  then  removed  by  washing  with  hot  water, 
and  the  platinum  is  dissolved  by  aqua-regia,  in  which  the  peroxide  of  iridium 
remains  untouched.  To  complete  the  separation  of  the  iridium,  the  precipitation 
by  chloride  of  potassium  and  ignition  with  carbonate  of  potash  may  require  to  be 
repeated  several  times.  The  platinum-solution  thus  freed  from  iridium  is  mixed 
with  sal-ammoniac,  which  throws  down  a  yellow  precipitate  of  the  double  chloride 
of  platinum  and  ammonium.  From  this  precipitate,  when  heated  to  redness, 
chlorine  and  sal-ammoniac  are  given  off,  and  the  platinum  remains  in  the  form  of 
a  loosely  coherent  mass,  called  sponyy  platinum.  When  it  is  not  required  to 
have  platinum  absolutely  pure,  the  solution  first  obtained  from  the  ore  is  precipi- 
tated by  sal-ammoniac,  and  the  precipitate  treated  in  the  manner  just  described  : 
much  of  the  platinum  of  commerce  is  obtained  in  that  way.  The  small  trace  of 
iridium  which  is  left  in  commercial  platinum  greatly  increases  its  hardness  and 
tenacity. 

Platinum  is  too  refractory  to  be  fused  in  coal  furnaces  :  but  at  a  high  tempera- 
ture its  particles  cohere  like  those  of  iron,  and  it  may,  like  that  metal,  be  welded, 
and  thereby  rendered  malleable.  For  this  purpose,  the  spongy  platinum  obtained 
by  igniting  the  double  chloride  of  platinum  and  ammonium,  is  in- 
troduced into  a  brass  cylinder  efg  h  (fig.  205),  the  lower  part  of 
which  fits  into  a  steel  socket  abed.  The  cylinder  being  half 
filled  with  spongy  platinum,  a  steel  piston  i  k,  which  fits  it  exactly, 
is  introduced,  and  driven  down  by  blows  of  a  hammer,  gently  at 
first,  but  afterwards  with  greater  force.  The  spongy  platinum  is 
thereby  much  reduced  in  bulk,  and  after  a  while  is  converted  into  a 
coherent  disc  of  metal.  This  disc  is  heated  to  whiteness  in  a 
muffle,  and  afterwards  hammered  on  a  steel  anvil.  By  repeating 
these  operations  several  times,  the  platinum  is  rendered  perfectly 
malleable  and  ductile,  and  may  be  rolled  into  sheets.  Platinum  in 
this  state  is  the  densest  body  at  present  known ,  its  specific  gravity 
was  fixed  by  Dr.  Wollaston  at  21.53.  This  metal  may  be  fused  by 
the  oxyhydrogen  blow-pipe,  or  even  made  to  boil,  and  be  dissipated 
with  scintillations.  It  is  not  acted  upon  by  any  single  acid,  not 
even  by  concentrated  and  boiling  sulphuric  acid.  Its  resistance  to 
the  action  of  acids,  conjoined  with  its  difficult  fusibility,  renders 
platinum  invaluable  for  chemical  experiments,  and  for  some  purposes 
in  the  chemical  arts,  particularly  for  the  concentration  of  oil  of 
vitriol. 

39 


FIG.  205. 


610  PLATINUM. 

The  remarkable  influence  of  a  clean  surface  of  platinum  in  determining  the  com- 
bustion of  oxygen  and  hydrogen,  has  already  been  considered.  This  property 
platinum  shares  with  osmium,  iridium,  palladium,  and  rhodium.  It  is  exhibited 
in  the  greatest  degree  by  the  highly  divided  metal,  such  as  platinum-sponge,  the 
condition  in  which  the  metal  is  left  on  igniting  the  double  chloride  of  platinum 
and  ammonium.  Platinum  precipitated  from  solution  by  zinc,  causes  the  combus- 
tion of  alcohol  vapour.  The  black  powder  of  platinum,  commonly  called  platinum- 
black,  is  the  form  in  which  that  metal  is  most  active.  This  is  prepared  by  dis- 
solving the  protochloride  of  platinum  in  a  hot  and  concentrated  solution  of 
potash,  and  pouring  alcohol  into  it  while  still  hot,  by  small  quantities  at  a  time ; 
violent  effervescence  then  occurs  from  the  escape  of  carbonic  acid  gas,  by  which 
the  contents  of  the  vessel,  unless  capacious,  may  be  thrown  out.  The  liquor  is 
decanted  from  the  black  powder  which  appears,  and  the  latter  boiled  successively 
with  alcohol,  hydrochloric  acid,  and  potash,  and  finally  four  or  five  times  with 
water,  to  divest  it  of  all  foreign  matters.  Platinum-black  may  also  be  obtained 
by  decomposing  a  hot  solution  of  sulphate  of  platinum  with  alcohol;  and  by 
boiling  a  solution  of  the  bichloride  with  carbonate*  of  soda  and  sugar;  chloride 
of  sodium  is  then  formed,  water  and  carbonic  acid  are  produced  by  oxidation  of 
the,  sugar,  and  the  platinum  is  precipitated  in  the  finely-divided  state.  The 
powder,  when  dried,  resembles  lamp-black,  and  soils  the  fingers,  but  still  it  is 
only  metallic  platinum  extremely  divided,  and  may  be  heated  to  full  redness  with- 
out any  change  of  appearance  or  properties.  It  loses  these  properties,  however, 
by  the  effect  of  a  white  heat,  and  assumes  a  metallic  aspect.  Platinum-black, 
like  wood  charcoal,  absorbs  and  condenses  gases  in  its  pores,  with  evolution  of 
heat,  a  property  which  must  assist  its  action  on  oxygen  and  hydrogen,  although 
not  essential  to  that  action.  When  moistened  with  alcohol,  it  determines  the 
oxidation  of  that  substance  in  air,  and  the  formation  of  acetic  acid ;  and,  in  a 
similar  manner,  it  converts  wood-spirit  into  formic  acid. 

Platinum  is  insoluble  in  all  acids  except  aqua-regia.  It  may  be  oxidated  in  the 
dry  way  by  fusing  it  with  hydrate  of  potash  or  nitre.  Palladium,  osmium,  and 
iridium  resemble  platinum  in  their  chemical  relations,  the  corresponding  com- 
pounds of  these  four  metals  being  isomorphous ;  platinum  and  iridium  have  also 
the  same  atomic  weight.  Of  platinum,  only  two  degrees  of  oxidation  are  known 
with  certainty,  the  protoxide,  PtO,  and  binoxide,  Pt02. 

Protoxide  of  platinum,  Platinous  oxide,  PtO,  106-68  or  1333-5. — This  oxide 
is  obtained  by  digesting  the  corresponding  chloride  of  platinum  with  potash,  as  a 
black  powder,  which  is  a  hydrate.  It  is  dissolved  by  an  excess  of  the  alkali,  and 
forms  a  green  solution,  which  may  become  black  like  ink  with  a  large  quantity  of 
oxide.  Protoxide  of  platinum  forms  the  platinous  class  of  salts,  which  have  a 
greenish,  or,  sometimes  red  colour,  and  are  distinguished  from  the  platinic  salts 
by  not  being  precipitated  by  sal-ammoniac.  With  hl/drosufphuric  acid  and  hydro- 
sulphate  of  ammonia,  they  form  a  black  precipitate,  soluble  in  a  large  excess  of 
the  latter;  with  mercurous  nitrate,  a  black  precipitate;  with  potash,  no  precipi- 
tate ;  with  carbonate  of  potash  or  soda,  a  brownish  precipitate.  Ammonia  added 
to  the  hydrochloric  acid  solution  throws  down  a  green  crystalline  precipitate  of 
ammonio-platinous  chloride;  carbonate  of  ammonia  forms  no  precipitate. 

Protosulphide  of  platinum,  PtS,  is  thrown  down  as  a  black  precipitate,  when 
the  protochloride  of  platinum  is  decomposed  by  hydrosulphuric  acid.  It  may  be 
washed  and  dried  without  decomposition. 

Protochloride  of  platinum,  Platinous  chloride,  PtCl,  is  obtained  by  evaporating 
a  solution  of  the  bichloride  of  platinum  to  dryness ;  triturating  the  dry  mass  ;  and 
heating  it  in  a  porcelain  capsule  by  a  sand-bath  at  the  melting  point  of  tin,  taking 
care  to  stir  it  at  the  same  time,  so  long  as  chlorine  is  evolved.  It  remains  as 
a  greenish  grey  powder,  quite  insoluble  in  water,  and  repelling  that  liquid  so  as 
not  to  be  moistened  by  it.  This  chloride  is  not  decomposed  by  sulphuric  or  nitric 
acid,  but  is  partially  soluble  in  boiling  and  concentrated  hydrochloric  acid.  From 


PLATINIC    COMPOUNDS.  611 

the  last  solution,  alkalies  throw  down  a  black  precipitate  of  protoxide.  When  the 
calcination  of  the  bichloride  of  platinum,  at  420°  or  460°,  is  interrupted  before 
the  whole  of  the  chlorine  is  expelled,  the  residue  yields  to  water  a  compound  of  a 
brown  colour,  so  deep,  that  the  .liquid  becomes  opaque.  This,  Professor  Magnus 
believes  to  be  a  combination  of  the  two  chlorides  of  platinum.  A  double  proto- 
chloride of  platinum  and  potassium,  or  chloroplatinite  of  potassium,  PtCl .  KC1, 
is  obtained  on  adding  chloride  of  potassium  to  the  solution  of  platinous  chloride  in 
hydrochloric  acid,  and  evaporating  the  liquid.  The  salt  crystallizes  in  red  four- 
sided  prisms,  the  form  of  which  is  the  same  as  that  of  a  corresponding  salt  of  palla- 
dium; it  is  anhydrous.  A  protochloride  of  platinum  and  sodium  also  exists,  but 
does  not  crystallize  easily. 

Corresponding  platinous  iodides  and  cyanides  have  been  formed.  The  cyanide 
forms  a  numerous  class  of  double  salts,  called  platinocyanides,  whose  general 
formula  is  MCy.PtCy.  The  potassium  salt  is  obtained  by  heating  spongy  plati- 
num with  ferrocyanide  of  potassium ;  exhausting  the  mass  with  hot  water  and 
crystallizing;  or  by  treating  platinous  chloride  with  aqueous  cyanide  of  potassium. 
The  salt  crystallizes  in  needles  and  rhombic  prisms,  pale  yellow  by  transmitted 
light,  yellow  or  blue  by  reflected  light,  according  to  the  direction  in  which  they 
are  viewed.  From  the  solution  of  this  salt,  the  platino-cyanides  of  zinc,  lead, 
copper,  mercury,  and  silver,  which  are  insoluble,  are  obtained  by  precipitation. 
The  sodium,  barium,  strontium,  and  calcium-salts,  which  are  soluble,  are  obtained 
by  treating  the  copper-salt  with  caustic  soda,  baryta,  &c. ;  and  the  magnesium  and 
aluminum-salts,  by  precipitating  the  barium-salt  with  sulphate  of  magnesia  or 
alumina.  The  ammonium-salt  is  prepared  like  the  potassium- salt.  Platinous 
oxide  has  also  been  united  with  several  acids,  particularly  sulphuric,  mtric,  oxalic, 
and  acetic  acids ;  but  none  of  these  salts  have  been  crystallized  except  the  oxalate. 

Bioxide  of  platinum ,  Peroxide  of  platinum,  Platinic  oxide,  Pt02,  114*68  or 
1483-5. — By  precipitating  sulphate  of  platinum  with  nitrate  of  baryta,  nitrate  of 
platinum  is  obtained.  One  half  of  its  oxide  may  be  precipitated  by  soda,  from  the 
last  salt,  but  when  a  larger  quantity  of  alkali  is  added,  a  subsalt  is  thrown  down. 
The  precipitated  oxide  is  hydrated,  very  bulky,  and  exactly  resembles  sesquioxide 
of  iron  precipitated  by  ammonia.  When  heated,  it  first  loses  its  water,  and 
becomes  black,  then  its  oxygen,  and  leaves  metallic  platinum.  Bioxide  of  plati- 
num combines  with  acids,  and  forms  a  class  of  salts,  which  are  either  yellow  or 
reddish-brown.  From  the  solutions  of  these  salts,  the  platinum  is  precipitated  in 
the  metallic  state  by  phosphorus  and  by  most  metals.  Hydrosulphuric  acid 
and  sulphide  of  ammonium  form  a  black  precipitate  soluble  in  a  large  excess  of 
the  latter.  In  a  solution  of  platinic  chloride,  potash  or  ammonia  forms  a  yellow 
crystalline  precipitate  of  chloroplatinate  of  potassium  or  ammonium  ;  so  likewise 
do  the  chlorides  of  potassium  or  ammonium  ;  sodium-salts  form  no  precipitate.  In 
the  solution  of  platinic  nitrate  or  sulphate,  potash  or  ammonia  forms  a  yellow- 
brown  precipitate;  chloride  of  potassium  or  ammonium  produces,  after  some  time, 
a  slight  yellow  precipitate  of  the  double  chloride.  Platinic  oxide  has  also  a  decided 
affinity  for  bases,  and  forms  insoluble  compounds  with  the  alkalies,  earths,  and 
many  metallic  oxides.  It  forms  also,  like  sesquioxide  of  gold,  a  fulminating 
ammoniacal  compound,  discovered  by  Mr.  E.  Davy. 

Bisulphide  of  platinum,  PtS2,  is  formed  by  adding  a  solution  of  bichloride  of 
platinum,  drop  by  drop,  to  a  solution  of  sulphide  of  potassium.  It  is  a  dark 
brown  and  becomes  black  by  desiccation.  When  dried  in  open  air,  a  portion  of 
its  sulphur  is  converted  into  sulphuric  acid,  by  absorption  of  oxygen,  and  the  mass 
becomes  strongly  acid. 

Bichloride  of  platinum,  PtCl2,  2121  or  169-68,  is  obtained  by  concentrating 
the  solution  of  platinum  in  aqua-regia,  as  a  red  saline  mass,  which  becomes  brown 
when  deprived  of  its  water  of  crystallization  by  heat.  The  solution  of  this  salt 
when  pure  has  an  intense  and  unmixed  yellow  colour,  the  red  colour  which  it 
usually  exhibits  being  due  to  iridium  or  to  protochloride  of  platinum.  Bichloride 


612  PLATINUM. 

of  platinum  is  soluble  in  alcohol,  and  the  solution  is  used  to  separate  potash  and 
ammonia  in  analysis. 

Chloride  of  platinum  and  potassium,  Chloroplatinate  of  potassium,  KC1  . 
PtCl2>  is  the  salt  which  falls  on  mixing  chloride  of  platinum  with  chloride  of  potas- 
sium or  any  other  salt  of  potash.  The  crystalline  grains  of  which  it  is  composed 
are  regular  octohedrons.  This  salt  is  soluble  to  a  certain  extent  in  water,  but  is 
wholly  insoluble  in  alcohol.  It  is  anhydrous.  A  very  intense  red-heat  is  required 
for  its  complete  decomposition.  Chloroplatinate  of  sodium,  NaCl  .  PtCl2-f  6HO, 
crystallizes  in  beautiful  transparent  prisms  of  a  bright  yellow  colour.  It  is  soluble 
in  alcohol  as  well  as  in  water.  When  a  solution  of  this  salt  in  alcohol  is  distilled 
till  only  one-fourth  of  the  liquid  remains,  the  solution  yields  by  evaporation  a  salt 
containing  the  elements  of  ether,  and  belonging  to  a  class  of  compounds  discovered 
by  Professor  Zeise,  and  known  as  the  etherized  salts  of  Zeise. 

Chloroplatinate  of  ammonium  resembles  the  double  salt  of  potassium.  When 
ignited,  it  leaves  metallic  platinum  in  the  spongy  state.  Bonsdorff  has  formed  a 
large  class  of  compounds  of  bichloride  of  platinum  with  the  alkaline,  earthy,  and 
metallic  chlorides,  in  all  of  which  the  salts  are  united  in  single  equivalents.  The 
bromides  and  iodides  of  platinum  have  likewise  been  formed,  and  classes  of  double 
salts  derived  from  them.  Bioxide  of  platinum  has  also  been  combined  with  acids  ; 
but  none  of  its  salts,  with  the  exception  of  the  oxalate,  is  obtained  in  a  crystalline 
state. 

Bicyanide  of  platinum,  or  platinic  cyanide,  does  not  appear  to  exist  in  the 
separate  state;  but  it  forms  double  salts  with  the  cyanides  of  potassium  and 
ammonium  ;  it  likewise  combines  with  chloride  of  potassium,  forming  the  com- 
pound KC1  .  PtCy2. 

The  sulphocyanides  of  platinum,  PtCyS2,  and  Pt  .  (CyS2)2,  likewise  form  two 
series  of  double  salts,  viz.,  the  platino-bisulphocyanides  or  sulphocyanoplatinites  = 
MPt(CyS2)2,  or  MCyS2+PtCyS2,  and  the  platino-tersulphocyanides  or  sulpho- 
cyanoplatinates  =  lnl¥i(iuy'&y)z,  or  MCyS2=Pt(CyS2)2.  The  potassium  salts  are 
formed  by  the  action  of  sulphoeyanide  of  potassium  on  protochloride  and  bichloride 
of  platinum  respectively.  All  these  salts  are  strongly  coloured,  exhibiting  all 
shades  of  colour  from  light  yellow  to  deep  red.  They  are  quickly  decomposed  by 
heat(G.  B.  Buckton).*" 

AMMONIACAL  PLATINUM    SALTS. 

The  oxides,  chlorides,  sulphates,  &c.,  of  platinum  are  capable  of  taking  up  the 
elements  of  1  or  2  equivalents  of  ammonia,  giving  rise  to  four  series  of  compounds, 
whose  composition  may  be  represented  by  the  following  general  formulae,  in  which 
the  symbols  R,  H'  denote  acid  elements  : 

1.  Ammonio-platinous  compounds,  or  protosalts  of  platammouium, 


2.  Biammonio-platinous  compounds,  or  protosalts  of  ammo-platammonium; 


N2H6PtR  =  NH2(NH4)Pt  .  ft. 
3.  Ammonio-platinic  compounds,  or  bisalts  of  platammonium, 


4.  Biammonio-platinic  compounds,  or  bisalts  of  ammo-platammonium, 
N'H«Pt{or  Ik-NH^WHr  RR'. 


*  Chem.  Soc.  Qu.  J.  vii  22. 


PLATINUM    SALTS.  613 

The  third  and  fourth  classes  of  these  compounds  may  also  be  regarded  as  proto- 
salts  of  compound  ammoniums,  in  which  1  eq.  of  hydrogen  is  replaced  by  PtO  or 

PtCl  :  for  example,  the  bichloride  NH3PtCl2  =  NH3(PtCl)  .  Cl;  the  chloronitrate 
N2H6PtClN06  =  NH^NH^PtcT.  N06. 

1.  Ammonio-platinous  compounds,  or  Protosalts  of  Platammonium.  —  These 
compounds  are  formed  by  the  action  of  heat  on  those  of  the  following  series,  half 
the  ammonia  of  the  latter  being  then  given  off.  They  are  for  the  most  part  in- 
soluble in  water,  but  dissolve  in  ammonia,  reproducing  the  biammoniacal  platinous 
compounds;  they  detonate  when  heated. 

Oxide,  NH3PtO  =  NH3Pt  .  0.  —  Obtained  by  heating  the  hydrated  oxide  of 
biammo-platammonium  to  230°.  It  is  a  greyish  mass  which,  when  heated  to 
392°  in  a  close  vessel,  gives  off  water,  ammonia,  and  nitrogen,  and  leaves,  metallic 
platinum.  Probably  the  compound,  Pt3N,  is  first  produced  and  is  afterwards  re- 
solved into  nitrogen  and  platinum  : 

3NH3PtO  =  Pt3N  +  3HO  +  2NH3. 

The  oxide,  heated'  to  392°  in  contact  with  the  air,  becomes  incandescent,  and 
burns  vividly,  leaving  a  residue  of  platinum. 

Chloride,  NH3PtCl  =  NH3Pt  .  Cl.  —  Of  this  compound  three  isomeric  modifica- 
tions exist:  a.  Yellow,  obtained  by  adding  hydrochloric  acid,  or  a  soluble  chloride, 
to  a  solution  of  nitrate  or  sulphate  of  platammonium.  Or,  by  boiling  the  green 
modification,  y,  with  nitrate  or  sulphate  of  ammonia,  whereupon  it  dissolves  and 
forms  a  solution  which,  on  cooling,  deposits  the  yellow  salt.  Or,  by  neutralizing 
a  solution  of  platinous  chloride  in  hydrochloric  acid  with  carbonate  of  ammonia, 
heating  the  mixture  to  the  boiling  point,  and  adding  a  quantity  of  ammonia  equal 
to  that  already  contained  in  the  liquid,  filtering  from  a  dingy  green  substance, 
which  deposits  after  a  while,  then  leaving  the  solution  to  cool,  and  decanting  the 
supernatant  liquid  as  soon  as  the  yellow  salt  is  deposited.  /3.  Red.  —  If,  in  the  last 
mode  of  preparation,  the  carbonate  of  ammonia,  instead  of  being  added  at  once  in 
excess,  be  added  drop  by  drop  to  the  hydrochloric  acid  solution  of  platinous 
chloride,  the  liquid  on  cooling  deposits  small  garnet-coloured  crystals  having  the 
form  of  six-sided  tables.  This  red  modification  may  also  be  obtained  in  other 
ways  (Peyrone).*  y.  Green.  —  This  modification,  usually  denominated  the  green 
salt  of  Magnus,  was  the  first  discovered  of  the  ammoniacal  platinum  compounds. 
It  is  obtained  by  gradually  adding  an  acid  solution  of  platinous  chloride  to  caustic 
ammonia,  or  by  passing  sulphurous  acid  gas  into  a  boiling  solution  of  bichloride 
of  platinum  till  it  is  completely  converted  into  protochloride  (and  therefore  no 
longer  gives  a  precipitate  with  sal-ammoniac),  and  neutralizing  the  solution  with 
ammonia  ;  the  compound  is  then  deposited  in  green  needles.  The  same  modifica- 
tion of  the  salt  may  also  be  obtained  by  adding  an  acid  solution  of  platinous 
chloride  to  a  solution  of  biammonio-platinous  chloride,  N2H6PtCl.  Hence  it  would 
appear  that  the  true  formula  of  this  green  salt  is  (NH3PtCl)2  =  PtCl  + 


•  Cl,  that  of  the  yellow  or  red  modification  being  simply  NH3PtCl. 
Either  modification  of  the  salt,  when  heated  to  572°,  gives  off  nitrogen,  hydro- 
chloric acid,  and  sal-ammoniac,  and  leaves  a  residue  of  platinum. 

A  red  crystalline  compound  of  chloride  of  platammonium  with  chloride  of  ammo- 
nium, viz.  NHgPtCl  +  NH4C1,  is  formed  when  a  solution  of  chloride  of  ammo- 
platammonium,  containing  a  large  quantity  of  sal-ammoniac,  is  evaporated  to  the 
crystallizing  point.  Thus,  when  a  solution  of  platinous  chloride  in  hydrochloric 
acid  is  precipitated  by  ammonia,  and  the  green  salt  of  Magnus  thereby  formed  is 

*  Vide  Translation  of  Gmelin's  Handbook,  vi.  303. 


612  PLATINUM. 

of  platinum  is  soluble  in  alcohol,  and  the  solution  is  used  to  separate  potash  and 
ammonia  in  analysis. 

Chloride  of  platinum  and  potassium,  Chloroplatinate  of  potassium,  KC1  . 
PtCl2,  is  the  salt  which  falls  on  mixing  chloride  of  platinum  with  chloride  of  potas- 
sium or  any  other  salt  of  potash.  The  crystalline  grains  of  which  it  is  composed 
are  regular  octohedrons.  This  salt  is  soluble  to  a  certain  extent  in  water,  but  is 
wholly  insoluble  in  alcohol.  It  is  anhydrous.  A  very  intense  red-heat  is  required 
for  its  complete  decomposition.  Chloroplqtinate  of  sodium,  NaCl  .  PtCl2  +  6HO, 
crystallizes  in  beautiful  transparent  prisms  of  a  bright  yellow  colour.  It  is  soluble 
in  alcohol  as  well  as  in  water.  When  a  solution  of  this  salt  in  alcohol  is  distilled 
till  only  one-fourth  of  the  liquid  remains,  the  solution  yields  by  evaporation  a  salt 
containing  the  elements  of  ether,  and  belonging  to  a  class  of  compounds  discovered 
by  Professor  Zeise,  and  known  as  the  etherized  salts  of  Zeise. 

Chloroplatinate  of  ammonium  resembles  the  double  salt  of  potassium.  When 
ignited,  it  leaves  metallic  platinum  in  the  spongy  state.  Bonsdorff  has  formed  a 
large  class  of  compounds  of  bichloride  of  platinum  with  the  alkaline,  earthy,  and 
metallic  chlorides,  in  all  of  which  the  salts  are  united  in  single  equivalents.  The 
bromides  and  iodides  of  platinum  have  likewise  been  formed,  and  classes  of  double 
salts  derived  from  them.  Bioxide  of  platinum  has  also  been  combined  with  acids  ; 
but  none  of  its  salts,  with  the  exception  of  the  oxalate,  is  obtained  in  a  crystalline 
state. 

Bicyanide  of  platinum,  or  platinic  cyanide,  does  not  appear  to  exist  in  the 
separate  state  ;  but  it  forms  double  salts  with  the  cyanides  of  potassium  and 
ammonium  ;  it  likewise  combines  with  chloride  of  potassium,  forming  the  com- 
pound KC1  .  PtCy2. 

The  sulphocyanides  of  platinum,  PtCyS2,  and  Pt  .  (CyS2)2,  likewise  form  two 
series  of  double  salts,  viz.,  the  platino-bisulphocyanides  or  sulphocyanoplatinites  = 
MPt(CyS2)2,  or  MCyS2+PtCyS2,  and  the  platino-ter  sulphocyanides  or  sulpho- 
cyanoplatinates  =  MPt(CyS2)3,  or  MCyS2=Pt(CyS2)2.  The  potassium  salts  are 
formed  by  the  action  of  sulphocyanide  of  potassium  on  protochloride  and  bichloride 
of  platinum  respectively.  All  these  salts  are  strongly  coloured,  exhibiting  all 
shades  of  colour  from  light  yellow  to  deep  red.  They  are  quickly  decomposed  by 
heat(O.  B.  Buckton).*1" 

AMMONIACAL  PLATINUM    SALTS. 

The  oxides,  chlorides,  sulphates,  &c.,  of  platinum  are  capable  of  taking  up  the 
elements  of  1  or  2  equivalents  of  ammonia,  giving  rise  to  four  series  of  compounds, 
whose  composition  may  be  represented  by  the  following  general  formulae,  in  which 
the  symbols  R,  R'  denote  acid  elements  : 

1.  Ammonio-platinous  compounds,  or  protosalts  of  platammouium, 


2.  Biammonio-platinous  compounds,  or  protosalts  of  ammo-platammonium; 


N2H6PtR  =  NH2(NH4)Pt  .  R. 
3.  Ammonio-platinic  compounds,  or  bisalts  of  platammonium, 


4.  Biammonio-platinic  compounds,  or  bisalts  of  ammo-platammonium, 
N<H«Pt{or  !tf=NH^WHr  ER'. 


*  Chem.  Soc.  Qu.  J.  vii  22. 


PLATINUM    SALTS.  613 

The  third  and  fourth  classes  of  these  compounds  may  also  be  regarded  as  proto- 
salts  of  compound  ammoniums,  in  which  1  eq.  of  hydrogen  is  replaced  by  PtO  or 

PtCl  :  for  example,  the  bichloride  NH3PtCl2  =  NH3(PtCl)  .  01;  the  chloronitrate 
N2H6PtClN06  =  NH^NHOPtcT.  N06. 


1.  Ammonio-platinous  compounds,  or  Protosalts  of  Platammonium.  —  These 
compounds  are  formed  by  the  action  of  heat  on  those  of  the  following  series,  half 
the  ammonia  of  the  latter  being  then  given  off.  They  are  for  the  most  part  in- 
soluble in  water,  but  dissolve  in  ammonia,  reproducing  the  biammoniacal  platinous 
compounds  ;  they  detonate  when  heated. 

Oxide,  NH3PtO  =  NH3Pt  .  0.  —  Obtained  by  heating  the  hydrated  oxide  of 
biammo-platammonium  to  230°.  It  is  a  greyish  mass  which,  when  heated  to 
392°  in  a  close  vessel,  gives  off  water,  ammonia,  and  nitrogen,  and  leaves,  metallic 
platinum.  Probably  the  compound,  Pt3N,  is  first  produced  and  is  afterwards  re- 
solved into  nitrogen  and  platinum  : 

3NH3PtO  =  Pt3N  +  3HO  +  2NH3. 

The  oxide,  heated'  to  392°  in  contact  with  the  air,  becomes  incandescent,  and 
burns  vividly,  leaving  a  residue  of  platinum. 

Chloride,  NH3PtCl  =  NH3Pt  .  01.  —  Of  this  compound  three  isomeric  modifica- 
tions exist  :  a.  Yellow,  obtained  by  adding  hydrochloric  acid,  or  a  soluble  chloride, 
to  a  solution  of  nitrate  or  sulphate  of  platamrnonium.  Or,  by  boiling  the  green. 
modification,  y,  with  nitrate  or  sulphate  of  ammonia,  whereupon  it  dissolves  and 
forms  a  solution  which,  on  cooling,  deposits  the  yellow  salt.  Or,  by  neutralizing 
a  solution  of  platinous  chloride  in  hydrochloric  acid  with  carbonate  of  ammonia, 
heating  the  mixture  to  the  boiling  point,  and  adding  a  quantity  of  ammonia  equal 
to  that  already  contained  in  the  liquid,  filtering  from  a  dingy  green  substance, 
which  deposits  after  a  while,  then  leaving  the  solution  to  cool,  and  decanting  the 
supernatant  liquid  as  soon  as  the  yellow  salt  is  deposited.  )3.  Red.  —  If,  in  the  last 
mode  of  preparation,  the  carbonate  of  ammonia,  instead  of  being  added  at  once  in 
excess,  be  added  drop  by  drop  to  the  hydrochloric  acid  solution  of  platinous 
chloride,  the  liquid  on  cooling  deposits  small  garnet-coloured  crystals  having  the 
form  of  six-sided  tables.  This  red  modification  may  also  be  obtained  in  other 
ways  (Peyrone).*  y.  Green.  —  This  modification,  usually  denominated  the  green 
salt  of  Magnus,  was  the  first  discovered  of  the  arnmoniacal  platinum  compounds. 
It  is  obtained  by  gradually  adding  an  acid  solution  of  platinous  chloride  to  caustic 
ammonia,  or  by  passing  sulphurous  acid  gas  into  a  boiling  solution  of  bichloride 
of  platinum  till  it  is  completely  converted  into  protochloride  (and  therefore  no 
longer  gives  a  precipitate  with  sal-ammoniac),  and  neutralizing  the  solution  with 
ammonia  ;  the  compound  is  then  deposited  in  green  needles.  The  same  modifica- 
tion of  the  salt  may  also  be  obtained  by  adding  an  acid  solution  of  platinous 
chloride  to  a  solution  of  biamnionio-platinous  chloride,  N2H6PtCl.  Hence  it  would 
appear  that  the  true  formula  of  this  green  salt  is  (NH3PtCl)2  =  PtCl  -f 

NlfrrNHTTPt  .  01,  that  of  the  yellow  or  red  modification  being  simply  NH3PtCl. 
Either  modification  of  the  salt,  when  heated  to  572°,  gives  off  nitrogen,  hydro- 
chloric acid,  and  sal-ammoniac,  and  leaves  a  residue  of  platinum. 

A  red  crystalline  compound  of  chloride  of  platammonium  with  chloride  of  ammo- 
nium, viz.  NH3PtCl  +  NH4C1,  is  formed  when  a  solution  of  chloride  of  ammo- 
platammonium,  containing  a  large  quantity  of  sal-ammoniac,  is  evaporated  to  the 
crystallizing  point.  Thus,  when  a  solution  of  platinous  chloride  in  hydrochloric 
acid  is  precipitated  by  ammonia,  and  the  green  salt  of  Magnus  thereby  formed  is 

*  Vide  Translation  of  Gmelin's  Handbook,  vi.  303. 


616  PLATINUM. 

Nitrates.  —  A    mononitrate,    NH3PtG2.N05  +  8HO,   or   oxynitrate,    NPI3Pt. 

!~\"o  '  —  ~~*^*~^ 

Q6-f-  3HO,  or  nitrate  of  oxyplatammonium,  NH3(PtO).N06  -f  3HO  is  ob- 

tained by  boiling  the  chloride  NH3PtCl2  for  several  hours  with  a  dilute  solution  of 
nitrate  of  silver.  It  is  a  yellow,  crystalline  powder,  sparingly  soluble  in  cold, 

more  soluble  in  boiling  water.  The  binitrate,  NH3Pt  .  2N06  +  2HO,  is  obtained 
by  dissolving  the  mononitrate  in  nitric  acid;  it  'is  yellowish,  insoluble  in  cold 
water,  soluble  in  hot  nitric  acid. 


The  oxalnte,  NH3Pt02.C203  +  2HO,  or  NH3Pt  j  °2°4  +  2HO,  or 

C204  -f  2HO,  is  formed  by  decomposing  the  nitrate  with  oxalate  of  ammonia.  It 
is  a  light  yellow  precipitate,  soluble  in  boiling  water,  and  detonating  when  heated. 

4.  Biammonio-platinic  compounds,  or  Bi-salts  of  ammoplatammoninum.  —  The 
oxide  of  this  series  has  not  yet  been  isolated. 

Chloride.—  N2H6PtCl2  =  N^NS^Pt?Clt=a:|rt^^p^.Cl.---Obtainei 

by  passing  chlorine  gas  into  a  solution  of  biammonio-platinous  chloride,  N2H6PtCl; 
by  dissolving  ammonio-platinic  chloride,  NH3PtCl2,  in  ammonia,  and  expelling 
the  excess  of  ammonia  by  evaporation  ;  or  by  precipitating  a  solution  of  one  of  the 
nitrates, 

N2H6Pt02.N05,  or  N2H6PtC10  .  N05, 

with  hydrochloric  acid.  It  is  white,  and  dissolves  in  small  quantity  in  boiling 
water,  from  which  solution  it  is  deposited  in  the  form  of  transparent,  regular 
octohedrons,  having  a  faint  yellow  tint.  When  a  solution  of  this  salt  is  treated 
with  nitrate  of  silver,  one  half  of  the  chlorine  is  very  easily  precipitated,  but  to 
remove  even  a  small  portion  of  the  remainder  requires  a  long-continued  action  of 
the  silver-salt  ;  a  result  easily  explained  if  the  salt  be  regarded  as  a  chloride  of 

ammo-chlorplatammonium,  NH2(NH4)(PtCl)  .  Cl  (Grimm.)*  A  compound  having 
the  formula  N2H5PtCl,  containing,  therefore,  1  eq.  Cl  and  1  eq.  H  less  than  the 
preceding,  is  obtained  by  dissolving  chloroplatinate  of  ammonium  in  ammonia,  and 
precipitating  by  alhocol  ;  but  it  does  not  crystallize,  merely  drying  up  to  a  pale 
yellow,  resinous  mass  :  hence  its  composition  is  doubtful. 

Nitrates.  —  A  mononitrate,  N2HcPt02.N05,  or  oxynitrate  of  ammoplatammonium, 
^-—  —  —  ^-~  -  —  <  (  ]sjry  ^—  —  -^-—  ^—  —  -^ 

N  H2  (N  H4)  Pt  \     Q6,  or  nitrate  of  ammoxyplatamrnonium,  NH2(NH4)(PtO).N06, 

is  obtained  by  boiling  the  following  salt  6,  with  ammonia  :  it  is  a  white  amorphous 
powder,  slightly  soluble  in  cold,  more  soluble  in  boiling  water. 
Sesquinitrate,  2(N3H6Pt02).3N05,  or 


NH2(NH4)(PtN06) 

Formed  by  boiling  the  mononitrate  of  ammoplatammonium  with  nitric  acid.     It 
is  a  colourless,  crystalline,  detonating  salt,  slightly  soluble  in  cold  water,  more 
soluble  in  boiling  water,  insoluble  in  nitric  acid  (Gerhardt). 
Chlorondrates.—a.  N2H6PtC10.N05;  or 

NH27NH01Pt:  |  N^J6  or  N^S^)(P5^  N06.  —  This  salt  was  discovered  by 

Gros.  It  is  obtained  by  treating  Magnus's  green  salt  with  strong  nitric  acid. 
The  green  compound  first  turns  brown^and  is  afterwards  converted  into  a  mixture 
of  platinum  and  a  white  powder,  which  is  dissolved  out  by  boiling  water,  J»nd 

*  Ann.  Ch.  Pharin.  xcix.  77 


f 
AMMONIACAL    PLATINUM    SALTS.  617 

crystallizes  on  cooling  in  shining  flattened  prisms,  colourless,  or  having  a  pale 
yellow  tint.  The  reaction  may  be  thus  represented  :  — 

2(NH,PtCl)  +  HO.N05  =  NgH.PtCl.NO.  +  Pt  +  HC1. 

This  compound  dissolves  readily  in  water,  especially  when  heated.  The  chlorine 
and  platinum  contained  in  the  solution  cannot  be  detected  by  the  ordinary  reagents  j 
thus,  nitrate  of  silver  and  hydrosulphuric  acid  yield  but  very  trifling  precipitates, 
even  after  a  long  time. 

b.  4NH,Pt2C10,2N05,  or   N  H^NH^lRCl) ]    2XO$> 

NH2(NH4)  (PtCl)J 

Discovered  by  Raewsky.  When  Magnus's  green  salt  is  boiled  with  a  large  excess 
of  nitric  acid,  red  fumes  are  evolved,  and  the  resulting  solution  deposits  this  salt 
in  small,  brilliant,  needle-shaped  prisms,  which  deflagrate  when  heated,  giving  off 
water  and  chloride  off  ammonium,  and  leaving  metallic  platinum.  Kaewsky 
assigns  to  this  salt  the  formula  4NH3.Pt2C105.2N05;  but  the  formula,  above  given, 
which  is  deduced  from  Gerhardt' s  analysis,  and  contains  20  less,  is  much  more 
probable,  as  it  accords  with  the  constitution  of  the  other  compounds  of  the  series. 
The  2  atoms  of  nitric  acid  contained  in  this  salt  may  be  replaced  by  2  atoms  of 
carbonic  or  oxalic  acid,  yielding  sparingly  soluble  crystalline  salts  of  exactly 
similar  constitution.  There  is  also  a  phosphate  containing  4NH3.Pt2C103.P05.HO, 
obtained  by  mixing  the  solution  of  the  nitrate  with  ordinary  phosphate  of  soda. 
According  to  Raewsky,  the  mother-liquor  from  which  the  preceding  nitrate  has 
crystallized,  contains  another  nitrate  whose  formula  is  4NH3.Pt2Cl204.2N05;  but 
Gerhardt  finds  this  salt  to  be  identical  with  the  nitrate  discovered  by  Gros. 


Chloromlphate,  N2H6PtClS04  =  NH2  (N  H4)  (PtCl)  .  S04.—  Obtained  by  treat- 
ing biammonio-platinic  chloride,  or  Gros's  nitrate,  with  dilute  sulphuric  acid,  or 
by  mixing  the  solution  of  the  nitrate  with  a  strong  solution  of  a  soluble  sulphate. 
It  crystallizes  in  slender  needles,  sparingly  soluble  in  cold  water,  but  dissolving 
with  tolerable  facility  in  boiling  water.  The  sulphuric  acid  in  the  solution  is  not 
precipitated  by  baryta-salts.  The  salt  is,  however,  decomposed  by  hydrochloric 
or  nitric  acid,  either  of  which  takes  the  place  of  the  sulphuric  acid,  reproducing 
the  chloride  or  nitrate  (Gros). 

CMoroxalate,  NaHePtClO.CA^NH^NE^  j  C2^=NH^NH4XPtcT).G204. 

Oxalic  acid  or  an  alkaline  oxalate  added  to  the  solution  of  the  corresponding  sul- 
phate or  nitrate,  throws  down  this  salt  in  the  form  of  a  white  granular  precipitate, 
insoluble  in  water. 

Oxalonitrates.—a.  N2H6Pt02.  N05.  C203  = 

==  NH2(NH4)(PtN06).C204- 

o 

2C204 

b.    2(N2H6Pt02).N05.2C203   =   2(NH2(NH4)Pt)  .      N06  = 
_  (.      O 

NHYNH  )(PtNO  )  [  ^2^4'  —  Obtained  by  adding  oxalate  of  ammonia  to  a  solu- 
tion of  the  sesquinitrate  ;  it  is  insoluble  in  water  (Gerhardt). 

GERHARDT'S  THEORY  or  THE  AMMONIACAL  PLATINUM  COMPOUNDS. 

These  compounds  may  be  regarded  as  salts  of  peculiar  bases  or  alkalies,  formed 
from  ammonia  by  the  substitution  of  one  or  two  atoms  of  platinum  for  hydrogen  ; 
admitting,  however,  that  platinum  (like  other  metals)  may  enter  into  its  com- 


Deposited  as  a  white  crystalline  body  from  a  solution  of  the  following  salt  b  in 
dilute  nitric  acid. 


618  PLATINUM. 

pounds  with  two  different  equivalent  weights,  viz.,  in  the  platinows  compounds,  as 
/Ya&'nosww=98-68  =  Pt,  and  in  the  platin/e  compounds,  as  Platinicum  =  49-34 
=  pt.  This  being  admitted,  the  ammonio-platinous  compounds  may  he  regarded 
as  salts  of  an  alkali,  called  Platosamine  =  NH2Pt,  formed  from  ammonia  by  the 
substitution  of  1  atom  of  platinosum  for  1  atom  of  hydrogen  ;  and  the  biammonio- 
platinous  compounds,  as  salts  of  Diplatosamine  =  N2H5Pt,  formed  by  the  union 
of  two  atoms  of  ammonia  into  one,  and  the  substitution  therein  of  1  Pt  for  1  H  : 
thus  for  the  chlorides  :  — 

NH3PtCl  =  Hydrochlorate  of  Platosamine  =  NH2Pt.HCl; 

N2H6PtCl  =  Hydrochlorate  of  Diplatosamine  =  N2H5Pt.HCl; 
and  for  the  nitrates  :  — 

NH3Pt.N06  =  Nitrate  of  Platosamine  =  NH2Pt.HN06; 

N2H6Pt.N06  =  Nitrate  of  Diplatosamine  =  N2H5Pt.HN06. 

In  a  similar  manner,  the  ammonio-platinic  compounds  may  be  regarded  as  salts 
of  Platinamine  =  NHpt2,  and  the  biammonio-platinic  compounds  as  salts  of  Di- 
plat  in  a  mine  =  N2H4pt2  ;  thus  — 

NH3PtCl2  =  Bihydrochlorate  of  Platinamine  =  NHPt2.2HCl. 

N2H6PtCl2  =  Bihydrochlorate  of  Diplatinamine  =  N2H4pt2,2HCl. 

Diplatiuaraine  forms  three  kinds  of  salts,  viz.,  inono-acid,  sesqui-acid,  and  bi- 
acid  salts  ;  and,  moreover,  exhibits  a  peculiar  tendency  to  form  double  salts  con- 
taining two  acids  :  thus,  the  salts  discovered  by  Gros  may  be  regarded  as  bi-acid 
salts,  and  those  discovered  by  Raewsky,  as  sesqui-acid  salts  of  diplatinamine  con- 
taining hydrochloric  together  with  another  acid  ;  thus  :  — 

Mononitrate  =  N2H6Pt02.N05  =  N2H4pt2.HN06  -f  HO. 

Sesquinitrate  =  2(N2H6Pt02).3N05  =  2N2H4pt2.3HN06  +  HO. 

Chloronitrate      \       M  „  pfnin  NO        \r  TT  ^ 
(Gros's  nitrate)     =    N2H6PtC10.N05  =  N  H4pt2. 


Scsquichloronitrate    \  _  N  TT  Pf  rin  9NO  __91«-  rr    .     f  HC1 
(Raewsky's  nitrate)       '  N4H12Pt2C103.2N05-.N2H4pt2. 


Oxalonitrate  =  N2H6Pt02.N05.C203  =  N^pt^  j 
Sesqui-oxalonitrate  =  2(N2H6Pt02).N05.2C203 


ESTIMATION    AND    SEPARATION    OF   PLATINUM. 

For  quantitative  estimation,  platinum  is  usually  precipitated  from  its  solutions 
in  the  form  of  chloroplatinate  of  ammonium.  The  acid  solution  of  platinum, 
after  sufficient  concentration,  is  mixed  with  a  very  strong  solution  of  sal-ammo- 
niac, and  a  sufficient  quantity  of  strong  alcohol  added  to  render  the  precipitation 
complete.  The  precipitate  of  chloroplatinate  of  ammonium  is  then  washed  with 
alcohol,  to  which  a  small  quantity  of  sal-ammoniac  has  been  added,  and  then 
heated  to  redness  in  a  weighed  porcelain  crucible,  whereupon  it  is  decomposed  aud 
leaves  metallic  platinum.  Great  care  must,  however,  be  taken  in  the  ignition  to 
prevent  loss,  as  the  evolved  vapours  are  very  apt  to  carry  away  small  particles  of 
the  salt  and  of  the  reduced  metal.  The  best  mode  of  avoiding  this  source  of 
error  is  to  place  the  precipitate  in  the  crucible  enclosed  in  the  filter,  and  expose  it 
for  some  time  to  a  moderate  heat,  with  the  cover  on  the  crucible,  till  the  filter  is 
charred,  and  then  to  a  somewhat  higher  temperature  to  expel  the  chlorine  and 
chloride  of  ammonium.  The  crucible  is  then  partially  opened,  and  the  carbona- 
ceous matter  of  the  filter  burnt  away  in  the  usual  manner.  When  these  precau- 
tions are  duly  observed,  not  a  particle  of  platinum  is  lost.  Instead  of  igniting 
the  precipitate  and  weighing  the  platinum,  the  precipitate  is  sometimes  collected 
on  a  weighed  filter,  dried  over  the  water-bath  and  weighed ;  but  this  method  is 


PALLADIUM.  619 

less  accurate,  because  the  precipitate  always  contains  an  excess  of  sal-ammoniac 
(II.  Rose). 

Chloride  of  potassium  may  also  be  used  instead  of  chloride  of  ammonium  to 
precipitate  platinum,  the  concentrated  solution  of  the  platinum  being  previously 
mixed  with  a  sufficient  quantity  of  strong  alcohol  to  bring  the  per  centage  of  alco- 
hol in  the  liquid  to  between  60  and  70  per  cent.  The  precipitated  chloroplatinate 
of  potassium  is  then  washed  with  alcohol  of  60  to  70  per  cent.,  and  decomposed 
by  simple  ignition  in  a  porcelain  crucible,  if  its  quantity  is  small,  or  in  an  atmo- 
sphere of  hydrogen  if  its  quantity  is  larger;  the  chloride  of  potassium  washed 
out  by  water;  and  the  platinum  dried,  ignited,  and  weighed. 

Potash  and  ammonia  may  also  be  estimated  by  precipitating  their  solutions  with 
chloride  of  platinum,  and  treating  the  precipitates  in  the  manner  just  described. 
Every  100  parts  of  platinum  correspond  to  47 '83  parts  of  potash,  and  17*25  parts 
of  ammonia. 

The  same  methods  of  precipitation  serve  also  for  the  separation  of  platinum 
from  most  of  the  preceding  inetals.  To  separate  platinum  from  silver,  when  the 
two  metals  are  combined  in  an  alloy,  the  best  method  is  to  heat  the  alloy  with  pure 
and  strong  sulphuric  acid,  diluted  with  about  half  its  weight  of  water,  till  the  sul- 
phuric acid  begins  to  escape  in  dense  fumes.  The  silver  is  thereby  converted  into 
sulphate,  and  the  platinum  remains  behind  in  the  metallic  state.  The  sulphate 
of  silver  is  dissolved  by  a  large  quantity  of  hot  water,  the  platinum  washed  with 
hot  water,  and  again  treated  with  sulphuric  acid,  to  separate  the  last  traces  of 
silver. 

SECTION    II. 

PALLADIUM. 

V 

Eq.  53-36  or  665-9;  Pd. 

This  metal  was  discovered  in  1803  by  Dr.  Wollaston.  It  is  precipitated  by 
cyanide  of  mercury  from  the  solution  of  the  ore  of  platinum,  after  the  removal 
of  that  metal  by  sal-ammoniac,  and  is  gradually  deposited  as  a  yellowish  white 
flocculent  powder,  which  is  cyanide  of  palladium,  and  yields  the  metal  when  cal- 
cined. Palladium  likewise  occurs,  associated  with  a  larger  quantity  of  gold  and 
a  small  quantity  of  silver,  in  a  peculiar  gold-ore  from  Brazil,  called  oropudre. 
This  mineral,  which  contains  10  per  cent,  of  palladium,  and  is  the  chief  source 
of  that  metal,  is  dissolved  in  aqua-regia,  the  acid  solution  saturated  with  potash, 
and  the  palladium  precipitated  by  cyanide  of  mercury. 

In  external  characters,  palladium  closely  resembles  platinum.  It  is  nearly  as 
infusible,  but  can  more  easily  be  welded.  The  density  of  the  fused  metal  is  11 -3 ; 
after  being  laminated,  11-8.  At  a  certain  temperature,  the  surface  of  palladium 
tarnishes  and  becomes  blue  from  oxidation,  but  at  a  stronger  heat  the  oxide  is  re- 
duced. Palladium  is  very  slightly  attacked  by  boiling  and  concentrated  hydro- 
chloric and  sulphuric  acids.  It  dissolves  in  nitric  acid,  communicating  a  brownish 
red  colour  to  the  acid,  while  no  gas  is  evolved  if  the  temperature  is  low,  the  nitric 
acid  being  converted  into  nitrous  acid.  Palladium  dissolves  with  facility  in  aqua- 
regia  ;  its  surface  is  blackened  by  tincture  of  iodine,  which  has  no  effect  upon 
platinum. 

Palladium  is  sometimes  used  for  making  the  divided  scales  of  astronomical  in- 
struments; being  nearly  as  white  as  silver,  and  not  blackened  by  sulphurous 
emanations,  it  is  well  adapted  for  that  purpose.  An  alloy  of  palladium  with 
l-10th  of  its  weight  of  silver  is  used  by  dentists. 

Palladium  has  a  much  greater  affinity  for  oxygen  than  platinum.  It  forms  two 
oxides,  the  protoxide  PdO,  and  the  bioxide  Pd02. 

Protoxide  of  palladium,  Palladous  oxide.  PdO,  61-27  or  765 -9. — This  oxide 


620  PALLADIUM. 

is  obtained  by  dissolving  palladium  in  nitric  acid,  evaporating  the  solution  to  dry- 
ness,  and  calcining  the  nitrate  at  a  gentle  heat.  It  forms  a  black  mass,  which 
dissolves  with  difficulty  in  acids.  When  carbonate  of  potash  or  soda  is  added  in 
excess  to  a  palladous  salt,  the  hydrated  protoxide  precipitates  of  a  very  dark  brown 
colour.  This  oxide  is  easily  deprived  of  its  water  by  heat,  but  a  violent  calcina- 
tion is  necessary  to  reduce  it  to  the  metallic  state. 

The  palladous  salts  are  for  the  most  part  brown  or  red ;  their  taste  is  astringent, 
but  not  metallic.  When  ignited  alone,  or  when  gently  heated  in  hydrogen  gas, 
they  yield  metallic  palladium.  The  metal  is  precipitated  from  the  solutions  of 
palladous  salts  by  phosphorus,  by  sulphurous  acid,  by  nitrate  of  potash,  by  all 
the  metals  which  reduce  silver,  by  formiate  of  potash,  and  by  alcohol  at  a  boiling 
heat.  Hydrosulphuric  acid  and  hydrosulphate  of  ammonia  throw  down  the 
brown  sulphide  of  palladium,  insoluble  in  the  latter  reagent.  Hydriodic  acid  and 
iodide  of  potassium  throw  down  a  black  precipitate  of  iodide  of  palladium,  visible 
even  to  the  500,000th  degree  of  dilution.  This  reaction  serves  for  the  separation 
of  iodine  from  bromine ;  for  alkaline  bromides  do  not  precipitate  palladous  salts. 
Potash  or'soda  forms  a  brown  precipitate  of  a  basic  salt,  soluble,  with  the  aid  of 
heat,  in  excess  of  the  reagent.  Ammonia  produces  no  precipitate  in  a  solution 
of  palladous  nitrate ;  but  from  a  solution  of  the  chloride  it  throws  down  a  flesh- 
coloured  precipitate  of  ammonio-chloride  of  palladium,  soluble  in  excess  of 
ammonia.  The  carbonates  of  potash  and  soda  form  a  brown  precipitate  of 
hydrated  palladous  oxide.  Carbonate  of  ammonia  acts  like  ammonia.  Phosphate 
of  soda  forms  a  brown  precipitate.  Ferrocyanide  and  ferricyanide  of  potassium 
form  no  precipitates,  but  the  liquid  after  a  while  coagulates  into  a  jelly.  Cyanide 
of  mercury  throws  down  a  white  pre6ipitate  of  cyanide  of  palladium.  Protochlo- 
ride  of  tin  forms  a  black  precipitate,  which  dissolves  with  intense  green  colour  in 
hydrochloric  acid.  Protosulphate  of  iron  precipitates  palladium  slowly  from  the 
nitrate,  but  not  from  the  chloride.  The  reactions  of  palladium  with  hydrosul- 
phuric  acid,  cyanide  of  mercury,  and  iodide  of  potassium  taken  together,  serve  to 
distinguish  it  from  all  other  metals. 

Protosulphide  of  palladium,  PdS,  is  obtained  by  precipitating  a  palladous 
salt  by  hydrosulphuric  acid,  and  is  of  a  dark  brown  colour;  it  may  also  be  pre- 
pared by  the  direct  union  of  its  elements. 

Protochloride  of  palladium,  PdCl,  is  prepared  by  dissolving  palladium  in 
hydrochloric  acid,  to  which  a  little  nitric  acid  is  added,  and  evaporating  the  solu- 
tion to  dryness,  to  expel  the  excess  of  acid.  The  compound  is  a  mass  of  a  dark 
brown  colour,  which  becomes  black  when  made  anhydrous  by  heat,  and  may  be 
fused  in  a  glass  vessel.  When  heated  in  platinum  vessels,  it  becomes  contami- 
nated with  the  protochloride  of  that  metal.  When  dissolved  with  chloride  of 
potassium,  it  forms  a  double  salt,  KCl.PdCl,  which  is  soluble  in  cold,  and  consi- 
derably more  so  in  hot  water,  and  crystallizes  in  four-sided  prisms,  of  a  dull  yellow 
colour.  Protochloride  of  palladium  also  combines  with  chloride  of  ammonium 
and  chloride  of  sodium,  according  to  Bonsdorff,  and  forms  double  salts  with  most 
other  chlorides. 

Protocyanide  of  palladium,  PdCy,  is  always  formed  when  cyanide  of  mercury 
is  added  to  a  neutral  solution  of  palladium,  as  a  light-coloured  precipitate,  which 
becomes  grey  after  drying.  When  the  solution  of  palladium  is  acid,  no  precipitate 
is  formed,  and  when  the  solution  contains  copper,  the  precipitate  has  a  green 
colour.  Palladium  appears  to  have  a  greater  affinity  for  cyanogen  than  any  other 
metal.  Even  cyanide  of  mercury  is  decomposed  when  boiled  with  protoxide  of 
palladium,  and  cyanide  of  palladium  formed.  When  this  cyanide  is  dissolved  in 
ammonia,  and  the  excess  of  the  latter  allowed  to  escape  by  evaporation,  a  preci- 
pitate of  brilliant,  colourless,  crystalline  plates  is  formed,  which  appears  to  consist 
of  ammoniacal  cyanide  of  palladium. 

Nitrate  of  palladium,  PdO.N05,  is  formed  by  dissolving  the  metal  in  nitric 
acid;  the  solution  dries  up  into  a  dark  red  saline  mass.  When  an  excess  of 


AMMONIACAL    COMPOUNDS    OF    PALLADIUM.  621 

ammonia  is  added  to  an  acid  solution  of  this  salt,  and  the  solution  evaporated  by 
a  gentle  heat,  a  colourless  nitrate  of  palladium  and  ammonium  is  deposited  in  rec- 
tangular tables. 

Bioxi.de  of  palladium,  Peroxide  of  palladium,  Palladic  oxide,  Pd02,  69*27 
or  865-9. — To  prepare  this  oxide,  Berzelius  recommends  a  solution  of  the  hydrate 
or  carbonate  of  potash  to  be  added  by  small  quantities  at  a  time,  to  the  dry  bichlo- 
ride of  palladium  and  potassium,  mixing  well  after  each  addition.  A  yellowish 
brown  powder  separates,  which  is  the  hydrated  bioxide,  retaining  a  little  alkali. 
Washed  with  boiling  water,  it  loses  the  greater  part  of  its  combined  water,  and 
becomes  black.  This  oxide  dissolves  with  difficulty  in  acids ;  the  solutions  are 
yellow.  The  corresponding  bisulphide  of  palladium  has  not  been  formed. 

Bichloride  of  palladium,  PdCl2,  is  obtained  in  solution,  when  the  protochloride 
is  dissolved  in  concentrated  aqua-regia,  and  the  solution  only  slightly  heated.  Its 
solution  is  of  so  dark  a  brown  as  to  appear  black,  and  gives  a  red  precipitate 
with  chloride  of  potassium.  When  the  solution  is  diluted  or  heated,  chlorine  gas 
is  evolved,  and  protochloride  of  palladium  reproduced.  The  double  salt  of  this 
chloride  and  chloride  of  potassium  is  obtained  by  treating  the  double  protochloride 
of  palladium  and  potassium  in  fine  powder  with  aqua-regia,  and  evaporating  the 
supernatant  fluid  to  dryness.  It  forms  a  cinnabar  red  powder,  in  which  little 
octohedral  crystals  can  be  perceived,  both  the  palladic  and  *  palladous  double 
chlorides  being  isomorphous  with  the* corresponding  compounds  of  platinum. 
When  treated  with  hot  water,  this  double  salt  emits  chlorine,  and  is  in  a  great 
measure  decomposed.  The  salts  of  bioxide  of  palladium  are  scarcely  known. 

Ammoniacal  compounds  of  palladium. — A  moderately  concentrated  solution 
of  protochloride  of  palladium  treated  with  a  slight  excess  of  ammonia,  yields  a 
beautiful  flesh-coloured  or  rose-coloured  precipitate,  consisting  of  NH3PdCl.  This 
precipitate  dissolves  in  a  larger  excess  of  ammonia;  and  the  ammoniacal  solution, 
when  treated  with  acids,  yields  a  yellow  precipitate  having  the  same  composition. 
This  yellow  modification  is  likewise  obtained  by  heating  the  red  compound  in  the 
moist  state  to  212°,  or  in  the  dry  state  to  392°.  The  yellow  compound  dissolves 
abundantly  in  aqueous  potash,  forming  a  yellow  solution,  but  without  giving  off 
ammonia,  even  when  the  liquid  is  heated  to  the  boiling  point ;  the  red  compound 
behaves  in  a  similar  manner,  but,  before  dissolving,  is  converted  into  the  yellow 
modification.  For  this  reason,  Hugo  Miiller,  who  has  lately  made  the  ammoniacal 
compounds  of  palladium  the  subject  of  an  elaborate  examination,  regards  the  red 
compound  as  ammonio-palladous  chloride,  NH3.PdCl,  and  the  yellow,  as  chloride 

of  pattadammonium,  NH3Pd  .  Cl.  The  yellow  compound,  digested  with  water 
and  oxide  of  silver,  yields  the  oxide  of  pallad  ammonium  (or  pallada.mi'nf), 
NH3Pd.O.  This  compound  is  a  strong  base,  analogous  to  oxide  of  plat  ammonium 
(p.  614).  It  is  soluble  in  water,  to  which  it  communicates  a  strong  alkaline  taste 
and  reaction ;  by  evaporating  the  solution  in  vacuo,  the  base  is  obtained  in  the 
form  of  a  crystalline  mass,  which  absorbs  carbonic  acid  rapidly  from  the  air, 
especially  when  moist.  It  unites  with  acids,  forming  definite  salts.  Its  solution 
precipitates  the  salts  of  silver  and  copper,  and  an  excess  of  it  does  not  redissolve 

the  precipitates.  Sulphite  of  palladammonium,  NH3Pd .  S03,  is  formed  by 
saturating  the  solution  of  the  oxide  with  sulphurous  acid,  or  by  the  action  of  that 
acid  on  the  yellow  chlorine-compound  :  it  crystallizes  in  orange-yellow  octohedrons. 

The  sulphate,  NII3Pd.  S04,  crystallizes  in  a  similar  manner.  The  nitrate,  iodide, 
and  bromide  have  also  been  formed.  The  fluoride  is  obtained  by  adding  the 
chloride  to  a  solution  of  fluoride  of  silver. 

Chloride  of  ammopalladammonium  (or  chloride  of  palladdiamine}  according 
to  Miiller), 

2NH3 .  PdCl  =  NH7(NH;)"pd .  01, 


622  IRIDIUM. 

separates  from  the  ammoniacal  solution  of  chloride  of  palladammonium,  in  colour- 
less, oblique  rhombic  prisms,  which  at  392°  give  off  half  their  ammonia  and  are 
reduced  to  NH3Pd  .  Cl.  The  iodide  and  bromide  of  ammopalladammonium  are 
likewise  obtained  by  treating  the  solutions  of  iodide  and  bromide  of  palladium  or 
palladammonium  with  ammonia.  They  both  crystallize  readily.  The  fluoride  is 
obtained  by  adding  ammonia  to  the  solution  of  chloride  of  palladammonium  ii 
fluoride  of  silver,  and  evaporating  :  it  forms  oblique  rhombic  prisms.  The  silico- 
fluorlde  is  obtained  in  crystalline  scales  on  adding  hydrofluosilicic  acid  to  any 
soluble  salt  of  ammopalladammonium.  Oxide  of  ammopalladammonium  , 

NH3Pd  .  0.  —  By  decomposing  the  solution  of  the  chloride  with  oxide  of  silver,  — 
or  better,  the  sulphate  with  hydrate  of  baryta,  a  strongly  alkaline  solution  is  ob- 
tained, which,  on  evaporation,  leaves  the  hydrated  oxide  in  the  form  of  a  crystal- 
line mass,  though  not  quite  pure.  The  solution  precipitates  the  salts  of  aluminium, 
iron,  cobalt,  nickel,  and  copper,  but  not  those  of  silver;  expels  ammonia  from 
chloride  of  ammonium,  on  boiling;  and  absorbs  carbonic  acid  from  the  air.  The 
carbonate  obtained  in  this  manner,  or  by  decomposing  the  chloride  with  carbonate 
of  silver,  or  the  sulphate  with  carbonate  of  baryta,  crystallizes  in  shining,  colour- 
less prisms,  which  turn  yellow  a  little  above  212°;  the  solution  is  strongly  alka- 
line, and,  gives  copious  precipitates  with  salts  of  lime,  baryta,  copper,  and  silver. 


The  sulphite,  NfCNH)^-  S03,  obtained  by  direct  combination,  or  by  the  ac- 
tion of  ammonia  on  sulphite  of  palladammonium,  forms  small  prismatic  crystals, 
sparingly  soluble  in  water,  insoluble  in  alcohol,  and  turning  yellow  at  about  392°. 
The  sulphate  obtained  by  treating  palladous  sulphate  with  excess  of  ammonia, 
forms  small  colourless  prisms,  easily  soluble  in  water,  but  insoluble  in  alcohol 
(Hugo  Miiller).* 

ESTIMATION   AND   SEPARATION   OF   PALLADIUM. 

Palladium  is  always  estimated  in  the  metallic  state.  It  is  precipitated  from  its 
solutions  in  the  form  of  cyanide  by  means  of  a  solution  of  cyanide  of  mercury,  the 
liquid  not  containing  any  excess  of  acid.  The  precipitated  cyanide  of  palladium 
is  then  reduced  to  the  metallic  state  by  calcination. 

Palladium  may  be  separated  from  nearly  all  other  metals  either  by  precipitation 
as  cyanide,  or  by  precipitation  with  hydrosulphuric  acid,  or  by  the  solubility  of  its 
oxide  in  ammonia.  But  to  separate  it  from  copper,  with  which  it  is  associated  in. 
platinum  ore,  the  two  metals  are  precipitated  together  by  hydrosulphuric  acid,  and 
the  precipitate,  while  still  moist,  roasted,  together  with  the  filter,  as  long  as  sul- 
phurous acid  continues  to  escape.  The  metals  are  thereby  converted  into  basic 
sulphates,  which  must  be  dissolved  in  hydrochloric  acid,  the  solution  mixed  with 
nitric  acid  and  chloride  of  potassium,  and  evaporated  to  dryness.  A  dark  saline 
mass  is  thus  obtained,  consisting  of  chloride  of  potassium,  chloride  of  copper  and 
potassium,  and  chloride  of  palladium  and  potassium  ;  and  on  treating  this  mass 
with  alcohol  of  sp.  gr.  0-833,  the  two  former  salts  are  dissolved,  and  the  double 
chloride  of  palladium  and  potassium  remains. 


SECTION    III. 

IRIDIUM. 

Ey.  98-68  or  1233-5;   Ir. 

The  black  scales  which  remain  when  native  platinum  is  dissolved  in  aqua-regia, 
were  discovered  by  Mr.  Saiithson  Tennant  to  contain  iridium  and  osniium.f     The 

*  Ann.  Ch.  Phann.  Ixxxvi.  341.  f  Phil.  Trans.  1804. 


IRIDIUM.  623 

same  alloy  occurs  in  flat  white  metallic  grains  in  native  platinum.  Iridium  has 
also  been  observed  in  combination  with  about  20  per  cent,  of  platinum,  crystallized 
in  octahedrons,  which  are  whiter  than  platinum,  and  are  said  to  have  a  greater 
density,  namely  22-66. 

The  separation  of  the  osmium  and  iridium  is  effected  by  the  following  methods  : 
—  1.  The  osmide  of  iridium  is  mixed  with  an  equal  weight  of  common  salt,  and 
subjected  to  the  action  of  a  stream  of  chlorine  in  a  porcelain  tube  heated  to  red- 
ness. Double  chlorides  of  iridium  and  sodium,  and  of  osmium  and  sodium,  are 
then  formed ;  and  if  the  chlorine  is  moist,  a  certain  quantity  of  osmic  acid,  which 
volatilizes,  and  may  be  condensed  in  aqueous  ammonia.  The  mixture  of  the 
double  chlorides  is  detached  from  the  tube  and  boiled  with  nitric  acid.  Osmic 
acid  is  then  evolved,  and  may  be  condensed  in  an  alkaline  solution,  while  the 
chloride  of  sodium  and  iridium  remains  in  the  solution,  and,  when  mixed  with 
sal-ammoniac,  yields  a  precipitate  of  chloride  of  iridium  and  ammonium,  which, 
on  ignition,  leaves  pure  metallic  iridium  (Wohler). — 2.  A  mixture  of  100  grammes 
of  osmide  of  iridium  and  300  grammes  of  nitre  is  placed  in  an  earthen  crucible, 
and  heated  to  bright  redness  for  an  hour,  the  resulting  mixture  of  osmiate  and 
iridiate  of  potash  poured  out  on  a  cold  metal  plate,  then  introduced  into  a  tubu- 
lated retort,  and  distilled  with  a  large  excess  of  nitric  acid.  A  large  quantity  of 
osmic  acid  then  volatilizes  and  condenses  in  the  receiver  in  beautiful  white  crys- 
tals. As  soon  as  the  evolution  of  osmic  acid  ceases,  water  is  added,  and  the  resi- 
due, consisting  of  oxide  of  iridium,  with  a  certain  quantity  of  oxide  of  osmium,  is 
collected  on  a  filter  and  boiled  with  aqua-regia,  which  dissolves  the  two  metals  as 
chlorides.  Tht  solution  is  then  mixed  with  sal-ammoniac,  which  precipitates 
chloride  of  osmium  and  ammonium,  and  bichloride  of  iridium  and  ammonium ; 
and  the  mixed  precipitate  suspended  in  water  and  exposed  to  a  current  of  sulphu- 
rous acid,  whereby  the  compound  IrCl2.NH4Cl,  is  converted  into  IrCl.NH4Cl, 
which  dissolves,  while  the  chloride  of  osmium  and  ammonium  remains  unaltered 
and  does  not  dissolve :  this  latter  chloride  yields  pure  metallic  osmium  by  calci- 
nation. The  solution  of  protochloride  of  iridium  and  ammonium  leaves,  when 
evaporated,  beautiful  brown  crystals,  which  yield  metallic  iridium  by  calcination. 

Iridium  is  obtained  immediately  from  the  chloride,  by  decomposing  that  salt 
with  hydrogen  at  a  gentle  heat,  or  by  exposing  it  alone  to  a  very  high  temperature, 
in  the  form  of  a  grey  metallic  powder,  much  resembling  spongy  platinum  j  also, 
as  above  described,  from  the  chloride  of  iridium  and  ammonium.  It  is  one  of  the 
most  refractory  bodies  known,  not  being  fused  by  the  oxyhydrogen  blowpipe.  Mr. 
Children,  however,  succeeded  in  fusing  a  portion  of  iridium  into  a  globule,  by  the 
discharge  of  a  very  large  voltaic  battery.  This  globule  was  white  and  very  bril- 
liant, but  still  a  little  porous;  its  density  was  18-68.  Iridium  is  neither  ductile 
nor  malleable ;  but  it  may  be  obtained  in  the  form  of  a  compact  mass,  very  hard, 
and  capable  of  taking  a  good  polish,  by  moistening  the  pulverulent  metal  with  a 
small  quantity  of  water,  compressing  it  lightly  at  first  with  filtering  paper,  after- 
wards very  forcibly  in  a  press,  and  calcining  it  at  a  strong  white  heat  in  a  forge 
fire.  The  metal  thus  aggregated  is  very  porous,  and  its  density  does  not  exceed 
16-0.  Iridium  becomes  white  and  brilliant  by  strong  ignition,  without  fusion, 
and  is  afterwards  insoluble  in  acids.  If  reduced  by  hydrogen  at  a  low  tempera- 
ture, it  oxidates  slowly  when  heated  to  redness,  or  when  digested  in  aqua-regia. 
This  metal  is  generally  rendered  soluble  by  one  or  other  of  the  following  opera- 
tions. It  is  calcined  with  hydrate  of  potash  or  nitre,  or  with  a  mixture  of  these 
salts,  which  gives  a  compound  of  sesquioxide  of  iridium  and  potassium.  Or,  the 
metal  is  reduced  to  a  fine  powder,  and  intimately  mixed  with  an  equal  weight  of 
chloride  of  potassium  or  sodium,  and  the  mixture  heated  to  low  redness  in  a  stream 
of  chlorine  gas.  The  metal  then  combines  with  chlorine,  and  the  double  chloride 
of  iridium  and  potassium  or  sodium  is  formed,  which  is  soluble  in  water. 

Oxides  of  iridium.  —  Iridium  forms  four  compounds  with  oxygen,  which  are 
obtained  by  decomposing  the  corresponding  chlorides.  The  protoxide  of  iridium, 


624  IKIDIUM. 

IrO,  is  obtained  from  the  chloride  produced  when  indium  is  heated  in  chlorine 
gas;  also  by  precipitating  the  double  chloride  of  indium  and  potassium  (KCl.IrCl) 
with  carbonate  of  potash.  The  hydrate  is  then  obtained  of  a  greenish  grey  colour, 
which  is  soluble  in  an  excess  of  the  alkaline  carbonate.  This  oxide  is  the  base 
of  a  class  of  salts.  The  sesquioxide  of  iridium,  Ir203,  is  formed  when  the  metal 
is  calcined  with  hydrate  of  potash  or  nitre.  Berzelius  recommends  as  the  best 
process  for  procuring  it,  to  mix  the  double  bichloride  of  iridium  and  potassium 
(KC1  +  IrCl2)  with  twice  its  weight  of  carbonate  of  potash,  and  expose  it  to  a 
low  red  heat.  On  dissolving  out  the  alkaline  salt,  the  sesquioxide  remains  as  a 
very  fine  powder,  of  a  black  colour  with  a  shade  of  blue.  A  heat  above  the  melt- 
ing point  of  silver  is  required  to  expel  the  oxygen  from  this  oxide.  It  is  reduced 
to  the  metallic  state  by  hydrogen  gas  at  the  usual  temperature,  an  effect  which  ap- 
pears to  arise  from  the  oxide  of  iridium  having  the  property,  as  well  as  the  metal, 
to  determine  the  oxidation  of  hydrogen,  a  reaction  which  causes  the  oxide  to  be 
heated  to  the  temperature  at  which  it  is  itself  reduced  by  hydrogen.  The  hydrate 
of  this  oxide  dissolves  in  acids  and  forms  a  particular  class  of  salts,  the  solutions 
of  which  are  sometimes  of  a  very  dark  colour,  resembling  a  mixture  of  water  and 
venous  blood. 

Bioxide  of  iridium,  or  Iridic,  oxide,  Ir02.  —  A  solution  of  sesquichloride  of 
iridium  mixed  with  potash  yields  no  precipitate  at  first;  but  if  the  liquid  be 
heated  out  of  contact  with  the  air,  it  quickly  assumes  an  indigo  colour,  absorbs 
oxygen  from  the  air,  and  deposits  hydrated  iridic  oxide,  Ir02.2HO,  which  may  be 
rendered  anhydrous  by  calcination.  This  oxide  is  likewise  obtained  by  dissolving 
the  hydrated  sesquioxide  in  potash,  and  treating  the  solution  Tfith  an  acid.  A 
greenish-blue  precipitate  is  then  formed,  which  gradually  absorbs  oxygen  from  the 
air,  and  assumes  an  indigo  colour  (Glaus).  This  oxide  forms  salts  whose  solutions 
are  of  a  dark,  brown-red  colour  and  almost  opaque  when  concentrated,  but  reddish- 
yellow  when  dilute.  Hydrosulphuric  acid  decolorizes  the  solutions  at  first,  and 
afterwards  forms  a  brown  precipitate;  hydrosulphate  of  ammonia  also  forms  a 
brown  precipitate.  Potash  and  ammonia  decolourize  the  solution,  and  produce  only 
a  slight  black  precipitate;  but  the  liquid,  on  exposure  to  the  air,  soon  acquires  a 
very  fine  blue  colour.  Carbonate  of  potash  forms  a  red-brown  precipitate,  which 
gradually  dissolves,  the  liquid  afterwards  turning  blue  when  exposed  to  the  air. 
Carbonate  of  ammonia  imparts  a  blue  colour  to  the  liquid  under  the  influence  of 
the  air.  Chloride  of  ammonium  forms  a  dark,  cherry-red  pulverulent  precipitate 
of  bichloride  of  iridium  and  ammonium.  Ferrocyanide  of  potassium  and  proto- 
sulphate  of  iron  decolourize  the  solution.  Protochloride  of  tin.  forms  a  light  brown 
precipitate.  Zinc  precipitates  metallic  iridium  as  a  black  powder. 

Teroxide  of  iridium,  Ir03,  is  formed  in  small  quantity  when  the  alloy  of 
osmium  and  iridium  fused  in  nitre  is  digested  in  aqua-regia.  The  double  terchloride 
of  iridium  and  potassium  then  formed  yields  a  rose-red  solution,  which,  when 
treated  with  an  alkali,  slowly  deposits  the  teroxide  as  a  greenish-yellow  precipitate, 
retaining,  however,  a  certain  quantity  of  the  alkali.  The  salts  of  the  protoxide 
and  teroxide  afford  blue  and  purple  solutions  when  mixed,  depending  probably  on 
the  formation  of  one  or  more  combinations  of  these  oxides.  The  name  iridium 
(from  Iris)  was  applied  to  this  metal,  from  the  variety  of  colours  which  its  pre- 
parations exhibit. 

Sulphides  of  iridium,  corresponding  with  the  oxides  of  the  same  metal,  have 
been  formed. 

Chlorides  of  iridium.  —  The  protochloride,  IrCl,  is  formed  when  iridium  in 
powder  is  heated  to  low  redness  in  chlorine  gas.  As  thus  prepared,  it  is  insoluble 
in  water,  but  slightly  soluble  in  hydrochloric  acid.  It  forms  double  salts  with  tht 
chlorides  of  potassium,  ammonium,  and  sodium. 

The  xrsquic.hlnride,  Ir2Cl3,  is  prepared  by  dissolving  the  sesquioxide  in  hydro- 
chloric acid.  It  is  black,  deliquescent,  and  does  not  crystallize.  It  forms  soluble 
double  chlorides,  which  are  decomposed  by  ebullition  into  iridous  double  chlorides 


AMMONIACAL    COMPOUNDS    OF    IRIDIUM.  625 

(containing  IrCl),  which  remain  in  solution,  and  iridic  double  chlorides  (con- 
taining IrCl2),  which  are  precipitated.  Glaus  has  obtained  the  compounds, 
3KC1 .  Ir2Cl3  +  6HO ;  3NH4C1 .  Ir2Cl3  +  3HO > ;  and  SNaCl .  Ir2Cl3  +  24HO. 

The  bichloride,  IrCl2,  is  obtained  by  dissolving  very  finely-divided  iridium,  or 
one  of  its  oxides,  in  aqua-regia,  the  liquid  being  heated  to  the  boiling  point.  It 
dissolves  in  water,  forming  a  reddish-yellow  solution.  It  combines  with  other 
chlorides,  forming  very  definite  salts.  The  potassium-salt,  chloridiate  of  potas- 
sium, IrCl2 .  KC1 .  HO,  crystallizes  in  black  octohedrons,  yielding  a  red  powder, 
and  soluble  in  water,  to  which  it  imparts  a  red  colour.  Chloridiate  of  am- 
monium, IrCl2 .  NH4C1 .  HO,  is  obtained,  on  mixing  the  solutions  of  the  two 
chlorides,  as  a  very  dark  brown  precipitate,  which  dissolves  in  boiling  water,  and 
crystallizes  in  octohedrons  on  cooling.  Its  colouring  power  is  very  great,  1  part 
of  it  sufficing  to  impart  a  distinct  coloration  to  40,000  parts  of  water.  The  red 
colour  often  exhibited  by  chloroplatinate  of  ammonium  is  due  to  traces  of  this 
salt.  Chloridiate  of  ammonium  dissolves  in  sulphurous  acid,  and  is  thereby  con- 
verted into  a  soluble  and  crystallizable  compound  of  NH4C1,  and  IrCl ;  the  sepa- 
ration of  iridium  and  osmium  depends  upon  this  property.  Bichloride  of  iridium, 
free  or  combined  with  other  chlorides,  is  also  reduced  to  the  state  of  protochloride 
by  potash,  hydrosulphuric  acid,  ferrocyanide  of  potassium,  and  alcohol.  Accord- 
ing to  Glaus,*  the  bichloride  is  converted  by  potash  into  the  olive-green  sesqui- 
chlorfde,  hypochlorite  of  potash  being  formed  at  the  same  time.  The  alkaline 
solution  when  heated  becomes  colourless,  and  afterwards  violet-red,  and  yields  a 
blue  precipitate  of  the  hydrated  bioxide ;  the  decolourized  alkaline  solution,  mixed 
with  a  few  drops  of  alcohol  and  heated,  deposits  metallic  iridium.  Nitrate  of 
silver  added  to  the  solution  of  the  bichloride  forms  a  blue  precipitate,  which 
quickly  loses  its  colour  and  passes  into  the  compound  Ir2Cl3 .  3AgCl.  Mercurous 
nitrate  forms  a  light  ochre-yellow  precipitate  of  Ir2Cl3 .  3Hg2Cl. 

Terchloride  of  iridium,  IrCl3,  is  formed  by  treating  an  oxide  or  a  lower  chloride 
of  iridiura  with  very  strong  aqua-regia,  at  a  temperature  not  exceeding  104°  or 
122°  (40°  or  50°  C.)  Its  colour  is  a  deep  brown,  nearly  approaching  to  black ; 
it  is  soluble  in  water,  and  deliquescent.  It  forms  double  chlorides  of  the  alkali- 
metals. 

Carburet  of  iridium. — When  a  coherent  mass  of  iridium  is  held  in  the  flame 
of  a  spirit  lamp,  black  masses  appear  on  its  surface,  which  are  a  carburet,  contain- 
ing 19-83  per  cent,  of  carbon,  or  IrC4.  The  carbon  burns  off  readily  in  the  air. 

Iridic  sulphate  is  obtained  by  dissolving  bisulphide  of  iridium  in  nitric  acid, 
and  expelling  the  excess  of  acid  by  evaporation.  It  dissolves  in  water  and  alcohol, 
forming  orange^yellow  solutions,  which  on  evaporation  leave  the  salt  in  the  form 
of  a  syrupy  uncrystallizable  mass. 

AMMONIACAL  COMPOUNDS  OP  IRIDIUM. — Ammonio-iridious  chloride,  NH3. 

/^-^ 

IrCl,  or  Chloride  of  iridammonium,  NH3Ir .  Cl. — Prepared  by  heating  bichloride 
of  iridium  till  it  is  converted  into  protochloride,  dissolving  the  brown  resinous 
residue  in  carbonate  of  ammonia,  and  adding  hydrochloric  acid  in  slight  excess. 
The  compound  then  separates  in  the  form  of  a  yellow  granular  precipitate,  inso- 
luble in  water.  The  oxide  corresponding  to  this  chloride  has  not  been  obtained 

in  the  free  state.  The  sulphate  NH3Ir .  S04  is  obtained  by  heating  the  chloride 
with  dilute  sulphuric  acid.  It  crystallizes  in  large  orange-yellow  laminae,  easily 
soluble  in  water.  Biammonio-iridious  chloride,  2NH, .  IrCl,  or  Chloride  of 

ammi  rid  ammonium,  NH2(NH4)Ir .  Cl,  is  obtained,  as  a  white  precipitate,  by 
boiling  the  compound,  NH3Ir .  Cl,  with  excess  of  ammonia.  Treated  with  mode- 
rately strong  sulphuric  acid,  it  yields  the  corresponding  sulphate,  NHa(NH4)Ir .  S04, 

*  Liebig  and  Kopp's  Jahresbericht,  1855,  p.  427. 
40 


626  IRIDIUM. 

in  rhombic  prisms  ;  and,  by  decomposing  this  salt  with  nitrate  of  baryta,  or  decom- 
posing the  chloride  with  nitric  acid,  the  nitrate  is  obtained  in  yellow  needles, 
which  dissolve  readily  in  water,  melt  when  heated,  and  then  suddenly  decompose 

with  flamje.  A  chloronitrate  of  ammirid  ammonium,  NH2(NH4)Ir  .  j     Q\>  or  nitrate 

of  ammochlorir  id  ammonium,  NH2(NII4)  (IrCl).N06,  analogous  to  Gros's  plati- 
num-nitrate (p.  616),  is  obtained  as  a  yellowish,  crystalline,  granular  mass,  by 
heating  the  chloride  of  iridammonium,  NH3Ir.  Cl,  with  strong  nitric  acid;  when 
recrystallized  from  water,  it  forms  shining  yellow,  laminar  crystals.  J3ichlori.de  of 

ammiridam.monium,  NH2(NH4)Ir  .  C12,  or  chloride  of  ammo-chloriridammonium, 

NH2(NH4)(IrCl)  .  Cl,  is  obtained  by  treating  the  last-mentioned  salt  with  hydro- 
chloric acid,  in  the  form  of  a  violet  precipitate,  which  dissolves  readily  in  hot 
water,  and  separates  from  the  solution  in  violet  crystals.  Nitrate  of  silver  added 
to  the  solution  throws  down  only  half  the  chlorine.  The  nitrate,  treated  with 
dilute  sulphuric  acid,  yields  the  chlorosulphate  of  ammiridammonium  in  delicate 
greenish,  needle-shaped  crystals  (Skoblikoff). 


The  compound  5NH3  .  IrCl3,  or       -  -  A  -  >      C13,  is  obtained  by  mixing  a-dilute 

NH(NH4)2Ir  ) 

solution  of  Ir2Cl3  +  3NH4C1,  mixed  with  excess  of  ammonia,  and  leaving  the 
mixture  in  a  well-closed  and  completely  filled  bottle  for  some  weeks  in  a  warm 
place  ;  heating  the  liquid,  which  has  then  acquired  a  rose-colour,  to  expel  the 
excess  of  ammonia;  neutralizing  with  hydrochloric  acid;  evaporating  to  dryness; 
and  treating  the  greenish  yellow  residue  with  cold  water  to  extract  the  chloride 
of  ammonium.  A  light  flesh-coloured,  finely  crystalline  powder  then  remains, 
which,  when  dissolved  in  boiling  water,  acidulated  with  hydrochloric  acid,  yields, 
on  cooling,  a  crystalline  precipitate  of  5NH3  .  Ir2Cl3  mixed  with  sesquichloride  of 
iridium.  This  compound  when  dissolved  in  a  boiling  solution  of  ammonia,  is 
partially  decomposed,  with  separation  of  blue  hydrated  bioxide  of  iridium  ;  when 
digested  with  water  and  oxide  of  silver,  it  yields  a  rose-coloured  alkaline  solution 
of  the  base  5NH3  .  Ir203.  This  solution,  saturated  with  various  acids,  yields  :  — 
the  carbonate  5NH3  .  Ir203  .  3C02  -f  3HO,  in  the  form  of  a  finely  crystalline  powder, 
having  a  light  flesh-coloured  and  alkaline  reaction;  the  nitrate,  5NH3.Ir203.3N05, 
in  indistinct,  light  flesh-coloured,  neutral  prisms  ;  and  the  sulphate,  5NH3  .  Ir203  . 
2S04,  as  a  neutral  crystalline  salt  of  similar  colour.  All  these  salts  are  soluble  in 
water  (Claus). 

ESTIMATION    AND    SEPARATION    OF    IRIDIUM. 

The  quantitative  estimation  of  iridium  is  effected  in  the  same  manner  as  that 
of  platinum,  viz.,  by  precipitating  with  sal-ammoniac  and  igniting  the  precipitate. 
The  same  method  serves  to  separate  iridium  from  all  the  preceding  metals  except 
platinum.  The  separation  of  these  two  metals  is  effected  by  the  method  already 
described  for  the  preparation  of  pure  platinum  (p.  610);  viz.,  by  precipitating 
with  chloride  of  potassium,  fusing  the  precipitate  with  carbonate  of  potash,  and 
dissolving  out  the  platinum  with  aqua-regia. 


OSMIUM.  627 


SECTION   IV. 

OSMIUM. 

^.99  -56  or  1244-5;  Os. 

In  the  treatment  of  the  alloy  of  iridium  and  osmium,  the  latter  is  separated  as 
a  volatile  oxide,  or  osmic  acid  (p.  624).  To  obtain  the  metal,  a  solution  of  osmic 
acid  is  mixed  with  hydrochloric  acid,  and  digested  with  mercury  in  a  well  closed 
bottle  at  a  temperature  of  104°  (40°  Cent.).  The  osmium  is  reduced  by  the 
mercury,  and  an  amalgam  formed,  which  is  distilled  in  a  retort,  through  which  a 
stream  of  hydrogen  is  passed,  till  all  the  mercury  and  calomel  formed  are  removed : 
osmium  then  remains  as  a  black  powder  without  metallic  lustre.  Metallic  osmium 
is  also  obtained  by  igniting  the  sesquichloride  of  osmium  and  ammonium  mixed 
with  sal-ammoniac. 

When  rendered  coherent,  osmium  is  a  white  metal,  less  brilliant  than  platinum, 
and  very  easily  pulverized.  Its  density  is  about  10.  As  obtained  from  the  amal- 
gam, osmium  is  highly  combustible ;  when  a  mass  of  it  is  ignited  at  a  point,  it 
continues  to  redden,  and  burns  without  residue,  being  converted  into  the  volatile 
oxide  or  osmic  acid.  Osmium  in  the  same  condition  is  oxidated  by  nitric  acid  or 
aqua-regia,  and  the  osmic  acid  formed  distils  over  with  the  water  and  acid.  But 
after  being  exposed  to  a  red  heat,  osmium  becomes  much  less  combustible  in  air, 
and  is  not  oxidated  by  the  humid  way,  resembling  silicon  and  titanium  in  that 
respect.  Six  different  oxides  of  this  metal  have  been  obtained,  namely,  OsO; 
Os203;  Os02;  Os03;  Os04;  and  Os05.  The  three  lowest  of  these  oxides  are 
analogous  in  composition  to  the  oxides  of  iridium. 

Chlorides  and  oxides  of  osmium. — When  osmium  is  heated  in  a  long  glass  tube 
by  a  spirit  lamp,  and  chlorine  gas  passed  over  it,  two  chlorides  are  formed,  which 
condense  separately  in  the  tube,  owing  to  a  difference  in  their  volatility.  The 
protochloride,  OsCl,  which  is  the  least  volatile,  crystallizes  in  needles  of  a  deep 
green  colour.  It  is  deliquescent,  and  forms  a  green  solution  remarkable  for  its 
beauty.  This  solution  is  instantly  discoloured  by  great  dilution,  metallic  osmium 
being  deposited,  and  hydrochloric  and  osmic  acids  remaining  in  solution.  Chloride 
of  osmium  combines  with  alkaline  chlorides,  and  acquires  greater  stability.  The 
protoxide,  OsO,  is  obtained  by  adding  potash  to  a  solution  of  protochloride  of 
osmium  and  potassium ;  after  some  hours,  a  deep  green,  almost  black,  powder  is 
precipitated,  which  is  the  hydrated  oxide.  This  hydrate  contains  alkali.  It  dis- 
solves slowly  but  completely  in  acids,  and  gives  solutions  of  a  deep  green  colour. 

tfesquioxide  of  osmium,  Os203,  is  not  known  in  the  separate  state ;  but  when  a 
mixture  of  osmic  acid  and  ammonia  is  kept  for  some  hours  at  a  temperature  of 
100°  to  120°,  nitrogen  gas  is  evolved,  and  a  black  substance  is  deposited,  contain- 
ing the  sesquioxide  in  combination  with  ammonia.  It  dissolves  slowly  in  acids, 
and  forms  yellowish  brown  solutions,  which  become  brown-black  when  they  con- 
tain much  oxide.  The  metal  is  not  precipitated  from  these  solutions  by  zinc  or 
iron.  The  corresponding  sesquichloride  of  osmium  is  obtained  in  combination 
with  chloride  of  potassium  as  a  double  salt,  when  the  preceding  oxide  containing 
ammonia  is  dissolved  in  hydrochloric  acid,  and  evaporated  to  dryness;  the  com- 
pound is  not  crystalline. 

Bichloride  of  osmium,  OsCl2,  is  the  more  volatile  chloride  produced  when 
osmium  is  heated  in  chlorine.  It  condenses  as  a  dark  red  floury  powder.  Ex- 
posed to  air,  it  attracts  a  little  moisture,  and  forms  dendritic  crystals.  It  is  solu- 
ble in  a  small  quantity  of  water,  giving  a  yellow  solution,  but  is  decomposed  by  a 
large  quantity,  like  the  protochloride.  The  bichloride  of  osmium  and  potassium 
is  prepared  in  the  same  manner  as  the  corresponding  salt  of  iridium.  In  powder, 


628  OSMIUM. 

it  is  of  a  red  colour  like  minium,  but  forms  also  the  usual  octohedral  crystals, 
KC1.0sCl2,  which  are  brown.  A  solution  of  this  double  salt,  mixed  with  carbo- 
nate of  potash  or  soda,  affords  after  a  time,  or  immediately,  if  heated,  the  corres- 
ponding bioxide  of  osmium  or  osmic  oxide,  Os02,  as  a  brown  powder,  which 
appears  black  when  collected.  This  oxide,  like  the  peroxide  of  iridium,  is  reduced 
by  hydrogen  at  ordinary  temperatures.  It  is  a  base  capable  of  uniting  with  acids 
at  the  moment  of  its  formation. 

Osmic  sulphate  is  obtained  by  treating  one  of  the  sulphides  of  osmium  with 
nitric  acid ;  when  dried  as  completely  as  possible,  it  forms  a  dark  yellowish  brown 
syrup,  which  dissolves  in  water.  The  reaction  of  osmic  salts  (e.  g.  of  the  bichlo- 
ride of  osmium  and  potassium)  in  solution,  are  as  follows : — Potash  forms  a  black 
precipitate,  slowly  in  the  cold,  immediately  on  boiling ;  ammonia,  a  brown  preci- 
pitate, after  some  time;  carbonate  of  potash,  the  same;  chloride  of  ammonium, 
a  red  precipitate;  protochloride  of  tin,  a  brown  precipitate;  mercurous  nitrate, 
yellowish  white;  nitrate  of  silver,  dark  olive-green;  hydrosulphuric  acid,  a 
yellowish  brown  precipitate  after  some  time ;  hydrosulphate  of  ammonia,  a  yel- 
Jpwish  brown  precipitate  insoluble  in  excess.  No  precipitate  is  formed  by  oxalic 
acid,  ferrocyanide  or  ferricyanide  of  potassium,  or  ferrous  sulphate.  Zinc  throws 
down  part  of  the  osmium  in  the  metallic  state.  Iodide  of  potassium  does  not 
form  any  precipitate,  but  imparts  a  deep  purple-red  colour,  which  does  not  dis- 
appear when  the  liquid  is  heated.  Tannic  acid  imparts  a  deep  blue  colour. 

Osmious  acid,  Os03.  —  This  acid  is  not  known  in  the  separate  state,  being  re- 
solved at  the  moment  of  separation  from  its  combinations,  into  osmic  acid  and 
osmic  oxide,  20s03  =  Os04  -f  Os02.  Osmite  of  potash,  K0.0s03  +  2HO,  is 
obtained  by  the  action  of  reducing  agents  on  the  osmiate ;  thus,  when  a  few  drops 
of  alcohol  are  added  to  a  solution  of  osmiate  of  potash,  the  osmite  is  precipitated 
in  the  form  of  a  rose-coloured  crystalline  powder,  a  strong  odour  of  aldehyde 
being  at  the  same  time  evolved,  due  to  the  oxidation  of  the  alcohol.  Osmite  of 
potash  may  be  obtained  in  octohedral  crystals  of  considerable  size,  by  mixing  a 
solution  of  osmiate  with  nitrite  of  potash,  and  leaving  the  mixture  to  evaporate 
slowly.  The  salt  is  likewise  obtained  by  dissolving  osmic  oxide  in  osmiate  of 
potash.  It  is  rose-coloured,  soluble  in  water,  insoluble  in  alcohol  and  ether,  per- 
manent in  dry  air,  but  changes  into  osmiate  under  the  influence  of  air  and  water. 
Chlorine  converts  it  into  osmic  oxide  and  osmiate  of  potash.  *  It  is  decomposed 
by  acids,  even  by  the  weakest,  osmic  oxide  being  precipitated  and  osmic  acid 
evolved.  Sulphurous  acid  introduced  into  a  solution  of  this  salt,  previously  ren- 
dered alkaline,  throws  down  a  yellow  crystalline  precipitate,  containing  a  salt  whose 
acid  is  formed  of  osmium,  oxygen,  and  sulphur.  Chloride  of  ammonium  decom- 
poses osmite  of  potash,  forming  a  nearly  insoluble  yellow  salt,  NH4C1.0S02NH2, 
which  may  be  regarded  as  a  compound  of  sal-ammoniac  with  osmiamide,  Os02NH2. 
This  compound,  heated  in  a  stream  of  hydrogen,  gives  off  ammonia  and  sal-am- 
moniac, and  leaves  metallic  osmium.  Osmite  of  soda  is  prepared  in  the  same 
manner  as  osmite  of  potash,  but  does  not  crystallize  so  easily;  its  solutions  are 
rose-coloured.  Osmious  acid  does  not  combine  with  ammonia;  the  osmites  of 
potash  and  soda  are  rapidly  reduced  by  ammonia. 

A  terchloride  of  osmium  has  been  obtained  in  combination  with  chloride  of  am- 
monium, as  a  double  salt,  when  osmic  acid  is  saturated  with  ammonia,  and  treated 
after  a  while  with  excess  of  hydrochloric  acid,  mercury  being  also  placed  in  con- 
tact with  it.  After  a  few  days,  the  liquid  loses  the  odour  of  osmic  acid,  and 
when  evaporated  to  dryness,  leaves  the  double  salt  in  brown  dendritic  crystals. 

Osmic  acid,  Os04,  or  the  volatile  oxide  of  osmium,  is  best  obtained  by  the 
combustion  of  osmium  in  a  glass  tube  through  which  a  stream  of  oxygen  gas  is 
passed ;  it  is  also  obtained  by  the  action  of  nitric  acid  on  osmium,  and  in  the  de- 
composition of  osmites  or  osmates  by  acids.  It  condenses  in  long,  colourless, 
regular  prismatic  needles.  The  odour  of  this  compound  is  extremely  acid  and 
penetrating,  resembling  that  of  the  chloride  of  sulphur.  It  was  from  this  pro- 


ESTIMATION    OF    OSMIUM.  629 

perty  of  its  acid,  which  is  so  constantly  observed  when  the  oxidable  compounds 
of  osmium  are  heated  in  air,  that  osmium  obtained  its  name  (from  6<j^o??  odour). 
Its  taste  is  acrid  and  burning,  but  not  acid.  It  becomes  soft  like  wax  by  the  heat 
of  the  hand,  melts  into  a  colourless  liquid  like  water,  considerably  below  212°, 
and  enters  into  ebullition  a  very  little  above  its  point  of  fusion.  It  is  dissolved 
slowly,  but  in  considerable  quantity,  by  water.  The  solution  has  no  acid  reaction. 
Osmic  acid  is  also  soluble  in  alcohol  and  ether,  but  these  solutions  are  apt  to 
deposit  metallic  osmium.  It  is  a  weak  acid,  being  incapable  of  displacing  carbonic 
acid  from  the  carbonates,  in  the  humid  way,  but  forms  a  class  of  salts,  the  os- 
miates.  Osmic  acid  is  expelled  by  heat  from  most  of  its  combinations  with  bases. 

An  acid  containing  more  oxygen  than  osmic  acid,  and  apparently  having  the 
formula  Os05,  is  formed  by  submitting  the  osmiates  to  the  action  of  oxygen  and 
oxidizing  agents.  It  is  very  unstable ;  its  potash  and  soda-salts  have  a  dark  brown 
colour,  and  sometimes  crystallize  in  the  alkaline  liquids.  If  the  formula  Os05  be 
correct,  the  oxidation-series  of  osmium  will  present  remarkable  analogies  with 
those  of  nitrogen,  phosphorus,  and  arsenic  (Fremy). 

Osmiamic  acid,  Os2N05.  —  Formed  by  the  action  of  ammonia  on  osmic  acid, 
20s04-|-NTIs.Os2N050-f3HO.  Its  potash-salt  is  obtained  by  adding  ammonia  to 
a  hot  solution  of  osmic  acid  in  excess  of  potash ;  the  deep  orange  colour  of  the 
liquid  soon  changes  to  light  yellow,  and  osmiamate  of  potash  separates  in  the  form 
of  a  yellow  crystalline  powder.  The  osmiamates  of  the  alkalies  and  alkaline 
earths  and  the  zinc-salt  are  soluble  in  water;  the  lead,  mercury,  and  silver-salts 
insoluble.  The  aqueous  acid  is  obtained  by  decomposing  the  baryta-salt  with  sul- 
phuric, or  the  silver-salt  with  hydrochloric  acid.  It  may  be  kept  for  some  days 
when  dilute,  but  soon  decomposes  in  the  concentrated  state.  It  is  a  powerful 
acid,  decomposing  not  only  the  carbonates,  but  even  chloride  of  potassium. 
Fritzsche  and  Struve,*  who  discovered  this  acid,  assign  to  it  the  formula  Os2N04, 
regarding  it  as  a  compound  of  nitride  of  osmium  with  osmic  acid;  OsN.Os04. 
Gerhardt,  on  the  contrary,f  assigns  to  it  the  formula  above  given,  viz.,  Os2N05, 
which  is  the  more  probable  of  the  two,  inasmuch  as,  if  Fritzsche  and  Struve's 
were  correct,  the  formation  of  the  acid  must  be  attended  with  the  evolution  of  1 
eq.  oxygen ;  but  they  particularly  observe  that  no  escape  of  gas  takes  place. 

Sulphides  of  osmium. — Osmium  has  a  great  affinity  for  sulphur,  and  burns  in 
its  vapour.  Five  sulphides  of  osmium  are  known,  corresponding  to  all  the  oxides 
except  the  highest,  viz.,  OsS,  Os2S3,  OsS2,  OsS3,  OsS4.  The  first  four  of  these 
sulphides  are  obtained  by  decomposing  the  corresponding  chlorides  with  hydro- 
sulphuric  acid.  The  tetrasulphide  is  prepared  by  passing  hydrosulphuric  acid  gas 
into  a  solution  of  osmic  acid  :  it  is  a  sulphur-acid,  completely  insoluble  in  water; 
whereas  the  others  are  sulphur  bases,  slightly  soluble  in  water,  and  forming  deep 
yellow  solutions. 

ESTIMATION   AND    SEPARATION   OF   OSMIUM. 

Osmium  is  generally  estimated  in  the  metallic  state.  The  best  mode  of  sepa- 
rating it  from  the  metals  with  which  it  is  usually  accompanied,  is  to  volatilize  it 
in  the  form  of  osmic  acid  —  by  distillation  with  aqua-regia,  if  the  compound  be 
perfectly  soluble  therein,  or  by  roasting  in  a  stream  of  oxygen  —  receiving  the 
vapours  of  osmic  acid  in  a  strong  solution  of  potash ;  and  to  reduce  this  salt,  by 
the  addition  of  a  few  drops  of  alcohol,  to  osmiate  of  potash,  which  is  insoluble  in 
the  alcoholic  liquor.  The  osmite  of  potash  is  then  digested  in  a  cold  solution  of 
sal-ammoniac,  whereby  the  compound  NH4C1 .  Os02NH2  is  produced,  and  the 
osmium  reduced  to  the  metallic  state  by  igniting  this  last-mentioned  compound  in 
a  current  of  hydrogen  gas  (Fremy). 

Another  mode  of  proceeding  is  to  condense  the  acid  vapours  evolved  by  dis- 
tilling a  compound  of  osmium  with  aqua-regia  in  a  well-cooled  receiver,  and  pre- 

*  J.  pr.  Chem.  xli.  97.  f  Compt.  rend,  de  Trans,  en  Chimie,  1847,  304 


630  RHODIUM. 

cipitate  the  osmium  from  the  solution  by  metallic  mercury.  A  precipitate  is 
thereby  obtained  consisting  of  calomel,  a  pulverulent  amalgam  of  osmium,  and 
metallic  mercury  containing  a  very  small  quantity  of  osmium.  This  mixture  is 
heated  in  a  glass  bulb,  through  which  a  stream  of  hydrogen  is  passed,  whereupon 
the  mercury  and  its  chloride  volatilize,  and  metallic  osmium  is  left  in  the  form  of 
a  black  powder.  The  liquid,  however,  still  retains  a  small  quantity  of  osmium, 
which  may  be  isolated  by  saturating  the  liquid  with  ammonia,  evaporating  to  dry- 
ness,  and  calcining  the  residue  (Berzelius).  The  osmium  may  also  be  precipitated 
from  the  distilled  liquid  by  hydrosulphuric  acid,  the  solution,  after  complete  satu- 
ration, being  left  for  several  days  in  a  stoppered  bottle,  till  the  sulphide  of  osmium 
is  completely  deposited.  The  sulphide  is  then  washed,  dried,  and  weighed ;  but 
as  it  is  apt  to  retain  moisture,  and,  moreover,  oxidizes  to  a  certain  extent  in  the 
air,  the  method  is  not  very  exact.  It  is  recommended,  however,  for  the  estimation 
of  small  quantities  of  osmium,  the  method  of  precipitating  by  mercury  being 
better  adapted  for  larger  quantities  (Berzelius). 


SECTION   V. 

RHODIUM. 

Eq.  52  or  651 4;  R. 

This  metal  was  discovered,  by  Wollaston,  in  the  ore  of  platinum  He  found 
the  ore  from  Brazil  to  contain  04  per  cent. ;  native  platinum  from  another  locality 
has  been  found  with  as  much  as  3  per  cent,  of  rhodium. 

After  the  precipitation  of  the  palladium  from  the  solution  of  native  platinum, 
by  cyanide  of  mercury,  the  solution,  in  order  to  obtain  the  rhodium,  may  be  mixed 
with  carbonate  of  soda  and  excess  of  hydrochloric  acid,  and  evaporated  to  dryness. 
The  cyanide  of  mercury  in  excess  is  decomposed  by  the  hydrochloric  acid,  and 
converted  into  chloride  of  mercury.  The  dried  mass  is  reduced  to  a  very  fine 
powder,  and  washed  with  alcohol  of  density  0-837,  which  takes  up  the  double 
chlorides  of  sodium  with  platinum  and  indium,  the  copper  and  the  mercury,  but 
leaves  the  double  chloride  of  rhodium  and  sodium  in  the  form  of  a  fine  deep  red 
powder.  The  rhodium  is  most  easily  reduced  by  gently  heating  the  double  chlo- 
ride in  a  stream  of  hydrogen  gas,  and  afterwards  washing  out  the  chloride  of 
sodium  by  water. 

Rhodium,  when  rendered  coherent,  is  a  white  metal  like  platinum ;  its  density 
is  about  10-6.  It  is  brittle  and  very  hard,  and  may  be  reduced  to  powder.  When 
pure,  it  is  not  dissolved  by  any  acid ;  but  when  alloyed  with  certain  metals,  such 
as  platinum,  copper,  bismuth,  or  lead,  and  exposed  to  aqua-regia,  it  dissolves  along 
with  those  metals.  When  fused  with  gold  or  silver,  however,  it  is  not  dissolved 
with  the  other  metal.  But  the  most  eligible  mode  of  rendering  rhodium  soluble, 
is  to  mix  it  in  fine  powder  with  chloride  of  potassium  or  sodium,  and  to  heat  the 
mixture  to  low  redness  in  a  stream  of  chlorine  gas.  A  double  chloride  is  then 
formed,  as  with  the  other  platinum  metals  in  similar  circumstances,  which  is  very 
soluble  in  water.  The  solutions  of  rhodium  have  a  beautiful  red  colour,  the  cir- 
cumstance from  which  the  metal  derives  its  name  (from  £66ov,  a  rose).  Rhodium 
may  also  be  rendered  soluble  in  the  dry  way,  by  fusing  it  with  bisulphate  of  potash, 
when  the  metal  is  oxidated  with  escape  of  sulphurous  acid  gas.  Rhodium  is  the 
most  oxidable  of  the  platinum  metals,  combining  with  oxygen  when  heated  to 
redness  in  an  open  vessel,  and  very  readily  when  in  fine  powder  and  heated  to  a 
3herry-red  heat.  It  appears  to  form  two  oxides,  the  rhodous  and  the  rhodic,  of 
which,  however,  the  last  only  has  been  completely  isolated. 

Oxides  of  rhodium. — The  protoxide  or  rliodous  oxide,  RO,  is  formed  when 
rhodium  is  ignited  in  contact  with  the  air.  One  hundred  parts  of  rhodium  thus 


SALTS    OF    RHODIUM.  631 

treated  quickly  increase  to  115-3  parts,  corresponding  to  the  protoxide;  then 
slowly,  if  the  ignition  be  continued,  to  118-07  parts ;  a  black  powder  being  formed, 
consisting  of  3RO.R203  (Berzelius). 

Rhodic  oxide,  R203,  is  produced  when  the  metal  is  ignited  with  hydrate  of 
potash  and  a  little  nitre,  in  a  silver  crucible.  The  metal  swells  up,  assumes  a 
coffee-brown  colour,  and  is  converted  into  a  compound  of  rhodic  oxide  and  potash, 
which  must  be  washed  with  water,  and  afterwards  digested  in  hydrochloric  acid ; 
the  hydrated  oxide  remains  of  a  grey  colour,  with  a  shade  of  green,  and  insoluble 
in  acids.  The  same  hydrated  oxide,  as  obtained  from  the  double  chloride  of  rho- 
dium and  potassium,  or  sodium,  by  precipitation  with  an  alkali  and  evaporation, 
dissolves  slowly  in  acids,  together  with  a  certain  quantity  of  alkali  which  is 
attached  to  it,  assuming  a  yellow  colour,  and  producing  double  salts.  The  solution 
in  hydrochloric  acid  is  also  pale,  although  it  contains  chloride  of  potassium,  while 
a  solution  of  the  double  chloride,  prepared  in  the  way  formerly  mentioned,  has  a 
fine  red  colour.  Hence  Berzelius  infers  that  there  are  two  isomeric  modifications 
of  this  oxide,  whose  compounds,  when  in  solution,  are  respectively  yellow  and 
rose-coloured.  Hydrated  rhodic  oxide  contains  one  atom  of  water,  R203.HO. 
Two  compounds  of  rhodic  oxide  with  the  protoxide  of  the  same  metal  appear  to 
exist:  R203.3RO,  and  R203.2RO.  The  known  compounds  of  rhodium  are  not 
isomorphous  with  compounds  of  platinum;  but  this  may  arise  from  these  two 
metals  affecting  combination  in  different  proportions,  so  that  their  compounds  are 
not  analagous  in  composition.  Their  association  and  resemblance  in  other  re- 
spects afford  a  strong  presumption  of  their  being  isomorphous  bodies. 

Solutions  of  rhodic  salts  yield,  with  tydrowlphuric  acid,  a  brown  precipitate  of 
protosulphide,  which  is  slowly  deposited ;  with  ht/drosulphate  of  ammonia  a 
brown  precipitate,  insoluble  in  excess;  with  sulphurous  acid  and  sulphites,  a  pale 
yellow  precipitate;  with  potash,,  a  yellow  precipitate  of  hydrated  rhodic  oxide, 
soluble  in  excess;  with  ammonia,  a  yellow  precipitate  of  rhodate  of  ammonia, 
which,  however,  does  not  form  immediately;  with  alkaline  carbonates,  a  yellow 
precipitate  after  a  while.  Iodide  of  potassium  produces  a  slight  yellow  precipitate ; 
protochloride  of  tin  imparts  a  dark  colour  to  the  solutions,  but  forms  no  precipi- 
tate. Acetate  of  lead,  mercurous  nitrate,  and  nitrate  of  silver  form  precipitates 
analogous  in  composition  to  the  iridium-salts  already  mentioned  (p.  625).  Zinc 
precipitates  metallic  rhodium.  In  a  solution  of  rhodium  mixed  with  excess  of 
potash,  alcohol  forms,  even  at  ordinary  temperatures,  a  black  precipitate,  probably 
consisting  of  metallic  rhodium  ;  with  the  other  platinum-metals,  this  reaction  takes 
place  only  when  the  liquid  is  heated.  No  precipitate  is  formed  by  phosphate  of 
soda,  sal-ammoniac,  chloride  of  potassium,  chromate  of  potash,  oxalic  acid,  cyanide 
of  potassium,  cyanide  of  mercury,  ferrocyanide  or  ferricyanide  of  potassium,  or 
gallic  acid.  Hydrogen  gas  reduces  the  anhydrous  salts  at  a  moderate  heat. 

Sulphide  of  rhodium.  —  Rhodium  maybe  united  with  sulphur  by  either  the 
dry  or  the  humid  way.  The  sulphide  of  rhodium  was  used  by  Wollaston  to  obtain 
the  metal  in  a  coherent  mass. 

Protochloride  of  rhodium,  RC1,  is  obtained  by  heating  the  protosulphate  (pre- 
cipitated from  rhodic  salts  by  hydrosulphuric  acid)  in  a  stream  of  chlorine;  or  by 
digesting  one  of  the  intermediate  oxides  with  hydrochloric  acid,  whereupon  the 
sesquichloride  dissolves,  and  the  protochloride  remains  in  the  form  of  a  reddish 
grey  powder,  insoluble  in  water. 

Sesquichloride  of  rhodium,  R2C13,  is  obtained  from  the  double  chloride  of 
rhodium  and  potassium,  by  precipitating  the  latter  metal  with  fluosilicic  acid. 
The  dry  salt  thus  obtained  is  brown  black,  and  not  crystalline;  it  requires  a  pretty 
high  temperature  to  decompose  it,  and  then  resolves  itself  at  once  into  chlorine 
and  rhodium.  This  salt  deliquesces  in  air;  its  solution  in  water  is  of  a  beautiful 
red  colour  (Berzelius).  Sesquichloride  of  rhodium  is  also  obtained  in  the  form 
of  a  rose-red  powder  by  heating  the  metal  to  low  redness  in  a  stream  of  chlorine 
(Glaus).  This  red  powder,  which  was  regarded  by  Berzelius  as  R,jCl3.2RCl;  is 


632  RHODIUM. 

elowly  decomposed  when  heated  in  hydrogen  gas,  is  insoluble  in  strong  hydro- 
chloric and  aqua-regia  even  at  the  boiling  heat,  is  coloured  yellow  by  continued 
boiling  with  potash,  and  if  afterwards  boiled  with  strong  hydrochloric  acid,  dis- 
solves in  small  quantity,  forming  a  rose-coloured  solution,  the  greater  part,  how- 
ever, remaining  unaltered. 

A  chloride  of  rhodium  and  potassium,  containing  2KC1.E2C13  +  2HO,  is 
obtained  by  the  action  of  chlorine  on  a  mixture  of  rhodium  and  chloride  of  potas- 
sium, or  by  evaporating  a  solution  of  the  sesquichloride  of  rhodium  and  sodium 
with  chloride  of  potassium.  It  forms  brown,  doubly  oblique  prisms,  which 
dissolve  sparingly  in  water.  Another  double  salt,  containing  3KCl.R2Cl3-f  6HO, 
is  obtained  in  dark  red,  sparingly  soluble,  efflorescent  prisms,  by  spontaneous 
evaporation  of  a  solution  of  the  hydrated  sesquioxide  in  hydrochloric  acid  mixed 
with  chloride  of  potassium.  The  sodium  double-salt,  3NaCl.R2Cl3-f  24HO,  forms 
doubly  oblique  prisms  of  a  deep  cherry-red  colour.  With  chloride  of  ammonium, 
two  double  salts  are  obtained,  viz.,  2NH4C1.R2C13  +  2HO,  and  3NH4C1.R2C13  -f 
3 HO,  both  of  which  form  red  prismatic  crystals.  By  precipitating  either  of  the 
above  double  chlorides  containing  2  or  3  eq.  of  the  basic  chloride  to  1  eq.  R2C13, 
with  acetate  of  lead,  mercurous  nitrate,  or  nitrate  of  silver,  rose-coloured  precipi- 
tates are  formed,  containing  2  or  3  eq.  of  PbCl,  Hg2Cl,  or  AgCl,  to  1  eq.  of 
R2C13  (Glaus). 

A  sulphate  of  rhodium  is  formed  when  rhodium  is  ignited  with  bisulphate  of 
potash  ;  it  gives  a  yellow  solution.  Another  sulphate  in  combination  with  sulphate 
of  potash  gradually  falls  as  a  white  powder,  when  sulphuric  acid  is  added  to  a 
solution  of  the  double  chloride  of  these  bases.  •  It  is  nearly  insoluble  in  water ;  its 
formula  is  KO.S03  +  203.3S03.  Nitrate  of  rhodium  is  formed  by  dissolving 
the  oxide  in  nitric  acid.  It  forms  a  deliquescent  salt  of  a  dark  red  colour, 
R203.  3N05;  the  last  salt  combines  with  nitrate  of  soda,  forming  dark  red  crystals 
soluble  in  water  but  not  in  alcohol :  NaO .  N05  -f-  R203 .  3N05. 

The  salts  of  rhodium  are  often  mixed  with  peculiar  rose-coloured  salts,  whose 
nature  is  not  exactly  known.  These  new  salts  are  not  precipitated,  either  by 
iodide  of  potassium  in  the  cold,  or  by  sulphurous  acid,  or  by  ammonia;  they 
form,  with  chloride  of  ammonium,  double  salts,  which  crystallize,  not  in  scales, 
but  in  red  prisms  (Frerny). 

ESTIMATION   AND    SEPARATION    OF   RHODIUM. 

Rhodium  is  estimated  in  the  metallic  stnte.  The  solution  containing  it  is 
mixed  with  excess  of  carbonate  of  soda  and  evaporated  to  dry  ness,  the  residue 
ignited,  and  the  calcined  mass  treated  with  cold  water :  oxide  of  rhodium  then 
remains,  and  may  be  reduced  by  hydrogen. 

Rhodium  is  separated  from  many  metals  with  which  it  may  be  alloyed,  by 
fusing  the  alloy  with  bisulphate  of  potash  ;  the  rhodium  is  thereby  converted  into 
sulphate  of  rhodium  and  potassium,  which  may  be  dissolved  out  by  water.  The 
method  of  separating  it  from  platinum  and  the  allied  metals  has  already  been 
given. 

The  separation  of  rhodium  from  other  metals  in  solution  is  somewhat  difficult, 
because  it  is  not  completely  precipitated  by  hydrosulphuric  acid.  To  separate 
rhodium  from  copper,  the  solution  is  saturated  with  hydrosulphuric  acid  and  left 
to  stand  in  a  stoppered  bottle  for  twelve  hours,  then  filtered,  and  the  filtrate 
heated  to  separate  an  additional  portion  of  sulphide  of  rhodium.  The  whole  of 
the  precipitate  is  then  roasted  in  a  platinum  crucible  till  the  sulphides  are  com- 
pletely oxidized,  and  the  product  treated  with  strong  hydrochloric  acid,  which 
dissolves  the  copper  and  leaves  the  oxide  of  rhodium.  The  liquid  filtered  from 
the  hydrosulphuric  acid  precipitate  still  contains  a  small  portion  of  rhodium,  which 
may  be  precipitated  by  carbonate  of  soda  and  converted  into  oxide  as  above.  The 
whole  of  the  oxide  is  then  reduced  by  hydrogen. 


RUTHENIUM.  633 

To  separate  rhodium  from  iron,  the  rhodium  is  precipitated  as  completely  as 
possible  by  hydrosulphuric  acid ;  the  liquid  filtered ;  and  the  iron  in  the  filtrate 
precipitated  by  ammonia,  after  having  been  brought  to  the  state  of  sesquioxide. 
The  iron-precipitate  carries  down  with  it  a  certain  portion  of  rhodium,  which  may 
be  separated  by  igniting  the  precipitate  in  a  current  of  hydrogen,  and  treating 
the  reduced  metals  with  hydrochloric  acid,  which  dissolves  the  iron  and  leaves  the 
rhodium  :  the  latter  is  then  converted  into  oxide  by  ignition  in  the  air.  The 
precipitated  sulphide  of  rhodium  is  likewise  oxidized  by  roasting.  The  small 
quantity  of  rhodium  which  remains  in  solution  after  precipitation  by  ammonia  is 
precipitated  by  carbonate  of  soda,  and  converted  into  oxide  by  ignition.  The 
whole  of  the  oxide  of  rhodium  is  then  reduced  to  the  metallic  state  by  hydrogen. 

The  separation  of  rhodium  from  the  alkali-metals  is  easily  effected  by  convert- 
ing the  metals  into  chlorides,  and  igniting  the  chlorides  in  a  current  of  hydrogen, 
which  reduces  only  the  chloride  of  rhodium. 


SECTION  VI. 

RUTHENIUM. 

Eq.  52-1  or  651-25;  Ru. 

This  metal  was  discovered  by  Claus  in  1846.  It  occurs  in  platinum  ores, 
chiefly  in  the  native  osmide  of  iridium,  which  contains  from  3  to  6  per  cent,  of  it. 
To  separate  it,  the  osmide  of  iridium  is  pulverized,  mixed  with  about  half  its 
weight  of  common  salt,  and  heated  to  low  redness  in  a  current  of  moist  chlorine 
gas.  The  disintegrated  mass  is  then  digested  in  cold  water,  and  the  concentrated 
solution,  which  is  brown-red  and  almost  opaque,  mixed  with  a  few  drops  of  am- 
monia and  gently  heated,  whereupon  it  deposits  a  copious  black-brown  precipitate, 
consisting  of  sesquioxide  of  ruthenium  and  bioxide  of  osmium.  This  precipitate, 
after  being  washed  with  nitric  acid,  is  heated  in  a  retort,  till  the  osmium  is  ex- 
pelled in  the  form  of  osmic  acid.  The  residue  is  then  ignited  for  an  hour  in  a 
silver  crucible  with  caustic  potash  free  from  silica,  and  the  ignited  mass  softened 
and  dissolved  by  cold  distilled  water.  The  solution  is  left  in  a  corked  bottle  for 
two  hours  to  clarify;  after  which  the  perfectly  transparent  orange-coloured  liquid 
is  separated  by  a  siphon,  and  neutralized  with  nitric  acid.  It  then  deposits  vel- 
vet-black sesquioxide  of  ruthenium,  which,  when  washed,  dried,  and  ignited  in  an 
atmosphere  of  hydrogen,  yields  the  pure  metal. 

Ruthenium  is  a  grey  metal,  very  much  like  iridium.  Its  specific  gravity  is 
8-6.*  It  is  very  brittle,  does  not  fuse  even  in  the  flame  of  the  oxy-hydrogen 
blowpipe,  and  is  scarcely  attacked  by  aqua-regia.  It  combines  with  oxygen  in  four 
proportions,  forming  the  three  oxides,  RuO,  Ru203,  Ru02,  and  ruthenic  acid,  Ru03. 
Its  affinity  for  oxygen  is  greater  than  that  of  any  of  the  other  platinum  metals, 
except  osmium.  When  heated  to  redness  in  the  air,  it  oxidizes  readily,  forming 
a  bluish  black  oxide,  which  does  not  part  with  its  oxygen  at  a  white  heat.  When 
fused  with  nitre  or  with  cautic  potash,  it  is  converted  into  rutheniate  of  potash. 
It  is  not  dissolved  by  fused  bisulphate  of  potash. 

Protoxide  of  ruthenium,  RuO. — Obtained  by  igniting  the  protochloride  with 
carbonate  of  soda,  in  a  stream  of  carbonic  acid  gas,  and  washing  the  residue  with 
water.  It  is  a  blackish  grey  powder,  containing  13  4  per  cent,  of  oxygen.  It  is 
insoluble  in  acids,  and  consequently  its  salts  have  not  been  directly  formed. 

*  This  is  much  less  than  the  density  usually  attributed  to  iridium  (p.  624).  It  is  probable, 
however,  that  the  two  metals  do  not  really  differ  much  in  density ;  for  a  specimen  of  porous 
iridium  prepared  from  the  blue  oxide,  by  reduction  with  hydrogen,  exhibited  a  density  of 
only  9-3  (Claus). 


634  RUTHENIUM. 

The  Protochloride,  RuCl,  is  obtained  in  the  anhydrous  state,  by  heating  the 
metal  to  low  redness  in  a  stream  of  chlorine.  It  is  a  black  crystalline  substance, 
insoluble  in  water  and  acids,  and  imperfectly  decomposed  by  alkalies.  A  soluble 
protochloride  appears,  however,  to  be  formed  by  passing  hydrosulphuric  acid  gas 
through  a  solution  of  the  sesquichloride. 

Srsquioxide  of  ruthenium,  Ru203. — Pulverulent  ruthenium,  strongly  heated 
before  a  powerful  blowpipe,  turns  black,  and  rapidly  absorbs  oxygen,  100  parts  of 
the  metal  increasing  to  118  parts ;  afterwards  the  oxidation  slowly  proceeds  fur- 
ther till  the  oxide  acquires  a  blackish  blue  colour,  and  contains  23  or  24  parts  of 
oxygen  to  100  parts  of  metal,  which  is  about  the  proportion  required  for  the  ses- 
quioxide.  The  hydrated  sesquioxide  is  formed  by  precipitating  a  solution  of  the 
sesquichloride  with  an  alkali,  by  decomposing  a  solution  of  rutheniate  of  potash 
with  nitric  acid,  or  by  heating  the  aqueous  solution  of  the  sesquichloride.  It  is  a 
black-brown  powder,  which  becomes  suddenly  incandescent  when  heated.  Hy- 
drogen gas  reduces  it  imperfectly  at  ordinary  temperatures.  It  is  insoluble  in 
alkalies,  but  dissolves  in  acids,  forming  orange-yellow  solutions.  The  solution  in 
hydrochloric  acid  exhibits  the  following  reactions  :  —  PJydrosulphuric  acid  partly 
precipitates  the  ruthenium  in  the  form  of  a  black  sulphide,  but  at  the  same  time 
reduces  the  sesquichloride  to  protochloride,  the  reduction  being  attended  with  a 
change  of  colour  from  orange-yellow  to  a  fine  azure  blue :  this  reaction  is  ex- 
tremely delicate,  and  very  characteristic  of  ruthenium.  Zinc  effects  the  same 
reduction.  Hydrosulphate  of  ammonia  throws  down  the  greater  part  of  the 
ruthenium  in  the  form  of  a  black-brown  sulphide,  not  perceptibly  soluble  in  excess. 
The  caustic  alkalies,  alkaline  carbonates,  and  phosphate  of  soda  precipitate  the 
black  sesquioxide,  insoluble  in  excess  of  the  reagent.  Borax  forms  no  precipitate 
at  first,  but,  on  heating  the  solution,  the  hydrated  sesquioxide  is  thrown  down.  Sul- 
phurous acid,  oxalic  acid,  and  formiate  of  soda  do  not  precipitate  the  metal,  but 
merely  decolourize  the  solution.  Ferrocyanide  of  potassium  decolourizes  the  solu- 
tion at  first,  but  afterwards  turns  it  bluish  green.  Acetate  of  lead  forms  a  pur- 
ple-red precipitate,  inclining  to  black.  Cyanide  of  mercury  colours  the  solution 
blue,  and  throws  down  a  blue  precipitate.  Nitrate  of  silver  forms  a  black  pre- 
cipitate, which  is  a  mixture  of  chloride  of  silver  and  sesquioxide  of  ruthenium  j 
the  oxide  dissolves,  after  a  while,  in  the  nitric  acid,  leaving  a  white  residue  of 
chloride  of  silver ;  and,  if  ammonia  be  then  added  in  excess,  the  chloride  of  silver 
dissolves,  and  the  sesquioxide  of  ruthenium  is  reprecipitated ;  this  is  also  a  very 
delicate  reaction.  The  chlorides  of  potassium  and  ammonium  throw  down  from 
concentrated  solutions,  crystalline  precipitates  of  double  chlorides,  exhibiting  a 
play  of  colours  inclining  to  violet. 

SesquichJori.de  of  ruthenium,  Ru2Cl3,  is  obtained  in  the  solid  state  by  evapo- 
rating the  solution  of  the  sesquioxide  in  hydrochloric  acid.  The  residue  is  deli- 
quescent, has  a  very  astringent  but  not  metallic  taste,  and  dissolves  in  water  and 
alcohol,  forming  beautiful  orange-coloured  solutions,  but  leaving  a  yellow  basic 
compound  undissolved.  When  heated,  it  turns  green  and  blue.  The  dilute  solu- 
tion is  resolved  by  heat  into  hydrochloric  acid  and  the  hydrated  sesquioxide  (p. 
634).  The  sesquichloride  forms  double  salts  with  the  chlorides  of  potassium  and 
ammonium,  and  apparently  also  with  those  of  sodium  and  barium. 

Bioxide  of  ruthenium,  Ruthenic  oxide,  Ru02,  is  formed  by  roasting  and  igniting 
the  bisulphide,  or  by  strongly  igniting  the  sulphate,  Ru02.2S03;  the  former 
method  yields  a  black-blue  powder,  with  a  tinge  of  green ;  the  latter,  grey  parti- 
cles, with  metallic  lustre  and  bluish  or  greenish  iridescence.  The  hydrate, 
Ru02.2HO,  is  obtained  as  a  gelatinous  precipitate  by  decomposing  the  bichloride 
of  ruthenium  and  potassium  with  carbonate  of  soda.  The  precipitate,  when  dried 
and  heated  in  a  platinum  spoon,  deflagrates  with  vivid  incandescence,  and  is  scat- 
tered about.  It  dissolves  in  acids,  forming  solutions  which  are  yellow  when  dilute, 
and  rose-coloured  when  concentrated. 

The  bichloride  is  not  known  in  the  separate  state,  but  forms  with  chloride  of 


TREATMENT    OF    PLATINUM-RESIDUES.  635 

potassium  a  double  salt,  KCl,IluC]2,  which  is  obtained  by  treating  the  sesqui- 
chloride  of  ruthenium  and  potassium  with  aqua-regia.  This  double  salt  is  very 
soluble  in  water,  but  insoluble  in  alcohol;  its  colour  is  brown,  inclining  to  rose-red. 
The  aqueous  solution  has  a  deep  rose-colour,  strongly  resembling  that  of  sesqui- 
chloride  of  rhodium.  Hydrosulphuric  acid  acts  but  slowly  on  this  solution,  pro- 
ducing first  a  milky  turbidity  from  precipitated  sulphur,  and  afterwards  throwing 
down  a  yellowish  brown  sulphide ;  the  solution,  however,  still  retains  a  deep  rose- 
colour  and  does  not  turn  blue. 

Ruthenic  sulphate,  Ru02.2S03 — When  the  sulphide  obtained  by  treating  the 
sesquichloride  with  hydrosulphuric  acid  is  digested  in  moderately  strong  nitric 
acid,  an  orange-yellow  solution  is  formed,  which,  on  evaporation,  yields  this  salt  in 
the  form  of  a  yellowish  brown  amorphous  mass.  It  is  deliquescent,  and  dissolves 
readily  in  water.  Alkalies  added  to  the  solution  form  no  precipitate  at  first ;  but, 
on  evaporating,  a  yellowish  brown  gelatinous  precipitate  is  obtained,  consisting  of 
hydrated  ruthenic  oxide,  and  strongly  resembling  impure  rhodic  oxide.  The 
solution  of  this  salt  does  not  turn  blue  when  treated  with  hydrosulphuric  acid. 

Rvthenic  acid,  Ru03,  is  known  only  in  the  form  of  a  potash-salt,  which  is  ob- 
tained by  igniting  ruthenium  with  a  mixture  of  potash,  and  nitrate  or  chlorate  of 
potash.  It  dissolves  in  water,  forming  an  orange-yellow  solution,  which  has  an 
astringent  taste,  colours  organic  substances  black  by  coating  them  with  oxide,  and 
is  decomposed  by  acids,  yielding  a  precipitate  of  the  sesquioxide. 

Sulphides  of  ruthenium.  —  This  metal  probably  forms  with  sulphur  a  series  of 
compounds  analogous  to  the  oxides ;  but  it  is  difficult  to  obtain  them  in  a  definite 
state.  Sulphur  and  ruthenium  do  not  combine  directly,  and  the  precipitates 
thrown  down  by  hydrosulphuric  acid  from  the  chlorides  always  contain  excess  of 
sulphur.  When  the  sulphide  obtained  by  precipitation  from  the  sesquichloride  is 
heated  in  an  atmosphere  of  carbonic  acid,  incandescence  and  explosion  take  place, 
sulphur  and  water  pass  off,  and  a  blackish  grey  metallic  powder  is  left,  whose 
analysis  agrees  with  the  formula  Ru2S3.  All  the  sulphides  are  dissolved  by  nitric 
acid  of  ordinary  strength  (Claus). 

ESTIMATION   AND    SEPARATION   OF  RUTHENIUM. 

This  metal  is  precipitated  from  its  solutions  in  the  form  of  oxide,  and  generally 
as  sesquioxide,  viz.  from  a  solution  of  the  sesquichloride,  either  by  alkalies  or  by 
simply  heating  the  solution,  and  from  a  solution  of  rutheniate  of  potash  by  nitric 
acid.  The  precipitated  oxide  is  reduced  to  the  metallic  state  by  ignition  in  an 
atmosphere  of  hydrogen.  As,  however,  the  precipitate  generally  contains  alkali, 
which  cannot  be  removed  by  washing,  the  reduced  mass  must  be  treated  with 
water;  the  liquid  filtered  from  the  ruthenium;  and  the  metal,  before  weighing, 
must  be  again  ignited  and  left  to  cool  in  an  atmosphere  of  hydrogen,  as  it  oxidizes 
when  heated  in  the  air.  Ruthenium  has  hitherto  been  found  only  associated  with 
the  metals  of  the  platinum-residues,  and  from  these  it  is  separated  by  the  method 
described  at  page  633,  depending  on  the  resolution  of  the  aqueous  sesquichloride 
by  heat  into  hydrochloric  acid  and  sesquioxide  of  ruthenium. 

NEW   METHOD   OP   TREATING   PLATINUM-RESIDUES.* 

When  platinum-ore  has  been  exhausted  by  aqua-regia,  a  residue  is  left,  com- 
monly  known  by  the  name  of  osmide  of  iridium.  This  residue  is  a  mixture  of 
two  different  substances,  one  of  which  is  scaly,  and  consists  of  osmium,  iridium, 
and  ruthenium ;  while  the  other,  which  is  granular,  contains  but  mere  traces  of 
osmium  and  ruthenium,  but  is  very  rich  in  iridium  and  rhodimm.  Now  oxide  of 
ruthenium  can  bear  a  red  heat  without  decomposing,  and  osmium  is  actually  * 

*  Fremy,  Compt.  rend,  xxxviii.  1008 ;  also  Traitg  de  Chimie  Generate,  par  Pelouze  et 
Fremy,  iii.  452. 


636  PLATINUM-RESIDUES. 

roasted  by  the  action  of  oxygen,  producing  a  volatile  acid,  just  as  sulphur  and 
arsenic  do ;  hence  the  residue  of  platinum-ore  may  be  decomposed  by  roasting ; 
and  by  submitting  it  to  this  operation,  osmic  acid  is  produced  in  large  quantity 
and  very  pure,  and  oxide  of  ruthenium  is  obtained  in  well-defined  crystals.  The 
roasting  is  performed  as  follows  : — 

About  200  grammes  of  platinum-residue  (the  scaly  and  granular  alloys  toge- 
ther) are  heated  to  bright  redness  in  a  porcelain  tube  placed  in  a  long  furnace. 
Air  is  drawn  through  the  tube  by  means  of  an  aspirator,  being  first  made  to  pass 
through  solution  of  potash  to  free  it  from  carbonic  acid,  and  through  strong  sul- 
phuric acid  to  remove  organic  matter.  The  air  thus  purified  passes  over  the 
heated  platinum-residue,  and  forms  osmic  acid  and  oxide  of  ruthenium.  The 
latter  crystallizes  in  the  colder  parts  of  the  roasting  tube,  while  the  more  volatile 
osmic  acid  is  carried  forward,  first  into  a  series  of  empty  tubes,  in  which  part  of 
it  settles  in  the  form  of  crystals,  and  then  through  two  bottles  filled  with  solution 
of  potash,  which  retains  the  uncondensed  vapours  :  the  apparatus  terminates  with 
an  aspirator.  The  products  of  the  operation  are :  —  1.  Oxide  of  ruthenium,  in 
violet  crystals,  the  form  of  which  is  similar  to  that  of  native  oxide  of  iron ;  2. 
Osmic  acid,  very  pure,  and  sometimes  amounting  to  40  per  cent,  of  the  platinum- 
residue  used;  3.  Osmiate  of  potash,  which,  by  the  addition  of  a  few  drops  of 
alcohol,  may  be  converted  into  osniite  of  potash,  a  salt  from  which  metallic  osmium 
may  be  obtained  (p.  628) ;  4.  An  alloy  of  iridium  and  rhodium,  which  remains 
in  the  roasting  tube. 

This  last  residue  may  be  used  for  the  preparation  of  iridium  and  rhodium. 
For  this  purpose,  it  is  calcined  in  an  earthen  crucible  with  four  times  its  weight 
of  nitre,  care  being  taken  not  to  carry  the  process  too  far;  and  the  residue  is  ex- 
hausted with  boiling  water  and  filtered.  A  copious  precipitate  is  thereby  formed, 
which  remains  on  the  filter,  and  the  filtrate  consists  of  an  alkaline  liquid,  which, 
when  left  to  evaporate,  deposits  crystals  of  osmite  of  potash,  the  osmium  never 
being  completely  removed  by  the  previous  roasting. 

The  precipitate  which  remains  on  the  filter  and  retains  a  considerable  quantity 
of  potash,  is  subjected  to  the  action  of  aqua-regia,  which  converts  the  iridium 
into  chloriridiate  of  potassium,  nearly  insoluble  in  cold  water:  the  action  of  the 
aqua-regia  must  be  continued  for  several  hours.  The  mass  is  then  treated  with 
boiling  water,  which  dissolves  the  chloriridiate  of  potassium,  the  washing  being 
continued  till  the  extract  no  longer  exhibits  a  brown  colour.  The  solutions  are 
then  evaporated,  and  the  chloriridiate  of  potassium  obtained  in  crystals. 

The  undissolved  portion,  which  contains  the  rhodium,  is  dried,  mixed  with  an 
equal  weight  of  chloride  of  sodium,  and  subjected  for  three  or  four  hours  to  the 
action  of  dry  chlorine  at  a  dull  red  heat.  Chlororhodiate  of  sodium  is  thereby 
formed,  and  may  be  obtained,  by  solution  in  water  and  evaporation,  in  beautiful 
rose-coloured  octohedral  crystals,  resembling  chrome  alum. 

Rhodium  is  likewise  obtained  in  another  stage  of  the  treatment  of  platinum- 
ore.  When  this  ore  is  treated  with  aqua-regia  a  certain  quantity  of  rhodium  is 
dissolved  together  with  the  platinum,  although  rhodium  by  itself  is  insoluble  in 
aqua-regia.  The  solution  is  evaporated  to  dryness,  the  residue  dissolved  in 
water,  and  the  solution  mixed  with  sal-ammoniac  to  precipitate  the  platinum.  The 
rhodium  then  remains  in  solution,  together  with  a  small  quantity  of  platinum,  to 
separate  which  a  plate  of  iron  is  immersed  in  the  liquid,  and  the  pulverulent 
mixture  of  platinum  and  rhodium  thereby  precipitated  is  digested  in  weak  aqua- 
regia,  which  dissolves  the  platinum  and  leaves  the  rhodium  nearly  pure.  From 
this  residue,  pure  well-defined  crystals  of  chlororhodiate  of  sodium  may  be  ob- 
tained in  the  manner  just  described  (Fremy). 


SUPPLEMENT. 


HEAT. 


EXPANSION   OF   SOLIDS. 


THE  following  determinations  of  the  amount  of  the  cubical  expansion  of  soli-Is 
for  each  degree  Centigrade,  at  temperatures  not  exceeding  100°  C.,  are  given  by 
H.  Kopp,*  the  volume  of  the  solid  at  0°  being  taken  equal  to  1 : — 

TABLE  I.  —  CUBICAL  EXPANSION  OF  SOLIDS. 


Substance. 

Formula. 

Cubical  Exp. 
for  1°  C. 

Substance. 

Formula. 

Cubical  Exp. 
for  1°  C. 

Copper      .  . 

Cu 

0-000051 

Arragonite  ... 

CaO.CO, 

0-000065 

Lead       ..    . 

Pb 

0-000089 

Calcspar  

CaO.C02 

0-000018 

Tin  

Sn 

0-000069 

f       CaO.COo       "1 

Iron  

Fe 

0-000037 

Bitterspar  .... 

1   +MeO.C09      J 

0-000035 

Zinc  

Zn 

0-000089 

/  Fe(Mn,Mg)0.  \ 

Cadmium  
Bismuth  
Antimony  .... 
Sulphur  
Galena      . 

Cd 
Bi 

Sb 

s 

PbS 

0-000094 
0-000040 
0-000033 
0-000183 
0-000068 

Iron-spar  

Heavy  spar  .. 
Coelestin  

Quartz  

I           C02          / 
BaO.S03 
SrO.S03 

Si03             { 

0-000035 

0-000058 
0-000061 
0-000042 
0-000039 

Zinc-blende  .. 
Iron  pyrites  . 
Rutile  ..  

ZnS 
FeS2 
Ti02 

0-000036 
0-000034 
0-000032 

Orthoclase  ... 
Soft     soda 

f      KO.SiOa       \ 
\  +Al203.3Si08  / 

0-000026 
0-000017 

Tin  stone  

Sn02 

0-000016 

0-000026 

Iron  -glance... 

Fe,0, 

0-000040 

Another  sort 

0-000024 

Magnetic  iron 
ore  

Fe«0 

0-000029 

Hard  potash 

fflass 

0-000021 

Fluor-spar  :.. 

CaF4 

0-000062 

The  mode  of  experimenting  consisted  in  taking  the  specific  gravity  of  the  solid 
substance  at  a  lower  and  at  a  higher  temperature,  by  ascertaining  the  quantity  of 
water  together  with  a  known  weight  of  the  solid  substance,  and  also  the  quantity 
of  water  alone,  which  filled  a  vessel  of  constant  capacity  at  the  different  tempera- 
tures. The  determinations  in  the  instances  of  iron  and  glass,  and  the  second  de- 
terminations of  quartz  and  orthoclase,  were  made  with  mercury  instead  of  water, 
and  calculated  in  a  similar  manner. 

Kopp  has  also  determined  the  expansion  of  some  other  solids,  especially  near 
the  melting  points. f  Most  bodies,  at  temperatures  near  their  melting  points, 


*  Ann.  Ch.  Phann.  Ixxxi.  1. 


f  Ann.  Ch.  Pharm.  xciii.  129. 
(637) 


638  EXPANSION    OF    LIQUIDS. 

exhibit  a  sudden  increase  in  the  rate  of  expansion.  The  increase  of  volume 
which  a  substance  exhibits  in  the  fused  state,  as  compared  with  the  same  sub- 
stance at  lower  temperatures,  arises,  partly  from  the  great  expansion  which  it 
undergoes  as  it  approaches  the  melting  point,  partly  from  the  sudden  expansion 
which  takes  place  in  fusing.  In  some  substances,  however,  only  one  of  these 
modes  of  expansion  is  at  all  considerable. 

PhospJioriis  (the  yellow  modification),  of  sp.  gr.  1-826  at  10°  C.  (50°  F.), 
expands  uniformly  up  to  its  melting  point  44°  C.  (111-2°  F.),  at  which  tempera- 
ture its  volume  is  1-017  of  the  volume  of  0°  C.;  but,  at  the  moment  of  fusion,  it 
exhibits  a  sudden  expansion  amounting  to  3-4  per  cent.,  so  that  its  liquid  volume 
at  44°  C.  is  1-052. 

Sulphur  (native  crystals,  sp.  gr.  2-069)  expands  irregularly  near  its  melting 
point  (115°  C.  or  239°  F.).  Its  volume  being  1  at  0°  C.,  is  1-010  at  50°  C. 
(122°  F.);  1-037  at  100°  C.;  1-096  at  115°  C. ;  at  the  moment  of  fusion,  the 
expansion  amounts  to  5  per  cent.,  the  volume  then  increasing  to  1-150. 

Wax  (bleached  beeswax,  sp.  gr.  0-976  at  10°  C.)  expands  very  rapidly  as  it 
approaches  its  melting  point  (64°  C.  or  147-2°  F.),  but  only  04  per  cent,  more 
at  the  moment  of  fusion.  If  the  volume  at  0°  C.  is  1,  the  volume  at  50°  C. 
(122°  F.),  is  1-068;  at  60°  C.  (14-0°  F.),  is  1-128;  at  64°  C.  (147-2°  F.),  is 
1.161,  and  increases  by  fusion  to  1-166. 

Water  expands  at  the  moment  of  freezing  by  about  10  per  cent.  1-1  volume 
of  ice  gives  1  volume  of  water  at  0°  C.,  which,  when  heated  to  4°  C.  (39-2°  F.), 
contracts  to  0-99988,  but  expands  progressively  at  higher  temperatures,  its  volume 
at  100°  being  1-043, 

Solid  hydrafed  sa-lt-x,  on  the  contrary,  expand  at  the  moment  of  fusion ;  e.  g. 
chloride  of  calcium  (CaCl-f  6HO),  by  9-6  per  cent. ;  ordinary  phosphate  of  soda 
(2NaO.HO.P05-f  24HO)  and  hyposulphite  of  soda  (NaOS2Oz-|-5HO),  each  by 
5-1  per  cent. 

Hose's  fusible  metal  (2  parts  bismuth,  1  part  tin,  and  1  part  lead,  sp.  gr 
8-906  at  10°  C.)  expands,  when  heated  from  0°  to  59°  C.  (32°  to  138-2°  F.),  in 
the  ratio  of  1  to  1-0027;  but  contracts  when  further  heated,  its  volume  at  82°  C. 
(179-6°  F.)  being  equal  to  that  at  0°  C.,  and  at  95°  C.  (203°  F.)  equal  to 
0-9947 ;  in  fusing,  between  95°  and  98°  C.,  it  expands  by  1-55  per  cent.,  so  that 
at  98°  C.  (208-4°  F.)  its  volume  is  equal  to  1-0101.  This  alloy,  therefore, 
contracts  from  59°  C.  up  to  its  melting  point. 


EXPANSION   OF   LIQUIDS. 

M.  Pierre's  researches  on  this  subject  have  been  continued.*  The  expansions 
of  a  great  number  of  liquids  have  also  been  determined  by  H.  Kopp.f 

Pierre  concludes  from  his  experiments  that  isomeric  liquids  in  general  do  not 
contract  equally  at  an  equal  number  of  degrees  below  their  respective  boiling 
points;  an  exception  is,  however,  presented  by  acetate  of  methyl  (CgH30.C4HsOa) 
and  formiate  of  ethyl  (C4H6O.C2H03),  in  which  the  contraction  for  equal  intervals 
below  the  boiling-points  appears  to  be  equal. J 

Table  II.  exhibits  the  contractions  of  several  groups  of  isomeric  liquids,  at 
D°  centigrade  below  the  boiling  point,  as  determined  by  Pierre  and  by  Kopp. 

*  Annales  de  Chimie  et  de  Physique,  [3],  xxi.  118,  xxxiii.  119. 

fPogg.  Ann.  Ixxii.  1  and  223;  and  Ann.  Ch.  Pharm.  xciii.  157;  xciv.  257;  xcv.  307; 
xcviii.  367. 

J  The  contrary  statement  originally  made  by  Pierre,  and  quoted  at  p.  37,  of  this  work, 
was  founded  on  an  error  of  calculation. 


EXPANSION    OF    LIQUIDS. 
TABLE  II. — EXPANSION  OF  LIQUIDS. 


639 


D. 

Aldehyde, 
C4*40a. 

Butyric  Acid, 
C«H804. 

Acetate  of  Ethyl, 
CeH«04. 

D. 

0 
10 
25 
45 
60 
75 
110 

Pierre 
(B.  P.  22°). 

Kopp 
(20-8°). 

Pierre 
(163P). 

$ft 

Pierre 
(74-1°). 

Kopp 

(74-3°). 

0 
10 
25 
45 
60 
75 
110 

10000 

9817 
9567 
9284 
9094 

10000 
9830 
9596 

10000 
9872 
9688 
9453 
9288 
9128 
8781 

10000 
9867 
9677 
9439 
9271 
9112 
8765 

10000 
9846 
9629 
9359 
9172 
8996 
8633 

10000 
9843 
9622 
9352 
9165 
8988 

D. 

Chloride  of 
Ethylene, 

C4H4C12. 

Pierre 
(84  9°). 

Mono- 
chlorinated 
Chloride  of 
Ethyl, 
C4H4C12. 
Pierre 
(64-8°). 

Mono- 
chlorinated 
Chloride  of 
Etbylene, 
C4H3C13. 
Pierre 
(114-2°). 

Bichlori- 

nated 
Chloride  of 
Ethyl, 
C4H3C]3. 
Pierre 
(74-9°). 

Formiate  of 
Ethyl, 
C6H604. 

Acetate  of 
Methyl, 
CeH804. 

D. 

Pierre       Kopp 
(52-9°).      (54-9°). 

Pierre 

(59-5°). 

Kopp 
(56-3°). 

0 
25 
55 

80 

10000 
9677 
9331 
9068 

10000 
9669 
9300 
9003 

10000 
9693 
9350 
9090 

10000 
9648 
9267 

8988 

10000     10000 
9632       9631 
9241       9243 
8953     

10000 
9633 
9243 
8955 

10000 
9631 
9243 

0 
25 
55   . 

80 

Expansion  of  water. — Table  III.  contains  the  results  obtained  by  Kopp,*  and 
also  those  of  Pierre  as  calculated  by  Frankenheim,f  with  regard  to  the  expansion 
of  water  between  0°  and  100°  C.,  the  volume  at  zero  being  taken  as  the  unit. 


TABLE  III.  —  EXPANSION  OP  WATER. 


Temp. 

Volume. 

Temp. 

Volume. 

Kopp. 

Pierre. 

Kopp. 

Pierre. 

150C. 

1-003758* 

TOO 

1  '001370 

]Q 

1-001658 

L  t7 

on 

1   UUl  O  /  \) 

i  .nni  cc7 

1.OO1  f^QA 

5 

1  -000582 

43U 

01 

J.  UUlOOi 
1  -001  77fi 

•UU10»4: 

0 

1-000000 

1-000000 

Zll 

22 

J.  U  \J  1  /  i  D 

1-001995 

1 

0-999947 

23 

1-002225 

2 

0-999908 

24 

1-002465 

3 

0-999885 

i 

25 

1-002715 

1-002708 

4 

'  0-999877 

30 

1  -004064 

1-004071 

5 

0-999883 

0-999890 

35 

1-005697 

1-005677 

6 

0-999903 

40 

1-007531 

1-007512 

7 

0-999938 

45 

1-009541 

1-009563 

8 

0-999986 

50 

1-011766 

1-011815 

9 
10 

1-000048 
1.000124 

1-000148 

55 
60 

1-014100 
1-016590 

1-014360 
1-017118 

11 
12 

1-000213 
1-000314 

65 
70 

1-019302 
1-022246 

1-019947 
•022938 

13 

1-000429 

75 

1-025440 

!  -026078 

14 

1  -000556 

80 

1-028581 

•029360 

15 

1-000695 

1-000728 

85 

1-031894 

•032769 

16 

1-000846 

90 

1-035397 

•036294 

17 
L18 

1-001010 
1-001184 

95 
100 

1-039094 
1-042986 

1-039925 
1  -043649 

*  Pogg.  Ann.  Ixxii.  223. 


f  Pogg.  Ann.  Ixxxvi.  451. 


640 


SPECIFIC     HEAT. 


The  maximum  density  Frankenheim  finds,  from  the  same  data,  to  exist  at  the 
temperature  of  3-86°  C.  or  38-95°  F. ;  Playfair  and  Joule*  fix  the  point  of 
maximum  density  at  3-945°  C.  or  39-1°  F. ;  PJiicker  and  Gessler,t  at  3-8°  C. 
or  38  8°  F. 

Absolute  expansion  of  mercury.  —  From  numerous  measurements  of  the  pres- 
sures exerted  by  columns  of  mercury  of  equal  height,  but  different  temperatures, 
Regnault  J  finds  that  if  the  volume  of  mercury  at  0°  C.  be  =  1,  the  volume  at  t° 
of  the  air-thermometer  is  given  by  the  formula  — 


1  +  0-000179007  t  +  0-0000000252316 


Hence,  the  values  in 


TABLE  IV. — EXPANSION  or  MERCURY. 


Temp. 

Volume. 

Temp. 

Volume. 

50° 

1-009013 

250° 

1-046329 

100 

1-018153 

300 

1-055973 

150 

1-027419 

350 

1-066743 

200 

1-036811 

Militzer  has  also  determined  the  absolute  expansion  of  mercury  by  similar 
means,  but  only  at  ordinary  temperatures,  the  temperature  of  the  colder  column 
of.  mercury  ranging,  in  his  experiments,  between  2°  and  4°  C.,  and  that  of  the 
warmer  column  between  19°  and  23°.  The  mean  coefficient  of  expansion  for  1°, 
deduced  from  these  experiments,  is  0-00017405  ±  0-00000082. §  The  experi- 
ment* of  Dulong  and  Petit  (37,  38,)  give  for  1D  the  coefficient  0-00018018. 


SPECIFIC   HEAT. 


The  specific  heat  of  most  bodies  is  greater  in  the  liquid  than  in  the  solid  state. 
The  following  determinations  are  by  Regnault :  — 


TABLE  V.  —  SPECIFIC  HEAT. 


Solid. 

• 

Liquid. 

Substance. 

Temperature. 

Sp.  Heat. 

Temperature. 

Sp.  Heat. 

Lead  

0°  to      1  00°  C 

0-0314 

350°    to      450°  C 

0-0402 

Bromine  

—  78              —  20 

0  08432 

10      "         48 

0-1109 

0             100 

0-05412 

0-10822 

—78           —  40 

0-0247 

0      "       100 

0-0333 

Sulphur  

0             100 

0-2026 

120      "       150 

0-234 

Bismuth  

0             100 

0-03084 

280      "       380 

0-0363 

0             100 

00956 

Tin  

0             100 

0-0562 

250      "       350 

00637 

Phosphorus  

10               30 

0-1887 

50      "       100 

0-2120 

Amorphous  
Water  

15               98 

below    0 

0-1700 
0-502 

0      "        20 

1-0000 

Crystallized   chloride 

below    0 

0-345 

83      "         80 

0-555 

Nitrate  of  soda  
Nitrate  of  potash  

0    to      100 
0     «       100 

0-27821 
0-23875 

320      "      430 
350      «       435 

0413 
0-3319 

*  Phil.  Mag.  i[3],  xxx.  41.  f  Pogg.  Ann.  Ixxxv.  238. 

J  "  Relations  des  Experiences  entreprises,  pour  determiner  les  principales  lois  physiques 
et  les  donn^es  nunieViques  qui  entrent  dans  le  calcul  des  machines  a  vapeur."     Paris,  1847. 
g  Pogg.  Ann.  Ixxx.  55. 


SPECIFIC    HEAT. 


641 


Table  VI.  exhibits  the  specific  heats  of  several  liquids  as  determined  by  H. 
Kopp,*  and  by  Favre  and  Silbermann.f  The  second  column  shows  the  intervals 
of  temperature  in  Kopp's  determinations.  Those  of  Favre  and  Silbermann  wero 
made  by  cooling  the  liquids  in  a  mercurial  calorimeter  of  peculiar  construction, 
from  their  several  boiling  points  to  temperatures  nearly  equal  to  that  of  the  sur- 
rounding atmosphere. 

TABLE  VI. — SPECIFIC  HEAT. 


Liquids. 

Temperature. 

Sp.  Heat. 

Observers. 

44°    to    24°  C. 

0-0332 

Kopp. 

0-10822 

F.  S. 

45     «     11 

0-107 

Andrews. 

46     "     21 

0-343 

Kopp. 

43     "    23 

0-645 

Kopp. 

43     "    23 

0-6713 
0-615 

F.  S. 

Kopp. 

44     "    26 

0-6438 
0-564 

F.  S. 
Kopp. 

Ethnl                    

0-5873 
0-5059 

F.  S. 

Ether    

0-50342 

« 

Formic  acid          

45     "    24 

0-536 

Kopp. 

Acetic  acid  

45     "    24 

0-509 

4£     "    21 

0-503 

39     "     20 

0-513 

41     "    21 

0-507 

45     "    21 

0-496 

Butyrate  of  methyl     .       .    .        . 

45     "    21 

0-48344 

0-487 

F.  S. 
Kopp. 

Valerate  of  methyl                  ... 

45     "     21 

0-49176 
0-491 

F.SP 

Kopp. 

Acetone  

41     "     20 

0-530 

ii 

Benzole  

46     "     19 

0-450 

ii 

Oil  of  mustard  

48     "     28 

0432 

11 

0-46727 

F.  S. 

The  specific  heat  of  water  at  different  temperatures  has  been  determined  by 
Regnault,  J  from  whose  experiments  it  appears  that  the  quantity  of  heat  expressed 
in  heat-units^  which  one  gramme  of  water  loses  in  cooling  down  from  t°  to  0°  C. 
is  given  by  the  formula  — 

Q  =  t  +  0-00002  t*  -f  0  0000003  f1; 

and  the  specific  heat  C.  at  the  temperature  £°,  that  is  to  say,  the  quantity  of  heat 
required  to  raise  one  gramme  of  water  from  t°  to  (t  + 1°),  is  — 

C  =  1+0-00004  t  +  0-0000009  **. 

From  this  formula,  the  following  numbers  are  obtained :  — 
TABLE  VII. — SPECIFIC  HEAT. 


t. 

Q. 

C. 

t. 

Q. 

C. 

0° 

0-000 

1-0000 

150° 

151-462 

1-0262 

50 

60-087 

1-0042 

200 

203-200 

1-0440 

100 

100-500 

1-0130 

230 

234-708 

0-0568 

r*  Pog£.  Ann.  Ixxv.  98 
I  '•  Relations,"  &c.  (see  note,  p.  640),  729. 
41 


f  Comptes  Rendus,  xxiiL  &24. 
\  See  page  654. 


642 


SPECIFIC    HEAT. 


Specific  lieat  of  gases  and  vapours.  —  On  this  subject  numerous  experiments 
have  been  made  by  Regnault,*  who  finds,  contrary  to  the  statement  of  Delaroche 
and  Berard,  that  the  specific  heat  of  a  gas  does  not  vary,  either  with  its  density 
or  with  its  temperature.  The  specific  heat  of  atmospheric  air,  referred  to  water 
as  unity  is  found  to  be  0-2377  between  —  30°  and-f  10°  0. ;  it  is  0-2379  between 
10°  and  100°;  and  0-2376  between  100°  and  225°. 

Table  VIII.  contains  Reg-nault's  determinations  of  the  specific  heats  of  a  con- 
siderable number  of  gases ;  in  column  A,  as  referred  to  equal  weights  (water  =  1) ; 
in  column  B,  as  referred  to  equal  volumes. 

TABLE  VIII.  —  SPECIFIC  HEAT  OF  GASES  (REGNAULT). 


A. 

B- 

A. 

B. 

1 

0-2182 

0-2412  ! 

Ether  

0-4810 

1 
1-2296 

Nitrogen                   

0-2440 

0-2370  ! 

Chloride  of  ethvl 

0-2737 

0-6117 

3-4046 

0-2356  i 

Bromide  of  ethyl  

0-1816 

0-6717 

0-1214 

0-2967  l 

Sulphide  of  ethyl  

0-4005 

1-2568 

Bromine  

0-0552 

0-2992 

Cyanide  of  ethyl  

0-4255 

0-8293 

Nitrous  oxide  

0-2238 

0-3413  ! 

0-1568 

0-8310 

Nitric  oxide  

0-2315 

0-2406  i 

Chloride  of  ethylene  

0-2293 

0-7911 

Carbonic  oxide 

0  2479 

0-2399 

Acetate  of  ethyl  

0-4008 

1-2184 

Carbonic  acid      .           . 

5  2164 

0-3308 

Acetone    

0-4125 

0-8341 

Sulphide  of  carbon       .... 

0-1575 

0-4146 

Benzole    

0-3754 

1-0114 

Sulphurous  acid  

0-1553 

0-3489 

0-5061 

2-3776 

Hydrochloric  acid  

0-1845 

0-2302 

Terchloride    of    phospho- 

0-2423 

0-°886 

rus                        ,     , 

0-1346 

0-6386 

0-5080 

0-2994 

Chloride  of  arsenic  

0-1122 

0-7013 

0-5929 

0-3277 

Chloride  of  silicon  

0-1329 

0-7788 

•Olefiant  gas     

0-3694 

0  3572 

0-0939 

0-8639 

Water-vapour     

0-4750 

0-2950 

Bichloride  of  titanium  ... 

0-1263 

0-8634 

Alcohol-vapour  

0-4513 

0-7171 

LIQUEFACTION. 


The  melting  point  of  a  body  appears  to  be  influenced  to  a  minute  but  certain 
amount,  by  the  pressure  to  which  it  is  subjected.  W.  Thomson, f  by  enclosing 
transparent  pieces  of  ice  and  water  in  an  Oersted's  water-compressing  apparatus, 
found  that  the  melting  point  of  the  ice  was  lowered  0-059°  u.  by  a  pressure  of 
8-1  atmospheres,  and  0*129°  by  a  pressure  of  16-8  atmospheres.  Bunsen  J  has 
obtained  similar  results  with  spermaceti  and  paraffin. 


SPERMACETI. 


PARAFFIN. 


Pressure  in 
Atmospheres. 
1   

Solidifying 
Point. 

...  47-7°  C. 

29  

...  48-3 

96    

...  49-7 

141  

...  505 

156  .. 

.  50-9 

Pressure  in 
Atmospheres. 

1    

85  

100  . 


Solidifying 
Point. 

46-3°  C. 

48-9 

49-9 


Such  results  are  in  conformity  with  the  deductions  by  J.  Thomson  §  from  the 
mechanical  theory  of  heat. 

The  latent  heat  of  water  was  found  by  Regnault,  and  by  Provostaye  and 
Desains,  to  be- 79°  C.  or  142°  R  According  to  Person,  this  number  denotes  the 


*  Compt.  Rend,  xxxvi.  676. 
J  Pogg.  Ann.  Ixxxi.  562. 


fPhil.  Mag.  [3],  xxxvii.  123. 
{  Edin.  Phil.  Trans,  vol.  xvi. 


LATENT    HEAT    OF    VAPOURS. 


643 


quantity  of  heat  required  to  convert  ice  at  0°  C.  into  water,  but  not  the  total 
quantity  of  the  latent  heat  in  the  water,  inasmuch  as  a  certain  additional  portion 
of  heat  is  rendered  latent  as  the  temperature  of  the  ice  rises  from  — 2°  to  0°.* 
In  six  experiments  on  the  fusion  of  ice  previously  cooled  to  temperatures  between 
—  2°  and  — 21°,  the  latent  heat  was  found  to  vary  between  79-9  and  80-1,  the 
mean  quantity  being  80°  C.,  or  144°  Fah.  Regnault  also  found  greater  values 
for  the  latent  heat  of  water  in  proportion  as  the  ice  used  in  the  experiments  had 
been  cooled  to  a  lower  temperature.  According  to  Hess,  the  true  latent  heat  of 
water  is  80-34°  C.  =  144-6  Fah.  For  the  specific  heat  of  ice,  Hess  finds  the 
number  0-533 ;  Person  finds  0-48  for  the  temperatures  between  — 21°  and  — 2°, 
the  specific  heat  of  water  being  1. 

Table  IX.  contains  the  latent  heats  of  fusion,  and  the  melting  points  of  various 
solids,  as  determined  by  Person. •(* 

TABLE  IX. — LATENT  HEAT  OP  FUSION. 


Substances. 

Melting  point. 

Latent  Heat. 

Tin    

235°  C 

14-3 

270 

12-4 

332 

5-15 

Alloy,  Pb2,  Sn2,  B3«,  

96 

5-96 

Alloy,  Pb  Sn2  Bi  

145 

7-63 

44-2 

4-71 

115 

9-175 

Nitrate  of  Soda  

310-5 

62-98 

Nitrate  of  Potash   

339 

46-18 

A  mixture  of  1  eq.  Nitrate  of  Soda  and  1  eq.  Nitrate 
of  Potash  

219-8 

51-4 

Phosphate  of  Soda,  2NaO,  HO,  P06  -f  24HO  

36-4 

66-80 

Chloride  of  Calcium,  CaCl,  6HO  

28-5 

40-70 

62  0 

43-51 

Zinc  

423-0 

27-46             : 

LATENT   HEAT   OF  VAPOURS. 

Water.  —  It  is  stated  at  p.  70,  of  this  work,  that  the  sum  of  the  latent 
and  sensible  heats  of  steam  is  the  same  at  all  temperatures.  This  is  commonly 
known  as  Watt's  law.  Southern,  on  the  other  hand,  maintained  that  the  latent 
heat  alone  is  constant  at  all  temperatures.  But  the  late  elaborate  researches  of 
RegnaultJ  have  shown  that  both  these  statements  are  incorrect,  and  that  the  total 
quantity  of  heat  (expressed  in  heat-units§),  which  a  unit  of  weight  of  saturated 
aqueous  vapour  contains  at  the  temperature  t°  centigrade,  exceeds  the  amount 
contained  in  the  same  weight  of  water  at  0°,  by  the  quantity 

x  ==  606-5  +  0-305  /. 

If  from  this,  we  subtract  the  quantity  of  heat  which  a  unit  of  weight  of  water  at 
t°  contains,  beyond  that  which  is  contained  in  the  same  weight  of  water  at  0° 
(see  Regnault's  determinations  of  the  specific  heat  of  water  at  different  tempera- 


xxx.  73. 

;  Ann.  Ch.  Phys.  [3],  xxvii,  250. 


*  Ann.  Ch.  Phys. 

t  P°gg-  Ann.  Ixx. 

j  "Relations  des  Experiences,"  &c.  (see^Note,  p  640),  271;  also  "Works  of  Cavendish 
Society,"  i.  294. 

g  A  unit  of  heat  is  the  quantity  required  to  raise  the  temperature  of  a  unit  of  weight 
(1  gramme,  1  pound,  &c.)  of  water  at  0°,  by  1°  Centigrade. 


644 


LATENT    HEAT    OF    VAPOURS. 


tures,  p.  641),  we  shall  obtain  the  latent  heat  L  of  the  vapour  of  water  at  the  tem- 
perature t°.  The  values  of  ?i  and  L  for  various  temperatures  are  given  in  Table  X., 
together  with  the  tensions  expressed  in  millimetres  and  in  atmospheres. 

TABLE  X.  —  LATENT  HEAT  OF  STEAM. 


Temperature. 

Tension. 

A 

L. 

nun. 

atm. 

o°c. 

4-60 

0-006 

606-5 

606-5 

60 

91-98 

0-121 

621-7 

571-6 

100 

760-00 

1-000 

637-0 

536-5 

150 

3581-23 

4-712 

652-2 

500-7 

200 

11688-96 

15-380 

667-5 

464-3 

230 

20926-40 

27-535 

676-6 

441-9 

The  latent  heats  of  the  vapours  of  several  other  liquids  at  their  boiling  points 
have  been  determined  by  Andrews,*  and  by  Favre  and  Silbermann.f  The  results 
are  given  in  — 

TABLE  XI. —  LATENT  HEAT  OF  VAPOURS. 


Substances. 

Boiling  point. 

Latent  Heat  of 
Vapour. 

Obseryers. 

Water  *  

100°    at  760  mm. 

535-9 

Andrews. 

<« 

100 

636 

F   and  S 

Iodine    

23-95 

« 

58      "     760 

45-60 

A. 

94-56 

F.  and  8. 

Terchloride  of  phosphorus... 
Bichloride  of  tin  

78-5    «     767 
112-5    '     752 

51-42 
3-053 

A. 

a 

Bisulphide  of  cftrbon  

46-2    «     769 

86-67 

« 

77-9    <     760 

202-40 

« 

« 

78-4    « 

208-92 

F.  S. 

Wood-spirit  

65-8    '     767 

263-70 

A 

(t 

66-5 

263-86 

F.  S. 

Fusel-oil   

132 

121-37 

« 

Ether  

35-6 

91-11 

« 

34-9   "     752 

90-45 

A. 

113 

69-40 

F.  S. 

120 

101-91 

« 

Formic  acid  

100 

120-72 

« 

Valerianic  acid    

175 

103-52 

« 

16-4 

114-67 

F.  S 

74 

105-80 

« 

«              « 

74-6         762 

92-68 

A. 

55            762 

110-20 

« 

54-3         762 

105-30 

« 

32-9         752 

117-10 

u 

Iodide  of  ethyl    

71-3         760 

46-87 

ti 

Iodide  of  methyl  

42-2         752 

46-07 

tc 

Oxalate  of  ethyl  

184-4         779 

,72-72 

« 

Butyrate  of  methyl    .  ..  . 

93  -O2        779 

87-33 

F.  S. 

Ethal... 

360-02 

58-48 

« 

156 

68-73 

ti 

Terebene    

156 

67-21 

« 

Oil  of  lemons  

165 

70-02 

« 

Hydrocarbons  — 
(a]  C,»  H,a 

198 

69-9 

Ci 

WCfcH,,  

255 

59-7 

a 

*  Chem.  Soc.  Qu.  J.  i.  27. 


f  Ann.  Ch.  Phys.  [3],  xxxvii.  461. 


TENSION    OF    VAPOURS.  645 


TENSION   OF  VAPOURS. 

Regnault*  has  made  a  vast  number  of  observations  on  the  tension  of  aqueous 
vapour  in  vacuo,  between  the  temperatures  of  —  32°  and  -I-  147-5°  C.,  and  given 
formulae  of  interpolation  for  calculating  the  tension  at  any  given  temperature 
between  those  limits. 

For  temperatures  between  0°  and  100°  the  interpolation  formula  is  — 

log.  e  s=  a  -f  bo?  -f-  cj3'; 

in  which  t  denotes  the  temperature,  e  the  tension,  and  a,  b,  c,  a,  j3  are  constants 
whose  values  are  determined  by  five  equations  of  condition,  obtained  by  substitu- 
ting in  the  preceding  equation  the  corresponding  observed  values  of  t  and  e  for  the 
temperatures  0°,  25°,  50°,  75°,  and  100°.  (See  Table,  p.  74).  The  values 
thus  obtained  are  — 

log.  a  =  0-006865036  log.  c  =  0-6116485 

log.  3  =  1-9967249  a  =  +  4-7384380. 

log.  b  =  2-1340339 

For  temperatures  below  0°,  Regnault  adopts  the  formula  — 

e  =  a  +  feax; 
in  which  — 

x  =  t  —  32  ;  log.  b  =  1-4724984  j  log.  a  =  0-0371566  ; 
a  =  +  0-131765. 

For  temperatures  above  100°  C.  the  interpolation  formula  is  — 

log.  e  =  a  —  ia*;  x  =  £—100°; 
in  which  — 

log.  a  =  1-9977641;  log.  b  =  0-4692291 
a  =  +  5-8267890. 

It  has  not  yet  been  found  possible  to  include  the  whole  series  of  observations  in 
one  formula  of  interpolation. 

From  the  first  and  second  of  these  formulae,  the  following  table  of  tensions  f  is 
calculated  for  every  half  degree  between  —  10°  and  +  35°.  This  table  (which 
is  the  one  alluded  to  in  the  note  at  page  93,)  is  of  great  utility  in  hygrometric 
observations  :— 


Ann.  Ch.  Phys.  [3],  xi.  273.  f  Ann.  Ch.  Phys.  [3],  xv.  138. 


646 


TENSION    OF    VAPOURS. 


TABLE  XII. 
Tension  of  Aqueous  Vapour  from  — 10°  to  +35°  C. 


Degrees. 

Tension. 

Diff. 

Degrees. 

Tension. 

Diff. 

Degrees. 

Tension. 

Diff. 

mm. 

mm. 

mm. 

—10-0 

2-078 

+  5-0 

6-534 

+  20-0 

17-391 

0-544 

9-5 

2-168 

0-090 

5-5 

6-763 

0-229 

20-5 

17-935 

0-560 

9-0 

2-261 

0-093 

6-0 

6-998 

0-285 

21-0 

18-495 

0-574 

8-5 

2-356 

0-095 

6-5 

7-242 

0-244 

21-5 

19-069 

0-690 

8-0 

2-456 

0-100 

7-0 

7-492 

0-250 

22-0 

19-659 

0-601 

7-5 

2-561 

0-105 

7-5 

7-751 

0-259 

22-5 

20-265 

0-623 

7-0 

2-666 

0-105 

8-0 

8-017 

0-265 

23-0 

20-888 

0-640 

6-5 

2-776 

0-110 

8-5 

8-291 

0-274 

23-5 

21-528 

0-656 

6-0 

2-890 

0-114 

9-0 

8-574 

0-283 

24-0 

22-184 

0-674 

5-5 

3-010 

0-120 

9-5 

8-865 

0-291 

24-5 

22-858 

0-692 

5-0 

3-131 

0-121 

10-0 

9-165 

0-300 

25-0 

23-550 

0-711 

4-5 

3-257 

0-126 

10-5 

9-474 

0-309 

25-5 

24-261 

0-727 

4-0 

3-387 

0-130 

11-0 

9-792 

0-318 

26-0 

24-988 

0-750 

3-5 

3-522 

0-135 

11-5 

10-120 

0-328 

26-5 

25-738 

0-767 

3-0 

3-662 

0-140 

12-0 

10-457 

0-337 

27-0 

26-505 

0-789 

2-5 

3-807 

0-145 

12-5 

10-804 

0-347 

27-5 

27-294 

0-807 

2-0 

3-955 

0-148 

13-0 

11-162 

0-358 

28-0 

28-101 

0-830 

1-5 

4-109 

0-154 

13-5 

11-530 

0-368 

28-5 

28-931 

0-851 

1-0 

4-267 

0-158 

14-0 

11-908 

0-378 

29-0 

29-782 

0-872 

0-5 

4-430 

0-163 

14-5 

12-298 

0-390 

29-5 

30-654 

0-894 

0-0 

4-600 

0-170 

15-0 

12-699 

0-401 

30-0 

31-548 

0-915 

+  0-5 

4-767 

0-167 

15-5 

13-112 

0-413 

30-5 

32-463 

0-942 

1-0 

4-940 

0-173 

16-0 

13-536 

0-424 

31-0 

33-405 

0-963 

1-5 

5-118 

0-178 

16-5 

13-972 

0-436 

31-5 

34-368 

0-991 

2-0 

5-302 

0-184 

17-0 

14-421 

0-449 

32-0 

35-359 

1-011 

2-5 

5-491 

0-189 

17-5 

14-882 

0-461 

32-5 

36-370 

1-030 

3-0 

5-687 

0-196 

18-0 

15-357 

0-475 

33-0 

37.410 

1-063 

3-5 

5-889 

0-202 

18-5 

15-845 

0-488 

33-5 

38-473 

1-092 

4-0 

6-097 

0-208 

19-0 

16-346 

0-501 

34-0 

39-565 

1-115 

4-5 

6-313 

0-216 

19-5 

16-861 

0-515 

34-5 

40-680 

1-147 

35.0 

41-827 

Regnault  has  also  determined  the  tensions  of  several  other  liquids  in  vacuo. 
The  results  (given  in  Table  XIII.)  were  obtained  either  by  direct  measurement 
of  the  elastic  forces  in  vacuo,  or  by  determining  the  temperature  of  the  vapour  of 
a  boiling  liquid  under  the  pressure  of  an  artificial  atmosphere.  The  former  method 
was  adopted  for  low,  the  latter  for  high  temperatures.  The  series  of  experiments 
made  by  the  two  methods  were,  however,  in  all  cases  made  to  include  a  certain 
common  range  of  temperature,  so  that  the  corresponding  curves  of  tension  might 
overlap  each  other  within  that  range.  With  liquids  which  could  be  obtained  per- 
fectly pure,  such  as  water  and  sulphide  of  carbon,  the  two  curves  thus  obtained 
were  found  to  coincide  exactly ;  but  with  alcohol,  ether,  and  still  more  with  chlo- 
roform, which  are  more  difficult  to  purify,  the  presence  of  foreign  substances  gave 
rise  to  more  or  less  divergence  in  the  results.  Thus  the  tension  of  chloroform 
vapour  at  36°,  was  found  to  be  342-2  mm.  by  the  first  method,  and  3134  mm. 
by  the  second.  Regnault  finds  that  an  extremely  small  amount  of  impurity  may 
be  detected  in  this  manner. 


TENSION    OF    VAPOURS. 


647 


TABLE  XIII. — TENSION  OF  VAPOURS. 


Temperature. 

Alcohol. 

Ether. 

Sulphide  of  Carbon. 

Chloroform. 

Oil  of  Turpentine. 

—21°  C. 
—20 
16 

mm. 
3-12 
3-34 

mm. 
69-2 

mm. 

58-8 

mm. 

mm. 

—10 
0 
10 
20 
30 
40 
50 
60 
70 
80 
90 
100 
110 
116 

6-50 
12-73 
24-08 
44-00 
78-4 
134-10 
220-3 
850-0 
539-2 
812-8 
1190-4 
1685-0 
2351-8 

113-2 
182-3 
286-5 
434-8 
637-0 
913-6 
1268-0 
1730-3 
2309-5 
2947-2 
3899-0 
4920-4 
6249-0 
7076-2 

79-0 
127-3 
199-3 
298-2 
434-6 
617-5 
852-7 
1162-6 
1549-0 
2030-5 
2623-1 
3321-3 
4136-3 

•      130-4 
190-2 
276-1 
364-0 
524-3 
738-0 
976-2 
1367-8 
1811-5 
2354-6 
3020-4 

2-1 
2-3 
4-3 
7-0 

11-2 
17-2 
26-9 
41-9 
61-2 
91-0 
134-9 
187-3 

120      . 

3207-8 

5121  6 

3818-0 

257-0 

130 
136 

4351-2 

• 



6260-6 
7029-2 

4721-0 

347-0 

140 

5637-7 

462-3 

150 

7257-8 

604-5 

152 
160 

7617-3 

777-2 

170 

989-0 

180 

1225-0 

190 

1514-7 

200 

1865-6 

210 

2251-2 

220 

2690-3 

222 

2778-5 

Vapours  of  saline  solutions. — It  is  well  known  that  the  boiling  point  of  a  saline 
solution  is  higher  than  that  of  pure  water,  the  affinity  of  the  water  for  the  salt 
being,  in  fact,  an  additional  obstacle  which  the  heat  must  overcome  before  ebul- 
lition can  take  place.  Nevertheless,  it  appeared  to  Rudberg  that  the  vapours 
rising  from  such  solutions  do  not  exhibit  a  higher  temperature  than  steam  from 
boiling  water;  a  result  which  was  attributed  to  the  sudden  expansion  which  the 
vapour  undergoes  at  the  moment  of  escaping  from  the  liquid.  Regnault  finds, 
however,  that  a  thermometer  having  its  bulb  immersed  in  the  vapour  of  a  boiling 
saline  solution  does  not  give  a  correct  indication  of  the  temperature  of  that  vapour, 
because  the  bulb  becomes  covered  with  a  film  of  condensed  water,  and,  therefore, 
the  thermometer  exhibits  only  the  temperature  due  to  the  boiling  of  that  water. 
But  when  proper  precautions  are  taken,  by  the  interposition  of  screens,  to  prevent, 
as  far  as  possible,  this  deposition  of  water,  the  temperature  of  the  vapour  appears 
very  nearly  equal  to  that  of  the  liquid.  It  is,  however,  extremely  difficult  to 
remove  this  source  of  error  completely. 

The  observation  of  the  elastic  force  of  a  vapour  arising  from  a  saline  solution 
appears  to  afford  excellent  means  of  detecting  chemical  changes  in  the  constitution 
of  the  liquid,  every  such  change  being  indicated  by  the  occurrence  of  a  singular 
point  in  the  curve  which  represents  the  law  of  the  tension.  For  example,  in  the 
case  of  salts,  like  the  sulphates  of  sodium,  copper,  iron,  manganese,  &c.,  which 
crystallize  at  different  temperatures  with  different  proportions  of  water,  Ilegnault 
suggests  that  the  variations  in  the  tension  of  the  vapour  might  indicate  whether 


648 


TENSION    OF    VAPOURS. 


the  water  is  chemically  combined  with  the  salt  while  still  in  solution,  or  whether 
the  combination  takes  place  at  the  moment  of  crystallization, 

Mixtures  of  vapours  and  gases. — The  law  of  Dalton,  that  the  tension  of  any 
saturated  vapour  in  air  is  the  same  for  any  given  temperature  as  in  vacuo,  must 
be  received  with  certain  limitations.  It  has  been  already  stated  (p.  91)  that 
Regnault  found  the  tension  of  saturated  aqueous  vapour  in  air  to  be  always  some- 
what less  than  in  vacuo ;  the  differences,  however,  seldom  exceeding  "2  per  cent, 
of  the  entire  value.  The  following  are  a  few  of  the  results  obtained  : 

TABLK  XIV. 


Temperature. 

Observed  Tension  in  Air. 

Calculated  Tension  in  Vacuo. 

Difference. 

mm. 

mm. 

0°0. 

4-47 

4-60 

—0-13 

12-59 

10-31 

10-85 

—0-54 

15 

12-38 

12-70 

—0-32 

21 

18-27 

18-49 

—0-22 

24-69 

22-70 

23-13 

—0-40 

31 

32-97 

33-41 

—0-44 

35-97 

43-39 

44-13 

—0-74 

38 

48-70 

49-30 

—0-60 

Similar  differences  are  observed  with  other  liquids.     "With  ether  the  following 
results  are  obtained  :  — 

TABLE  XV. 


Tension  of  Ether-vapour. 

Temperature. 

In  Air. 

In  Vacuo. 

Difference. 

mm. 

mm. 

mm. 

33-62°  C. 

705-09 

726-0 

20-9 

30-97 

645-52 

659-0 

13-4 

26-52 

652-67 

559-2 

6-5 

22-63 

479-63 

484-0 

4-4 

20-05 

429-69 

433-9 

4-2 

19-99 

428-88 

433-0 

4-1 

14-26 

337-71 

341-0 

3-3 

In  air  and  in  hydrogen  gas,  the  tension  of  ether  vapour  was  found  to  be  always 
lower  in  vacuo,  unless  the  gas  was  strongly  compressed;  in  carbonic  acid  gas, 
which  (as  a  liquid)  dissolves  ether  in  considerable  quantity,  the  tension  never 
becomes  equal  to  that  in  vacuo. 

The  tension  of  a  vapour  in  a  gas  is  very  much  affected  by  the  condensation  of 
the  vapour  on  the  sides  of  the  vessel,  an  effect  which  takes  place  considerably 
below  the  point  of  saturation.  Regnault  is  of  opinion  that  Dalton's  law  with 
regard  to  the  tensions  of  vapours  in  gases  could  never  be  strictly  true,  unless  the 
gas  were  enclosed  in  a  vessel  whose  walls  were,  to  a  certain  thickness,  formed  of 
the  liquid  itself. 

Vapours  of  mixed  liquids. — Gay-Lussac  found  that  the  tension  of  the  vapour 
arising  from  two  or  more  mixed  liquids  is  equal  to  the  sum  of  the  tensions  of  the 
vapours  which  each  would  produce  separately.  The  more  recent  experiments  of 
Magnus  and  of  Regnault  have  shown  that  this  law  is  true,  or  nearly  true,  only 
when  the  liquids  are  quite  immiscible,  such  as  benzol  and  water.  When  the 
liquids  are  mutually  soluble,  but  not  in  all  proportions,  the  tension  of  the  mixed 


CONDUCTION    OF    HEAT. 


649 


vapour  is  much  less  than  the  sum  of  the  separate  tensions.     "With  ether  and  water 
it  scarcely  differs  from  the  tension  of  the  ether- vapour  alone ;  thus  : — 


TABLE  XVI. 


Temperature. 

Tension  of 
water-Tapour. 

Tension  of 
ether-vapour. 

Sum  of  tensions. 

Observed  tension  of 
mixed  vapour. 

15-66°  C. 
24-21 
33-08 

mm. 
13-16 
22-47 
37-58 

mm. 
361-8 
510-0 
711-1 

mm. 
374-96 
532-47 

748-68 

mm. 
362-95 
510-08 
710-02 

When  the  mixed  liquids  dissolve  in  one  another  in  all  proportions,  the  tension 
of  the  mixed  vapour  is  in  most  cases  greater  than  that  of  the  less  volatile,  but 
less  than  that  of  the  more  volatile  substance ;  such,  for  example,  is  the  case  with 
mixtures  of  ether  and  sulphide  of  carbon.  In  a  mixture  of  benzol  and  alcohol, 
however,  the  tension  of  the  mixed  vapour  is  greater  than  that  of  either  of  the 
separate  vapours.  With  this  mixture  Regnault  obtained  the  results  given  in — 


TABLE  XVII. 


Temperature. 

Tension  of  vapour. 

7-22°  C. 
9-98 
13-11 
16-05 
18-59 

Of  the  mixture 
43-17 
50-22 
59-66 
69-43 
79-35 

Of  alcohol. 
40-4 
46-8 
54-4 
62-7 
71-0 

Of  benzol. 
20-1 
24-2 
29-2 
35-0 
41-0 

When  the  liquids  do  not  mix,  but  dispose  themselves  in  layers,  the  more  vola- 
tile liquid  forming  the  lower  stratum,  and  the  ebullition  being  but  feeble,  the  tem- 
perature and  corresponding  vapour-tension  agree  with  Gay-Lussac's  law.  But 
with  a  brisk  lire  and  violent  ebullition,  the  temperature  remains  nearly  at  the 
limit  at  which  the  more  volatile  liquid  would  boil  by  itself  under  the  same  pressure. 


CONDUCTION   OF  HEAT. 

Li  metal*. — From  the  experiments  of  Wiedemann  and  Franz,*  it  appears  that 
the  metals  follow  each  other  with  regard  to  their  heat-conducting  power,  in  the 
same  order  as  with  regard  to  their  power  of  conducting  electricity;  and,  more- 
over, that  the  numbers  which  express  their  relative  heat-conducting  powers,  do 
not  differ  from  those  which  express  their  relative  powers  of  conducting  electricity, 
more  than  the  latter  numbers,  as  determined  by  different  observers,  differ  from 
each  other. 

The  heat-conducting  power  of  metals  appears  also  to  diminish  as  their  tempera- 
ture rises. 


*  Phil.  Mag.  [4],  vii. 


650 


CONDUCTION    OF    HEAT. 


TABLE  XVIII. 


Metafe. 

Electric-conducting  power  according  to 

Heat-conducting 
power. 

Riess. 

Becquerel. 

Lenz. 

Silver  

100 

66-7 
69-0 
18-4 
10-0 
12-0 

To 

10-5 
5-9 

100 

91-5 
64-9 

14-b" 
12-35 

8-27 
7-93 

100 

73-3 
58-5 
21-5 
22-6 
13-0 

10-7 
10-3 

1-9 

100 
73-6 
53-2 
23-6 
14-5 
11-9 
11-6 
8-5 
8-4 
6-3 
1-8 

Gold   .   .   

Brass  ..  

Tin  

Strel  

Lead  

Platinum  
German  silver  ... 
Bismuth  .  ....... 

Conduction  of  heat  in  crystallized  bodies.  —  Bodies  of  perfectly  homogeneous 
etructure  conduct  heat  with  equal  facility  in  all  directions;  so  likewise  do  crystal- 
lized bodies  belonging  to  the  regular  system ;  but  in  crystals  belonging  to  any 
other  system,  the  rate  of  conduction  is  different  in  different  directions.  This  sub- 
ject has  been  very  ingeniously  investigated  by  Senarmont,*  whose  method  of  ob- 
servation was  as  follows :  —  A  small  tube  of  platinum  was  inserted  through  the 
centre  of  a  flat  cylindrical  plate  of  the  crystal,  in  the  direction  of  the  axis,  the 
tube  being  bent  at  right  angles  at  the  lower  extremity  and  .heated  by  a  lamp,  and 
a  current  of  air  made  to  pass  through  the  tube  by  means  of  an  aspirator.  The 
two  bases  of  the  cylindrical  plate  were  covered  with  wax,  which,  being  melted  by 
the  heat,  traced  on  the  surface  a  curve  line,  whose  form  was  determined  by  the 
conducting  power  of  the  crystal  in  different  directions.  Plates  of  non-crystalline 
substances,  such  as  glass  and  zinc,  treated  in  this  manner,  gave  circles  having 
their  centres  in  the  axis  of  the  platinum-tube.  On  a  plate  of  calc-spar,  cut  per- 
pendicularly to  the  axis  of  symmetry  (the  optic  axis),  the  curves  are  circles  with 
their  centres  in  the  axis.  On  plates  parallel  to  the  direction  of  natural  cleavage, 
the  curves  are  also  circles,  having  a  slight  tendency  to  elongate  in  the  direction  of 
the  principal  section.  On  plates  cut  parallel  to  the  axis  of  symmetry,  and  at 
right  angles  to  one  of  the  faces  of  the  primary  rhombohedron,  the  curves  are 
ellipses,  having  their  transverse  diameter  in  the  direction  of  the  axis  of  symme- 
try. The  ratio  of  the  axes  of  the  ellipse  thus  formed  is  1-118  :  1.  Similar 
results  are  obtained  with  quartz,  the  ratio  of  the  axes  being  1-31  :  1;  also  with 
crystals  belonging  to  the  square  prismatic  system,  such  as  rutile,  idocrase,  and  sub- 
chloride  of  mercury.  In  crystals  belonging  to  the  right  prismatic,  oblique  pris- 
matic, and  doubly  oblique  prismatic  systems,  —  that  is  to  say,  in  crystals  having 
two  axes  of  double  refraction, — three  directions  are  found  at  right  angles  to  each 
other,  in  which  the  thermal  curves,  obtained  in  the  manner  above  described,  are 
ellipses.  Hence  it  is  inferred  that : — 

1.  In  crystalline  media  having  two  optic  axes,  supposing  the  medium  to  be  in- 
definitely extended  in  all  directions,  and  a  centre  of  heat  to  exist  within  it,  the 
isothermal  surfaces  are  ellipsoids  with  three  unequal  axes. 

2.  In  crystals  with  one  optic  axis,  the  isothermal  surfaces  are  ellipsoids  of  revo- 
lution round  that  axis. 

3.  In  crystals  belonging  to  the  regular  system,  and  in  homogeneous  uncrystal- 
lized  media,  the  isothermal  surfaces  are  spherical. 


Ann.  Ch.  Phys.  [3],  xxi.  45. 


CONDUCTION"    OF    HEAT.  651 

Un crystallized  bodies,  however,  acquire  axes  of  different  heat-conducting  power 
when  their  molecular  structure  is  altered  by  pressure,  traction,  or  hardening. 
Plates  of  glass  subjected  to  lateral  pressure,  and  heated  in  the  manner  above  de- 
scribed, exhibit  distinct  thermic  ellipses,  having  their  shorter  axes  in  the  direction 
of  the  pressure,  that  is,  of  the  greatest  density  (Senarmont).  It  is  well  known 
that  glass,  and  other  transparent  non-crystalline  bodies,  when  similarly  treated, 
acquire  the  power  of  double  refraction. 

Crystalline  media  likewise  exhibit  peculiar  characters  in  the  transmission  of  heat 
by  radiation  as  well  as  by  conduction.  Through  crystals  with  one  optic  axis,  heat 
is  radiated  in  different  quantity  and  also,  of  different  quality  (p.  56),  according 
as  it  passes  in  a  direction  parallel  or  perpendicular  to  that  axis.  In  crystals  with 
two  optic  axes,  the  quantity  and  quality  of  the  transmitted  heat  differ  according 
as  the  direction  of  transmission  coincides  with  one  or  other  of  the  three  axes  of 
elasticity  (Knoblauch).* 

Conducting  power  of  wood.  —  The  dependence  of  heat-conduction  upon  mole- 
cular arrangement  is  exhibited  by  organic  structures  as  distinctly  as  by  crystalline 
media.  This  subject  has  been  very  ingeniously  investigated  by  Dr.  Tyndall,f 
who  has  examined  the  conducting  power  of  various  organic  substances,  especially 
of  wood.  The  bodies,  cut  into  cubes  of  equal  size,  were  enclosed  between  two 
chambers  filled  with  mercury,  that  liquid  being  confined  on  the  sides  next  the 
cube  by  membranous  diaphragms,  with  which  the  cube  was  in  close  contact.  The 
mercury  in  one  of  the  chambers  was  heated  by  a  spiral  of  platinum  wire  immersed 
in  it,  and  connected  with  a  galvanic  battery.  The  heat  thus  generated  was  trans- 
mitted through  the  organic  substance  to  the  mercury  in  the  other  chamber,  and 
the  quantity  of  heat  thus  communicated  in  a  given  time,  was  measured  by  means 
of  a  thermo-electric  couple  connected  with  a  galvanometer.  By  transmitting  heat 
in  this  manner  through  cubes  of  wood  in  different  directions,  it  was  found  that : 

At  all  points  not  situated  in  the  centre  of  the  tree,  wood  possesses  three  unequal 
axes  of  calorific  conduction.  The  first  and  principal  axis  is  parallel  to  the  fibres 
of  the  wood;  the  second  and  intermediate  axis  is  perpendicular  to  the  fibres  and 
to  the  ligneous  layers ;  and  the  third,  and  least  axis,  is  perpendicular  to  the  fibre 
and  parallel  to  the  layers. 

These  axes  of  heat-conduction  coincide  with  the  axes  of  elasticity,  which 
Savart  discovered  by  observing  the  figures  of  sand  formed  on  plates  of  wood 
when  thrown  into  acoustic  vibration.  The  same  directions  are  likewise  axes  of 
cohesion  and  of  permeability  to  liquids.  Wood  of  any  kind  may  be  most  easily 
split  by  laying  the  blade  of  the  cutting  instrument  parallel  to  the  fibres  and  across 
the  annual  rings ;  the  direction  of  least  cohesion  is,  therefore,  perpendicular  to 
the  fibres,  and  parallel  or  tangenital  to  the  rings.  The  direction  of  greatest  re- 
sistance is  parallel  to  the  fibres.  With  regard  to  permeability,  it  is  well  known 
that  plates  of  wood  cut  perpendicularly  to  the  fibres  are  not  fit  for  the  bottoms  of 
casks  to  hold  liquids;  also,  that  in  cutting  staves  for  casks,  it  is  indispensable  to 
cut  them  across  the  woody  layers,  the  direction  parallel  to  the  layers  being  that  of 
least  permeability. 

It  may,  therefore,  be  stated  as  a  general  law,  that :  the  axes  of  calorific  con- 
duction in  wood  coincide  with  the  axes  of  elasticity,  cohesion  and  permeability 
to  liquids,  the  greatest  with  the  greatest,  and  the  least  with  the  least. 

The  heat-conducting  power  of  wood  does  not  bear  any  definite  relation  to  its 
density.  American  birch,  which  is  one  of  the  lightest  woods,  conducts  heat 
better  than  any  other.  Oak  and  Coromandel  wood,  which  are  very  dense,  con- 
duct nearly  as  well;  but  iron-wood,  which  has  the  enormous  density  of  1426,  is 
very  low  in  the  scale  of  conduction. 

*  Pogg.  Ann.  Ixxxv.  169;  xciv,  161.  f  Phil.  Mag.  [4],  vi.  121. 


652  MECHANICAL    EQUIVALENT    OF    HEAT. 


RELATION   BETWEEN   HEAT   AND   MECHANICAL   FORCE   OR   WORK. — DYNAMI- 
CAL  THEORY   OF   HEAT. 

Heat  and  motion  are  convertible  one  into  the  other.  The  powerful  mechanical 
effects  produced  by  the  elasticity  of  the  vapours  evolved  from  heated  liquids  afford 
abundant  illustration  of  the  conversion  of  heat  into  motion ;  and  the  production 
of  heat  by  friction  shows  with  equal  clearness  that  motion  may  be  converted  into 
heat.  That  the  rise  of  temperature  thus  produced  is  not  due  to  any  change  in 
the  heat-capacity  of  the  bodies,  is  strikingly  shown  in  Davy's  experiment  of  melt- 
ing ice  by  rubbing  two  plates  of  the  substance  together  in  vacuo  (p.  97) ;  and 
Count  Rumford's  observations  on  the  heat  produced  by  the  boring  of  ordnance 
point  to  the  same  conclusion.  In  these  and  all  similar  cases,  the  heat  appears  as 
a  direct  result  of  the  force  expended :  the  motion  is  converted  into  heat. 

But  the  connection  between  heat  and  mechanical  force  appears  still  more  inti- 
mate when  it  is  shown  that  they  are  related  by  an  exact  numerical  law,  a  given 
quantity  of  the  one  being  always  convertible  into  a  determinate  quantity  of  the 
other.  The  first  approximate  determination  of  this  numerical  relation  —  the  me- 
chanical equivalent  of  heat  —  was  made  by  Count  Rumford  in  the  following  man- 
ner :  A  brass  cylinder,  enclosed  in  a  box  containing  a  known  weight  of  water  at 
60°  F.,  was  bored  by  a  steel  borer  made  to  revolve  by  horse-power,  and  the  time 
noted  which  elapsed  before  the  water  was  raised  to  the  boiling-point  by  the  heat 
resulting  from  the  friction.  In  this  manner  it  was  found  that  the  heat  required 
to  raise  the  temperature  of  a  pound  of  water,  1°  F.,  is  equivalent  to  1034  times 
the  force  expended  in  raising  a  pound  weight  one  foot  high,  or  to  1034  foot-pounds, 
as  it  is  technically  expressed.  This  estimate  is  now  known  to  be  too  high,  no 
account  having  been  taken  of  the  heat  communicated  to  the  containing  vessels, 
or  of  that  which  was  lost  by  dispersion  during  the  progress  of  the  experiment. 

For  the  most  exact  determinations  of  the  mechanical  equivalent  of  heat,  we 
are  indebted  to  the  careful  and  elaborate  experiments  of  Mr.  J.  P.  Joule.  From 
experiments  made  in  the  years  1840-43,  on  the  relations  between  the  heat  and 
mechanical  power  generated  by  the  electric  current,  Mr.  Joule  was  led  to  conclude 
that  the  heat  required  to  raise  the  temperature  of  a  pound  of  water  1°  F.,  is  equi- 
valent to  838  foot-pounds ;  and  a  nearly  equal  result  was  afterwards  obtained  by 
experiments  on  the  condensation  and  rarefaction  of  gases ;  but  this  estimate  has 
since  been  found  to  be  likewise  too  high. 

The  most  trustworthy  results  are,  however,  obtained  by  measuring  the  quantity 
of  heat  generated  by  the  friction  between  solids  and  liquids.  It  was  for  a  long 
time  believed*  that  no  heat  was  evolved  by  the  friction  of  liquids  and  gases.  But, 
in  1842,  Meyer  showed  that  the  temperature  of  water  may  be  raised  22°  or  23°  F. 
by  agitating  it.  The  warmth  of  the  sea  after  a  few  days  of  stormy  weather  is 
also,  probably,  an  effect  of  fluid  friction. 

In  1848  Mr.  Joule  showed  that  heat  is  evolved  in  the  passage  of  water  through 
narrow  tubes,  and  that  each  degree  of  heat  per  pound  of  water  required  for  its 
evolution  in  this  way  a  force  of  770  foot-pounds.  In  subsequent  experiments,  a 
paddle-wheel  was  employed  to  produce  fluid  friction,  and  the  equivalents  781-5, 
782*1,  and  787*6  obtained  from  the  agitation  of  water,  sperm-oil,  and  mercury 
respectively. 

The  apparatus  finally  employed  by  Mr.  Joule*  in  the  determination  of  this  im- 
portant constant,  by  means  of  the  friction  of  water,  consisted  of  a  brass  paddle- 
wheel  furnished  with  eight  sets  of  revolving  vanes,  working  between  four  sets 
of  stationary  vanes.  This  revolving  apparatus,  of  which  fig.  206  shows  a  vertical, 
and  fig.  207  a  horizontal  section,  was  firmly  fitted  into  a  copper  vessel  (A, 
fig.  208)  containing  water,  in  the  lid  of  which  were  two  necks,  one  for  the  axis 

*  Phil.  Trans.  1850,  i.  61 ;  Chem.  Soc.  Qu.  J.  iii.  316. 


MECHANICAL  EQUIVALENT  OF  HEAT. 


653 


FIG.  201; 


to  revolve  in  without  touching,  the  other  for  the  insertion  of  a  thermometer.  A 
similar  apparatus,  but  made  of  iron,  and  of  smaller  size,  having 
FIG.  206.  gjx  rotatory  and  eight  sets  of  stationary  vanes,  was  used  for  ex- 
periments on  the  friction  of  mercury.  The  apparatus  for  the  fric- 
tion of  solids  consisted  of  a  vertical  axis  carrying  a  bevelled  cast- 
iron  wheel,  against  which  a  fixed  bevelled  wheel  was 
pressed  by  a  lever.  The  wheels  were  enclosed  in 
a  cast-iron  vessel  filled  with  mercury,  the  axis  pass- 
ing through  the  lid.  In  each  apparatus  motion  was 
given  to  the  axis  by  the  descent  of  leaden  weights 
suspended  by  strings  from  the  axes  of  two  wooden 
pulleys  w,  one  of  which  is  shown  at  p  (fig.  208), 
their  axes  being  supported  on  friction- wheels  d  d ; 
and  the  pulleys  were  connected  by  fine  twine  with  a 

wooden  roller  r,  which,  by  means  of  a  pin,  could  be  easily  attached  to  or  removed 

from  the  friction  apparatus. 


FIG.  208. 


r\~ 


The  mode  of  experimenting  was  as  follows :  The  temperature  of  the  friotional 
apparatus  having  been  ascertained,  and  the  weights  wound  up,  the  roller  was 
fixed  to  the  axis,  and  the  precise  height  of  the  weights  ascertained,  after  which 
the  roller  was  set  at  liberty,  and  allowed  to  revolve  till  the  weights*  touched  the 
floor.  The  roller  was  then  detached,  the  weights  wound  up  again,  and  the  friction 
renewed.  This  having  been  repeated  twenty  times,  the  experiment  was  concluded 
with  another  observation  of  the  temperature  of  the  apparatus.  The  mean  tem- 
perature of  the  apartment  was  ascertained  by  observations  made  at  the  beginning, 
middle,  and  end  of  each  experiment.  Corrections  were  made  for  the  effects  of 
radiation  and  conduction ;  and,  in  the  experiments  with  water,  for  the  quantities? 
of  heat  absorbed  by  the  copper  vessel  and  the  paddle-wheel.  In  the  experiments 
with  mercury  and  cast-iron,  the  heat-capacity  of  the  entire  apparatus  was  ascer- 
tained by  observing  the  heating  effect  which  it  produced  on  a  known  quantity  of 
water  in  which  it  was  immersed.  In  all  the  experiments,  corrections  were  also 
made  for  the  velocity  with  which  the  weights  came  to  the  ground,  and  for  the 
friction  and  rigidity  of  the  strings.  The  thermometers  used  were  capable  of  in- 
dicating a  variation  of  temperature  as  small  as  ^^  of  a  degree  Fahrenheit. 

The  following  table  contains  a  summary  of  the  results  obtained  by  this  method , 
the  second  column  gives  the  results  as  they  were  obtained  in  air;  the  third  column, 
the  same  results  corrected  for  a  vacuum. 


654.  DYNAMICAL  THEORY  OF  HEAT. 

Material  Equivalent  Equivalent 

employed.  in  air.  in  vacuo.  Mean. 

Water 773-640  772-692  772-692 

M  f  773-762  772-814 )  „_,  ,QO 

Mercui7 ;  {  776-303  775-352  }  <74'083 

n    . .  f  776-997  776-045  ]  ,._  QQ7 

Cast-iron {  774-880  773-930  }  774'987 

In  the  experiments  with  cast-iron,  the  friction  of  the  wheels  produced  a  con- 
siderable vibration  of  the  frame-work  of  the  apparatus  and  a  loud  sound ;  it  was 
therefore  necessary  to  make  allowance  for  the  quantity  of  force  expended  in  pro- 
ducing these  effects.  The  number  772-692,  obtained  by  the  friction  of  water,  is 
regarded  as  the  most  trustworthy;  but  even  this  maybe  a  little  too  high  j  be- 
cause, even  in  the  friction  of  fluids,  it  is  impossible  entirely  to  avoid  vibration  and 
sound. 

The  conclusions  deduced  from  these  experiments  are  — 

1.  That  the  quantity  of  heat  produced  by  the  friction  of  bodies,  whether  solid 
or  liquid,  is  always  proportional  to  the  force  expended. 

2.  That  the  quantity  of  heat  capable  of  increasing  the  temperature  of  1  Ib.  of 
water  (weighed  in  vacuo,  and  between   55°  and  60°)   by  1°  P.,  requires  for  its 
evolution  the  expenditure  of  a  mechanical  force  represented  by  the  fall  0/772  Ibs. 
through  the  space  of  1  foot. 

Or,  the  heat  capable  of  increasing  the  temperature  of\  gramme  of  water  by  1° 
cent.,  is  equivalent  to  a  force  represented  by  the  fall  of  423  -55  grammes  through 
the  space  of\  metre.  This  is  consequently  the  effect  of  a  "  unit  of  heat. }) 

Kupffer*  has  also  determined  the  mechanical  equivalent  of  heat  by  comparing 
the  expansion  which  a  metal  wire  suffers  by  heat  with  the  elongation  produced  by 
stretching  it  with  a  given  weight.  By  this  method,  which  does  not  appear  to  be 
quite  so  accurate  as  that  above  described,  it  is  found  that  the  heat  necessary  to 
raise  a  pound  of  water  1°  Fahrenheit,  is  equivalent  to  661  foot-pounds. 

DYNAMICAL   THEORY   OF    HEAT. 

The  constant  relation  between  heat  and  work  affords  a  powerful  argument  in 
favour  of  the  mechanical  or  dynamical  theory  of  heat  —  the  theory  which  rests  on 
the  hypothesis  that  HEAT  is  MOTION.  This  theory  has  received,  of  late  years, 
many  important  additions  and  developments,  chiefly  by  the  labours  of  Clausius, 
Joule,  Rankine,  and  W.  Thompson.  It  is  impossible,  within  the  limits  of  this 
Supplement,  to  give  even  a  brief  account  of  the  whole  of  these  valuable  researches ; 
but  the  leading  points  of  the  theory  may,  perhaps,  be  sufficiently  elucidated  by 
the  following  summary  of  two  remarkable  papers  lately  published  in  "Poggen- 
dorffs  Annalen,"  one  by  Kronig,  entitled  "  Fundamental  Principles  of  a  Theory 
of  Gases  ;"f  the  other,  by  Clausius,  "  On  the  Kind  of  Motion  which  we  call  Heat."J 

First,  then,  it  is  assumed  that  the  particles  of  all  bodies  are  in  constant  motion, 
and  that  this  motion  ^constitutes  heat,  the  kind  and  quantity  of  motion  varying 
according  to  the  state  of  the  body,  whether  solid,  liquid,  or  gaseous. 

In  gases,  the  molecules — each  molecule  being  an  aggregate  of  atoms  —  are  sup- 
posed to  be  constantly  moving  forward  in  straight  lines,  and  with  a  constant 
velocity,  till  they  impinge  against  each  other  or  against  an  impenetrable  wall. 
This  constant  impact  of  the  molecules  produces  the  expansive  tendency  or  elas- 
ticity, which  is  the  peculiar  characteristic  of  the  gaseous  state.  The  rectilinear 
movement  is  not,  however,  the  only  one  with  which  the  particles  are  affected. 

*  Phil.  Mag.  [4],  xli.  393. 

f  Grandziige  einer  Theorie  der  Gase;  von  A.  Kronig.     Pogg.  Ann.  xcix.  315. 

J  Ueber  die  Art  der  Bewegung  welche  wir  Warme  nennen;  von  R.  Clausius.  Pogg.  Ann. 
c.  353.  See  also  a  former  paper  by  Clausius,  "  Ueber  die  bewegende  Kraft  der  Warme," 
ibid.  Ixxix.  394. 


DYNAMICAL    THEORY    OF    HEAT.  655 

For  the  impact  of  two  molecules,  unless  it  takes  place  exactly  in  the  line  joining 
their  centres  of  gravity,  must  give  rise  to  a  rotatory  motion ;  and,  moreover,  the 
ultimate  atoms  of  which  the  molecules  are  composed  may  be  supposed  to  vibrate 
within  certain  limits,  being,  in  fact,  thrown  into  vibration  by  the  impact  of  the 
molecules.  This  vibratory  motion  is  called,  by  Clausius,  the  motion  of  the  con- 
stituent atoms  (Bewegungen  der  Bestandtheile*).  The  total  quantity  of  heat  in  the 
gas  is  made  up  of  the  progressive  motion  of  the  molecules,  together  with  the 
vibratory  and  other  motions  of  the  constituent  atoms ;  but  the  progressive  motion 
alone,  which  is  the  cause  of  the  expansive  tendency,  determines  the  temperature. 
Now,  the  outward  pressure  exerted  by  the  gas  against  the  containing  envelop, 
arises,  according  to  our  hypothesis,  from  the  impact  of  a  great  number  of  gaseous 
molecules  against  the  sides  of  the  vessel.  But,  at  any  given  temperature,  that  is, 
with  any  given  velocity,  the  number  of  such  impacts  taking  place  in  a  given  time, 
must  vary  inversely  as  the  volume  of  the  given  quantity  of  gas ;  hence  the  pres- 
sure varies  inversely  as  the  volume,  or  directly  as  the  density,  which  is  Mariotte's  law. 

When  the  volume  of  the  gas  is  constant,  the  pressure  resulting  from  the  impact 
of  the  molecules  is  proportional  to  the  sum  of  the  masses  of  all  the  molecules 
multiplied  into  the  squares  of  their  velocities ;  in  other  words,  to  the  so-called 
vis  viva  or  living  force  of  the  progressive  motion.  If,  for  example,  the  velocity 
be  doubled,  each  molecule  will  strike  the  sides  of  the  vessel  with  a  two-fold  force, 
and  its  number  of  impacts  in  a  given  time  will  also  be  doubled ;  hence  the  total 
pressure  will  be  quadrupled. 

Now  we  know  that  when  a  given  quantity  of  any  perfect  gas  is  maintained  at  a 
constant  volume,  it  tends  to  expand  by  2i^  of  its  bulk  for  each  degree  centigrade. 
Hence  the  pressure  or  elastic  force  increases  proportionately  to  the  temperature 
reckoned  from  —  273°  C. ;  that  is  to  say,  to  the  absolute  temperature.  Conse- 
quently, the  absolute  temperature  is  proportional  to  the  vis  viva  of  the  progressive 
motion.* 

*  Suppose  a  vessel  of  the  form  of  a  rectangular  parallelopiped,  the  length  of  whose  sides 
are  x,  y,  z,  to  contain  n  gas-molecules,  each  having  the  mass  m.  Suppose,  also,  the  space 

enclosed  by  this  vessel  to  be  divided  into  -  equal  cubes ;  and  at  a  given  instant  let  there  be 

in  each  of  these  cubes  six  gas-molecules,  moving  severally  in  the  directions  -}-  x,  —  x,  -f-  y, 
—  y,  -|-  z,  —  z,  and  with  the  common  velocity  c.  Let  it  also  be  supposed  that  the  molecules 
exert  no  mutual  action  upon  each  other,  but  pass  without  hindrance  from  side  to  side  of  the 
vessel.  It  is  required  to  determine  the  pressure  which  the  gas  exerts  against  one  of  the 
sides,  yz,  of  the  vessel.  The  pressure  arising  from  the  impact  of  a  single  gas-molecule  is 
mca,  if  a  denote  the  number  of  impacts  which  take  place  in  a  unit  of  time.  Now,  a  molecule 
moving  at  right  angles  to  yz,  or  parallel  to  x,  strikes  against  yz  every  time  that  it  passes 

over  the  space  2z;  therefore  a  =  — . 

2iX 

To  find  the  total  pressure  Pupon  yz,  the  quantity,  mca,  must  be  multiplied  by  the  number 
of  molecules  which  move  parallel  to  x,  which  number,  since  two  atoms  out  of  every  six  arc 

parallel  to  x,  is  -.     Hence  P  =  m .  c .—  .  -.     And  the  pressure  p  upon  a  unit  of  surface  of 

the  side  yz,  is  p  —  m .  c.  —  .  -  —  ;  or  if  we  put  xyz  =  v,  and  leave  out  the  constant  factor : 

nmc2 

f=—- 

This  expression  shows  that  the  pressure  exerted  upon  a  unit  of  surface  is  the  same  for  each 
side  of  the  vessel ;  also,  that  the  pressure  is  inversely  in  proportion  to  the  volume  of  the 
gas,  which  is  Mariotte's  law. 

The  product,  me2,  or  the  vis  viva  of  an  atom,  is  the  expression  of  the  temperature  reckoned 
from  the  absolute  zero,  or  —  273°  C. 

If,  in  the  preceding  value  of  p,  we  put  rwc2  =  t,  we  have 

nt 

?=v 

that  is  to  say,  when  the  volume  is  constant,  the  pressure  varies  directly  as  the  absolute 
temperature  (Kronig). 


656  DYNAMICAL     THEORY    OF    HEAT. 

Moreover,  as  the  motions  of  the  constituent  particles  of  a  gas  depend  on  the 
manner  in  which  its  atoms  are  united,  it  follows  that  in  any  given  gas  the  different 
motions  must  be  to  one  another  in  a  constant  ratio;  and  therefore  the  vis  viva  of 
the  progressive  motion  must  be  an  aliquot  part  of  the  entire  vis  viva  of  the  gas ; 
hence,  also,  the  absolute  temperature  is  proportional  to  the  total  vis  viva  arising 
from  all  the  motions  of  the  particles  of  the  gas. 

From  this  it  follows  that  the  quantity  of  heat  which  must  be  added  to  a  gas  of 
constant  volume  in  order  to  raise  its  temperature  by  a  given  amount,  is  constant 
and  independent  of  the  temperature.  In  other  words,  the  specific  heat  of  a  gas 
referred  to  a  given  volume,  is  constant,  a  result  which  agrees  with  the  experiments 
of  Regnault,  mentioned  on  pages  141-42.  This  result  may  be  otherwise  expressed  as 
follows  :  The  total  vis  viva  of  the  gas  is  to  the  vis  viva  of  the  progressive  motion 
of  the  molecules,  which  is  the  measure  of  the  temperature,  in  a  constant  ratio. 
This  ratio  is  different  for  different  gases,  and  is  greater  as  the  gas  is  more  complex 
in  its  constitution ;  in  other  words,  as  its  molecules  are  made  up  of  a  greater 
number  of  atoms.  The  specific  heat  referred  to  a  constant  pressure  is  known  to 
differ  from  the  true  specific  heat  only  by  a  constant  quantity. 

The  relations  just  considered  between  the  pressure,  volume  and  temperature  of 
gases,  presuppose,  however,  certain  conditions  of  molecular  constitution,  which  are, 
perhaps,  never  rigidly  fulfilled ;  and  accordingly,  the  experiments  of  Magnus  and 
Regnault  show  (40)  that  gases  do  exhibit  slight  deviations  from  Gray-Lussac  and 
Mariotte's  laws.  What  the  conditions  are  which  strict  adherence  to  these  laws 
would  require,  will  be  better  understood  by  considering  the  differences  of  molecu- 
lar constitution  which  must  exist  in  the  solid,  liquid,  and  gaseous  states. 

A  movement  of  molecules  must  be  supposed  to  exist  in  all  three  states.  In  the 
solid  state,  the  motion  is  such  that  the  molecules  oscillate  about  certain  positions 
of  equilibrium,  which  they  do  not  quit,  unless  they  are  acted  upon  by  external 
forces.  This  vibratory  motion  may,  however,  be  of  a  very  complicated  character. 
The  constituent  atoms  of  a  molecule  may  vibrate  separately ;  the  entire  molecules 
may  also  vibrate  as  such  about  their  centres  of  gravity,  and  the  vibrations  may  be 
either  rectilinear  or  rotatory.  Moreover,  when  extraneous  forces  act  upon  the  body, 
as  in  shocks,  the  molecules  may  permanently  alter  their  relative  positions. 

In  the  liquid  state,  the  molecules  have  no  determinate  positions  of  equilibrium. 
They  may  rotate  completely  about  their  centres  of  gravity,  and  may  also  move 
forward  into  other  positions.  But  the  repulsive  action  arising  from  the  motion  is 
not  strong  enough  to  overcome  the  mutual  attraction  of  the  molecules  and  sepa- 
rate them  completely  from  each  other.  A  molecule  is  not  permanently  associated 
with  its  neighbours,  as  in  the  solid  state ;  it  does  not  leave  them  spontaneously, 
but  only  under  the  influence  of  forces  exerted  upon  it  by  other  molecules,  with 
which  it  then  comes  into  the  same  relation  as  with  the  former.  There  exists, 
therefore,  in  the  liquid  state,  a  vibratory,  rotatory  and  progressive  movement  of  the 
molecules,  but  so  regulated,  that  they  are  not  thereby  forced  asunder,  but  remain 
within  a  certain  volume  without  exerting  any  outward  pressure. 

In  the  gaseous  state,  on  the  other  hand,  the  molecules  are  removed  quite  beyond 
the  sphere  of  their  mutual  attractions,  and  travel  onward  in  straight  lines  accord- 
ing to  the  ordinary  laws  of  motion.  When  two  such  molecules  meet,  they  fly 
apart  from  each  other,  for  the  most  part,  with  a  velocity  equal  to  that  with  which 
they  came  together.  The  perfection  of  the  gaseous  state,  however,  implies : 
1.  That  the  space  actually  occupied  by  the  molecules  of  the  gas  be  infinitely  small 
in  comparison  with  the  entire  volume  of  the  gas.  2.  That  the  time  occupied  in 
the  impact  of  a  molecule,  either  against  another  molecule,  or  against  the  sides  of 
the  vessel,  be  infinitely  small  in  comparison  with  the  interval  between  any  two 
impacts.  3.  That  the  influence  of  the  molecular  forces  be  infinitely  small.  When 
these  conditions  are  not  completely  fulfilled,  the  gas  partakes  more  or  less  of  the 
nature  of  a  liquid,  and  exhibits  certain  deviations  from  Gay-Lussac  and  Mariotte's 
laws.  Such  is,  indeed,  the  case  with  all  known  gases;  to  a  very  slight  extent 


DYNAMICAL    THEORY    OF    HEAT.  657 

with  those  which  have  not  yet  been  reduced  into  the  liquid  state;  but  to  a  greater 
extent  with  vapours  and  condensable  gases,  especially  near  the  points  of  conden- 
sation. 

Let  us  now  return  to  the  consideration  of  the  liquid  state.  It  has  been  said 
that  the  molecule  of  a  liquid,  when  it  leaves  those  with  which  it  is  associated, 
ultimately  takes  up  a  similar  position  with  regard  to  other  molecules.  This,  how- 
ever, does  not  preclude  the  existence  of  considerable  irregularities  in  the  actual 
movements.  Now,  at  the  surface  of  the  liquid,  it  may  happen  that  a  particle,  by 
a  peculiar  combination  of  the  rectilinear,  rotatory,  and  vibratory  movements,  may 
be  projected  from  the  neighbouring  molecules  with  such  force  as  to  throw  it  com- 
pletely out  of  their  sphere  of  action,  before  its  projectile  velocity  can  be  annihi- 
lated by  the  attractive  force  which  they  exert  upon  it.  The  molecule  will  then  be 
driven  forward  into  the  space  above  the  liquid,  as  if  it  belonged  to  a  gas,  and  that 
space,  if  originally  empty,  will,  in  consequence  of  the  action  just  described,  become 
more  and  more  filled  with  these  projected  molecules,  which  will  comport  them- 
selves within  it  exactly  like  a  gas,  impinging  and  exerting  pressure  upon  the  sides 
of  the  envelop.  One  of  these  sides,  however,  is  formed  by  the  surface  of  the 
liquid;  and  when  a  molecule  impinges  upon  this  surface,  it  will,  in  general,  not 
be  driven  back,  but  retained  by  the  attractive  forces  of  the  other  molecules.  A 
state  of  equilibrium,  not  static,  but  dynamic,  will  therefore  be  attained,  when  the 
number  of  molecules  projected  in  a  given  time  into  the  space  above,  is  equal  to 
the  number  which  in  the  same  time  impinge  upon  and  are  retained  by  the  surface 
of  the  liquid.  This  is  the  process  of  vapourization.  The  density  of  the  vapour 
required  to  ensure  the  compensation  just  mentioned,  depends  upon  the  rate  at  which 
the  particles  are  projected  from  the  surface  of  the  liquid,  and  this  again  upon  the 
rapidity  of  their  movement  within  the  liquid,  that  is  to  say,  upon  the  temperature. 
It  is  clear,  therefore,  that  the  density  of  a  saturated  vapour  must  increase  with  the 
temperature. 

If  the  space  above  the  liquid  is  previously  filled  with  a  gas,  the  molecules  of 
this  gas  will  impinge  upon  the  surface  of  the  liquid,  and  thereby  exert  pressure 
upon  it ;  but  as  these  gas-molecules  occupy  but  an  extremely  small  proportion  of 
the  space  above  the  liquid,  the  particles  of  the  liquid  will  be  projected  into  that 
space  almost  as  if  it  were  empty.  In  the  middle  of  the  liquid,  however,  the  exter- 
nal pressure  of  the  gas  acts  in  a  different  manner.  There  also  it  may  happen  that 
the  molecules  may  be  separated  with  such  force  as  to  produce  a  small  vacuum  in 
the  midst  of  the  liquid.  But  this  space  is  surrounded  on  all  sides  by  masses 
which  afford  no  passage  to  the  disturbed  molecules ;  and  in  order  that  they 
may  increase  to  a  permanent  vapour-bubble,  the  number  of  molecules  projected 
from  the  inner  surface  of  the  vessel  must  be  such  as  to  produce  a  pressure  out- 
wards, equal  to  the  external  pressure  tending  to  compress  the  vapour-bubble.  The 
boiling  point  of  the  liquid  will,  therefore,  be  higher  as  the  external  pressure  is 
greater. 

According  to  this  view  of  the  process  of  vapourization,  it  is  possible  that  vapour 
may  rise  from  a  solid  as  well  as  from  a  liquid ;  but  it  by  no  means  necessarily  fol- 
lows that  vapour  must  be  formed  from  all  bodies  at  all  temperatures.  The  force 
which  holds  together  the  molecules  of  a  body  may  be  too  great  to  be  overcome  by 
any  combination  of  molecular  movements,  so  long  as  the  temperature  does  not 
exceed  a  certain  limit. 

The  production  and  consumption  of  heat  which  accompany  changes  in  the  state 
of  aggregation,  or  of  the  volume  of  bodies,  are  easily  explained,  according  to  the 
preceding  principles,  by  taking  account  of  the  work  done  by  the  acting  forces. 
This  work  is  partly  external  to  the  body,  partly  internal.  To  consider  first  the 
internal  work  : 

When  the  molecules  of  a  body  change  their  relative  positions,  the  change  may 
take  place  either  in  accordance  with  or  in  opposition  to  the  action  of  the  molecular 
forces  existing  within  the  body.  In  the  former  case,  the  molecules,  during  the 
42 


658  POLARIZATION    OF    LIGHT. 

passage  from  one  state  to  the  other,  have  a  certain  velocity  imparted  to  thorn, 
which  is  immediately  converted  into  heat ;  in  the  latter  case,  the  velocity  of  their 
movement,  and  consequently  the  temperature  of  the  body,  is  diminished.  In  the 
passage  from  the  solid  to  the  liquid  state,  the  molecules,  although  not  removed 
from  the  spheres  of  their  mutual  attractions,  nevertheless  change  their  relative 
positions  in  opposition  to  the  molecular  forces,  which  forces  have,  therefore,  to  be 
overcome.  In  evaporation,  a  certain  number  of  the  molecules  are  completely  sepa- 
rated from  the  remainder,  which  again  implies  the  overcoming  of  opposing  forces. 
In  both  cases,  therefore,  work  is  done,  and  a  certain  portion  of  the  vis  viva  of  the 
molecules,  that  is,  of  the  heat  of  the  body,  is  lost.  But  when  once  the  perfect 
gaseous  state  is  attained,  the  molecular  forces  are  completely  overcome,  and  any 
further  expansion  may  take  place  without  internal  work,  and,  therefore,  without 
loss  of  heat,  provided  there  is  no  external  resistance. 

But  in  nearly  all  cases  of  change  of  state  or  volume,  there  is  a  certain  amount 
of  external  resistance  to  be  overcome,  and  a  corresponding  loss  of  heat.  When 
the  pressure  of  a  gas,  that  is  to  say,  the  impact  of  its  atoms,  is  exerted  against  a 
moveable  obstacle,  such  as  a  piston,  the  molecules  lose  just  so  much  of  their 
moving  power  as  they  have  imparted  to  the  piston,  and,  consequently,  their 
velocity  is  diminished  and  the  temperature  lowered.  On  the  contrary,  when  a 
gas  is  compressed  by  the  motion  of  a  piston,  its  molecules  are  driven  back  with 
greater  velocity  than  that  with  which  they  impinged  on  the  piston,  and  conse- 
quently, the  temperature  of  the  gas  is  raised. 

When  a  liquid  is  converted  into  vapour,  the  molecules  have  to  overcome  the 
Atmospheric  pressure  or  other  external  resistance,  and,  in  consequence  of  this, 
together  with  the  internal  work  already  spoken  of,  a  large  quantity  of  heat  dis- 
appears, or  is  rendered  latent,  the  quantity  thus  consumed  being  to  a  considerable 
extent  affected  by  the  external  pressure.  The  liquefaction  of  a  solid  not  being 
attended  with  much 'increase  of  volume,  involves  but  little  work;  nevertheless, 
the  atmospheric  pressure  does  influence,  in  a  slight  amount,  both  the  latent  heat 
jf  fusion  and  the  melting  point. 


LIGHT. 

POLARIZATION. 

The  phenomena  of  circular  polarization  have  lately  acquired  so  much  importance 
in  chemistry,  as  to  make  it  highly  necessary  for  the  student  to  be  acquainted  with 
them.  But  to  render  a  description  of  these  phenomena  intelligible,  a  few  elemen- 
tary explanations  of  the  subject  of  polarization,  in  general,  must  first  be  offered. 

Suppose  a  ray  of  light,  A  C  (fig.  209),  to  fall  upon  a  plate  of  glass  (not 
silvered,  but  blackened  at  the  lower  surface)  at  C,  making  an  angle  of  54^°  with 
the  normal  PC,  or  35 J°  with  the  reflecting  surface.  This  ray  will  be  reflected 
in  the  direction  C  D,  making  an  angle  P  C  D  =  A  C  P,  and  in  the  same  plane  as 
A  C  and  C  P.  Now  suppose  the  reflected  ray  to  fall  upon  a  second  surface  of 
glass  at  the  same  angle  of  54 £°  with  the  normal.  If,  then,  the  second  mirror  be 
so  placed,  that  its  plane  of  reflection  is  parallel  to  the  plane  of  reflection  from  the 
first  surface  (see  left-hand  figure),  then  the  ray  will  be  reflected  from  the  second 
surface  in  the  direction  D  E,  just  as  if  it  proceeded  directly  from  a  luminous 
source,  and  had  not  undergone  previous  reflection  ;  but  if  the  second  mirror  be  so. 
adjusted  that  its  plane  of  reflection  is  perpendicular  to  that  of  the  first  (see  right- 
hand  figure),  then  the  ray,  C  D,  will  not  be  reflected  from  it  at  all.  In  inter- 
mediate positions,  still  at  the  same  angle  of  incidence,  the  ray,  C  D,  will  be  par- 


POLARIZATION    OF    LIGHT. 


659 


FIG.  209. 


tially  reflected,  the  quantity  of  light  in  the  reflected  ray,  D  E,  being  greater  as 
the  planes  of  reflection  of  the  two  mirrors  are  more  nearly  parallel. 

The  ray,  after  reflection  from  glass  at  an  angle  of  54£°,  appears  then  to  exhibit 
different  properties,  according  to  the  direction  in  which  it  is  a  second  time  re- 
flected ;  one  side  of  the  ray  appearing  to  be  reflectible,  and  the  other  side  not  so. 
The  ray  has  now  different  properties  on  different  sides,  and  is  said  to  be  polarized. 

The  angle,  54£°,  is  called  the  polarizing  angle  for  glass.  For  every  medium 
there  is  a  particular  polarizing  angle,  the  magnitude  of  which  depends  upon  the 
refracting  power  of  the  medium.*  Now,  as  the  different  coloured  rays  which 
compose  white  light,  differ  in  refrangibility  (p.  99),  there  must  be  for  each 
coloured  ray  a  distinct  polarizing  angle.  Hence  it  is  evident  that  only  homoge- 
neous light  can  be  completely  polarized  by  reflection.  Solar  light,  or  ordinary 
gas  or  candle-light,  can  never  be  made  to  disappear  completely  in  the  manner 
above  mentioned. 

The  plane  in  which  a  polarized  ray  is  most  easily  reflected  is  called  its  plane 
vf  polarization :  it  coincides  with  the  plane  of  reflection  (or  of  incidence). 

Light  is  also  polarized  by  refraction,  and  the  refracted  ray  is  polarized  in  a 
plane  perpendicular  to  the  plane  of  refraction,  or  of  incidence,  and,  therefore, 
also  perpendicular  to  the  plane  of  polarization  of  the  reflected  ray ;  so  that  it 
would  be  reflected  from  a  surface  of  glass  at  an  angle  of  54£°,  just  under  the  cir- 
cumstances in  which  the  ray  polarized  by  reflection  would  not.  Light,  however, 
is  never  completely  polarized  by  one  refraction ;  but  by  successive  refractions 
through  a  number  of  surfaces  of  glass,  or  other  medium,  it  may  be  brought 
within  any  assigned  limit  of  complete  polarization. 

All  crystalline  bodies  not  belonging  to  the  regular  system,  possess  the  power  of 
double  refraction  (p.  99),  that  is  to  say,  a  ray  of  light  entering  such  a  medium 


*  In  all  cases,  the  polarizing  angle,  AGP  (fig.  210),  is  that  for  which  the  refracted  ray, 
C  D,  is  perpendicular  to  the  reflected  ray,  C  B.     Let  TO 
denote  the  index  of  refraction,  then :  j?ICL  210. 

sin  AGP 


but  angle  A  C  P  =  B  C  P  [  =  0]  ;  and  since  B  C  is  per- 
pendicular to  C  D,  and  Q  C  to  C  N,  angle  Q  C  D  =  B  C  N 
—  90°  —  0-  therefore 


sin  0 

m  =  -  =  tan  6  ; 


that  is  to  say,  the  polarizing  anyle  is  the  angle  whose  tan- 
gent is  equal  to  the  index  of  refraction. 


660 


POLARIZATION    OF    LIGHT. 


is  split  up  into  two  rays  of  equal  intensity,  which  traverse  the  crystal  in  different 
directions.  In  all  such  media,  however,  there  are  either  one  or  two  directions  in 
which  double  refraction  does  not  take  place,  and  these  lines  are  called  the  optic 
axes  of  the  crystal.  Transparent  calcspar,  or  Iceland  spar,  which  crystallizes  in 
rhombohedrons,  and  exhibits  double  refraction  more  distinctly  than  any  other 
substance,  is  a  crystal  with  one  optic  axis,  the  direction  of  that  axis  being  parallel 
to  the  line  joining  the  obtuse  summits  of  the  rhomb.  A  ray  traversing  the  crystal 
in  a  direction  parallel  to  this  axis  is  not  divided  into  two ;  but  in  all  other  direc- 
tions the  ray  is  doubly  refracted  j  and  the  two  rays  into  which  it  is  thus  divided  are 
both  completely  polarized,  the  one  in  the  principal  section,  that  is  to  say,  in  a  plane 
passing  through  the  optic  axis  and  the  direction  in  which  the  ray  traverses  the  crystal  • 
the  other  at  right  angles  to  that  plane.  The  ray  which  is  polarized  in  the  prin- 
cipal section  follows  the  ordinary  laws  of  refraction,  remaining  always  in  the  plane 
of  incidence,  and  having  for  all  incidences  a  constant  index  of  refraction ;  but 
the  ray  polarized  perpendicularly  to  the  principal  section  follows  different  laws  of 
refraction,  its  direction  not  being  confined  within  the  plane  of  incidence,  unless 
that  plane  coincides  with  or  is  perpendicular  to  the  principal  section,  and  its  index 
of  refraction,  excepting  in  the  last-mentioned  case,  varying  continually  with  the 
angle  of  incidence.  The  former  of  these  rays  is  called  the  ordinary,  the  latter 
the  extraordinary  ray. 

When  these  two  oppositely  polarized  rays  fall  on  a  plate  of  glass  at  the  angle 
of  54J,  so  placed  that  the  plane  of  reflection  is  parallel  to  the  principal  section 
of  the  crystal,  the  ordinary  ray  is  reflected,  and  the  extraordinary  ray  is  not,  the 
contrary  effect  taking  place  when  these  planes  are  at  right  angles  to  each  other. 
When  the  plane  of  reflection  is  inclined  to  the  principal  section  at  any  angle 
between  0°  and  90°,  both  rays  are  reflected,  but  with  different  intensities. 

Nicliol's  Prism.. — It  is  often  desirable  to  get  rid  of  one  of  the  images  produced 
by  a  double-refracting  crystal.  This  is  effected  by  the  arrangement  shown  in  fig. 
211,  which  consists  of  two  similar  prisms  of  calcspar,  A  B  C  D,  C  D  E  F,  cemented 
together  with  Canada  balsam  at  the  faces,  C  D.  The 
faces,  A  B,  E  F,  are  cut  so  as  to  make  an  angle  of  68° 
with  the  obtuse  edges,  A  E,  B  F,  of  the  natural  crystal 
(the  natural  faces  make  an  angle  of  71°  with  the  obtuse 
edges),  and  the  faces,  C  D,  are  perpendicular  to  A  B  and 
E  F.  With  this  arrangement,  it  is  found  that  of  the  two 
rays,  n  o,  n  e,  into  which  an  incident  ray,  m  n,  is  divided, 
the  ordinary  ray,  n  o,  on  reaching  the  surface  of  Canada 
balsam  (whose  index  of  refraction  is  less  than  that  of  the 
ordinary  and  greater  than  that  of  the  extraordinary  ray), 
suffers  total  reflection  in  the  direction  o  P,  while  the  ex- 
traordinary ray  passes  on  in  the  direction  eft  and  emerges 
in  fg,  parallel  to  mn.  An  eye  placed  at/,  therefore, 
sees  but  one  image,  viz.,  that  formed  by  the  extraordinary 
ray.  This  apparatus,  called  a  NichoPs  prism,  is  of  great 
use  in  experiments  with  polarized  light.  For,  as  it  trans- 
mits only  the  extraordinary  ray,  a  beam  of  ordinary  light 
passing  through  it  will  be  polarized  in  a  plane  perpen- 
dicular to  the  principal  section  —  that 
is  to  say,  to  the  shorter  diagonal  of  the 
rhomb,  a  b  (fig.  212) ;  and  a  ray,  already 
polarized,  will  be  stopped  by  the  prism 
if  its  plane  of  polarization  is  parallel  to 
a  b,  but  will  pass  freely  through  it 
when  the  plane  of  polarization  is  perpen- 
dicular to  a  b,  or  parallel  to  the  longer 
diagonal,  c  d.  Hence,  also,  two  Nichol's 


FIG.  211. 


Fio.  212. 


POLARIZATION    OF    LIGHT.  661 

prisms,  placed  one  behind  the  other,  appear  perfectly  opaque  when  their  principal 
sections  are  at  right  angles  to  each  other,  perfectly  transparent  when  the  principal 
sections  are  parallel,  and  transmit  light  with  diminished  intensity  in  intermediate 
positions. 

Polarization  by  Tourmalines. — The  tourmaline,  which  is  a  crystallized  mineral 
having  one  optic  axis,  possesses  the  remarkable  property  of  transmitting  light 
only  when  polarized  in  a  plane  perpendicular  to  that  axis.  Hence,  a  plate  of 
tourmaline  cut  with  faces  parallel  to  the  optic  axis,  acts  exactly  like  a  Nichol's 
prism,  and  may  be  used  in  the  same  manner.  It  is,  however,  less  convenient,  on 
account  of  its  colour,  which,  in  the  best  tourmalines,  is  rather  a  dark  yellow- 
brown. 

Nature  of  Polarized  Light.  —  Light  is  supposed  to  consist  of  undulations  ex- 
cited in  an  ethereal  medium  pervading  all  space,  and  filling  up  the  intervals  be- 
tween the  particles  of  ponderable  bodies.  Moreover,  the  particles  of  this  ether 
are  supposed  to  vibrate,  not  in  the  direction  of  the  ray,  like  the  particles  of  air  in 
conveying  sound,  but  in  planes  at  right  angles  to  the  length  of  the  ray,  like  the 
transverse  vibrations  of  a  stretched  cord. 

Further,  the  difference  between  ordinary  and  polarized  light,  is  supposed  to  be 
this :  that  in  the  former,  the  particles  of  the  ether  vibrate  in  all  imaginable 
directions,  at  right  angles,  to  the  length  of  the  ray; 
while,  in  the  latter,  they  are  confined  to  one  particular  FIG.  213. 

plane.  Thus,  if  A  (fig.  213)  represents  the  projection 
of  an  unpolarized  ray,  travelling  at  right  angles  to  the 
plane  of  the  paper,  the  particles  of  the  ether  at  all 
points  of  this  ray  vibrate  parallel  to  the  plane  of  the 
paper,  but  some  may  move  in  the  direction  a  a',  others 
in  6  &',  c  c'j  d  df,  &c.  Now  imagine  all  these  vibra-  a 
tions  to  be  reduced  to  one  plane,  in  the  direction  a  a', 
for  example.  Then  the  ray  will  become  polarized. 
In  fact,  since  its  particles  now  vibrate  in  one  direction 
only,  it  is  no  longer  a  matter  of  indifference  whether 
the  ray  is  presented  to  a  reflecting  surface  on  one  side 
or  the  other;  whereas  the  unpolarized  ray,  whose  particles  vibrate  in  all  direc- 
tions, will  be  reflected  in  the  same  manner  on  whichever  side  it  meets  the  surface 
of  any  medium. 

Now,  from  considerations  into  which  we  cannot  at  present  enter,  it  is  found 
that  a  plate  of  tourmaline  transmits  only  those  vibrations  which  are  parallel  to  its 
axis.  Since  then,  a  ray  of  polarized  light  is  transmitted  through  a  tourmaline 
only  when  its  plane  of  polarization  is  perpendicular  to  the  axis  of  the  tourmaline 
(p.  660),  it  follows  that  the  plane  of  polarization  of  the  ray  is  perpendicular  to 
the  plane  of  vibration,  Hence,  also,  the  plane  of  vibration  of  a  ray  polarized  by 
reflection  is  at  right  angles  to  the  plane  of  incidence  (or  of  reflection) ;  the  plane 
of  vibration  of  a  ray  polarized  by  refraction  is  parallel  to  the  plane  of  incidence ; 
and  of  the  two  rays  into  which  a  beam  of  light  is  divided  by  double  refraction 
through  a  rhomb  of  calcspar,  the  ordinary  ray  vibrates  at  right  angles  to  the 
principal  section,  and  the  extraordinary  ray  parallel  to  that  section.  The  vibra- 
tions of  a  ray  polarized,  by  passing  through  a  Nichol's  prism,  are,  therefore, 
parallel  to  the  principal  section,  that  is,  to  the  shorter  diagonal  of  the  prism  (fie. 
212). 

Let  m  n  (fig.  214),  be  the  plane  of  vibration  of  a  polarized  ray  moving  at  right 
angles  to  the  plane  of  the  paper,  and  meeting  it  at  the  point  a.  If  this  ray  enters 
a  plate  of  tourmaline,  whose  axis  is  parallel  to  m  n}  or  a  Nichol's  prism,  whose 
principal  section  is  in  that  direction,  the  ray  will  be  transmitted  with  its  full  in- 
tensity. But  if  the  axis  of  the  tourmaline  or  the  principal  section  of  the  prism 
be  turned  round  into  the  position  m!  n',  the  intensity  of  the  transmitted  light  will 
be  diminished,  because  the  tourmaline  or  the  prism  will  only  transmit  vibrations 


662  CIRCULAR    POLARIZATION. 

in  the  direction  a  m,  and  there  is  always  a  loss  of  power  in  changing  the  direction 
of  motion.     Let  a  I  represent  the  utmost  length  of  the  excursion  of  a  particle  of 

the  ether  in  the  original  direction  of  vibration,  in 
other  words,  the  original  intensity  of  the  light. 
Draw  b  c  at  right  angles  to  a  m' ;  then  a  c  repre- 
sents the  component  of  the  force  a  b  in  the  direc- 
tion a  m',  and  a  c  is  clearly  less  than  a  b.  If  the 
tourmaline  or  the  prism  be  turned  still  further  into 
the  position  m"  n"  the  reduced  portion  of  the  in- 
tensity ad  will  be  found  to  be  still  less;  and, 
lastly,  when  the  axis  or  the  principal  section  is  per- 
pendicular to  m  n,  the  reduced  portion  of  the  motion 
becomes  equal  to  nothing,  and  there  is  no  light 
transmitted.  Generally,  if  u  be  the  original  in- 
tensity of  the  light,  and  8  the  angle  between  the 
old  and  new  planes  of  vibration,  the  reduced  intensity  will  be  u  cos  8. 

Circular  Polarization. — Some  media  possess  the  singular  property  of  changing 
the  direction  of  vibration  of  a  ray  of  polarized  light;  in  other  words,  of  causing 
the  plane  of  polarization  to  rotate  through  a  certain  angle,  either  to  the  right  or 
to  the  left.  This  property  is  exhibited  in  a  remarkable  degree,  by  quartz  or  rock- 
crystal,  a  mineral  which  crystallizes  in  six-sided  prisms  terminated  by  six-sided 
pyramids,  the  axis  being  a  straight  line  joining  the  two  pyramidal  summits. 
Suppose  now,  a  ray  polarized  by  passing  through  a  Nichol's  prism  to  be  viewed 
through  another  such  prism,  having  its  principal  section  at  right  angles  to  that  of 
the  first.  The  field  will,  of  course,  appear  dark.  Then  let  a  plate  of  quartz, 
bounded  by  parallel  faces  cut  perpendicularly  to  its  axis,  be  interposed  between 
the  two  prisms.  Immediately  the  field  of  view  will  appear  brilliantly  illuminated 
and  coloured,  exhibiting  a  tint  of  red,  yellow,  green,  blue,  &c.,  according  to  the 
thickness  of  the  quartz-plate.  If  the  Nichol's  prism,  which  serves  as  the  eye- 
piece, be  turned  on  its  axis,  the  colours  will  go  through  the  regular  prismatic 
series,  from  red  to  violet,  or  the  contrary,  according  to  the  direction  of  rotation ; 
but  no  alteration  of  colour  is  produced  by  rotating  the  quartz-plate  while  the  eye- 
piece remains  stationary.  Exactly  similar  effects  are  produced  if  either  of  the 
Nichol's  prisms  be  replaced  by  a  tourmaline  or  a  glass  reflector,  or  a  bundle  of 
glass  plates  which  polarize  by  ordinary  refraction ;  but  the  two  Nichol's  prisms 
form  by  far  the  most  convenient  apparatus,  and  we  shall  therefore  suppose  them 
to  be  always  used.  For  distinction,  the  one  is  called  the  polarizing  prism  or 
polarizer,  the  other,  the  eye-piece. 

To  understand  the  phenomena  just  described,  we  must  examine  what  takes 
place  when  homogeneous  light  is  used.  Suppose,  then,  a  plate  of  dark-red  glass 
coloured  with  red  oxide  of  copper,  to  be  interposed  anywhere  between  the  two 
prisms  placed  as  before,  with  their  principal  sections  at  right  angles,  so  that  no 
light  is  transmitted  by  the  eye-piece.  On  interposing  the  plate  of  quartz,  a  red 
light  immediately  makes  its  appearance,  and,  to  render  the  field  again  dark,  it  is 
necessary  to  turn  the  eye-piece  through  a  certain  angle,  either  to  the  right  or  to 
the  left.  Now,  as  the  Nichol's  prism  stops  a  ray  of  light  only  when  the  plane  of 
vibration  of  that  ray  is  perpendicular  to  its  principal  section,  it  follows  that  the 
ray  which  has  traversed  the  quartz  must  have  had  its  plane  of  vibration  thereby 
deflected  through  an  angle  equal  to  that  through  which  the  eye-piece  has  been 
moved.  This  effect  is  called  circular  polarization. 

Precisely  similar  effects  are  produced  with  yellow,  green,  violet,  or  any  other 
kind  of  homogeneous  light;  but  the  angle  of  rotation  varies  according  to  tho 
nature  of  the  ray,  being  least  for  red,  and  greatest  for  violet  light. 

Some  crystals  of  quartz  rotate  the  plane  of  polarization  of  a  ray  to  the  right, 
others  to  the  left;  the  former  are  called  right-handed,  the  latter  left-handed 
quartz.  But  in  whichever  direction  the  rotation  takes  place,  a  plate  of  quartz  of 


CIRCULAR    POLARIZATION. 


663 


given  thickness  always  produces  the  same  amount  of  angular  deviation  for  a  ray 
of  given  refrangibility ;  and  for  plates  of  different  thickness,  the  deviation  for  any 
particular  ray  increases  in  direct  proportion  to  the  thickness.  The  following  table 
gives  the  angles  of  deviation  for  the  principal  rays  of  the  spectrum  produced  by 
plates  of  quartz  of  the  thickness  of  1  millimeter  and  3-75  millimetres. 


Colours. 

Angle  of  rotation. 

Plate 
1  mm.  thick. 

Plate 
3  75  mm.  thick. 

Medium  red  

15° 
19 
24 
27 
32 
38 
44 

56^° 
71J 
90 
101  J- 
120 
142J 
165 

blue             

indigo  

violet... 

We  can  now  explain  the  succession  of  colours  produced  when  ordinary  daylight 
is  used.  Suppose  a  beam  of  white  light,  polarized  by  a  Nichol's  prism,  whose 
principal  section  is  parallel  to  A  A'  (fig.  215),  to  pass  through  a  plate  of  right- 
handed  quartz,  3-75  mm.  thick.  The  vibrations  of 
the  several  coloured  rays  composing  the  beam  of 
polarized  light,  are  all  at  first  parallel  to  A  A';  but 
by  passing  through  the  quartz,  their  planes  of  vibra- 
tion are  deflected  through  the  several  angles  given 
in  the  above  table,  the  red  ray  then  vibrating  in  the 
line  r  /,  the  yellow  in  yy',  the  violet  in  vv',  &c. 
Now,  let  the  ray  be  viewed  through  another  Nichol's 
prism,  placed  with  its  principal  section  also  parallel 
to  A  A' ;  then,  by  reference  to  the  explanation  given 
at  page  661,  it  will  be  seen  that  the  red  and  violet 
rays  will  be  transmitted  with  but  slightly  diminished 
intensity,  the  orange  and  blue  with  less,  the  yellow 
with  still  less,  and  the  green  not  at  all.  The  result 
will,  therefore,  be  a  purple  tint.  Now  let  the  eye- 
piece be  turned  from  left  to  right.  As  the  principal 
section  passes  successively  over  the  lines  rr',oof, 
&c.,  the  red,  orange,  yellow,  &c.,  will,  in  succession,  be  more  fully  transmitted 
than  the  other  rays,  so  that  a  succession  of  tints  will  be  produced  agreeing  nearly 
with  the  colours  of  the  spectrum,  and  following  in  the  same  order,  from  red  through 
yellow  to  violet.  If  the  eye-piece  be  turned  the  contrary  way,  the  order  of  the 
tints  will  be  reversed.  If  the  quartz  were  left-handed,  the  phenomena  would  be 
precisely  similar,  excepting  that  the  colours  would  change  from  red  through  yellow 
to  violet,  when  the  eye-piece  was  turned  from  right  to  left. 

Similar  changes  of  colour  will  be  produced  with  a  plate  of  quartz  of  any  other 
thickness ;  but  the  tint  produced  at  any  given  inclination  of  the  polarizer  and 
eye-piece,  will  of  course  be  different. 

The  tint  produced  with  a  quartz  plate  of  3-75  mm.  thick,  when  the  principal 
sections  of  the  polarizer  and  eye-piece  are  parallel  to  one  another,  deserves  par- 
ticular notice.  This  tint,  as  already  observed,  is  a  purple,  and  moreover  changes 
very  quickly  to  red  or  to  violet,  when  the  eye-piece  is  turned  one  way  or  the  other, 
the  change  of  colour  thus  produced  being,  in  fact,  very  much  more  rapid  and 
decided  than  in  any  other  part  of  the  circuit.  It  is  accordingly  distinguished  by 
the  term  sensitive-tint,  or  transition-tint  (couleur  sensible,  teinte  de passage).  Ou 
account  of  the  facility  and  certainty  with  which  it  may  be  recognized,  it  is  fre- 
quently adopted  as  the  standard  tint  in  measuring  the  angles  of  rotation  produced 
by  different  substances ;  it  is,  in  fact,  much  easier  to  determine  when  this  particu- 


6G4  CIRCULAR    POLARIZATION. 

lar  colour  makes  its  appearance,  than  to  seize  the  exact  moment  when  a  ray  of  red, 
yellow,  or  other  homogeneous  light  completely  disappears. 

The  rotatory  power  of  quartz  is  essentially  related  to  its  crystalline  form.  It  is 
not  exhibited  by  opal,  or  any  other  amorphous  variety  of  silica,  or  by  silica  dis- 
solved in  potash  or  fused  by  the  oxy-hydrogen  blowpipe.  The  same  is  true  with 
regard  to  a  few  other  inorganic  compounds  possessing  the  rotatory  power,  viz., 
chlorate  of  soda,  bromate  of  soda,  and  acetate  of  uranic  oxide  and  soda;  these 
salts  exhibiting  that  power  only  when  crystallized,  not  in  solution. 

Circular  Polarization  in  Organic  Bodies.  —  The  power  of  rotating  the  plane 
of  vibration  of  a  polarized  ray,  is  much  more  widely  diffused  in  the  organic,  than 
in  the  inorganic  world ;  moreover,  inorganic  bodies  possess  it  in  the  liquid,  as  well 
as  in  the  crystalline  state.  Among  organic  compounds  which  rotate  the  plane  of 
polarization  to  the  right,  may  be  mentioned :  —  Cane-sugar,  grape-sugar,  diabetic 
sugar,  milk-sugar,  dextrin,  camphor,  asparagin,  cinchonine,  quinidine,  narcotine, 
tartaric  acid,  camphoric  acid,  aspartic  acid,  oil  of  lemons,  castor-oil,  croton-oil. 
The  following  rotate  to  the  left:  —  uncrystallizable  sugar  of  fruits,  starch,  albu- 
men, amygdalin,  quinine,  nicotine,  strychnine,  brucine,  morphine,  codeine,  malic 
acid,  anti-tartaric  acid,  oil  of  turpentine,  oil  of  valerian. 

By  passing  a  polarized  ray  through  tubes  of  different  lengths,  filled  with  the 
same  solution  of  cane-sugar,  or  other  rotatory  substance,  it  is  .found  that  the  angle 
of  deviation  is  proportional  to  the  length  of  the  column  of  liquid;  and,  by  filling 
the  same  tube  with  solutions  containing  different  quantities  of  sugar,  &c.,  it  is 
found  that  the  angle  of  deviation  is  proportional  to  the  quantity  of  the  substance 
contained  in  a  column  of  given  length.  Generally,  then,  the  angle  of  deviation 
is  proportionate  to  the  number  of  active  particles  which  the  light  has  to  pass. 

If,  then,  s  be  the  quantity  of  active  substance  contained  in  a  unit  of  weight  of 
the  solution,  I  the  length  of  the  column,  and  a  the  observed  angle  of  rotation  for 
a  particular  tint,  the  transition-tint,  for  example,  the  angle  of  rotation  for  the  unit 
of  length,  and  supposing  the  entire  column  to  be  filled  with  the  optically  active 

substance,  will  be  — -.     But  as  the  solution  of  a  substance  is  often  attended  with 
s  I 

condensation  of  volume,  it  is  best,  in  order  to  obtain  a  measure  of  the  rotatory 
power,  independent  of  such  irregularities,  to  refer  the  observed  angle  of  deviation 

to  a  hypothetical  unit  of  density,  that  is  to  say,  to  divide  the  quantity  —  by  the 

.  si 

density  8  of  the  solution.     The  fraction  thus  obtained,  viz.,  [a]  =  — — ,  is  called 

the  specific  rotatory  power,  and  expresses  the  angle  of  rotation  which  the  pure 
substance  in  a  column  of  the  unit  of  length  and  density  =  1  would  impart  to  the 
ray  corresponding  to  the  transition-tint.  For  example,  a  solution  containing  155 
milligrammes  of  cane-sugar  in  a  gramme  of  liquid,  has  a  specific  gravity  =  1-06, 
and  deflects  the  transition-tint  by  24°,  in  a  column  20  centimeters  long ;  its  specific 

rotatory  power  is  therefore  — 

94 

[1  _ 7-8° 
~  0-155  .  20  .  1-06  ~ 

Saccharimetry.  —  An  important  practical  application  of  the  principles  just 
explained  relates  to  the  determination  of  the  quantity  of  sugar  contained  in  sac- 

Fia.  216. 


sharine  solutions.     The  apparatus  used  for  this  purpose  consists  of  a  glass  tube 
(fig.  216),  surrounded  with  a  case  of  wood  or  brass,  and  closed  at  both  ends  with 


CIRCULAR    POLARIZATION. 


665 


plate-glass  discs  ground  to  fit  water-tight  and  pressed  against  the  tube  by  means 
of  screw-caps.  The  tube  being  completely  filled  with  the  liquid,  is  placed  on  the 
supports,  c  d  (fig.  217),  between  two  Nichol's  prisms,  one  of  which,  A,  serves  as  a 


FIG.  217. 


polarizer,  the  other,  B,  as  an  eye-piece.  The  latter  carries  a  vernier,  m,  moving 
round  a  graduated  circle.  The  simplest  way  of  using  this  apparatus  is  to  inter- 
pose between  the  tube  and  the  polarizer  a  glass  coloured  with  sub-oxide  of  copper, 
the  tint  of  which  corresponds  with  the  red  of  the  fixed  line  C  of  the  spectrum  — 
and  having  set  the  eye-piece  with  its  principal  section  at  right  angles  to  that  of 
the  polarizer  (which  makes  the  field  of  view  dark  so  long  as  the  tube  is  not  inter- 
posed), to  adjust  the  tube  in  its  place,  and  turn  the  eye-piece  round  till  the  red  light 
completely  disappears.  The  angle  through  which  the  eye-piece  is  turned  mea- 
sures the  deviation  produced  by  the  saccharine  liquid. 

A  solution  of  164-71  grammes  of  pure  and  dry  cane-sugar  in  a  litre  of  water, 
produces  in  a  tube,  20  centimetres  long,  an  optical  effect  equal  to  that  of  a  plate 
of  right-handed  quartz,  1  millimeter  thick,  that  is  to  say,  it  turns  the  plane  of 
polarization  of  the  red  ray  corresponding  to  the  fixed  line  C,  through  an  angle  of 
15-3°.  Hence,  if  any  other  solution  of  cane-sugar  in  a  tube  of  the  same  length 
produces  a  deviation  of  a  degrees,  one  litre  of  that  solution  will  contain 

.164-71  grammes  of  sugar. 


The  direct  measurement  of  the  rotation  of  the  red  ray  is,  however,  by  no  means 
the  best  mode  of  observation,  because,  as  already  observed  (p.  664),  it  is  difficult 
to  tell  with  precision  when  the  light  completely  disappears.  For  this  reason  it  is 
better  to  introduce  behind  the  polarizing  prism,  instead  of  the  red  glass,  a  plate 
of  quartz  3-75  millimeters  thick,  which,  when  the  polarizer  and  eye-piece  are  set 
with  their  principal  sections  parallel,  exhibits  the  transition-tint.  The  interposi- 
tion of  the  saccharine  liquid,  which  rotates  to  the  right,  causes  this  tint  to  change; 
and  the  rotation  is  measured  by  the  number  of  degrees  through  which  the  prism 
must  be  turned  to  restore  the  transition-tint. 

Greater  exactness  is  obtained  by  using  a  double  plate  of  quartz  3-75  millimeters 


666  CIRCULAR    POLARIZATION. 

thick,  one-half  being  composed  of  right-handed,  the  other  half  of  left-handed 
quartz.  Such  a  plate  will  exhibit  the  transition-tint  with  perfect  uniformity  on 
both  halves,  when  the  polarizer  and  eye-piece  are  set  with  their  principal  sections 
parallel;  but  on  turning  the  eye-piece  to  the  right,  one-half  of  the  plate  will 
incline  to  red,  and  the  other  to  blue.  The  same  change  will,  of  course,  take 
place  on  introducing  the  tube  containing  the  saccharine  liquid ;  and  to  restore  the 
uniformity  of  tint,  the  eye-piece  must  be  turned  a  certain  number  of  degrees  the 
contrary  way.  If  the  liquid  has  but  a  slight  rotatory  power,  this  method  is  quite 
satisfactory ;  but  if  the  rotatory  power  is  considerable,  an  error  arises  from,  the 
different  angles  of  rotation  imparted  to  the  different  coloured  rays. 

To  obviate  this  last  source  of  inaccuracy,  a  contrivance,  called  the  compensator, 
has  been  invented.     It  consists  of  two  prismatic  plates  of  quartz,  rr'(fig.  218), 

FIG.  218. 


having  their  faces,  c  c  ,  perpendicular  to  the  crystallographic  axis,  and  the  oppo- 
site faces  inclined  to  this  axis  at  equal  angles.  These  prisms  are  introduced  into 
the  polarizing  apparatus  between  the  tube  and  the  eye-piece,  and  one  of  them  is 
made  to  slide  over  the  other  by  means  of  a  rack  and  pinion,  so  that  the  two 
together  form  a  plate  of  variable  thickness.  To  the  frame  of  one  of  these  prisms 
is  attached  a  linear  scale,  a  &,  and  to  the  other  an  index,  or  a  vernier,  v  v'.  One 
hundred  divisions  of  the  scale  correspond  to  an  increase  of  1  millimeter  in  the 
thickness  of  the  compound  plate.  Suppose  now  these  two  prisms  to  consist  of 
left-handed  quartz ;  a  flat  plate  of  right-handed  quartz,  whose  thickness  is  equal  to 
that  of  the  two  compensating  prisms  together  when  the  index  points  to  0°,  is  like- 
wise introduced  between  the  tube  and  the  eye-piece.  This  plate  then  completely 
neutralizes  the  action  of  the  compensator,  and  the  effect  is  the  same  as  if  neither 
the  compensator  nor  the  plate  of  right-handed  quartz  were  introduced,  the  double 
quartz-plate  (p.  665)  still  exhibiting  the  transition-tint  on  its  two  halves,  when  the 
tube  containing  the  saccharine  solution  is  not  in  its  place.  Now  let  the  tube  con- 
taining the  dextro-rotatory  saccharine  liquid  be  introduced.  Immediately  the  two 
halves  of  the  double-plate  assume  different  colours;  and  to  restore  the  uniformity 
of  tint,  the  compensator  must  be  shifted  so  as  to  give  the  combined  left-handed 
prisms  a  greater  thickness.  Suppose  that,  to  produce  this  compensation,  the 
index  is  moved  through  eighteen  divisions  of  the  scale.  Then  the  rotatory  action 
of  the  liquid  in  the  tube  is  equal  to  that  of  a  quartz-plate  having  a  thickness  of 
J^  Of  a  millimeter,  that  is  to  say,  it  turns  the  red  ray  through  an  angle  of 
15-3°  x  T'<f0  =  2|°. 

In  order  that  the  preceding  method  may  be  directly  applied  to  determine  the 
strength  of  a  solution  of  any  optically  active  substance,  it  is  necessary :  1.  That 
the  solution  contain  only  one  such  substance.  2.  That  the  quantity  of  the  active 
substance  present  be  proportioned  to  the  angle  of  rotation.  3.  That  the  rotation 
of  the  red  ray  be  known  for  one  given  degree  of  concentration. 

Now,  in  determining  the  quantity  of  crystallizable  sugar  in  the  syrups  obtained 
from  plants,  in  molasses,  &c.,  a  difficulty  arises  from  the  presence  of  other  kinds 
of  sugar,  viz.,  glucose,  and,  more  especially,  the  un crystallizable  sugar  of  fruits, 
which  rotates  to  the  left.  This  difficulty  may,  in  most  cases,  be  obviated  by 


CIRCULAR    POLARIZATION.  667 

boiling  the  liquid  with  hydrochloric  acid,  whereby  the  crystallizable  sugar  (cane- 
sugar)  is  converted  into  the  laevo-rotatory  sugar  of  fruits,  while  the  other  kinds  of 
sugar  remain  unaltered.  The  rotatory  power  of  cane-sugar  is  not  sensibly  affected 
by  heat;  but  that  of  uncrystallizable  sugar  decreases  considerably  as  the  tempera- 
ture rises.  Thus  when  cane-sugar  is  heated  with  hydrochloric  acid  to  68°  C.,  the 
resulting  fruit-sugar  exhibits  at  different  temperatures  the  following  rotatory 
powers  :  — 

Temperature  ...........  .................................  10°       15°       20°       25°        30°  35° 

Rotatory  power  (that  of  cane-sugar)  —  100°  ......  39        36         34        3-15       29     26-5 

Suppose,  now,  a  solution  of  cane-sugar  containing  164-71  grammes  in  a  litre, 
which,  in  a  column  20  centimeters  long,  deflects  the  red  ray  15-3°  to  the  right, 
to  be  heated  to  68°  C.,  with  y^  of  its  volume  of  hydrochloric  acid,  and  the  liquid, 
after  cooling  to  15°  C.,  to  be  introduced  into  the  polarizing  apparatus  in  a  tube  22 
centimeters  long,  which  will  contain  the  same  number  of  atoms  of  sugar  as  a  tube 
20  centimeters  long  of  the  liquid  before  the  addition  of  the  acid.  The  red  ray 
will  then  be  deflected  to  the  left  by  0-36  x  15-3°  =  5-5°.  Consequently,  the 
difference  in  the  positions  of  the  eye-piece  before  and  after  the  conversion  will 
amount  to  15'3°  +  5-5°  =  20-8°. 

If,  then,  any  mixed  solution  of  cane-sugar  and  uncrystallizable  fruit-sugar, 
taining  164-71  grammes  of  sugar  in  a  litre,  be  treated  as  above,  and  the  difference 
in  the  positions  in  the  eye-piece  before  and  after  the  conversion  be  5  '2°,  the 
temperature  being  15°  C.,  the  amount  of  crystallizable  sugar  in  the  mixture  is 

~  .  164-71  =  41-2  grammes.* 

ZO'o 

If  the  mixture  contains  grape  or  starch-sugar  mixed  with  cane-sugar,  it  must 
be  heated  to  80°  C.  before  being  introduced  into  the  saccharimeter,  because  the 
rotatory  power  of  grape  or  starch-sugar  decreases  considerably  after  a  while  at 
ordinary  temperatures,  but  quickly  attains  its  minimum  value  when  the  liquid  is 
heated  to  80°. 

If  grape  or  starch-sugar  is  present,  together  with  uncrystallizable  fruit-sugar, 
the  problem  is  indeterminate,  because  neither  of  these  sugars  has  its  rotating 
action  reversed  by  treatment  with  acids. 

The  following  table  contains  a  few  of  the  results  obtained  by  the  method  just 
described.  If  the  liquid  to  be  examined  contains  nothing  but  crystallizable  sugar, 
we  have  merely  to  look  in  the  last  column  but  one  for  the  number  of  degrees  read 
off  on  the  compensator;  and  the  corresponding  number  in  the  last  column  gives 
the  number  of  grammes  of  sugar  in  a  litre  of  the  liquid.  If  other  optically  active 
substances  are  present,  and  inversion  is  consequently  necessary,  the  results  are 
found  by  means  of  the  readings  in  the  first  six  columns. 

*  Let  n  be  the  observed  deviation  before  inversion,  n'  the  dextro-rotation  produced  by  the 
crystallizable  sugar,  nff  the  laevo-rotation  produced  by  the  uncrystallizable  fruit-sugar. 
Also,  let  Wj  be  the  observed  deviation  in  a  column  of  liquid  of  the  same  length,  after  the 
liquid  has  been  heated  with  T'n  of  its  volume  of  hydrochloric  acid  ;  and  suppose  that  a 
quantity  of  cane-sugar  which  produces  a  deviation  of  nf  to  the  right,  yields,  when  thus 
treated,  a  quantity  of  uncrystallizable  sugar,  which  produces  a  deviation  of  Knf  to  the  left 
at  15°  C.,  K=  0-36).  Then,  for  the  determination  of  nf  and  n",  we  have  the  two  equations  :  — 

n  =  n'  —  n" 
VX  =  «"+£>»' 

A  mixture  of  cane-sugar  with  starch-sugar  or  grape-sugar  may  be  treated  in  exactly  the 
same  manner,  since  only  the  cane-sugar  has  its  direction  of  rotation  reversed  ;  and  in  this 
case,  n'  and  n"  will  be  determined  by  the  equations  :  — 


n  =  n'  -f-  n 


" 


668 


CIRCULAR    POLARIZATION. 


TABLE  FOR  THE  ANALYSIS  OF  SACCHARINE  SOLUTIONS.* 


Sum  or  difference  of  the  readings  before  and  after  the  inversion  of  the 
sugar,  the  last  reading  being  made  at  the  temperature  of 

Degrees. 

Grammes 
of  sugar 
in  a  litre. 

10° 

15° 

20° 

25° 

30° 

35° 

1-4 

1-4 

1-3 

1-3 

1-3 

1-3 

1 

1-64 

13-9 

13-6 

13-4 

13.1 

12-9 

12-6 

10 

16-47 

27-8 

27-3 

26-8 

26-3 

25-8 

25-3 

20 

32-94 

41-7 

40-9 

40-2 

39-4 

38-7 

37-9 

30 

49-41 

55-6 

54-6 

53-6 

52-6 

51-6 

50-6 

40 

65-88 

69-5 

68-2 

67-0 

65-7 

64-5 

63-2 

50 

82-35 

83-4 

81-9 

80-4 

78-9 

77-4 

75-9 

60 

98-82 

'       97-3 

95-5 

93-8 

92-0 

90-3 

88-5 

70 

115-29 

111-2 

109-2 

107-2 

105-2 

103-2 

101-2 

80 

131-76 

125-1 

122-8 

120-6 

118-3 

116-1 

113-9 

90 

148-23 

139-0 

136-5 

134-0 

131-5 

129-0 

126-5 

100 

164-71 

152-9 

150-1 

147-4 

144-6 

141-9 

139-1 

110 

181-18 

166-8 

163-8 

160-8 

157-8 

'  154-8 

151-8 

120 

191-65 

180-7 

177-4 

174-2 

170-9 

167-7 

164-4 

130 

214-21 

Relations  between  Rotatory  Power  and  Crystalline  Form. — It  has  already  been 
observed  that  silica  and  a  few  other  inorganic  bodies  exhibit  circular  polarization, 
only  when  crystallized.  Moreover,  crystals  of  the  same  substance  —  quartz,  for 
example  —  which  exert  opposite  actions  on  polarized  light,  often  exhibit  a  remark- 
able opposition  in  their  crystalline  forms.  Thus,  the  ordinary  form  of  quartz,  the 
gix-sided  prism  with  pyramidal  six-sided  summits,  is  sometimes  found  modified  in 
the  manner  shown  in  figs.  219,  220,  the  solid  angles  formed  by  the  meeting  of  two 


FIG.  219. 


FIG.  220. 


pyramidal  with  two  prismatic  faces,  being  truncated  with  faces,  a,  obliquely 
inclined  to  the  faces  of  the  prism  j  these  truncation  faces,  however,  are  only  six 
in  number,  whereas  to  form  a  complete  holohedral  combination  (since  these  faces 
are  unequally  inclined  to  those  of  the  prism),  there  should  be  twenty-four  of  them, 
two  at  each  of  the  twelve  angles  above-mentioned  :  the  form  is  therefore  tetarto- 
hedral. f  But,  further,  these  tetartohedral  faces  are  not  always  placed  alike, 

*  This  table  is  extracted  from  the  much  more  extensive  one  given  in  the  "  Trait6  de  Chimie 
Ge*n4rale,"  par  Pelouze  et  Fremy.  Paris,  1855,  t.  iv.  pp.  620-622. 

•}•  Holohedral  forms  are  those  which  are  bounded  by  similar  faces  occurring  in  the  greatest 
possible  number  consistent  with  the  law  of  symmetry  which  determines  their  position ;  if 
the  number  of  such  faces  is  only  one-half  of  what  it  might  be,  the  form  is  hemihedral;  if  only 
one-fourth,  it  is  tetartohedral.  The  regular  octohedron  is  a  holohedral  crystal,  and  the 
tetrahedron  is  the  hemihedral  form  corresponding  to  it;  similarly,  the  rhombohedron  is  the 
hemihedral  form  of  the  double  six-sided  pyramid.  Hemihedral  and  tetartohedral  forms 
tften  occur  associated  with  holohedral  forms  in  the  same  crystal. 


CIRCULAR    POLARIZATION. 


669 


occurring  in  some  crystals  on  the  right  of  a  prismatic  face  above,  and  on  the  left 
below,  and  the  contrary  in  others,  as  shown  in  the  above  figures.  The  two  forms 
of  crystal  thus  produced,  though  their  faces  are  alike  in  number  and  in  form,  are 
evidently  not  superposible,  but  the  one  may  be  regarded  as  the  reflected  image  of 
the  other.  Now,  the  crystals  of  the  one  kind  invariably  exhibit  dextro-rotatory, 
and  those  of  the  other  kind  laevo-rotatory,  power.  The  same  kind  of  opposite 
tetartohedry,  and  accompanied  by  a  corresponding  opposition  of  rotatory  power,  is 
found  in  the  few  other  inorganic  compounds  (p.  664)  which  exhibit  circular 
polarization. 

This  remarkable  relation  between  rotatory  power  and  crystalline  form  is,  how- 
ever, much  more  strikingly  exhibited  by  certain  organic  compounds. 

Tartaric  acid  and  its  salts  turn  the  plane  of  polarization  to  the  right :  racemic 
acid,  which  is  identical  in  chemical  composition  with  tartaric  acid,  and  agrees 
with  it  in  nearly  all  its  chemical  relations,  has  no  action  whatever  on  polarized 
light,  either  in  the  free  state  of  the  acid  or  when  combined  with  bases.  Now,  the 
crystals  of  tartaric  acid  and  the  tartrates  are  hemihedral,  those  of  racemic  acid 
and  the  rac.emates,  with  one  exception,  are  holohedral.  The  exception  alluded  to 
is  the  racemate  of  soda  and  ammonia.  A  solution  of  racemate  of  soda  and  race- 
mate  of  ammonia,  in  equivalent  proportions,  yields  by  evaporation  crystals  of  a 
double  salt,  the  form  of  which  is  represented  in  figs.  221,  222. 


FIG.  221. 


It  is  a  right  rectangular  prism  P,  M,  T,  having  its  lateral  edges  replaced  by 
the  faces  5',  and  the  intersection  of  these  latter  faces,  with  the  face  T,  replaced 
by  a  face  h.  If  the  crystal,  were  holohedral,  there  would  be  eight  of  these  faces, 
four  above,  and  four  below;  but,  as  the  figures  shows  there  are  but  four  of  them, 
placed  alternately :  moreover,  these  hemihedral  faces  occupy  in  different  crystals, 
not  similar,  but  opposite  positions;  so  that,  as  in  the  case  of  quartz,  the  one  kind 
of  crystal  is,  as  it  were,  the  reflected  image  of  the  other. 

But  further;  by  carefully  picking  out  the  two  kinds  of  crystals,  and  dissolving 
them  separately  in  water,  solutions  are  obtained,  which,  at  the  same  degree  of 
concentration,  exert  equal  and  opposite  actions  upon  polarized  light,  the  one  de- 
flecting the  plane  of  polarization  to  the  right,  the  other,  by  an  equal  amount,  to 
the  left.  Moreover,  the  solutions  of  the  right  and  left-handed  crystals,  yield,  by 
evaporation,  crystals,  each  of  its  own  kind  only;  and  by  mixing  the  solutions  of 
these  crystals  with  chloride  of  calcium,  lime-salts  are  obtained,  which,  when  de- 
composed by  sulphuric  acid,  yield  acids,  agreeing  with  each  other  in  composition, 
and  in  every  other  respect,  except  that  their  crystalline  forms  exhibit  opposite 
hemihedral  modifications,  and  their  solutions,  when  reduced  to  the  same  degree 
of  concentration,  exhibit  equal  and  opposite  effects  on  polarized  light. 

Of  the  two  acids  thus  obtained,  the  one  which  turns  the  plane  of  polarization 
to  the  right  is  identical  in  every  respect  with  ordinary  tartaric  acid.  The  other 
may  be  called,  for  distinction,  antitartaric  acid.  When  equal  weights  of  these 
two  acids  are  dissolved  in  water,  and  the  solutions  mixed,  a  liquid  is  obtained, 
which  has  no  action  whatever  on  polarized  light,  and  yields  by  evaporation,  holo- 


670  CIRCULAR  POLARIZATION. 

hedral  crystals  of  racemic  acid.  A  similar  result  is  obtained  by  mixing  equal 
quantities  of  any  of  the  salts  of  the  two  acids,  excepting  the  double  salt  of  soda 
and  ammonia. 

Hence  it  appears  that  racemic  acid,  a  body  which  has  no  action  upon  polarized 
light,  and  crystallizes  in  holohedral  forms,  is  a  compound  of  two  acids  (tartaric 
and  antitartaric),*  which  have  equal  and  opposite  effects  on  polarized  light,  and 
crystallize  in  similar  but  opposite  hemihedral  forms.  There  is  also  another 
property  in  which  these  acids  differ,  viz.,  in  their  pyro-electric  relations.  The 
crystals  of  both  these  acids  become  electric  when  heated,  but  the  corresponding 
extremities  of  the  two  exhibit  opposite  electrical  states.  Racemic  acid  is  not 
pyro-electric. 

Tartaric  acid  may  be  converted  into  racemic  acid  by  the  action  of  heat,  pro- 
vided only  it  be  associated  with  some  substance  which  will  enable  it  to  bear  a 
somewhat  high  temperature  without  decomposing.  There  are  many  substances 
whose  effect  on  polarized  light  is  altered  by  heat.  This  is  remarkably  the  case 
with  the  alkaloids  of  the  cinchona  bark.  When  cinchonine,  or  any  of  its  salts 
(which  rotate  to  the  right),  is  heated  in  such  a  manner  as  not  to  produce  decom- 
position, it  is  transformed  into  an  isomeric  alkaloid,  cinchonicine,  which  turns  the 
plane  of  polarization  to  the  left.  Similarly,  quinine,  which  rotates  the  plane  of 
polarization  to  the  left,  is  converted  by  heat  into  quinicine,  which  turns  it  to  the 
right.  Now,  when  tartrate  of  cinchonine  is  heated,  it  is  first  converted  into 
tartrate  of  cinchonicine,  and  if  the  heat  be  then  continued,  the  change  extends 
to  the  tartaric  acid,  half  of  which  is  converted  into  antitartaric  acid.  If  the  pro- 
cess be  stopped  at  a  certaint  point,  and  the  fused  mass  treated  with  water,  a  solu- 
tion is  obtained  which  yields,  first,  crystals  of  antitartrate,  and  afterwards,  of  tar- 
trate of  cinchonicine.  But  if  the  heat  be  longer  continued,  the  two  acids  unite, 
and  form  racemate  of  cinchonicine,  from  which  raceuiic  acid  may  be  prepared, 
identical  in  every  respect  with  ordinary  racemic  acid,  and  separable  by  the  same 
means  into  the  two  opposite  tartaric  acids. 

But,  what  is  very  remarkable,  there  is  formed  at  the  same  time  a  modification 
of  tartaric  acid,  which  has  no  action  whatever  on  polarized  light,  and  yet  is  not 
separable  into  the  two  opposite  acids.  In  fact,  when  the  fused  mass  obtained  by 
heating  tartrate  of  cinchonine  is  treated  with  water,  and  chloride  of  calcium 
added,  a  precipitate  is  formed,  consisting  of  racemate  of  lime,  and  the  filtrate,  if 
left  at  rest,  deposits  crystals  of  the  lime-salt  of  inactive  tartaric  acid. 

There  are  other  organic  compounds  which  are  also  optically  active  in  their 
ordinary  forms,  but  exhibit  inactive  and  inseparable  modifications.  Malic  acid, 
as  it  exists  in  fruits,  turns  the  plane  of  polarization  to  the  right;  so  likewise  does 
aspartic  acid  obtained  by  the  action  of  acids  and  alkalies  on  asparagin.  Now  both 
these  acids  may  be  formed  from  fumaric  acid,  an  optically  inactive  substance. 
Acid  fumarate  of  ammonia  is  C8H3(NH4)08=C8H7N08,  which  is  also  the  formula 
of  aspartic  acid,  and  this  acid  is  actually  formed  by  heating  the  acid  fumarate  of 
ammonia.  But  the  aspartic  acid  thus  produced  is,  like  fumaric  acid,  optically 
inactive.  Again,  aspartic  acid  is  converted  into  malic  acid  by  the  action  of 
nitrous  acid : — 

C8H7N08  +  N03  -  C8  H6  O10  +  2N  +  HO. 

Aspartic  acid.  Malic  acid. 

Both  active  and  inactive  aspartic  acids  undergo  this  transformation ;  but  active 
aspartic  acid  yields  active  malic  acid,  and  inactive  aspartic  acid  yields  inactive 
malic  acid.  Neither  inactive  aspartic  nor  inactive  malic  acid  can  be  separated 
into  two  acids  oppositely  active. 

Common  oil  of  turpentine  possesses  considerable  dextrorotatory  power;  but  the 

*  Thence  also  called  respectively  dezlro-racemic  and  Icevo-racemic  acids. 


FLUORESCENCE.  671 

isomeric  substance  obtained  by  heating  the  artificial  solid  camphor  of  turpentine 
with  quick-lime  is  optically  inactive. 

Fusel  oil  has  lately  been  shown  by  Pasteur  to  be  a  mixture  of  two  kinds  of 
amylic  alcohol,  which  differ  slightly  in  boiling  point.  One  of  these  alcohols  is 
optically  active,  the  other  inactive. 

Rotatory  Power  induced  by  Magnetic  Action. — Faraday  has  made  the  remark- 
able discovery,  that  bodies  which,  in  their  ordinary  state,  exert  no  particular  action 
on  polarized  light,  acquire  the  circular-polarizing  structure  when  subjected  to  the 
action  of  powerful  electric  or  magnetic  forces.  A  polarized  ray  passing  along  the 
axis  of  a  prism  or  cylinder  of  any  transparent  substance,  such  as  water  or  glass, 
has  its  plane  of  polarization  deflected  to  the  right  or  left,  as  soon  as  the  medium 
is  subjected  to  -the  action  of  an  electric  current  passing  round  it  at  right  angles  to 
the  axis,  or  to  that  of  two  powerful  opposite  magnetic  poles,  so  placed  that  their 
line  of  junction  shall  be  parallel  to  the  axis  of  the  column  of  the  transparent  sub- 
stance. The  rotation  ceases  as  soon  as  the  electric  or  magnetic  force  ceases  to  act  j 
its  amount  varies  directly  as  the  strength  of  the  current;  and  its  direction  changes 
with  that  of  the  current  or  of  the  magnetic  force.  If  the  medium  has  a  rotatory 
power  of  its  own,  the  total  effect  is  equal  to  the  sum  or  difference  of  the  natural 
and  induced  rotations,  according  as  the  electric  or  magnetic  force  acts  with  or 
against  the  natural  rotatory  power  of  the  medium. 

CHANGE    OF   REFRANGIBILITY   OF   LIGHT.  —  FLUORESCENCE. 

It  was  observed  some  years  ago  by  Sir  John  Herschel,  that  a  solution  of  sul- 
phate of  quinine,  though  perfectly  colourless  by  transmitted  light,  exhibits  in  cer- 
tain aspects  a  peculiar  blue  colour.  This  blue  light  was  found  to  be  produced 
only  by  a  very  thin  stratum  of  the  liquid  adjacent  to  the  surface  by  which  the 
light  entered ;  and  the  incident  beam,  after  having  passed  through  the  stratum 
from  which  the  blue  light  came,  was  not  sensibly  weakened  or  coloured,  but  had 
lost  the  power  of  producing  the  usual  blue  colour  when  admitted  into  another 
solution  of  sulphate  of  quinine.  Light  thus  modified  was  said  by  Sir  J.  Herschel 
to  be  eptpolized. 

Similar  phenomena  were  observed  by  Sir  D.  Brewster  in  an  alcoholic  solution 
of  chlorophyll,  the  green  colouring  matter  of  leaves,  the  path  of  a  beam  of  sun- 
light admitted  into  the  green  solution  being  marked  by  a  bright  light  of  a  blood- 
red  colour.  The  same  appearance  was  afterwards  observed  in  various  vegetable 
solutions  and  essential  oils,  and  in  some  solids.  Brewster  distinguished  this  phe- 
nomenon by  the  name  of  internal  dispersion,  attributing  it  to  the  irregular  reflec- 
tion of  the  light  from  coloured  particles  suspended  in  the  liquid,  and  was  of 
opinion  that  Eterschel's  epipolic  dispersion  was  only  a  particular  case  of  this  in- 
ternal dispersion. 

The  true  explanation  of  these  remarkable  phenomena  has,  however,  been  given 
by  Professor  Stokes,*  who  has  submitted  the  whole  subject  to  the  most  searching 
investigation,  and  shown  that  the  peculiar  dispersion  produced  by  sulphate  of 
quinine,  and  the  other  liquids  above  mentioned,  is  due  to  a  change  of  re/ran- 
gibility  in  the  rays  of  light.  The  following  experiment  renders  this  evident :  — 

A  solar  spectrum  is  formed  by  means  of  an  achromatic  lens,  and  one  or  more 
prisms  of  flint  glass,  sufficiently  pure  to  render  visible  the  principal  fixed  lines, 
and  a  tube  filled  with  a  solution  of  sulphate  of  quinine  is  passed  along  this  spec- 
trum, from  the  red  towards  the  violet  end.  Nothing  peculiar  is  observed  while 
the  tube  is  held  in  the  less  refrangible  part  of  the  spectrum,  the  light  passing 
through  it  freely  and  without  sensible  modification  ;  but  just  before  it  reaches  the 
extremity  of  the  violet,  a  peculiar  blue  diffused  light  makes  its  appearance  at  the 
surface  of  the  fluid  by  which  the  light  enters,  and  remains  visible  even  after  the 

*  Phil.  Trans.  1852,  ii.  463. 


672  FLUORESCENCE. 

tube  has  passed  beyond  the  violet  into  the  invisible  portion  of  the  spectrum,  ac- 
quiring in  fact  its  greatest  intensity  at  a  certain  distance  beyond  the  extreme 
violet. 

The  stratum  of  liquid  from  which  the  diffused  blue  light  emanates  is  thinner  in 
proportion  as  the  incident  rays  are  more  refrangible;  and,  from  a  little  beyond  the 
extreme  violet  to  the  end  of  the  spectrum,  the  blue  space  is  reduced  to  an  exces- 
sively thin  stratum  adjacent  to  the  surface  by  which  the  rays  enter.  It  appears,  there- 
fore, that  the  solution,  though  transparent  with  respect  to  nearly  the  whole  of  the 
visible  rays,  is  of  an  inky  blackness  with  respect  to  the  invisible  rays  more  infran- 
gible than  the  violet.  Nevertheless,  these  rays,  when  once  they  have  been  con- 
verted into  the  visible  blue  light,  pass  through  the  liquid  with  facility.  They 
must,  therefore,  be  essentially  altered  in  character.  Now  a  change  in  the  quality 
of  light  must  consist,  either  in  a  modification  of  its  state  of  polarization,  or  in  its 
period  of  undulation.  The  former  supposition  is  excluded  by  the  fact  that  the 
light  thus  modified  is  not  polarized  at  all.  It  must,  therefore,  have  undergone  a 
change  in  its  rate  of  vibration,  and  consequently  a  change  of  refrangibility.  The 
existence  of  this  change  is,  moreover,  distinctly  proved  by  examining  the  diffused 
light  with  a  prism.  It  is  then  found  to  be  by  no  means  homogeneous,  but  to  be 
resolvable  into  rays  of  unequal  refrangibility,  the  whole  of  which  are  however 
comprised  within  the  limits  of  the  visible  spectrum.  The  diffused  blue  light  con- 
sists of  the  chemical  rays  rendered  visible  by  a  change  in  their  refrangibility. 

The  diffusion  thus  produced  is  entirely  distinct  from  that  which  is  due  to  reflec- 
tion from  irregularities  or  suspended  particles.  The  two  phenomena  are  often 
produced  together  in  the  same  medium  ;  but  they  are  easily  distinguished  by  the 
fact  that  the  light  diffused  by  irregular  reflection  is  more  or  less  polarized, 
whereas  the  light  diffused  in  the  manner  above  described  is  entirely  unpolarrzed, 
even  if  the  incident  rays  were  themselves  polarized.  This  phenomenon,  to  which 
Professor  Stokes  originally  gave  the  name  of  true  diffusion,  to  distinguish  it  from 
the  false  diffusion  produced  by  irregular  reflection,  is  now  called  FLUORESCENCE. 

It  is  exhibited  by  many  solutions,  and  by  many  solid  bodies,  opaque  as  well  as 
transparent,  the  colour  of  the  diffused  light  varying  with  the  nature  of  the  medium. 
An  aqueous  infusion  of  horse-chesnut  bark  exhibits  it  very  strongly,  producing 
the  same  blue  colour  as  sulphate  of  quinine.  Many  compounds  of  sesquioxide  of 
uranium  are  also  highly  fluorescent,  and  diffuse  a  greenish-blue  light,  especially 
the  nitrate,  and  canary-glass  (p.  556).  A  decoction  of  madder  mixed  with  alum 
gives  a  yellow  or  orange-yellow  fluorescence ;  tincture  of  turmeric  and  alcoholic 
extract  of  thorn-apple  seeds  diffuse  a  greenish  light ;  an  alcoholic  solution  of  chlo- 
rophyll, a  red  light. 

When  the  fluorescence  is  strong,  as  with  sulphate  of  quinine,  it  may  be  seen 
by  merely  viewing  the  substance  by  ordinary  diffused  daylight  For  more  accurate 
observation,  and  for  detecting  fluorescence  when  it  exists  only  in  a  slight  degree, 
the  following  method  is  recommended  by  Professor  Stokes  :  *  — 

Light  is  admitted  into  a  darkened  room  through  a  hole  several  inches  in  diame- 
ter in  the  window  shutter,  and  the  object  to  be  examined  is  placed  on  a  small 
shelf,  blackened  at  the  top,  and  fixed  just  below.  The  hole  is  covered  with  an 
absorbing  medium,  called  the  principal  absorbent,  so  selected  as  to  transmit  only 
the  feebly  luminous  and  invisible  rays  of  high  refrangibility.  The  body  on  the 
shelf  is  viewed  through  the  second  medium,  the  complementary  absorbent,  which 
is  chosen  so  as  to  be  as  transparent  as  possible  to  those  rays  which  are  absorbed 
by  the  first,  and  to  absorb  all  the  rays  which  are  transmitted  by  the  first.  If  the 
media  are  well  selected,  they  produce  a  very  near  approach  to  perfect  darkness ; 
and  if  the  object  appears  unduly  luminous,  that  effect  most  probably  arises  from 
fluorescence.  To  determine  whether  the  illumination  is  really  due  to  that  cause, 
the  complementary  absorbent  is  removed  from  before  the  eyes  to  the  front  of  the 

*  Phil.  Mag.  [4],  vi.  304. 


SPECTRA  PRODUCED  BY  COLOURED  MEDIA.     673 

aperture,  when  the  illumination,  if  really  due  to  fluorescence,  almost  wholly  dis- 
appears ;  whereas,  if  it  be  due  merely  to  scattered  light  capable  of  passing  through 
both  media,  it  remains.  In  examining  feebly  fluorescent  substances,  however,  it 
is  better  to  keep  the  second  medium  in  its  place  before  the  eye,  and  to  use  a  third 
medium,  the  transfer-medium,  placing  the  last  alternately  in  the  path  of  the  inci- 
dent rays,  and  between  the  object  and  the  eye.  Still  greater  delicacy  of  observa- 
tion is  attained  by  placing  the  substance  side  by  side  with  a  small  white  porcelain 
tablet,  which  is  quite  destitute  of  fluorescence,  and  examining  the  two  as^  above. 
Or,  again,  the  object  being  placed  on  the  tablet,  a  slit  is  held  close  to  it,  in  such 
a  position  as  to  be  seen  projected,  partly  on  the  object,  partly  on  the  tablet,  and 
the  slit  is  viewed  through  a  prism.  The  fluorescence  of  the  object  is  evidenced 
by  light  appearing  in  regions  of  the  spectrum,  in  which  the  rays  coming  through 
the  principal  absorbent,  and  scattered  by  the  tablet,  produce  nothing  but  dark- 
ness. These  methods  are  delicate  enough  to  show  the  fluorescence  of  white 
paper,  even  on  a  very  gloomy  day. 

It  is  not  merely  the  most  refrangible  rays  that  are  capable  of  producing  fluores- 
cence; the  rays  of  any  part  of  the  spectrum  may  undergo  this  change.  By 
examining  different  media  with  the  spectrum  in  the  manner  already  described,  it 
is  seen  that  the  fluorescence  begins,  sometimes  in  the  blue,  sometimes  in  the 
yellow.  With  an  alcoholic  solution  of  chlorophyll,  it  begins  in  the  red.  But 
wherever  the  change  of  refrangibility  may  begin,  it  is  always  in  one  direction, 
consisting  in  a  diminution  of  the  index  of  refractien,  and  a  consequent  depression 
of  the  light  in  the  scale  of  colours.  In  other  words,  the  length  of  the  wave  is 
increased,  and  its  velocity  of  undulation  diminished.  The  vibrations  of  the  ether 
in  the  incident  ray  appear  to  excite  disturbances  within  the  complex  molecules  of 
the  fluorescent  medium,  whereby  new  vibrations  are  excited  in  the  ether,  differ- 
ing in  period  from  those  of  the  incident  ray.  The  portion  of  the  light  which  has 
produced  this  molecular  disturbance  is  used  up,  or  absorbed,  and  thereby  lost  to 
visual  perception,  just  as  heat  is  converted  into  mechanical  work.  It  is  probable 
that  the  absorption  of  light  always  takes  place  in  this  manner.  The  well-known 
fact  of  the  conversion  of  luminous  rays  into  invisible  calorific  rays,  is  a  striking 
instance  of  diminution  of  refrangibility  accompanied  by  absorption. 

As  the  most  refrangible  rays  are  the  most  active  in  producing  fluorescence,  it 
is  natural  that  this  effect  should  be  most  strikingly  exhibited  by  the  light  of 
flames  which  are  rich  in  those  rays,  —  the  flame  of  alcohol  and  of  sulphur,  for 
example.  These  flames  do,  in  fact,  produce  the  effect  in  a  higher  degree  even 
than  sunlight.  An  extremely  beautiful  effect  is  produced  by  exposing  a  number 
of  highly  fluorescent  media,  such  as  sulphate  of  quinine,  infusion  of  horse-chesnut 
bark,  'and  canary-glass,  to  the  flame  of  sulphur  burning  in  oxygen  in  a  dark  room. 
The  similarity  of  the  blue  light  diffused  by  most  fluorescent  media  to  the  phos- 
phorescence exhibited  by  certain  bodies,  might  lead  us  to  suppose  that  the  two 
phenomena  proceed  from  the  same  cause.  Such,  however,  is  not  the  case :  for 
fluorescence  is  entirely  dependent  on  the  incidence  of  certain  rays,  whereas  phos- 
phorescence is  not;  and,  moreover,  there  is  no  apparent  connection  between 
fluorescent  and  phosphorescent  bodies.  So  far  as  observation  has  yet  gone, 
phosphorescent  bodies  are  not  fluorescent. 

SPECTRA   EXHIBITED   BY   COLOURED   MEDIA. 

The  colour  of  an  object  depends  upon  the  rays  which  it  reflects  or  transmits  to 
the  eye  ;  it  is,  in  fact,  the  mixture  or  resultant  of  all  the  rays  which  the  body  does 
not  absorb.  We  cannot,  however,  from  observation  with  the  unassisted  eye,  judge 
with  certainty  of  the  rays  which  are  transmitted  or  reflected  ;  because  the  same, 
or  nearly  the  same,  compound  tint  may  result  from  the  union  of  very  different 
primary  colours.  Thus  a  body  may  exhibit  an  indigo  or  violet  tint,  either  because 
it  absorbs  all  the  rays  excepting  those  which  form  the  indigo  or  violet  portions  of 


674 


SPECTRA  PRODUCED  BY  COLOURED  MEDIA. 


the  spectrum,  or  because  it  reflects  or  transmits  the  red  and  blue  rays  in  certain 
proportions ;  similarly,  a  green  colour  may  be  the  pure  green  of  the  spectrum,  or 
a  mixture  of  yellow  and  blue.  In  such  cases,  examination  with  the  prism  will 
show  of  what  primary  rays  the  colour  is  composed,  and  may  thus  afford  the  means 
of  distinguishing  between  substances  which,  to  ordinary  observation,  appear  of  the 
same  colour. 

Dr.  Gladstone,  who  has  lately  made  some  very  interesting  observations  on  the 
absorption  of  light  by  coloured  liquids,*  introduces  the  liquid  into  a  wedge-shaped 
vessel  placed  before  a  slit  in  the  window-shutter  of  a  darkened  room,  so  that  the 
line  of  light  may  be  seen  through  various  thicknesses  of  the  liquid,  from  the 
thinnest  possible  film  to  a  stratum  perhaps  three-quarters  of  an  inch  thick,  and 
examines  this  line  of  coloured  light  with  a  prism  held  with  its  refracting  angle 
parallel  to  the  line  of  light.  The  whitish  portion  of  the  line,  where  the  light  tra- 
verses but  a  thin  film  of  the  liquid,  is  thereby  expanded  into  a  spectrum  differing 
but  little  from  that  which  is  given  by  unaltered  daylight;  but  as  the  line  of  light 
is  viewed  through  deeper  portions  of  the  liquid,  some  rays  are  seen  to  diminish  in 
intensity,  others  gradually  to  die  out,  while  others  almost  immediately  disappear, 
giving  place  to  perfect  darkness.  With  a  good  prism,  on  a  tolerably  clear  day, 
the  most  conspicuous  of  Fraunhofer's  lines  may  be  seen.  The  appearances  pre- 
sented may  be  understood  from  the  following  representations  of  the  effects  pro- 
duced by  solutions  of  sesquichloride  of  chromium  (fig.  223),  and  permanganate 
of  potash  (fig.  224). f  The  right-hand  side  of  these  figures  corresponds  with  the 
red  extremity  of  the  spectrum  :  the  letters  refer  to  Fraunhofer's  lines. 


FIG.  223. 


FIG.  224. 


A  comparison  of  the  spectra  exhibited  by  different  salts,  only  one  constituent 
of  which  is  coloured,  shows  that,  with  very  few  exceptions,  all  the  compounds  of 
the  same  base  or  acid  have  the  same  effect  on  the  rays  of  light.  This  law  is  seen 
to  hold  good  in  many  instances  which  at  first  sight  appear  exceptional.  Thus  it 
is  well  known  that  some  salts  of  chromic  oxide  are  green,  others  red  or  purple. 
Now  these  differently-coloured  chromic  salts  all  exhibit  the  same  general  form  of 
spectrum  (fig.  223),  in  which  the  violet  and  indigo  rays  are  very  soon  cut  off;  and 
as  the  thickness  increases,  the  light  is  more  and  more  concentrated  about  two 
points,  one  in  the  red,  the  other  in  the  bluish  green,  the  red  ray  penetrating  with 
the  greatest  facility.  Hence  it  is  that  the  chloride  an.d  other  salts  of  chromium, 
which  are  green  in  moderately  dilute  solutions,  appear  purple  or  red  when  we  look 
through  a  strong  or  very  deep  solution.  The  acetate  absorbs  the  green  rays  more 
readily,  and  therefore  appears  green  only  in  very  weak  solutions,  or  in  thin  strata, 

*  Chem.  Soc.  Qu.  J.  x.  79. 

f  For  representations  of  the  spectra  exhibited  by  a  considerable  number  of  coloured 
liquids,  see  Dr.  Gladstone's  paper  above  referred  to. 


MEASUREMENT   OF   THE   CHEMICAL   ACTION   OF   LIGHT.          675 

while  the  "red  potassio-oxalate  "  absorbs  the  green  so  speedily  that  the  thinnest 
portion  of  it  appears  bluish  red. 

Salts  composed  <*f  a  coloured  base  and  a  coloured  acid  exhibit  colours  com- 
pounded of  the  rays  which  are  not  absorbed  by  either,  the  resultant  colour  bear- 
ing, in  many  instances,  but  little  resemblance  to  the  original  colours.  Thus,  the 
acid  chromate  of  chromic  oxide,  a  compound  of  two  substances  which  give  re- 
spectively yellow  and  green  solutions,  is  not  bright  green,  but  brownish-red, 
because  the  chromic  acid  cuts  off  nearly  all  the  blue  and  violet  rays,  while  the 
oxide  of  chromium  absorbs  the  yellow  and  the  greater  part  of  the  green. 

Some  salts,  which  are  but  slightly  coloured,  nevertheless  exhibit  very  characte- 
ristic spectra.  Thus,  a  solution  of  sulphate  of  didymium,  which  has  but  a  faint 
rose  colour,  exhibits,  when  examined  by  the  hollow  wedge  and  prism,  a  spectrum 
containing  two  very  black  lines,  one  in  the  yellow,  the  other  in  the  green.  These 
lines  are  visible  in  very  weak  solutions  of  didymium,  and  therefore  serve  as  a 
delicate  test  for  that  metal ;  they  moreover  afford  the  means  of  distinguishing  it 
from  cerium  and  lanthanum,  in  the  spectra  of  which  they  do  not  occur. 


MEASUREMENT   OF   THE    CHEMICAL   ACTION   OF   LIGHT. 

Chlorine  and  hydrogen  combine  under  the  influence  of  light,  and  form  hydro- 
chloric acid.  Moreover,  if  the  gaseous  mixture  is  in  contact  with  water,  the  re- 
sulting hydrochloric  acid  is  immediately  absorbed,  and  the  diminution  of  volume 
thus  produced  affords  a  measure  of  the  amount  of  chemical  action.  This  mode 
uf  measurement  was  first  adopted  by  Dr.  Draper,  of  New  York,  whose  experi- 
ments led  to  the  important  conclusion  that  the  chemical  action  of  light  varies  in 
direct  proportion  to  the  intensity  of  the  light)  and  to  the  time  of  exposure. 

But  to  give  to  this  method  all  the  exactness  of  which  it  is  susceptible,  certain 
conditions  require  to  be  fulfilled  ;  the  chief  of  which  are  perfect  uniformity  in  the 
gaseous  mixture,  constancy  of  pressure  on  the  gas  and  liquids  throughout  the 
apparatus,  and  elimination  of  the  disturbing  action  of  radiant  heat.  These  and 
other  essential  conditions  are  completely  fulfilled  in  the  apparatus  used  by  Pro- 
fessor Bunsen  and  Dr.  H.  Roscoe,  in  their  late  elaboratere  searches  on  the  chemi- 
cal action  of  light.*  > 

This  apparatus  is  represented  in  figure  225.  To  furnish  the  mixture  of  chlo- 
rine and  hydrogen  gases  required,  hydrochloric  acid  is  decomposed  in  the  glass 
vessel  a,  containing  two  carbon  poles,  connected  by  platinum  wires  with  the  four- 
celled  Bunseo's  battery,  c.  Between  the  battery  and  this  vessel  is  interposed  an 
instrument  called  the  gyrotrope,  by  means  of  which  the  current  may  be  made  to  pass 
either  directly  through  the  acid  vessel  a,  or  previously  through  the  vessel  d  contain- 
ing very  slightly  acidulated  water,  whereby  the  current  is  greatly  weakened,  and 
the  evolution  of  gas  in  the  vessel  a  reduced  to  a  small  amount.  The  mixture  of 
chlorine  and  hydrogen  passes  from  the  vessel  a  through  the  washing-tube  w,  con- 
taining water,  then  forward  through  a  horizontal  tube  provided  with  a  glass  cock, 
7i,  into  the  insolation  vessel  i,  where  the  gases  are  exposed  to  the  action  of  light. 
The  lower  part  of  this  vessel,  containing  water,  is  blackened  to  protect  it  from 
the  action  of  the  light.  From  the  insolation  vessel,  the  gas  passes  through  the 
horizontal  measuring-tube  K,  provided  with  a  millimeter  scale,  then  through  the 
water  in  the  small  vessel  I,  and  finally  into  a  vessel  filled  with  fragments  of  char- 
coal and  hydrate  of  lime,  to  absorb  the  excess  of  chlorine. 

When  the  gas  is  made  to  stream  through  the  apparatus,  the  liquids  in  a,  w,  i, 
and  /,  become  gradually  saturated  with  gas;  and  as  the  saturation  goes  on,  the 
composition  of  the  gas  varies.  At  length,  however,  after  the  stream  of  gas  has 
been  continued  for  three  or  four  days,  the  liquids  become  saturated,  and  then  the 

*  Pogg.  Ann.  c.  43.  481  ;  abstr.     Proceedings  of  the  Royal  Society,  viii.  235,  236,  516. 


676 


MEASUREMENT  OF   THE   CHEMICAL  ACTION   OF   LIGHT. 


evolved  gas  is  found  to  consist  of  exactly  equal  volumes  of  chlorine  and  hydrogen. 
This  normal  state  having  been  attained,  the  apparatus  is  ready  for  use,  and  retains 

its  constant  sensibility  for  weeks, 
requiring  only  a  short  saturation 
each  day,  previous  to  the  actual 
observations. 

To  make  an  observation,  the 
stopcock  h  is  closed,  and  the 
light  allowed  to  act  on  the  gas 
in  the  upper  part  of  the  vossel  i. 
Combination  then  takes  place, 
accompanied  by  diminution  of 
volume,  and  the  external  pres- 
sure forces  the  water  in  I  through 
the  tube  K  towards  i.  The  po- 
sition of  the  end  of  the  column 
in  the  scale  measures  the  dimi- 
nution of  volume. 

The  pressure  on  the  gas  in 
the  insolation  vessel  and  the 
measuring-tube  during  the  ob- 
servations, is  necessarily  uniform 
from  the  construction  of  the 
apparatus ;  but  it  is  further  ne- 
cessary that  uniformity  of  pres- 
sure be  ensured  in  all  parts  of 
the  apparatus  in  the  intervals 
between  the  observations }  other- 
wise the  composition  of  'the 
gaseous  mixture  will  be  altered, 
and  the  results  will  no  longer 
be  exact.  To  ensure  this  uni- 
formity of  pressure,  the  gas, 
after  the  stopcock  h  is  closed, 
is  made  to  pass  through  the 
bent  tube  m  vv,  containing  water, 
and  thence  through  the  tube  p, 
which  dips  under  the  water  in 
the  vessel  r,  the  pressure  being 
regulated  by  raising  or  depres- 
sing this  tube  through  the  ca- 
outchouc mouth-piece  t.  From 
the  vessel  F  the  gas*  is  -conveyed 
by  a  flexible  tube  into  the  con- 
densing vessel  G,  containing 
charcoal  and  hydrate  of  lime. 
As  soon  as  the  stopcock  h  is 

closed,  the  gyrotrope  wire  is  turned,  so  as  to  cause  the  current  to  pass  through 
the  vessel  d,  and  thereby  slacken  the  evolution  of  gas.  When  the  stopcock  h  is 
open,  the  gas  will  pass  one  way  or  the  other,  according  to  the  depth  at  which  the 
tube  p  is  immersed  below  the  water  in  F. 

To  prevent  any  disturbance  from  the  effects  of  radiant  heat,  the  light  from  a 
coal  gas  flame,  or  other  source,  after  being  condensed  by  the  convex  lens  m,  is 
made  to  pass  through  the  cylinder  n,  closed  with  plate-glass  ends,  and  filled  with 
water.  A  screen  is  placed  in  front  of  the  insolation  vessel,  to  prevent  radiation 
of  heat  from  the  body  of  the  observer;  and  this,  together  with  the  screen  L, 


PHOTO-CHEMICAL    INDUCTION.  677 

serves  also  to  prevent  radiation  from  external  objects.  The  heat  evolved  in  the 
insolation  vessel  by  the  combustion  of  the  mixed  gases,  was  found  by  direct  ex- 
periment, not  to  exert  any  sensible  influence  on  the  results.  All  the  parts  of  the 
apparatus  between  a  and  I  are  connected  by  ground-glass  joints  or  by  fusing;  no 
caoutchouc,  or  any  other  organic  matter,  which  could  be  acted  upon  by  the 
chlorine,  being  introduced,  excepting  in  those  parts  which  merely  serve  to  carry 
away  the  waste  gas. 

Photo-chemical  Induction.  —  On  exposing  the  gas  to  the  light,  the  quantity  of 
hydrochloric  acid  formed  does  not  at  once  attain  the  maximum  :  a  certain  time 
always  elapses  before  any  alternation  of  volume  is  perceptible ;  a  slight  alteration 
is,  however,  soon  observed,  and  this  gradually  increases  till  the  permanent  maxi- 
mum is  reached.  This  remarkable  fact  was  first  observed  by  Draper,  who  ex- 
plained it  by  supposing  that  the  chlorine  underwent,  by  exposure  to  light,  a  per- 
manent allotropic  modification,  in  which  it  possessed  more  than  usually  active  pro- 
perties. But  Bunsen  and  Roseoe  have  shown  that  neither  chlorine  nor  hydrogen, 
when  separately  insolated,  undergoes  any  such  modification,  no  difference  being 
indeed  perceptible  between  the  action  of  light  on  a  mixture  of  the  gases  which 
have  been  separately  insolated  before  mixing,  and  on  a  mixture  of  the  same  gases 
evolved  and  previously  kept  in  the  dark.  The  light  appears  then  to  act  by  in- 
creasing the  attraction  between  the  chemically  active  molecules,  or  by  overcoming 
certain  resistances  which  oppose  their  combination.  This  peculiar  action  is  called 
photo-chemical  induction. 

The  time  which  elapses  from  the  beginning  of  the  exposure  till  the  maximum 
action  is  attained,  varies  considerably  according  to  circumstances,  the  maximum 
being  sometimes  reached  in  fifteen  minutes,  sometimes  in  three  or  four  minutes. 
In  one  instance,  the  first  action  was  visible  only  after  six  minutes  insolation, 
whilst  in  some  experiments  a  considerable  action  was  observed  in  the  first 
minute. 

The  duration  of  the  inductive  action  varies  with  the  mass  of  the  gas,  and  with 
the  amount  of  light.  With  a  constant  quantity  of  light,  it  increases  with  the 
volume  of  the  exposed  gas.  With  a  constant  volume  of  gas  it  is  found  : — 1.  That 
the  time  necessary  to  effect  the  first  action  decreases  with  increase  of  light,  and  in 
a  greater  ratio  than  the  increase  of  light.  —  2.  That  the  time  which  elapses  until 
the  maximum  is  attained,  also  decreases  with  increase  of  light,  but  in  a  less  ratio. 
—3.  That  the  increase  of  the  induction  proceeds  at  first  in  an  expanding  series, 
and  then  converges  till  the  true  maximum  is  attained. 

The  condition  of  increased  combining  power  into  which  the  mixture  of  chlorine 
and  hydrogen  is  brought  by  the  action  of  light,  is  not  permanent ;  on  the  con- 
trary, the  resistance  to  combination  overcome  by  the  influence  of  the  light,  is  soon 
restored  when  the  gas  is  allowed  to  stand  in  the  dark. 

The  resistance  to  combination  which  prevents  the  union  of  the  gases  until  the 
action  is  assisted  by  light,  may  be  increased  by  various  circumstances,  especially 
by  the  presence  of  foreign  gases,  even  in  very  small  quantity.  An  excess  of 
TQ3o^  of  hydrogen  above  that  contained  in  the  normal  mixture,  reduces  the  action 
from  100  to  38.  Oxygen,  in  quantity  amounting  to  only  7^0  of  the  total  volume 
of  gas,  diminishes  the  action  from  100  to  4-7;  and  yj§a  reduces  it  from  100  to 
1-3.  An  excess  of  T-J-§o  of  chlorine  reduces  the  action  from  100  to  60-2;  and 
iWu  fr°m  100  to  41 '3-  A  small  quantity  of  hydrochloric  acid  gas  does  not 
produce  any  appreciable  diminution ;  T(fo^  of  the  non-insolated  mixture  reduces 
the  action  from  100  to  55. 

The  increase  in  the  rate  at  which  combination  goes  on  up  to  a  certain  point 
under  the  influence  of  light,  appears  to  arise,  not  from  any  peculiar  property  of 
light,  but  rather  from  the  mode  of  action  of  chemical  affinity  itself.  Chemical 
induction  is  in  fact  observed  in  cases  in  which  there  is  nothing  but  pure  chemical 
action  to  produce  the  alteration.  Thus,  when  a  dilute  aqueous  solution  of  bromine 


678  CHEMICAL    ACTION    OF    LIGHT. 

mixed  with  tartaric  acid  is  left  in  the  darli,  hydrobromic  acid  is  formed;  and,  by 
determining  the  amount  of  free  bromine  present  in  the  liquid  at  different  times,  it 
is  found  that  the  rate  at  which  the  production  of  hydrobromic  acid  goes  on  is  not 
uniform,  but  increases  up  to  a  certain  point,  according  to  a  law  similar  to  that 
which  is  observed  in  photo-chemical  induction. 

These  phenomena  seem  to  point  to  the  conclusion  that  the  affinity  between  any 
two  bodies  is  in  itself  a  force  of  constant  amount,  but  that  its  action  is  liable  to 
be  modified  by  opposing  forces,  similar  to  those  which  affect  the  conduction  of 
heat  or  electricity,  or  the  distribution  of  magnetism  in  steel.  We  overcome  these 
resistances  when  we  accelerate  the  formation  of  a  precipitate  by  agitation,  or  a 
decomposition  by  insolation. 

Optical  and  Chemical  Extinction  of  the  Chemical  Rays.  —  When  light  passes 
through  any  medium,  part  of  it  is  lost  by  reflection  at  the  surface,  another  portion 
by  absorption  within  the  medium,  so  that  the  quantity  of  emergent  light  is  only  a 
fraction  of  the  incident  light.  This  is  true  with  regard  to  the  chemical  as  well  as 
to  the  luminous  rays.  By  passing  light  from  a  constant  source  through  cylinders 
with  plate-glass  ends  filled  with  dry  chlorine,  it  is  found  that,  with  a  given  length 
of  cylinder,  the  quantity  of  the  chemical  rays  transmitted,  when  no  chemical 
action  takes  place,  is  to  the  quantity  in  the  incident  light  in  a  constant  ratio ;  in 
other  words,  the  absorption  of  the  chemical  rays  is  proportional  to  the  intensity  of 
the  light.  It  is  also  found  that  the  quantity  of  chemical  rays  transmitted  varies 
proportionally  to  the  density  of  the  absorbing  medium. 

But  further,  when  light  passes  through  a  medium  in  which  it  excites  chemical 
action,  it  is  found  that,  in  adition  to  the  optical  extinction  already  spoken  of,  a 
quantity  of  light  is  lost  proportional  to  the  amount  of  chemical  action  produced. 
The  depth  of  pure  chlorine  at  0°  C.  and  0'76  mm.  pressure,  through  which  the 
light  of  a  coal-gas  flame  must  pass  in  order  to  be  reduced  to  y1^,  is  found  to  be 
173-3  millimeters.  Hence,  since  the  quantity  of  light  absorbed  varies  as  the 
density,  the  depth  of  chlorine  diluted  with  an  equal  volume  of  air,  or  other 
chemically  inactive  gas,  required  to  produce  the  same  amount  of  extinction,  would 
be  346-6  mm.  But  when  the  sensitive  mixture  of  equal  volumes  of  chlorine  and 
hydrogen  is  used,  the  depth  of  the  mixture  which  the  light  must  penetrate  to  be 
reduced  to  j1^,  is  found  to  be  only  234  mm.  Hence,  it  appears  that  light  is 
absorbed  in  doing  chemical  work. 

With  light  from  other  sources,  results  are  obtained  similar  in  character,  but 
differing  in  amount.  Diffuse  morning  light  reflected  from  the  zenith  of  a  cloud- 
less sky  is  reduced  to  ,-3  by  passing  through  45-6  mm.  of  chlorine,  and  through 
73-5  mm.  of  the  sensitive  mixture;  diffuse  evening  light  is  reduced  to  y^  by 
passing  through  19 -7  mm.  of  chlorine  and  through  57*4  mm.  of  the  standard 
mixture.  Hence  it  appears  that  the  chemical  rays  of  diffuse  morning  light  are 
absorbed  by  chlorine  much  more  quickly  than  those  of  lamp-light ;  and  those  of 
evening  light  with  still  greater  facility.  From  this  we  may  conclude  that  the 
chemical  rays  reflected  at  different  times  and  hours,  possess,  not  only  quantitative 
but  also  qualitative  differences,  similar  to  the  various  coloured  rays  of  the  visible 
spectrum.  It  is  a  fact  well  known  to  photographers,  that  the  amount  of  light 
photometrically  estimated  gives  no  measure  of  the  time  in  which  a  given  photo- 
chemical effect  is  produced.  For  the  taking  of  pictures,  a  less  intense  morning 
light  is  always  preferred  to  a  bright  evening  light. 


THE    TANGENT-COMPASS. 


679 


FIG.  226. 


ELECTRICITY. 

Measurement  of  the  Force  of  Electric  Currents.  —  There  are  two  methods  by 
which  the  forces  of  electric  currents  are  compared  with  each  other,  viz.,  the 
chemical,  or  electrolytic,  and  the  electromagnetic  methods. 

Faraday  has  shown  that  the  amount  of  chemical  work  done  is  the  same  in  all 
parts  of  the  circuit;  that,  if  two  decomposing  cells  be  introduced,  one  containing 
dilute  sulphuric,  the  other  hydrochloric  acid,  the  quantity  of  hydrogen  evolved  is 
the  same  in  both,  and  equal  to  the  hydrogen  evolved  (by  true  current  action)  in 
each  cell  of  the  battery ;  moreover,  that  the  quantities  of  different  elements  elimi- 
nated in  any  part  of  the  circuit,  are  always  in  the  ratio  of  their  equivalent  weights. 
The  voltameter  (p.  221)  affords,  therefore,  a  true  and  exact  measure  of  the  amount 
of  the  chemical  or  electrical  force  developed  by  the  battery.  But  its  indications 
are  not  always  sufficiently  rapid.  In  fact,  in  using  this  instrument,  it  is  necessary 
to  wait  till  a  measurable  quantity  of  gas  is  collected.  It  will,  therefore,  indicate 
the  relative  .quantity  of  electricity  which  has  passed  through  the  circuit  in  a  cer- 
tain finite  interval,  say  in  a  minute ;  but  it  gives  no  information  of  any  variations 
that  may  have  taken  place  during  that  interval ;  moreover,  it  can  only  be  used  to 
measure  currents  of  considerable  strength. 

• 

The  Tangent-compass. — To  supply  these  deficiencies,  and  obtain  exact  and 
instantaneous  indications  of  the  relative  forces  of  electric  currents,  recourse  is  had 
to  the  electro-magnetic  method,  which  consists  in 
observing  the  deflection  of  a  magnetic  needle  pro- 
duced by  the  current.  Instruments  for  this  pur- 
pose are  called  Galvanometers  or  Rheometers.  The 
effect  of  a  coil  of  wire  in  intensifying  the  effect  of 
the  current  upon  a  magnetic  needle,  is  described  at 
page  221  of  this  work.  But  the  kind  of  instru- 
ment there  described,  though  commonly  called 
a  galvanometer,  is  really  only  a  galvanoscope,  or 
multiplier.  It  indicates  with  great  delicacy  the 
existence  and  direction  of  an  electric  current,  but 
it  is  not  constructed  for  quantitative  determinations. 

In  the  true  galvanometer  (Fig.  226)  the  current, 
instead  of  passing  through  a  long  coil  of  wire  placed 
close  to  the  needle,  is  made  to  pass  through  a  broad 
circular  band  of  brass  or  copper,  p  Q,  of  considerable 
dimensions,  in  the  centre  of  which  is  placed  a  mag- 
netic needle,  n,  the  length  of  which  is  very  small  in 
comparison  with  the  diameter  of  the  circular  con- 
ductor, so  that  the  distance  of  the  extremity  of  the 
needle  from  the  conductor  p  Q,  and  consequently  the  force  exerted  upon  it  by  the 
current,  is  sensibly  the  same  at  all  angles  of  deflection.  The  instrument  is  so 
placed  that  the  plane  of  the  circle  p  Q  coincides  with  the  magnetic  meridian.  To 
determine  the  relation  which  exists  under  these  circumstances  between  the 
deflection  of  the  needle  and  the  force  of  the  current,  let  p  Q  (fig.  227)  represent 
the  circular  conductor  seen  from  above ;  a  z  the  direction  of  the  needle  under  the 
influence  of  the  current.  The  extremity  of  the  needle  is  then  acted  upon  by  two 
forces,  viz.,  the  force  of  terrestrial  magnetism  acting  parallel  to  P  Q,  and  the  force 
of  the  current  acting  at  right  angles  to  that  direction.  Let  these  forces  be  repre- 
sented in  magnitude  and  direction  by  the  lines  a  6,  a  c.  Draw  also  the  line  fa  d 


FIG.  227. 


G80  ELECTRICITY. 

perpendicular  to  a  z,  and  If,  c  d,  perpendicular  to  d  f.     Then  the  lines,  a  f,  a  d, 

represent  the  resolved  portions  of  the  forces  a  6, 
a  c,  which  act  at  right  angles  to  the  needle,  and 
tend  to  turn  it  one  way  or  the  other.  In  order, 
therefore,  that  the  needle  may  be  at  rest,  a  d  must 
be  equal  to  a/,  or 

a  c .  cos  c  a  d  =  a  b,  sin  a  b  f. 

Now  the  angle  c  a  d  is  equal  to  v,  the  angle  of 
deflection  of  the  needle  from  the  meridian,  because 
a  c  is  perpendicular  to  p  Q,  and  a  d  to  a  z;  and 
the  angle  a  bf  is  also  equal  to  v,  because  a  I  is 
parallel  to  p  Q,  and  bf  to  a  z.  Hence  the  pre- 
ceding equation  becomes 

a  c .  cos  v  =  a  b  .  sin  v ; 
therefore  a  c  =  a  b  .  fan  v. 

Or,  if  we  denote  the  force  of  the  earth's  magnetism 
by  M,  and  that  of  the  electric  current  by  E,  we 
have 

E  =  M  tan  v. 

Consequently,  since  the  magnetic  force  of  the 
earth  is  constant  at  the  same  place  (at  least  for 
short  intervals  of  time),  the,  magnetic  force  of  the 
current  is  proportional  to  the  tangent  of  the  angle 
of  deflection  :  hence  the  name  of  the  instrument. 

Comparison  between  the  chemical  and  magnetic 
actions  of  the  current.  —  By  introducing  into  the 
same  voltaic  circuit,  a  voltameter  and  a  tangent- 
compass,  it  is  found  that  the  chemical  action  of 
fhe  current  is  directly  proportional  to  its  magnetic  action.  The  tangent-compass 
affords,  therefore,  a  measure  of  the  chemical  as  well  as  of  the  magnetic  force 
of  the  current,  the  quantity  of  chemical  or  electrical  force  in  the  circuit  being 
proportional  to  the  tangent  of  the  angle  of  deflection  of  the  needle. 

If  m  milligrammes  of  hydrogen  are  evolved  in  a  second  in  the  voltameter, 
when  the  galvanometer  exhibits  a  deflection  of  45°,  and  therefore  a  current 
force  =1=  1  (since  tan  45°  =  1),  then,  when  the  same  galvanometer  shows  a  de- 
flection =  a,  jbhe  quantity  of  hydrogen  evolved  in  t  seconds  will  be  m  .  t  .  tan  a. 
The  quantity  of  any  other  element  eliminated  in  the  same  circuit,  will  be  found 
by  multiplying  this  quantity  by  the  equivalent  weight  of  that  element. 

With  a  tangent-compass,  the  diameter  of  whose  conductor  measures  one  deci- 
meter, it  is  found  that,  when  the  deflection  is  45°,  one  milligramme,  or  11-2  cubic 
centimeters  (at  0°  C.  and  Bar.  0-76  met.)  of  hydrogen  is  eliminated  in  32-3 
seconds.  Hence  with  any  other  circular  current  whose  radius  is  r  decimeters  and 
force  =  tan  a,  the  time  t  in  which  1  milligramme  of  hydrogen  is  evolved,  or  9 
milligrammes  of  water  are  decomposed,  is 

32-3 


r  .  tan  a 


Ohm's  Formulse.  —  The  amount  of  electrical  or  chemical  power  developed  in 
the  voltaic  circuit,  —  or,  in  other  words,  the  quantity  of  electricity  which  passes 
through  a  transverse  section  of  the  circuit,  in  a  unit  of  time,  evidently  depends 
upon  two  conditions;  viz.,  the  power,  or  electromotive  force  of  the  battery,  and 
the  resistance  offered  to  the  passage  of  the  current  by  the  conductors,  liquid  or 
solid,  which  it  has  to  traverse.  With  a  given  amount  of  resistance,  the  power  of 


OHM'S  FORMULAE.  681 

the  battery  is  proportional  to  the  quantity  of  electricity  developed  in  a  given 
time  ;  and  by  a  double  or  treble  resistance,  we  mean  simply  that  which,  with  a 
given  amount  of  exciting  power  in  the  battery,  reduces  the  quantity  of  electricity 
developed,  or  work  done,  to  one-half  or  one-third.  If,  then,  we  denote  the  elec- 
tromotive force  of  the  battery  by  E,  and  the  resistance  by  R,  we  have,  for  the 
quantity  of  electricity  passing  through  the  circuit  in  a  unit  of  time,  the  expres- 


son : 


This  is  called  Ohm's  law,  from  the  name  of  the  distinguished  mathematician 
who  first  announced  it.  It  must  be  understood,  not  as  a  theorem,  but  as  a  defi- 
nition. To  say  that  the  strength  of  the  current  varies  directly  as  the  electro- 
motive force,  and  inversely  as  the  resistance,  is  simply  to  define  what  we  mean  by 
electromotive  force  and  what  we  mean  by  resistance.*  , 

Let  us  now  endeavour,  by  means  of  the  formula  (1),  to  estimate  the  effect  pro- 
duced on  the  strength  of  the  current  by  increasing  the  number  and  size  of  the 
plates  of  the  battery.  The  resistance  R  consists  of  two  parts;  viz.,  that  which 
the  current  experiences  in  passing  through  the  cells  of  the  battery  itself,  and  that 
which  is  offered  by  the  external  conductor  which  joins  the  poles.  This  conductor 
may  consist  either  wholly  of  metal,  or  partly  of  metal  and  partly  of  electrolytic 
liquids.  Let  the  resistance  within  the  battery  be  r,  and  the  external  resistance 
i*  j  then,  in  the  one-  celled  battery,  we  have 


Now  suppose  the  battery  to  consist  of  n  cells  perfectly  similar  ;  then  the  electro- 
motive force  becomes  nE,  the  resistance  within  the  battery  wr;  if,  then,  the  ex- 
ternal resistance  remains  the  same,  the  strength  of  the  current  will  be  denoted  by 

nE  E 


-nr  +  r'   ~    "  ~P  ...... 

r  +  - 
n 

F1 

If  r'  be  small,  this  expression  has  nearly  the  same  value  as  -  -,  ;  that  is  to  say, 

r  -\-  r 

if  the  circuit  be  closed  by  a  good  conductor,  such  as  a  short  thick  wire,  the 
quantity  of  electricity  developed  by  the  compound  battery  of  n  cells,  is  sensibly 
the  same  as  that  evolved  by  a  single  cell  of  the  same  dimensions.  But  if  V  is  of 
considerable  amount,  as  when  the  circuit  is  closed  by  a  long  thin  wire,  or  when  an 
electrolyte  is  interposed,  the  strength  of  the  current  increases  considerably  with 
the  number  of  plates.  In  fact,  the  expression  (3)  is  always  greater  than  (2)  ; 
for  — 

nE  E  (n—\  )  E  V 

«r  -f  /  ~~  r  +  /   ~~    (nr  +  /)  (r  -f  /)  5 

a  quantity  which  is  necessarily  positive  when  n  is  greater  than  unity. 

Suppose,  in  the  next  place,  that  the  size  of  the  plates  is  increased,  while  their 
number  remains  the  same.  Then,  according  to  the  chemical  theory,  an  increase 
in  the  surface  of  metal  acted  upon  must  produce  a  proportionate  increase  in  the 
quantity  of  electricity  developed,  provided  the  conducting  power  of  the  circuit  is 

*  It  must  be  remembered  that  we  are  here  merely  comparing  the  strength  of  electric  cur- 
rents one  with  the  other,  not  reducing  the  current  force  to  absolute  mechanical  measure  or 
even  comparing  it  with  the  electro-static  forces  of  attraction  and  repulsion.  (See 


CS2 


ELECTRICITY. 


sufficient  to  give  it  passage.  According  to  the  theory  which  attributes  the  de- 
velopment of  the  electricity  to  the  contact  of  dissimilar  metals,  an  increase  in  the 
(size  of  the  plates  does  not  increase  the  electromotive  force,  but  it  diminishes  the 
resistance  within  the  cells  of  the  battery  by  offering  a  wider  passage  to  the  elec- 
tricity. Hence  in  the  single  cell,  if  the  surface  of  the  plates,  and  therefore  the 
transverse  section  of  the  liquid,  be  increased  m  times,  the  expression  for  the 
strength  of  the  current  becomes 

E  mE 


1* 


r  -f  mr*. 


mE 


If  /  be  small,  this  expression  is  nearly  the  same  as -,  that  is  to  say,  the 

quantity  of  electricity  in  the  current  increases  very  nearly  in  the  same  ratio  as 
the  size  of  the  plates ;  but  when  the  external  resistance  is  considerable,  the  ad- 
vantage gained  by  increasing  the  size  of  the  plates  is  much  less. 

We  may  conclude,  then,  that  when  the  resistance  in  the  circuit  is  small,  as  in 
electro-magnetic  experiments,  a  small  number  of  large  plates  is  the  most  advan- 
tageous form  of  battery ;  but  in  overcoming  great  resistances,  power  is  gained  by 
increasing  the  number  rather  than  the  size  of  the  plates. 

Electric  Resistance  of  Metals.  —  The  preceding  principles  enable  us  to  deter- 
mine the  manner  in  which  the  resistance  of  a  metallic  wire  varies  with  its  length. 
For  this  purpose  suppose  a  one-celled  battery  (Daniell's)  to  be  used,  which  main- 
tains a  constant  action  during  the  time  of  the  experiment.  First  let  the  current 
be  made  to  pass  directly  through  the  tangent-compass,  and  afterwards  let  wires, 
of  uniform  thickness  and  of  the  lengths  of  5,  10,  40,  70,  and  100  meters,  be  in- 
terposed in  the  circuit,  and  the  resulting  deflections  observed.  Now,  as  the  force 
of  the  battery  is  constant,  the  resistance  is  inversely  as  the  strength  of  the 
current.  But  the  total  resistance  is  made  up  of  that  of  the  interposed  wires, 
together  with  that  of  the  battery  itself,  and  that  of  the  conductor  of  the  tangent- 
Compass.  These  last  two  resistances  we  may  suppose  to  be  equal  to  that  of  a 
wire  of  the  same  thickness  as  the  above,  and  of  a  certain  unknown  length,  x. 
Instead,  therefore,  of  the  lengths  of  wire  5,  10,  40,  &c.,  we  must  substitute 
x  +  5,  x  +  10,  x  +  40,  &c.  An  experiment  of  this  kind*  gave  the  following 
results :  — 


Length  of  Wire. 

Observed  Deflection. 

Tangent  of  Deflection. 

x  meters 

62°      0' 

1-880 

x  +       5 

40     20 

0-849 

x  +     10 

28    30 

0-543 

x  +     40 

9    45 

0-172 

x  +    70 

6      0 

0-105 

x  +  100 

4    15 

0-074 

Now,  let  us  assume,  as  most  probable,  that  the  resistance  of  a  wire  increases  in 
direct  proportion  to  its  length,  then,  according  to  Ohm's  law,  the  first  two  experi- 
ments give  — 

x  :  ;c-h5  =  0-849  :  1-880. 

whence,  x  =  4-11.  And,  by  combining  in  a  similar  manner  the  first  experiment 
with  all  the  others,  we  obtain  for  x  the  several  values  4-06,  4-03,  4-14,  4-09,  the 
mean  of  the  whole  being  4-08.  Substituting  this  value  for  x  in  the  preceding 
table,  and  calculating  the  corresponding  deflections  on  the  supposition  that  the 
strength  of  the  current  varies  inversely  as  the  resistance,  that  is  as  the  length  of 
the  conductor,  we  obtain  the  following  results  :  — 

*  Muller,  Lehrbuch  der  Physik.  1853,  ii.  177. 


THE    RHEOSTAT. 


683 


Length  of  Conductor. 

Calculated  Deflection. 

Observed  Deflection. 

Difference. 

4-08  meters 

62°      0' 

62°     0' 

9-08 

40      18 

40     20 

+     2' 

14-08 

28     41 

28     30 

—  11 

44-08 

9     56 

9    45 

—  11 

74-08 

5    57 

6       0 

+     3 

104-08 

4     14 

4     15 

+      1 

FIG.  228. 


From  the  results  of  this  and  similar  experiments,  it  is  inferred  that-r-^e  re- 
sistance of  a  conductor  of  uniform  thickness  varies  directly  as  its  length. 

The  Rheostat  or  Current-regulator. — The  various  forms  of  the  so-called  constant 
battery,  Darnell's  for  example  (p.  218),  attain  their  end  but  imperfectly,  a  galvan- 
ometer included  in  the  circuit  always  exhibiting  more  or  less  variation.  A 
really  constant  current  can  only  be  obtained  by  interposing  in  the  circuit  a  con- 
ducting wire  of  variable  length,  so  that  the  resistance  may  be  increased  or 
diminished  as  the  action  of  the  battery  becomes 
stronger  or  weaker.  Various  instruments  have 
been  contrived  for  this  purpose.  The  one  most 
used,  invented  by  Professor  Wheatstone,  is  re- 
presented in  fig.  228.  A  and  B  are  two  cylin- 
ders of  the  same  dimensions  —  the  first  of  dry- 
wood,  the  second  of  brass  —  placed  with  their 
axes  parallel  to  each  other.  The  wooden 
cylinder  A  has  a  fine  screw  cut  on  its  surface, 
and  around  it,  following  the  thread  of  the 
screw,  is  coiled  a  thin  brass  wire.  One  ex- 
tremity of  this  wire,  is  attached  to  a  brass 
ring,  v,  at  the  nearer  end  of  the  wooden 
cylinder,  and  the  other  to  the  farther  extremity 
of  the  brass  cylinder.  The  ring  v  and  the 
near  end  of  the  brass  cylinder  are  connected  with  the  wires  of  the  battery  through 
the  medium  of  the  screw-joints  CD.  A  movable  handle,  A,  serves  to  turn  the 
cylinders  alternately  round  their  axes.  By  turning  B  to  the  right,  the  wire  is  un- 
coiled from  A  and  coiled  upon  B  ;  and  the  contrary  when  A  is  turned  to  the  left. 
The  number  of  coils  of  wire  upon  A  are  indicated  by  a  scale  placed  between  the 
cylinders,  the  fractions  of  a  turn  being  measured  by  an  index  moving  round  the 
ring  v,  which  is  graduated  accordingly.  As  the  coils  of  the  wire  are  insulated 
on  the  wooden  cylinder,  but  not  on  the  brass,  it  is  evident  that  the  path  of  the 
current  will  be  longer,  and  therefore  the  resistance  greater,  in  proportion  to  the 
number  of  coils  of  wire  upon  the  wooden  cylinder. 

By  means  of  the  rheostat  and  the  tangent-compass,  the  resistances  afforded  by 
different  conductors  to  the  passage  of  the  current  may  be  measured  with  great 
facility.  Suppose  that  when  the  wire  of  the  rheostat  is  completely  uncoiled  from 
the  wooden  cylinder  (the  index  then  standing  at  0°),  a  tangent-compass  intro- 
duced into  the  circuit  shows  a  deflection  of  46°.  Then  let  a  copper  wire  four 
yards  long  and  ^th  of  an  inch  thick,  be  introduced  into  any  part  of  the  same 
circuit.  The  galvanometer-needle  will  then  exhibit  a  smaller  deflection,  say  37°. 
On  removing  the  wire,  the  galvanometer  will  again  exhibit  its  former  deflection 
>f  46°.  Now  let  the  rheostat  wire  be  coiled  round  the  wooden  cylinder  till  the 
needle  returns  to  37°,  and  suppose  that  to  produce  this  effect  twenty  turns  of  the 
rheostat  wire  are  necessary.  This  length  of  the  rheostat  wire  produces  a  resist- 
ance equal  to  that  of  the  wire  under  examination.  Next  let  a  similar  experiment 
be  made  with  a  wire  of  the  same  length  but  of  twice  the  thickness,  and  conse- 


684  ELECTRICITY. 

quently  having  a  transverse  section  four  times  as  great  as  that  of  the  former.  It 
will  be  found  that  five  turns  of  the  rheostat  wire, 'or  one-fourth  of  the  former 
length,  are  sufficient  to  produce  a  resistance  equal  to  that  of  the  second  wire.  By 
experiments  thus  conducted  it  is  found  that :  The  resistance  of  a  wire  or  any  other 
conductor  of  given  length  varies  inversely  as  its  transverse  section.  And  com- 
paring this  result  with  that  which  was  established  at  page  682,  we  find  that: 
Conductors  of  the  same  material  offer  equal  resistances,  when  their  lengths  are  to 
one  another  in  the  same  proportion  as  their  transverse  sections. 

In  a  similar  manner,  the  relative  conducting  powers  of  different  metals  may  be 
ascertained.  Taking  the  resistance  of  pure  copper  as  the  unit,  it  is  found  that 
that  of  iron  is  7'02,  of  brass  3-95,  of  German  silver  l5'47.  The  conducting 
powers  are  of  course  inversely  as  these  numbers  (p.  650). 

Heating  Power  of  the  Voltaic  Current The  degree  of  heat  excited  in  a 

metallic  wire  by  the  passage  of  the  current,  increases  with  the  strength  of  the 
current  and  with  the  resistance  of  the  wire.  To  determine  the  numerical  rela- 
tions of  this  phenomenon,  the  wire  to  be  heated  is  formed  into  a  spiral  and  enclosed 
within  a  vessel  containing  strong  alcohol,  or  some  other  non-conducting  liquid,  in 
order  that  the  current  may  pass  entirely  through  the  wire,  and  not  through  the 
liquid  itself.  The  rise  of  temperature  in  the  liquid  is  noted  by  a  delicate  ther- 
mometer ;  the  strength  of  the  current  measured  by  the  tangent-compass ;  and  the 
resistance  of  the  wire  afterwards  determined  in  the  manner  above  described.  By 
this  method  Lenz*  has  shown  that :  — 

The  quantity  of  heat  evolved  in  a  given  time  is  directly  proportioned  to  the 
resistance  of  the  wire,  and  to  the  square  of  the  quantity  of  electricity  which  passes 
through  it. 

The  same  result  has  been  obtained  by  Joule, f  both  for  wires  and  liquid  con- 
ductors; by  E.  Becquerel  for  liquids;  and  by  BiessJ  for  the  heat  produced  by  the 
discharge  of  the  electricity  accumulated  in  a  Ley  den  jar. 

Reduction  of  the  Force  of  the  Current  to  absolute  mechanical  Measure  :  —  This 
important  determination  has  been  made  the  subject  of  an  extensive  research  by 
Weber  and  Kohlrausch.§  To  understand  the  results  obtained  by  these  philoso- 
phers, it  is  necessary  to  define  exactly  the  several  units  of  measurement  adopted : 

a.  The  unit  of  electric  fluid  is  the  quantity  which,  when  concentrated  in  a 
point,  and  acting  on  an  equal  quantity  of  the  same  fluid  also  concentrated  in  a 
point,  and  at  the  unit  of  distance,  exerts  a  repulsion  equal  to  the  unit  of  force. 

b.  The  unit  of  electrochemical  intensity  is  the  force  of  the  current  which,  in  a 
unit  of  time,  decomposes  a  unit  of  weight  of  water,  or  an  equivalent  quantity  of 
any  other  electrolyte. 

c.  The  unit  of  electromagnetic  force,  is  the  force  of  a  current  which  —  when  it 
traverses  a  circular  conductor  whose  area  is  equal  to  the  unit  of  surface,  and  acts 
upon  a  magnet  whose  magnetic  moment  is  equal  to  unity,  the  magnet  being  placed 
at  a  great  distance,  and  in  such  a  manner  that  its  axis  is  parallel  to  the  plane  of 
the  conductor,  and  its  centre  on  a  line  drawn  through  the  centre  of  the  circular 
conductor,  and  perpendicular  to  its  plane — exerts  upon  the  magnet  a  rotatory  force 
equal  to  unity  divided  by  the  cube  of  the  distance  between  the  centre  of  the  needle 
and  the  centre  of  the  conductor. 

Weber  had  shown  by  previous  experiments  that  the  unit  of  electrochemical 
force  is  to  that  of  electromagnetic  force  as  106|  to  1.  It  remained,  therefore,  to 
determine  the  relation  between  the  electromagetic  unit  and  the  electrostatic  unit 

*  Pogg.  Ann.  Ixi.  18.  f  Phil.  Mag.  [3],  xix.  210, 

%  Pogg.  Ann.  xl.  335 ;  xliii.  47  ;  xlv.  1. 

\  Abhandlungen  der  Mathematisch-physischen  Classe  der  Konigl.  Sachsischen  Gesellsch. 
d.  Wiss.  Leipzig.,  1856. 


CHEMICAL    NOTATION.  685 

(1),  and  thus  to  establish  a  numerical  relation  between  statical  and  dynamical 
electricity.  The  mode  of  experimenting  was  as  follows  :  — 

1.  A  Leyden  jar  having  been  strongly  charged,  its  knob  was  touched  with  a 
large  metallic  ball,  which  took  from  it  a  certain  portion  of  its  charge,  determined 
by  previous  experiments.  The  charge  of  the  ball  was  then  transferred  to  the 
torsion-balance,  and  the  repulsive  force  measured.  At  the  same  time,  the  remainder 
of  the  charge  of  the  jar  was  made  to  traverse  the  wire  of  a  galvanometer,  prev- 
iously, however,  having  been  passed  through  a  long  column  of  water,  in  order  to 
give  it  a  sensible  duration,  and  prevent  it  from  passing  from  one  coil  of  the  wire 
to  another  in  the  form  of  a  spark.  In  this  manner,  a  relation  was  established 
between  the  statical  and  dynamical  effects  of  the  charge  of  the  jar. — 2.  The  inten- 
sity and  duration  of  a  voltaic  current  were  determined,  which  imparted  to  the 
galvanometer  needle  the  same  deflection  as  that  produced  by  the  discharge  of  the 
Leyden  jar. 

The  results  of  the  experiments  were  as  follows  :  — 

Through  each  section  of  a  conductor  traversed  by  a  current  whose  force  is  equal 
to  the  electromagnetic  unit,  there  passes  in  a  second  of  time  a  quantity  of  positive 
electricity  equal  to  155,370  X  106  statical  units  (p.  684,  or),  and  an  equal  quantity 
of  negative  electricity  travelling  in  the  opposite  direction. 

The  quantity  of  electricity  required  to  decompose  one  milligramme  of  water, 
amounts  to  106f  times  this  quantity,  or  16,573  x  109  units  of  electricity,  of  each 
kind.  To  decompose  nine  milligrammes  of  water,  or  one  equivalent,  requires  of 
course  nine  times  this  amount  of  electricity.  This  quantity  of  positive  electricity 
(9  X  16,573  x  109)  accumulated  on  a  cloud  situated  1000  meters  above  the  sur- 
face of  the  earth,  and  acting  on  an  equal  quantity  of  negative  electricity  on  the 
surface  of  the  earth  below  the  cloud,  would  exert  an  attractive  force  equal  to 
226,800  kilogrammes,  or  208  tons. 

From  the  same  data  it  is  calculated  that,  if  all  the  particles  of  hydrogen  in  one 
milligramme  of  water  in  the  form  of  a  column  one  millimeter  long,  were  attached 
to  a  thread,  and  all  the  particles  of  oxygen  to  another  thread,  then,  to  effect  the 
decomposition  of  the  water  in  a  second,  the  two  threads  would  require  to  be  drawn 
in  opposite  directions,  each  with  a  force  of  147,380  kilogrammes,  or  145  tons.  If 
the  water  were  decomposed  with  less  velocity,  the  tension  would  be  proportionally 


CHEMICAL  NOTATION  AND  CLASSIFICATION. 


ATOMS   AND   EQUIVALENTS. 

Equivalent  quantities  of  any  two  substances  are  such  as  can  replace  one  an- 
other in  combination,  producing  compounds  of  similar  chemical  character.  Thus, 
when  copper  is  immersed  in  a  solution  of  nitrate  of  silver,  31-7  parts  of  copper 
take  the  place  of  108  parts  of  silver,  forming  a  neutral  nitrate  of  copper. 
Similarly,  the  31-7  parts  of  copper  may  be  replaced  by  32-5  parts  of  zinc,  and 
these  again  by  39  parts  of  potassium,  the  product  of  the  substitution  being  in 
each  case  a  neutral  salt.  These  quantities  of  silver,  copper,  zinc,  and  potassium, 
are  therefore  equivalent  to  one  another :  they  discharge  analogous  chemical 


686  CHEMICAL    NOTATION. 

functions.  In  like  manner,  47  parts  of  potash,  and  31  parts  of  soda  are  equiva- 
lent, because  they  unite  with  the  same  quantity  of  an  acid  to  form  neutral  salts. 

Equivalent  numbers  cannot,  however,  be  always  determined  by  actual  substitu- 
tion.  Six  parts  of  carbon  are  said  to  be  equivalent  to  14  parts  of  nitrogen;  but 
there  is  no  known  instance  of  the  direct  replacement  of  nitrogen  by.  carbon. 
Moreover,  certain  quantities  of  sulphuric  acid  and  soda  are  spoken  of  as  equiva- 
lent to  one  another,  although  it  is  plainly  impossible  that  bodies  so  opposite  in 
character  should  discharge  the  same  chemical  function.  In  fact,  the  term  equi- 
valent is  frequently  used,  not  in  its  strict  etymological  sense,  but  as  synonymous 
with  combining  number.  Eight  parts  of  oxygen  are  said  to  be  equivalent  to  1 
part  of  hydrogen,  because  the  bodies  unite  in  this  proportion  to  form  water  (p. 
113).  This  confusion  of  the  terms  equivalent  and  combining  number,  arises 
from  the  circumstance  that  the  combining  numbers  in  most  general  use  have  been 
selected  so  as  to  represent,  in  many  cases,  the  true  equivalents.  Nevertheless,  the 
ideas  of  equivalent  and  combining  proportion  are  essentially  different,  and  the 
numbers  which  relate  to  them  cannot  be  made  to  coincide  in  all  cases.  The  num- 
bers which  represent  the  proportions  in  which  bodies  combine,  though  to  a  certain 
extent  arbitrary,  may  be  regarded  as  fixed  when  once  selected ;  but  the  equivalent 
of  a  body  varies  according  to  the  chemical  function  which  it  discharges.  When 
iron  dissolves  in  hydrochloric  acid,  producing  ferrous  chloride,  FeCl,  every  grain 
of  hydrogen  expelled  from  the  acid  is  replaced  by  28  grains  of  iron ;  but  when 
the  same  metal  dissolves  in  aqua  regia,  forming  ferric  chloride,  Fe2Cl3  or  FefCl, 
each  grain  of  hydrogen  in  the  acid  is  replaced  by  18f  grains  of  iron  ;  in  other 
words,  the  equivalent  of  iron  (H  =  1)  is  28  in  the  ferrous  acid,  18f  in  the  ferric 
compounds.  Similarly,  the  equivalent  of  mercury  is  200  in  the  mercurous,  100 
in  the  mercuric  compounds.  By  comparing  the  perchlorates  with  the  perman- 
ganates, it  appears  that  55-7  parts  of  manganese  are  equivalent  to  35-5  parts  of 
chlorine.  Now  this  same  quantity  of  chlorine  is  equivalent  to  8  parts  of  oxygen, 
and  to  16  parts  of  sulphur:  moreover,  the  analogy  of  the  sulphates  and  man- 
gauates  shows  that  16  parts  of  sulphur  are  equivalent  to  27'7  parts  of  manganese, 
v'.  e.,  half  the  former  quantity.  Lastly,  by  comparing  the  manganous  with  the 
manganic  salts,  it  appears  that  if  the  equivalent  of  manganese  be  27'7  in  the 
former,  it  must  be  18-5  in  the  latter.  Manganese  has,  therefore,  three  different 
equivalents,  according  to  the  kind  of  compound  into  which  it  enters;  and,  gene- 
rally, the  number  of  equivalents  which  may  be  assigned  to  a  body  is  equal  to  the 
number  of  chemical  functions  which  it  discharges. 

The  so-called  tables  of  equivalents  are  really,  as  already  observed,  tables  of 
combining  proportion.  How  are  these  combining  proportions  determined  ?  Most 
bodies  unite  with  others  in  more  than  one  proportion.  Eight  parts  of  oxygen 
combine  with  14,  7,  4-7,  3-5,  and  2-8  parts  of  nitrogen.  Which  of  these  num- 
bers is  to  be  taken  as  the  combining  number  of  nitrogen?  Again,  —  1  part  of 
hydrogen  unites  with  4|  parts  of  nitrogen,  and  yet  the  combining  number  of 
nitrogen  (H  =  1),  is  said  to  be  not  4|,  but  three  times  that  number,  viz.,  14. 
Why  is  this  last  number  adopted?  The  solution  of  such  questions  leads  to  a 
variety  of  considerations.  Obviously,  the  combining  numbers  should  be  so  selected 
as  to  represent  all  series  of  compounds  by  the  simplest  formulae,  and  to  express 
analogous  combinations  by  similar  formulae.  Practically,  however,  this  rule  is  not 
found  to  be  a  sufficient  guide  in  all  cases;  and,  in  the  actual  determination  of 
combining  numbers,  reference  is  constantly  made  to  considerations  intimately  re- 
lated to  the  atomic  theory,  such  as  isomorphism,  the  specific  heat  of  atoms,  vapour- 
densities,  and  the  basicity  of  acids.  Suppose,  for  example,  the  combining  num- 
ber of  an  acid  is  to  be  determined ;  the  first  thing  to  be  ascertained  is  its  satu- 
rating power.  But  then  arises  the  question,  —  is  the  acid  monobasic,  bibasic,  or 
tribasic  ?  Now,  on  the  system  of  combining  numbers  or  equivalents,  viewed  with- 
out reference  to  atomic  constitution,  such  a  question  has  no  meaning.  Why,  for 
example,  is  citric  acid  said  to  be  tribasic  ?  Because  the  formula  of  a  neutral  citrate 


GERHARDT'S  UNITARY   SYSTEM.  687 

is  Ci8M30M;  a  formula  which  does  not  admit  of  division  by  3,  without  introducing 
a  fractional  number  of  oxygen-atoms.  But  if  the  symbols  merely  denote  com- 
bining numbers  or  equivalents,  there  can  be  no  valid  objection  to  the  use  of  such 
fractional  numbers.  There  is  nothing  absurd  in  the  idea  of  L4  of  the  quantity  of 
oxygen  which  unites  with  one  pound  of  hydrogen  to  form  water.  But  if  the 
symbols  denote  atoms,  the  case  is  altered,  the  idea  of  a  divided  atom  being  self- 
contradictory. 

This  is  but  one  instance  out  of  many  of  the  influence  exerted  by  the  atomic 
theory  on  the  construction  of  chemical  formulae,  and  consequently  on  the  determi- 
nation of  combining  numbers.  These  numbers  do,  in  fact,  represent  the  supposed 
relative  weights  of  atoms.  Different  views  maybe  entertained  of  the  atomic  con- 
stitution of  bodies,  and,  in  the  present  state  of  chemical  knowledge,  the  determi- 
nations of  the  atomic  weight  of  a  body  from  different  points  of  view  may  not 
always  agree :  the  specific  heat,  for  example,  sometimes  leading  to  one  conclusion, 
the  vapour-density  to  another  ;  but  the  idea  of  atoms  and  of  their  relative  weights, 
and  of  the  building  up  of  compounds  by  the  juxtaposition  of  elementary  atoms, 
is  perfectly  definite,  and  affords  the  only  satisfactory  explanation  yet  given  of  the 
observed  laws  of  chemical  combination  (p.  120). 


GERHARDT  S   UNITARY    SYSTEM. 

There  are  three  systems  of  atomic  weight  in  use  among  chemists:  —  1.  The 
system  adopted  in  this  work,  which  is  the  same  as  that  in  G-melin's  Hand-book. 
In  this  system,  water  is  represented  by  the  formula  HO,  and  the  metallic  oxides 
(protoxides)  most  resembling  it,  by  the  formula  MO.  The  atomic  weights  corres- 
pond, for  the  most  part,  with  the  equivalents,  substitution  being  supposed  to  take 
place,  atom  for  atom. 

2.  The  system  of  Berzelius,  based  upon  the  hypothesis  that  all  elementary  gases 
contain  equal  numbers  of  atoms  in  equal  volumes,  so  that  the  atomic  constitution 
of  a  compound  corresponds  with  its  constitution  by  volume.     Thus,  water  being 
composed  of  2  vol.  H  to  1  vol.  0,  is  H20;  hydrochloric  acid,  being  composed  of 
equal  volumes  of  chlorine  and  hydrogen,  is  HC1,  &c.     The  atomic  weights  in  this 
system  are  the  same  as  those  in  the  former  (p.  102),  excepting  those  of  hydrogen, 
nitrogen,  phosphorus,  chlorine,  bromine,  iodine,  and  fluorine,  which  have  half  the 
values  there  assigned  to  them,  viz.  :  —  (0  =  8);  H  =  0-5 ;  N  =  7 ;  P  =  16-01 ; 
01  =  17-75;  1  =  63-18;  Br=40;    F  =  9-35.     Metallic  protoxides  are  repre- 
sented by  the  formula  MO:  e.  g.  potash  =  KO;  black  oxide  of  copper  =  CuO. 

3.  The  system  of  Gerhardt  is  based,  like  that  of  Berzelius,  on  the  hypothesis 
that  all  simple  gases  contain  equal  numbers  of  atoms  in  equal  volumes,  but  carry- 
ing out  that  system   more  consistently.     The   formula   of  water  in   Grerhardt's 
system  is  H20,  as  in  that  of  Berzelius.     Moreover,  as  the  vapour-density  of  mer- 
cury is  to  that  of  oxygen  as  6976  : 1106  (p.  130),  and  mercuric  oxide  contains  8 
parts  by  weight  of  oxygen  to  100  parts  of  mercury,  it  follows  that  the  proportions 
by  volume  of  mercury-vapour  and  oxygen  which  compose  this  oxide  must  be  2 
vol.  mercury  to  1  vol.   oxygen  :  for  2  X  6976  :  1106  =  100  :  8  (nearly).     Hence 
mercuric  oxide  is  Hg20;  and  from  the  analogy  of  cupric  oxide,  ferrous  oxide, 
potash,  soda,  &c.,  with  mercuric  oxide,  it  follows  that  these  oxides  must  be  Cu20, 
Fe20,  K20,  Na20,  &c.;  or,  generally,  the  formula  of  a  protoxide  is  M20,  analo- 
gous to  that  of  water,  H20. 

If  0  =  8,  the  atomic  weights  of  sulphur,  selenium,  tellurium,  and  carbon  are 
the  same  in  Grerhardt's  system  as  in  that  adopted  in  the  present  work,  but  those 
of  all  the  other  dements  have  only  half  the  usual  values :  —  H=0-5,  Cl  =  17'75, 
K  =  19-5,  &c.  Or,  what  is  more  convenient,  assuming  H=l,  the  atomic  weights 


688 


CHEMICAL     NOTATION. 


of  0,  Se,  Te,  and  C  will  be  doubled,  while  those  of  all  the  other  elements  will 
remain  the  same.* 

In  the  following  explanations  and  applications  of  Gerhardt's  system,  these  double 
atomic  weights  of  oxygen,  &c.,  will,  to  avoid  confusion,  be  denoted  by  letters  with 
bars  through  the  middle :  thus,  O  =  16,  S  =  32,  O  =  12. 

The  following  table  presents  a  comparative  view  of  the  formulae  of  some  of  the 
most  important  chemical  compounds  in  the  ordinary  notation,  and  in  that  of  Ger- 
hardt. 


Ordinary  System. 

Gerhardt's  System. 

Water  

HO 

HgO 

Peroxide  of  hydrogen    

HO- 

HO 

ES 

H2$ 

Sulphuric  acid  (anhydrous)              ....         . 

sos 

&O3 

"             "    (hydrated)    

SHO4 

8H.& 

Hydrochloric  acid  

HC1 

HC1 

Hypochlorous  acid  (anhydrous) 

CIO 

C120 

«                   "     (hydrated)     

C1HO, 

C1HO 

Carbonic  oxide    

CO 

GO 

CO., 

NO. 

NoOc 

"       "      (hydrated)      

NHO- 

NHOS 

Phosphoric  acid  (anhydrous)  '.  

PO. 

P»Or 

"           «<      (hydrated)  

PH.O. 

PHoO 

MO 

M,O 

«           (hydrated)              

/      MH02      •> 

MHO 

(or  MO.HOj 
M203 

INLOa 

SK04 

&K0O, 

"                "       (acid)  

S,KHOfl 

&KHO; 

Nitrate  of  potash  ..... 

NK06 

NKO3 

Alum  (anhydrous)  •  

S,KA1oO,« 

SeK  412O 

C2NH 

ONH 

C.NHO, 

ON  HO 

Cyanate  of  soda         I....  

C2NNa02 

ONNaO 

C2NHSj 

ONHS 

CoNAgS, 

GNAgft 

C.H«Oo 

OaH6O 

Ether  

CJLO 

O^H1nO 

CAi.O. 

O,H4O2 

C.FLO, 

O4HeO, 

Benzoic  acid  (hydrated)    

C,.HC0, 

GwH«O. 

CI4H503 

0..H,J9L 

C,,HSK04 

eSK 

Oxalic  acid  .  .. 

C,H.O. 

G.HoO, 

These  two  systems  of  notation  possess  in  common  the  advantage  of  represent- 
ing the  metallic  protoxides  by  formulae  analogous  to  that  of  water,  whereas  in  the 
system  of  Berzelius,  this  analogy  is  lost,  water  being  represented  by  H2O,  and  the 
protoxides  of  the  metals  by  MO.  But  the  representation  of  water  by  HHO,  as 
in  Gerhardt's  system,  possesses  the  additional  advantage  of  corresponding  with  the 
important  fact,  that  it  is  possible  to  replace  either  the  half  or  the  whole  of  the 
hydrogen  in  water  by  a  metal.  Thus  potassium  thrown  into  water  displaces  half 
the  hydrogen,  and  forms  hydrate  of  potash,  HKO;  and  when  this  compound,  in 


*  Gmelin,  in  his  Handbook  (Translation,  vol..  vii.  p.  27),  objects  to  Gerhardt's  atomic 
•weights,  that  they  do  not  correspond  with  the  equivalent  numbers ;  but  this,  as  already 
shown  (p.  686),  must  necessarily  be  the  case  with  all  systems  of  atomic  weights  or  combi- 
ning numbers,  inasmuch  as  a  body  may  have  several  equivalents,  but  can  have  only  one 
atomic  weight. 


GERHAKDT'S  UNITARY  SYSTEM.  689 

the  solid  state,  is  heated  with  an  additional  quantity  6f  potassium,  the  remaining 
half  of  the  hydrogen  is  displaced,  and  anhydrous  potash,  KKO,  is  formed.  On 
the  contrary,  when  potassium  acts  on  hydrochloric  acid,  HC1,  it  displaces  the 
whole  of  the  hydrogen,  and  forms  chloride  of  potassium,  KC1.  This  is  an  im- 
portant difference,  which  is  easily  understood  on  the  supposition  that  water  con- 
tains two  atoms  and  hydrochloric  acid  only  one  atom  of  hydrogen  ]  whereas,  if 
these  two  compounds  are  represented  by  the  analogous  formulas,  HO  and  HC1,  the 
cause  of  the  difference  of  action  is  by  no  means  apparent. 

Assuming  as  the  unit  of  vapour-volume  the  space  occupied  by  1  gramme  of 
hydrogen  (or  by  16  grammes  of  oxygen,  14  of  nitrogen,  35-5  of  chlorine,  &c.), 
and  calculating  by  formulae  analogous  to  those  in  third  column  of  the  preceding 
table,  the  weights  of  the  compound  atoms  or  molecules  of  those  compounds  which 
are  capable  of  assuming  the  gaseous  form,  it  will  be  found  that  they  correspond 
to  2  volumes  of  vapour.  Thus,  for  hydrochloric  acid  :  H  +  Cl  =  1  +  35-5  = 
36-5 ;  and  as  the  density  of  hydrochloric  acid  gas  is  18-25  times  that  of  hydrogen. 
(see  Table  I.  p.  131),  it  follows  that  the  number  36'5  represents  the  weight  of  2 
volumes  of  vapour.  Similarly,  for  water:  H2Q  =  2  -f  16  =  18,  which  is  also 
the  weight  of  2  volumes  of  vapour,  the  specific  gravity  of  aqueous  vapour  com- 
pared with  hydrogen  as  the  unit  being  9.  Alcohol  =  G2H6O  =  24  -f  6  -f-  16 
—  46:  and  the  specific  gravity  of  alcohol  vapour  (H  =  1)  is  23.  Ether. 
=  O4H10O  =  48  -f  10  +  16  =  74,  which  is  twice  37,  the  weight  of  a  unit- 
volume  of  ether-vapour. 

In  the  formulas  of  the  second  column,  this  uniformity  of  vapour-volume  is  not 
observed.  Some  of  them,  as  those  of  water  HO,  ether  C4H50,  anhydrous  acetic 
acid  C4H303,  and  hydrated  sulphuric  acid  SH04,  represent  1  volume  of  vapour, 
when  referred  to  the  unit  above-mentioned,  viz.  the  space  occupied  by  1  gramme 
of  hydrogen,  or  2  volumes,  if  compared  with  the  volume  of  half  a  gramme  of 
hydrogen,  or  8  grammes  of  oxygen  ;  while  the  rest,  for  example,  hydrochloric  acid, 
HC1,  and  hydrated  acetic  acid,  C4H404,  represent  2  volumes  or  4  volumes  of 
vapour,  according  to  the  unit  adopted.  (See  the  table  on  pp.  130-136.) 
To  bring  all  these  formulae  to  the  same  standard  of  vapour-volume,  it  is  necessary, 
therefore,  to  double  those  first  mentioned,  thus:  water  =  H202;  ether,  C8Hi002; 
anhydrous  acetic  acid,  C8H606;  hydrated  sulphuric  acid,  S2H208,  &c. ;  and  if  the 
corresponding  change  be  made  in  the  formulae  of  the  analogous  compounds,  which 
are  not  known  to  exist  in  the  gaseous  state,  e.  g.  anhydrous  metallic  protoxides, 
M202;  neutral  sulphate  of  potash,  S2K208,  &c.,  it  will  be  found  that  Gerhard t's 
formulas  may,  in  all  cases,  be  converted  into  those  of  the  ordinary  notation,  by 
doubling  the  number  of  atoms  of  carbon,  oxygen,  sulphur,  selenium,  and  tellurium.* 

There  is  yet  one  class  of  bodies  whose  atomic  weights  represent,  not  two,  but 
one  volume  of  vapour,  viz.  the  elementary  bodies.  To  reduce  these  bodies  to  the 
same  standard,  it  is  necessary  to  assume  that  each  molecule  of  an  elementary  body 
in  the  free  state  consists  of  two  elementary  atoms,  e.  g.  hydrogen,  HH ;  chlorine, 
C1C1. 

This  hypothesis  is  justified  by  numerous  considerations.  First :  It  accords  with 
the  polar  view  of  the  constitution  of  bodies  suggested  by  the  phenomena  of  elec- 
trolysis (p.  189).  Secondly :  It  is  justified  by  certain  relations  of  boiling  point 
and  vapour-density,  to  be  considered  hereafter.  Thirdly :  There  are  numerous 
instances  of  chemical  action  in  which  two  atoms  of  an  elementary  body  unite 
together  at  the  moment  of  chemical  change,  just  like  heterogeneous  atoms.  Thus, 

*  Gerhardt  applied  the  term  unitary  to  his  system  of  notation,  because  it  is  based  on  the 
reduction  of  all  formulae  to  one  common  standard,  the  formulae  being  derived,  one  from  the 
other,  by  substitution.  The  ordinary  system,  being  founded  rather  on  the  formation  of 
compounds?  in  successive  binary  groups  (e.  g.  potash  =  KO ;  sulphuric  acid  =  S03 ;  sulphate 
of  potash  =  KO.S03),  is  called  the  Dualistic  system. 

44 


690 


CHEMICAL    NOTATION. 


when  the  hydride  of  copper,  Cu2H,  is  decomposed  by  hydrochloric  acid,  cuprous 
chloride  is  formed,  and  a  quantity  of  hydrogen  evolved  equal  to  twice  that  which 
is  contained  in  the  hydride  itself :  — 

Cu2H  4.  HC1  =  Cu2Cl  +  HH. 

This  action  is  analogous  to  that  of  hydrochloric  acid  on  cuprous  oxide  :  — 
Cu4O  +  2HC1  =  2Cu2Cl  +  H2O. 

In  the  latter  case,  the  hydrogen  separated  from  the  hydrochloric  acid  unites  with 
oxygen ;  in  the  former,  with  hydrogen.  When  solutions  of  sulphurous  and 
hydrosulphuric  acids  are  mixed,  the  whole  of  the  sulphur  is  precipitated  :  —  '. 

802  +  2H2S  =  2H20  +  g.g., 

the  action  being  similar  to  that  of  sulphurous  acid  on  hydroselenic  acid  :  — 
g02  +  SH.ge  =  2H20  +  g.ge2. 

In  the  one  case,  a  sulphide  of  selenium  is  formed ;  in  the  other  a  sulphide  of 
sulphur.  The  precipitation  of  iodine  which  takes  place  on  mixing  hydriodic  with 
,  iodic  acid,  affords  a  similar  instance  of  the  combination  of  homogeneous  atoms. 
The  reduction  of  certain  metallic  oxides  by  peroxide  of  hydrogen,  is  another 
striking  example  of  this  kind  of  action.  When  oxide  of  silver  is  thrown  into  this 
liquid,  water  is  formed  j  the  silver  is  reduced  to  the  metallic  state ;  and  a  quantity 
of  oxygen  is  evolved  equal  to  twice  that  which  is  contained  in  the  oxide  of  silver. 
It  appears,  indeed,  as  if  atoms  could  not  exist  in  a  state  of  isolation.  An  atom  of 
an  elementary  body  must  unite,  either  with  an  atom  of  another  element,  or  with 
one  of  its  own  kind. 

The  same  tendency  of  homogeneous  atoms  to  combine  together  is  exhibited  by 
certain  groups  of  atoms  called  compound  radicals,  which  behave  in  most  respects 
like  elementary  substances,  and  pass  as  entire  groups  from  one  state  of  combina- 
tion to  another.  Thus  there  is  a  series  of  hydrocarbons  called  the  ah-oliol-radicah 
(p.  697),  e.g.  methyl,  £H3;  ethyl,  Q2H5,  which  may  be  regarded  as  compound 
metals,  capable  of  taking  the  place  of  hydrogen  in  combination  with  chlorine, 
iodine,  oxygen,  &c.,  just  as  simple  metals  do.  Now  when  zinc-ethyl,  Q2H5Zn, 
and  iodide  of  methyl,  OH3I,  are  heated  together,  double  decomposition  takes  place, 
the  products  being  iodide  of  zinc,  and  methyl-ethyl :  — 

G2H5.Zn  +  £H3I  =  Znl  +  (£2H5) .  (OH3) . 

And  when  zinc-ethyl  is  heated  with  iodide  of  ethyl,  a  similar  action  takes  place, 
but  attended  with  formation  of  free  ethyl :  — 

C2H5.Zn  +  £AI  =  Znl  +  (O2H5) .  (O2H5). 

Moreover,  the  boiling  points  and  vapour-densities  of  these  radicals  are  related  to 
each  other  and  to  those  of  the  compound  radicals,  methyl-ethyl,  butyl-amyl,  &c., 
in  a  manner  which  can  only  be  explained  by  supposing  the  radicals  in  the  free 
state  to  consist  of  double  atoms.  This  will  be  seen  from  the  following  Table  :  — 


Sp.  gr.  at  0°  C. 

Vapour-density. 

Boiling-point. 

Ethyl-butyl  O2H5  ...  O4H9 
Ethyl-amyl  O2H6  ...  O6Hn 
Butyl  O4H9  ...  O4H9 

0-7011 
0-7069 
0-7057 

3-053 
3-522 

4-070 

62°  C. 
88 
106 

Butyl-amyl  O4H9  ...  O6H,, 
Amyl  G5Hn...  O5Hn 

0-7247 
0-7413 

4-465 
4-956 

132 
158 

Butyl-caproyl  ...  O4H9  ...  O6H13 
Caproyl  66H13...  O0H13 

0-7564 

4-917 
5-983 

155 
202 

GERHARDT'S  UNITARY  SYSTEM.  691 

The  regular  gradation  of  these  densities  and  boiling  points  plainly  shows  that 
the  proper  places  of  butyl,  amyl,  and  caproyl  in  the  series,  are  those  which  they 
occupy  in  the  table,  and  consequently  that  their  atomic  weights  in  the  free  state 
are  double  of  those  which  appertain  to  them  in  combination  :  e.  $.,  amyl  in  com- 
bination =  £5HM  =  71;  free  amyl  =  (O5Hn)2  =  142. 

Fourthly :  Elementary  bodies  frequently  act  upon  others  as  if  their  atoms  were 
associated  in  binary  groups.  Thus  chlorine  acting  upon  potash  forms  two  com- 
pounds, chloride  of  potassium  and  hypochlorite  of  potash :  — 

KKO  -f  C1C1  =  C1K  +  C1K0; 

just  as  chloride  of  cyanogen  would  form  chloride  of  potassium  and  cyanate  of 
potash.  The  quantity  of  chlorine  which  acts  upon  an  atom  of  potash,  is  not  1  at. 
=  35-5,  but  2  at.  =  70.  Similarly,  when  metallic  sulphides  oxidize  in  the  air, 
both  the  metal  and  the  sulphur  enter  into  combination  with  oxygen.  Sulphur 
acting  upon  potash  forms  a  sulphide  and  a  hyposulphite.  Lastly,  when  zinc-ethyl 
is  exposed  to  the  action  of  chlorine,  iodine,  &c.,  these  elements  unite  separately 
with  the  zinc  and  with  the  ethyl,  thus:  — 

£2H5Zn  +  C1C1  =€2H5C1  +  ZnCl. 

Double  Decomposition  regarded  as  the  Type  of  Chemical  Action  in  general. — 
Double  decomposition. is  generally  understood  as  an  action  taking  place  between 
four  elements  or  groups  of  elements;  but  since  it  appears  that  homogeneous  atoms 
may  exhibit  towards  one  another  the  same  chemical  relations  as  atoms  of  different 
bodies,  it  follows  that  the  same  kind  of  action  may  be  supposed  to  take  place  when 
less  than  four  bodies  are  concerned.  The  extension  of  this  view  of  chemical  action 
to  cases  in  which  three  elements  or  groups  of  elements  come  into  play,  is  suffici- 
ently illustrated  by  the  examples  just  given.  But  we  may  proceed  still  furthei 
in  the  same  direction,  and  regard  as  double  decompositions  those  reactions  which 
are  commonly  viewed  as  the  simple  combination  or  separation  of  two  elements,  or 
as  the  substitution  of  one  element  for  another.  Thus,  when  potassium  burns  in 
chlorine  gas,  the  reaction  may  be  supposed  to  take  place  between  two  atoms  of 
chlorine  and  two  atoms  of  potassium  :  — 

KK  +  C1C1  =  KC1  +  KC1. 

Again,  the  decomposition  of  cyanide  of  mercury  by  heat  may  be  represented 
thus :  — 

CyHg.CyHg  =  CyCy  +  HgHg. 

The  simple  replacement  of  one  element  by  another  may  also  be  regarded  as  a 
double  decomposition,  by  supposing  the  formation  of  an  intermediate  compound 
to  take  place.  Thus,  the  action  of  zinc  upon  hydrochloric  acid  may  be  supposed 
to  consist  of  two  stages  :  — 

ZnZn  -f  HC1  =  ZnH  +  ZnCl, 
and  ZnH   -f  HC1  =  ZnCl  -f  HH. 

It  is  true  that  the  formation  of  the  intermediate  compound,  the  hydride  of  zinc, 
cannot  be  actually  demonstrated  in  this  case,  because  it  is  decomposed  as  fast  as 
it  is  formed ;  but  in  other  cases  the  two  stages,  of  the  action  can  be  distinctly 
traced.  Thus,  it  is  well  known  that  hydrochloric  acid  does  not  dissolve  copper; 
but  an  alloy  of  zinc  and  copper,  Cu8Zn,  dissolves  in  it  readily,  with  evolution  of 
hydrogen.  Here  it  may  be  supposed  that  the  first  products  are  chloride  of  zinc 
and  hydride  of  copper,  a  known  compound :  — 


692  TYPES    AND    RADICALS. 

Cu2Zn  -f  HC1  =  Cu2H  +  ZnCl ; 

and  that  the  hydride  is  afterwards  acted  upon  by  the  acid  in  the  manner  already 
explained.  Again,  when  zinc  and  iodide  of  ethyl  are  heated  together  in  a  sealed 
tube,  iodide  of  zinc  and  zinc-ethyl  are  obtained,  thus :  — 

ZnZn  +  (€2H5) .  I  =ZnI  -f  Zn  (O2H5); 

and  the  zinc-ethyl,  when  heated  with  excess  of  iodide  of  ethyl,  yields  iodide  of 
zinc  and  free  ethyl :  — 

Zn  (02H5)  +  £2H5)  .  I  =  Znl  +  (O2H5)  (O2H5). 

In  this  manner,  all  chemical  reactions  may  be  reduced  to  one  type,  viz.,  a 
mutual  interchange  of  atoms  between  two  binary  groups. 


TYPES   AND    RADICALS.  —  RATIONAL   FORMULAE. 

The  rational  formula  of  a  compound  is  inferred  from  its  modes  of  formation  and 
decomposition.  When  cyanide  of  sodium  is  mixed  with  nitrate  of  silver,  an  inter- 
change of  elements  takes  place,  resulting  in  the  formation  of  nitrate  of  soda  and 
cyanide  of  silver :  — 

ON.Na  +  N03.  Ag  =  GN.Ag  +  N03-.Na. 

Here  the  group,  or  radical  N03  passes  from  the  silver  .to  the  sodium,  and  in  a 
similar  manner  it  may  be  transferred  to  potassium,  barium,  copper,  &c.  Hence  it 
may  be  inferred  that  the  nitrates  consist  of  NO3  associated  with  a  metal.  Simi- 
larly, ON,  may  be  regarded  as  the  radical  of  the  cyanides ;  £04  of  the  sulphates, 
&c.  When  alcohol,  £2H60,  is  treated  with  potassium,  one-sixth  of  the  hydrogen 
is  evolved,  and  the  compound  Q2H5K0  is  formed.  Again, — alcohol  treated  with 
chloride,  bromide,  and  iodide  of  phosphorus,  yields  the  compounds,  02H5C1, 
O2H5Br,  and  O2H5I;  and  when  the  compound  O2H5KO  is  treated  with  O2H5I, 
iodide  of  potassium  and  ether  are  formed :  — 

£l  TT  T  _i-  ^****8  I  A TTT 

Kp       Ki 

From  these  and  other  reactions,  alcohol  and  its  derivatives  are  supposed  to  contain 

Q  H 
the  radical  ethyl,  02H5,  alcohol  being  its  hydrated  oxide,     2rr5  \  O,  analogous  to 

T7-  £1    TT 

hydrate  of  potash,   TT  j  0,   and  ether  its  anhydrous  oxide,  p2yj5  j  Q>   analogous 

to  1(0- 

It  must  be  especially  observed,  however,  that  the  reason  for  admitting  the  exist- 
ence of  ethyl  as  a  radical  in  the  alcohol  compounds,  is  that  this  supposition  affords 
the  readiest  explanation  of  certain  reactions.  Other  reactions  may  point  to  a  dif- 
ferent conclusion.  Thus,  since  alcohol  heated  to  a  high  temperature  with  strong 
sulphuric  acid  is  resolved  into  olefiant  gas  and  water,  it  may  be  regarded  as  a 
hydrate  of  olefiant  gas,  O2H4.H2O.  Again,  —  certain  sulphates,  when  heated 
to  redness,  give  off  anhydrous  sulphuric  acid ;  and  sulphate  of  baryta  may  be 
formed  by  the  direct  combination  of  the  same  anhydrous  acid  with  anhydrous 
baryta.  '  Such  reactions  might  lead  to  the  conclusion  that  oxygen-salts  are  com- 
pounds of  anhydrous  metallic  oxides  with  anhydrous  acids,  rather  than  of  metals 
with  salt-radicals,  which  is,  in  fact,  the  ordinary  view.  Similarly,  ammoniacal 
salts  are  regarded  as  compounds  of  NH3  with  hydrated  acids,  or  of  NH4  with  acid 
radicals,  according  to  the  actions  specially  under  consideration. 


TYPES    AND    RADICALS.  693 

Tt  appears,  then,  that  the  same  compound  may  have  several  rational  formulae. 
This  of  course  implies  that  the  formula  is  an  expression,  not  of  the  constitution 
of  the  body  in  a  state  of  rest,  but  of  the  manner  in  which  the  atoms  are  supposed 
to  arrange  themselves  when  subjected  to  certain  influences.  It  is  no  longer  the 
question  what  the  absolute  constitution  of  a  substance  may  be,  but  of  how  many 
forms  of  constitution  the  substance  fulfils  the  conditions.  For  in  chemical  sub- 
stances, as  in  the  objects  of  a  branch  of  natural  history,  any  one  individual  exhibits 
more  or  less  distinctly  the  features  of  every  other. 

The  greater  the  number  of  elementary  atoms  entering  into  the  constitution  of 
a  compound,  the  more  numerous  will  be  the  possible  arrangements  of  those  atoms, 
and  the  greater,  therefore,  the  number  of  rational  formulae  which  may  be  assigned 
to  the  compound.  Practically,  however,  it  is  found  that  a  small  number  of  rational 
formulas — seldom  more  than  two  or  three — suffices  for  each  compound ;  and  more- 
over, that  the  formulae  of  all  bodies  whatever  may  be  reduced  to  a  small  number 
of  general  types.  Of  these,  Gerhardt  adopts  four,  viz.  :  — 

Water,  TT}O,  from  which  are  derived  the  oxides,  sulphides,  selenides,  and  tel- 

lurides. 
Hydrochloric  acid,  HC1,  the  type  of  the  chlorides,  bromides,  iodides,  fluorides, 

and  cyanides. 

fH 
Ammonia,  NX  H,  the  type  of  the  nitrides,  phosphides,  arsenides,  &c. 

Hydrogen,  HH,  the  type  of  the  elementary  bodies,  compound  radicals,  hydrides 
of  metals  and  radicals,  &c. 

These  typical  formulae  all  correspond  to  2  volumes  of  vapour. 

The  formulae  of  the  several  compounds  included  under  each  of  these  types  are 
obtained  by  replacing  one  or  more  of  the  elementary  atoms  contained  in  them  by 
another  radical,  simple  or  compound.  The  derivative  compound  is  called  primary, 
secondary,  or  tertiary,  according  to  the  number  of  atoms  of  hydrogen  in  the  type 
which  are  thus  replaced.  For  example,  the  hydrated  metallic  oxides,  which  are 
formed  from  the  type  water  by  the  substitution  of  1  at.  of  a  metal  for  1  at.  hydro- 

TT 

gen,  are  primary  oxides ;  e.  g.  hydrate  of  potash,  ^  j  O ;  the  anhydrous  oxides,  in 
which  both  atoms  of  hydrogen  are  similarly  replaced,  as  in  anhydrous  potash, 
j^-JO,  are  secondary  oxides.  The  replacement  of  1  at.  H  in  ammonia  by  ethyl, 

Q2H5,  forms  a  primary  nitride,  viz.,  ethylamine,  N(O2H5)H2;  similarly,  biethyla- 
mine,  N(O2H5)2H,  is  a  secondary  nitride ;  and  triethylamine,  N(02H5)3,  a  tertiary 
nitride. 

Equivalent  Values  of  Radicals. — A  radical  is  monatomic,  biatomic,  triatomic, 
&c.,  according  as  its  atom  or  molecule  is  equivalent  to  one,  two,  three,  &c.,  atoms 
of  hydrogen.  Potassium  and  ethyl  are  monatomic  radicals.  Sulphury!,  SO2,  is 

a  biatomic  radical,  and  by  replacing  2  at.  H  in  two  molecules  of  water,  „*  j  O2, 
forms  hydrated  sulphuric  acid,  |j  j  O.  Phosphoryl,  PO,  is  a  triatomic  radical,  and 
by  replacing  3  atoms  of  hydrogen  in  three  molecules  of  water,  jT3}O3,  forms  the 
ordinary  hydrate  of  phosphoric  acid,  PH3Q4  =  ^  }O3. 

When  a  metal  forms  two  classes  of  salts,  its  atom  has  a  different  equivalent 
value  in  each.  Thus,  in  the  platinous  compounds,  Pt  (  =  98)  is  monatomic;  in 


694:  TYPES    AttD    RADICALS. 

the  platinic  salts,  it  is  biatomic:  thus,  platinic  chloride  =  Pt  j  p,.  In  the  ferrous 
compounds,  Fe  (  =  28)  is  mouatomic;  in  the  ferric  compounds,  it 'is  sesquiatomic, 
Fe2,  being  equivalent  to  H3,  or  Fe|  to  H  :  thus,  ferric  oxide  =  t,e*  j  Q3.  In  the 

mercuric  compounds,  Hg  (  =  100)  is  monatomic;  in  the  mercurous  compounds, 
it  is  semi-atomic ;  the  double  atom,  Hg2  (  =  200),  being  the  equivalent  of  1  atom 
of  hydrogen.  In  arseuious  acid,  As2O3,  which  is  derived  from  3  molecules  of 
water,  As2,  is  equivalent  to  H6,  and  therefore  As  to  H3j  but  in  arsenic  acid,  As2O5, 
derived  from  5  molecules  of  water,  As  is  equivalent  to  H5.* 

Since  a  compouhd  may  have  several  rational  formulae,  j>r,  in  other  words,  ma1" 
be  represented  as  containing  different  radicals,  it  is  necessary  to  determine  the  re- 
lation which  exists  between  the  equivalents  of  such  radicals.  This  relation  is 
determined  by  the  following  general  law  :  —  Every  equivalent  of  hydrogen  added, 
to  a  radical  diminishes  Iry  unify  the  equivalent  value  of  the  entire  radical ;  and 
every  equivalent  of  hydrogen  subtracted  from  a  radical  increases  by  unity  the  total 
equivalent  value  of  the  entire  radical.  Thus,  nitric  acid  may  be  represented  by 
the  three  following  formula  : — 


H  **  H 

In  the  first  of  these  formulae,  which  represents  nitric  acid  as  formed  from  one 
molecule  of  water,  H2O,  the  radical  nitryl  f  NO^,  is  equivalent  to  1  atom  of  hy- 
drogen ;  in  the  second,  which  is  formed  from  2  molecules  of  water,  H4O2,  the 
radical  azotyl,  NO,  formed  from  nitryl  by  abstraction  of  O,  the  equivalent  of  H2, 
takes  the  place  of  3  atoms  of  hydrogen ;  and  in  the  third,  which  is  formed  from 
3  molecules  of  water,  H6Q3,  the  radical  nitricum,  N,  formed  from  nitryl  by  ab- 
straction of  O2,  the  equivalent  of  H4,  takes  the  place  of  5  atoms  of  hydrogen. 

Again,  uranic  oxide  maybe  represented   either  as  Tj2}O3,  or  as  ^  n(Q.     The 

first  of  these  formulae  represents  three  molecules  of  water,  H6O3,  and  contains  the 
radical  U2  =  H3;  the  second  represents  one  molecule  of  water,  and  contains  the 
radical  uranyl,  U2Q,  equivalent  to  H;  and  accordingly,  U2  —  O,  is  equivalent  to 
H3  —  H2  =  H.  Another  example  of  the  general  law  above  stated  is  afforded  by 
the  radicals  of  the  monatomic,  biatomic,  and  triatomic  alcohols  (p.  697). 

Conjugate  Radicals.  —  Any  compound  radical  may  be  regarded  as  a  compound 
of  two  or  more  simpler  radicals.  Thus,  ethyl,  O2H5,  may  be  represented  as 
OH2  -f  CH3,  or  as  £2H3  -f  H2;  acetyl,  O2H3O,  the  radical  of  acetic  acid  may  be 
regarded  as  QO  -f-  QH3,  or  as  £2H3  -f  O,  &c.  Radicals  viewed  in  this  manner 
are  said  to  be  conjugated.  A  radical  may  be  conjugated  either  by  addition,  as  in 
the  preceding  examples,  or  by  substitution  of  another  radical  for  one  or  more  atoms 

*  If  the  notion  of  equivalents  be  strictly  adhered  to,  independently  of  the  atomic  theory, 
the  formulae  of  bisalts  and  sesquisalts  may  be  dispensed  with,  and  the  different  classes  of 
salts  of  the  same  metal  regarded  as  containing  different  radicals:  thus  the  mercurous  salts 
may  be  regarded  as  salts  of  mercurosum,  Hg  =  200;  the  mercuric  salts  as  containing  mer- 
curicum,  hg  —  100:  thus — 

Mercurous  chloride  or  chloride  of  mercurosum HgCl  —  200  -|-  35-5 

Mercuric  chloride  or  chloride  of  mercuricum hgCl  =  100  -f-  35-5 

Ferrous  chloride  or  chloride  of  ferrosum Fed  =    28 -f-  35-5 

Ferric  chloride  or  chloride  of  ferricum feCl   =  18f  -f-  35'5 

This  mode  of  representation  might  be  made  consistent  with  the  atomic  theory,  by  sup- 
posing that  the  ultimate  atom  of  iron  weighs  9£ ;  that  a  double  atom  of  iron^  constitutes  fer- 
ricum —  18| ;  and  a  triple  atom,  ferrosum,  =  28 ;  similarly,  the  atom  of  mercury  weighing 
100,  a  double  atom  constitutes  mercurosum.  In  organic  compounds,  such  relations  between 
radicals  are  actually  observed:  thus,  ethylene,  G2H4=2xGH2;  propylene,  03H6=:3xOH2; 
butylene,  O4H8=4  x  £H2,  &c. 


CLASSIFICATION.  695 

of  hydrogen;  e.  g.,  from  benzoyl,  C7H50,  is  formed  nitro-benzoyl,  Q7H4(NQ2)Q, 
by  substitution  of  a  molecule  of  nitryl,  NQ2,  for  1  at.  H.  Similarly,  from  acetyl, 
O2H3O,  are  fowned  monochloracetyl,  O2(H2C1)O,  and  terchloracetyl,  £2C13O. 

An  important  class  of  conjugate  radicals  consists  of  those  which  are  formed  of 
certain  metals — arsenic,  antimony,  tin,  bismuth,  &c., — associated  with  the  alcohol- 
radicals.  For  example:  cacodyl,  or  arsen-bi methyl,  As(QH3)"2;  stibethyl, 
Sb(O2H5)3;  arsenethylium,  As(-C2H5\ ;  stannethyl,  Sn.O2H5.  The  same  radicals 
may  be  regarded  as  conjugated  by  substitution  :  e.  g.,  arsenethyl,  As(Q2H5)3,  as 
formed  from  ammonia,  NH3,  the  3  at.  H  being  replaced  by  ethyl,  and  the  nitro- 
gen by  arsenic.  In  like  manner,  arsenethylium,  As(Q2H5)4,  may  be  derived  from 
ammonium,  NH4. 

The  equivalent  in  hydrogen  of  a  conjugate  radical  may  be  determined  by  the 
two  following  rules,  deduced  from  the  general  law  given  at  page  694 : — 

1.  The  equivalent  in  hydrogen  of  a  radical  conjugated  by  addition  is  equal  to 
the  difference  of  the  equivalents  of  the  constituent  radicals.     Thus,  acetyl  (O2H3)O, 
which  is  equivalent  to  H,  is  composed  of  acetosyl,  Q2H3,  eq.  to  H,  and  O  eq.  to 
H2;  arsenethyl.  As(Q2H5)3,  which  is  equivalent  to  H2,  is  composed  of  As(arse- 
nicum),  eq.  to  H5,*  and  (O2H5)3,  eq.  to  H3;  cacodyl,  As(QH3")2,  which  is  equiva- 
lent to  H,  is  composed  of  As(arsenosum),  eq.  to  H3,  and  (£H3)2,  eq.  to  H2. 

2.  The  equivalent  in  hydrogen  of  a  radical  conjugated  by  substitution  is  equal 
to  the  difference  between  the  sum  of  the  equivalents  of  the  constituent  radicals  and 
the  equivalent  of  the  hydrogen  replaced.      For  example,  — acetyl  O2H3Q,  which  is 
equivalent  to  H,  may  be  regarded  as  C2H5  -f  O  (eq.  to  H  -f-  H2)  minus  H2. 


CLASSIFICATION    OF   CHEMICAL    COMPOUNDS. 

Bodies  may  be  classified  in  two  ways.  1.  According  to  their  origin,  as  when 
the  acids,  salts,  oxides,  &c.,  of  copper  are  made  to  form  one  group;  those  of 
chromium  another,  those  of  ethyl  a  third,  &c.  2.  According  to  their  chemical 
functions,  independenly  of  origin ;  the  acids  forming  one  group,  the  bases  a 
second,  the  alcohols  a  third,  the  ethers  a  fourth,  &c.  The  former  mode  of  classi- 
fication is  best  adapted  to  the  detailed  description  of  compounds ;  the  latter  for 
giving  a  general  view  of  their  mutual  relations. 

The  following  table  exhibits  Gerhardt's  system  of  classification  by  types,  or 
according  to  chemical  functions  :  — 

*  Oxide  of  arsenethyl  is  As(O2TJ5)3Q  or  As2(C2H5)6Og:  now  as  (O2H5)2is  equivalent  to  O, 
this  last  formula  may  be  derived  from  that  of  arsenic  acid,  As2O5  or  As2O3.O2  by  the  substi- 
tution of  (O2Hg)6  for  O3;  hence  As  has  in  oxide  of  arsenethyl  the  same  equivalent  value  that 
it  has  in  arsenic  acid :  that  is  to  say,  it  is  equivalent  to  H5.  On  the  other  hand,  oxide  of 
cacodyl  is  As2(QH3)40;  which  has  the  same  equivalent  value  as  As2.02O,  or  As2O8,  which 
is  the  formula  of  arsenious  acid.  Hence  the  radical  As  in  cacodyl  has  the  same  value  as  in 
arsenious  acid,  viz.,  equivalent  to  H3. 


(696) 


ALCOHOLS.  697 

WATER-TYPE. 

POSITIVE  OXIDES. — A.  Bases  proper,  or  Metallic  Oxides. — These  compounds 
are  formed  by  the  substitution  of  a  metallic  radical,  simple  or  compound,  for  the  : 
hydrogen,  in  one,  two,  or  three  molecules  of  water :  — 

a.  Monatomic. — Hydrate  of  potash,  tr  (O;  anhydrous  potash  or  oxide  of  potas- 
sium, j^}O; — cupric  hydrate,  TrjO; — cupric  oxide,  ^  JO; — hydrate  of  ammo- 
nium, TT  4 } O ; — hydrate  of  tetramercurammonium,  TT*4  JO ; — hydrate  of  tetre- 
thylium,  >  VT  5'4  JO; — oxide  of  cacodyl,  .  (CH^2}^' — oxide  of  arsenethy- 
lium, 


Pt  Pt 

|3.  Biatomic. —  Platinic  hydrate,  jj  JO2;  platinic  oxide,  p  JO2;  oxide  of  sti- 


>sb(c2H5y~ 

y.    Triatomic. — Hydrate  of  alumina,  tr^Oa;   anhydrous  alumina,    A12]-O3: 

±13  '  A12J 

CJT  Oiv  "D* 

antimonic  hydrate,  TT  JO3;  antimonic  oxide,  ™  JO3;  teroxide  of  bismuth,  -r,*!O3. 
n3  ) 

Certain  triatomic  bases  may  be  represented  as  monatomic,  by  supposing  a  por- 
tion of  the  oxygen  to  be  associated  with  the  positive  radical ;  thus,  sesquioxide 

of  uranium,  U4O3,  may  be  represented  as  protoxide  of  uranyl,  r^2r\  JO;  and  ter- 

Ot   £\ 

oxide  of  antimony,  Sb2O3,  as  protoxide  of  antimonyl,  ^  ~  JO.  Nonbasic  bioxides, 
or  peroxides,  may  be  represented  in  a  similar  manner;  e.  g.,  peroxide  of 
hydrogen,  =  TT  !  O. 

B.  Alcohols. — These  bodies,  all  of  which  belong  to  organic  chemistry,  are  also 
monatomic,  biatomic,  or  triatomic.  The  primary  monatomic  alcohols,  or  alcohols 
proper,  are  derived  from  water  by  the  replacement  of  1  atom  of  hydrogen  by  a 
hydrocarbon  of  the  form  OnH2n  +  u  £nH2n_,;  orOnH2n_7. 

a.  Alcohols  containing  radicals  of  the  form  QnH2n  +  K  The  number  of  these  at 
present  known  is  ten,  viz.  : — 

nTT 

Methylic  alcohol,  wood-spirit,  or  hydrate  of  methyl  (protyl).  OH3O  =     jj}O. 

r\  TT 

Ethylic  alcohol,  spirit  of  wine,  or  hydrate  of  ethyl  (deutyl).  O2H6O  = 

Propylic  alcohol,  or  hydrate  of  trityl O3H8O  = 

Butylic  alcohol,  or  hydrate  of  tetryl O4HIOO  = 

Amylic  alcohol,  or  hydrate  of  amyl  (pentyl) O5H12O  = 

Caproic  alcohol,  or  hydrate  of  hexyl O6HMO  = 

j.j. 

Caprylic  alcohol,  or  hydrate  of  octyl €8H,8O  =     V? 

Cetylic  alcohol,  or  hydrate  of  cetyl OjeH^O  —     iV 

*  The  radical  stibethyl  is  biatomic,  like  arsenethyl  (p.  695). 

• 


698 


WATER-TYPE. 


Cerylic  alcohol,  or  hydrate  of  ceryl  ...........................  £27H5bO  =    27^55  j  O. 

Melissic  alcohol,  or  hydrate  of  melissyl  .......................  ^3oH62O  =^3|?61  JO. 

The  first  of  these  liquids  is  found  among  the  products  of  the  destructive  distil- 
lation of  wood  ;  the  second,  third,  fourth,  and  fifth,  are  formed  by  the  fermenta- 
tion of  saccharine  substances  ;  caprylic  alcohol  is  obtained  by  saponifying  castor- 
oil  with  hydrate  of  potash  and  distilling  the  product  with  excess  of  the  alkali  at 
a  high  temperature  ;  cetylic  alcohol  is  obtained  from  spermaceti  :  cerylic  alcohol 
from  Chinese  wax,  and  melissic  alcohol  from  bees-wax. 

Compounds,  whose  formulae  differ  from  one  another  by  n  .  OH2,  are  said  to  be 
homologous  :  e.  g.,  the  alcohols,  the  fatty  acids  (p.  701),  the  compound  ethers 
(p.  706),  &o. 

j3.  Alcohols  containing  radicals  of  the  form  CI1H2n_1  :  — 

£t    TT 

Acrylic  or  allylic  alcohol,  O3H6O  =    |p  j  O.     This  is  the  only  term  of  the 

series  at  present  known. 

y.  Alcohols  containing  the  radicals,  CnH2n_7  :  —  Of  this  series,  there  are  two 
isomeric  groups,  distinguished  by  their  behaviour  with  oxidizing  agents,  the 
bodies  of  the  one  group  being  thereby  converted  into  aldehydes,  the  others  not. 
To  the  first  group  belong  :  — 

Benzoic  alcohol. 


Cuminic  alcohol  ................................  .  ...............  OIOH14O^1 

To  the  second  :  — 

£(    TT 

Phenylic  alcohol,  carbazotic  acid,  or  hydrate  of  phenyl  ....O6H6Q  =      r  5 
Cresylic  alcohol 


All  these  alcohols  contain  1   atom  of  hydrogen  replaceable  by  a  metal  ;  thus  : 
common   alcohol,   treated   with  potassium,  gives  off  one  sixth  of  its    hydrogen,' 

r\  rr 

and  yields  ethy  late  of  potassium,     |r6j^-     I*  is  not  found  possible  to  replace 

another  atom  of  hydrogen  in  a  similar  manner. 

Biatomic  Alcohols,  or   Glycols.  —  The  general  formula  of  these  compounds  is 


Three  of  them  have  been  obtained,  viz.,  ethylic  glycol, 

Ifopylic  glycol,  ^IejO2;  and  amylic  glycol,  ^I'°}O2.     The  2  at.  hydrogen  in 

each  of  these  formulae  may  be  replaced  by  other  radicals,  positive  or  negative; 
so  that  the  glycols  are  bibasic  and  biacid.  By  mixing  iodide  of  ethylene, 
Q2H4.I2  with  2  atoms  of  acetate  of  silver,  and  distilling  the  product,  a  distillate 
,  of  acetate  of  glycol  is  obtained,  while  iodide  of  silver  remains  behind  :  — 


Acetate  of  silver.  Acetate  of  glycol. 

and  acetate  of  glycol  distilled  with  hydrate  of  potash  yields  glycol  and  acetate 
of  potash  :  — 


K 

The  propylic  and  amylic  glycols  are  obtained  in  a  similar  manner  with  bromide 
of  propylene  and  bromide  of  amylene. 


ACIDS.  699 

Triatomic  Alcohols,  or  Glycerines.  —  The  general  formula  of  these  compounds  is 

£1    TT 

^•u  "20-1  j  Q^     rpne  tnree  atoms  of  hydrogen  wliich  they  contain  may  be  wholly  or 

£13 
partly  replaced  by  radicals  positive  or  negative.     One  term  of  the  series  has  been 

long  known,  viz.  :  ordinary  glycerine,  O3H8O3  =  O3jj5}O3.  The  neutral  fats, 
olein,  stearin,  palmitin,  &c.,  consist  of  glycerin,  in  which  the  3  atoms  of  free 

£t  TT 

hydrogen  are  replaced  by  acid  radicals;  e.g.,  stearin,  O57H,,0O6  =  ^  ^  ^  (O3. 

A  great  number  of  similar  compounds  have  been  formed  artificially  by  heating 
glycerine  with  acids.  Conversely,  when  neutral  fats,  stearin  for  example,  are 
heated  with  hydrate  of  potash,  or  other  metallic  oxides,  the  acid  radical  passes  to 
the  metal,  forming  a  salt,  and  glycerine  is  formed,  e.g., 


This  is  the  process  of  saponification.  Glycerine  may  also  be  formed  synthetically, 
viz.  by  heating  the  terbromide  of  allyl,  O3H5Br3,  with  acetate  of  silver.  Teracetate 
of  glycerine  (triacetin)  is  thus  formed  ;  and  this,  when  heated  with  hydrate  of 
baryta,  yields  glycerine.  The  other  glycerines  have  not  yet  been  obtained  in  the 

free  state  ;  but  the  acetate  of  ethyl-glycerine,  /£  j|  AN  j  O3,  is  obtained  at  the  same 
time  as  glycol,  by  the  action  of  iodide  of  ethylene  on  acetate  of  silver. 

The  secondary  alcohols,  or  Ethers,  bear  the  same  relation  to  the  primary  alcohols 
that   anhydrous   metallic   oxides   bear   to   the   hydrates;   e.  g.,  amylic   alcohol, 

C5glljO;  amylic  ether,  ^JO. 

There  are  likewise  ethers  containing  two  different  radicals;  e.g.,  methyl-amylic 

£1TT 
ether,  r  TT*  JO.     Ethers  may  be  formed  by  the  action  of  the  iodides  of  methyl, 


ethyl,  &c.,  on  alcohols  in  which  1  atom  of  hydrogen  is  replaced  by  potassium  ; 
thus,  common  alcohol  treated  with  potassium  gives  off  hydrogen,  and  yields 
O2H5KO;  and  this  compound,  treated  with  iodide  of  amyl,  yields  ethyl-amylic 
ether  :  — 


The-  same  potassium-alcohol,  treated  with  iodide  of  ethyl,  yields  common  ether  :  — 


K 


i  " 


Ethers  are  also  formed  by  the  action  of  strong  sulphuric  acid  on  the  alcohols, 
as  will  be  more  fully  explained  hereafter. 

C.  —  Aldehydes.  —  These  compounds  differ  from  the  alcohols,  in  containing  2 

•C  TT 
atoms  of  hydrogen  less.     Thus,  to  an  alcohol,  ^nTT2n+1^O,  there  corresponds  an 

•G-  TT 

aldehyde,     "-^""'JO.     They  are  obtained  by  the  action  of  oxidizing  agents  on 

the  alcohols.     Thus,  common  alcohol,  treated  with  bichromate  •  of  potash  and  sul- 

jQ   TT 

phuric  acid,  yields  ethylic  or  acetic  aldehyde,      tr3}^- 

There  are  likewise  aldehydes  corresponding  to  the  other  series  of  alcohols. 
Thus,  to  the  alcohols  containing  the  radicals,  QnH2D_T;  there   correspond   aide- 


700  WATER    TYPE. 

hydes  containing  radicals  of  the  form  QnH2n_9.     Oil  of  bitter  almonds.  O7H6O-  = 

OH 
7TT5  JO,  belongs  to  the  series. 

The  aldehydes  are  especially  distinguished  by  forming  crystalline  compounds  with 
the  alkaline  bisulphites  ;  e.  </.,  sulphite  of  acetosyl  and  sodium,  O2H3NaO,  &O2  = 
SO 


One  atom  of  hydrogen   in  the  radical  of  an  aldehyde  may  be  replaced  by  an 
alcohol  radical  ;  the  compounds  thus  produced  are  called  ketones.     Thus,  acetone, 


£3H6O,  the  ketone  of  the  acetic  series,  is         23   j^ 

ACIDS,  OR  NEGATIVE  OXIDES.  —  These,  like  the  positive  oxides,  are  divided 
into  primary  or  hydrated,  and  secondary  or  anhydrous.     Thus,  hydrated  nitric 

acid,     TT2}O;  anhydrous  nitric  acid,  ]sj£\2|^' 

Acids   are  also  monatomic,    like   nitric   acid  just   noticed,    and   acetic   acid. 

£\  TT  r\  c\r\  • 

2Tj3     j  O  )  biatomic,  like  sulphuric  acid,  JT  2  j  O2  ;  or  triatomic,  as  phosphoric  acid, 


j03;  citric  acid, 

A  monatomic  hydrated  acid,  having  only  one  atom  of  replaceable  hydrogen,  is 
necessarily  monobasic  ;  a  biatomic  acid,  having  two  atoms  of  replaceable  hydrogen, 
is  generally  (but  not  necessarily)  bibasic  ;  a  triatomic  acid,  generally  tribasic.  The 
determination  of  the  basicity  of  an  acid  is  a  matter  of  some  difficulty.  In  many 
cases,  the  formation  or  non-formation  of  acid  and  double  salts  may  serve  as  a  dis- 

tinction.    Thus,  tartaric  acid,  which  is  a  bibasic  acid,     4U       JO2,  forms  a  neutral 

H2      > 

tartrate  of  potash,         4°4<>  and  an  acid  tartrate,  4O2;  so,  likewise,  sul- 


phuric acid  forms  £K2O4,  and  SKHQ4  ;  whereas  nitric  acid,  having  but  one  atom  of 
hydrogen,  forms  but  one  potash-salt,  viz.,  NKO3.  But  acetic  acid,  generally 

regarded  as  monobasic,  Q2H4O2  =     *  jj3     j  O,  also  forms,  not  only  a  neutral  pot- 

ash salt,  G2H3KO2,  but  likewise,  an  acid  potash-salt,  usually  represented  by  the 
formula,  O2H3KO2  .  QaH4O2  •  but  if  the  formula  of  acetic  acid  be  doubled,  making 
it€4H8O4,  the  neutral  potash-salt  will  be  O4HgK2O4,  and  the  acid  salt,  €4H6(KH)O4. 
Acetic  acid  will  thus  be  represented  as  a  bibasic  acid  ;  and  in  fact,  this  quantity, 
G4H8O4  (=  120),  is  the  equivalent  of  £H2O4  (=  98),  that  is  to  say,  it  saturates 
the  same  quantity  of  potash.  Why,  then,  is  acetic  acid  universally  regarded  as 
monobasic  ?  On  this  point,  we  shall  quote  the  observations  of  Gerhardt  :  — 

"  The  basicity  of  acids  is  a  question,  not  of  equivalents,  but  of  molecules.  .  .  . 
If  we  examine,  under  the  same  volume,  the  composition  of  the  vapour  of  certain 
volatile  bodies,  corresponding  to  the  acids,  and  compare  together  the  similar  terms, 
guch  as  the  chlorides  of  the  acid  radicals,  or  the  neutral  compound  ethers,  we 
observe  perfectly  regular  differences,  which  are  always  related  to  the  chemical 
properties  of  the  corresponding  bodies  :  thus,  — 

„      ,     f  ("Chloride  of  acctyl  ............  contain  C1.O2H3O. 

^  of  sulphuryl  ........       «       C12.SO2. 


Acetate  of  methyl  ............  contain 

2  vol.  of. 

Sulphate  of  methyl  ..........        "       Jf^2,  }O2. 


[n  the  same  volume,  therefore,  chloride  of  acetyl  contains  the  radical  chlorine 
ODce,  while  chloride  of  sulphuryl  contains  it  twice  :  In  the  same  volume,  again, 


ACIDS. 


701 


sulphate  of  methyl  contains  twice  the  quantity  of  methyl  that  is  contained  in  the 
acetate.  With  these  differences  of  composition  of  the  chlorides  and  neutral  ethers, 
are  connected  other  properties,  such  as  the  following  :  —  Acetic  acid  forms  but  one 
compound  ether  (p.  705),  whereas  sulphuric  acid  forms  two,  a  neutral  and  an 
acid  ether  ;  acetic  acid  forms  but  one  amide  (p.  714)  ;  sulphuric  acid  forms  several, 
&c.  In  short,  on  inquiring  what  are  the  smallest  quantities  of  the  radicals, 
acetyl  and  sulphuryl,  that  are  concerned  in  chemical  metamorphoses,  we  find  that 
they  are  Q2H3O,  equivalent  to  H,  and  SO2  equivalent  to  H2;  hence,  we  are  led  to 
represent  the  molecule  of  acetic  acid  as  rnonatomic,  and  that  of  sulphuric  acid  as 
biatomic." 


2 


The   principal    monobasic   inorganic   acids   are   nitric,    Tj2jO,  hypochlorous, 


,  chloric, 


,  and  metaphosphoric, 


Of  monobasic  organic  acids,  the  most  important  are  the  so-called  fatty  acids, 
whose  general  formula  is  — 


They  correspond  to  the  alcohols  OnH2n+,O,  and  those  which  contain  the  same 
number  of  carbon  atoms  as  the  known  alcohols  may  be  obtained  from  the  latter  by 
the  action  of  oxidizing  agents,  such  as  chromic  acid.  The  number  of  these  acids 
at  present  known  to  exist  is  sixteen,  viz.  :  — 


Formic  acid ^i^s 

Acetic       '*  G2H,, 

Propionic  " ^3^< 

Butyric     "  £4^$ 

Valerianic    ^5^1 

Caproic     " ^6^1 


Qq 


CEnanthylic  acid.. 

O-  H,,O9 

Palmitic 

acid. 

Caprylic            "   .. 

0  H  0, 

Stearic 

Pelargonic       "   .. 

^^8        16     2 

OHO 

Cerotic 

tt 

Rutic  or  capric  .. 

^9        J8^^2 

Melissic 

tt 

Laurie               "   .. 
Myristic           "  .. 

OHO 

^14  "28^2 

O27H54O2 


These  acids  occur  in  the  vegetable  and  animal  organism ;  they  are  formed  by 
the  saponification  of  fats,  and  by  the  action  of  oxidizing  agents  on  fatty  and  waxy 
matters,  and  on  albumin,  fibrin,  casein,  &c.  The  first  ten  acids  of  the  series  are 
liquid  at  ordinary  temperatures;  the  next  four  are  solid  fats;  the  last  two  are 
waxy.  Cerotic  acid  is  obtained  from  Chinese  wax;  melissic  acid  from  bees' -wax. 

A  second  series  of  monobasic  organic  acids  consists  of  acids  whose  radical  is  of 
the  form  £nH2n_aO;  e.g.,  oleic  acid,  C18H34O2  =  ^j^*}£,  obtained  by  the  sa- 
ponification of  various  fixed  oils.  A  third  series  consists  of  acids  whose  radical 
has  the  form  €nH2n_9O.  These  are  called  the  aromatic  acids;  only  three  of  them 

are  known,  viz.  benzoic  acid,      7H5     JO;    toluic  acid,       j^jO,  and  cuminic 
acid,  °'°g'l0JO. 

There  are  a  few  monatomic  organic  acids  not  included  in  either  of  these  groups, 
among  which  must  be  particularly  mentioned  cyanic  acid,  ^}O.  The  cyanates 

are  formed  from  the  cyanides  by  oxidation  ;  thus,  cyanide  of  potassium  fused  with 
oxide  of  lead,  or  bioxide  of  manganese,  yields  cyanate  of  potash,  ONKO. 

Bibasic  acids.  —  These  acids,  as  already  observed,  generally  form  two  salts,  a 
neutral  and  an  acid  salt,  and  are  peculiarly  inclined  to  form  double  salts ;  e.  g. 

potassio-cupric  sulphate,  KCu}O2;  tartrate  of  potash  and  soda,  ^1^4JO2. 
With  the  alcohols  they  form  two  compound  ethers,  a  neutral  and  an  acid  ether ; 


702  WATER-TYPE. 


e.  g.,  neutral  oxalate  of  ethyl,  /^  jj\  }^;  acid  oxalate  of  ethyl,  or  oxalovinic 


Within  the  same  vapour  volume,  the  neutral  ethers  of  the  bibasic  acids  contain 
twice  as  much  of  the  alcohol-radical  as  the  neutral  ethers  of  the  monobasic  acids 

(p.  706).     Thus,  2  vols.  oxalate  of  ethyl  =  /^f  g2  (  JO;    2  vols.  benzoate  of 


The  chlorides  of  bibasic  acids  (obtained  by  the  action  of  pentachloride  of  phos- 
phorus on  the  acids)  contain,  within  a  given  vapour  volume,  twice  as  much  chlo- 
rine as  the  chlorides  of  monobasic  acids  (p.  708). 

QQ  OQ 

The  principal  bibasic  inorganic  acids  are  carbonic,  TT  j  O2  ;  sulphurous,  TT  j  Q2; 
sulphuric,  ^  j  O2;  and  chromic  acid,  £j  }Q2.  Pyro-phosphoric  acid,  P2H4O7, 

•»  p  TT  r\ 

may  be  regarded  as  bibasic  acid,  containing  the  radical,  P2H2O5;  viz.,     2jj2    5}Q2; 

or  as  a  compound  of  metaphosphoric  and  ordinary  phosphoric  acid. 

The  greater  number  of  the  bibusic  organic  acids  may  be  arranged  in  three 
erroups,  viz.  :  — 

OH      O 

a.  —  Acids  whose  general  formula  is     "   ^f"4    2jO2.     Eight  of  these  are  known, 

viz.  :  —  Oxalic  acid,    ^  2  j  Q2;  succinic  acid,  (€4)  ;  pyro-tartaric,  (O5);  adipic, 


pimelic,  (O7);  suberic,  (O8)  ;  anchoic,  (€9)  ;  arid  sebacic  acid,  (C10).  They  are 
formed  by  the  action  of  oxidizing  agents  on  fatty  matters,  and  are  related  to  the 
monobasic  fatty  acids,  £nH2nO4,  by  the  relation  — 


C02  +  £n_,H2n_202 
e.g.,  04H604  =  €O2  +      asH6O4 

Succinic  acid.  Propionic  acid. 

j3.—General  formula:  ^nHg-^2  j  O2.     For  example,  lactic  acid  =  O6H12O6 
=  (€3H502)2j0i 

n  TT         r\ 

y.  —  General  formula  :     n    g~10    2  j  O2.     Two  acids  of  this  group  are  known, 

viz.,  phthalic  acid,  Q8H6Q4,  obtained  by  the  action  of  nitric  acid  on  bichloride  of 
napthalin,  and  insolinic  acid,  O9H8O4,  by  the  action  of  chromic  acid  on  cuminic 
acid.  They  are  related  to  the  aromatic  acids  in  the  same  manner  as  the  acids  a 
to  the  fatty  acids.  Thus  :  — 


Insolinic  acid.  Toluic  acid. 

Of  bibasic  acids  not  included  in  the  preceding  groups,  the  most  important  are 
malic  acid,  O4H6O5  =  °4^4°3}02;  and  tartaric  acid,  O4H6O6  =  ^f*}®* 

Tribasic  acids.  —  These  acids,  containing  three  atoms  of  replaceable  hydrogen, 
form    three   kinds   of  salts,  viz.,  one  neutral,  and  two  acid  salts.     Thus,  from 

*       pn 
fcribasic  phosphoric  acid,  PH3O4  =*  ^    I  OB  are  formed  PH8KO4,  PHKgO4,  and 

PK304. 


ACIDS.  703 

With  alcohols  they  form  three  compound  ethers.  Phosphoric  acid  and  common 
alcohol  yield  ethylophosphoric  acid,  PH2(Q2H5)O4;  bi-ethylophosphoric  acid, 
PH(02H5)2O4;  phosphoric  ether,  P(O2H5)3O4. 

The  neutral  ethers  of  tribasic  acids  contain,  within  a  given  vapour  volume, 
three  times  as  much  of  the  alcohol  radical  as  the  ethers  of  the  monobasic  acids 

Thus,  2  vols.  citric  ether  contain   ,/(  TT\4}Q3:  and  2  vols.  acetic  ether  contain 

tlJ 


02H5  I 

The  chlorides  of  the  tribasic  acid  radicals  contain,  within  a  given  volume, 
three  times  as  much  chlorine  as  the  chlorides  of  the  monobasic  acid  radicals. 
Thus,  2  vols.  chloride  of  phosphoryl  (oxychloride  of  phosphorus)  contain  PQ.  C13  ; 
and  2  vols.  chloride  of  benzoyl  contain  Q7H5Q.C1. 

The  tribasic  mineral  acids  are,  —  boracic  acid,  BH3O3;  phosphorous  acid, 
PH3O3  ;  phosphoric  acid,  PH3Q4  ;  and  arsenic  acid,  AsH3Q4. 

Five  tribasic  organic  acids  are  known,  viz.  :  — 

Cyanuric  acid  .  ..........................  O6H3N3O3  = 

Citric  acid  .............  ...................    O6H807  = 

Aconiticacid  .............................    G6H606  = 

Meconicacid  .............................    O.HA  = 

Chelidonic  acid  ..........................    G7H4O6= 

Oyanuric  acid  may  be  regarded  as  a  triple  molecule  of  cyanic  acid.  It  is 
formed  by  the  destructive  distillation  of  uric  acid,  by  the  action  of  chlorine 
gas  on  urea,  and  by  the  action  of  water  on  fixed  chloride  of  cyanogen,  Cy3Cl3. 
Aconitic  acid  is  obtained  by  the  destructive  distillation  of  citric  acid.  Meconic 
acid  is  contained  in  opium,  and  chelidonic  acid  in  the  chelidonium  majus. 

Conjugated  acids.  —  This  name  is  given  to  acids  containing  a  conjugated  radical. 
Thus,  there  are  chloro-,  bromo-,  and  iodo-conjugated  acids,  containing  chlorine, 
bromine,  or  iodine  in  place  of  hydrogen  in  the  radical  ;  e.  g.,  chloracetic  acid, 

H       }&  J  terchloracetic  acid,     2jj3     j  Q  :  nitro-conjugated  acids,  containing 
NO2  ;  e.  g.,  nitro-benzoic  acid,     7    ^H   2'     j  O  :  sulpho-conjugated  acids,  contain- 


ing SO2;  e.g.,  sulpho-benzoic  acid,     v42}a2,  &c. 

These  acids  are  formed  by  the  action  of  sulphuric  acid,  nitric  acid,  chlorine,  &c., 
on  the  primitive  acids  :  — 

=  H  jo 


*•  —  Amidogen   acids.  —  These    are    derived    from    hydrate    of    ammonium, 
NH 
Tg  4}O,  by  the  substitution  of  an  acid  radical  for  two  or  more  atoms  of  the 

hydrogen  in  ammonium.     Thus  :  — 


704  WATER     TYPE. 

Sulphamic  acid  ..............................  SH3NO3  = 

Phosphamic  acid  ............................  PH2NO2  = 

Osmiamic  acid  ...........  .  ...................  Os2HNO3  =  2       JO. 

Oxamicacid  ..................................  02H3N03  =  NHiO|A)  j  o 

These  acids  are  formed  by  the  action  of  ammonia  on  the  anhydrides,  or  by  the 
action  of  heat  on  the  acid  ammonia-salts  of  bibasic  acids,  an  atom  of  water  being 
thus  eliminated  :  — 


TT  £\  222      )  f^ 

~  H 


Acid  oxalate  of  Oxamic  acid. 

ammonia. 


ANHYDROUS  ACIDS,  OR  ANHYDRIDES.  —  These  compounds  are  formed  by  the 
substitution  of  an  acid  radical  for  the  whole  of  the  hydrogen  in  one  or  two  mole- 

KTQ 

cules  of  water,  thus  :  —  citric  anhydride,  N2Q5  =  yj£i2^;  sulphuric  anhydride, 


. 

=  &O2  .  O;  phosphoric  anhydride,  P2O5  =  p^  j  O3. 

Anhydrous  nitric  acid  is  obtained  by  the  action  of  chlorine  on  dry  nitrate  of 
silver.  The  anhydrides  of  bibasic  acids  may  be  formed  by  the  abstraction  of  water 
from  the  hydrated  acids,  either  by  heat  or  by  the  action  of  anhydrous  phosphoric 
acid  ;  e.  g.  :  — 

°4JJ2°2}  °2  ~~  H2°  =  ^3£^£: 

7^       TT~^*~rT  Succinic 

Succimc  acid.  anhydride. 

The  bibasic  acids  may,  indeed,  be  supposed  to  contain  water.  Thus,  succinic 
acid  =  Q4H4O2  .  O  -f  H2O.  But  the  anhydrides  of  the  monobasic  acids  cannot 
be  obtained  in  this  way;  in  fact,  according  to  the  formulae  of  the  unitary  system, 
they  do  not  contain  water,  and  even  supposing  H2O  to  be  abstracted  from  them, 

the  remainder  will  not  be  the  formula  of  the  anhydrides  :  thus,  the  formula  of 

p  TT  r\ 
acetic  acid  being     2Tj3     j  O,  the  abstraction  of  H2O  would  leave  O2H2O  ;  whereas, 

the  formula  of  anhydrous  acetic  acid  is  Q^Q  j  O  =  2  X  €2H3O|.     This  is  a  fact 

which  the  ordinary  formulas  do  not  explain.  If  the  formula  of  hydrated  acetic 
acid  be  C4H404  =  C4H303  .  HO,  it  is  by  no  means  evident  why  the  HO  should  not 
be  separated  from  it,  and  leave  the  anhydrous  acid. 

The  anhydrides  of  organic  monobasic  acids  are  obtained  by  the  action  of  the 
chlorides  of  their  radicals  on  the  alkaline  salts  of  the  acids  ;  thus  :  — 

=  KC1 


Chloride  of 
potash.  dride. 

There  are  some  organic  anhydrides  containing  two  different  radicals  ;  thus,  by 
the  action  of  chloride  of  benzoyl  on  acetate  of  potash,  aceto-benzoic  anhydride  is 
formed  :  — 


C1  =  KC1 


COMPOUND    ETHERS.  705 

These  compounds  are  resolved  by  heat  into  the  simple  anhydrides,  thus  :  — 


OXYGEN-SALTS,  OR  INTERMEDIATE  OXIDES.  —  Salts  are  formed  by  the  substi- 
tution of  a  metal  or  other  positive  radical  for  the  basic  hydrogen  of  an  acid,  and 
may  therefore  be  regarded  as  water,  the  hydrogen  of  which  is  replaced  partly  by 
a  basic,  partly  by  an  acid  radical.  If  all  the  basic  hydrogen  of  the  acid  is  thus 
replaced,  the  salt  is  neutral  or  normal  ;  if  only  part  of  the  hydrogen  is  thus  re- 
placed, the  salt  is  acid  ;  and  such  salts  may  be  regarded  as  compounds  of  neutral 
salts  with  the  free  acid,  thus  :  — 


Bisulphate         Sulphuric     Neutral    sul- 
of  soda.  acid.         phateofsoda. 


KH     $-      H  K 


Biacetate   of  Acetic         Neutral  acetate 

potash.  acid.  of  potash. 

Basic  salts  may  be  regarded  as  compounds  of  a  neutral  salt  and  an  oxide,  or  as 
double  or  triple  molecules  of  water,  in  which  the  hydrogen  is  replaced  by  a  posi- 
tive radical  in  a  larger  proportion  than  is  required  to  form  a  neutral  salt  ;  thus  :  — 


Pb3 


Subacetate        Oxide  of    Neutral  acetate 
of  lead.  lead.  of  lead. 


Subsulphate     Oxide  of    Neutral  sulphate 
of  copper.        copper.         of  copper. 

In  the  neutral  salts  of  sesquioxides,  as  in  the  oxides  themselves,  3  at.  hydrogen 
of  the  type  water  are  replaced  by  2  at.  of  the  metal  ;  thus  — 


Ferric  nitrate.  Ferric  sulphate. 

Compound  ethers.  —  When  the  basic  hydrogen  of  an  acid  is  replaced  by  an 
alcohol-radical,  the  product  is  a  compound  ether;  these  compounds  may  also  be 
regarded  as  alcohols  in  which  one  atom  of  hydrogen  is  replaced  by  an  acid  radi- 
cal. As  already  observed,  monobasic  acids  form  but  one  compound  ether;  bibasic 
acids  form  two,  a  neutral  and  an  acid  ether;  and  tribasic  acids,  one  neutral  and 
two  acid  ethers.  The  acid  ethers  are  true  acids,  and  form  salts.  Thus,  from  sul- 
phuric acid  are  formed  — 


Neutral  sulphate  of  ethyl  .......  .  .............     =  £    }O2,  and 

SO2] 
Acid  sulphate  of  ethyl,  or  sulphovinic  acid     =       H    \Q2 

02Hj 
The  remaining  atom  of  hydrogen  in  the  latter  may  be  replaced  by  K,  Na,  &c. 


706  WATER-TYPE. 

From  citric  acid  are  'formed  — 

Neutral  citrate  of  methyl 


Citrobimethylic  acid  (monobasic)  ....................  (£H3)2  [O3. 

'   H 


Citromonomethylic  acid  (bibasic)  ..................    £H3    [  O3. 

H2     J 

The  glycerides  or  neutral  fats  (p.  699)  also  belong  to  the  compound  ethers, 
being  derived  from  a  triatomic  alcohol  or  glycerine  by  the  substitution  of  an  acid 

r\  TT 

radical,for  the  replaceable  hydrogen;  e.  </.,  triacetin  =  /n  jj  AN  |^3 

SULPHIDES,    SELENIDES,    TELLUBIDES. 

The  formula  of  these  bodies  are  precisely  similar  to  those  of  the  oxides,  being 
derived  from  hydrosulphuric  acid,  ^  jg,  &c.,  just  as  the  oxides  are  derived  from 

water.     These  series,  however,  especially  the  selenides  and  tellurides,  are  much 
less  complete  than  that  of  the  oxides. 

The  analogy  between  the  metallic  sulphides  and  oxides  has  been  sufficiently 
pointed  out  in  the  preceding  part  of  this  work.     The  alkali-metals,  potassium, 

41      '.  TT"  T> 

sodium,  &c.,  form  hydrated  sulphides,  or  hydro-sulphates,  such  as  „  j  S,  vj  ?  j  S, 


&c.  ;  and  anhydrous  sulphides,  TT}&,  &c.     Most  of  the  other  metals  form  only 

anhydrous  sulphides. 

The  alcoholic  sulphides,  primary  and    secondary,  bear   the  same    relation    to 
hydrosulphuric  acid  that  the  alcohols  and  ethers  bear  to  water.     The  primary 

Q   TT 

alcoholic  sulphides,     n  TTD+I  j  &,  generally  called  mercaptans,  are  fetid  oils,  or  crys- 

talline solids,  which  are  obtained  by  the  action  of  the  alkaline  hydrosulphates  on 
the  chlorides  of  the  alcohol  radicals  :  — 

=  KC1  +  €ff5jS; 

Chloride  of  Ethylic  mer- 

ethyl.  captan. 

or  by  the  action  of  the  same  alkaline  hydrosulphates  on  the   sulphovinates  or 
homologous  salts  :  — 


2        H         *   K2         H        ' 
The  basic  hydrogen  in  the  mercaptans  may  be  replaced  by  metals,  forming 
compounds  called  mercaptides  ;  eg.,    jj  5j-£. 

The  secondary  alcoholic  sulphides  .or  hydrosulphuric  ethers  are  obtained  by  the 
action  of  the  anhydrous  alkaline  sulphides  on  the  chlorides  of  the  alcohol- 
radicals  :  — 

2£2H6C1  +  |}&  =  2KC1  +  f22H55}&- 

Sulphur-acids.  —  The  mineral  sulphur-acids  are  but  little  known  in  the  hydrated 
state.  The  anhydrous  sulphur-acids  are  analogous  to  the  oxygen-acids.  Thus, 


HYDROCHLORIC    ACID    TYPE.  70? 

A  g  A  g 

sulpharsenious  acid,   .    JS3,  sulpharsenic  acid,   .    JS6,  the  arsenic  being  triato- 

mic  in  the  former,  and  pentatomic  in  the  latter. 

But  few  organic  sulphur-acids  have  been  obtained.     Hydrosulphocyanic  acids, 

ONH£  =  TTJ&J  is  analogous  to  cyanic  acid,  -rJ|O.  Its  potassium-salt  is  ob- 
tained by  heating  sulphur  with  ferrocyanide  of  potassium  (p.  377). 

r\  TT  r\ 

Thiacetic  acid  2TT3  I  &,  is  obtained  by  the  action  of  pentasulphide  of  phos- 
phorus on'  acetic  acid :  — 

)  +  P2S5  =±  PA  + 

This  reaction  is  instructive  when  viewed  in  relation  to  that  of  pentachloride  of 
phosphorus  on  acetic  acid;  the  latter  giving  rise  to  two  chlorides,  {^HgQ.Cl,  and 
HC1,  whereas  the  action  of  the  sulphide  of  phosphorus  yields  not  two,  but  one 

/H  TT  .Q. 
sulphur  compound,     2Tj3    1$.     A  similar  difference  is  observed  in  the  action 

of  the  sulphide  and  chloride  of  phosphorus  on  alcohol,  the  former  producing  a 

n  TT 
single  compound,  viz.,  mercaptan,  the  sulphide  of  ethyl  and  hydrogen,     |r  5|8, 

the  latter  producing  two  separate  compounds,  viz.,  €2H5C1,  and  HC1.  This 
difference  of  action  shows  in  a  striking  manner  the  propriety  of  representing  the 
oxides  and  sulphides  by  a  type  containing  two  atoms  of  hydrogen,  and  the 
chlorides,  bromides,  &c.,  by  a  type  containing  only  one  atom  of  hydrogen. 

Sulphur-salts. — These  compounds  are  formed  from  the  type  TT  }&,  by  the  sub- 
stitution of  a  positive  and  a  negative  radical  for  the  two  atoms  of  hydrogen  : 
Thus,  monobasic  sulpharseniate  of  potassium,  tr}^;  tribasic  sulpharseniate  of 


potassium,   j^    t£3;  these  formulae  are  evidently  analogous  to  those  of  the  mono- 

basic and  tribasic  phosphates. 

The  compound  sulphur-ethers  are  sulphur-salts,,  in  which  the  positive  element 

is  an  alcohol  radical:  —  For  example,  sulphocyanide  of  ethyl,  £,  -£  J£;  sulphocy- 

anide  of  allyl,  or  oil  of  mustard,  =  ^  Z  jg. 

Sulphide  of  acetyl  and  ethyl,  or  thiacetic  ether,  is  obtained  by  the  action  of 
persulphide  of  phosphorus  on  acetic  acid  :  — 


HYDROCHLORIC   ACID   TYPE. 

CHLORIDES.  —  The  basic  metallic  chlorides  are,  like  the  oxides,  either  monato- 
mic  or  polyatomic  ;  e.  g.  — 

KC1  PtCl2  Fe2013.AuCl3. 

Monatomic.  Biatomic.  Tritaomic. 

< 

The  biatomic  and  triatomic  chlorides  unite  with  the  monatomic  chlorides,  form- 
ing crystalline  compounds,  whose  composition  may  be  illustrated  by  the  formulae 
of  — 

Chloro-aurate  of  sodium  .................................  NaCl.AuCl3  =          C14. 


708  HYDROCHLORIC    ACID    TYPE. 


Chloroplatinate  of  ammonium,  NH4Cl.PtCl2  =        *   CI3. 

The  chlorides  of  gold  and  platinum  form  similar  compounds  with  the  hydro- 
chlorates  of  the  organic  bases,  which  may  be  represented  by  analogous  formulae. 
Thus,  chloroplatinate  of  ethylamine,  O2H5 

H 

II 

The  hydrochlorate  of  any  organic  alkali  may  be  represented  as  the  chloride  of  a 
basic  radical  containing  an  additional  atom  of  hydrogen,  just  as  sal-ammoniac  may 
be  represented  either  as  NH8.HC1,  or  as  NH4C1.  Thus,  hydrochlorate  of  ethyla- 
mine,  NH2(02H6).HC1=NH3(02H5).C1. 

The  chlorides  of  the  alcohol-radicals,  or  hydrochloric  ethers,  are  obtained  either 
by  the  action  of  hydrochloric  acid,  or  one  of  the  chlorides  of  phosphorus,  on  the 
alcohols  :  — 


-r  Chloride  of 

Alcohol.  Phosphorous  ^    i 

"    *  ' 

These  chlorides  are  more  volatile  than  the  corresponding  alcohols. 

The  acid,  or  negative  chlorides,  are  also  monatonric,  biatoniic,  or  triatoinic,  ac- 
cording to  the  acids  from  which  they  are  derived. 

The  monatomic  chlorides,  derived  from  one  atom  of  hydrochloric  acid,  contain, 
in  two  vapour-volumes,  one  atom  of  chlorine,  capable  of  forming  a  metallic  chlo- 
ride with  mineral  alkalies;  e.  g.,  chloride  of  cyanogen,  ONC1  =  Cy.Cl;  chloride 
of  acetyl,  =  Q^I^O-Ch  They  are  obtained  by  the  action  of  one  of  the  chlorides 
of  phosphorus  on  the  acids,  thus  :  —  • 

+  PO.C13 


Perchloride  of          ^  ~v—  —  **  Oxychloride 

phosphorus.     ,C,  ]T      °   ?cet?1    of  phosphorus. 
-f-  hydrochloric  acid. 

PC13  =  ^J03  +  3(02H3O.C1.) 

Or,  by  the  action  of  oxychloride  of  phosphorus  on  an  alkaline  salt  of  the  same 
acid  :  — 

PO.C13  =  ^?  J03  +  3(02H3O.C1.) 

The  biatomic  chlorides,  derived  from  two  molecules  of  hydrochloric  acid,  con- 
tain, within  two  vapour-volumes,  two  atoms  of  chlorine,  capable  of  forming  a  me- 
tallic chloride  with  alkalies  :  — 

Chloride  of  carbonyl,  oxychloride  of  carbon,  or  phosgene  ......  =  OO.C12 

Chloride  of  sulphuryl  .................................................   =  &O2.C12 

Chloride  of  succinyl  ...........  .....................................  =  £4H4Q4.C12 

Chloride  of  chromyl,  or  chlorochromic  acid  .......................  =  Cr2O2.CJ2 

These  chlorides  may  be  obtained  by  the  action  or  pentachloride  of  phosphorus 
upon  the  corresponding  anhydrous  acids. 

The  action  of  pentachloride  of  phosphorus  on  a  bibasic  acid  is  supposed  by 
Gerhardt  to  consist  of  two  stages,  —  the  first  being  the  formation  of  an  anhydrous 
acid,  the  second  the  conversion  of  that  compound  into  a  chloride.  For  example  :  — 


CHLORIDES.  709 


44H2oJ  +  PC12.C13=  G4HA-0  +  2HC1  +  POC13; 
and  04H402-0  +  PC12.C13  =  O4H4O2.C12  +  POC13; 

whereas,  in  the  case  of  a  monobasic  acid,  the  action  consists  of  one  stage  only. 
This  difference  is  connected  by  Gerhardt  with  the  fact,  that  a  bibasic  acid  may  be 
supposed  to  contain  water,  whereas  a  monobasic  acid  cannot  (p.  704).  Accord- 
ing to  Williamson,  on  the  contrary,  the  two  stages  of  the  reaction,  in  the  case  of 
a  bibasic  acid,  are  precisely  similar  to  one  another,  and  to  the  single  reaction  which 
takes  place  with  monobasic  acids.  Thus,  with  sulphuric  acid  — 


\  02  +  PCla.Cl,  =       u  i  O  +  HC1  +  POC13, 
g°2-Cl2  +  HC1+ 


The  difference  in  the  two  views  of  the  reaction  is  this  :  —  that  the  former  supposes 
the  first  stage  of  the  action  to  consist  in  the  formation  of  an  anhydrous  acid  ;  the 
second  supposes  an  intermediate  compound,  —  a  chloro-hydrate  of  the  acid,  to  be 
produced.  The  formation  of  this  chloro-hydrate  has  been  shown  by  Professor 
Williamson  to  take  place  with  sulphuric  acid.  If,  however,  one  of  the  two  mole- 
cules of  hydrochloric  acid  in  Gerhardt'  s  first  equation  be  supposed  to  remain  as- 
sociated with  the  anhydrous  acid,  the  two  views  will  nearly  coincide.  In  every 
case,  indeed,  the  reaction  consists  essentially  in  the  interchange  of  O  and  C12. 

The  triatomic  chlorides,  or  ter  chlorides,  contain,  within  two  vapour-volumes, 
three  atoms  of  chlorine  capable  of  forming  a  metallic  chlorine  when  acted  upon 
by  the  mineral  alkalies. 

The  following  acid  chlorides  are  triatomic  :  — 

Terchloride  of  phosphorus  ....................................................  P.C13. 

Chloride  of  phosphoryl  (oxychloride  of  phosphorus)  ....................   PQ'C13. 

Chloride  of  sulphophosphoryl  (sulphochloride  of  phosphorus)  .........  PS.C13. 

Chloride  of  chlorophosphoryl  (pentachloride  of  phosphorus)  ...........  PC12.C13. 

Chloride  of  boron  ..............................................................  B.C13. 

Chloride  of  cyanuryl  (solid  chloride  of  cyanogen)  ........................   Cy3.Cl3. 

The  BROMIDES,  IODIDES,  and  FLUORIDES,  are  exactly  analogous  to  the  chlorides. 
There  are  very  few  organic  fluorides  known. 

The  CYANIDES  are  also  analogous  to  the  chlorides. 

The  metallic  cyanides  have  a  great  tendency  to  unite  and  form  double  cyanides, 
which  may  be  regarded  as  derivatives  of  two  or  more  atoms  of  hydrochloric  acid. 

Thus,  the  ferrocyanides  may  be  represented  by  the  formula  ,  j  }Cy3,  and  the  fer- 

ricya.nides,  by  ™  3  }Cy6;  the  Fe2  in  the  latter  formula  being  equivalent  to  H3. 
re2 

The  cyanides  of  the  alcohol-radicals  are  obtained  by  distilling  a  sulphovinate  or 
homologous  salt  with  cyanide  of  potassium  :  thus,  — 


or  by  the  action  of  anhydrous  phosphoric  acid  on  the  ammoniacal  salts  of  the 
fatty  acids,  the  action  of  the  phosphoric  acid  consisting  in  the  abstraction  of  water : 
thus,— 

T^Ujtr  ")   /-\  (y  -r-r    /-^ 

AJJJ    5"^ ^±l2tf  = 

Acetate  of 
or,  generally, 


710  HYDROCHLORIC    ACID    TYPE. 

The  ammonia-salt  of  each  acid  in  the  series  yields  when  thus  treated,  the  cyanide, 
not  of  the  corresponding  alcohol-radical,  but  of  the  next  lowest;  thus:  the  pro- 
pionate  yields  cyanide  of  ethyl  ;  the  acetate,  cyanide  of  methyl  ;  and  the  foriniate, 
cyanide  of  hydrogen,  or  hydrocyanic  acid. 

When  these  cyanides  are  heated  with  caustic  alkalies,  the  opposite  change  takes 
place  ;  that  is  to  say,  an  alkaline  salt  of  the  acid  corresponding  to  the  next  highest 
alcohol  is  formed,  and  ammonia  is  evolved  :  thus,  — 


ONH 


Cyanide 
of  hy- 
drogen. 

ON.OH3  -f  g  JO  +  H20  =  °2|3°|0  +  NH8; 

Cyanide  of  Acetate  of 

methyl.  potash. 

ON.OnH2n+1  +  ]|  JO  +  H20  =  a»+'H2n  +  iOj0  + 

These  alcoholic  cyanides  may  also  be  regarded  as  nitriles  :  thus,  — 
ONH  =  N  .  OH;  ON  .  CH3  =  N  .  O2H3; 

Cyanide          Formo-  Cyanide  of  Aceto- 

ofhy-  nitrile.  methyl.  nitrile. 

drogen. 

generally :  ON  .  OnH2n+1  =  N .  On+1  H2n+1. 


AMMONIA    TYPE. 

NITRIDES.  —  a.  Positive.  —  These  compounds  are  chiefly  organic,  constituting  in 
fact  the  organic  bases  or  alkaloids.  A  few  mineral  nitrides  have,  however,  been 
obtained  by  the  action  of  ammonia  on  the  metals  or  their  oxides;  e.  #.,  amide  of 
potassium,  N(H2K)  ;  nitride  of  potassium,  NK3;  nitride  of  mercury,  NHg3. 

The  primary  nitrides  of  the  alcohol-radicals,  such  as  methylamine,  OH6N  = 
N(OH3.H2),  amylamine,  O5H,3N  =  N(05Hn  .  H2),  are  obtained:  —  !.  By  the 
action  of  the  bromides  or  iodides  of  the  alcohol-radicals  on  ammonia  :  — 

)02H5 
NH3  -f  02H5I  =  HI  +  N  f     H. 

"-v-'  J         II 

Iodide  of  ethyl.  t__  ^   _> 

Ethylamine. 

2.  By  the  action  of  potash  on  the  cyanates  OK  cyanurates  of  the  same  radicals  :  — 


Cyanate  of      Hydrate  of      Carbonate  of     Ethylamine. 
ethyl.  potash.  potash. 

3.  By  the  action  of  reducing  agents,  such  as  hydrosulphuric  acid,  or  acetate  of 
iron,  or  certain  nitro-conjugated  hydrocarbons;  thus:  — 


NITRIDES.  711 


€6H5(N02)  +  3H2g  =  N      H    +  2H2O  +  38. 
*    H 

Nitrobenzol.  Aniline  or 

phenylamine. 

They  are  also  frequently  produced  in  the  destructive  distillation  of  nitrogenized 
organic  substances,  and  are  consequently  found  in  coal-tar,  bone-oil,  &c. 

These  bodies  are  all  volatile  liquids,  having  more  or  less  of  an  ammoniacal  odour. 
The  bases  of  the  same  series  —  for  instance,  those  formed  from  the  alcohol-radi- 
cals QnH2n_|_, — are  less  volatile  and  more  oily,  as  they  contain  more  carbon.  They 
all  combine  with  acids  in  the  same  manner  as  ammonia,  and  form  crystallizable 
double  salts  with  bichloride  of  platinum.  Nitrous  acid  converts  them  into  alcohols 
or  nitrous  ethers,  with  elimination  of  nitrogen :  — 

VJN  +   ^ja3  =  NN   H 

Ethylamine.  Nitrous  acid.  Nitrite  of  ethyl. 


2(         '}N  )  +Ni°3  = 
V    H  )     J 


2  mol.  hydrate 
of  phenyl. 


Secondary  alcoholic  nitrides.  —  The  constitution  of  these  bodies  may  be  under- 
stood from  the  following  examples  :  — 


JBiethylamine,  O4HUN 
Metethylamine.  O3H9N 


H 

0 

Ethaniline,  or  ethyphenylamine, 


They  are  obtained  by  the  action  of  the  bromides  or  iodides  of  the  alcohol-radi- 
cals on  the  primary  nitrides  :  — 


H  \N  +  02H3Br  =  02H5  f  N  +  HBr. 
H-1  H-1 

Tertiary  alcoholic  nitrides,  or  nitrite  bases :  — 

Triethylamine,      O6H15N  =  O2Hg  JN. 

Biethamylamine,  C9H2IN  =  O2H*  fN. 

£1  H    J 


Methamylaniline, O12H19N  =  €5HU  \N. 


712  AMMONIA    TYPE. 

These  compounds  are  formed  by  the  action  of  the  iodides  and  bromides  of  the 
alcohol-radicals  on  the  secondary  alcoholic  nitrides ;  also  by  the  distillation  of  the 
ammonium-bases,  thus :  — 


Hydrate  of  Trie  thy  lamine.      Ethylene. 

tetrethylium. 

Triethylamine  is  likewise  obtained  by  the  action  of  ethylate  of  potassium  on 
cyan  ate  of  ethyl  :  — 


Cynate  of  2  at.  ethylate  of          Carbonate  Triethylamine. 

ethyl.  potassium.  of  potash. 

This  action  is  analogous  to  that  of  hydrate  of  potash  or  cyanate  of  ethyl  (p.  710). 
The  other  tertiary  alcoholic  nitrides  might  doubtless  be  obtained  in  a  similar 
manner. 

There  are  also  nitrides  containing  conjugated  alcohol-radicals  ;  e.  g.  :  — 

02H3C12 
Bichlorethylamine  ........................  O2H5C12N       =      H 

H 

O6H4Ch 
Chloraniline  ................................  O9H6C1N        =      H      [N. 

H      ) 

06H4(N02)) 
Nitraniline  .................................  O6H6(N02)N  =     H  VN. 

H 

Nitrides  of  aldehyde-radicals.  —  These  bodies  are  but  little  known. 
Acetosylamine,  N(H2  .  O2H3),  is  obtained  by  the  action  of  ammonia  on  chloride 
of  ethylene  (chloride  of  acetosyl  and  hydrogen)  :  — 

°2I3SC12    +    2NH3  =      VJN.HCl  +  NH4C1. 

H  J 

Chloride  of  aceto-  Hydrochlorate  of 

syl  and  hydrogen.  acetosylamine. 

The  natural  vegeto-alkalies,  morphine,  strychnine,  &c.,  are  most  probably  of 
similar  nature  to  these  artificial  alkalies,  but  they  have  not  yet  been  reduced  to 
regular  series. 

b.  Negative  or  acid  nitrides.  —  These  are  the  compounds  generally  called 
amides. 

Primary  amides.  —  In  these  compounds,  one-third  of  the  hydrogen  in  1,  2,  or 
3  molecules  of  ammonia  is  replaced  by  an  acid  radical. 

a.  Monatomic  :  — 

r<yH,0 
Acetamide,  or  nitride  of  acetyl  and  hydrogen  ..........  £2H5NQ  —  N-j        I  . 

^     H 


AMIDES.  %  713 


Butyramide,  or  nitride  of  butyryl  and  hydrogen  .......  O4H9NO  =  Ns      H   . 

H 


Benzamide,  or  nitride  of  benzoyl  and  hydrogen  ........  O7H7NQ  =  N-j      H    . 

^     H 

These  amides  differ  from  the  corresponding  ammoniacal  salts  by  the  elements 
of  one  atom  of  water  :  — 


Acetate  of  ammonia.  Acetamide. 

They  are  produced  by  the  action  of  ammonia  on  the  anhydrous  acids : 

-M 


Benzole  anhydride.  Benzoic  acid.       Benzamide. 

by  the  action  of  ammonia  on  the  acid  chlorides  :  — 

07H5O.C1  +  NH3  =  HC1  +  N  j  °7g5°; 
and  by  the  action  of  ammonia  on  the  compound  ethers  :  — 


Acetate  of  ethyl.  Alcohol.         v^^_, 

Acetamide. 

These  amides  are  neutral  crystalline  bodies,  which,  when  boiled  with  aqueous 
acids  or  alkalies,  take  up  water,  and  are  converted  into  ammonia-salts.  When 
treated  with  anhydrous  phosphoric  acid,  they  give  up  the  elements  of  1  at.  water, 
and  are  converted  into  cyanides  of  the  alcohol  radicals  :  — 

N  °2    3°  —  H2O  =  € 


Acetamide.  Cyanide  of  methyl. 

|3.  Biatomic.     Primary  biamides  or  diamides  :  — 

Oxamide,  or  nitride  of  oxalyl  and  hydrogen  .........  £2H4N202  =;  NJ    H2  . 

H2 


Succinamide,  or  nitride  of  succinyl  and  hydrogen ..  .€4H8N2O2  =  NJ      H2    . 

1     H2 

Urea  and  carbamide,  or  nitride  of  carbonyl  and>nTT  vrn        xr  I  TJ 
hydrogen  fTfrf*  =  **\  £2  ' 

**9 

Tartramide,  or  nitride  of  tartryl  and  hydrogen O4H8N2O4  =  N2|      H2  . 


They  are  produced  by  the  action  of  heat  on  the  neutral  ammonia-salts  of  bibasic 
acids : — 


14  AMMONIA    TYPE. 


22 

(NH4)2  }  °2  —  2  H2O  =  N2  1  H2  ; 

**i 

Oxamide. 
by  the  combination  of  ammonia  with  secondary  amides  :  — 


r€0 

NH3=  N2    H2; 
(H 


Cyanic  acid,  Urea. 

or  carbonimide. 

and  by  the  action  of  ammonia  on  compound  ethers  or  acid  chlorides  :— 

2NH°  = 

Oxalate  of  ethyl.  2  at.  alcohol.         Oxamide. 

.  €4H4O2.C12  +  2NH3  =  2HC1 


Chloride  of  Succinamide. 

succinyl. 

y.  —  Triatomic.     Primary  triamrdes  :  — 

pA 
Triphosphamide,  or  nitride  of  phosphoryl  and  hydiogen  ............  N3j  TT 

Citramide,  or  nitride  of  citryl  and  hydrogen  .........  G^^^  =  N3j 

Melamine  and  melam,  or  nitride  of  cyanuryl  and  -j 
hydrogen  ..............................................  I 

Secondary  amides.  —  In  these  compounds,  two-thirds  of  the  hydrogen  in  a 
molecule  of  ammonia  are  replaced  by  acid  radicals,  viz.  : 
1.  By  two  monatomic  radicals  j  e.g.  :  — 


Nitride  of  bisulphophenyl  and  hydrogen  ........  O,2HnNS204  =  N    06H5&02- 

H 


f652 

Nitride  of  sulphophenyl,  benzoyl  and  hydrogen...  OBH,,NSgO4  =  N  j   O7H5O  . 

^      H 

These  amides  are  produced  by  the  action,  of  acid  chlorides  on  the  primary 
amides  or  their  metallic  salts. 


N        H       +  C7H6O.C1  =  N  07H50   +  HC1. 
H                                     t       H 

2.  The  two  atoms  of  hydrogen  are  replaced  by  one  molecule  of  a  biatomic 

mides. 


radical.     These  compounds  are  called  imi 
Carbonimide  (cyanic  acid)  or  nitride 

TIT 

and  hydrogen  ...  ....................  . 

Succinimide,  or  nitride  of  succinyl  and  hydrogen  ,...O4H5NO2  =  N|    4  TT   2- 


Carbonimide  (cyanic  acid)  or  nitride  of  carbonyl  .     nxrTTA    _TMf^ 

TIT  /  "T^i^l  jTi-TT"    ^—  1^1  <       TT 

and  hydrogen  ...  ....................  .  ..................  I  (.  H 


INTERMEDIATE    NITRIDES.  715 

Most  of  them  are  produced  by  the  action  of  heat  on  the  acid  ammoniacal  salts 
of  bibasic  acids,  the  change  consisting  in  the  elimination  of  2  molecules  of 
water : — 

£4H«d) 

H 

NH4 

Acid  succinate  of  Succinimide. 

ammonia. 

by  the  action  of  heat  on  the  biamides  of  bibasic  acids,  ammonia   being   then 
given  off: — 


N2{  V2  2  -  NH3  =  N{°4^°2  ; 
H2 


Succinamide.  Succinimide. 

or  by  the  action  of  heat  on  the  amidogen  acids. 

Tertiary  Amides.  —  In  these  compounds,  all  the  hydrogen  in  ammonia  is  re* 
placed  by  acid  radicals. 

a.  Monatomic.  —  1.  The  hydrogen  is  replaced  by  three  monatomic  radicals; 
e.g.'.— 


Nitride  of  sulphophenyl,  benzoyl,  and  acetyl  ........................  Ns  O7H5O. 


r 
Nitride  of  sulphophenyl  and  benzoyl  .............  ....................  N  j  O7H5O. 

t 


2.     One  atom  of  hydrogen  is  replaced  by  a  monatomic,  and  the  other  two  by 
a  biatomic  radical  :  — 

Nitride  of  succinyl  and  sulphophenyl  ..................................  N!  nu  an  * 


These  amides  are  formed  by  the  action  of  acid  chlorides  on  the  secondary  amides, 
or  their  silver-salts. 

3.  All  the  hydrogen  is  replaced  by  a  triatomic  radical.     The  composition  of 
several  inorganic  compounds  may  be  expressed  in  this  manner  :  — 

Monophosphamide,  or  nitride  of  phosphoryl  ............................  =  N  .  PO. 

Boramide,  or  nitride  of  boron  ............................................  =  N  .  B. 

Free  nitrogen,  or  nitride  of  nitrogen,  the  amide  of  nitrous  acid  ...  =  N  .  N. 
Protoxide  of  nitrogen,  or  nitride  of  azotyl,  the  amide  of  nitric  acid  =  N  .  NO. 

p.  Biatomic.  —  Compounds  in  which  all  the  hydrogen  of  2  molecules  of  am- 
monia is  replaced  by  monatomic  or  biatomic  radicals  :  — 

rO4H4O2 
•  Trisuccinamide,  or  biamide  of  trisuccinyl  ..........................  NJ  O4H4O2. 

l 


Biamide  of  succinyl,  bibenzoyl,  and  bisulphophenyl  ............  NJ  (€7H5O)2. 


These  tertiary  biamides  are  produced  by  the  action  of  acid  chlorides  on  other 
amides  or  biamides. 

Intermediate  nitrides,  or  amid  og  en-salts.  —  These  are  compounds  in  which  the 
hydrogen  of  ammonia  is  replaced  partly  by  a  basic,  partly  by  an  acid  radical. 
Most  of  the  primary  and  secondary  amides  form  such  salts,  which  are  produced 


716  HYDROGEN    TYPE. 

by  the  direct  action  of  the  amides  on  the  corresponding  oxides  or  their  salts  ; 
e.g.:  — 


Benzaniidate  of  mercury 


r07H50 
Nj      Hg. 
v     H 


When  the  positive  radical  is  an  alcohol-radical,  the  compounds  are  called  alcala- 
mides  ;  those  which  contain  phenyl,  Q6H5,  are  also  called  anilides  :  tjius,  — 

r^eHs 
Phenyl-acetamide  or  acetanilide  .....................................  N-j  Q2H3Q. 

I     H 

{Q2H5 
Cy. 

PHOSPHIDES.  —  These  compounds  are  derived  from  the  type  ammonia  by  the 
substitution  of  phosphorus  for  nitrogen,  and  of  various  radicals  for  the  hydrogen. 
Phosphuretted  hydrogen,  PH3,  is  analogous  to  ammonia,  and  forms  with  hydriodic 
acid  a  compound,  PH3  .  HI,  or  PH4I,  which  crystallizes  in  cubes  like  iodide  of 
ammonium,  or  iodide  of  potassium. 

With  the  alcohol-radicals,  phosphorus  forms  compounds  analogous  to  the  alco- 
holic nitrides,  and  like  those  bodies  possessing  alkaline  properties;  e.  g.,  triphos- 
phomethylamine,  or  trimethyphosphine,  P(OH3)3.  These  compounds  may  be  ob- 
tained by  the  action  of  terchloride  of  phosphorus  on  zinc-methyl,  zinc-ethyl,  &c., 
the  reaction  being  expressed  by  the  following  general  equation  :  — 

PC13  +  30nH2n  +  1  Zn  =  SZnCl  +  P(£DH2n+1)3. 

These  phosphides,  treated  with  the  iodides  of  the  corresponding  alcohol-radicals, 
yield  compounds  analogous  to  the  ammonium  bases  :  thus,  — 


P(OH3)3  +  02H5I  =  ^e73  j  P  .  I. 

The  only  negative  or  acid  phosphide  known  is  chloracetyphide,  or  phosphide  of 
terchloracetyl  =  P(O2C13G .  H  .  H). 

ARSENIDES  AND  ANTIMONIDES.  —  Arsenic  and  antimony  also  form  compounds 
of  the  ammonia  type;  e.g.,  AsH3;  SbH3;  As(€2H5)3;  Sb(O2H5);  but  the 
arsenides  and  antimonides  of  tho  alcohol-radicals  differ  considerably  in  their  pro- 
perties from  the  nitrides  and  phosphides,  not  combining  with  hydrochloric  acid, 
&c.,  in  the  same  manner  as  ammonia,  but  rather  combining  with  oxygen,  chlorine, 
iodine,  &c.,  like  metals.  They  belong,  therefore,  rather  to  the  hydrogen  type  (p. 
719). 

HYDROGEN   TYPE. 

The  primary  derivatives  of  this  type  are  :  — 

1.  The  hydrides  of  the  metals  proper.     A  small  number  only  of  these  are  known, 
viz.,  Cu2H,  AsH3,  and  SbH3.     The  two  latter  may  also  be  regarded  as  derivatives 
of  ammonia. 

2.  The  hydrides  of  the  alcohol-radicals,  £nII2n  +  ,,  viz.,  marsh-gas,  or  hydride 
of  methyl,  €H4  =  H .  OH3;    hydride  of  ethyl,  O2H6  =  H  .  O2H6;   hydride  of 
amyl,  O5H,2  =  H  .  €5Hn,  &c,     These  compounds  are  formed  by  the  action  of  zinc 
on  the  chlorides  or  iodides  of  the  corresponding  alcohol-radicals  :  — 

2O2H5I  +  Zn  Zn  =  2ZnI  +  H  .  €2H5  +  £2H4 ; 


Iodide  of  Hydride  of    Ethylene. 

ethyl.  ethyl. 

ftl«o  by  the  action  of  water  on  zinc-methyl,  zinc-ethyl,  &c. :  — 


HYDRIDES    OF    ACIDS.  717 

Zn  .  02H5  +        0=  H  .  02H5  +         O; 


occasionally  also  in  the  destructive  distillation  or  spontaneous  decomposition  of 
vegetable  and  animal  substances.  Marsh-gas,  for  example,  is  formed  by  the  putre- 
faction of  vegetable  matter  under  water  (p.  278).  The  hydrides  of  methyl  and 
ethyl  are  gaseous  at  ordinary  temperatures,  the  rest  are  liquid  or  solid.  They  are 
decomposed  by  chlorine,  with  formation  of  substitution-products;  thus  — 

II  .  £2H5  -f  C1C1  =  H  .  O2(H4C1)  -f  HC1. 

There  are  likewise  hydrides  of  alcohol-radicals  of  the  form  H  .  OnH2n_7,  the 
best  known  of  which  is  benzol,  or  hydride  of  phenyl,  £6H6,  or  H  .  £6H5.  These 
compounds  are  obtained  in  the  destructive  distillation  of  many  organic  substances; 
benzol,  for  instance,  by  the  distillation  of  coal.  They  are  also  formed  by  the  dry 
distillation  of  the  monobasic  acids,  GnH2n_9O,  with  excess  of  lime  or  baryta,  a 
carbonate  of  the  base  being  formed  at  the  same  time  :  — 

£7H6O2  =  £O2  -f  *O6H6. 
Benzoic  acid.  Benzol. 

3.  The  hydrides  of  the  aldehyde-radicals,  On  H^.  ,.     These  are  :  — 

Ethylene,  olefiant  gas,  or  hydride  of  acetosyl  ..............   O2H4  =  H  .  O2H3. 

Propylene,  or  hydride  of  propionyl  ..........................   O3H6  =  H  .  Q3H5. 

Butylene,  or  hydride  of  butyryl  .............................   O4H8  =  H  .  O4H7. 

Amylene,  or  hydride  of  valeryl  ..............................  ^sHi0  =  H  .  G5H9. 

These  compounds  might  also  be  regarded  as  hydrides  of  the  alcohol-radicals, 
On  H2n_,;  for  example,  propylene  as  hydride  of  allyl  (p.  698).  Possibly,  how- 
ever, there  may  be  two  isomeric  series  of  these  compounds,  the  one  derived  from 
the  alcohols,  the  other  from  the  aldehydes. 

These  hydro-carbons  are  formed  by  the  destructive  distillation  of  organic  sub- 
Stances,  several  of  them  being  found  among  the  products  of  the  distillation  of 
coal.  They  are  also  produced  by  the  action  of  strong  sulphuric  acid  at  a  high 
temperature  on  the  alcohols,  the  change  consisting  in  the  abstraction  of  the  ele- 
ments of  water  :  thus  :  — 


02H60  —  H20  = 

Alcohol.  Ethylene. 

The  only  body  of  the  series  which  is  gaseous  at  ordinary  temperatures  is  ethylene 
(p.  285);  the  rest  are  liquid  or  solid.  The  first  term,  methylene,  has  not  been 
obtained  in  the  free  state.  These  compounds  are  especially  distinguished  by  com- 
bining with  two  atoms  of  chlorine,  bromine,  &c.,  forming  compounds  homologous 
with  Dutch  liquid  or  chloride  of  ethylene,  O2H4  .  C12;  whereas  the  hydrides  of 
the  radicals  QnH2n+i  are  decomposed  by  chlorine. 

The  lower  compounds  of  the  series  also  combine  with  anhydrous  sulphuric  acid.. 
Thus,  'defiant  gas  is  immediately  absorbed  by  the  anhydrous  acid,  or  by  a  coke 
ball  soaked  in  fuming  oil  of  vitriol.  This  property,  and  that  of  forming  liquid 
compounds  with  chlorine  and  bromine,  is  made  available  for  separating  olefiant 
gas,  and  the  other  more  volatile  hydrocarbons  of  the  series,  from  gaseous  mix- 
tures. 

4.  The  hydrides  of  the  acid  radicals, 

a.  Monatomic.  —  The  hydrides  of  the  acid  radicals  OnH2n_lO,  are  evidently  the 
aldehydes  of  the  fatty  acids  (p.  699)  :  thus  :  — 


718  ALCOHOL    METALS.  • 

Acetic  aldehyde....  ..................................    =  H.£2H03  = 

Butyric  aldehyde  .....................................  =  H  .  O^^  =  GJ^7  j  O. 

Benzole  aldehyde  (bitter  almond  oil)  .............  =  H  .  O7H5O  ==  ^7^5°  JO. 

The  following  compounds  may  be  regarded  as  the  aldehydes  of  monobasic 
mineral  acids  ;  that  is  to  say,  as  the  hydrides  of  the  radicals  contained  in  those 
acids  considered  as  derivatives  of  water  :  — 

Nitrous  acid,  or  aldehyde  of  nitric  acid  ...........................  NHQ2  =  H  .  N02. 

Hydrochloric  acid,  or  aldehyde  of  hypochlorous  acid  ............  C1H      =  H.  Cl. 

Hydrocyanic  acid,  or  aldehyde  of  cyanic  acid  ....................  QHN    =  H  .  Cy. 

Spontaneous  inflammable  phosphuretted   hydrogen,  or  alde- 

hyde of  hypophosphorous  acid  ...................................  PH        =  H  .  P. 

0.  Hydrides  of  biatomic  acid  radicals  :  — 
Hydrosulphuric  acid,  or  aldehyde  of  hyposulphurous  acid  ......  SH2       =  H2.&. 

Hydroselenic  acid,  or  aldehyde  of  hyposelenious  acid  ...........  £eH2     =  H2.&e. 

y.  Hydrides  of  triatomic  acid  radicals  :  — 
Non-spontaneously  inflammable  phosphurretted  hydrogen,  or 

aldehyde  of  phosphorous  acid  ....................................  PH3       =  H3.P. 

Antimoniuretted  hydrogen,  or  aldehyde  of  antimonious  acid..  SbH8      —  H3.Sb. 

The  secondary  derivatives  of  the  hydrogen-type  are  — 

1  .  The  ordinary  metals  :  —  Potassium,  K'K,  derived  from  HH  ;  antimony,  SbSb, 
derived  from  H3H3;  aluminium,  A12A12,  derived  from  H3H3,  &c. 

2.  The  alcohol-metals,  derived  from  the  type  HH,  both  atoms  of  hydrogen 
being  replaced  by  alcohol  radicals.  The  only  bodies  of  this  class  which  have  yet 
been  obtained  are  those  containing  the  radicals  £nH2n+,  ;  viz.  (a.)  Those  in  which 
the  two  atoms  of  hydrogen  are  replaced  by  the  same  radical  :  methyl,  •GH3  .  OH3  ; 
ethyl,  O2H5.O2H5;  butyl  or  tetryl,  O4H9.O4H9;  amyl,  £5HU.O5HU;  caproyl  or 
hexyl,  O6H,3  .  O6H13;  and  copryl  or  octyl,  £8H17  .  Q8H,7.  —  (&.)  Those  in  which  the 
two  atoms  of  hydrogen  are  replaced  by  different  radicals  :  ethylo-butyl,  ethyl-amyl, 
methylo-caproyl,  butyl-amyl,  and  butylo-caproyl.  The  reasons  for  representing 
the  bodies  of  the  class  (a.)  in  the  free  state,  by  the  double  formulae,  have  been 
already  given  (p.  690). 

These  alcohol-metals  are  obtained  by  the  action  of  zinc  on  the  iodides  of  the 
alcohol-radicals  (p.  697)  ',  by  the  action  of  sodium  on  the  chlorides  of  the  same 
radicals  ;  and  by  the  electrolysis  of  the  alkaline  salts  -of  the  fatty  acids,  carbonic 
acid  and  hydrogen  being  evolved  at  the  same  time  :  — 


Acetate  of  potash.  Methyl.  Carbonate 

of  Potash. 

The  alcohol-metals,  containing  two  different  radicals,  are  obtained  by  the  action 
of  sodium  on  a  mixture  of  the  corresponding  iodides  :  thus,  with  the  iodides  of 
ethyl  and  butyl  — 

€2H5T  +  Na  Na    =  Nal  +  Na€2H5 
and  £4H9I  +  Na02H5  =  Nal  +  £2H6.€4Hfl; 

also,  by  the  electrolysis  of  a  mixture  of  the  alkaline  salts  of  two  of  the  fatty  acids. 


CONJUGATE    METALS.  719 

Methyl  and  ethyl  are  gaseous  at  ordinary  temperatures;  the  other  alcohol- 
metals  are  liquids  more  or  less  volatile.  They  exhibit  but  little  tendency  to  unite 
with  other  bodies.  The  alcohols  and  ethers  cannot  be  formed  from  them  directly. 
Oxygen  and  sulphur  do  not  act  upon  them,  and  chlorine  and  bromine  do  not 
unite  with  them,  but  decompose  them,  forming  substitution-products;  they  are  not 
attacked  by  hydrochloric  acid  or  by  potash.  For  their  boiling  points  and  vapour- 
densities,  see  page  690. 

3.  Mixed  metals,  containing  a  metal  proper  and  an  alcohol-radical;  e.g.  zinc- 
methyl,  CH3.  Zn;  zinc-ethyl,  O2H5.  Zn  ;  zinc-amyl,  O5H,,Zn;  stannethyl,  O2H5Sn; 
arsenethyl,  (£2H5)3As;  stibmethylj  (GH3)Sb,  &c. 

These  compounds  are  obtained  by  the  action  of  iodide  of  ethyl,  &c.,  on  the 
corresponding  metals,  or  their  alloys  with  potassium  or  sodium  ;  thus,  the  com- 
pounds of  ethyl  and  arsenic  are  ob.tained  by  distilling  iodide  of  ethyl  with  arsenide 
of  sodium  ;  arsen-bimethyl  or  cacodyl,  (GH3)2As,  is  likewise  produced  by  the 
dry  distillation  of  a  mixture  of  acetate  of  soda  and  arsenious  acid.  To  understand 
this  reaction,  it  must  be  remembered  that  the  radical  of  acetic  acid,  €2H3O, 
be  supposed  to  consist  of  GO  conjugated  with  methyl,  GH3  :  — 


Acetate  of  soda.  Oxide  of  cacodyl. 


These  compounds  are  liquids  more  or  less  volatile,  and  generally  having  a  very 
offensive  odour;  they  oxidize  rapidly  in  the  air,  and  sometimes  take  fire.  Zinc- 
methyl,  zinc-ethyl,  and  cacodyl  take  fire  instantly  on  coming  in  contact  with  the  air. 

Zinc-methyl,  zinc-ethyl,  and  zinc-amyl  differ  in  some  respects  from  the  other 
mixed  metals  in  their  behaviour  with  oxygen,  sulphur,  chlorine,  iodine,  &c.  When 
these  metals  are  exposed  to  the  air,  but  not  freely  enough  to  cause  them  to  take 
fire,  they  are  converted  into  mixed  ethers ;  thus,  — 

2  (£H3.Zn)  +  OO=  2 

Similarly  with  sulphur.  Chlorine,  bromine,  and  iodine,  on  the  other  hand, 
decompose  them,  producing  a  chloride  of  the  metal  and  a  chloride  of  the  alcohol- 
radical  :  — 

OH3 .  Zn  -f-  C1C1  =  GH3 .  Cl  +  ZnCl. 

This  difference  of  reaction  is  in  perfect  accordance  with  the  bibasic  character  of 
oxygen  and  sulphur,  and  the  monobasic  character  of  chlorine,  bromine,  and  iodine 
(compare  pp.  689,  707).  The  same  mixed  metals  decompose  water,  forming  a 
hydrate  of  zinc  and  a  hydride  of  the  alcohol-radical :  — 

OH3Zn  +  gjO  ==  H.€H3  +  ^(&- 

The  other  mixed  metals  —  thence  called  conjugate  metals  —  containing  tin, 
antimony,  arsenic,  bismuth,  lead,  and  mercury,  combine  as  simple  radicals  with 
oxygen,  chlorine,  &c.,  forming  oxides,  chlorides,  &c.  The  oxides  of  these  conju- 
gate metals  may  be  regarded  as  derivatives  of  the  oxides  of  the  simple  metals 
contained  in  them,  one  or  more  atoms  of  oxygen  being  replaced  by  its  equivalent 
quantity  of  ethyl,  &c. ;  that  is,  O  by  (G2H5)2,  &c.  This  will  be  seen  from  the 
following  table,  in  which  the  symbol  Et  stands  for  (C2H5)2 :  — 


720                           ATOMIC    VOLUME    OF  LIQUIDS. 

Type.  Derivative. 

Arsenious  acid,  As203.  Oxide  of  arsen-biethyl  As2(Et20)  =  0  / 

I 

Arsenic  acid,  As206....  Oxide  of  arsen-triethyl  As2(Et3O2)  =  O2  1 

.  I 

Arsenic  acid,  As206....  Oxide  of  arsenetbylium  As2(Et40)  =  O2{ 

L 

Stannic  oxide,  Sn2O2...  Oxide  of  stannethyl  Sn2(EtO)  =  0  j 

Oxide  °f  *  stanneh^  sn4(Etso)=o2  { 

O   J  Qxide  of  mercurethyl  Hg4(EtO)=O2 

»*  -lenethyl  J 
Oxide  of  tetrethylium 


The  method  of  determining  the  equivalent  in  hydrogen  of  these  conjugate  radi- 
cals has  been  already  explained  (p.  694). 

Acid  metals,  or  metalloids.  —  These  are  the  elements  commonly  called  negative 
or  chlorous  :  e.  y.  oxygen,  sulphur,  phosphorus,  &c. 


RELATIONS  BETWEEN  CHEMICAL  COMPOSITION 
AND  DENSITY. 

Atomic  Volume  of  Liquids.*  —  The  atomic  volumes  of  bodies  are  the  spaces 
occupied  by  quantities  proportional  to  their  atomic  weights,  and  are  calculated  by 
dividing  the  atomic  weights  by  the  specific  gravities  (p.  172)  }  thus,  the  atomic 
weights  of  copper  and  silver  being,  on  the  hydrogen  scale,  317  and  108-1,  and 
their  specific  gravities  (water  =  1)  being  8-93  and  10-57,  their  atomic  volumes 

01.  "7  108'1 

are,  respectively,  -^-^  and  *•„-£•-,  or  3-6  and  10-2.    These  numbers  are,  of  course, 
'  10'57 


only  relative  ;  their  actual  values  depend  on  the  units  of  atomic  volume  and  density 
adopted. 

It  has  already  been  observed,  that  the  relations  between  atomic  weight  and 
density  are  much  less  simple  in  solids  and  liquids  than  in  gases,  the  diversities  in 
the  rates  of  expansion  by  heat  of  liquid  and  solid  bodies  being  alone  sufficient  to 
complicate  these  relations  to  a  considerable  extent.  With  regard  to  liquids  in 
particular,  the  researches  of  Professor  Kopp  have  shown  that  their  atomic  volumes 
are  comparable  only  at  temperatures  for  which  the  tensions  of  the  vapours  are  equal  ; 
for  example,  at  the  boiling  points  of  the  liquids.  If  the  atomic  weights  of  liquids 
are  compared  with  their  densities  at  equal  temperatures,  no  regular  relations  can 
be  perceived  ;  but  when  the  same  comparison  is  made  at  the  boiling  temperatures 
of  the  respective  liquids,  several  remarkable  laws  become  apparent.  The  density 
of  a  liquid  at  its  boiling  point  cannot  be  ascertained  by  direct  experiment;  but 
when  the  density  at  any  one  point,  say  at  15'5°  C.  (60°  F.),  has  been  ascertained, 
and  the  rate  of  expansion  is  also  known,  the  density  at  the  boiling  point  may  be 
calculated.  Abundant  data  for  these  calculations  are  supplied  by  the  labours  of 
Kopp  and  Pierre  (p.  644). 

*  H.  Kopp,  Ann.  Ch.  Pharm.  xcvi.  2,  330. 


ATOMIC    VOLUME   .OF    LIQUIDS. 


721 


The  following  table  contains  Kopp's  determinations  of  the  atomic  volumes  of  a 
considerable  number  of  liquids  containing  carbon,  hydrogen,  and  oxygen  at  their 
boiling  points.  The  atomic  weights  are  those  of  the  hydrogen-scale.  The  calcu- 
lated atomic  volumes  in  the  fourth  column  are  determined  by  a  method  to  be  pre- 
sently described  ;  the  observed  atomic  volumes  in  the  fifth  column  are  the  quotients 
of  the  atomic  weights,  on  the  hydrogen-scale,  divided  by  the  specific  gravities 
referred  to  water  as  unity. 


•TABLE  A. 
Atomic  Volumes  of  Liquids  containing  Carbon,  Hydrogen,  and  Oxygen. 


Substance. 

Formula. 

Atomic 
Weight. 

Atomic  Volume  at  the  Boiling  Point. 

Calculated. 

Observed. 

a 

32 

§, 
»t 

EH 

d> 

a 

i" 

£ 

<3> 
BS 
32 
f\  ' 

& 
>> 

c-- 

Benzol                         .         .  ... 

e«*e 
e*HM 

SlOH8 

02H402 

^ 

6C 

03H60 

H20 
OH4O 
02H60 
05H120 
06H60 
07H80 
OH3O2 
02?1402 
03H602 
04H802 

£5HI0o2 

07H602 
04HI00 
04H603 
£2HA 
03H602 
03H602 
04H802 
€*H10Oa 
£5H1002 

06H'2Q2 
O6H1202 

^6H1202 
06H1202 
07H1402 
07H1402 

%H^ 

^9H1002 

OHO 

^11  ll  12^2 

08H803 

^5H,o03 
04H804 

«eHio^4 
08H1404 

78 
134 
128 
44 
86 
106 
148 
114 
58 

18 
32 
46 
88 
94 
108 
46 
60 
74 
88 
102 
122 
74 
102 
60 
74 
74 
88 
102 
102 
116 
116 
116 
116 
130 
130 
172 
136 
150 
192 
176 

152 
118 
118 
146 
174 

99-0 
187-0 
154-0 
56-2 
122-2 
122-2 
188-2 
187-0 
78-2 

18-8 
40-8 
62-8 
128-8 
106-8 
128-8 
42-0 
64-0 
86-0 
108-0 
130-0 
130-0 
106-8 
109-2 
64-0 
86-0 
86-0 
108-0 
130-0 
130-0 
152-0 
152-0 
152-0 
152-0 
174-0 
174-0 
240-0 
152-0 
174-0 
240-0 
207-0 

159-8 
137-8 
117-0 
161-0 
2050 

96-0...  99-7  at    80° 
183-5.  ..185-2    «  175 
149-2  '  218 
56-0...  56-9    <     21 
117-3...120-3    '  101 
118-4                 '  179 

Cymol  

Aldehyde 

Valeraldehyde       

Bitter  almond  oil  

189-2                 '  236 

Butyl     .             ... 

184-5.  ..186-8    '  108 
77-3...  77-6    '    56 

18-8                  '  100 

Acetone  

r  Water  . 

Wood-spirit  

4«-9...  42-2    '     59 
61-8...  62-5    '     78 
123-6...124-4    •  135 
103-6.  ..104-0    '  194 
123-7                 «  213 

Alcohol  

Amylic  alcohol  

Phenylic  alcohol 

Benzoic  alcohol  

Formic  acid  

40-9...  41-8    «     99 
63-5...  63-8    «  118 
85-4                 '  137 

Butyric  acid  

106-4.  ..107-8    «  156- 
1302.  ..131-2    '  175 
126-9  «  253 
105-6...  1064    '     34 
109-9.  ..110-1    «  138 
63-4                 '     36    ' 

Benzoic  acid                             . 

Vinic  ether  ...        ..  .. 

Acetic  acid  (anhydrous)  
Forrniate  of  methyl  

Acetate  of  methyl 

83-7...  £5-8    «     55 
84-9...  85-7    «     55 
107-4.  ..107-8    '     74 
125-7...1273    '     93 
1958                 '     93 

Formiate  of  ethyl  

Acetate  of  ethyl  

Butyrate  of  methyl 

Propionate  of  ethyl  

Valerate  of  methyl  

148-7.  ..149-6    •  112 
149-1.  ..149-4    '  112 
149-3                 '  112 

Butyrate  of  ethyl  

Acetate  of  butyl  

Forruiate  of  amyl  

149-4.  ..150-2    «  112 
173-5.  ..173-6    '  131 
173  3...175-5    <  131 
244-1                 '  188 

Valerate  of  ethyl  

Acetate  of  amyl      ... 

148-5...  150-3    «  190 
172-4...  174-8    '  209 
247-7                 «  266 

Benzoate  of  ethyl 

Ciiuiiimate  of  ethyl  

211-3  «  260 

156-2.  ..157-0    '  223 
138-8.  ..139-4    '  126 
116-3                 '  162 

'Acid  salicylate  of  methyl  
Carbonate  of  ethyl  
Oxalate  of  methyl  

Oxalate  of  ethyl 

166-8.  ..167-1    '  186 
209-0                 '  217 

Succinate  of  ethyl  

43 

722  ATOMIC'  VOLUME  OF  LIQUIDS. 

A  comparison  of  the  numbers  in  this  table  leads  to  the  following  remarkable 
results  :  — 

1.  Differences  of  atomic  volume  are  in  numerous  instances  proportional  to  the 
differences  between   the  corresponding  chemical  formulae.  —  Thus  liquids,  whose 
formulae  differ  by  n  .  OH2,  differ  in  atomic  volume  by??.  22;  for  example,  the 
atomic  volumes  of  formiate  of  methyl,  452H4Q2,  and  butyrate  of  ethyl,  Q6H202,  differ 
by  nearly  4  X  22.     Acetate  of  ethyl,  €4HS02,  and  butyrate  of  methyl,  €5IIIOO2, 
whose  formulae  differ  by  OH2,  differ  in  atomic  volume  by  nearly  22.     The  same  law 
holds  good  with  respect  to  liquids  containing  sulphur,  chlorine,  iodine,  bromine, 
and  nitrogen  (see  Tables  B,  C,  D).     Again  :  by  comparing  the  atomic  volumes  of 
analogous  chlorine  and  bromine  compounds,  it  is  found  that  the  substitution  of  1, 
2,  or  3  atoms  of  bromine  for  an  equivalent  quantity  of  chlorine,  increases   the 
atomic  volume  of  a  compound  by  once,  twice,  or  three  times  5.     This  will  be  seen 
by  comparing  the  atomic  volumes  of  PBr3  and  PC13;  £2H5Br  and  €2H5C1,  &c. 
(Table  C.) 

2.  Isomeric  liquids  belonging  to  the  same  chemical  type  have  equal  atomic 

volumes.  —  The  atomic  volume  of  acetic  acid,    2    ^    JQ,  is  between  63-5  and  63-8; 

/-1TT/~V 

that  of  formiate  of  methyl,  ^        JQ,  is  634;  the  atomic  volume  of  butyric  acid, 


ig  between  J064  and  107-8;  that  of  acetate  of  ethyl, 

is  between  1074  and  107-8. 

3.  In  liquids  of  the  same  chemical  type,  the  replacement  of  hydrogen   by  an 
equivalent  quantity  of  oxygen  (that  is  to  say,  of  1  pt.  of  hydrogen  by  8  pts.  of 
oxygen)  makes  bu$  a  slight  alteration  in  the  atomic  volume.  —  This  may  be  seen 
by  comparing  the  atomic  volumes  of  alcohol,  C2H6O,  and  acetic  acid,  C2H4O2;  of 
ether,  C4H,0O,  acetate  of  ethyl,  C4H8O2,  and  anhydrous  acetic  acid,  C4H603;  of 
cymol,  C)0H14,  and  cuminol,  Ci0H,2O.     The  alteration  caused  by  the  substitution 
of  O  for  H6  is  always  an  increase. 

4.  In  liquids  of  the  same  chemical  type,  the  replacement  of  2  at.  H  by  1  at.  0 
(1  pt.  by  weight  of  hydrogen  by  6  parts  of  carbon)  makes  no  alteration  in  the 
atomic  volume.  —  Such,  for  example,  is  the  case  with  benzoate  of  ethyl,  £9H10O2, 
and  valerate  of  ethyl,  O7H,4O2,  and  with  the  corresponding  benzoates  and  valerates 
in  general  ;  also  with  bitter  almond  oil,  O7H6O,  and  valeraldehyde,  £6H,00. 

In  liquids  belonging  to  different  types,  the  same  relations  are  not  found  to  hold 
good.  Moreover,  the  types  within  which  these  relations  are  observed,  are  pre- 
cisely those  of  Gerhardt's  classification  (p.  696).  Further,  when  liquid  com- 
pounds are  represented  by  rational  formulae  founded  on  these  types,  their  atomic 
volumes  may  be  calculated  from  certain  fundamental  values  of  the  atomic  volumes 
of  the  elements,  on  the  supposition  that  the  atomic  volume  of  a  liquid  compound 
is  equal  to  the  sum  of  the  atomic  volumes  of  its  constituent  elements. 

Since  the  addition  of  OHj  to  a  compound  increases  the  atomic  volume  by  22, 
this  number  may  be  taken  to  represent  the  atomic  volume  of  OH2;  moreover,  since 
O  (or  C2)  may  take  the  place  of  H2  in  combination,  without  altering  the  atomic 
volume  of  the  compound,  it  follows  that  the  atomic  volume  of  O  must  be  equal  to 

22 

that  of  H2;  and  therefore  the  atomic  volume  of  Q  =  —-  =  11,  and  that  of  H2  also 

equal  to  11,  or  that  of  H  =  5-5.  Further,  as  the  substitution  of  O  for  H2  pro- 
duces a  slight  increase  in  the  atomic  volume  of  a  compound,  the  atomic  volume 
of  Q  must  be  rather  greater  than  11  ;  and  it  is  found  that,  by  assuming  the  atomic 
volume  of  0,  when  it  takes  the  place  of  H2  (that  is  to  say,  in  a  radical,  as  when 
acetyl,  Q2H30.,  is  formed  from  ethyl,  O2H5),  to  be  equal  to  12-2,  results  are 
obtained  agreeing  very  nearly  with  those  of  observation.  But  when  oxygen  occu- 

pies the  position  which  it  has  in  water,    rO,  its  atomic  volume  is  smaller.     The 


ATOMIC    VOLUME    OF    LIQUIDS.  723 

specific  gravity  of  water  at  the  boiling  point  is  0*9579  ;  hence  its  atomic  volume  at 

18 

that  temperature  is  frfc^=^  =  18.8  •  now  the  2  atoms  of  hydrogen  occupy  a  space 
0'9579 

equal  to  11 ;  hence  the  volume  of  the  oxygen  is  7*8.  The  same  value  of  the  atomic 
volume  substituted  for  O  in  the  forniulse  of  the  several  compounds  belonging  to 
the  water-type,  in  which  it  occupies  a  similar  place,  that  is  to  say,  outside  the 
radical,  gives  results  agreeing  nearly  with  observation.  That  a  given  quantity  of 
a  substance  should  occupy  different  spaces,  under  different  circumstances,  is  a 
fact  easily  explained,  when  it  is  remembered  that  the  particles  of  a  body  cannot 
be  supposed  to  be  in  absolute  contact,  but  are  separated  by  certain  spaces,  which 
increase  or  diminish  according  to  the  temperature  of  the  body,  and  according  as  it 
is  in  the  solid,  liquid,  or  gaseous  state. 

From  these  values  of  the  atomic  volumes  of  the  elements  carbon,  hydrogen,  arid 
oxygen ;  viz.  — 

Atomic  volume  of  O =  11 

«  «         H =    5-5 

"  "          O   (within  the  radical) =12-2 

"  "          O   (without  the  radical) =    7-8; 

the  calculated  volumes  of  the  atomic  volumes  of  liquids,  in  the  fourth  column  of 
Table  A,  are  deduced.  The  metho'd  of  calculation  may  be  understood  from  the 
following  examples : 

Benzol,  O6H6  =  O6H5 .  H. 

Atomic  volume  of  O6 =  66 

H6 : =33 

«  «         benzol =99 

Aldehyde,  O2H4O  =  £2H3O.  H. 

Atomic  volume  of  O2 =  22 

H4 =22 

"  "          O  (within  the  radical)  =-12-2 

"  "          aldehyde =  56-2 

Alcohol,  €2H,jO  =  ^2g5  j  O. 

Atomic  volume  of  O2 =  22 

"  "         H6 =  33 

"  "          O  (without  the  radical) =    7*8 

"  "          alcohol..  ..  =  62-8 


Acetic  acid,  02H4O2  =     2^3     JO. 

Atomic  volume  of  O2 =  22 

"  "          H4 =  22 

"  "          O  (within  the  radical) =  12-2 

"  "          a  (without  the  radical) =    7'8 

"  "          acetic  acid...  ,.  =  64-0 


724 


ATOMIC    VOLUME    OF    LIQUIDS 


Anhydrous  acetic  acid,  €4H6O3  == 


Atomic  volume  of  Q4 

"  "          H6 . 

"  "          Oz  (within  the  radical).. 

"  "          O  (without  the  radical) 


=  44 

=  33 

==  24-4 

=  7-8 


anhydrous  acetic  acid —  109-2 


Oxalate  of  methyl,  O4H6O4  = 


Atomic  volume  of  £4 

«  «          H6 

"  "          O2  (within  the  radical).. 

"  "          O2  (without  the  radical) 


44 
33 
244 
15-6 


"  "          oxalate  of  methyl =  117-0 

Liquids  containing  Sulphur.  —  Sulphur  enters  into  combination  in  various 
ways;  sometimes  taking  the  place  of  oxygen  in  the  type  HH  .O  (as  in  mercap- 
tan); sometimes  taking  the  place  of  carbon  within  a  radical  (as  in  anhydrous 
sulphurous  acid)  SO .  O,  compared  with  anhydrous  carbonic  acid,  £0  .  O;  some- 
times replacing  oxygen  within  a  radical  (as  in  sulphide  of  carbon),  Qg  .  g,  com- 
pared with  anhydrous  carbonic  acid.  In  the  first  and  second  cases,  the  atomic 
volume  of  sulphur-compounds  may  be  calculated  by  attributing  to  sulphur  (8  = 
32),  the  atomic  volume  22-6,  those  of  the  other  elements  remaining  as  above;  in 
the  third  case,  the  atomic  volume  of  sulphur  appears  to  be  greater;  viz.,  28*6. 

Examples.  —  Mercaptan,  QjHeS  =     2tr5  j  &. 

Atomic  volume  of  O2 =  22 

"  "          H6 =33 

"  "          & ..=226 


=  77-6 


os-s. 


mercaptan 
Sulphide  of  carbon, 

Atomic  volume  of  O  ..............................................  =  11 

"  "  g  (within  the  radical)  .....................  =28-6 

"  "  g  (without  the  radical)  ....................  =22-6 


"  sulphide  of  carbon =  62-2 

TABLE  B. 

Atomic  Volumes  of  Liquid  Sulphur-compounds. 


Substance. 

Formula. 

Atomic 
Weight. 

Atomic  Volume  at  the  Boiling  Point. 

Calculated. 

Observed. 

Mercaptan  . 

02H6S 
£5H12S 
02H8S 
€>4HI03 

°&of2 

OTT       CTV 
4n,gOtf| 

O&, 

62 
104 
62 
90 
94 
64 
138 
76 

77-6 
143-6 
77-6 
121-6 
100-2 
42-6 
149-4 
62-2 

76-0...  76-1  at   36°  C. 
140-1...140-5  "  120 
75-7  "     41 

Amylic  tnercaptan  

Sulphide  of  methyl 

Sulphide  of  ethyl   

120-5...121-5  '      91 
100-6.  ..100-7  '    114 
43-9..  '    —8 

Bisulphide  of  methyl  

Sulphurous  acid  

Sulphite  of  ethyl  

148-8.  ..149-5'    160 
62-2...  62-4'      47 

Bisulphide  of  carbon..., 

ATOMIC    VOLUME    OF    LIQUIDS. 


725 


Chlorides,  Bromides,  and  Iodides.  —  In  liquid  compounds  of  this  class,  the 
atomic  volume  of  Cl  is  supposed  to  be  22-8,  that  of  Br  =  27 -8,  and  that  of  I  =  37-5, 
those  of  the  other  elements  remaining  as  above. 


TABLE  C. 

Atomic  Volumes  of  Liquid  Chlorides,  Bromides,  and  Iodides. 


Substance. 

Formula. 

Atomic 
Weight 

Atomic  Volume  at  the  Boiling  Point. 

Calculated. 

Observed. 

Bichlorinated  ethylene                 . 

iii  m  si« 

97 
166 
99 
133-5 
168 
202-5 
127 

85 
119-5 
154 
64-5 
99 
133-5 
106-5 
147-5 
78-5 
140-5 

160 
95 
109 
151 
188 

142-1 
156-1 
198-1 

67-5 
137-5 
271 
127-8 
261-3 
181-5 
235-5 
369 
129 
96 

78-6 
113-2 
89-6 
106-9 
124-2 
141-5 
133-6 

67-6 
84-9 
102.2 
72-3 
89-6, 
106-9 
138-3 
108-1 
73-5 
139-5 

55-6 
55-3 
77-3 
143-3 
99-6 

65-0 
87-0 
153-0 

79-9  at    37°  C. 
115-4  «  123 
85-8...  86-4"    85 
105-4.  ..107-2  "  115 
120-7...121-4  «  137 
143    ....          "  154 

Chloride  of  carbon          

Chloride  of  ethylene  

Chloride  of  butylene  

129-5...133-7  "  123 
64-5  "     30-5 

Monochlorinated      chloride     of 
methyl 

Chloroform 

84-8...  85-7'      62 
104-3...  107-0  '      78 
71-2...  74-5'      11 
86-9...  89-9  «.    64 
105-6.  ..109-7  *      75 
135-4.  ..137-0'    102 
108-4...  108-9  "     96 
74-4...  75-2"    55 
134-2...137-8"  198 

54    ...  57-4  «    63 
58-2  "     13 

Chloride  of  carbon   

Chloride  of  ethyl  

Chloride  of  amyl      .              .     . 

Chloral  

Chloride  of  acetyl  

Bromine  

Bromide  of  methyl     

Bromide  of  ethyl  ,. 

78-4  "    41 

Bromide  of  amyl 

149-2  «  119 

Bromide  of  ethylene  .      . 

97-5...  99-9  «  130 

65-4...  68-3  "     43 
85-9...  86-4"     71 
152-5...155-8  »  147 

45-7  «  140 

Iodide  of  methyl..  

Iodide  of  ethyl  

Iodide  of  amyl    

Chloride  of  sulphur  

Chloride  of  phosphorus  

93-9  <     78 

Bromide  of  phosphorus 

108-6               '  175 

Chloride  of  silicon  

91-6  <    59 
108-2  «  153 
94-8  ,   <  133 
100-7               '  223 

Bromide  of  silicon  

Chloride  of  antimony     . 

Bromide  of  antimony    

116-8  "  275 

Chloride  of  tin  

65-7  «  115 
63-0  "  136 

The  compounds  PC13,  SiCl3,  and  AsCl3,  have  nearly  equal  atomic  volumes, 
whence  it  may  be  inferred  that  phosphorus,  silicon,  and  arsenic,  in  their  liquid 
compounds,  have  equal  atomic  volumes.  The  same  conclusion  may  be  drawn 
regarding  tin  and  titaninum,  since  the  atomic  volumes  of  SnCl2  and  Ti012  are 
equal. 

Nitrogen-compounds.  —  In  compounds  belonging  to  the  ammonia  type,  the 
atomic  volume  of  nitrogen  is  2-3.  This  result  is  deduced  from  the  observed 
atomic  volume  of  aniline,  O6H7N,  which  is  106-8.  Now  the  atomic  volume  of 
6  O  +  7  H  =  6  . 11  +  7  .  5-5  =  104-5,  which  number,  deducted  from  106-8 
leaves  2-3  for  the  atomic  volume  of  nitrogen. 


726 


ATOMIC    VOLUME    OF    LIQUIDS. 


The  atomic  volume  of  cyanogen  deduced  from  the  observed  at.  vol.  of  cyanide 
of  phenyl,  GN .  O6H6,  or  O7H5N,  is  nearly  28.     Thus  — 
Atomic  volume  of  €7H5N  =  121-6 
"  "          €«EL     =    93-5 


=    28-1 


A  similar  calculation,  founded  on  the  observed  atomic  volume  of  cyanide  of 
methyl,  4^2H3N,  gives,  for  the  at.  vol.  of  cyanogen,  the  number  26-8.  The  atomic 
volume  of  liquid  cyanogen  determined  directly  at  87°  or  39°  C.  above  its  boiling 
point,  is  between  28-9  and  30-0.  As  a  mean  of  these  values,  the  atomic  volume  of 
cyanogen  may  be  assumed  to  be  28  ;  and  with  this  value  the  atomic  volumes  cf 
the  liquid  cyanides  are  calculated.  Thus,  for 

Oil  of  mustard  (sulpho-cyanide  of  allyl),  OJI5N8    =  ^  }g. 

Atomic  volume  of  £3H5  ............................  =     60-5 

"'  «  ON  ............................  =    28-0 

"  "  g  (without  the  radical)  ......  =     22-6 

"  "  oil  of  mustard  .................  =  111-1 

The  atomic  volumes  of  compounds  containing  the  radical  NO2,  are  calculated 
on  the  hypothesis  that  the  at.  vol.  of  that  radical  is  33,  which  agrees  nearly  with 
the  observed  atomic  volume  of  liquid  peroxide  of  nitrogen.  Thus  :  —  the  at.  vol. 
of  nitrate  of  amyl,  €5HnNO2  ==  at  vol.  of  O6Hn  -f  at.  vol.  of  NO2  =  115-5  -f  33 
=  148-5. 

TABLE  1). 

Atomic   Volumes  of  Liquids  containing  Nitrogen. 


Substance. 

Formula. 

Atomic 
Weight. 

Atomic  Volume  at  the  Boiling  Point. 

Calculated. 

Observed. 

Ammonia     

H3N 
02H7N 
04HMN 
05H13N 
G8H19N 
06H7N 
07H9N 
08HnN 

£lOH15N 

ON 
OHN 
O2H3N 
03H5N 
05H9N 
O.H6N 
O2H3N& 
03H6NS 
04H6NS 
£3H6N0 

NO3 
OTI3NO3 
02H6N03 
06H5N02 
OH3N02 
02H5N02 
OeH,,NO0 

17 
45 
73 
87 
129 
93 
107 
121 
149 

26 
27 
41 
55 
83 
103 
73 
87 
99 
71 

30 
77 
101 
123 
61 
75 
117 

18-8 
62-8 
106-8 
128-8 
194-8 
106-8 
128-8 
150-8 
194-8 

28-0 
33-5 
55-5 
77-5 
121-5 
121-5 
78-1 
100-1 
111-1 
85-3 

33-0 
68-3 
90-3 
126-5 
60-5 
82-5 
148-5 

22-4  ..  23-3  at  10°  .  16°* 
65-3  at    18-7 

Ethylamine  

Butylamine 

125-0  ....                 «    94 

Amylamine     • 

190-0  "  170 

Aniline                            ... 

106-4  .  106-8  "  184 
150-6  "  204 

Toluidine    .  

Bietliaiiilino             

190-5                        "  213-5 

28-9.    30-0  "    16f 
39-1  ...  .                "    27 

Hydrocyanic  acid  

Cyanide  of  methyl  

54-3  «    74 

77-2  "    88 

Cyanide  of  butyl  

121-6  .  121-9  "    191 
75-2  .    78-2  "    133 
99-1  «    146 

Sulphycyanide  of  methyl 
Sulphocyanide  of  ethyl  ... 

113-1  •  114-2  «    148 
84-3  •    84-8  "      60 

31-7  •    32-4  "    40J 
69-4  "    66 

Cyanate  of  ethyl  

Peroxide  of  nitrogen  
Nitrate  of  methyl   

Nitrate  of  ethyl  

90-0.    90-1  »    86 
122-6  .  124-9  "  218 
61-6  ...              ,.    "    143 

Nitrobenzol     .. 

Nitrite  of  methyl  
Nitrite  of  ethyl  

79-2.    84-6  •«    18 
148-4  «    95 

Nitrite  of  amyl  .. 

*  Between  44°  and  50°  above  the  boiling  point. 
f  Between  37°  and  39°  above  the  boiling  pnoiut. 
J  About  35°  above  the  boiling  point. 


\  27°  above  the  boding  point. 


ATOMIC    VOLUME    OF    LIQUIDS. 


727 


From  the  preceding  observations  and  calculations,  it  appears  that  the  atomic 
volume  of  a  compound  depends,  not  merely  on  its  empirical,  but  likewise  on  its 
rational  formula;  in  other  words,  not  merely  on  the  number  of  atoms  of  its 
elements,  but  further  on  the  manner  in  which  those  atoms  are  arranged.  Now  it 
has  been  shown  (p.  693)  that  a  compound  ^jnay  have  more  than  one  rational 
formula,  according  to  the  manner  in  which  it  decomposes;  and  hence  it  might 
appear  that  the  calculation  of  atomic  volumes  must  be  attended  with  considerable- 
uncertainty,  inasmuch  as  the  atomic  volumes  of  certain  elements,  as  oxygen  and 
sulphur,  vary  according  to  the  manner  in  which  they  enter  into  the  compound. 

n  u  AH 

Aldehyde,  for  example,  may  be  represented  either  as     2jr3  j  O,  or  as     Vj3  JO;  and, 

as  the  atomic  volume  of  oxygen  is  12-2  or  7 '8,  according  as  it  is  within  or  with- 
out the  radical,  the  atomic  volume  of  aldehyde  will  be  56-2  if  deduced  from  the 
type  HH,  and  51-8  if  deduced  from  the  type  HH.O.  But  the  atomic  weight  of 
aldehyde,  and  its  specific  gravity  at  a  given  temperature  are  invariable;  it  cannot, 
therefore,  have  two  different  atomic  volumes.  It  must  beremembered,  however, 
that,  in  speaking  of  a  compound  as  having  several  rational  formulae,  we  consider 
it  rather  in  a  dynamical  than  in  a  statical  point  of  view ;  as  under  the  influence 
of  disturbing  forces,  and  on  the  point  of  undergoing  chemical  change.  But  if, 
on  the  other  hand,  we  regard  a  compound  in  its  fixed  statical  condition,  as  a  body 
possessing  definite  physical  properties,  a  certain  specific  gravity,  a  certain  boiling 
point,  rate  of  expansion,  refractive  power,  &c.,  we  can  scarcely  avoid  attributing 
to  it  a  fixed  molecular  arrangement,  or,  at  all  events,  supposing  that  the  disposi- 
tion of  its  atoms  is  confined  within  those  limits  which  constitute  chemical  types. 
It  is  found,  indeed,  that  isomeric  liquids  exhibit  equal  atomic  volumes  only  when 
they  belong  to  the  same  chemical  type.  If  this  view  be  correct,  the  relation 
between  the  atomic  volumes  of  elements  and  compounds,  may  often  render  valuable 
service  in  determining  the  rational  formula  .which  belongs  to  a  compound  in  the 
state  of  rest.  Thus,  of  the  two  atomic  volumes  just  calculated  for  aldehyde,  the 
number  56-2,  deduced  from  the  formula,  Q2H3O.H,  agrees  with  the  observed 
atomic  volume  of  aldehyde,  which  is  between  56-0  and  56-9,  better  than  51-8. 

O  H 
the  number  deduced  from     2    3*Q.     This  result  leads  to  the  conclusion  that  the 

aldehydes  belong  to  the  hydrogen-type  (p.  718),  rather  than  to  the  water-type. 

There  are  many  groups  of  liquid  compounds,  irrespective  of  isomerism  or 
similarity  of  type,  the  members  of  which  have  equal  or  nearly  equal  atomic 
volumes.  The  following  table  exhibits  the  calculated  atomic  volumes  of  several 
of  these  groups  : — 

Atomic    Volume  of  Liquids. 


Water  

H2O 

18-8 

Ether  

O,H,nO 

106-8 

Ammonia  •  

NH. 

18-8 

Butylic  alcohol 

€,H    O 

106-8 

Bromine      .. 

Br 

55-6 

Phenylic  alcohol  

06H60 
OWN 

106-8 
106-8 

Cyanogen  

CON^ 

56-0 

OgH  N 

106-8 

Q2H4Q 

56-2 

Butyric  acid                    • 

O  H  O» 

108-0 

O2H3N 

55-5 

Acetate  of  ethyl      ...  . 

O  FLO* 

108-0 

Bromide  of  methyl  

€2H313r 

55-3 

Anhydrous  acetic  acid  . 
Chloral  

G4H603 
02HC1O 

109-2 
108-1 

G,,HC0 

fV>-8 

Bichlorinated  chloride  of 

Acetic  acid  

O0H,O™ 

64-0 

ethyl  .. 

OoH.Cl. 

106-9 

Formiate  of  methyl  
Cyanate  of  methyl  
Ethylamine    

02H402 
02HaN02 
O  H  N 

64-0 
63-3 
62-8 

Monochlorinated     chlo- 
ride of  ethylene   

™ 

106-9 
108-6 

Sulphide  of  carbon  

TTOft 

OH3I 

62-3 
65-0 

Valeraldehyde  

OeH       O 

122-2 

Cyanide  of  butyl  

€  H  N 

121-5 

Acetone  

O«HCQ 

78-2 

Bitter  almond  oil 

&  HO 

122-2 

O,HeN 

77-5 

Cyanide  of  phenyl    .    . 

O  H  N 

121-5 

Sulphocyanide  of  methyl 

£2H3NS 

78--1 

Sulphide  of  ethyl  

O  H,  S 

121-6 

Sulphide  of  methyl  

O2H6& 

77-6 

728     RELATIONS   OF   COMPOSITION   AND   BOILING   POINT. 

These  groups  exhibit  an  approach  to  the  uniformity  of  atomic  volume  which  is 
observed  in  the  gaseous  state. 

Berthelot  has  adduced  a  number  of  examples,  showing  that  when  a  liquid  com- 
pound is  formed  by  the  union  of  two  other  liquids,  whose  specific  volumes  are 
denoted  by  A  and  B,  with  elimination  of  x  atoms  of  water,  the  specific  volume 
of  the  compound  is  nearly  =  A  -f  B  —  icC  (the  atomic  volume  of  water  being 
denoted  by  C).  Berthelot's  observations,  however,  were  made  at  medium  tempe- 
ratures, not  at  the  boiling  points  of  the  liquids. 

Atomic  Volume  of  Solids.  —  The  principal  results  obtained  by  Kopp,  with  re- 
ference to  the  atomic  volume  of  solid  bodies,  are  given  in  pp.  172-176.*  The 
difficulty  of  reducing  the  results  to  general  laws  is  similar  to  that  which  has  been 
noticed  in  the  case  of  liquids,  but  exists  to  &  still  greater  extent,  inasmuch  as  our 
knowledge  of  the  expansion  of  solids  by  heat  is  much  more  limited  than  that  of 
liquids.  It  is  probable  that  the  atomic  volumes  of  solids  should  be  compared  at 
their  melting  points;  since  it  is  only  at  those  temperatures  that  the  effects  of  heat 
upon  different  solids  can  be  said  to  be  equal.  Now  the  specific  gravities  of  most 
solids  are  determined  only  at  medium  temperatures,  from  which  the  melting 
points  of  different  solids  are  separated  by  intervals  of  very  different  magnitude ; 
moreover,  there  are  but  few  solids  whose  rate  of  expansion  at  different  tempera- 
tures has  been  ascertained  with  sufficient  accuracy  to  render  it  possible  to  calculate 
the  specific  gravities  at  the  melting  points.  A  further  complication  arises  from 
the  different  densities  which  the  same  solid  often  exhibits,  according  as  it  is 
amorphous  or  crystalline,  or  according  to  the  particular  form  in  which  it 
crystallizes. 


RELATIONS  BETWEEN   CHEMICAL  COMPOSITION 
AND  BOILING  POINT.f 

In  compounds  of  similar  constitution,  and  especially  among  the  members  of 
homologous  series  (p.  699),  difference  of  boiling  point  is  frequently  proportional 
to  difference  of  composition. 

1.  In   the   alcohols,  OnH2n+20,  the  fatty  acids,  O,,H2n02,  and  the  compound 
ethers  (p.  705)  isomeric  with  the  fatty  acids,  a  difference  of  £H2  in  the  formula 
corresponds  to  a  difference  of  19°  C.  in  the  boiling  point. 

2.  The  boiling  point  of  a  fatty  acid,  £DH2nO2,  is  higher  by  40°  C.  than  that 
of  .the  corresponding  alcohol,  QnH2n+2O. 

8.  The  boiling  point  of  a  compound  ether,  QnH2nO2,  is  lower  by  82°  C.  than 
that  of  the  isomeric  acid. 

Starting  from  the  observed  boiling  point  of  common  alcohol,  78°  C.,  and  cal- 
culating by  these  rules  the  boiling  points  of  the  other  alcohols  and  of  the  fatty 
acids  and  ethers,  we  obtain  the  numbers  in  the  third  column  of  the  following 
table,  which  do  not  differ  from  the  observed  boiling  points  in  the  fourth  column, 
more  than  these  latter,  as  determined  by  different  observers,  differ  from  one 
another. 

*  The  numbers  there  given  refer  to  the  oxygen-scale  of  atomic  weights.     (0  =  100.) 
f  H.  Kopp.  Ann.  Ch.  Pharm.  xcvi.  2,  330. 


RELATIONS   OF   COMPOSITION   AND   BOILING   POINT.      729 


Substance. 

Formula. 

Boiling  point. 

Observers. 

Calculated. 

Observed. 

Alcohols. 
Methylic  alcohol  
Propylic  alcohol      .... 

GH40 

O3H8O 
04H100 

06H120 

^16^34^ 

OH202 
02H402 
G3H602 

04H802 

£5H10Q2 
06H1202 

G8H1602 
09HI802 

€2H402 

O.HA 

e.H.0, 
04tf802 

05H1002 
06H1002 

£6H1002 

06H1202 
06H1202 

06H1202 
02H)202 
07H1402 

€7H1402 
GAO, 

59°    J 

97 

116 

135     I 
344 

99     | 
118     | 
137     | 

156     | 

i«    { 

194 

232 

251 

36     | 
55     j 

55     | 

«  { 

93     j 

93 
93 
112 

112 

112 
112 
131      j 

131 

188 

60°   at  744  mm 

Kane. 
Delffs. 
H.  Kopp. 
H.  Kopp. 
Chancel. 
Wurtz. 
H.  Kopp. 
Cahours. 
Delffs. 
Favre  and 
Silbermann. 

Liebig. 
H.  Kopp. 
II.  Kopp. 
Delffs. 
H.  Kopp. 
Limpricht  & 
v.  Uslar. 
H.  Kopp. 
I.  Pierre. 
Delffs. 
H.  Kopp. 
Brazier  and 
Gossleth. 
Fehling. 
Cahours. 

H.  Kopp. 
Andrews. 
Andrews. 
H.  Kopp. 
I.  Pierre. 
I.  Pierre. 
Delffs. 
H.  Kopp. 
H.  Kopp. 
I.  Pierre. 
Delffs. 
H.  Kopp. 
I.  Pierre. 
Berthelot. 
H.  Kopp. 
H.  Kopp. 
H.  Kopp. 
I.  Pierre. 
Delffs. 
H.  Kopp. 
Wurtz. 
Delffs. 
H.  Kopp. 
Delffs. 
H.  Kopp. 
H.  Kopp. 
H.  Kopp. 

61      "  755     " 

64-9  "  754     " 

65          .         "  752     " 

96     «*     f       " 

Butylic  alcohol  
Amylic  alcohol  
Cetylic  alcohol  

Acids. 
Formic  acid  

109     "     ?       " 

130-4  "  742     " 

132      "  760    /« 

132                    "  766     " 

360        "     *       '• 

98  5  "  753     " 

Acetic  acid        

116-9  «  750     " 

Propionic  acid  

116      «  754     " 
141-6  .   .          "  754-6" 

141     «     ?       « 

156     "  733     " 

163     "  751     " 

174-5  "  762     " 

175-8                '«  746-5  " 

198     -  "     ?       " 
236      "     '       «« 

Caprylic  acid  

Pelargonic  acid  

260      ««     ?       «« 

Compound  Ethers. 
Formiate  of  methyl  ... 

Acetate  of  methyl  

Formiate  of  ethyl  
Acetate  of  ethyl  

32-7  ,..    "  741     » 

22-9  "  752      « 

55     «  762      « 

57-7  «'  757      * 
59-5  .             "  761      < 

52-9  ..            "  752      ' 

53     .              ««  736      • 

54-7  "  754      < 

73-7  »  745     " 

74-1  ««  766     " 

Butyrate  of  methyl  ... 

Acetate  of  propyl  
Propionate  of  ethyl  ... 
Valerate  of  methyl  ... 

Butyrate  of  ethyl  

93      "  744     " 

95-1  .              "  742     " 

102-1  .'.           "  744     <« 

90     (about) 
95-8  ...  98 
114     .  115      «  756     » 
114-6  »  756     «« 

1  1  Q                          «    7J.7      «' 

Formiate  of  amyl  
Acetate  of  butyl  
Valerate  of  ethyl  

Acetate  of  amyl  
Valerate  of  amyl  

114     «*  771     " 

116     (about) 
114 
131-3  «  735     " 
133-2  «  754     « 

133      "  760     " 
133-3  «  749     « 

137-6  ,    ««  746     " 
1878.  188-3    ««  730     » 

It  appears  from  this  tabl§  that  isomeric  compound  ethers  have  equal  boiling 
points;  e.  y.,  formiate  of  ethyl  and  acetate  of  methyl  boil  at  55°;  valerate  of 
methyl,  butyrate  of  ethyl,  formiate  of  amyl,  and  acetate  of  butyl,  boil  at  112°. 


730  CHEMICAL    AFFINITY. 

It  follows,  also,  from  the  preceding  laws,  that  the  boiling  point  of  an  acid. 
OnH2llO.2,  is  63°  higher  than  that  of  its  methylic  ether,  44°  higher  than  that  of 
its  ethylic  ether,  and  13°  lower  than  that  of  its  amylic  ether :  thus,  valerianic 
acid  boils  at  175°;  valerate  of  methyl  at  112°;  valerate  of  ethyl  at  131°;  valerate 

of  amyl  at  188°.     Common  ether,  (O2H5)2O,  is  the  ethyl-salt  of  alcohol,  %?5}O, 

regarded  as  an  acid  j  that  is  to  say,  it  bears  the  same  relation  to  alcohol  that 
acetate  of  ethyl  bears  to  acetic  acid  :  hence  its  boiling  point  should  be  78° — 44° 
==34°.  The  actual  observations  of  the  boiling  point  of  ether  vary  from  34°  to 
3j-7°. 

In  the  same  series  of  homologous  compounds,  it  is  found  that  the  addition  of 
«Q  raises  the  boiling  point  by  n .  29° ;  and  the  addition  of  wH  lowers  the  boiling 
point  by  ft. 5°  [consequently,  the  addition  of  wGH2  raises  it  by  u  .  (29  —  2  X  5) 
=  71.19°].  The  same  law  is  likewise  observed  in  other  series  of  compounds  of 
similar  character.  Thus,  benzoate  of  ethyl,  O9H,0O2,  boils  at  209°,  which  is 
Jiigher  by  4x29,  or  116,  than  the  boiling  point  of  the  ethers,  G5H1002, — butyrate 
of  methyl  for  example.  The  boiling  point  of  angelic  acid,  O5H802,  is  higher  by 
29°  than  that  of  butyric  acid,  O^HjA;  and  2  X  5,  or  10°,  higher  than  that  of 
valcriauic  acid,  G5H1002.  The  boiling  point  of  phenylic  alcohol,  O6H6O,  is  higher 
by  about  4x29,  or  116°,  than  that  of  common  alcohol,  Q2H60;  and  about  8x5, 
or  40°,  higher  than  that  of  caproic  alcohol,  O6H,4Q. 

Constant  relations  of  composition  and  boiling  point  are  observed  also  in  other 
series  of  homologous  compounds ;  but  the  difference  of  boiling  point  correspond- 
ing with  a  difference  of  OH2,  is  not  always  19°.  In  the  series  of  hydrocarbons : 
—benzol,  €6H6  (B.P.  80°),  toluol,  O7H8,  xylol,  £8H10,  cumol,  O9HI2,  cymol,  OIOHM, 
the  difference  is  24°;  in  the  homologous  compounds:  —  bromide  of  ethylene, 
O2H4Br2,  bromide  of  propylene,  Q3H6Br2,  bromide  of  butylene,  O4H8Br2,  it  is  15°, 
their  boiling  points  being  130°,  145°,  and  160°,  respectively.  In  the  series  of 
alcohol-radicals  (in  the  free  state),  the  difference  is  about  23° ;  in  the  auydrous 
acids,  homologous  with  anhydrous  acetic  acid,  it  is  about  13°.  . 

These  differences  of  boiling  point  would  probably  be  the  same  in  all  series  of 
homologous  compounds,  if  the  boiling  points  were  determined  at  different 
pressures.  It  is  not,  indeed,  to  be  expected  that  two  substances  should  exhibit 
the  same  difference  of  boiling  point  under  all  pressures;  for  if  B  and  B'  denote 
the  boiling  points  of  two  liquids  at  the  ordinary  atmospheric  pressure,  b  and  b', 
the  boiling  points  of  the  same  liquids  at  another  pressure ;  and  if  we  suppose 
that 

B  —  B'  =  b  —  V,  / 

it  will  follow  that 

B_b  =  B'  — b'; 

that  is  to  say,  the  boiling  points  of  the  two  liquids  would  vary  equally  for  equal 
differences  of  pressure,  which  is  contrary  to  observation. 


CHEMICAL    AFFINITY. 

Influence  of  mass  on  chemial  action.  — That  the  relative  degrees  of  affinity  of 
a  body  for  a  number  of  others  to  which  it  is  simultaneously  presented,  are  greatly 
modified  by  their  relative  masses,  was  first  pointed  out  by  Berthollet.  The  law- 
laid  down  by  that  philosopher  respecting  the  action  of  masses,  is  this  :  —  A  body 
to  which  two  different  substances,  capable  of  uniting  with  it  chemically,  are  pre- 


CHEMICAL    AFFINITY. 


731 


sented  in  different  proportions,  divides  itself  between  them  in  the  ratio  of  the  pro- 
ducts of  their  masses,  and  the  absolute  strengths  of  their  affinities  for  the  first 
lody.  Thus,  if  we  denote  by  A  and  B  the  masses  of  the  two  bodies  which  are 
present  in  excess,  by  a  and  j3,  the  coefficients  of  their  absolute  affinities  for  the 
body  G  ;  and  by  a  and  b,  the  quantities  of  A  and  B,  which  actually  combine  with 
C,  the  law  just  stated  will  be  expressed  by  the  proportion  :  — 


If  this  view  be  correct,  any  alteration,  however  small,  in  the  relative  quantities 
of  A  and  B,  must  produce  a  corresponding  alteration  in  the  relative  quantities 
of  the  two  which  unite  with  C.  That  this  is  not  the  case  under  all  circum- 
stances, is  shown  by  the  following  experiments  of  Bunsen  and  of  Debus. 

Bunsen's  experiments,*  which  were  made  in  such  a  manner  that  all  the  pheno- 
mena of  combination  concerned  in  them  took  place  simultaneously,  lead  to  the 
following  remarkable  laws  :  — 

1.  When  two  or  more  bodies,  BB'  .  .  .  are  presented  in  excess  to  the  body  A, 
under  circumstances  favourable  to  their  combination  with  it,  the  body  A  always 
selects  of  the  bodies  BB'  .  .  .  quantities  which  stand  to  one  another  in  a  simple 
atomic  relation,  so  that  for  1,  2,  3  ...  atoms  of  the  one  compound,  there  are 
always  formed  1,  2,  3  ...  atoms  of  the  other;  and  if  in  this  manner  there  is 
formed  an  atom  of  the  compound  AB'  in  conjunction  with  an  atom  of  AB,  the 
mass  of  the  body  B  may  be  increased  relatively  to  that  of  B'}  up  to  a  certain 
limit,  without  producing  any  alteration  in  the  atomic  proportion. 

When  carbonic  oxide  and  hydrogen  are  exploded  with  a  quantity  of  oxygen 
not  sufficient  to  burn  them  completely,  the  oxygen  divides  itself  between  the  two 
gases  in  such  a  manner  that  the  quantities  of  carbonic  acid  and  water  produced 
stand  to  one  another  in  a  simple  atomic  proportion.  The  results  of  Bunsen's  ex- 
periments are  given  in  the  following  table,  the  numbers  in  which  denote 
volumes  :  — 


Composition  of  Gaseous  Mixture. 

Quantities  of  CO  and  H  consumed 
by  Detonation. 

Ratio  of 
CO  :  H. 

72-57  CO  18-29  H 
59-93   «    26-71  " 
36-70  "    42-17  " 
40  12   "    47-15  " 

9-14  0 
13-36  « 
21-13  " 
12-73  « 

12-18  CO  6-10  H 

2  :  1 
1  :  1 
1  :  3 
1  :  4 

13-06    "    13-66  " 
10-79    "    .     ..                     31-47  " 

4-97    "    20-49  " 

The  results  were  the  same  whether  the  explosion  took  place  in  the  dark,  in 
diffused^ daylight,  or  in  sunshine;  and  were  not  affected  by  the  pressure  to  which 
the  gaseous  mixture  was  subjected. 

The  proportions  of  hydrogen  and  carbonic  acid  consumed  in  these  several  ex- 
periments, correspond  with  the  composition  of  five  hydrates  of  carbonic  acid,  con- 
taining, respectively  — 

H0.2C02;  HO.C02;  2HO.C02;  3HO.C02;  4HOCOa; 

but  the  results  cannot  be  attributed  to  the  actual  formation  of  these  hydrates,  in- 
asmuch as  hydrates  of  acids  containing  several  atoms  of  water  are  incapable  of 
existing  at  high  temperatures. 

2.  When  a  body,  A,  exerts  a  reducing  action  on  a  compound,  BC,  present  in 
excess,  so  that  A  and  B  combine  together,  and  C  is  set  free;  then,  if  0  can,  in 
its  turn,  exert  a  reducing  action  on  the  newly-formed  compound,  AB,  the  final 
result  of  the  action  is,  that  the  reduced  portion  of  BCis  to  the  unreduced  portion 
in  a  simple  atomic  proportion. 

In  this  case,  also,  the  mass  of  the  one  constituent  may,  without  altering  the 

*  Ann.  Ch.  Pharra.  Ixxxv.  137. 


732  CHEMICAL    AFFINITY. 

existing  atomic  relation,  be  increased  to  a  certain  limit,  above  which  that  relation 
undergoes  changes  by  definite  steps,  but  always  *in  the  proportion  of  simple 
rational  numbers. 

When  vapour  of  water  is  passed  over  red-hot  charcoal,  the  carbon  is  oxidized 
and  hydrogen  is  separated ;  but  the  process  does  not  go  on  so  far  as  the  complete 
formation  of  carbonic  acid,  but  stops  at  the  point  at  which  1  vol.  carbonic  acid 
and  2  vol.  carbonic  oxide  are  formed  to  every  4  vol.  of  hydrogen. 

In  the  imperfect  combustion  of  cyanogen — the  gaseous  mixture  being  so  far 
diluted  that  it  will  but  just  explode,  in  order  that  the  temperature  may  not  rise 
too  high,  and  the  result  be  consequently  vitiated  by  the  partial  oxidation  of  the 
nitrogen— carbonic  acid  and  carbonic  oxide  are  formed,  and  nitrogen  set  free,  like- 
wise in  simple  atomic  proportion.  A  mixture  of  18 '05  vol.  cyanogen,  28*87 
oxygen,  and  53-08  nitrogen,  gave,  by  detonation,  2  vol.  carbonic  oxide,  and  4  vol. 
carbonic  acid  to  3  vol.  nitrogen. 

In  the  combustion  of  a  mixture  of  carbonic  acid,  hydrogen,  and  oxygen,  in 
which  the  carbonic  acid  is  exposed  at  the  same  time  to  the  reducing  action  of  the 
hydrogen  and  the  oxidizing  action  of  the  oxygen,  the  reduced  portion  of  the  car- 
bonic acid  is  likewise  found  to  bear  to  the  unreduced  portion  a  simple  atomic  re- 
lation. In  the  combustion  of  a  mixture  of  8-52  carbonic  acid,  70-33  hydrogen, 
and  21-15  oxygen,  the  resulting  carbonic  oxide  was  to  the  reduced  carbonic  acid 
in  the  ratio  of  3:2.  After  the  combustion  of  a  mixture  of  4-41  vol.  carbonic 
oxide,  2-96  carbonic  acid,  68-37  hydrogen,  and  24-<^6  oxygen,  the  volume  of  the 
carbonic  oxide  converted  into  carbonic  acid  by  oxidation,  was  to  that  of  the  re- 
sidual carbonic  oxide  as  1:3. 

That  these  remarkable  laws  had  not  been  previously  observed  is  attributed  by 
Bunsen  to  the  fact  that  they  held  good  only  when  the  phenomena  of  combination, 
which  are  regulated  by  them,  take  place  simultaneously ;  for,  even  if  a  body  A, 
were  originally  to  select  for  combination  from  the  bodies  B  and  C,  quantities 
bearing  to  one  another  a  simple  atomic  relation,  but  the  combination  of  A  and  B 
were  to  take  place  in  a  shorter  time  than  that  of  A  and  C,  it  would  follow  of 
necessity,  that  during  the  whole  of  the  process,  the 'ratio  of  B  to  C,  and  therefore, 
also  the  atomic  relations  of  the  associated  compounds,  would  change,  so  that  the 
observed  proportion  would  be  no  longer  definite.  The  same  result  must  follow  if 
the  bodies  which  are  combining  side  by  side  are  not  homogeneously  mixed  in  the 
beginning. 

With  regard  to  the  bearing  of  these  results  on  Berthollet's  law,  it  might  be 
objected  that,  in  some  of  the  experiments,  as  in  the  combustion  of  a  mixture  of 
carbonic  oxide,  hydrogen,  and  oxygen,  one  of  the  products,  viz.  the  water,  is  re- 
moved from  the  sphere  of  action  by  condensation,  and  that  the  circumstances  are 
therefore  similar  to  the  removal  of  an  insoluble  product  by  precipitation  (p.  185). 
It  is  scarcely  conceivable,  however,  that  a  reverse  action  would  take  place,  even 
if  the  gaseous  mixture  were  to  remain  at  the  temperature  which  exists  during  the 
combustion.  Moreover,  in  the  decomposition  of  vapour  of  water  by  red-hot 
charcoal,  the  whole  of  the  products  remain  in  the  gaseous  state. 

Debus*  has  obtained  results  similar  to  those  of  Bunsen  by  precipitating  mixtures 
of  lime  and  baryta-water  with  aqueous  carbonic  acid,  or  mixtures  of  chloride  of 
barium  and  chloride  of  calcium,  with  carbonate  of  soda.  A  small  quantity  of  a 
very  dilute  solution  of  carbonate  of  soda,  added  to  a  liquid  containing  5  pts.  of 
chloride  of  barium  to  1  pt.  of  chloride  of  calcium,  threw  down  nearly  pure  car- 
bonate of  lime;  but  when  the  proportion  of  the  chloride  of  barium  in  the  mixture 
was  5-7  times  as  great  as  that  of  the  chloride  of  calcium,  2-3  pts.  of  the  former 
A^ere  decomposed  to  1  pt.  of  the  latter.  Hence  it  appears  that,  in  this  reaction 
also,  limits  exist  at  which  the  ratio  of  the  affinities  undergoes  a  sudden  change. 
In  these  experiments,  however,  the  products  are  immediately  removed  from  the 

*  Ann.  Ch.  Pharm.  Ixxxv.  103;  Ixxxvi.  156;  Ixxxvii.  238. 


CHEMICAL    AFFINITY.  733 

sphere  of  action,  and  the  results  are  therefore  not  comparable  with  those  which 
are  obtained  when  all  the  substances  present  remain  mixed  and  free  to  act  upon 
each  other. 

The  latter  condition  is  most  completely  fulfilled  in  the  mutual  actions  of  liquid 
compounds,  such  as  solutions  of  salts,  when  all  the  possible  products  of  their 
mutual  actions  are  likewise  soluble ;  as,  for  example,  when  nitrate  of  soda  in  solu- 
tion is  mixed  with  sulphate  of  copper.  The  question  to  be  solved  in  such  cases 
is  this.  Suppose  two  salts  AB,  CD,  the  elements  of  which  can  form  only  soluble 
products  by  their  mutual  interchange,  to  be  mixed  together  in  solution.  Will 
these  elements,  according  to  their  relative  affinities,  either  remain  in  their  original 
state  of  combination,  as  AB  and  CD,  or  pass  completely  into  the  new  arrange- 
ment AD  and  CB? — or  will  each  of  the  two  acids  divide  itself  between  each  of 
the  two  bases,  producing  the  four  compounds  AB,  AD,  BC,  BD  ? — and,  if  so,  in 
what  manner  will  the  relative  quantities  of  these  four  compounds  be  affected  by 
the  original  quantities  of  the  two  salts  ?  Do  the  amounts  of  AD  and  CB,  pro- 
duced by  the  reaction,  increase  progressively  with  the  regular  increase  of  AB,  as 
required  by  Berthollet's  theory?  or  do  sudden  transitions  occur,  like  those 
observed  in  the  experiments  of  Bunsen  and  Debus  ? 

The  solution  of  this  question  is  attended  with  considerable  difficulty.  For 
when  two  salts  in  solution  are  mixed,  and  nothing  separates  out,  it  is  by  no  means 
easy  to  ascertain  what  change^  may  have  taken  place  in  the  liquid.  The  ordinary 
methods  of  ascertaining  the  composition  of  the  mixture,  such  as  concentration,  or 
precipitation  by  re-agents,  are  inadmissible,  because  any  such  treatment  imme- 
diately alters  the  mutual  relation  of  the  substances  present.  In  some  cases,  how- 
ever, the  mixture  of  two  salts  is  attended  with  a  decided  change  of  colour,  with- 
out any  separation  of  either  of  the  constituents,  and  such  alterations  of  colour 
may  afford  indications  of  the  changes  which  take  place  in  the  arrangement  of  the 
molecules.  This  method  has  been  employed  by  Dr.  Gladstone,*  who  has  carefully 
examined  the  changes  of  colour  attending  the  mixture  of  a  great  variety  of  salts, 
•and  applied  the  results  to  the  determination  of  the  effect  of  mass  in  influencing 
chemical  action. 

Dr.  Gladstone's  principal  experiments  were  made  with  the  blood-red  sulpho- 
cyanide  of  iron,  which  is  formed  on  adding  hydro-sulphocyanic  acid  or  any  soluble 
sulphocyanide  to"  a  solution  of  a  ferric  salt  (p.  377).  On  mixing  known  quanti- 
ties of  different  ferric  salts  with  known  quantities  of  different  sulphocyanides,  it 
was  found  that  the  iron  was  never  completely  converted  into  the  red  salt;  that  the 
amount  of  it  so  converted  depended  on  the  nature  both  of  the  acid  combined  with 
the  ferric  oxide,  and  of  the  base  combined  with  the  sulphocyanogen ;  and  that  it 
mattered  not  how  the  bases  and  acids  had  been  combined  previous  to  their  mix- 
ture, so  long  as  the  same  quantities  were  brought  together  in  solution.  The  effect 
of  mass  was  tried  by  mixing  equivalent  proportions  of  ferric  salts  and  sulphocya- 
nides, and  then  adding  known  amounts  of  one  or  the  other  compound.  It  was 
found  that,  in  either  case,  the  amount  of  the  red  salt  was  increased,  and  in  a  regu- 
lar progression  according  to  the  quantity  added.  When  sulphocyanide  of  potas- 
sium was  mixed  in  various  proportions  with  ferric  nitrate,  chloride,  or  sulphate, 
the  rate  of  variation  appeared  to  be  the  same,  but  with  hydrosulphocyanic  acid  it 
was  different.  The  deepest  colour  was  produced  when  ferric  nitrate  was  mixed 
with  sulphocyanide  of  potassium ;  but  even  on  mixing  1  eq.  of  the  former  with 
3  eq.  of  the  latter,  only  0-194  eq.  of  the  red  sulphocyanide  of  iron  was  formed; 
and  even  when  375  eq.  of  sulphocyanide  of  potassium  had  been  added,  there  was 
still  a  recognizable  amount  of  ferric  nitrate  undecomposed.  The  results  of  a 
series  of  experiments  with  ferric  nitrate  and  sulphocyanide  of  potassium  are  given 
in  the  following  table  : — 

*  Phil.  Trans.  1855,  179;  Chem.  Soc.  Qu.  Jo.  ix.  54. 


734 


CHEMICAL    AFFINITY. 


Ferric 
Nitrate. 

Sulphocyanide  of 
Potassium. 

Red  Salt 
produced. 

Ferric 
Nitrate. 

Sulphocyanide  of 
Potassium. 

Red  Salt 
produced. 

1  equiv. 

3  equiv. 

88 

1  equiv. 

63  equiv. 

356 

1 

6 

127 

1 

99 

419 

1 

9-6 

156 

1 

135 

487 

1 

12-6 

176 

1 

189 

508 

1 

16-2 

195 

1 

243 

539 

1 

19-2 

213 

1 

297 

560 

1 

28-2 

266 

1 

375     ,« 

587 

1 

46-2 

318 

The  addition  of  a  colourless  salt  reduced  the  colour  of  a  solution  of  ferric  sulpho- 
cyanide,  the  reduction  increasing  in  a  regularly  progressive  ratio,  according  to  the 
mass  of  the  colourless  salt. 

Similar  results  were  obtained  with  other  ferric  salts,  viz.,  with  the  black  gal- 
late,  the  red  meconate  and  pyrorneconate,  the  blue  solution  of  Prussian  blue  in 
oxalic  acid,  &c.,  and  likewise  with  the  coloured  salts  of  other  metals,  e.  g.,  the 
scarlet  bromide  of  gold,  the  red  iodide  of  platinum,  the  blue  sulphate  of  copper, 
when  treated  with  different  chlorides,  &c. 

The  amount  of  fluorescence  exhibited  by  a  solution  of  acid  sulphate  of  quinine, 
was  found  to  be  affected  by  the  mixture  of  a  chloride,  bromide,  or  iodide,  accord- 
ing to  the  nature  and  mass  of  the  salt  added }  and  the  addition  of  sulphuric, 
phosphoric,  nitric,  and  other  acids  was  found  to  produce  a  fluorescence  in  solutions 
of  hydrochlorate  of  quinine  or  of  sulphate  which  had  been  rendered  non-fluores- 
cent by  the  addition  of  hydrochloric  acid.  Solutions  of  horse-chestnut  bark,  and 
of  tincture  of  thorn-apple,  yielded  similar  results. 

The  conclusions  to  be  drawn  from  Dr.  Gladstone's  experiments,  which  afford  a 
complete  confirmation  of  Berthollet's  theory,  so  far  at  least  as  relates  to  the  action 
of  substances  in  solution,  are  as  follows : — 

When  two  or  more  binary  compounds  are  mixed  under  such  circumstances  that 
all  the  -resulting  compounds  are  free  to  act  and  react,  each  electro-positive  element 
enters  into  combination  with  each  electro-negative  element  in  certain  constant  pro- 
portions, which  are  independent  of  the  manner  in  which  the  different  elements 
are  primarily  arranged,  and  are  not  merely  the  resultant  of  the  various  strengths 
of  affinity  of  the  several  substances  for  each  other,  but  are  dependent  also  on  the 
mass  of  each  of  the  substances  present  in  the  mixture.  All  deductions  respect- 
ing the  arrangement  of  substances  in  solution,  drawn  from  such  empirical  rules  as 
that  the  strongest  acid  combines  with  the  strongest  base,  must  therefore  be  falla- 
cious. 

An  alteration  in  the  mass  of  any  of  the  binary  compounds  present  alters  the 
amount  of  every  one  of  the  other  binary  compounds,  and  that  in  a  regularly  pro- 
gressive ratio ;  sudden  transitions  only  occurring  where  a  substance  is  present 
which  is  capable  of  combining  with  another  in  more  than  one  proportion. 

This  equilibrium  of  affinities  arranges  itself  in  most  cases  in  an  appreciably 
short  time;  but,  in  certain  instances,  the  elements  do  not  attain  their  final  state 
of  combination  for  hours. 

Totally  different  phenomena  present  themselves  where  precipitation,  volatiliza- 
tion, crystallization,  and  perhaps  other  actions  occur,  simply  because  one  of  the  sub- 
stances is  thus  removed  from  the  field  of  action,  and  the  equilibrium,  which  was 
at  first  established,  is  thus  destroyed  (p.  185). 

The  reciprocal  action  of  salts  in  solution  has  also  been  examined  by  Malaguti,* 
whose  method  consists  in  taking  two  salts,  both  of  which  are  soluble  in  water, 
but  only  one  of  which  is  soluble  in  alcohol,  mixing  them  in  equivalent  proportions 
in  water,  then  pouring  the  aqueous  solution  into  a  large  quantity  of  alcohol,  and 


*  Ann.  Ch.  Phys.  [3],  xxxvii.  198. 


CHEMICAL    AFFINITY.  735 

analyzing  the  precipitate,  in  order  to  ascertain  the  quantities  of  the  original  salts 
which  have  been  decomposed.  Malaguti  concludes  from  his  experiments  that,  in 
the  mutual  action  of  two  salts,  if  nothing  separates  from  the  liquid,  the  decompo- 
sition is  most  complete  when  the  strongest  acid  and  the  strongest  base  are  not 
originally  united  in  the  same  salt,  and  that  two  experiments  of  this  kind,  made 
in  opposite  ways,  must  lead  to  the  same  final  result  5  that,  for  example,  when  1 
eq.  of  acetate  of  baryta  is  added  to  1  eq.  of  nitrate  of  lead,  the  quantities  of 
nitrate  of  baryta  and  nitrate  of  lead  ultimately  present  in  the  liquid  are  the  same 
as  when  1  eq.  nitrate  of  baryta  is  mixed  with  1  eq.  acetate  of  lead.  The  greater 
the  quantity  of  the  two  salts  decomposed  in  the  one  case,  the  smaller  will  be  the 
quantity  decomposed  in  the  other;  so  that  if  the  quantity  of  any  salt,  out  of  100 
parts,  which  is  decomposed  by  the  action  of  another  salt  (always  supposing  that 
the  whole  remains  iu  solution)  be  called  the  coefficient  of  decomposition,  the  law 
of  the  reaction  is,  that  the  sum  of  the  coefficients  of  decomposition  in  the  two 
cases  is  always  equal  to  100.  For  example :  if  1  at.  sulphate  of  potash  and  1  at. 
acetate  of  soda  act  upon  each  other,  and  Tfi^  of  the  original  quantity  of  sulphate 
of  potash  remain  in  solution  as  such,  the  coefficient  of  decomposition  is  36.  The 
numerical  values  of  the  coefficients  of  decomposition,  determined  in  several  cases 
by  the  method  above  described,  are  given  in  the  following  table : — 

Coefficient  of  Coefficient  of 

Salts.  Decomposition.  Salts.  Decomposition. 

Acetate  of  potash t  qo.n          Acetate  of  lead 

Nitrate  of  lead \  Nitrate  of  potash 

Chloride  of  potassium...  )  %.  ft          Chloride  of  zinc t          17  fi 

Sulphate  of  zinc  {  Sulphate  of  potash £ 

Acetate  of  baryta I  77  n         Acetate  of  lead )          99.ft 

Nitrate  of  lead ]  Nitrate  of  baryta { 

Chloride  of  sodium  /  ,-n.Q          Chloride  of  zinc ) 

Sulphate  of  zinc (  Sulphate  of  soda ( 

Acetate  of  baryta )  ^n.n          Acetate  of  potash  

Nitrate  of  potash $  Nitrate  of  baryta 

Acetate  of  potash >  67-0         Acetate  of  strontia 

Nitrate  of  strontia £  Nitrate  of  potash 

Acetate  of  strontia >  P*  r         Acetate  of  lead )          oo  A 

Nitrate  of  lead (  Nitrate  of  strontia $ 

Acetate  of  potash >  A9  ft         Acetate  of  soda I          qc  c 

Sulphate  of  soda {  Nitrate  of  potash 

Chloride  of  potassium...  t  gg^          Manganous  chloride.... 

Manganous  sulphate \  Sulphate  of  potash 

Chloride  of  potassium...  i  ^  n          Chloride  of  magnesium 

Sulphate  of  magnesia...  (  Sulphate  of  potash 

Chloride  of  sodium t  t4  E          Chloride  of  magnesium  )          „  R 

Sulphate  of  magnesia...  (  Sulphate  of  soda \ 

In  all  these  cases,  except  one,  the  coefficients  of  decomposition  are  greatest  when 
the  strongest  acid  and  the  strongest  base  are  not  originally  united  in  the  same 
salt.  The  exceptional  case  is  presented  by  the  mixture  of  nitric  acid,  acetic  acid, 
potash,  and  baryta,  in  which  the  greatest  coefficient  of  decomposition  is  obtained 
when  the  nitric  acid  is  at  first  united,  not  with  the  baryta,  but  with  the  potash. 
A  similar  result  was  obtained  by  the  action  of  potash  on  nitrate  of  baryta,  and  of 
baryta  on  nitrate  of  potash,  wood-spirit  being  used  as  the  precipitating  agent 
instead  of  alcohol.  The  coefficient  of  decomposition  was  6-9  in  the  former  case, 
and  93-6  in  the  latter. 

It  is  not  easy  to  determine  how  far  the  particular  numerical  results  of  these 
experiments  were  influenced  by  the  presence  of  the  alcohol ;  but  as  its  action  was 
the  same  in  both  cases  of  each  pair  of  experiments,  the  results  certainly  justify 


736  CHEMICAL    AFFINITY. 

the  conclusion  that  the  two  salts,  when,  mixed,  resolve  themselves  into  four;  that 
the  partition  takes  place  in  a  definite  manner ;  and  that  the  proportions  of  the 
resulting  salts  are  independent  of  the  manner  in  which  their  elements  were 
originally  combined. 

Experiments  bearing  on  the  same  point,  have  also  been  published  by  Margueritte,* 
who  finds  that  two  salts  in  solution  mutually  decompose  each  other,  even  when  one 
of  them  is  already  the  least  soluble  of  the  four  salts  that  may  be  produced  from 
the  two  acids  and  the  two  bases  present.  A  saturated  solution  of  chlorate  of 
potash,  to  which  chloride  of  sodium  is  added,  becomes  capable  of  dissolving  an 
additional  quantity  of  chlorate  of  potash,  showing  that  a  portion  of  the  chlorate 
has  been  decomposed,  and  a  more  soluble  salt  formed.  Chloride  of  ammonium  is 
precipitated  from  its  saturated  aqueous  solution  on  addition  of  a  small  quantity  of 
nitrate  of  ammonia ;  but  the  previous  addition  of  chlorate  of  potash  prevents  the 
precipitation;  whence  it  would  appear  that  the  chlorate  of  potash  and  chloride  of 
ammonium  are  partially  converted  into  chlorate  of  ammonia  and  chloride  of  potas- 
sium. The  precipitation  of  sulphate  of  lime  from  its  aqueous  solution  by  alcohol, 
is  prevented  by  the  presence  of  the  nitrates  or  chlorides  of  potassium,  sodium,  or 
ammonium,  evidently  because  a  portion  of  the  sulphate  is  converted  into  nitrate 
or  chloride.  A  solution  of  chloride  of  ammonium  dissolves  the  carbonates  of 
baryta,  strontia,  and  lime  more  readily  than  pure  water,  because  it  partially  con- 
verts them  into  chlorides,  the  liquid  at  the  same  time  acquiring  an  alkaline 
reaction,  in  consequence  of  the  formation  of  carbonate  of  ammonia. 

The  decomposition  of  insoluble  by  soluble  salts  affords  a  striking  instance  of  the 
tendency  of  atoms  to  interchange,  and  of  the  influence  of  mass  on  chemical  action. 
According  to  H.  Hose,")"  sulphate  of  baryta  is  completely  decomposed  by  boiling 
with  solutions  of  alkaline  carbonates,  provided  that  each  equivalent  of  sulphate  of 
baryta  is  acted  upon  by  at  least  15  eq.  of  the  alkaline  carbonate.  If  1  eq.  of 
sulphate  of  baryta  is  boiled  with  only  1  eq.  of  carbonate  of  potash,  only  ^  of  it  is 
decomposed,  and  only  Jy  by  boiling  with  1  eq.  of  carbonate  of  soda,  further 
decomposition  being  prevented  by  the  presence  of  the  alkaline  sulphate  already 
formed.  If,  however,  the  liquid  be  decanted  after  a  while,  the  residue  boiled 
with  a  fresh  portion  of  the  alkaline  carbonate,  and  these  operations  repeated 
several  times,  complete  decomposition  is  effected.  Carbonate  of  baryta  is  con- 
verted into  sulphate  by  the  action  of  an  aqueous  solution  of  sulphate  of  potash  or 
soda,  even  at  ordinary  temperatures.  Solution  of  carbonate  of  ammonia  does  not 
decompose  sulphate  of  baryta  either  at  ordinary  or  at  higher  temperatures ;  car- 
bonate of  baryta  is  not  decomposed  by  sulphate  of  ammonia  at  ordinary  tempera- 
tures, but  easily  on  boiling.  Sulphate  of  baryta  is  not  decomposed  by  boiling 
with  caustic  potash-solution,  provided  the  carbonic  acid  of  the  air  be  excluded; 
but  by  fusion  with  hydrate  of  potash,  it  is  decomposed,  with  formation  of  carbonate 
of  baryta,  because  the  carbonic  acid  of  the  air  cannot  then  be  completely  excluded. 
Hydrochloric  and  nitric  acids,  left  in  contact  at  ordinary  temperatures  with  sul- 
phate of  baryta,  either  crystallized  or  precipitated,  dissolve  only  traces  of  it ;  at 
the  boiling  heat,  a  somewhat  larger  quantity  is  dissolved,  and  the  solution  forms 
a  cloud,  both  with  a  dilute  solution  of  chloride  of  barium  and  with  dilute  sulphuric 
acid.  Sulphate  of  strontia  is  dissolved  by  hydrochloric  acid  at  ordinary  tempera- 
tures, sufficiently  to  form  a  slight  precipitate  with  dilute  sulphuric  acid,  and  with 
chloride  of  strontium.  Sulphate  of  lime  treated  with  hydrochloric  acid,  either 
cold  or  boiling,  yields  a  liquid  in  which  a  precipitate  is  formed,  after  a  while,  by 
dilute  sulphuric  acid,  but  not  by  chloride  of  calcium. 

Sulphate  of  strontia  and  sulphate  of  lime  are  completely  decomposed  by  solu- 
tions of  the  alkaline  carbonates  and  bicarbonates  at  ordinary  temperatures,  and 
more  quickly  on  boiling,  even  if  considerable  quantities  of  an  alkaline  sulphate 
are  added  to  the  solution  :  the  decomposition  is  also  effected  by  carbonate  of 

*  Compt,  rend,  xxxviii.  304.  f  Pogg.  Ann.  xciv.  481 ;  xcv.  96,  284. 


CHEMICAL    AFFINITY.  737 

ammonia,  even  at  ordinary  temperatures.  The  carbonates  of  strontia  and  lime  are 
not  decomposed  by  solutions  of  the  sulphates  of  potash  or  soda  at  any  temperature  ; 
sulphate  of  ammonia  does  not  decompose  them  at  ordinary  temperatures,  but 
readily  with  the  aid  of  heat. 

Sulphate  of  lead  is  completely  converted  into  carbonate  by  solutions  of  the 
alkaline  carbonates  and  bicarbonates,  even  at  ordinary  temperatures ;  the  neutral 
carbonates,  but  not  the  bicarbonates,  then  dissolving  small  quantities  of  oxide  of 
lead.  Carbonate  of  lead  is  not  decomposed  by  solutions  of  the  alkaline  sulphates, 
either  at  ordinary  temperatures  or  or  on  boiling. 

Chromate  of  baryta  is  decomposed  at  ordinary  temperatures  by  solutions  of  the 
neutral  alkaline  carbonates,  and  much  more  easily  by  boiling  with  excess  of  an 
alkaline  bicarbonate.  When  equivalent  quantities  of  the  chromate  of  baryta  and 
carbonate  of  soda  are  boiled  with  water,  ^  of  the  whole  is  decomposed ;  when  the 
same  quantities  of  the  salts  are  fused  together,  and  the  mass  treated  with  water, 
only  ^y  of  the  baryta-salt  is  decomposed.  Carbonate  of  baryta  is  completely  con- 
verted into  chromate  by  digestion  with  a  solution  of  an  alkaline  monochromate ; 
and  the  decomposition  of  chromate  of  baryta  by  alkaline  carbonates,  even  at  the 
boiling  heat,  is  completely  prevented  by  the  presence  of  a  certain  quantity  of  an 
alkaline  monochromate. 

Seleniate  of  baryta  is  easily  and  completely  decomposed  by  solutions  of  alkaline 
carbonates,  even  at  ordinary  temperatures :  this  salt  is  somewhat  soluble  in  water, 
and  more  readily  in  dilute  acids. 

Oxalate  of  lime  is  decomposed  by  alkaline  carbonates  even  at  ordinary  tempera- 
tures ;  but  to  effect  complete  decomposition  the  liquid  must  be  frequently  decanted 
and  renewed.  The  decomposition  takes  place  rapidly  at  the*boiling  heat;  but  in 
all  cases  it  is  completely  prevented  by  the  presence  of  a  certain  quantity  of  a  neu- 
late  alkaline  oxalate.  When  the  salts  are  mixed  in  equivalent  proportions,  T2T  of 
the  oxalate  of  lime  are  decomposed  at  ordinary  temperatures,  and  |  on  boiling. 
Carbonate  of  lime  is  partially  converted  into  oxalate  by  the  action  of  a  solu- 
tion of  neutral  oxalate  of  potash  at  ordinary  temperatures,  and  more  quickly  on 
boiling;  —  but  the  decomposition  is  never  complete,  even  when  the  liquid  is  fre- 
quently decanted  and  renewed.  —  Oxalate  of  lead  is  completely  converted  into 
carbonate  at  ordinary  temperatures  by  the  solution  of  an  alkaline  carbonate,  a 
small  portion  of  the  carbonate  of  lead  dissolving  in  the  liquid.  (Rose). 

The  preceding  experiments  exhibit  in  a  striking  manner  the  influence  of  differ- 
ence of  solubility  in  determining  the  order  of  decomposition.  Sulphate  of  baryta 
is  less  soluble  than  the  carbonate,  and,  accordingly,  carbonate  of  baryta  is  more 
readily  decomposed  by  alkaline  sulphates,  than  the  sulphate  by  alkaline  carbonates. 
Precisely  the  contrary  relations  are  exhibited  by  the  sulphates  and  carbonates  of 
strontia*  and  lime,  both  as  regards  solubility  and  order  of  decomposition.  On 
the  other  hand,  oxalate  of  lime  is  less  soluble  than  the  carbonate,  and  yet  its 
decomposition  by  alkaline  carbonates  takes  place  more  easily  than  the  opposite 
reaction  :  in  this  case,  the  order  of  decomposition  appears  rather  to  be  determined, 
as  in  Malaguti's  experiments,  by  the  tendency  of  the  strongest  acid  to  unite  with 
the  strongest  base. 

The  effect  of  a  soluble  sulphate,  &c.,  in  arresting  the  decomposition  of  the 
corresponding  insoluble  salts  by  alkaline  carbonates,  is  evidently  due  to  its  ten- 
dency to  produce  the  reverse  action  :  hence  the  acceleration  produced  by  decant- 
ing and  renewing  the  liquid.  Some  insoluble  salts,  however,  phosphate  of  lime 
for  example,  are  never  completely  decomposed,  even  by  this  treatment. 

The  constant  tendency  to  interchange  of  atoms,  exhibited  in  the  phenomena 
above  described,  arid,  indeed,  in  all  cases  of  chemical  action,  suggests  the  idea 

*  According  to  Fresenius,  carbonate  of  strontia  dissolves  in  11,862  parts,  and  the  sul- 
phate in  f>895  parts  of  cold  water. 

47 


738  CHEMICAL    AFFINITY. 

that  the  atoms  of  all  bodies,  at  least  in  the  fluid  state,  are  in  constant  motion. 
We  have  already  seen  that  the  same  idea  is  suggested  by  the  phenomena  of  heat, 
and  leads  to  a  consistent  theory  of  those  phenomena  (p.  654).  On  a  similar 
hypothesis,  Professor  Williamson  proposes  to  construct  a  general  theory  of  chemi- 
cal action.*  The  fundamental  notion  of  this  theory  is,  that  the  atoms  of  all  com- 
pounds, whether  similar  or  dissimilar,  are  continually  changing  places,  the  inter- 
change taking  place  more  readily  as  the  atoms  resemble  each  other  more  closely. 
Thus,  in  a  mass  of  hydrochloric  acid,  each  atom  of  hydrogen  is  supposed  not  to 
remain  quietly  in  juxtaposition  with  the  atom  of  chlorine  with  which  it  happens 
to  be  first  united,  but  to  be  continually  changing  places  with  other  atoms  of  hydro- 
gen, or,  what  comes  to  the  same.thing,  continually  becoming  associated  with  other 
atoms  of  chlorine.  This  interchange  is  not  perceptible  to  the  eye,  because  one 
molecule  of  hydrochloric  acid  is  exactly  like  another.  But  suppose  the  hydro- 
chloric acid  to  be  mixed  with  a  solution  of  sulphate  of  copper  (the  component 
atoms  of  which  are  likewise  undergoing  a  change  of  place),  the  basylous  elements, 
hydrogen  and  copper,  then  no  longer  limit  their  change  of  place  to  the  circle  of 
atoms  with  which  they  were  at  first  combined,  but  the  hydrogen  and  copper  like- 
wise change  places  with  each  other,  forming  chloride  of  copper  and  sulphuric 
acid.  Thus  it  is  that,  when  two  salts  are  mixed  in  solution,  and  nothing  sepa- 
rates out  in  consequence  of  their  mutual  action,  the  bases  are  divided  between 
the  acids,  and  four  salts  are  produced.  If,  however,  the  analogous  elements  of 
the  two  compounds  are  very  dissimilar,  and,  consequently,  interchange  but  slowly, 
it  may  happen  that  the  stronger  acid  and  the  stronger  base  remain  almost  entirely 
together,  leaving  the  weaker  ones  combined  with  each  other.  This  is  strikingly 
seen  in  a  mixture  of  sulphuric  acid  (sulphate  of  hydrogen)  and  borate  of  soda, 
which  soon  becomes  almost  wholly  converted  into  sulphate  of  soda  and  free  boracic 
acid  (borate  of  hydrogen). 

Now  suppose  that,  instead  of  sulphate  of  copper,  sulphate  of  silver  is  added  to 
the  hydrochloric  acid.  At  the  first  moment  the  interchange  of  elements  may  be 
supposed  to  take  place  as  above,  and  the  four  compounds,  £O4H2  SQ4Ag2,  C1H, 
and  ClAg,  to  be  formed;  but  the  last,  being  insoluble,  is  immediately  removed 
by  precipitation  ;  the  remaining  elements  then  act  upon  each  other  in  the  same 
way,  and  this  action  goes  on  till  all  the  chlorine  or  all  the  silver  is  removed  in  the 
form  of  chloride  of  silver;  if  the  original  compounds  are  mixed  in  exactly  equivalent 
proportions,  the  final  result  is  the  formation  of  only  two  salts,  viz.,  in  this  case, 
SO4H2  and  ClAg.  A  similar  result  is  produced*  when  one  of  the  products  of  the 
decomposition  is  volatile  at  the  existing  temperature*,  as  when  hydrate  or  car- 
bonate of  soda  is  boiled  with  chloride  of  ammonium. 

This  theory  affords  a  simple  explanation  of  the  action  of  sulphuric  acid  upon 
alcohol,  whereby  sulphovinic  acid  (sulphate  of  ethyl  and  hydrogen)  is  first  formed, 
and  afterwards,  at  a  certain  temperature,  ether  and  water  are  eliminated  (p.  182). 

OH  H 

When  alcohol,     2jr5}O,  and  sulphuric  acid,-g  JSO4,  are  mixed  together,  the  in- 

terchange between  the  atoms  of  ethyl  in  the  former  and  of  hydrogen  in  the  latter 
gives  rise  to  the  formation  of  sulphovinic  acid  and  water  :  — 


But  the  change  does  not  stop  here,  for  the  sulphoviuic  acid  thus  produced,  meet- 
ing with  fresh  molecules  of  alcohol,  exchanges  its  ethyl  for  the  hydrogen  of  the 
alcohol,  producing  ether  and  sulphuric  acid  :  — 

art     ,   O2H5  i  £v 
H    ^<  7       H  i^ 

*  Cbem.  Soc.  Qu.  J.,  iv.  110. 


CHEMICAL    AFFINITY.  739 

The  sulphuric  acid  is  thus  restored  to  its  original  state,  and  is  ready  to  act  upon 
fresh  quantities  of  alcohol  ;  so  that  if  alcohol  be  allowed  to  run  into  the  mixture 
in  a  constant  stream,  the  temperature  being  kept  within  certain  limits  (between 
140°  and  160°  C.),  the  process  goes  on  without  interruption,  ether  and  water  con- 
tinually distil  over,  and  the  same  quantity  of  sulphuric  acid  suffices  for  the  etheri- 
fication  of  an  unlimited  quantity  of  alcohol.  This  is  the  peculiarity  of  the  pro- 
cess ;  it  has  given  rise  to  a  variety  of  explanations  ;  in  fact,  the  process  of  etherin- 
cation  has  long  been  a  battle-ground  of  chemical  theories.*  The  discussion  of 
these  various  theories  would  be  foreign  to  the  present  purpose  ;  it  is  sufficient  to 
remark  that  the  hypothesis  of  atomic  interchange  affords  a  ready  explanation  of 
the  most  obscure  point  in  the  reaction,  viz.,  the  formation  and  decomposition  of 
sulphovinic  acid  following  each  other  continuously,  without  any  change  of  tem- 
perature or  other  determining  cause.  .  If  it  be  admitted  that  the  atoms  of  ethyl 
and  hydrogen  in  the  mixture  are  continually  interchanging  in  all  possible  ways, 
this  series  of  alternate  actions  follows  as  a  necessary  consequence. 

The  formation  of  ether  by  the  mutual  action  of  sulphovinic  acid  and  alcohol  is 
also  analogous  to  its  production  by  the  action  of  iodide  of  ethyl  on  potassium- 
alcohol  (pi  699):  — 


The  same  view  is  corroborated  by  the  fact  recorded  by  Williamson,  in  the  paper 
above  quoted,  that  sulphamylic  acid  (sulphate  of  amyl  and  hydrogen)  distilled 
with  common  alcohol,  yields  an  ether  containing  both  ethyl  and  amyl  :  — 


__  j   v    ,   H 

H    r  H 


and  that  the  same  compound  is  obtained  by  distilling  a  mixture  of  vinic  and 
amylic  alcohols  with  sulphuric  acid  ;  also  with  the  fact  discovered  by  Chancel, 
that  sulphovinate  of  potassium  distilled  with  potassium-alcohol,  yields  ether:  — 


K         4          K 

and  that  the  same  salt  distilled  with  methylate  of  potassium,  OH3KO,  yields 

•Ct  TI 
methamylic  ether,  ^r  5  1  0. 

The  idea  of  atomic  motion  is  in  accordance  with  physical  as  well  as  chemical 
phenomena.  To  suppose  that  rest,  rather  than  motion,  is  the  normal  state  of  the 
particles  of  matter,  is  at  variance  with  all  that  we  know  of  the  effects  of  light, 
heat,  and  electricity.  In  the  heat-theory  of  Clausius,  (p.  653),  the  particles  of 
bodies  are  supposed  to  be  affected  with  progressive,  as  well  as  with  rotatory  and 
vibratory  movements  j  and  this  same  hypothesis  of  progressive  movement  which, 
of  course,  implies  change  of  relative  position  among  the  particles,  affords,  as 
already  stated,  a  ready  explanation  of  certain  chemical  reactions,  otherwise  some- 
what obscure.  It  is  worth  while  to  observe  that,  in  the  heat-theory  of  Clausius, 
the  progressive  motion  of  the  particles  is  supposed  to  exist  only  in  the  liquid  and 
gaseous  states,  the  particles  of  solid  bodies  merely  performing  rotatory  and  vibra- 
tory movements  about  certain  positions  of  equilibrium.  This  is  quite  in  accord- 
ance with  the  well-known  fact  that  chemical  reaction  rarely  takes  place  between 
solid  bodies. 

*  See  the  translation  of  Gmelin's  Handbook,  vol.  viii.  pp.  231  —  237. 


740 


DIFFUSION    OF    LIQUIDS. 


FIG.  229. 


DIFFUSION   OF   LIQUIDS. 

Intimately  connected  with  the  interchange  of  atoms  resulting  in  chemical  de- 
composition, is  the  process  by  which  a  saline,  or  other  soluble  substance,  is  spread 
or  diffused  uniformly  through  the  mass  of  the  solvent  ;  in  some  cases,  indeed,  as 
will  presently  be  seen,  the  decomposition  of  salts  is  greatly  facilitated  by  the 
tendency  of  one  or  more  of  the  products  of  decomposition  to  diffuse  into  the  sur- 
rounding liquid. 

The  phenomena  of  liquid  diffusion  have  been  minutely  in- 
vestigated by  Mr.  Graham.*  The  apparatus  used  consisted  of 
a  set  of  phials,  of  nearly  equal  capacity,  cast  in  the  same 
mould,  and  further  adjusted  by  grinding  to  a  uniform  size  of 
aperture.  The  phials  were  38  inches  high,  with  a  neck  0-5 
inch  in  depth,  and  aperture  1-25  inch  wide;  capacity  to  base 
of  neck  equal  to  2080  grains  of  water,  or  between  4  and  5 
ounces.  For  each  diffusion-phial,  a  plain  glass  water-jar  was 
also  provided,  4  inches  in  diameter  and  7  inches  deep.  (Fig. 
229.) 

The  diffusion -phial  was  filled  with  the  saline  solution,  sal- 
ammoniac  for  instance,  to  the  base  of  the  neck,  or  more  cor- 
rectly to  a  distance  of  0-5  inch  from  the  ground  surface  of 
the  lip.  The  neck  of  the  phial  was  then  filled  up  with  distilled  water,  a  light 
float  being  first  placed  on  the  surface  of  the  solution,  and  care  being  taken  to 
avoid  agitation.  After  the  phial  had  been  placed  within  the  jar,  water  was 
poured  into  the  jar,  so  as  to  cover  the  open  phial  to  the  depth  of  an  inch, 
which  required  about  20  ounces  of  water.  The  saline  liquid  in  the  phial  is  thus 
allowed  to  communicate  freely  with  the  water  in  the  jar.  The  diffusion  is  inter- 
rupted by  placing  a  small  plate  of  ground  glass  on  the  mouth  of  the  phial,  and 
raising  the  latter  out  of  the  jar.  The  amount  of  salt  diffused,  called  the  diffusion- 
product,  or  di/usate,  is  ascertained  by  evaporating  the  water  in  the  jar  to  dryness, 
or,  in  the  case  of  chlorides,  by  precipitating  with  nitrate  of  silver. 

The  results  of  several  series  of  experiments  made  in  this  manner  are  given  in 
the  following  Table,  the  second  column  of  which  shows  the  quantity  of  salt  in 
100  parts  of  the  solution;  the  third,  the  time  of  diffusion;  the  fourth,  the 
temperature,  on  the  Fahrenheit  scale ;  the  fifth,  the  quantity  of  salt  diffused  :  — 

*  DIFFUSION  OF  SALINE  SOLUTIONS. 


Substance. 

Per  Cent. 

Days. 

Fahr. 

Diffusate. 

1 
2 
2 

5 
5 
5 

51° 
•51 

59-7 

7-41 
15-04 
16-55 

4 

8 
2 

5 
5 
5 

51 
51 
51 

30-72 
67-68 
15-11 

2 

5 

59-7 

16-58 

0-864 

10 

60-1 

5-84 

1.766 

5 

64-2 

11-68 

Hydrated  nitric  acid  (N08H)  < 

' 

1 
2 

5 
5 

61-2 
51-2 

6-99 
14-74 

[ 

4 

8 

5 
5 

51-2 
51-2 

28-76 
57-92 

*  Phil.  Trans.  1850,  pp.  1,  805  ;  Chem.  Soc.  Qu.  J.  ii.  60,  257  ;  IT.  83. 


DIFFUSION    OF    LIQUIDS. 

DIFFUSION  OF  SALINE  SOLUTIONS  —  continued. 


741 


Substance. 


1 

Hydrated  sulphuric  acid  (S04H) ^ 

8 
Chromic  acid v  1-76$ 

2 
Acetic  acid  (C4H404) J  4 

8 
1 

Sulphurous  acid ^ 

8 

1 
2 
Ammonia J 

4 

8 
2 
Alcohol J  4 

8 
1 

Nitrate  of  baryta \  4 

8 

Nitrate  of  strontia "  0.82 

1 

Nitrate  of  lime J 

8 

Acetate  of  baryta *  1 

Acetate  of  lead 1 

1 

n 

Chloride  of  barium J 

4 

8 

1 

o 

Chloride  of  strontium -J 

8 
1 
2 

Chloride  of  calcium -!  4 

8 
1 

Chloride  of  manganese *"  1 

Nitrate  of  magnesia 1 

Nitrate  of  copper 1 

Chloride  of  zinc 1 

Chloride  of  magnesium 1 

Cupric  chloride 1 

Ferrous  chloride 1 

1 
2 
4 

Sulphate  of  magnesia -|  8 

8 
16 
24 
1 
2 
4 

Sulphate  of  zinc -j  8 

8 
16 
24 


Per  Cent. 


Days. 


10 
10 
10 
10 
10 
10 
10 
10 
10 
10 
10 
10 
4.04 
4-04 
4-04 
4-04 
10 
10 
10 

11-43 
11-43 
11-43 
11-43 
11-43 
11-43 
11-43 
11-43 
11-43 
16-17 
16-17 
8-57 
8-57 
8-57 
8-57 
8-57 
8-57 
8-57 
8-57 
11-43 
11-43 
11-43 
11-43 
11-43 
11-43 
11-43 
11-43 
11-43 
11-43 
11-43 
11-43 
16-17 
16-17 
16-17 
16-17 
16-17 
16-17 
16-17 
16-17 
16-17 
16-17 
16-17 
16-17 
16-17 
16-17 


Fahr. 


49-7c 
49-7 
49-7 
49-7 

48-8 
48-8 
48-8 
68-1 
68-1 
68-1 
68-1 
63-4 
63-4 
63-4 
63-4 
48-7 
48-7 
48-7 
64-1 
64-1 
64-1 
64-1 
51-5 
64-1 
64-1 
64-1 
64-1 
53-5 
53-1 
6-3 
6-3 
6-3 
6-3 
6-3 
6-3 
6-3 
6-3 
63-8 
63-8 
63-8 
63-8 
50-8 
50-8 
50-8 
50-8 
50-8 
50-8 
50-8 
63-5 
65-4 
65-4 
65-4 
65-4 
62-8 
62-8 
62-8 
65-4 
65-4 
65-4 

62-8 
62-8 
62-8 


Diffusate. 


8-69 

16-91 

33-89 

68-96 

19-78 

11-31 

22-02 

41-80 

8-09 

16-96 

33-00 

66-38 

4-93 

9-59 

19-72 

41-22 

8-62 

16-12 

35-50 

7-72 

15-04 

29-60 

54-50 

5-59 

7-66 

15-01 

29-04 

55-10 

7-50 

7-84 

6-32 

12-07 

23-96 

45-92 

6-09 

11-66 

23-56 

44-46 

7-92 

15-35 

30-78 

61-56 

6-51 

6-63 

6-49 

6-44 

6-29 

6-17 

6-06 

6-30 

7-31 

12-79 

23-46 

42-82 

42-66 

75-06 

102-04 

6-67 

12-22 

23-12 

42-26 

39-62 

74-40 

101-42 


742 


DIFFUSION    OF    LIQUIDS. 
DIFFUSION  OF  SALINE  SOLUTIONS  —  continued. 


Substance. 


1 

2 
Sulphate  of  alumina - 

8 
2 

Nitrate  of  silver -I  4 

8 
2 

Nitrate  of  soda..... -|  4 

I  8 

1 
2 

Chloride  of  sodium 1  4 

8 
2 

Iodide  of  sodium 2 

Bromide  of  sodium  2 

Chloride  of  potassium 2 

Bromide  of  potassium 2 

Iodide  of  potassium 2 

Chloride  of  ammonium 1 

1 

Bicarbonate  of  potash ,1 

8 
1 
2 
Bicarbonate  of  ammonia J 

8 
1 
2 
Bicarbonate  of  soda  

I     ! 

2 
Hydrate  of  potash -|  4 

8 
1 
2 
Hydrate  of  soda -{  4 

8 
1 
2 
Carbonate  of  potash -|  4 

8 
1 

n 

Carbonate  of  soda. 

8 

1 

Sulphate  of  potash -j  4 

8 
1 
2 
Sulphate  of  soda -{  4 

8 

Sulphite  of  potash 

Sulphite  of  soda  2 

Hyposulphite  of  potash 

Hyposulphite  of  soda 

Sulphovinate  of  potash 

Sulphovinate  of  soda 


Per  Cent. 


Days. 

~16-1~7~ 
16-17 
16-17 
16'17 
7 
7 
7 
7 
7 
7 
7 
7 
7 
7 
7 
7 
7 

5-716 
5-716 
5-716 
5.716 
8-08 
8-08 
8-08 
8-08 
8-08 
8-08 
8-08 
8-08 
9-87 
9-87 
9-87 
9-87 
4-04 
4-04 
4-04 
4-04 
4-95 
4-95 
4-95 
4-95 
8-08 
8-08 
8-08 
8-08 
9-9 
9-9 
9-9 
9-9 
8-08 
8-08 
8-08 
8-08 
9-9 
9-9 
9-9 
9-9 
8-08 
99 
8-08 
9-9 
8-08 
9-9 


Fahr. 


65-4 

65-4 

65-4 

65-4 

.63-4 

63-4 

63-4 

63-4 

63-4 

63-4 

63-4 

63-4 

63-4 

63-4 

63-4 

59-8 

59-8 

59-8 

59-8 

59-8 

59-8 

68-2 

68-2 

68-2 

68-2 

68-2 

68-2 

68-2 

68-2 

68-2 

68-2 

68-2 

68-2 

63-3 

63-3 

63-3 

63-3 

63-2 

63-2 

63-2 

63-2 

63-6 

63-6 

63-6 

63  •& 

63-4 

63-4 

63-4 

63-4 

60-2 

60-2 

60-2 

60-2 

59-9 

599 

59-9 

59-9 

59-5 

59-5 

59-7 

59-9 

59-7 

59-5 


DIFFUSION    OF    LIQUIDS. 

DIFFUSION  OF  SALINE  SOLUTIONS  —  continued. 


743 


Substance. 

Per  Cent. 

Days. 

Fahr. 

Diffusate. 

r 

1 
2 

8-08 
8-08 

59-9° 
59-9 

6-20 
12-17 

4 
8 
1 

8-08 
8-08 
9-9 

59-9 
59-9 
59-9 

23-04 

42-82 
6-24 

1 
2 

8-08 
8-08 

60-2 
60-2 

6-44 
12-52 

4 

8 
1 
2 

8-08 
8-08 
9-9 
9-9 

60-2 
60-2 
59-5 
59-5 

23-44 
47-26 
6-67 
12-46 

4 

8 
2 

99 
9-9 

808 

59-5 
59-5 
59-9 

25-04 
48-04 
10-96 

2 

9-9 

59-5 

10-65 

Hydrochlorate  of  morphine    

2 

11-43 

64-1 

11-60 

Hydrochlorate  of  strychnine  

2 

11-43 

64-1 

11-49 

These  experiments,  and  a  number  of  others  made  in  a  similar  manner,  lead  to 
the  following  general  conclusions:  — 

1.  Different  salts,  in  solutions  of  equal  strength,  diffuse  unequally  in  equal 
times. 

2.  With  each  salt,  the  rate  of  diffusion  increases  with  the  temperature,  and  at 
any  given  temperature,  is  proportionate  to  the  strength  of  the  solution,  at  least 
•when  the  quantity  of  salt  dissolved  does  not  exceed  4  or  5  per  cent. 

3.  There  exist  classes  of  equidiffusive  substances  which  coincide  in  many  cases 
with  the  isomorphous  groups,  but  are,  on  the  whole,  more  comprehensive  than  the 
latter.     Thus,  the  same  rate  of  diffusion   is  exhibited  by  hydrochloric,  hydro- 
bromic,  and  hydriodic  acid ;  by  the  chlorides,  iodides,  and  bromides  of  the  alkali- 
metals ;  by  the  nitrates  of  baryta,  strontia,  and  lime;  the  sulphates  of  magnesia 
and  zinc,  &c.  &c. 

4.  For  several  groups  of  salts  it  is  found  that  the  squares  of  the  times  of  equal 
diffusion,  from  solutions  of  the  same  strength,  stand  to  one  another  in  a  simple 
numerical  relation.     Thus,  the  diffusate  from  a  solution  of  nitrate  of  potash,  in  7 
days,  was  equal  to  that  obtained  from  an  equally  strong  solution  of  carbonate  of 
potash,  in  9-9  days,  numbers  which  are  to  one  another  as  1  :   </  2.     Similar  re- 
sults were  obtained  with  2  per  cent,  solutions  of  nitrate  and  sulphate  of  potash, 
equal  diffusates  of  the  two  being  obtained  in  3-5  and  4-95  days,  in  7  and  9-9 
days,  and  in  10-5  and  14-85  days;  also,  with  hydrate  and  nitrate  of  potash,  and 
with  nitrate  and  carbonate  of  soda.     The  times  of  equal  diffusion  of  1  per  cent, 
solutions  of  chloride  of  ammonium  and  chloride  of  sodium,  were  to  one  another 
as  v^  2  :  -v/  3.    Now,  according  to  Mr.  Graham's  experiments  (p.  739),  the  squares 
of  the  times  of  equal  diffusion  of  gases  are  to  one  another  in  the  ratio  of  their 
densities.     Hence,  by  analogy,  it  may  be  inferred  that  the  molecules  of  these 
several  salts,  as  they  exist  in  solution,  possess  densities  which  are  to  one  another 
as  the  squares  of  the  times  of  equal  diffusion.     Thus,  the  solution- densities  of 
sulphate,  nitrate,  and  hydrate  of  potash,  are  to  one  another  as  the  numbers  4,  2, 
and  1.     These  solution-densities  appear  to  relate  to  a  kind  of  molecules  different 
from  the  chemical  atoms,  and  the  weights  of  which  are  either  equal,  or  bear  to 
one  another  a  simple  numerical  relation. 

The  diffusion  of  a  salt  into  the  solution  of  another  salt  takes  place  with  nearly 
the  same  velocity  as  into  pure  water;  at  least,  when  the  solutions  are  dilute.  Mr 
Graham  has  shown  that  the  diffusion  of  a  4  per  cent,  solution  of  carbonate  of 
soda,  is  not  sensibly  affected  by  the  presence  of  4  per  cent,  of  sulphate  of  soda  iu 
the  liquid  atmosphere ;  nor  that  of  a  4  per  cent,  solution  of  nitrate  of  potash,  by 


744  DIFFUSION    OF    LIQUIDS. 

the  same  proportion  of  nitrate  of  ammonia.  The  presence  of  4  per  cent,  of  sul- 
phate of  soda  reduced  the  diffusion  of  carbonate  of  soda  by  only  J  of  the  whole. 
In  stronger  solutions  the  retardation  would  probably  be  greater.  There  is,  indeed, 
reason  to  believe  that  the  phenomena  of  liquid  diffusion  are  exhibited  in  their 
simplest  form  only  by  weak  solutions,  the  effect  of  concentration,  like  that  of  com- 
pression in  gases,  being  to  produce  a  departure  from  the  normal  character. 

The  rate  of  diffusion  is,  however,  materially  affected  when  the  liquid  atmosphere 
already  contains  a  portion  of  the  diffusing  salt.  The  consideration  of  this  case 
leads  to  the  general  question  of  the  motion  of  particles  of  a  dissolved  substance 
in  a  solution  of  unequal  concentration.  The  general  law  which  regulates  such 
movements  appears  to  be  this:  —  The  velocity  with  which  a  soluble  salt,  diffuses 
from  a  stronger  into  a  weaker  solution,  is  proportional  to  the  difference  of  con- 
centration between  two  contiguous  strata.  This  law  has  not  yet  been  experi- 
mentally demonstrated  in  a  sufficient  number  of  cases  to  establish  it  completely ; 
but  in  the  case  of  chloride  of  sodium,  it  has  been  shown  to  be  true  by  the  follow- 
ing experiments  of  Fick.* 

A  cylindrical  glass  tube,  open  at  both  ends,  was  cemented  into  a  vessel  com- 
pletely filled  with  common  salt,  the  cylindrical  space  filled  up  with  water,  and  the 
whole  immersed  in  a  large  jar  containing  water.  The  apparatus  was  then  left  to 
itself  for  several  weeks,  the  water  in  the  jar  being  from  time  to  time  taken  out 
and  renewed.  Now,  as  the  lowest  stratum  of  liquid  in  the  tube,  being  in  contact 
with  un dissolved  salt,  must  remain  constantly  saturated,  while  the  uppermost 
layer,  which  is  in  contact  with  pure  water,  contains  no  salt  at  all,  a  certain  normal 
state  of  diffusion  will  ultimately  establish  itself  throughout  the  length  of  the  tube, 
characterized  by  the  condition,  that  each  horizontal  stratum  will,  in  a  given  time, 
give  up  to  the  stratum  immediately  above  it  as  much  salt  as  it  receives  from  the  one 
below.  When  this  state  is  attained,  the  densities  of  the  successive  strata  decrease 
from  below  upwards  in  arithmetical  progression.  This  law  of  decrease  was  verified 
experimentally  by  immersing  in  the  liquid,  at  various  depths,  a  glass  bulb  sus- 
pended from  the  arm  of  a  balance,  and  counterpoised  by  weights  in  the  opposite 
scale.  This  law  of  decrease,  however,  is  true  only  with  regard  to  cylindrical 
columns  of  liquid,  or  others,  in  which  the  horizontal  section  is  of  uniform  magni- 
tude. In  other  cases,  the  law  of  decrease  of  density  may  be  calculated  according 
to  the  form  of  the  vertical  section.  In  funnel-shaped  tubes,  Fick  has  shown  that 
the  results  of  calculation  agree  with  those  of  experiment. 

Now  let  K  denote  the  quantity  of  salt  which,  in  the  normal  state  of  diffusion, 
passes  in  a  unit  of  time  through  a  unit  of  horizontal  section  of  a  cylindrical  tube 
whose  height  is  equal  to  the  unit  of  length  :  this  quantity  is  called  the  aiffusion- 
c.oejficient ;  also,  let  Q  be  the  quantity  of  salt  which,  in  the  time  t,  flows  from  the 
mouth  of  the  tube  into  the  water-atmosphere ;  h,  the  height  of  the  tube ;  s,  its 
horizontal  section  ;  and  d,  the  density  of  the  liquid  at  the  bottom ;  then  ' 

Q  =  K.d.~t. 

Hence,  with  a  tube  of  given  dimensions,  and  a  solution  of  known  and  constant 
density  at  the  bottom,  the  diffusion-coefficient,  K,  of  any  salt,  may  be  calculated 
from  the  quantity  Q,  diffused  out  in  a  given  time. 

This  method  has  been  applied  by  Fick  only  in  the  case  of  chloride  of  sodium. 
It  is,  in  fact,  though  simple  in  principle,  somewhat  inconvenient  of  application, 
on  account  of  the  long  time  —  at  least  14  days  —  which  must  elapse  before  the 
normal  state  is  attained. 

Another  method  of  determining  the  diffusion  co-efficient  of  a  salt  has  been 

*  Phil.  Mag.  [4],  x.  30. 


DIFFUSION    OF    LIQUIDS. 


745 


devised  by  Jolly,  and  applied  in  several  cases  by  Beilstein.*     The  apparatus  used 

consists  of  a  glass  tube  (fig.  230),  about  three  inches  long,  bent  • 

round  at  the  bottom,  and  cut  off  near  the  bend,  so  that  the  level 

of  the  orifice  is  not  much  more  than  a  millimeter  above  the  bottom 

of  the  bend  at  a.     The  upper  end  of  the  tube  is  slightly  drawn 

out,  and  closed  with  a  stopper.     This  tube  is  filled  with  a  solution 

of  known  concentration,  and  fixed  upright  within  ajar  of  water,  the 

orifice  of  the  tube  being  two  or  three  lines  below  the  level  of  the 

water.     The  salt  then  immediately  begins  to  diffuse  into  the  water, 

nnd  as  the  liquid  near  the  orifice  becomes  diluted,  it  passes  round 

the  bend  to  the  upper  part  of  the  tube,  its  place  being  supplied 

by  more  concentrated  liquid  from  above.     With  this  apparatus, 

Ik-ilstein  has  obtained  the  following  diffusion-coefficients  (taking 

that  of  chloride  of  potassium  for  unity),  for  solutions  containing 

4  per  cent  of  salt,  and  at  the  temperature  of  6°  C.  (10-2°  F.). 


^         // 


Chloride  of  potassium 1 

Nitrate  of  potash 0-9487 

Chloride  of  sodium 0-8337 

Bichromate  of  potash 0-7548 

Carbonate  of  potash 0-7371 


Sulphate  of  potash 0-6987 

Carbonate  of  soda 0-5436 

Sulphate  of  soda 0-5369 

Sulphate  of  magnesia 0-3587 

Sulphate  of  copper 0-3440 


Beilstein  infers  from  his  experiments,  that  the  rate  of  diffusion  is  not  exactly 
proportional  to  the  difference  of  density  of  two  contiguous  strata,  but  increases  in 
a  somewhat  greater  ratio. 

Simmler  and  Wildef  are  of  opinion  that  the  want  of  agreement  of  Beilstein'g 
results  with  this  law  arises  from  a  defect  in  the  method  of  experimenting.  Beil- 
stein's  calculations,  indeed,  are  based  on  the  supposition  that  the  strength  of  the 
solution  in  the  tube  (fig.  230),  though  constantly  decreasing,  is  uniform  at  any 
instant  of  time  throughout  the  entire  length ;  whereas,  a  little  consideration  will 
show  that  the  density  near  the  orifice  must  be  less  than  that  in  the  larger  arm  of 
the  tube,  and  in  this  arm  less  than  near  the  bottom  of  the  bfrnd,  where  the  liquid 
must  stagnate  to  a  certain  extent.  From  this  source  of  error,  Fick's  mode  of 
observation  is  free.  Simmler  and  Wilde,  however,  propose  other  methods,  easier 
of  execution  than  Fick's,  and  not  subject  to  the  necessity  of  waiting  till  the  normal 
state  of  diffusion  is  established.  One  of  these  methods  is  similar  to  that  adopted 
by  Mr.  Graham,  excepting  that  the  vessel  containing  the  solution  is  perfectly 
cylindrical,  a  condition  which  greatly  simplifies  the  calculations;  and,  instead  of 
being  placed  at  the  bottom  of  the  water-jar,  is  supported  on  a  stand,  so  as  to 
bring  its  mouth  within  a  line  or  two  below  the  surface  of  the  water;  the  salt,  as 
it  diffuses  out,  is  thus  made  to  flow  over  the  sides  of  the  vessel  and  fall  to  the 
bottom,  leaving  an  atmosphere  of  pure  water  above.  Another  method,  proposed 
by  the  same  authors,  is  to  place  the  saline  solution  in  a  vessel  having  the  form  of 
a  triangular  prism,  and  determine  the  variation  of  density  at  different  depths 
below  the  surface  by  observation  of  the  indices  of  refraction.  The  numerical 
results  obtained  by  these  methods  have  not  yet  been  published. 

Mixed  salts  may  be  more  or  less  separated  by  their  unequal  diffusibility,  A 
solution  of  1  part  of  carbonate  of  potash  and  1  part  of  carbonate  of  soda  in  10 
parts  of  water,  yielded  ;n  19  days  at  60°  F.  a  diffusate  containing  63-6  parts  of 
carbonate  of  potash  to  364  parts  of  carbonate  of  soda;  the  diffusate  obtained  in 
25  days  contained  the  two  salts  in  nearly  the  same  proportion.  Sea-water  was 
also  partially  decomposed  by  diffusion,  the  diffusate  containing  a  smaller  propor- 
tion of  magnesia-salts  than  the  residue.  The  variation  of  composition  in  the  water 
of  the  Dead  Sea,  at  different  times  of  the  year,  probably  arises  from  the  unequal 
rate  of  diffusion  of  the  different  salts  contained  in  the  strong  saline  liquid  into  the 
layer  of  fresh  water  brought  down  to  it  during  the  rainy  season.  (Graham.) 


*  Ann.  Ch.  Pharm.  xcix.  165. 


f  Pogg.  Ann.  C.  217. 


740  OSMOSE. 

Diffusion  is  also  capable  of  effecting  the  decomposition  of  chemical  compounds. 
From  a  solution  of  bisulphate  of  potash,  saturated  at  20°  C.  (68°  F.),  there  were 
diffused  in  50  days,  31'8  parts  of  bisulphate  of  potash,  and  12-8  parts  of  hydrated 
sulphuric  acid.  A  solution  of  8  parts  of  anhydrous  alum  in  100  parts  of  water 
yielded,  in  8  days,  at  17-9°  C.  (64-2°  F.),  a  diffusate  of  5-3  parts  alum  and  2-2 
parts  sulphate  of  potash.  A  solution  of  1  part  of  sulphate  of  potash  in  100  parts 
of  lime-water,  left  to  diffuse  into  lime  water  for  seven  days,  yielded  as  a  mean 
result,  a  diffusate  containing  22-67  parts  of  hydrate  of  potash,  and  77 -33  parts  of 
sulphate  of  potash.  A  similar  experiment  with  sulphate  of  soda,  yielded  a  diffusate 
containing  about  12  per  cent,  of  hydrate  of  soda.  The  larger  quantity  of  the 
alkaline  hydrate  obtained  in  the  first  instance,  appears  to  be  due  to  the  superior 
diffusibility  of  the  sulphate  of  potash,  as  it  can  scarcely  be  supposed  that  ,the 
affinity  of  potash  for  sulphuric  acid  is  less  than  that  of  soda.  The  sulphates  of 
potash  and  soda  were  also  decomposed  by  carbonate  of  lime  dissolved  in  carbonic 
•acid  water,  when  the  liquid  was  allowed  to  diffuse  into  pure  water.  The  chlorides 
of  potassium  and  sodium  were  not  sensibly  decomposed  by  lime-water  in  this 
manner.  When  saturated  solutions  of  lime-water  and  sulphate  of  lime  were  mixed 
in  equal  volumes,  1  per  cent,  of  chloride  of  sodium  dissolved  in  the  mixture,  and 
the  solution  left  to  diffuse  into  pure  water,  scarcely  a  trace  of  hydrate  of  soda  was 
obtained ;  but  when  the  solution  of  sulphate  of  lime,  with  an  addition  of  2  per 
cent,  of  chloride  of  sodium,  was  kept  at  the  boiling  point  for  half  an  hour,  and 
the  solution  mixed  two  or  three  days  afterwards  with  an  equal  volume  of  lime- 
water,  and  diffused  into  pure  water  for  3£  days,  the  diffusate  in  three  cells  was 
found  to  contain  0*234  grains  hydrate  of  soda,  and  0-371  sulphate  of  soda.  It 
appears,  then,  that  more  than  one  condition  of  equilibrium  is  possible  for  mixed 
solutions  of  sulphate  of  lime  and  chloride  of  sodium.  Cold  solutions  of  these  salts 
may  be  mixed  without  decomposition,  or,  without  sensible  formation  of  sulphate; 
but,  on  heating,  this  change  is  induced,  and  is  permanent,  sulphate  of  soda  being 
formed,  and  continuing  to  exist  in  the  cold  solution ;  for  it  is  the  decomposition 
of  that  salt  alone  by  hydrate  of  lime  which  appears  to  yield  the  diffused  hydrate 
of  soda.  As  the  effects  of  time  and  temperature  are  often  convertible,  it  is  possi- 
ble that  the  same  decomposition  might  take  place  at  ordinary  temperatures  after  a 
considerable  time.  "  If  such  be  the  case,  we  have  an  agency  in  the  soil,  by  which 
the  alkaline  carbonates  required  by  plants  may  be  formed  from  the  chlorides  of 
potassium  and  sodium,  as  well  as  from  the  sulphates,  for  the  sulphate  of  lime, 
generally  present,  will  convert  those  chlorides  into  sulphates.  The  mode  in  which 
the  soil  of  the  earth  is  moistened  by  rain,  is  peculiarly  favourable  to  separations 
by  diffusion.  The  soluble  salts  of  the  soil  may  be  supposed  to  be  carried  down 
together,  to  a  certain  depth,  by  the  first  portion  of  rain  which  falls,  while  they  find 
afterwards  an  atmosphere  of  nearly  pure  water,  in  the  moisture  which  falls  last 
and  occupies  the  surface-stratum  of  the  soil.  Diffusion  of  the  salts  upwards  into 
the  water,  with  its  separations  and  decompositions,  must  necessarily  ensue.  The 
salts  of  potash  and  ammonia,  which  are  most  required  for  vegetation,  possess  the 
highest  diffusibility,  and  will  rise  first.  The  pre-eminent  diffusibility  of  the  alka- 
'  line  hydrates  may  also  be  called  into  action  in  the  soil  by  hydrate  of  lime,  par- 
ticularly as  quick-lime  is  applied  for  a  top-dressing  to  grass  lands/'  (Graham.*) 

PASSAGE   OF   LIQUIDS    THROUGH   POROUS    SEPTA.      OSMOSE. 

The  force  of  liquid  diffusibility  still  acts  when  the  two  liquids  are  separated  by 
a  porous  sheet  of  animal  membrane,  or  unglazed  earthenware ;  for  the  pores  of 
such  a  membrane  are  occupied  by  water,  and  an  uninterrupted  liquid  communi- 
cation exists  between  the  water  on  the  one  side,  and  the  saline  solution  on  the 
other.  Under  these  circumstances,  a  flow  of  liquid  takes  place,  generally,  though 

*  Chem.  Soc.  Qu.  J.  iii.  67. 


OSMOSE.  747 

not  always,  from  the  water  to  the  saline  solution,  .so  that  the  quantity  of  liquid 
diminishes  on  one  side  of  the  septum,  while  it  increases  on  the  other.  This  phe- 
nomenon was  originally  designated  by  the  correlative  terms,  Endosmote  and  Exos- 
mose  ;  but  it  is  better  expressed  by  the  shorter  word  Osmose  (from  <Sc/*o$,  impul- 
sion), which  includes  the  two  former. 

This  passage  of  liquids  through  porous  septa,  was  first  studied  by  Dutrochet, 
whose  apparatus,  called  an  endosmomefer,  consisted  of  a  narrow  glass  tube,  having 
a  funnel-shaped  expansion  at  the  bottom,  and  closed  at  that  end  by  a  piece  of 
bladder.  This  tube  was  filled  with  a  saline  solution,  and  placed  in  a  vertical  posi- 
tion, in  a  jar  containing  water.  The  flow  of  liquid  in  one  direction  or  the  other, 
was  measured  by  the  rise  or  fall  of  the  liquid  in  the  tube.  Dutrochet  inferred 
from  his  experiments  that  the  velocity  of  the  osmotic  current  is  proportional  to- 
the  quantity  of  salt  or  other  solid  substance  originally  contained  in  the  saline 
solution.  The  experiments  were,  however,  inexact,  because  no  allowance  was 
made  for  the  alteration  of  hydrostatic  pressure,  caused  by  the  rise  or  fall  of  liquid 
in  the  tube.  Vierordt,*  who  used  a  modification  of  Dutrochet' s  apparatus,  in 
which  this  source  of  error  was  removed,  found  that  the  velocity  of  the  current 
increases  with  the  initial  concentration  of  the  solution,  but  in  a  lower  ratio. 

Professor  Jolly,  of  Heidelberg,  has  examined  the  osmose  of  water  and  saline 
solutions  by  a  different  method.  The  saline  solution  containing  a  known  quantity 
of  salt,  is  contained  in  a  glass  tube  closed  at  the  bottom  with  bladder,  and  plunged 
into  water,  which  is  frequently  changed,  so  as  to  keep  it  nearly  pure.  The  tube 
with  its  contents  is  taken  out  from  time  to  time  and  weighed,  and  these  opera- 
tions are  repeated  till  the  weight  becomes  constant,  showing  that  the  whole  of  the 
salt  has  passed  out  from  the  tube,  and  nothing  but  water  remains. 

In  this  manner,  it  is  found  that  a  given  quantity  of  any  salt  which  passes 
through  the  septum  into  the  water  is  always  replaced  by  a  definite  quantity  of 
water.  The  quantity  of  water  which  is  thus  replaced  by  a  unit  of  weight  of  the 
salt,  is  called  the  endosmotic  (or  osmotic)  equivalent  of  that  salt.  This  quantity 
varies  with  the  nature  of  the  salt,  and  with  the  temperature,  increasing  as  the- 
temperature  rises,  but  it  is  independent  of  the  density  of  the  solution.  At  tem- 
peratures near  0°  C.,  the  endosmotic  equivalent  of  hydrate  of  potash  was  found  to- 
be  200  ]  of  chloride  of  sodium,  between  4-3  and  4-6 ;  of  sulphate  of  soda,  between 
11  and  12  j  of  neutral  sulphate  of  potash,  12 ;  of  acid  sulphate  of  potash,  2-3 ;  and 
of  hydrated  sulphuric  acid  (at  18°  C.),  0-35. 

.  These  results  point  to  the  conclusion,  that  the  osmose  between  water  and  saline 
solutions,  consists,  not  in  the  opposite  passage  of  two  liquid  currents,  but  in  the 
passage  of  particles  of  the  salt  in  one  direction,  and  of  pure  water  in  the  other. 
This  conclusion  is  strengthened  by  Mr.  Graham's  observation,  that  common  salt 
diffuses  into  water,  through  a  tin  membrane  of  ox-bladder  deprived  of  its  outer 
muscular  coating,  at  the  same  rate  as  when  no  membrane  is  interposed. 

The  flow  of  water  into  the  saline  solution  is  the  only  one  of  the  two  movements 
which  can  ,be  correctly  described  as  a  current.  This  is,  in  fact,  the  true  osmose, 
and  depends  essentially  on  the  action  of  the  membrane  or  other  porous  septum ; 
for  the  quantity  of  water  which  thus  passes  into  the  solution,  is  often  much 
greater  than  would  be  introduced  by  mere  liquid  diffusion,  amounting  in  same 
cases  to  several  hundred  times  that  of  the  salt  displaced. 

This  action  of  the  septum  has  been  explained  in  various  ways.  By  Dutrochet 
and  others,  it  was  attributed  to  capillarity ;  but  this  force  is  quite  insufii cient  to 
account  for  the  great  inequality  of  ascension  which  different  liquids  exhibit  in  the 
osmotic  apparatus ;  in  fact,  Mr.  Graham  has  shown,  that  solutions  of  the  most 
different  character  exhibit  very  nearly  equal  ascension  in  tubes  of  equal  diameter. 

Osmose  has  likewise  been  attributed  to  the  unequal  absorption  of  the  two 
liquids  by  the  porous  septum.  Suppose  the  septum  to  be  of  such  a  nature  as  to 

*  Pogg.  Ann.  Ixxiii.  519. 


748  OSMOSE. 

absorb  only  one  of  the  liquids,  the  water  for  instance.  The  water  will  then  pene- 
trate the  septum,  and  coming  in  contact  with  the  saline  solution,  will  diffuse  into 
it.  More  water  will  then  be  absorbed,  and  subsequently  diffused,  and  thus  a  con- 
tinuous current  will  be  set  up.  If  both  liquids  are  absorbed  by  the  septum,  but 
in  different  degrees,  and  each  is  capable  of  diffusing  into  the  other,  like  water  and 
alcohol,  the  result  will  be  the  formation  of  two  unequal  currents  in  opposite  direc- 
tions. Water  is  absorbed  by  animal  membrane  much  more  rapidly  than  most 
other  liquids,  and  accordingly,  when  a  septum  of  this  kind  is  used,  the  direction 
of  the  current  is  in  most  cases  from  the  water  to  the  other  liquid.  According  to 
Liebig,  a  given  weight  of  dried  ox-bladder  absorbs  in  the  same  time,  200  volumes 
of  water,  133  vols.  of  a  saturated  solution  of  common  salt,  38  vols.  of  alcohol  of 
the  strength  of  84  per  cent.,  and  17  vols.  of  bone-oil.  When  water  and  alcohol 
are  separated  by  an  animal  membrane,  the  quantity  of  water  which  passes  into  the 
alcohol,  is  greater  than  the  quantity  of  alcohol  which  passes  into  the  water;  but 
when  the  same  liquids  are  divided  by  a  thin  film  of  collodion,  which  absorbs 
alcohol  more  quickly  than  water,  the  contrary  effect  is  produced. 

On  the  other  hand,  the  numerous  experiments  recently  made  by  Mr.  Graham,* 
lead  to  the  conclusion,  that  osmose  depends  essentially  on  the  chemical  action  of 
the  liquid  on  the  septum.  These  experiments  were  made  partly  with  porous 
mineral  septa,  partly  with  animal  membrane.  The  earthenware  osmometer  con- 
sisted of  the  porous  cylinders  employed  in  voltaic  batteries,  about  five  inches  in 
depth,  surmounted  by  a  glass  tube  0-6  inch  in  diameter,  attached  to  the  mouth 
of  the  cylinder  by  means  of  a  cap  of  gutta  percha.  The  cylinder  was  filled  to  the 
base  of  the  glass  tube  with  a  saline  solution,  and  immediately  placed  in  a  jar  of 
distilled  water ;  and  as  the  fluid  within  the  instrument  rose  during  the  experiment, 
water  was  added  to  the  jar  to  equalize  the  pressure.  The  rise  (or  fall)  of  the 
liquid  in  the  tube  was  very  regular,  as  observed  from  hour  to  hour,  and  the  experi- 
ment was  generally  terminated  in  five  hours.  From  experiments  made  on  solu- 
tions of  every  variety  of  soluble  substance,  it  appeared  that  the  rise  or  osmose,  is 
quite  insignificant  with  neutral  organic  substances  in  general,  such  as  sugar,  alco- 
hol, urea,  tannin,  &c. ;  so  likewise  with  neutral  salts  of  the  earths  and  ordinary 
metals,  with  the  chlorides  and  nitrates  of  potassium  and  sodium,  and  with  chloride 
of  mercury.  A  more  sensible  but  still  very  moderate  osmose  is  exhibited  by 
hydrochloric,  nitric,  acetic,  sulphurous,  citric,  and  tartaric  acids.  These  are  sur- 
passed by  the  stronger  mineral  acids,  such  as  sulphuric  and  phosphoric,  and  by 
sulphate  of  potash,  which  are  again  exceeded  by  salts  of  potash  and  soda  possess- 
ing a  decided  acid  or  alkaline  reaction,  such  as  binoxalate  of  potash,  phosphate  of 
soda,  or  the  carbonates  of  potash  and  soda.  The  highly  osmotic  substances  were 
also  found  to  act  with  most  advantage  in  small  proportions,  producing,  in  fact,  the 
largest  osmose  in  the  proportion  of  one-quarter  per  cent,  dissolved.  (See  page  749). 
The  same  substances  are  likewise  always  chemically  active  bodies,  and  possess 
affinities  which  enable  them  to  act  on  the  material  of  the  earthenware  septum. 
Lime  and  alumina  were  always  found  in  solution  after  osmose,  and  the  corrosion 
of  the  septum  appeared  to  be  a  necessary  condition  of  the  flow.  Septa  of  other 
materials,  such  as  pure  carbonate  of  lime,  gypsum,  compressed  charcoal,  and 
tanned  sole-leather,  although  not  deficient  in  porosity,  gave  no  osmose,  apparently 
because  they  are  not  chemically  acted  on  by  the  saline  solutions. 

Similar  results  were  obtained  with  septa  of  animal  membrane.  Ox-bladder  was 
found  to  act  with  much  greater  strength  and  regularity  when  divested  of  its  outer 
muscular  coat.  Cotton  calico,  impregnated  with  liquid  albumen,  and  afterwards 
heated  to  coagulate  the  albumen,  formed  an  excellent  septum,  resembling  mem- 
brane in  every  respect.  The  osmometer  (fig.  231)  used  in  these  experiments  was 
arranged  like  the  original  instrument  of  Dutrochet;  but  the  membrane  was  sup- 
ported by  a  plate  of  perforated  zinc,  and  the  tube  was  of  considerable  diameter, 

*  Phil.  Trans.  1855,  177;  Chem.  Soc.  Qu.  J.,  viii.  43. 


OSMOSE. 


749 


FIG.  231. 


viz.,  one-tenth  of  that  of  the  mouth  of  the  bulb,  or  of  the  disc  of  membrane 
exposed  to  the  liquids.  £ 

Osmose  in  membrane  presents  many 
points  of  similarity  to  that  in  earthenware. 
The  membrane  is  constantly  undergoing 
decomposition,  and  its  osmotic  action  is 
exhaustible.  Salts  and  other  substances 
capable  of  determining  a  large  osmose,  are 
all  chemically  active  substances,  while  the 
great  mass  of  neutral  organic  substances 
and  perfectly  neutral  monobasic  salts  of  the 
metals,  such  as  chloride  of  sodium,  possess 
only  a  low  degree  of  action,  or  are  wholly 
inert.  The  active  substances  are  also  most 
efficient  in  small  proportions.*  With  a 
solution  containing  y^-  per  cent,  of  carbo- 
nate of  potash,  the  rise  in  the  osmometer 
was  167  millimeters ;  and  with  1  per  cent, 
of  the  same  salts,  206  millimeters  in  five 
hours.  With  another  membrane  and  a 
stronger  solution,  the  rise  was  863  millime- 
ters, or  upwards  of  88  inches,  in  the  same 
time.  To  induce  osmose,  the  chemical 
action  on  the  membrane  must  be  different 
on  the  two  sides,  and  apparently  not  in 
degree  only,  but  in  kind,  viz.,  an  alkaline 
action  on  the  albuminous  substance  of  the 
membrane  on  the  one  side,  and  an  acid 
action  on  the  other.  The  water  appears 
always  to  accumulate  on  the  alkaline  or 
basic  side  of  the  membrane.  Hence,  with 
an  alkaline  salt,  such  as  carbonate  of  soda,  in  the  osmometer,  and  water  outside, 
the  flow  is  inwards;  but  with  an  acid  in  the  osmometer,  there  is  negative  osmose, 
or  the  flow  is  inwards,  the  liquid  then  falling  in  the  tube.  The  chlorides  of 
barium,  sodium,  and  magnesium,  and  similar  neutral  salts,  are  wholly  indifferent, 
or  appear  to  act  merely  in  a  subordinate  manner  to  -some  other  active  acid  or 
basic  substance,  which  may  be  present  in  the  solution  or  the  membrane  in  the 
most  minute  quantity.  Salts  which  admit  of  division  into  a  basic  salt  and  free 
acid,  exhibit  an  osmotic  activity  of  the  highest  order,  e.  g.,  the  acetate  and  various 
other  salts  of  alumina,  ferric  oxide  and  chromic  oxide,  dichloride  of  copper,  proto- 
ehloride  of  tin,  nitrate  of  lead,  &c.  The  acid  travels  outwards  by  diffusion,  super- 
inducing a  basic  condition  of  the  inner  surface  of  the  membrane,  and  an  acid 
condition  of  the  outer  surface,  the.  most  favourable  condition  for  a  high  positive 
osmose.  Again,  the  bibasic  salts  of  potash  and  soda,  such  as  the  sulphate  and 
tartrate,  though  strictly  neutral  in  properties,  begin  to  exhibit  a  positive  osmose, 
in  consequence,  perhaps,  of  their  resolution  into  an  acid  supersalt  and  free  alka- 
line base. 

The  following  table  exhibits  the  osmose  of  substances  of  all  classes  through 
membrane,  the  degree  being  a  rise  or  fall  of  one  millimeter :  — 

*  The  action  increases  with  the  strength  of  the  solution  up  to  a  certain  point,  as  the  above 
examples  show  (see  also  p.  748).  With  stronger  solutions  the  pores  of  the  membrane  proba- 
bly become  stopped  up  with  particles  of  salt,  and  the  action  consequently  diminishes. 


750 


OSMOSE. 


OSMOSE  OF  1  PER  CENT.  SOLUTIONS  IN  MEMBRANE. 


Degrees. 

—  148 

—  92  . 

—  54 

—  46 

—  30 


Oxalic  acid 

Hydrochloric  acid  (0-1  per  cent.) 

Terchloride  of  gold 

Bichloride  of  tin 

Bichloride  of  platinum 

Chloride  of  magnesium  —      3 

Chloride  of  sodium -{-       2 

Chloride  of  potassium  18 

Nitrate  of  soda  2 

Nitrate  of  silver 34 

Sulphate  of  potash  21  to  60 

Sulphate  of  magnesia  14 

Chloride  of  calcium  20 

Chloride  of  barium  21 

Chloride  of  strontium 26 

Chloride  of  cobalt 26 

Chloride  of  manganese 34 


Degrees. 
54 


Chloride  of  zinc  

Chloride  of  nickel 

Nitrate  of  lead  125  to  211 

Nitrate  of  cadmium 137 

Nitrate  of  uranium 234  to  458 


Nitrate  of  copper  

Chloride  of  copper 

Protochloride  of  tin  .. 
Protochloride  of  iron 
Chloride  of  mercury  .. 

Mercurous  nitrate 

Mercuric  nitrate 

Ferric  acetate.... 


204 
351 
289 
435 
121 
356 
476 
194 

Acetate  of  alumina  280  to  393 

Chloride  of  aluminium  540 

Phosphate  of  soda 311 

Carbonate  of  potash  439 


The  osmotic  action  of  carbonate  of  potash  and  other  alkaline  salts  is  interfered 
with  in  an  extraordinary  manner  by  the  presence  of  chloride  of  sodium,  being  re- 
duced to  almost  nothing  by  an  equal  proportion  of  that  salt.  The  moderate  posi- 
tive osmose  of  sulphate  of  potash  is  converted  into  a  very  sensible  negative  osmose 
by  the  presence  of  the  merest  trace  of  a  strong  acid,  while  the  positive  osmose  of 
the  same  salt  is  singularly  promoted  by  a  small  proportion  of  alkaline  carbonate : 
thus  a  1  per  cent,  solution  of  sulphate  of  potash  gives  an  osmose  of  21  degrees, 
but  the  addition  of  0-1  per  cent,  of  carbonate  of  potash  raises  it  to  between  254 
and  264  degrees.  (G  fa  ham.) 

If  a  glass  tube,  bent  in  the  form  of  a  siphon,  and  having  its  shorter  leg  closed 
with  bladder,  be  partially  filled  with  salt-water,  the  shorter  leg  then  immersed  in 
a  vessel  of  pure  water,  and  mercury  poured  into  the  longer  leg,  so  that  its  pres- 
sure may  act  in  opposition  to  the  force  with  which  the  water  tends  to  enter  the 
saline  solution  through  the  bladder,  it  will  be  found  that,  when  the  column  of 
mercury  attains  a  certain  height,  the  two  liquids  will  mix  without  change  of 
volume,  the  force  of  the  osmotic  current  being  then  exactly  balanced  by  the  weight 
of  the  mercurial  column.  In  this  way  the  mechanical  force  of  the  osmotic  cur- 
rent may  be  measured.  (Liebig.) 

Osmose  appears  to  play  an  important  part  in  the  functions  of  life.  We  have 
seen  that  it  is  peculiarly  excited  by  dilute  saline  solutions,  such  as  the  animal  and 
vegetable  juices  are,  and  that  the  acid  or  alkaline  property  which  these  juices 
possess  is  another  favourable  condition  for  their  action  on  membrane.  The  natural 
excitation  of  osmose  in  the  substance  of  the  membranes  or  cell-walls  dividing  such 
solutions  seems  therefore  almost  inevitable. 

In  osmose  there  is  also  a  remarkably  direct  substitution  of  one  of  the  great 
forces  of  nature  by  its  equivalent  in  another  force,  the  conversion,  namely,  of 
chemical  action  into  mechanical  power.  Viewed  in  this  light,  the  osmotic  injec- 
tion of  fluids  may,  perhaps,  supply  the  deficient  link  which  intervenes  between 
chemical  decomposition  and  muscular  movement.  The  ascent  of  the  sap  in  plants 
appears  to  depend  upon  a  similar  conversion  of  chemical,  or,  at  least,  molecular 
action  into  mechanical  force.  The  juices  of  plants  are  constantly  permeating  the 
coatings  of  the  superficial  vessels  in  the  leaves  and  other  organs ;  and  these 
evaporating  into  the  air,  a  fresh  portion  of  liquid  is  then  absorbed  by  the  mem- 
brane and  evaporates;  and  thus  a  regular  upward  current  is  established,  by  which, 
the  sap  is  transferred  from  the  roots  to  the  highest  parts  of  the  tree.  In  a  similar 
manner,  the  evaporation  constantly  taking  place  from  the  skin  and  lungs  of 
animals,  causes  a  continuous  flow  of  the  animal  juices  from  the  interior  towards 
the  surface. 


HEAT    FROM    CHEMICAL    ACTION.  751 


DIFFUSION   OF   GASES    THROUGH    POROUS    SEPTA. 

It  appears  from*  Mr.  Graham's  experiments  (p.  88),  that  the  rates  of  diffusion 
of  gases  through  porous  diaphragms,  such  as  dry  gypsum,  cork,  unglazed  earthen- 
ware, or  bladder,  are  to  one  another  in  the  inverse  ratio  of  the  squares  of  their 
densities,  the  law  being,  in  fact,  the  same  as  that  of  the  effusion  of  the  same  gases 
into  a  vacuum  through1  minute  apertures  in  a  metal  plate  (p.  83).     Bunsen  has 
arrived  at  a  different  conclusion.*     He  finds,  for  example,  that  when  a  tube  con- 
taining hydrogen  is  closed  by  a  dry  gypsum  diaphragm,  and  a  current  of  oxygen 
passedn rapidly  over  the  diaphragm,  so  that  the  hydrogen  may  diffuse  into  an  in- 
finite atmosphere  of  oxygen,  the  volume  of  oxygen  which  enters  the  tube  is  to 
the  volume  of  hydrogen  which  issues  from  the  tube,  as  1  :  3-345,  this  ratio  re- 
maining constant  during  the  whole  time  of  the  diffusion.     The  law  of  the  inverse 
square  roots  of  the  densities  would  give  1  :  4.     Again,  when  oxygen  was  made  to 
pass  through  stucco  into  oxygen,  and  hydrogen  into  hydrogen,  by  difference  of 
pressure,  it  was  found  that,  under  the  same  pressure,  the  rate  of  issue  of  the 
oxygen  was  to  that  of  the  hydrogen  as  1  :  2-73  instead  of  1  :  4.     These  differences 
are  too  great  to  be  accounted  for  by  error  of  observation  •  they  probably  arise 
from  the  circumstance,  that  Graham's  experiments  were  made  with  thin  diaphragms, 
whereas  Bunsen  used  diaphragms  of  considerable  thickness, f  in  which  case,  the 
rates  of  diffusion  would  approximate  to  the  rates  of  transpiration  (p.  85)  rather 
than  to  those  of  effusion.     The  rate  of  transpiration  through  a  mass  of  porous 
stucco  was  ascertained  by  Mr.  Graham  to  be  the  same  as  through  capillary  tubes, 
namely,  1  volume  of  oxygen  to  2-3  volumes  of  hydrogen.     In  the  interior  of  a 
considerable  mass  of  stucco,  with  hydrogen  on  one  side  and  oxygen  on  the  other, 
the  stucco  acts  as  a  vessel,  a  partial  vacuum  being  formed  in  its  centre.     To  th'Lj 
point,  both  oxygen  and  hydrogen  are  impelled  by  pressure  (transpiration)  in  the 
ratio  of  1  to  2-3,  instead  of  1  to  4,  the  relation  of  diffusion.     Hence  the  oxygen 
travels  through  the  diaphragm,  partly  in  one  of  these  ratios  and  partly  in  the 
other,  and  the  proportion  of  oxygen  which  enters  the  vessel  is  increased,  as  in, 
Bunsen's  experiments. J 


DEVELOPMENT  OF  HEAT  BY  CHEMICAL  ACTION. 

From  the  ttaie  when  Lavoisier  pointed  out  the  true  nature  of  the  phenomenon 
of  combustion,  the  measurement  of  the  heat  evolved  in  chemical  combination  has 
occupied  a  .prominent  place  in  the  attention  of  chemists,  and  has  been  made  the 
subject  of  numerous  researches,  the  most  exact  and  comprehensive  of  which,  are 
those  of  Messrs.  Favre  and  Silbermann,  and  of  Dr.  Andrews. § 

The  apparatus  used  by  Favre  and  Silbermann  for  measuring  the  heat  evolved 
by  the  combustion  of  various  substances  in  oxygen  gas, -is  represented,  with  the 
omission  of  minor  details,  in  figure  232.  C  is  a  vessel  of  gilt  brass  plate,  im- 
mersed in  a  water-calorimeter,  A  A,  of  silvered  copper-plate,  and  the  latter  is 
enclosed  in  an  outer  vessel,  B  J5,  the  space  between  A  and  B  being  filled  with 

*  See  Bunsen's  "  Gasometry,"  translated  by  Dr.  Roscoe,  pp.  198 — 233. 

f  Compare  the  figure  at  page  88  of  this  work,  with  figure  53,  p.  202,  of  Bunsen's 
"  Gasometry." 

t  Ann.  Ch.  Phys.  [3],  xxxiv.  357 ;  xxxvi.  5 ;  xxxvii.  405 ;  Abstr.  Chem.  Soc.  Qu.  J.  vi. 
234. 

%  Phil.  Mag.  [3],  xxxii.  321,  392,  and  426. 


752 


HEAT    FEJM     CHEMICAL     ACTION. 


FIG.  232. 


swan-down,  to  prevent  the  escape  of  heat  from  the  water  in  A.     The  vessels  A 
and  B  are   closed  with   Ills  having-  apertures   for  the  insertion   of  tubes   and 

thermometers.  The  combustions  are  performed  in 
the  vessel  (7,  into  which  oxygen  gas  is  introduced 
through  the  tube  c  <7,  and  the  gaseous  products  of 
the  combustion  escape  by  the  tube  e  fy  h,  the 
lower  part  of  which  is  bent  into  numerous  coils, 
to  facilitate  as  much  as  possible,  the  transmission 
of  the  heat  of  these  gases  to  the  water  in  the 
calorimeter.  The  extremity  h,  of  this  tube  is  con- 
nected with  a  gasometer,  or  with  an  absorbing  ap- 
paratus. To  ensure  uniformity  of  temperature  in 
the  water,  a  flat  ring  of  metal  i  i,  is  moved  up  and 
down  by  means  of  the  rod  K i.  Combustible 
gases  were  introduced  into*the  vessel  0,  by  means 
of  fine  tubes,  the  gas  being  previously  set  on  fire 
at  the  aperture.  Solid  bodies  were  attached  to 
fine  platinum  wires  suspended  from  the  lid  of  the 
calorimeter :  liquids  were  burned  in  small  capsules 
or  in  lamps  with  asbestos  wicks ;  charcoal  was  dis- 
posed in  a  layer  on  a  sieve-formed  bottom,  through 
the  openings  of  which  the  oxygen  had  access  to 
it.  The  heat  evolved  was  measured  by  the  rise  of 
temperature  of  the  known  quantity  of  water  in  the 
calorimeter. 

For  processes  which  take  place  without  access  or  escape  of  gases,  simpler  ap- 
paratus may  be  used.  For  such  reactions  Favre  and  Silbermann  employed  a 

mercury-calorimeter  (fig.  233),  consist- 
ing of  a  glass  globe  filled  with  mercury, 
and  having  inserted  into  it  a  tube  a,  to 
contain  the  combining  substances,  an 
acid  and  a  base  for  instance.  The 
mercury  in  the  globe  communicates  by 
the  bent  tube  &,  with  the  capillary 
tube  c  (7,  on  which  its  expansion  is 
measured.  The  apparatus  forms,  in 
fact,  a  large  mercurial  thermometer. 

The  unit  of  weight  to  which  the  following  numbers  refer  is  the  gramme,  and 
the  unit  of  heat  is  the  quantity  required  to  raise  the  temperature  of  1  gramme 
of  water  from  0°  to  1°  C. 


FIG.  233. 


Heat  of  Combustion. 

Substance. 

Formula. 

Products. 

1  Grm.  of 
Substance 

1  Grm.  of 
Oxygen 

Observers. 

with 

with 

Oxygen. 

Substance. 

GASES. 

Fjydrofiren    t        

HH 

H2O 

/    34462 
\    33802 

4308 
4226 

F.  8. 
A. 

Carbonic  oxide  

00 

ooa 

f      2403 
\      2431 

4205 
4255 

F.  S. 
A. 

OH4 

002  and  HgO 

/    13063 
\    13168 

3266 
3277 

F.  S. 
A. 

G2H4 

« 

f    11858 
t    11942 

3458 
3483 

F.  S. 
A. 

HEAT  FROM  CHEMICAL  ACTION. 


753 


Substance. 

Formula. 

Products. 

Heat  of  Combustion. 

Observers. 

1  Grm.  of 
Substance 
with 
Oxygen. 

1  Grm.  of 
Oxygen 
with 
Substance. 

LIQUIDS. 

Amylene  

GgH]0 

« 

11491 

3352 

F.  S. 

Oil  of  turpentine  

«' 

10852 

3294 

1 

Ether  

G  H  0 

«< 

9028 

3479 

4< 

Wood-spirit     

G2H60 

(4 

5307 
7184 

3538 
3442 

- 

Alcohol     

Amylic  alcohol  

2      O 

" 

8959 

3285 

n 

Acetic  acid     

G  H  0 

« 

3505 

3286 

H 

Butyric  acid  

G^HgO! 

I* 

5647 

3106 

„ 

Valerianic  acid  

4      82 

it 

6439 

3158 

it 

Palmitic  acid  (solid). 
Stearic  acid  (solid).. 

$& 

f| 

9316 
9716 

3240 
3317 

it 

Formiate  of  methyl.. 

G2H402 

« 

4197 

3935 

« 

Acetate  of  methyl  ... 

(4 

5342 

3529 

it 

Formiate  of  ethyl.... 

G3H02 

" 

5279 

3488 

" 

Acetate  of  ethyl  

G4H802 

14 

6293 

3461 

" 

Butyrate  of  methyl.. 

G5Hj002 

it 

6791 

3334 

" 

Butyrate  of  ethyl.... 

G6H,202 

ft 

7091 

3213 

" 

Valerate  of  methyl... 

G6H1202 

M 

7376 

3342 

" 

Spermaceti  (solid)  ... 

" 

10342 

3301 

" 

Sulphide  of  carbon... 

G&2 

G02  and  &02 

3401 

2692 

tc 

SOLIDS. 

Carbon  (wood    char-  ^ 

G      1 

G0 

2473 

1855 

F.  S. 

coal                     .  .  C 

1 

r^i/~i 

8080 

3030 

Sulphur  (rhombic)... 

s 

£022 

2221 

2221 

Phosphorus  (yellow). 

pp 

P205 

5953 

4613 

Zinc 

ZnZn 

7i\  O 

1301 

5366 

Iron 

FeFe 

Fe,0« 

1575 

4134 

Tin  

SnSn 

j.  cjjx72 

1167 

4230 

Protoxide  of  tin  

Sn20 

Sn0 

521 

4349 

CuCu 

604 

2394 

Red  oxide  of  copper. 

Cu20 

256 

2288 

A  comparison  of  the  numbers  in  this  Table,  shows  that  the  quantities  of  heat 
evolved  by  the, combination  of  a  constant  weight  of  oxygen  with  different  combus- 
tible bodies,  are  much  more  nearly  equal  than  the  quantities  evolved  by  the  com- 
bustion of  equal  weights  of  these  several  bodies.  Nevertheless,  the  conclusion 
drawn  from  older  experiments  (p.  229),  that  the  quantity  of  heat  evolved  in 
combustion  is  always  proportionate  to  the  quantity  of  oxygen  consumed,  is  very 
far  from  being  confirmed  by  the  numbers  in  the  fifth  column  of  the  preceding 
Table. 

Equal  weights  of  isomeric  bodies  do  not  evolve  equal  quantities  of  heat  in  com- 
bustion. This  may  be  seen  by  comparing  the  numbers  for  formiate  of  ethyl  and 
acetate  of  methyl,  for  acetic  acid  and  formiate  of  methyl,  &c. 

In  homologous  organic  compounds,  the  heat  of  combustion  for  equal  weights 
of  the  compounds  increases,  as  the  carbon  and  hydrogen  bear  a  greater  proportion 
to  the  oxygen.  This  may  be  seen  in  the  series  of  alcohols,  fatty  acids,  and  com- 
pound ethers. 

In  general,  the  heat  evolved  by  the  combustion  of  an  oxidized  body,  such  as 
48 


754 


HEAT  OF  CHEMICAL  COMBINATION. 


carbonic  oxide,  or  protoxide  of  tin,  is  less  than  that  which  is  evolved  in  the  com- 
plete oxidation  of  the  combustible  constituent. 

But  little  is  known  respecting  the  relation  which  the  heat  of  combustion  of  a 
compound  of  two  or-  more  combustible  substances  bears  to  the  sum  of  the  heats 
of  combustion  of  its  constituents.  In  some  cases,  it  is  less  than  that  sum  (e.  g. 
marsh-gas  and  olefiant  gas)  ;  in  others,  greater  (bisulphide  of  carbon,  oil  of  tur- 
pentine). The  relation  in  question  is,  doubtless,  greatly  affected  by  the  mole- 
cular states  of  the  compound  and  of  its  elements  in  the  separate  state.  That 
the  heat  of  combustion  of  a  body  is  materially  influenced  by  its  state  of  aggrega- 
tion, is  shown  by  many  experiments ;  and  in  general  it  is  found  that,  of  two  modi- 
fications of  a  substance,  that  which  has  the  greater  specific  heat,  likewise  evolves 
the  greater  quantity  of  heat  in  combination.  Thus,  the  specific  heat  of  yellow 
phosphorus  is  greater  than  that  of  the  red  variety;  now  1  gramme  of  yellow 
phosphorus,  in  burning  to  phosphoric  acid,  evolves  5953  heat-units,  whereas  the 
same  quantity  of  red  phosphorus  evolves  only  5070  heat-units,  ^he  same  relation 
is  strikingly  shown  by  the  following  comparison  of  the  quantities  of  heat  evolved 
in  the  complete  combustion  of  equal  weights  of  different  kinds  of  carbon,  as  de- 
termined by  Favre  and  Silbermann,  with  their  specific  heats,  as  determined  by 
Hegrnault :  — 


Heat  of 
Combustion. 

Wood-charcoal 8080  ... 

Coke  from  gas-retorts 8047  ... 

Native  graphite 7797  ... 

Graphite  from  blast-furnaces 7762  ... 

Diamond 7770  ... 


Specific 
Heat. 

0-24150 
0-20360 
0-20187 
0-19702 
0-11687 


Sulphur  likewise  evolves  in  combustion  different  quantities  of  heat,  according 
to  its  state  of  aggregation.  Octohedral  sulphur,  native  or  artificial,  gives,  as  a 
mean  result,  2221  heat-units ;  prismatic  sulphur,  recently  crystallized  from  fusion, 
gives  2260  heat-units. 

Combination  of  Metals  ivith  Chlorine,  Bromine,  and  Iodine. — To  determine 
the  heat  evolved  in  the  combination  of  metals  with  chlorine,  Andrews  introduced 
the  metals,  enclosed  in  thin  glass  bulbs,  into  a  glass  vessel  filled  with  dry  chlorine. 
This  vessel  was  placed  within  the  water-calorimeter,  and  the  glass  bulb  broken  by 
shaking  the  vessel.  The  results  are  given  in  the  following  Table.  The  number 
for  hydrogen  is  from  the  experiments  of  Favre  and  Silbermann  : — 


Substance. 

Product, 

Heat  of  Combustion. 

1  Gramme  of  Substance 
with  Chlorine. 

1  Gramme  of  Chlorine 
with  Substance. 

Hydrogen          .   ... 

HC1 

KC1 
ZnCl 
CnCl 
Fe2Cl8 
SnC!2 
AsCl3 
SbCl3 

23783 

2655 
1529 
961 
1745 
1079 
994 
707 

670 
2932 
1404 
858 
317 
881 
700 
799 

Potassium    

Copper  

Tin.              

Antimony         .     .... 

If  we  multiply  the  numbers  which  express  the  heat  of  combination  of  1  gramm 
of  each  of  the  metals  with  oxygen  and  chlorine,  by  the  atomic  weights  of  the 
several  metals,  we  obtain  the  following  numbers  for  the  quantities  of  heat  evolved 
by  equivalent  quantities  of  these  metals  in  combining  with  oxygen  and  chlorine  : — 


HEAT  OF  CHEMICAL  COMBINATION. 


755 


With  8  gr.  Oxygen.         With  35-5  gr.  Cl. 

1  gramme  of  hydrogen 34462  23783 

32-6        «        zinc 42413 49844 

31-7        "        copper 19147  30464 

29  «        tin  (to  SnO  and  SnCl2) 33843 31291 

The  numbers  in  this  Table  do  not  exhibit  any  simple  relation  to  each  other,  so 
that  no  conclusion  can  be  drawn  from  them  as  to  the  quantity  of  heat  evolved  or 
absorbed  in  the  substitution  of  chlorine  for  oxygen,  or  of  one  metal  for  another 
in  combination  with  either  of  these  elements.  Here,  as  in  other  cases,  the 
difference  in  the  state  of  aggregation  doubtless  interferes  with  the  constancy  of 
action  which  might  otherwise  be  observed.  The  amount  of  interference  arising 
from  this  cause  is  much  diminished  when  compounds  are  compared  in  the  state 
of  aqueous  solution ;  and  accordingly  it  is  found  that,  when  the  quantities  of  heat 
evolved  by  the  combination  of  different  bases  and  acids  (or  metals  and  radicals), 
in  the  form  of  soluble  salts,  are  compared,  numbers  are  obtained  which  exhibit  a 
tolerably  near  approach  to  regular  progression. 

The  following  Table  exhibits  the  number  of  units  of  heat  evolved  by  equiva- 
lent quantities  of  different  bases  in  combining  with  various  acids,  as  determined 
by  Favre  and  Silbermann  :  — 


Bases. 

Acids. 

Sul- 
phuric. 

Nitric. 

Hydro- 
chloric. 

Hydro- 
bromic. 

Hy- 

driodic. 

Acetic. 

Grm. 
47-2  Potash  

16083 
15810 
14690 

15510 
15283 
13676 
15360 
16943 
12840 
10850 
8323 
8116 
6400 
10450 
9956 
9240 
6206 

15656 
15128 
13536 
15306 
16982 
13220 
11235 
'    8307 
8109 
6416 
10412 
10374 

15510 
15159 

15698 
15097 

13978 
13600 
12649 
13262 
14675 
12270 
9982 
7720 
7546 
5264 
9245 
9272 
7168 

31      Soda 

26      Oxide  of  ammonium. 
76-5  Baryta  





28      Lime  

20      Magnesia        

14440 
12075 
10455 
10240 
7720 
11932 
11780 

35-6  Manganous  oxide  
40-6  Zinc-oxide  

64      Cadmic  oxide 

39*7  Cupric  oxide    





37-6  Nickel-oxide  

37-5  Cobaltous  oxide  
111-7  Lead-oxide           

116-1   Silver-oxide... 

A  comparison  of  these  numbers  shows  that  nitric,  hydrochloric,  hydrobromic, 
and  hydriodic  acids,  in  combining  with  the  same  base,  evolve  nearly  equal  quan- 
tities of  heat ;  sulphuric  acid  a  considerably  greater,  and  acetic  acid  a  smaller 
quantity.  Auac-Qg  the  bases,  the  alkalies  evolve  the  greatest  quantity  of  heat  in 
combining  with  any  acid.  In  general,  it  appears  that  the  greatest  heat  is  evolved 
by  the  combination  of  the  strongest  acids  with  the  strongest  bases. 

The  corresponding  terms  of  any  two  horizontal  rows  in  the  preceding  table 
exhibit,  in  some  cases,  nearly  equal  differences ;  and  the  same  is  true  with  regard 
to  the  corresponding  terms  of  any  two  vertical  rows.  If  these  differences  were 
constantly  equal,  it  would  follow  that  the  quantities  of  heat  evolved  or  absorbed 
in  the  substitution  of  a  base  a  for  a  base  b  (potash  for  soda,  for  example),  would 
be  the  same  with  whatever  acid  the  base  were  united ;  and,  similarly,  the  heat 
evolved  or  absorbed  in  the  substitution  of  one  particular  acid  for  another,  would* 
be  independent  of  the  bases.  The  actual  differences,  however,  deviate  too  much 
from  this  law  to  warrant  its  reception  as  an  expression  of  the  results  of  observa- 
tion. Nevertheless,  there  is  a  considerable  degree  of  d  priori  probability  in  its 
favour;  and  the  observed  deviations  from  it  may  perhaps  arise  from  disturbing 


756  HEAT    OF    CHEMICAL    COMBINATION. 

causes,  such  as  the  different  quantities  of  heat  absorbed  in  the  solution  of  salts, 
&c.     Hofw  far  this  is  the  case,  remains  to  be  decided  by  further  experiments. 

Heat  is  likewise  evolved  in  the  combination  of  acids  with  water.  The  following 
are  the  quantities  of  heat  developed,  according  to  Favre  and  Silbermann,  by 
mixing  sulphuric  acid,  S04H,  with  various  proportions  of  water. 

Heat-units.  Differences. 

With  the  first         }  atom  water 9-4) 

second    |         "          8-8> 

first         i         «         ... 18-8)     ,  fi 

second    J         "         17-2) 

first        *         «         36-7) 

second    I         "         28-3> 

1         « 64-7 

!!  *$&    A"''* 

4  «      !""!.'""!*.'.!'.;'         "122-2! 10'8 

5  «      Z^""!l"ll!lll"ll!l!!;;  i3o-7 !   ?t 

6  "      136-2    22 

7  "         141-85     ot 

8  <•         145-1      2"? 

9  «         148-5| 

10         "         148-45     ™ 

20         "         I486* 

These  numbers  show  that  the  heat  evolved  by  adding  a  given  quantity  of  water 
to  hydrated  sulphuric  acid,  diminishes  as  the  quantity  of  water  already  present  is 
greater. 

Neat  evolved  by  the  solution  of  gases  in  water. — When  a  gas  dissolves  in  water, 
heat  is  evolved,  partly  in  consequence  of  the  chemical  combination,  and  partly 
from  the  condensation  of  the  gas  to  the  liquid  state.  According  to  Favre  and 
Silbermann  : — 

Heat-units. 

1  gramme  of  hydrochloric  acid  gas  dissolved  in  water  evolves 449-6 

1          "          hydrobromic       "  "  "     235  6 

1          "          hydriodic  "  "  "     147-7 

1          "          sulphurous          "  "  "     120-4 

1          "         ammoniacal  gas  "  "     514-3 

The  heat  evolved  varies,  however,  according  to  the  quantity  of  water  in  which 
a  given  quantity  of  the  gas  dissolves. 

Solution  of  salts,  &c.,  in  water. — The  calorific  effect  produced  by  the  solution 
of  a  solid  in  a  liquid,  depends  upon  several  circumstances;  viz.  on  the  chemical 
affinity  between  the  two,  on  the  quantity  of  heat  absorbed  in  the  passage  of  the 
solid  to  the  liquid  state,  on  the  quantity  of  the  solvent,  and  on  the  temperature 
at  which  the  solution  takes  place.  The  result  is,  in  most  cases,  an  absorption  of 
heat  or  reduction  of  temperature;  in  some  cases,  however,  as  when  the  act  of 
solution  is  preceded  or  accompanied  by  the  formation  of  a  definite  hydrate,  the 
effect  may  be  reversed.  The  combination  of  anhydrous  potash  with  water  to  form 
the  hydrate  KO.HO,  is  attended  with  a  rise  of  temperature  sufficient  to  produce 
incandescence;  the  hydrate  KO.HO  likewise  evolves  a  considerable  quantity  of 
heat  on  dissolving  in  water,  because  it  first  combines  with  a  definite  proportion 
of  water,  forming  the  hydrate  KH02.4HO;  but  the  solution  of  this  latter  com- 
pound in  water  produces  a  considerable  fall  of  temperature.  Anhydrous  chloride 
of  calcium  combines  with  water,  forming  the  hydrate  CaC1.6HO,  the  combination 


COLD   PRODUCED  BY   CHEMICAL  DECOMPOSITION.      757 

being  attended  with  great  evolution  of  heat;  but  the  solution  of  the  hydrate  in 
water  produces  cold. 

The  absorption  of  heat  accompanying  the  solution  of  salts  is  not  wholly  due  to 
the  liquefaction  of  the  solid;  for  the  heat  thus  absorbed  in  solution  is  sometimes 
greater,  sometimes  less  than  when  the  salt  is  liquefied  by  heat  alone.  Thus,  in 
the  fusion  of  1  gramme  of  nitrate  of  potash,  49  heat-units  are  rendered  latent; 
but  when  the  same  salt  is  dissolved  in  20  parts  of  water,  at  20°  C.,  80  heat-units 
are  absorbed.  The  latent  heat  of  fusion  of  crystallized  chloride  of  calcium  is  41 
heat-units;  but  when  this  hydrated  salt  dissolves  in  12  parts  of  water  at  8°  C., 
only  19  heat-units  are  absorbed.  (C.  Person.*) 

The  following  results  are  extracted  from  Person's  determinations  of  the  in- 
fluence of  the  temperature  and  quantity  of  the  solvent  on  the  quantity  of  heat 
absorbed :  — 


Name  of  Salt. 

Quantity  of 
Water. 

Temperature. 

Units  of  Heat 
absorbed. 

Chloride  of  sodium  1  gramme  J 
Nitrate  of  soda  "        / 

7-28 
7-28 
7-28 
5 

17-1  C. 
10-3 
0-2 

22-7 

13-5 
14-9 
18-7 
47-1 

Nitrate  of  potash  "        J 

20 
10 
10 

22-8 
23-8 
5-5 

55-7 

76-7 
80-2 

20 
20 

5-7 
19-7 

86-4 
80-5 

Hence  it  appears  that  when  a  given  quantity  of  a  salt  is  dissolved  in  the  same 
quantity  of  water  at  different  temperatures,  the  quantity  of  heat  absorbed  is 
greater  as  the  initial  temperature  is  lower;  and  at  the  same  temperature,  the 
quantity  of  heat  absorbed  increases 'with  the  quantity  of  the  solvent.  A  fall  of 
temperature  is  sometimes  produced  by  merely  diluting  a  solution  with  water. 
(Person). 

COLD   PRODUCED  BY  CHEMICAL  DECOMPOSITION. 

The  separation  of  any  two  bodies  is  attended  with  the  absorption  of  a  quantity 
of  heat  equal  to  that  which  is  evolved  in  their  combination.  The  truth  of  this 
proposition  has  been  established  by  Dr.  Woods")*  and  Mr.  Joule,!  by  comparing 
the  heat  evolved  in  the  electrolysis  of  water,  with  that  which  is  developed  in  a 
thin  metallic  wire  by  a  current  of  the  same  strength.  The  current  was  first  made 
to  pass  through  a  vessel  containing  acidulated  water,  the  quantity  of  gas  evolved 
in  a  given  time  determined,  and  also  the  rise  of  temperature,  the  strength  of  the 
current  being  at  the  same  time  measured  by  the  tangent-compass  (p.  679).  The 
electrolytic  cell  was  then  removed,  and  a  thin  platinum  wire  introduced  between 
the  poles,  of  such  a  length  as  to  produce  a  resistance  equal  to  that  of  the  electro- 
lyte. The  quantity  of  heat  evolved  in  this  wire  was  then  determined,  and  found 
to  exceed  that  which  was  previously  evolved  in  the  electrolytic  cell,  by  a  quantity 
equal  to  that  which  would  be  evolved  in  the  combination  of  the  oxygen  and 
hydrogen  eliminated  by  the  current  in  the  previous  experiment. 

The  same  proposition  is  likewise  established  by  many  other  chemical  pheno- 
mena. When  zinc  dissolves  in  dilute  sulphuric  acid,  the  action  may  be  supposed 
to  consist  of  three  stages,  viz.,  the  decomposition  of  water,  the  formation  of  oxide 
of  zinc,  and  the  combination  of  the  oxide  of  zinc  with  sulphuric  acid,  forming 
ZnO .  S03.  Now  : 


*  Ann.  Ch.  Phys.  [3],  xxxiii.  448. 
J  Phil.  Mag.  [4],  iii.  481. 


f  Phil.  Mag.  [4],  ii.  368. 


58   COLD  PRODUCED  BY  CHEMICAL  DECOMPOSITION. 

Heat-units. 

The  heat  evolved  in  the  oxidation  of  1  atom  or  32-6  parts  of  zinc,  =  42413 
The  heat  evolved  in  the  combination  of  1  atom  or  40'6  parts  oxide 
of  zinc  with  sulphuric  acid,  in  presence  of  a  large  quantity  of 
water  (p.  755) =  10455 


Surnt =  52868 

Deducting  from  this  the  heat  evolved  in  the  combination  of  1  atom 

or  1  gramme  of  hydrogen  with  oxygen =  34462 


There  remains  for  the  heat  evolved  in  the  entire  process 18406 

which  agrees  very  nearly  with  the  quantity  determined  by  direct  experiment,  viz. 
18,514  heat-units. 

Again,  when  metallic  oxides  are  reduced  by  hydrogen,  the  heat  evolved  is  not 
so  great  as  when  the  same  quantity  of  hydrogen  combines  with  free  oxygen, 
because  it  is  diminished  by  the  heat  absorbed  in  the  separation  of  the  oxygen  and 
the  metal. 

The  reduction  of  oxide  of  iron  by  hydrogen  takes  place  without  much  evolution 
of  heat,  because  the  heat  evolved  in  the  combination  of  1  grm.  of  oxygen  with 
hydrogen,  viz.  4308  heat-units  (p.  752),  is  not  much  greater  than  that  which  is 
evolved  when  the  same  quantity  of  oxygen  combines  with  iron,  viz.  4134  heat- 
units.  But  the  reduction  of  oxide  of  copper  is  attended  with  a  rise  of  tempera- 
ture amounting  to  incandescence,  because  the  heat  evolved  in  the  oxidation  of 
hydrogen  greatly  exceeds  that  which  is  evolved  in  the  oxidation  of  copper,  which 
is  only  2393  heat-units. 

The  absorption  of  heat  in  decomposition  is  also  demonstrated  by  the  fact  that 
no  alteration  of  temperature  takes  place  in  the  double  decomposition  of  salts,  pro- 
vided all  the  products  remain  in  solution;  in  fact,  the  heat  evolved  in  the  com- 
binations is-  exactly  compensated  by  the  cold  produced  by  the  decompositions 
which  take  place  at  the  same  time.  But  if  a  precipitate  is  formed,  heat  is  evolved 
in  consequence  of  the  passage  of  the  compound  from  the  liquid  to  the  solid  state. 

There  are  some  phenomena  which  appear  to  contradict  the  assertion  that  heat 
is  always  absorbed  in  chemical  decomposition.  The  decomposition  of  some  of  the 
oxides  of  chlorine,  and  of  the  chloride  and  iodide  of  nitrogen,  is  attended  with 
evolution  of  heat.  It  has  also  been  shown  by  Favre  and  Silbermann,  that,  in  the 
combustion  of  charcoal  in  nitrous  oxide,  more  heat  is  evolved  than  when  charcoal 
burns  in  pure  oxygen ;  and  that  the  decomposition  of  peroxide  of  hydrogen  by 
platinum  is  attended  with  considerable  rise  of  temperature.  These  apparent  ano- 
malies may,  however,  be  reconciled  with  the  general  law,  if  we  admit  that  all 
chemical  actions  may  be  regarded  as  double  decompositions  (pp.  690,  691). 
Thus,  in  the  last  case,  regarding  peroxide  of  hydrogen  as  water  plus  oxygen,  the 
decomposition  may  be  represented  by  the  equation  :  — 

HO .  0  +  HO .  0  =  2HO  -f  00. 

And  it  is  possible  that  the  heat  evolved  in  the  combination  of  oxygen  with  oxygen, 
may  be  greater  than  that  which  is  absorbed  in  the  separation  of  the  oxygen  from 
the  water;  and  similarly  in  the  other  cases. 


EXTRACTION   OF   OXYGEN   FROM   THE   AIR.  759 


NON-METALLIC   ELEMENTS. 

i 

OXYGEN   AND    HYDROGEN. 

• 

Extraction  of  Oxygen  from  Atmospheric  air.  —  Boussingault  has  shown*  that 
it  is  possible  to  obtain  oxygen  gas  in  considerable  quantity  from  the  air  by  the  use 
of  baryta,  that  substance  absorbing  oxygen  from  the  air  at  a  low  red  heat,  and 
being  converted  into  peroxide  of  barium,  and  the  latter,  when  raised  to  a  higher 
temperature,  —  or  still  more  easily  when  exposed  to  a  current  of  aqueous  vapour, 
— giving  up  its  second  atom  of  oxygen  in  the  free  state.  The  apparatus  used  con- 
sists of  a  tube  of  porcelain  or  glazed  earthenware,  communicating  at  the  one  end, 
by  means  of  smaller  tubes  provided  with  stopcocks,  with  an  aspirator  and  a  gas- 
holder, and  at  the  other  with  the  external  air  and  also  with  a  steam-boiler.  The 
tube  is  filled  with  hydrate  of  baryta,  —  mixed  with  lime  or  magnesia  to  diminish 
its  fusibility, — and  heated  to  low  redness,  a  current  of  air  being  at  the  same  time 
drawn  through  the  tube  by  the  aspirator.  The  hydrate  of  baryta  is  thereby  con- 
verted into  peroxide  of  barium  ;  and  when  the  oxidation  has  proceeded  far  enough, 
the  current  of  air  is  suspended,  a  jet  of  steam  sent  through  the  tube,  and  at  the 
same  time  the  connection  with  the  gas-holder  is  opened ;  the  peroxide  of  barium 
is  then  reconverted  into  hydrate  of  baryta,  and  the  excess  of  oxygen  passes  into 
the  gas-holder.  The  hydrate  of  baryta  may  now  be  reoxidized  by  a  fresh  current 
of  air,  the  resulting  peroxide  again  decomposed  by  vapour  of  water, — and  this 
series  of  operations  may  be  repeated  any  number  of  times.  Boussingault's  first 
experiments  were  made  with  anhydrous  baryta,  which  likewise  absorbs  oxygen 
when  heated  to  low  redness  in  a  current  of  air,  and  gives  it  up  again  at  a  bright 
red  heat.  It  was  found,  however,  that  the  baryta,  after  one  or  two  repetitions  of 
the  process,  lost  in  a  great  measure  its  power  of  absorbing  oxygen.  In  fact, 
baryta,  when  really  anhydrous,  shows  but  little  inclination  to  absorb  oxygen  ;  it  is 
only  the  hydrate  that  is  readily  converted  into  Ba02.  Now  baryta,  when  pre- 
pared in  the  ordinary  way,  by  calcining  the  nitrate,  always  contains  a  little  water, 
which  facilitates  the  absorption  of  the  oxygen  ;  but  after  being  heated  two  or  three 
times  in  a  current  of  dry  air,  it  becomes  really  anhydrous,  and  is  then  no  longer 
oxidized.  The  use  of  hydrate  of  baryta  is  therefore  much  more  advantageous, 
both  for  the  reason  just  stated,  and  likewise  because  the  decomposition  of  the  per- 
oxide by  vapour  of  water  takes  place  at  a  much  lower  temperature  than  by  simple 
ignition.  The  process  in  this  form  is  adapted  for  use  on  the  large  scale. •)• 

Ozone  (p.  232).  —  The  nature  of  ozone  is  still  a  matter  of  discussion.  That  it 
is  a  higher  oxide  of  hydrogen  was  first  suggested  by  Professor  Williamson, J  who 
passed  ozoniferous  oxygen,  obtained  by  electrolysis,  first  over  chloride  of  calcium 
to  dry  it,  and  then  through  a  glass  tube,  in  which  it  was  either  heated  by  a  Spirit- 
lamp  or  brought  in  contact  with  finely  divided  copper  at  a  red  heat.  The  ozone 
was  thereby  decomposed  and  deprived  of  its  odour,  and  water  was  deposited.  The 

*  Compt.  rend,  xxxii.  261 ;  Ann.  Ch.  Phys.  [3],  xxx.  5  ;  Chem.  Soc.  Qu.  J.  v.  269. 

f  A  patent  for  the  preparation  of  oxygen  in  this  manner,  and  its  application  in  various 
chemical  operations,  has  been  taken  out  by  Messrs.  Swindells  and  Nicholson.  (Chem.  Gaz. 
1855,  139). 

I  Ann.  Ch.  Pharm.  liv.  127.  This  view  was  afterwards  adopted  by  Schonbein  (Pogg.  Ann. 
Ixvii.  78),  but  he  has  since  abandoned  it,  inclining  rather  to  regard  ozone  as  an  allotropic 
modification  of  oxygen  (Ann.  Ch.  Phqrm.  Ixxxii.  232 ;  J.  pr.  Chem.  liii.  65). 


760  OXYGEN     AND    HYDROGEN. 

same  view  has  been  further  supported  by  the  more  recent  experiments  of  Baumert,* 
who  has  likewise  analyzed  the  ozone  quantitatively,  and  finds  that  it  is  a  teroxide 
of  hydrogen,  H03.  In  Baumert's  experiments,  ozoniferous  oxygen  evolved  at  the 
positive  pole  from  water  acidulated  with  sulphuric  and  chromic  acids  (which  mix- 
ture was  found  to  yield  the  largest  quantity  of  ozone,  not,  feowever,  exceeding  1 
milligramme  of  that  substance  to  8£  litres  of  oxygen)  was  passed,  after  thorough 
drying,  into  a  glass  tube  lined  with  a  film  of  anhydrous  phosphoric  acid.  On 
heating  the  tube  with  a  spirit-lamp,  the  phosphoric  acid  became  transparent,  and 
was  dissolved  at  the  part  of  the  tube  beyond  the  flame,  showing  that  water  was 
there  deposited.  It  would  appear  then  that  ozone,  obtained  by  electrolysis,  con- 
tains the  elements  of  water;  and  its  powerful  oxidizing  properties  show  that  it  also 
contains  an  excess  of  oxygen.  Hence,  to  analyze  it  quantitatively,  it  is  only 
necessary  to  determine  the  proportion  of  this  excess  of  oxygen  in  a  known  weight 
of  ozone.  The  analysis  was  made  by  passing  the  ozoniferous  oxygen,  first  through 
a  tube  containing  pumice-stone  soaked  in  sulphuric  acid,  to  dry  it;  then  through 
a  bulb-apparatus  containing  solution  of  iodide  of  potassifem,  which  completely 
absorbed  the  ozone,  and  was  itself  at  the  same  time  partially  decomposed,  a  certain 
quantity  of  iodine  being  set  free  by  the  excess  of  oxygen  in  the  ozone;  and,  lastly, 
through  a  second  bulb-apparatus  containing  strong  sulphuric  acid,  to  absorb  any 
water  mechanically  carried  forward  from  the  iodide  of  potassium  solution  by  the 
stream  of  gas  The  increase  of  weight  in  the  two  bulb-apparatus  gave  the  total 
quantity  of  ozone;  and  the  quantity  of  iodine  set  free  (estimated  byBunsen's 
volumetric  method)f  determined  the  amount  of  active  oxygen  therein.  Two  ex- 
periments made  in  this  manner  gave,  in  100  parts  of  ozone  : — 96-24  0  -f  3-76  H, 
and  95-700  +  4-30  H  respectively.  The  formula,  H03,  requires  95-660  -f 
4-34  H.  The  oxidizing  action  of  the  ozone  was  found  to  be  so  powerful,  that  it 
quickly  destroyed  any  organic  substance,  such  as  vulcanized  caoutchouc,  used  to 
connect  the  different  parts  of  the  apparatus :  hence  it  was  necessary  to  make  all 
the  connections  either  by  fusion  or  by  grinding. 

Baumert  has  also  found,  in  accordance  with  the  observations  of  previous  experi- 
menters, that  perfectly  dry  oxygen  gas,  subjected  for  some  time  to  the  action  of 
the  electric  spark,  is  brought  into  an  allotropic  state,  in  which  its  combining 
tendencies  are  highly  exalted,  so  that  is  capable  of  overcoming  the  most  powerful 
affinities,  such  as  that  of  chlorine  or  iodine  for  potassium,  at  ordinary  temperatures. 
Ozonized  oxygen  was  freed  from  ozone  and  aqueous  vapour  by  passing  through 
sulphuric  acid,  through  a  heated  glass  tube,  over  fragments  of  iodide  of  potassium, 
and  through  pulverulent  phosphoric  acid,  and  then  made  to  pass  through  a  glass 
tube  having  platinum  wires  fixed  into  its  sides.  On  passing  a  rapid  succession 
of  electric  sparks  between  these  wires,  the  gas  acquired  again  the  odour  of  ozone, 
and  the  power  of  decomposing  a  solution  of  iodide  of  potassium,  characters  which 
it  did  not  possess  before  the  sparks  were  passed  through  it.  When  heated  to  200°  C. 
it  lost  these  peculiar  properties,  and  was  restored  to  its  ordinary  state.  Results 
similar  to  this  had  previously  been  obtained  by  Marignac  and  Do  la  Hive,  and 
also  by  Fremy  and  Becquerel.|  In  the  experiments  of  the  last-mentioned  philo- 
sophers, perfectly  dry  oxygen  gas,  enclosed  in  sealed  glass  tubes,  and  subjected  to 
the  continued  action  of  electric  sparks  passed  along  the  outer  surface  of  the  glass, 
was  found  to  acquire  the  power  of  decomposing  iodide  of  potassium,  and  was 
absorbed  by  moist  mercury  or  silver,  and  by  solution  of  iodide  of  potassium.  From 
these  experiments  it  may  be  reasonably  concluded  that  oxygen  can  by  certain 
means  be  brought  into  a  modified  and  excited  condition ;  but  as  this  modified 
oxygen,  when  it  exhibits  the  odour  of  ozone,  or  any  of  its  peculiar  reactions,  is 
necessarily  brought  into  contact  with  moisture,  it  is  likewise  high  probable  that  it 

*  Pogg.  Ann.  Ixxxix.  38;  Chem  Soc.  Qu.  J.  vi.  169. 

f  Ann.  Ch.  Pharm.  Ixxxvi.  265. 

I  Ann.  Ch.  Phys.  [3],  xxxv.  62;  Chem.  Soc.  Qu.  J.  v.  272. 


OZONE.  761 

then  combines  with  the  elements  of  water,  forming  the  true  ozone  H03,  and  that 
to  this  the  odour  and  oxidizing  actions  are  really  due. 

Ozone,  formed  by  the  slow  oxidation  of  phosphorus  in  the  air,  exhibits  the 
same  characters  as  that  which  is  obtained  by  electrolysis  of  water,  &c.  Ozone 
thus  produced  is  generally  regarded  as  merely  allotropic  oxygen ;  but  as  water  is 
always  present  in  in  its  formation,  it  may  also  be  a  peroxide  of  hydrogen,  like  the 
ozone  obtained  from  electrical  sources.* 

According  to  Schonbein,  many  other  substances  besides  phosphorus  possess  the 
power  of  inducing  the  formation  of  ozone.  Thus,  ether,  oil  of  turpentine,  oil  of 
lemons,  linseed  oil,  alcohol,  wood-spirit,  various  vegetable  acids,  sulphuretted 
hydrogen,  arseniuretted  hydrogen,  and  sulphurous  acid,  in  contact  with  air  or 
oxygen  gas,  and  under  the  influence  of  light,  acquire  the  power  of  decolourizing 
indigo,  and  producing  various  oxidizing  actions.  A  similar  influence  is  exerted 
by  mercury  and  other  noble  metals  in  the  finely  divided  state ;  and  stibethyl  is 
found  to  be  a  more  powerful  ozonizer  than  even  phosphorus  itself. 

Houzeau  has  shown")*  that  active  oxygen  may  be  obtained  by  the  action  of 
strong  (monohydrated)  sulphuric  acid  on  peroxide  of  barium.  The  gas  thus 
evolved  has  a  very  powerful  odour,  and  a  taste  like  that  of  the  lobster ;  it  rapidly 
decolourizes  blue  litmus  paper;  oxidizes  silver;  burns  ammonia  spontaneously, 
transforming  it  into  nitrate  of  ammonia;  instantly  burns  phosphuretted  hydrogen 
(the  less  inflammable  variety,  p.  326)  with  emission  of  light;  decomposes  hydro- 
chloric acid,  setting  the  chlorine  free;  is  a  powerful  oxidizing  and  chlorinizing 
agent ;  is  stable  at  ordinary  temperatures,  but  loses  its  peculiar  properties  when 
heated  to  75°  C.  In  all  these  respects  it  differs  essentially  from  ordinary  oxygen ; 
in  fact  it  exhibits  the  properties  of  ozone.  Active  oxygen  may  also  be  obtained 
from  other  bodies  besides  the  peroxide  of  barium.  Oxygen  in  the  combined 
state  appears,  indeed,  to  possess  the  intensified  power  which  distinguishes  free 
oxygen  in  the  nascent  state. 

The  nature  of  ozone  has  also  been  investigated  by  Dr.  Andrews,^  who  has 
arrived  at  the  conclusion  that  electrolytic  ozone,  as  well  as  that  obtained  from 
other  sources,  is  nothing  but  active  oxygen.  The  excess  of  the  weight  of  ozone 
in  Baumert's  experiments,  over  that  of  the  active  oxygen,  is  attributed  by 
Andrews  to  the  presence  of  a  small  quantity  of  carbonic  acid,  which  he  states  is 
always  mixed  with  the  gases  resulting  from  the  decomposition  of  water,  unless 
especial  precautions  be  taken  to  get  rid  of  it,  and  being  absorbed  by  the  potash 
resulting  from  the  decomposition  of  the  neutral  solution  of  iodide  of  potassium, 
increases  the  weight  of  the  apparatus,  and  consequently  produces  an  apparent  in- 
crease in  the  quantity  of  ozone  absorbed. 

To  obviate  this  supposed  source  of  inaccuracy,  Andrews,  using  an  apparatus 
similar  to  that  of  Baumert,  acidulated  his  solution  of  iodide  of  potassium  with 
hydrochloric  acid ;  and,  in  five  experiments,  in  which  29  litres  of  the  ozoniferous 
gas  were  passed  through  the  apparatus,  obtained  an  increase  of  weight  in  the 
absorption-bulbs,  that  is  to  say,  a  quantity  of  ozone  —  amounting  to  0-1179  grm., 
while  the  quantity  of  active  oxygen,  estimated  according  to  the  quantity  of  iodine 
separated,  was  0  1178  grm.  From  this  result,  Andrews  concludes  that  ozone  is 
nothing  but  an  active  form  of  oxygen. 

In  another  series  of  experiments,  in  which  electrolytic  ozone  was  decomposed 
by  heat,  and  the  gas  subsequently  passed  over  strong  oil  of  vitriol  and  anhydrous 
phosphoric  acid,  not  a  trace  of  water  could  be  discovered.  Andrews  has  likewise 
confirmed  the  result  obtained  by  other  experimenters  that  pure  dry  oxygen  ac- 
quires peculiar  active  properties  by  the  action  of  the  electric  spark ;  and  by  com- 
paring the  properties  of  ozone  obtained  from  various  sources,  he  concludes  that 

*  Williamson,  Ann.  Ch.  Pharm.  Ixi.  32.  f  Compt.  rend.  xl.  947. 

%  Chem.  Soc.  Qu.  J.  ix.  168. 


OXYGEN    AND    HYDROGEN. 

ozone,  in  whatever  manner  produced,  is  essentially  the  same,  consisting  in  fact  of 
allotropic  oxygen. 

On  the  other  hand,  Baumert*  denies  the  existence  of  carbonic  acid  in  the 
ozoniferous  gas  which  he  obtained  by  electrolysis,  inasmuch  as  the  electrolyte 
used,  water  acidulated  with  sulphuric  and  chromic  acid,  could  scarcely  absorb  a 
sufficient  quantity  of  carbonic  acid  to  account  for  the  results  obtained.  He  more- 
over attributes  the  carbonic  acid  which  Andrews  obtained,  to  the  oxidizing  action 
of  the  ozone  on  the  diaphragm  of  bladder  with  which  the  positive  cell  of  the  de- 
composing apparatus  was  closed.  Baumert  finds,  indeed,  that  when  a  diaphragm 
of  bladder  is  used  for  this  purpose,  carbonic  acid  is  actually  produced  ;  but  when 
a  diaphragm  of  gypsum  is  employed,  not  a  trace  of  that  gas  can  be  detected. 
With  respect  to  the  use  of  iodide  of  potassium  acidulated  with  hydrochloric  acid, 
Baumert  calls  attention  to  the  fact  that  such  a  solution  must  contain  free  hydriodic 
acid,  which  is  decomposed  by  oxygen  in  its  ordinary  as  well  as  in  its  allotropic 
state.  In  fact,  oxygen  gas  evolved  by  electrolysis,  and  completely  freed  from 
ozone  by  passing  through  a  neutral  solution  of  iodide  of  potassium,  liberated, 
when  subsequently  passed  through  a  solution  of  the  same  salt  acidulated  with 
hydrochloric  acid,  a  quantity  of  iodine  much  larger  than  that  which  it  had  pre- 
viously separated  from  the  neutral  solution.  This  may  account  for  the  greater 
proportion  of  the  active  oxygen  to  the  total  quantity  of  ozone  obtained  in  the 
experiments  of  Andrews. 

The  true  nature  of  ozone  must  then  still  be  considered  a  matter  for  investiga- 
tion. The  existence  of  an  allotropic  modification  of  oxygen  possessing  peculiarly 
active  properties  appears  to  be  established  by  the  researches  of  numerous  inquirers  ; 
but  on  the  other  hand,  till  some  more  valid  objection  is  adduced  against  the  re- 
sults obtained  by  Baumert  and  Williamson,  the  existence  of  hydrogen  in  the  ozone 
obtained  by  electrolysis  of  acidulated  water  can  scarcely  be  denied. 

Quantitative  estimation  of  Oxygen  and  Hydrogen.  —  The  quantity  of  either 
of  these  gases  in  a  gaseous  mixture  may  be  determined  by  mixing  it  with  an 
excess  of  the  other,  and  inducing  combination  by  the  electric  spark,  or  by  spongy 
platinum  or  platinized  charcoal.  One-third  of  the  volume  of  gas  which  disap- 
pears is  oxygen,  and  two-thirds  hydrogen.  This,  of  course,  implies  that  no  other 
gases  are  present  capable  of  uniting  with  either  oxygen  or  hydrogen. 

The  amount  of  hydrogen  in  solid  or  liquid  compounds  (generally  organic),  when 
it  is  not  present  in  the  form  of  water,  is  estimated  by  heating  the  compound  in 
contact  with  some  oxidizing  agent,  generally  oxide  of  copper,  and  weighing  the 
water  produced  (p.  771).  Oxygen  in  such  compounds  is  generally  determined 
by  loss,  the  quantities  of  all  the  other  elements  being  determined  by  the  methods 
severally  applicable  to  them,  and  the  remainder  being  estimated  as  oxygen.  The 
quantity  of  oxygen  in  metallic  oxides  which  are  riot  reduced  by  heat  alone,  is 
generally  estimated  by  igniting  them  in  a  current  of  hydrogen  and  weighing  the 
water  produced. 

The  quantity  of  oxygen  in  the  atmosphere  may  be  determined  by  methods 
already  described  (p.  249).  A  very  good  method  has  since  been  given  by  Liebig,f 
viz.,  to  absorb  the  oxygen  by  means  of  an  alkaline  solution  of  pyrogallate  of 
potash.  Pyrogallic  acid  is  readily  obtained  as  a  crystalline  sublimate  by  the  dry 
distillation  of  gallic  acid ;  it  dissolves  easily  in  potash :  and  the  solution  intro- 
duced by  means  of  a  pipette  into  air  standing  over  mercury,  absorbs  the  oxygen 
quickly  and  completely. 

Estimation  of  Water.  —  The  quantity  of  water  in  a  solid  compound,  a  salt  for 
example,  is  determined  by  heating  a  weighed  quantity  of  the  substance  in  a  cap- 
sule or  crucible  over  a  lamp,  or  in  a  sand-bath,  or  over  a  water-bath,  according  to 

*  Pogg.  Ann.  xcix.  88.  f  Chem.  Soc.  Qu.  J.  iv.  221. 


ABSORPTION    OF    GASES.  763 

the  temperature  which  it  will  bear  without  giving  off  anything  hut  water.  Sub- 
stances which  will  not  bear  even  the  temperature  of  the  water-bath,  are  dehydrated 
by  placing  them  over  strong  sulphuric  acid,  sometimes  in  vacuo,  sometimes  by 
merely  placing  the  dish  containing  the  sulphuric  acid,  with  the  substance  sup- 
ported above  it  in  a  capsule,  on  a  ground  glass"  plate,  and  covering  the  whole  with 
a  bell  jar.  Another  method  of  drying  substances  which  will  not  bear  much  heat, 
is  to  place  them  in  a  bent  tube  immersed  in  a  water-bath  at  a  regulated  temperature, 
and  pass  through  the  tube  a  current  of  dry  air,  hydrogen,  or  carbonic  acid,  accord- 
ing to  the  nature  of  the  substance. 

Some  salts  when  heated  give  off  a  portion  of  their  acid  as  well  as  their  water, 
the  sulphates  of  alumina,  and  sesquioxide  of  iron  for  example.  To  determine  the 
quantity  of  water  in  such  cases,  the  salt  must  be  mixed  with  a  weighed  quantity 
of  protoxide  of  lead,  sufficient  to  cover  it  completely,  and  heated  in  a  platinum 
crucible  :  the  acid,  which  would  otherwise  escape,  is  then  retained  by  the  oxide 
of  lead,  and  nothing  but  water  goes  off. 

The  quantity  of  combined  water  in  a  base,  such  as  hydrate  of  potash,  is  de- 
termined by  heating  the  base  with  an  acid  which  will  form  with  it  a  compound 
not  decomposable  at  a  red  heat. 

In  all  cases,  the  water,  instead  of  being  estimated  merely  by  loss  of  weight, 
may  be  determined  by  receiving  it  in  a  tube  filled  with  dry  chloride  of  calcium, 
or  with  pumice  stone  soaked  in  strong  sulphuric  acid,  an  empty  glass  bulb,  pre- 
viously weighed,  being,  however,  interposed  when  the  quantity  of  water  is  large 
(p.  238,  fig.  108).  This  method  is  particularly  applicable  when  other  substances 
besides  water  are  given  off  at  the  same  time. 

The  methods  of  determining  tke  quantity  of  water  in  solutions  are  similar  to 
those  above  described  for  solids  (p.  385). 

Absorption  of  gases  by  water  and  other  liquids.  —  The  laws  relating  to  the  ab- 
sorption of  gases  by  liquids  have  lately  been  examined  with  great  care  by  Bunsen, 
whose  results  tend  partly  to  confirm,  partly  to  modify  those  of  the  older  experi- 
ments of  Dalton,  Henry,  and  Saussure  (p.  81,  240). 

The  absorption  of  the  more  soluble  gases,  such  as  ammonia,  sulphurous  acid, 
&c.,  was  estimated  by  saturating  the  liquid  with  the  gas  at  a  known  temperature, 
and  then  determining,  either  by  volumetric,  or  by  weighed  analyses,  the  quantity 
of  gas  dissolved  in  a  given  volume  of  the  liquid ;  for  example,  hydrosulphuric 
acid  was  precipitated  by  a  solution  of  copper,  sulphurous  acid  and  chlorine  were 
determined  by  the  iodometric  method,  to  be  afterwards  described. 

For  the  less  soluble  gases,  a  different  method  was  adopted.  The  apparatus  used 
for  the  purpose,  called  an  absorptiometert  consists  of  a  graduated  tube  closed  at 
the  top,  and  containing  mercury.  The  gas  is  first  introduced  into  this  tube  above 
the  mercury,  and  afterwards  the  absorbing  liquid.  This  tube  is  enclosed  within 
a  wider  one,  the  space  between  the  two  being  filled  with  water,  by  means  of  which 
any  required  temperature  may  be  imparted  to  the  contents  of  the  inner  tube.  The 
outer  tube  is  closed  at  top  with  a  lid,  in  the  middle  of  which  is  an  elastic  cushion 
pressing  firmly  on  the  inner  tube  containing  the  gas.  This  tube,  by  a  peculiar 
contrivance,  may  be  either  firmly  closed  at  the  bottom,  or  made  to  communicate 
with  the  mercury  in  the  cistern  in  which  it  stands.  The  tubes  being  filled  and 
firmly  closed  top  and  bottom,  the  whole  is  vigorously  shaken  for  about  a  minute, 
to  bring  the  gas  well  in  contact  with  the  liquid.  The  inner  tube  is  then  loosened 
at  the  bottom,  so  as  to  open  a  communication  with  the  mercury  in  the  cistern,  and 
equalize  the  pressure.  More  gas  is  then  introduced,  and  the  shaking  repeated, 
and  these  operations  are  continued,  till  the  mercury  in  the  inner  tube  no  longer 
exhibits  any  alteration  of  level.  The  volume  of  the  remaining  gas  is  then  read 
off,  and  observations  made  of  the  pressure  and  temperature. 

*The  volume  of  a  gas,  reduced  to  0°  C.,  and  760  mm.  pressure,  which  is  ab- 
sorbed by  the  unit  of  volume  of  any  liquid,  is  called  the  coefficient  of  absorption* 


764 


ABSORPTION    OF    GASES. 


The  formula  used  by  Bunsen  for  calculating  these  coefficients  is  founded  on  the 
law  of  gas-absorption  discovered  by  Dr.  Henry,  viz.  that  at  any  given  temperature, 
the  weight  of  a  gas  absorbed  by  a  given  quantity  of  a  liquid  is  proportional  to 
the  pressure  ;  or,  in  other  words,  that  the  volume  of  the  gas  absorbed  at  any 
given  temperature  is  the  same  under  all  pressures  (p.  81).  Bunsen  finds, 
indeed,  that  the  coefficient  of  absorption  of  any  gas  thus  determined  under 
different  pressures,  exhibits  a  constant  value,  a  result  which  affords  a  striking 
confirmation  of  the  truth  of  Henry's  law. 

If   Fand  V  denote  the  volumes  of  a  gas  reduced  to  0°,  before  and  after  ab- 
sorption. Pand  P'  the  corresponding  pressures,  the  quantity  of  gas  absorbed  under 

V  P        V  P' 
the  pressure  P'  is  -          —  n.^'     ^°  re(^uce  ^s  to  *^e  normal  presssure,  0760 


0-760 


mm.,  it  must  be  multiplied  by  ;  and  if  the  volume  of  the  absorbing  liquid 

is  h,  the  coefficient  of  absorption  a,  or  the  quantity  of  gas  absorbed  by  a  unit 
volume  of  the  liquid,  will  be 


a=  h\~r 


The  following  table  exhibits  the  coefficients  of  absorption  of  certain  gases  by 
water  and  alcohol  for  every  5  degrees  centigrade  of  temperature  : — 


Oxygen. 

Hydrogen. 

Nitrogen. 

Nitrous  Oxide. 

In 

Water. 

In 

Alcohol. 

In 
Water. 

In 

Alcohol. 

In 
Water. 

In 
Alcohol. 

In 

Water. 

In 

Alcohol. 

o°c. 

5 

10 
15 
20 
25 

0-04114 
0-03628 
0-03250 
0-02989 
0-02838 
? 

1  0-28397 

0-0193- 

0-06925 
0-06853 
0-06786 
0-06725 
0-06668 
0-06616 

0-02035 
0-01794 
0-01607 
0-01478 
0-01403 

0-12634 
0-12440 
0-12276 
0-12142 
0-12038 
0-11964 

1  -3052 
1  -0954 
0-9196 

0-7778 
0-6700 
0-5962 

4-1780 
3-8442 
3-5408 
3-2678 
3-0253 
2-8133 

Carbonic  Oxide. 

Carbonic  acid. 

Marsh  Gas. 

Olefiant  Gas. 

In 
Water. 

In 
Alcohol. 

In 
Water. 

In 
Alcohol. 

In 

Water. 

0-05449 
0-04885 
0-04372 
0-03909 
0-03499 

In 

Alcohol. 

In 

Water. 

In 

Alcohol. 

o°c. 

5 
10 
15 
20 
25 

008287 
0-02920 
0-02635 
0-02432 
0-02312 

0-20443 

1-7967 
1-4497 
1-1847 
1-0020 
0-9014 

4-3295 
3-8908 
3-5140 
3-1993 
2-9465 
2-7558 

0-52259 
0-50861 
0-49535 
0-48280 
0-47096 
0-45982 

0-2563 
0-2153 
0-1837 
0-1615 
0-1488 

3-5950 
3-3234 
3-0859 

2-8825 
2-7131 
2-5778 

Sulphurous  Acid. 

Hydrosulphuric  Acid. 

Chlorine. 

Nitric  Oxide. 

Ammonia. 

In 

Water. 

In 
Alcohol. 

In 
Water. 

In 
Alcohol. 

In 

Water. 

In 
Alcohol. 

In 

Water. 

o°c. 

5 
10 
15 
20 
25 
30 
35 
40 

79-789 
67-485 
56-647 
47-276 
39-374 
32-786 
27-161 
22-489 
18-766 

327-80 
251-24 
190-02 
144-13 
113-56 
98-33 

4-3706 
3-9652 
3-5858 
3-2326 
2-9053 
2-6041 
2-3290 
2-0790 
1-8569 

17-891 
14-766 
11-992 
9-539 
7-415 
5-623 

0-31606 
0-29985 
0-28609 
0-27478 
0-20592 
0-25951 

1049-60 
917-90 
812-76 
727-22 
653-99 
585-94 

2-5852 
2-3681 
2-1565 
1-9504 
1-7499 
1-5550 
1  -3655 

When  a  liquid  is  in  contact  with  a  mixture  of  several  gases,  with  none  of  whieh 
it  is  disposed  to  form  *a  definite  compound,  it  absorbs  of  each  gas  a  quantity  cor- 


NITROGEN.  765 

responding  to  the  pressure  which  this  same  gas  exerts  in  the  mixture  that  remains 
after  the  absorption  is  complete.  Now,  in  any  mixture  of  gases,  each  gas  exerts 
the  same  pressure  that  it  would  if  it  alone  filled  the  entire  space;  and  the  pressure 
of  the  entire  mixture  is  equal  to  the  sum  of  the  pressures  of  the  separate  con- 
stituents. If,  for  example,  atmospheric  air,  which  in  100  volumes  contains  20-9 
/ols.  oxygen,  and  79-1  vols.  nitrogen,  exerts  altogether  a  pressure  equal  to  that 

of  760  mm.  of  mercury,  the  pressure  of  the  oxygen  is  equal  to  -^rjr- .  760  =^ 

LOO 

79-1 
158-8  mm.  and  that  of  the  nitrogen  is  -^— .  760  =  601-2  mm. 

"When  water  is  saturated  with  atmospheric  air,  it  takes  up  of  each  constituent 
a  quantity  determined  by  the  existing  temperature,  and  the  partial  pressure  of 
each  gas.  For  example,  at  13°  C.,  and  under  a  pressure  corresponding  to  760 

158*8  • 

mm.  of  mercury,  1  volume  of  water  absorbs  0-03093  X  •  ==  00646  vols.  of 

7oU 

601-2 

oxygen,  measured  at  0°  C.  and  760  mm. ;  and  0-01530  x  -=™-  =  0-01210  vols. 

7oO 

nitrogen,  also  measured  at  the  standard  pressure  and  temperature.  Hence,  at 
13°  C.  and  760  mm.',  1  vol.  water  absorbs  0-00646  vols.  oxygen,  and  0-01210 
vols.  nitrogen,  making  together  0-01856  vols.  of  a  gaseous  mixture,  containing 
84-8  vols.  oxygen,  and  65-2  vols.  nitrogen.  Direct  analysis  of  a  gaseous  mixture 
evolved  by  boiling,  from  water  previously  saturated  with  atmospheric  air,  gave 
34-73  vols.  pure  oxygen  and  65.27  vols.  nitrogen. 

When  water  previously  saturated  with  oxygen  or  nitrogen  is  exposed  to  the 
air,  the  final  result  is  still  the  same,  the  excess  of  either  gas  being  given  off,  and 
the  oxygen  and  nitrogen  being  ultimately  absorbed  in  the  proportions  just  given. 
If  water  containing  any  other  gas  is  exposed  to  the  air,  the  whole  of  the  dissolved 
gas  is  ultimately  eliminated,  and  the  water  becomes  saturated  with  the  atmos- 
pheric gases,  in  the  same  proportion  as  if  no  other  gas  had  been  previously  dis- 
solved in  it.  An  exception,  however,  occurs  when  the  dissolved  gas  is  capable 
of  forming  a  definite  compound  with  the  water,  in  which  case  portions  of  the  gas 
and  the  water  evaporate  together. 

The  general  law  above  stated  with  regard  to  the  absorption  of  gaseous  mixtures 
is  found  to  hold  good  in  mixtures  of  sulphurous  acid  gas  with  hydrogen  and  car- 
bonic acid;  of  carbonic  oxide  and  carbonic  acid;  and  of  carbonic  oxide,  marsh- 
gas,  and  hydrogen ;  but  not  with  a  mixture  of  equal  volumes  of  chlorine  and 
hydrogen,  or  of  chlorine  with  twice  or  four  times  its  volume  of  carbonic  acid. 


NITROGEN. 

Preparation  of  Nitrogen  gas  (p.  244).  —  This  gas  maybe  obtained  in  great 
abundance,  and  perfectly  pure,  by  heating  a  solution  of  nitride  of  potash  with 
sal-ammoniac : — 

KO.N03+NH4C1  =  KC1  +  4HO  +  2N. 

The  solution  of  nitrite  of  potash  is  prepared  by  passing  the  nitrous  gas,  evolved 
by  heating  1  part  of  starch  with  10  parts  of  nitric  acid,  into  a  solution  of  caustic 
potash  of  sp.  gr.  1-38,  till  the  liquid  becomes  decidedly  acid,  and  then  adding  a 
sufficient  quantity  of  caustic  potash  to  restore  the  alkaline  reaction.  The  solu- 
tion of  nitrite  of  potash  thus  obtained  may  be  preserved  without  alteration.  On 
mixing  this  liquid  with  three  times  its  bulk  of  concentrated  solution  of  sal-ammo- 
niac, and  heating  the  mixture  in  a  flask,  nitrogen  gas  is  given  off  in  large  quantity 
and  with  perfect  regularity.  Pure  nitrogen  may  also  be  obtained  by  heating  a 


766  NITROGEN. 

solution  of  nitrite  of  ammonia;  but  this  salt  is  difficult  to  prepare  (Coren- 
winder.*) 

Another  method  of  obtaining  nitrogen,  mixed  however  with  chlorine,  is  to 
heat  a  mixture  of  nitrate  of  ammonia  and  sal-ammoniac  : — 

2(NH4.N06)  +  NH4C1  =  5N  +  Cl  +  12HO. 

After  the  mixture  has  been  heated  to  the  melting  point  of  the  nitrate,  the  reaction 
goes  on  by  itself.  The  chlorine  may  be  afterwards  absorbed  by  potash.  (Mau- 
mene.f) 

Nitrous  oxide  (p.  255). — This  gas  may  be  obtained  in  a  state  of  purity  by  the 
action  of  protochloride  of  tin  on  aqua-regia.  The  tin-salt  is  dissolved  in  hydro- 
chloric acid,  the  solution  heated  over  the  water-bath,  and  crystals  or  cylindrical 
lumps  of  nitre,  successively  dropped  into  it  through  a  wide  tube  dipping  into  the 
liquid.  (Gray-Lussac.J) 

Nitric  oxide  may  be  obtained  by  a  process  similar  to  that  above  described  for 
the  preparation  of  nitrous  oxide,  using  however  protochloride  of  iron  instead  of 
protochloride  of  tin.  (Pelouze  and  Gay-Lussac.§) 

Anhydrous  nitric  acid,  N05,  is  obtained  by  the  action  of  dry  chlorine  on 
nitrate  of  silver.  Chlorine  gas  contained  in  a  gasometer  standing  in  sulphuric 
acid,  is  made  to  pass  very  slowly,  first  over  chloride  of  calcium,  then  over  sulphuric 
acid,  and  lastly  over  thoroughly  dried  nitrate  of  silver,  which  is  heated,  first  to 
95°  C.,  and  afterwards  constantly  to  58°  or  60°  C.  The  products  of  decomposi- 
tion pass  into  a  U-tube  cooled  to  21°  G.,  in  which  a  very  volatile  liquid  (probably 
nitrous  acid)  collects,  together  with  crystals  of  anydrous  nitric  acid,  while  oxygen 
escapes.  The  different  parts  of  the  apparatus  must  be  connected  by  fusion,  as 
the  acid  vapours  would  quickly  corrode  caoutchouc  joints.  The  anhydrous  nitric 
acid  crystallizes  in  colourless  rhombic  prisms,  having  angles  of  about  60°  and 
120°,  and  in  hexagonal  prisms  derived  therefrom.  It  melts  at  29°  to  30°  C.,  and 
boils  at  45°  to  50°  0.,  but  begins  to  decompose  near  its  boiling  point.  It  becomes 
strongly  heated  by  contact  with  water,  in  which  it  dissolves  without  colouring  or 
evolution  of  gas,  forming  hydrated  nitric  acid  (H.  Deville.||)  According  to 
Dumas,^f  the  crystals  melt  spontaneously  when  left  to  themselves ;  and  on  one 
occasion,  when  an  attempt  was  made  to  recrystallize  the  fused  mass  by  immersion 
in  a  freezing  mixture,  the  tube  was  shattered  with  explosion. 

Quantitative  estimation  of  Nitrogen. — Nitrogen  is  estimated,  either  by  collect- 
ing it  as  a  gas  in  the  free  state  and  measuring  its  volume,  or  by  converting  it  into 
ammonia.  Most  nitrogen-compounds,  when  strongly  heated  with  the  hydrates  of 
the  fixed  alkalies,  give  off  the  whole  of  their  nitrogen  in  the  form  of  ammonia. 
This  reaction  is  especially  applied  to  the  estimation  of  nitrogen  in  organic  com- 
pounds, in  which  that  element  is  united  with  carbon,  hydrogen,  &c.  The  organic 
compound  is  mixed  with  a  large  excess  of  soda-lime  —  a  mixture  of  caustic  soda 
and  quick-lime,  the  latter  being  added  to  counteract  the  deliquescence  of  the 
hydrate  of  soda, — and  heated  to  redness  in  a  combustion-tube  (p.  277),  to  which 
is  attached  a  suitable  bulb-apparatus  containing  hydrochloric  acid.  The  ammonia 
is  thtreby  absorbed,  and  is  subsequently  precipitated  by  chloride  of  platinum,  in 
the  manner  described  at  page  619  of  this  volume.  This  method  gives  very  exact 
results ;  but  it  is  not  applicable  to  compounds  containing  nitrogen  in  the  form  of 
nitric  acid  or  of  peroxide  of  nitrogen,  because  in  such  compounds  the  conversion 

*  Ann.  Ch.  Phys.  [3],  xxvi.  296.  f  Compt.  rend,  xxxiii.  401. 

I  Ann.  Ch.  Phys.  [81,  xxiii.  229.  g  Ann.  Ch.  Phys.  [3],  216. 

|J  Ann.  Ch.  Phys.  [3],  xxviii.  241.  \  Compt.  rend,  xxviii.  323. 


ESTIMATION    OF    NITROGEN.  767 

of  the  nitrogen  into  ammonia  by  heating  with  caustic  alkalies  is  never  complete. 
For  such  compounds,  it  is  better  to  evolve  the  nitrogen  in  the  free  state,  and  deter- 
mine its  quantity  by  measurement.  This  may  be  done  either  comparatively  or 
absolutely. 

For  the  comparative  determination,  the  azotized  organic  compound  is  mixed 
with  oxide  of  copper,  and  heated  in  a  combustion-tube,  the  open  end  of  which, 
to  the  depth  of  four  or  five  inches,  is  filled  with  finely-divided  metallic  copper, 
obtained  by  reducing  the  oxide  with  hydrogen.  By  the  oxidizing  action  of  the 
oxide  of  copper,  the  carbon  of  the  organic  compound  is  converted  into  carbonic 
acid,  and  the  nitrogen  into  nitric  oxide  and  other  oxides  of  nitrogen,  all  of  which 
are,  however,  completely  decomposed  in  passing  over  the  red-hot  metallic  copper, 
so  that  nothing  but  nitrogen  and  carbonic  acid  pass  out.  These  gases  are  col- 
lected over  mercury  in  a  graduated  tube,  and  their  volume  measured.  The  car- 
bonic acid  is  then  absorbed  by  potash,  and  the  residual  nitrogen  also  measured. 
Now  the  weights  of  equal  volumes  of  nitrogen  and  carbonic  acid  are  to  one 
another  as  14  to  22  (p.  130),  that  is  to  say,  as  the  atomic  weights  of  N  and  C02; 
and  each  atom  of  carbonic  acid  contains  one  atom  of  carbon.  Consequently,  the 
volumes  of  nitrogen  and  carbonic  acid  produced  by  the  combustion  of  the  organic 
compound,  are  to  one  another  as  the  numbers  of  atoms  of  nitrogen  and  carbon. 
This  method,  of  course,  implies  that  the  carbon  in  the  organic  compound  has  been 
previously  determined. 

For  the  absolute  determination  of  nitrogen,  the  same  method  of  combustion  and 
collecting  the  gas  is  adopted,  excepting  that  a  longer  combustion-tube  is  used,  and 
a  quantity  of  bicarbonate  of  soda  is  placed  at  the  sealed  end,  sufficient  to  occupy 
about  eight  inches  of  the  tube.  The  process  is  commenced  by  heating  a  portion 
of  this  bicarbonate  of  soda,  so  as  to  evolve  carbonic  acid,  and  sweep  all  the  air  out 
of  the  tube.  The  substance  is  then  burned,  and  the  evolved  gases  collected  over 
mercury,  the  carbonic  acid  being  absorbed  by  strong  potash-ley  placed  at  the  top 
of  the  mercury ;  and  when  the  combustion  is  ended,  the  remainder  of  the  bicar- 
bonate of  soda  is  heated  so  as  to  evolve  more  carbonic  acid,  and  drive  all  the  re- 
maining gases  out  of  the  tube.  The  volume  of  nitrogen  collected  is  then  read  off 
and  its  weight  calculated,  the  proper  corrections  being  made  for  pressure  and  tem- 
perature. Dr.  M.  Simpson,  of  Dublin,  has  proposed  certain  modifications  both 
in  this  and  in  the  comparative  method  of  estimating  nitrogen,  with  the  view  of  faci- 
litating the  process  and  insuring  greater  accuracy.  The  principal  of  these  atten- 
tions is  the  replacement  of  the  oxide  of  copper  by  oxide  of  mercury,  which  gives 
up  its  oxygen  more  readily,  and,  therefore,  insures  a  more  complete  combustion, 
especially  when  the  substance  is  rich  in  carbon.* 

The  method  of  combustion  with  oxide  of  copper  and  decomposition  of  the 
oxides  of  nitrogen  by  metallic  copper,  is  applicable  to  all  nitrogen  compounds 
whatsoever.  For  the  analysis  of  nitrates,  in  which  the  nitrogen  is  already  com- 
pletely oxidized,  the  oxide  of  copper  may  be  dispensed  with,  the  salt  being  simply 
ignited  in  a  tube,  and  the  nitrous  vapours  passed  over  red-hot  metallic  copper. 
Nitric  acid  may  also  be  determined  by  several  other  methods.  When  it  exists  in 
the  free  state  in  aqueous  solution,  its  quantity  may  be  determined  by  shaking  up 
the  liquid  with  carbonate  of  baryta,  till  the  nitric  acid  is  completely  neutralized, 
then  filtering,  evaporating  the  filter  to  dryness,  care  being  taken  not  to  heat  the 
residue  too  strongly,  and  weighing  the  dry  nitrate  of  baryta  thus  obtained.  Or 
the  solution  of  nitrate  of  baryta  may  be  decomposed  by  sulphuric  acid,  th$  sul- 
phate of  baryta  weighed,  and  the  .equivalent  quantity  of  nitric  acid  calculated 
therefrom.  If  the  solution  of  nitric  acid  is  very  weak,  it  is  better  to  use  baryta- 
water  to  neutralize  it;  then  pass  carbonic  acid  gas  through  the  liquid  to  remove 
any  excess  of  baryta;  filter;  and  treat  the  filtered  solution  of  nitrate  of  baryta  as 
above. 

*  Chem.  Soc.  Qu.  J.  vi.  289 


768  NITROGEN. 

When  nitric  acid  is  combined  with  a  base,  it  may  be  liberated  by  distillation 
with  sulphuric  acid  (p.  260),  and  the  distillate  treated  with  carbonate  of  baryta 
or  baryta-water,  in  the  manner  already  described.  Or  a  weighed  portion  of  the 
nitrate  may  be  decomposed  by  sulphuric  acid  in  a  platinum  crucible,  the  residual 
sulphate  ignited  and  weighed,  and  the  quantity  of  nitric  acid  thence  determined 
by  calculation.  This  method,  however,  is  applicable  only  when  the  sulphate  thus 
formed  can  bear  a  red-heat  without  decomposition. 

For  the  estimation  of  small  quantities  of  nitric  acid,  such  as  exist  in  plants, 
soils,  and  waters,  some  very  ingenious  methods  have  been  inrented  by  M.  G. 
Ville.*  The  nitric  acid  is  first  converted  into  binoxide  of  nitrogen  by  boiling  the 
solution  of  the  nitrate  with  protochloride  of  iron  and  free  hydrochloric  acid : 

N05  +  6FeCl  +  3HC1  =  N02  +  3Fe2Cl3  +  3HO; 

and  the  nitric  oxide  then  converted  into  ammonia,  either  by  passing  it,  mixed 
with  excess  of  hydrogen,  over  spongy  platinum  heated  nearly  to  redness; 

N02  +  5H  =  NH3-f  2HO; 

or  by  passing  it,  mixed  with  excess  of  hydrogen  and  hydrosulphuric  acid,  over 
soda-lime  heated  nearly  to  redness : 

N02  +  3HS  +  2CaO  =  NH3  -f  CaO.S03  +  CaS2. 

The  second  method  is  generally  the  more  exact  of  the  two,  the  first  giving  accu- 
rate results  only  when  the  quantity  of  nitrogen  to  be  determined  is  very  small. 
The  ammonia  is  absorbed  by  an  acid  of  known  strength  contained  in  a  bulb-appa- 
ratus, and  its  quantity  determined  by  the  alkalimetric  method  (p.  386)  ;  or  it 
may  be  absorbed  by  hydrochloric  acid,  and  precipitated  by  chloride  of  platinum. 
Another  method  is  to  pass  the  nitric  oxide  over  red-hot  metallic  copper;  but  this 
method  is  not  so  exact  as  the  preceding.  To  apply  these  methods  to  the  determi- 
nation of  the  quantity  of  nitrates  in  vegetable  substances,  soils,  waters,  &c.,  the 
substance  (10  to  100  grammes)  is  exhausted  with  boiling  water,  and  the  concen- 
trated solution  treated  as  above. 

Professor  Way  has  also  devised  a  method  of  estimating  small  quantities  of  nitric 
acid,  especially  adapted  to  rain-water  and  other  waters.  This  process,  which  is  a 
modification  of  Bunsen's  volumetric  method,  consists  in  heating  the  solid  residue 
obtained  by  evaporating  about  a  pint  of  the  water  —  previously  rendered  alkaline 
by  lime-water  to  prevent  loss  of  nitric  acid — with  hydrochloric  acid  and  iodide  of 
silver,  in  an  apparatus  from  which  the  air  has  been  completely  excluded  by  a 
stream  of  carbonic  acid  gas,  and  exhaustion  with  the  air-pump.  The  nitrates  and 
the  hydrochloric  acid  then  decompose  each  other,  with  separation  of  nitric  oxide 
and  chlorine;  and  the  chlorine  decomposes  the  iodide  of  silver,  liberating  iodine, 
the  amount  of  which  is  afterwards  determined  by  a  standard  solution  of  sulphu- 
rous acid  in  the  manner  to  be  hereafter  described.  Organic  matter,  if  present  in 
the  water,  must  be  destroyed  by  adding  a  small  quantity  of  permanganate  of 
potash,  during  the  concentration  of  the  liquid. 

The  determination  of  the  quantity  of  nitric  acid  in  nitrate  of  potash  is  a  process 
of  considerable  commercial  importance,  and  several  methods  have  been  devised  for 
it.  Of  these,  however,  there  are  only  two  in  general  use.  The  first,  originally 
introduced  by  Gossart  and  improved  by  Pelouze,  consists  in  boiling  the  acidified 
solution  of  the  nitre  with  a  solution  of  protochloride  of  iron  of  known  strength, 
whereby  the  protoxide  of  iron  is  converted  into  sesquioxide,  and  binoxide  of 
nitrogen  is  evolved,  and  afterwards  determining  the  unoxidized  portion  of  the  iron 
by  the  method  of  Margueritte,  with  a  standard  solution  of  permanganate  of  potash, 
(p.  458).  According  to  Messrs.  Abel  and  Bloxam,f  this  method  does  not  alwaye 
give  exact  results,  because  a  portion  of  the  nitre  does  not  contribute  to  the  oxid- 
izing action,  either  from  not  being  completely  decomposed,  or  from  losing  a  portion 

*  Ann.  Ch.  Phys.  [3],  vi.  20.  f  Chem.  Soc.  Qu.  J.  ix.  97 ;  x.  107. 


CARBON.  769 

of  its  acid  before  it  comes  in  contact  with  the  iron-salt.  The  other  method,  intro- 
duced by  Gay-Lussac,  consists  in  deflagrating  the  nitre  with  one-fourth  of  its 
weight  of  finely  divided  charcoal  (lamp-black)  and  6  parts  of  common  salt,  the 
latter  being  added  merely  to  moderate  the  action.  The  nitrate  of  potash  is  then 
converted  "into  carbonate,  the  quantity  of  which  in  the  ignited  residue  may  be 
determined  by  the  process  of  alkalimetry  (p.  260).  This  method  is  also  variable 
in  its  results,  partly  because  a  portion  of  the  nitre  is  apt  to  escape  decomposition, 
partly  because  cyanate  of  potash  is  formed  during  the  reaction,  and,  when  subse- 
quently dissolved  in  water,  is  decomposed,  with  formation  of  carbonate  of  ammonia 
and  carbonate  of  potash  : 

C2NK02  +  4HO  =  KO.C02  +  NH4O.C02. 

Hence,  the  quantity  of  alkali  to  be  neutralized  by  the  acid  is  greater  than  it 
should  be.  The  presence  of  alkaline  sulphates  in  the  nitre  also  introduces  an 
error,  because  these  salts  are  reduced  by  ignition  with  charcoal  to  sulphides,  which 
have  an  alkaline  reaction.  Messrs.  Abel  and  Bloxaui  find  that  these  several 
sources  of  error  may  be  eliminated,  and  exact  results  obtained,  by  using  the  char- 
coal in  a  very  finely  divided  state,  and  subsequently  heating  the  ignited  mass 
with  chlorate  of  potash,  which  completely  decomposes  the  cyanates  and  reconverts 
the  sulphides  into  sulphates.  The  best  form  of  carbon  for  the  purpose  was  found 
to  be  the  pure  finely  divided  graphite  prepared  by  Mr.  Brodie's  process  (p.  770). 

CARBON. 

Volatility  of  carbon. — According  to  Despretz,  charcoal  exposed  in  vacuo  to  the 
heat  produced  by  a  Bunsen's  battery  of  500  or  600  pairs,  disposed  in  5  or  6  series, 
so  as  to  form  100  pairs  of  5  or  6  times  the  ordinary  size,  is  volatilized,  and  collects 
on  the  sides  of  the  vessel  in  the  form  of  a  black  crystalline  powder;  in  a  space 
filled  with  a  gas  with  which  the  carbon  does  not  combine,  volatilization  likewise 
takes  place,  but  more  slowly.  At  the  same  temperature,  charcoal  may  also  be 
bent,  welded,  and  fused,  every  kind  of  charcoal  when  thus  treated  becoming  softer 
the  longer  the  heat  is  continued,  and  being  ultimately  converted  into  graphite. 
Diamond  exposed  to  the  same  temperature  is  likewise  converted  into  graphite.* 

Charcoal  as  a  disinfectant. — The  power  which  wood-charcoal  possesses  of 
absorbing  and  decomposing  gaseous  bodies  has  lately  been  applied  by  Dr.  Sten- 
house  to  the  construction  of  ventilators  and  respirators  for  purifying  in/ected 
atmospheres.  In  a  pamphlet,  bearing  the  title  "  On  Charcoal  as  a  Disinfectant/7 
Dr.  Stenhouse  observes  —  "  Charcoal  not  only  absorbs  effluvia  and  gaseous  bodies, 
but,  especially,  when  in  contact  with  atmospheric  air,  rapidly  oxidizes  and  destroys 
many  of  the  easily  alterable  ones,  by  resolving  them  into  the  simplest  combinations 

they  are  capable  of  forming,  which  are  chiefly  water  and  and  carbonic  acid 

effluvia  and  miasmata  are  generally  regarded  as  highly  organized,  nitrogenous, 
easily  alterable  bodies.  When  these  are  absorbed  by  charcoal,  they  come  in  con- 
tact with  highly  condensed  oxygen  gas,  which  exists  within  the  pores  of  all  char- 
coal which  has  been  exposed  to  the  air,  even  for  a  few  minutes;  in  this  way  they 
are  oxidized  and  destroyed."  On  this  principle,  Dr.  Stenhouse  has  constructed 
ventilators,  consisting  of  a  layer  of  charcoal  enclosed  between  two  sheets  of  wire 
gauze,  to  purify  the  foul  air  which  accumulates  in  water-closets,  the  wards  of 
hospitals,  and  in  the  back  courts  and  lanes  of  large  cities.  By  the  use  of  these 
ventilators,  pure  air  may  be  obtained  from  exceedingly  impure  sources,  the  im- 
purities being  absorbed  and  retained  by  the  charcoal,  while  a  current  of  pure  air 
alone  is  admitted  into  the  neighbouring  apartments.  A  similar  contrivance  might 
also  be  applied  to  the  gully-holes  of  our  common  sewers,  and  to  the  sinks  in 
private  houses.  Dr.  Stenhouse  has  also  constructed  respirators,  consisting  of  a 

*  Compt.  rend,  xxviii.  755. 
49 


770  CARBON. 

layer  of  charcoal  a  quarter  of  an  inch  thick,  interposed  between  two  sheets  of  sil- 
vered wire  gauze,  covered  with  woollen  cloth.  They  are  made  either  to  cover  the 
mouth  and  nose,  or  the  mouth  alone  ;  the  former  kind  of  respirator  affords  an 
effectual  protection  against  malaria  and  the  deleterious  gases  which  accumulate 
in  chemical  works,  common  sewers,  &c.  The  latter  will  answer  the  same  purpose 
when  the  atmosphere  is  not  very  impure,  provided  the  simple  precaution  be  taken 
of  inspiring  the  air  by  the  mouth,  and  expiring  by  the  nose.  This  form  of  res- 
pirator may  also  be  useful  to  persons  affected  with  fetid  breath.  Freshly  heated 
wood-charcoal  simply  placed  in  a  thin  layer  in  trays,  and  disposed  about  infected 
apartments,  such  as  the  wards  of  hospitals,  is  also  highly  efficacious  in  absorbing 
the  noxious  matter. 

Platinized  charcoal.  —  The  power  of  charcoal  in  inducing  chemical  combina- 
tion is  greatly  increased  by  combination  with  minutely  divided  platinum.  In  this 
manner,  a  combination  may  be  produced  possessing  the  absorbent  power  of  char- 
coal (which  is  much  greater  than  that  of  spongy  platinum),  and  nearly  equal,  as 
a  promoter  of  chemical  combination,  to  spongy  platinum  itself.  In  order  to 
platinize  charcoal,  nothing  me '9  is  necessary  than  to  boil  it,  either  in  coarse 
powder  or  in  large  pieces,  in  a  solution  of  bichloride  of  platinum,  and,  when 
thoroughly  impregnated,  which  seluom  requires  more  than  ten  minutes  or  a 
quarter  of  an  hour,  to  heat  it  to  redness  in  a  close  vessel,  a  capacious  platinum 
crucible  being  well  adapted  for  the  purpose.  Charcoal  thus  platinized,  and  con- 
taing  3  grains  of  platinum  in  50  grains  of  charcoal,  causes  oxygen  and  hydrogen 
gases  to  unite  completely  in  a  few  minutes;  with  a  larger  proportion  of  platinum, 
the  gases  combine  with  explosive  violence,  just  as  if  platinum-black  were  used. 
Cold  platinized  charcoal,  held  in  a  jet  of  hydrogen,  speedily  becomes  incandescent, 
and  inflames  the  gas.  Platinized  charcoal,  slightly  warmed,  rapidly  becomes 
incandescent  in  a  current  of  coal  gas;  but  does  not  inflame  the  gas,  owing  to  the 
very  high  temperature  required  for  that  purpose.  In  the  vapour  of  alcohol,  or 
wood-spirit,  platinized  charcoal  becomes  red-hot,  and  continues  so  till  the  supply 
of  vapour  is  exhausted.  Spirit  of  wine,  in  contact  with  platinized  charcoal  and 
air,  is  converted  in  a  few  hours  into  vinegar.  Two  per  cent,  of  platinum  is  suffi- 
cient to  platinize  charcoal  for  most  purposes.  Charcoal  containing  this  amount  of 
platinum  causes  oxygen  and  hydrogen  to  combine  perfectly  in  about  a  quarter  of 
an  hour,  and  such  is  the  strength  of  platinized  charcoal  -which  seems  best  adapted 
for  disinfectant  respirators.  Charcoal  containing  only  one  per  cent,  of  platinum 
causes  oxygen  and  hydrogen  lo  combine  in  about  two  hours ;  and  charcoal  con- 
tainiri*g  the  extremely  small  amount  of  \  per  cent,  of  platinum  produces  the  same 
effect  in  six  6r  eight  hours.  Platinized  charcoal  seems  likely  to  admit  of  various 
useful  applications ;  one  of  the  most  obvious  of  these  is  its  excellent  adaptability 
to  air-filters  and  respirators.  From  its  powerful  oxidizing  properties,  it  may  also 
prove  a  highly  useful  application  to  malignant  ulcers  and  similar  sores,  on  which 
it  will  act  as  a  mild  but  effective  caustic.  It  will  probably  also  be  found  very 
useful  in  Bunsen's  carbon  battery  (Stenhouse).* 

Graphite. — This  substance  may  be  obtained  in  the  pure  and  finely  divided  state 
by  mixing  it  in  coarse  powder  with  y^th  "of  its  weight  of  'chlorate  of  potash, 
adding  the  mixture  to  a  quantity  of  strong  sulphuric  acid  equal  to  twice  the 
weight  of  the  graphite ;  heating  the  mixture  in  the  water-bath  as  long  as  vapours 
of  peroxide  of  chlorine  are  emitted;  washing  the  cooled  mass  with  water,  and 
igniting  the  dry  residue :  it  then  swells  up  and  leaves  finely-divided  graphite.  A 
chemical  compound  of  sulphuric  acid  with  a  peculiar  oxide  of  carbon  appears  to 
be  formed  during  the  process.  If  the  graphite  to  be  purified  contains  silicious 
matters,  a  small  quantity  of  fluoride  of  sodium  must  be  added  to  the  mixture 
before  heating  (Brodief). 

*  Chem.  Soc.  Qu.  J.  viii.  105.  f  Ann.  Ch.  Phys.  [3],  xlv.  351. 


ESTIMATION    OF    CARBON.  771 

Carbonic  oxide.  —  This  gas  is  rapidly  absorbed  by  a  solution  of  subchloride  of 
copper  in  hydrochloric  acid  or  ammonia,  and  indeed  by  the  ammoniacal  solutions 
of  cuprous  salts  in  general,  e.  g.,  the  sulphite.  A  definite  compound  is  probably 
formed,  containing  copper  and  carbonic  oxide  in  equal  numbers  of  atoms,  but  no 
such  compound  has  yet  been  isolated.  Ferrous  and  stannous  salts  have  no  action 
on  carbonic  oxide  (Leblanc*). 

Preparation  of  defiant  gas  (p.  285). — The  frothing  which  causes  so  much  in- 
convenience in  the  preparation  of  this  gas  by  the  action  of  sulphuric  acid  upon 
alcohol,  may  be  completely  prevented  by  adding  a  sufficient  quantity  of  sand  to 
convert  the  mixture  into  a  thick,  scarcely  fluid  mass.  The  decomposition  may 
then  be  carried  to  the  end  without  any  frothing,  and  nearly  all  the  carbon  of  the 
alcohol  is  obtained  in  the  form  of  olefiant  gas.  Fifty  grammes  of  alcohol  of  the 
strength  of  80  per  cent,  yield  by  this  process  more  than  22  litres  of  gas  (Wohlerf). 

Quantitative  estimation  of  Carbon  and  its  compounds.  —  The  greater  number 
of  carbon-compounds  are  of  organic  nature,  and  contain  hydrogen  as  well  as  carbon. 
Hence  these  two  elements  are  generally  estimated  together,  the  process  consisting 
in  burning  the  compound  with  a  large  excess  of  oxide  of  copper,  whereby  the 
carbon  is  converted  into  carbonic  acid,  and  the  hydrogen  into  water.  The  car- 
bonic acid  is  absorbed  in  a  weighed  apparatus  containing  caustic  potash,  and  the 
excess  of  weight  after  the  absorption,  gives  the  quantity  of  carbonic  acid  produced 
by  the  combustion,  T3T  of  which  is  the  weight  of  the  carbon.  The  water  is  ab- 
sorbed in  a  weighed  apparatus  containing  dry  chloride  of  calcium,  and  -|  of  its 
weight  gives  that  of  the  hydrogen.  The  apparatus  used  for  the  analysis  is  de- 
scribed and  delineated  at  page  277.  For  compounds  which,  like  oxalic  acid  and 
sugar,  are  easily  burned,  the  process  of  heating  with  oxide  of  copper  affords  a 
complete  combustion  of  the  carbon,  and  gives  exact  results;  but  when  the  pro- 
portion of  carbon  is  very  large,  especially  in  fatty  substances,  which  are  not  easy 
to  burn,  a  different  method  must  be  adopted.  Such  bodies  are  either  burned  with 
chromate  of  lead,  which  at  a  red  heat  gives  off  free  oxygen  j  or  they  are  burned 
with  oxide  of  copper,  and  towards  the  end  of  the  process,  a  stream  of  oxygen  is 
passed  through  the  tube,  either  by  placing  at  the  closed  extremity  a  quantity  of 
perfectly  dry  chlorate  of  potash,  and  heating  this  salt,  when  the  combustion  of 
the  organic  substance  by  the  oxide  of  copper  appears  to  be  nearly  ended,  —  or 
better,  by  leaving  that  end  of  the  tube  open  and  connecting  it  with  a  gas-holder 
containing  oxygen. J  In  this  manner,  the  last  traces  of  carbon  are  effectually 
burned. 

The  quantity  of  carbonic  acid,  in  a  carbonate  may  be  easily  determined  by  de- 
composing the  carbonate  with  sulphuric  or  hydrochloric  acid  in  the  apparatus  re- 
presented at  page  438,  the  flask  being  weighed  before  and  after  the  decomposition, 
and  the  quantity  of  carbonic  acid  estimated  by  the  decrease  of  weight  resulting 
from  its  evolution. 

The  quantity  of  carbonic  acid  contained  in  an  aqueous  solution,  a  mineral  water 
for  instance,  may  also  be  determined  by  mixing  the  solution  with  chloride  of  cal- 
cium and  excess  of  ammonia,  and  leaving  it  for  a  day  in  a  corked  flask.  The 
precipitated  carbonate  of  lime  is  then  collected  on  a  filter,  washed,  dried,  and 
weighed. 

The  amount  of  carbonic  acid  in  a  gaseous  mixture  not  containing  any  other 
acid,  is  estimated  by  absorbing  the  carbonic  acid  with  caustic  potash.  When  the 
proportion  of  carbonic  acid  in  the  mixture  is  considerable,  this  end  may  be  at- 

*  Compt.  rend.  xxx.  48.  f  Ann.  Pharm.  xci.  127. 

J  For  details  of  the  apparatus,  and  the  mode  of  proceeding,  see  H.  Rose  (Hanb.  d.  Analyt. 
Cftem.  ii.  956),  and  Gerhardt  ( Traite  de  Chimie  Organique,  i.  35).  A  very  convenient  appa- 
ratus for  the  purpose  has  lately  been  introduced  by  Dr.  Hofmann. 


772  CARBON. 

tained  by  placing  the  gaseous  mixture  in  a  graduated  tube  over  mercury  and  pass- 
ing up  into  it  a  small  coke  ball  containing  a  strong  solution  of  caustic  potash ;  but 
when  the  proportion  is  very  small,  as  in  the  air,  this  method  is  not  sufficiently 
delicate.  Accurate  results  may,  however,  be  obtained  by  drawing  a  considerable 

Quantity  of  air,  by  means  of  an  aspirator,  through  a  series  of  potash-bulbs 
p.  277)  previously  weighed,  the  quantity  of  air  drawn  through  being  of  course 
carefully  measured.  Another  method  has  recently  been  proposed  by  Dr.  Petten- 
kofer ;  it  consists  in  shaking  up  a  quantity  of  the  air  in  a  closed  vessel  of  known 
capacity,  with  an  excess  of  lime-water  of  known  strength,  and  then  determining 
the  quantity  of  lime  remaining  uncombined  by  means  of  a  standard  solution  of 
oxalic  acid.  This  method  is  very  easy  of  execution,  and  gives  the  means  of 
quickly  determining  the  varying  amount  of  carbonic  acid  in  the  several  parts  of 
an  inhabited  apartment  at  different  times. 

Carbonic  oxide  is  most  readily  estimated  and  removed  from  a  gaseous  mixture 
by  means  of  a  solution  of  dichloride  of  copper  (p.  478)  in  hydrochloric  acid, 
which  absorbs  it  as  quickly  and  completely  as  potash  absorbs  carbonic  acid.  When 
no  other  gaseous  compound  of  carbon  is  present,  the  quantity  of  this  gas  may  also 
be  determined  by  exploding  it  with  oxygen,  and  absorbing  the  resulting  carbonic 
acid  by  potash.  For,  since  carbonic  acid  contains  its  own  volume  of  oxygen,  and 
carbonic  oxide  contains  half  its  volume  of  oxygen,  it  follows,  that  if  carbonic 
oxide  be  exploded  with  half  its  volume  of  oxygen,  the  volume  of  carbonic  acid 
produced  will  be  equal  to  that  of  the  carbonic  oxide  consumed  :  hence  the  volume 
of  carbonic  oxide  is  equal  to  that  of  the  gas  which  disappears  by  absorption  with 
potash. 

The  quantity  of  marsh  gas  or  olefiant  gas  in  a  gaseous  mixture,  not  containing 
any  other  carbon  compound,  may  be  determined  in  a  similar  manner.  Four  volumes 
of  marsh  gas,  C2H4,  require  for  complete  combustion  8  volumes  of  oxygen,  and  pro- 
duce 4  volumes  of  carbonic  acid.  For  the  2  atoms  of  carbon  require  4  atoms  of 
oxygen,  to  convert  them  into  carbonic  acid ;  and  the  4  atoms  of  hydrogen  require 
4  atoms  oxygen  to  convert  them  into  water;  therefore,  in  all,  8  atoms  or  8  volumes 
(p.  130}  of  oxygen  :  moreover,  the  four  volumes  of  oxygen  required  to  consume 
the  carbon  produce  4  volumes  of  carbonic  acid ;  hence  the  volume  of  gas  which 
disappears  by  absorption  with  potash  is  equal  to  the  original  volume  of  the  marsh 
gas. 

By  a  similar  calculation,  it  is  found  that  4  volumes  of  olefiant  gas,  C4H4,  require 
12  volumes  of  oxygen  for  complete  combustion,  and  produce  8  volumes  of  car- 
bonic acid :  hence  the  volume  of  olefiant  gas  is  equal  to  half  the  volume  of  gas 
removed  by  potash  after  the  explosion.  Olefiant  gas  may  also  be  removed  from  a 
gaseous  mixture  by  the  introduction  of  a  coke-ball  saturated  with  anhydrous  sul- 
phuric acid  or  fuming  oil  of  vitriol  (p.  717). 

For  the  methods  of  analyzing  gaseous  mixtures  containing  marsh  gas  and  ole- 
fiant gas  mixed  with  hydrogen,  carbonic  oxide,  nitrogen,  and  other  gases,  I  must 
refer  to  works  in  which  the  operations  of  gas-analysis  are  explained  in  detail.* 

Oxalic  acid  is  precipitated  from  its  aqueous  solution,  or  from  solutions  of  the 
alkaline  oxalates,  by  chloride  of  calcium,  ammonia  being  added  if  necessary  to 
render  the  solution  neutral.  The  precipitated  oxalate  of  lime  is  converted  by 
ignition  at  a  low  red  heat  into  carbonate,  from  the  weight  of  which  the  quantity 
of  oxalic  acid  may  be  calculated,  each  atom  of  carbonate  of  lime  (CaO .  C02)  cor- 
responding to  1  atom  of  anhydrous  oxalic  acid,  C203 :  — 

CaO.CA   =   CaO.C02    +    CO. 

Oxalate  of  Carbonate  of 

lime.  lime. 

*  Bunsen's  "Gasometry,"  translated  by  Roscoe,  London,  1857;  and  Regnault,  "Conrs 
Etementaire  de  Chimie,"  2me.  ed.  Paris,  torn.  iv.  pp.  73-103. 


BORON.  773 

Consequently,  50  parts  of  carbonate  of  lime  give  36  parts  of  anhydrous  oxalic 
acid,  Ca03,  or  45  parts  of  the  hydrated  acid,  C2H04.  In  neutralizing  the  solu- 
tion of  an  acid  oxalate  with  ammonia,  care  must  be  taken  to  avoid  excess  of  the 
alkali,  as  in  that  case  carbonic  acid  will  be  absorbed  from  the  air,  and  carbonate 
of  lime  will  be  precipitated  as  well  as  oxalate.  It  is  better,  however,  to  precipi- 
tate oxalic  acid  from  its  acid  solutions  with  acetate  of  lime,  as  oxalate  of  lime  is 
quite  insoluble  in  acetic  acid. 

Oxalic  acid  may  also  be  very  exactly  estimated  by  means  of  a  solution  of  ter- 
chloride  of  gold.  The  gold  is  then  reduced  to  the  metallic  state,  water  is  decom- 
posed, and  the  liberated  oxygen  converts  the  oxalic  acid  into  carbonic  acid :  — 

3C203  +  AuCl3  +  3HO  =  6C02  +  3HC1  +  Au. 

The  decomposition  may  be  performed  in  the  flask  apparatus  already  referred  to 
(fig.  438,  p.  186).  It  takes  place  at  ordinary  temperatures,  but  the  liquid  must 
be  boiled  at  the  end  of  the  process  to  expel  the  last  portions  of  carbonic  acid.  This 
method  may  be  applied  to  the  decomposition  of  all  oxalates,  whether  soluble  or 
insoluble  in  water,  the  insoluble  oxalates  being  dissolved  in  hydrochloric  acid. 
An  excess  of  that  acid  in  the  concentrated  state,  however,  greatly  interferes  with 
the  action;  the  liquid  should,  therefore,  be  considerably  diluted  with  water,  and 
the  action  assisted  by  heat.  The  preceding  equation  shows  that  2  atoms  carbonic 
acid,  C02,  correspond  to  1  atom  of  anhydrous  oxalic  acid,  C203,  or  11  parts  by 
weight  of  carbonic  acid  to  9  parts  of  anhydrous  oxalic  acid. 

Another  mode  of  converting  oxalic  acid  into  carbonic  acid,  is  by  acting  upon  it, 
either  in  the  free  or  combined  state,  with  binoxide  of  manganese  and  sulphuric  or 
hydrochloric  acid  (p.  438). 

Oxalic  acid,  either  free  or  combined,  is  resolved,  by  heating  with  an  excess  of 
strong  sulphuric  acid,  into  a  mixture  of  equal  volumes  of  carbonic  acid  and  car- 
bonic oxide.  This  method  may  also  be  applied  to  the  estimation  of  oxalic  acid, 
but  it  is  not  so  accurate  as  the  preceding. 

Lastly,  the  quantity  of  oxalic  acid  in  an  oxalate  may  be  estimated  by  burning 
the  compound  with  oxide  of  copper  (p.  771). 

Estimation  of  Cyanogen.  — The  quantity  of  cyanogen  in  a  soluble  cyanide  is 
easily  determined  by  precipitation  with  nitrate  of  silver.  The  precipitated  cyanide 
of  silver  is  collected  on  a  weighed  filter  and  dried  at  100°  C.  Every  134  parts  of 
it  contain  26  parts  of  cyanogen.  Many  insoluble  cyanides  may  be  decomposed  by 
boiling  with  sulphuric  or  hydrochloric  acid,  hydrocyanic  acid  being  evolved,  and 
the  metal  remaining  as  sulphate  or  chloride,  from  the  weight  of  which  the  quantity 
of  cyanogen  which  has  gone  off  may  be  calculated.  Lastly,  all  cyanogen  com- 
pounds whatever  may  be  analyzed  by  burning  with  oxide  of  copper,  in  the  manner 
already  described. 

BORON. 

This  element  was  formerly  known  only  in  the  amorphous  state,  in  which  it  is 
obtained  by  the  action  of  potassium  on  boracic  acid  or  borofluoride  of  potassium. 
But  Wohler  and  Deville*  have  lately  obtained  it  in  two  distinct  crystalline  states, 
in  one  of  which  it  bears  a  close  resemblance  to  diamond,  and  in  the  other  to 
graphite. 

The  first  of  these  crystalline  forms  of  boron  is  obtained  by  decomposing  boracic 
acid  with  aluminium  at  a  high  temperature.  When  80  grammes  of  aluminium  in 
thick  lumps,  and  100  grammes  of  fused  or  pulverized  boracic  acid,  are  heated 
together  in  a  crucible  lined  with  charcoal  to  about  the  melting  point  of  nickel  for 
five  hours,  there  are  found  on  breaking  the  crucible  after  cooling,  two  distinct 
layers,  one  of  which  is  glassy,  and  consists  of  boracic  acid  and  alumina,  while  the 
other  is  metallic,  tumefied,  has  an  iron-grey  lustre,  and  consists  of  aluminium 

*  Compt.  rend,  xliii.  1088. 


774  BORON. 

mixed  with  a  considerable  quantity  of  crystallized  boron,  some  of  the  crystals  being 
distinctly  visible  at  the  surface.  The  aluminium  is  dissolved  out  by  strong  boiling 
soda-ley,  and  the  residual  boron  is  freed  from  iron  by  digestion  in  hydrochloric 
acid,  and  from  traces  of  silicon  by  a  mixture  of  nitric  and  hydrofluoric  acids.  It 
is  still,  however,  mixed  with  laminae  of  alumina,  which  must  be  carefully  picked 
out. 

The  pure  product  thus  obtained  is  diamond-boron,  mixed,  however,  with  a  small 
quantity  of  graphitoidal  boron,  which  latter  being  very  light,  may  be  removed  by 
suspension  in  water.  Diamond-boron  forms  transparent  crystals,  having  a  honey- 
yellow  or  garnet-red  colour,  due  to  the  presence  of  small  quantities  of  foreign  sub- 
stances }  it  has  hitherto  been  obtained  only  in  confused  aggregates  of  small  crystals. 
In  lustre  and  refractive  power,  it  is  scarcely  inferior  to  the  diamond ;  and  is  one 
of  the  hardest  bodies  known,  inasmuch  as  it  scratches  corundum,  and  even  the 
diamond  itself.  It  does  not  fuse  at  the  heat  of  the  oxyhydrogen  blowpipe,  and 
withstands  the  action  of  oxygen  even  when  strongly  heated ;  but  it  is  slightly 
oxidized  at  the  temperature  at  which  the  diamond  burns,  a  film  of  boracic  acid 
being  then  formed,  which  protects  the  remainder  of  the  crystals  from  oxidation. 
Heated  to  redness  in  chlorine  gas,  it  burns  and  produces  chloride  of  boron. 
Heated  by  the  blowpipe  between  two  pieces  of  platinum-foil,  it  forms  a  fusible 
boride  of  platinum.  It  is  not  attacked  by  acids  at  any  temperature,  but  when 
heated  to  redness  with  bisulphate  of  potash,  it  is  converted  into  boracic  acid.  It 
is  not  attacked  by  a  strong  boiling  solution  of  caustic  soda;  but  hydrate  and  car- 
bonate of  soda  dissolve  it  slowly  at  a  red  heat.  Nitre  does  not  appear  to  act  upon 
it  sensibly  at  that  temperature. 

Graphitoidal  Boron  is  produced  in  small  quantity  simultaneously  with  diamond- 
boron  by  the  process  above  described.  But  it  is  obtained  much  more  readily  by 
treating  borofluoride  of  potassium  with  aluminium,  adding  as  a  flux  a  mixture  of 
equal  parts  of  chloride  of  potassium  and  chloride  of  sodium ;  in  this  manner, 
small  masses  of  boride  of  aluminium  are  obtained,  which,  when  digested  in  hydro- 
chloric acid,  leave  graphitoidal  boron.  The  lamina  of  this  substance  are  often 
hexagonal :  they  have  a  slight  reddish  colour,  and  the  form  and  lustre  of  native 
graphite.  They  are  always  opaque. 

Amorphous  boron  is  formed  in  the  preparation  of  diamond-boron  when  a  small 
globule  of  aluminium  comes  in  contact  with  a  large  quantity  of  boracic  acid,  so 
that  the  boron  does  not  dissolve  in  the  aluminium  as  fast  as  it  is  set  free.  In  this 
case,  after  the  aluminium  has  been  removed  by  the  use  of  caustic  soda  and  hydro- 
chloric acid,  the  boron  remains  as  an  amorphous  mass  of  a  light  chocolate  colour, 
and  exhibiting  the  properties  which  have  long  been  known  as  belonging  to  boron. 
When  the  amorphous  boron  is  collected  on  a  filter,  ^he  portion  which  remains 
adhering  to  the  filter,  burns,  when  the 'paper  is  dried  and  set  on  fire,  very  easily 
and  with  an  intense  light;  graphitoidal  boron,  under  the  same  circumstances, 
does  not  burn  at  all. 

Boracic  acid. — According  to  A.  Vogel,*  the  brown  colour  imparted  to  turmeric 
by  boracic  acid  is  distinguished  from  that  produced  by  alkalies,  by  not  being 
destroyed  by  the  action  of  acids.  Thus,  when  an  alcoholic  tincture  of  turmeric 
diluted  with  water  till  its  colour  becomes  light  yellow,  is  added  to  a  concentrated 
solution  of  borax,  the  yellow  colour  is  changed  to  brown  by  the  alkaline  reaction 
of  the  salt,  but  on  adding  a  certain  quantity  of  sulphuric  acid,  the  yellow  colour  is 
restored.  A  larger  quantity  of  sulphuric  acid  sets  free  the  boracic  acid,  and  again 
produces  a  brown  colour ;  which,  however,  does  not  disappear  on  further  addition 
of  the  acid. 

For  detecting  small  quantities  of  boracic  acid  in  solutions,  mineral  waters,  for 
instance,  H.  Hosef  acidulates  the  liquid  with  hydrochloric  acid,  dips  a  strip  of 

»  Repert.  Pharm.  iii.  178.  f  Handb.  d.  Analyt.  Chem.  i.  919,  946. 


ESTIMATION    OF    BORON.  775 

turmeric  paper  into  the  liquid,  and  then  leaves  it  to  dry;  if  boracic  acid  is  present, 
the  part  of  the  paper  which  has  been  immersed  in  the  liquid,  assumes  a  red-brown 
colour. 

Boracic  acid  being  but  a  weak  acid,  its  salts  are  often  decomposed  by  water. 
A  concentrated  solution  of  borax,  added  to  nitrate  of  silver,  throVs  down  white 
borate  of  silver ;  but  a  dilute  solution  —  which  in  fact  consists  of  borate  of  water 
mixed  with  free  soda — forms  a  brown  precipitate  of  oxide  of  silver.  If  to  a  strong 
solution  of  borax,  an  alcoholic  tincture  of  litmus  reddened  by  acetic  acid  be  added 
in  such  quantity  that  the  red  colour  is  nearly  but  not  quite  destroyed,  and  the 
liquid  be  then  diluted  with  water,  the  red  colour  is  immediately  changed  to  blue 
(H.  Rose).* 

Nitride  of  Boron,  BN.  — This  compound  was  discovered  by  Balmain,f  who  at 
first  regarded  it  as  capable  of  uniting  with  metals  and  forming  compounds  analo- 
gous to  the  cyanides,  but  afterwards  found  that  all  these  supposed  metallic  com- 
pounds were  one  and  the  same  substance,  viz.  nitride  of  boron,  without  any  appre- 
ciable amount  of  metal.  Balmain  obtained  this  substanc.e  by  heating  boracic  acid 
with  cyanide  of  potassium  or  cyanide  of  zinc,  or  with  cyanide  of  mercury  and 
sulphur.  It  has  since  been  more  completely  investigated  by  Wbhler,t  who  pre- 
pares it  by  heating  to  bright  redness,  in  a  porcelain  or  platinum  crucible,  a  mix- 
ture of  2  pts.  of  dried  sal-ammoniac  and  1  pt.  of  pure  anhydrous  borax.  The  pro- 
duct is  a  white  porous  mass,  which  is  pulverized  and  washed  with  water  to  free  it 
from  chloride  of  sodium.  The  final  washings  must  be  made  with  boiling-water 
acidulated  with  hydrochloric  acid.  Boracic  acid  may  be  used  in  the  preparation 
instead  of  borax.  Wohler  formerly  obtained  the  nitride  of  boron  by  igniting 
anhydrous  borax  with  ferrocyanide  of  potassium. 

Nitride  of  boron  is  a  white  amorphous  powder,  tasteless,  inodorous,  soft  to  the 
touch,  insoluble  in  water,  infusible,  and  non-volatile.  Heated  at  the  point  of  the 
blowpipe-flame,  it  burns  with  a  bright  greenish-white  flame.  It  easily  reduces 
the  oxides  of  copper  and  lead,  giving  off  nitrous  fumes.  Heated  in  a  current  of 
aqueous  vapour,  it  yields  ammonia  and  boracic  acid  :  — 

BN  -f  3HO  =  B03  +  NH3. 

Alkalies  and  the  greater  number  of  acids,  even  in  the  state  of  concentrated 
solution,  have  no  action  on  nitride  of  boron ;  strong  sulphuric  acid,  however,  with 
the  aid  of  heat,  ultimately  converts  it  into  ammonia  and  boracic  acid.  Fuming 
hydrofluoric  acid  converts  it  into  borofluoride  of  ammonium.  Nitride  of  boron 
undergoes  no  alteration  when  heated  in  a  current  of  chlorine.  WThen  fused  with 
hydrate  of  potash,  it  gives  off  a  large  quantity  of  ammonia.  With  anhydrous  car- 
bonate of  potash,  it  yields  borate  and  cyanate  of  potash  :  — 

BN  +  2(KO .  C02)  =  B03 .  KO  +  C2NO .  KO. 

It  does  not  decompose  carbonic  acid,  even  at  the  highest  temperatures.  Marjgnac§ 
found  also  that  nitride  of  boron  does  not  form  definite  compounds  with  metals, 
and  that  its  formula  is  BN. 

Estimation  of  Boron  and  Boracic  acid. — The  most  exact  method  of  estimating 
boron  is  to  convert  it  into  borofluoride  of  potassium,  KF  .  BF3.  If  the  substance  to 
be  treated  is  free  boracic  acid  or  an  alkaline  borate,  a  sufficient  quantity  of  potash 
is  first  added,  then  an  excess  of  pure  hydrofluoric  acid  (so  that  the  escaping 
vapours  may  redden  litmus),  and  the  mixture  is  evaporated  to  dryness  in  a  silver 
or  platinum  vessel.  The  dry  saline  mass  is  then  stirred  up  with  a  solution  of 

*  Ann.  Ch.  Pharm.  Ixxxiv.  216. 

f  Phil.  Mag.  [3],  xxi.  170?  xxii.  467;  xxiii.  71 ;  xxiv.  19.. 

j  Ann.  Ch.  Pharm.  Ixxiv.  70.  \  Aim.  Ch.  Pharm.  Ixxix.  247 


776  SILICON. 

acetate  of  potash  containing  20  per  cent,  of  the  salt;  then,  after  a  few  hours, 
thrown  on  a  weighed  filter,  and  the  precipitate  washed,  first  with  the  solution  of 
acetate  of  potash,  till  the  filtrate  no  longer  gives  a  precipitate  with  chloride  of 
calcium,  then  with  strong  alcohol,  and  dried  at  100°.  The  residue  consists  of 
borofluoride  of  potassium,  every  124-7  parts  of  which  correspond  to  34  9  of  boracic 
acid  and  10-9  of  boron. 

The  twenty  per  'cent,  solution  of  acetate  of  potash  dissolves  chloride  of  potas- 
sium and  phosphate  of  potash,  and  likewise  the  sulphate,  though  less  readily;  it 
also  dissolves  soda-salts ;  the  fluoride,  however,  slowly.  Any  other  bases  which 
may  be  combined  with  the  boracic  acid,  must  be  previously  separated  by  boiling 
or  fusing  the  compound  with  carbonate  of  potash  (A.  Stromeyer.)* 

Boracic  acid  cannot  be  estimated  in  its  aqueous  solution  by  simple  evaporation 
to  dryness,  since  a  large  quantity  of  it  goes  off  with  the  watery  vapour. 

SILICON. 

Silicon,  like  boron,  may  be  obtained  in  three  states  analogous  to  the  amorphous, 
graphitoidal,  and  diamond  forms  of  carbon.  The  amorphous  variety  is  that  which 
Berzelius  obtained  by  the  action  of  potassium  on  silicofluoride  of  potassium 
(p.  289).  H.  Ste-Claire  Devillef  prepares  amorphous  silicon  by  passing  the 
vapour  of  the  chloride  over  red-hot  sodium  in  an  atmosphere  of  dry  hydrogen. 
The  silicon  thus  obtained  exhibits,  after  washing  and  drying  at  a  moderate  heat, 
the  properties  described  by  Berzelius. 

Silicon  is  fusible  —  its  melting  point  being  intermediate  between  the  melting 
points  of  steel  and  cast  iron ;  but  when  heated  in  the  air,  it  quickly  becomes 
encrusted  with  a  coating  of  silicic  acid,  which  being  exceedingly  difficult  of 
fusion,  causes  the  silicon  also  to  appear  infusible. 

Graphitoidal  Silicon. — This  modification  of  silicon  was  first  obtained  by  Deville 
in  preparing  aluminium  by  the  electrolysis  of  the  double  chloride  of  aluminium 
and  sodium.  The  first  portions  of  aluminium  thus  obtained  are  contaminated 
with  silicon  derived  from  the  charcoal  electrodes ;  and  when  this  alloy  of  silicon 
and  aluminium  is  treated  with  hydrochloric  acid,  the  silicon  remains  undissolved 
in  the  form  of  shining  metallic  scales  resembling  graphite.  A  more  productive 
method  of  obtaining  this  variety  of  silicon  is  given  by  Wohler.J  It  consists  in 
mixing  aluminium  with  between  20  and  40  times  its  weight  of  silico-fluoride  of 
potassium,  and  heating  the  mixture  in  a  Hessian  crucible  to  the  melting  point  of 
silver.  A  metallic  button  is  thus  obtained,  which,  when  treated  successively 
with  hydrochloric  and  hydrofluoric  acids,  yields  graphitoidal  silicon,  partly  in 
isolated  hexagonal  tables,  the  edges  of  which  are  often  curved.  This  graphitoidal 
silicon  exhibits  all  the  properties  ascribed  by  Berzelius  to  silicon  which  has  been 
strongly  heated.  Its  density  is  2-49,  which  is  less  than  that  of  quartz  (from  2-6 
to  2-8).  It  may  be  heated  to  whiteness  in  oxygen  gas  without  burning  or  under- 
going any  alteration  in  weight ;  but  when  heated  to  redness  with  carbonate  of 
potash,  it  decomposes  the  carbonic  acid,  with  vivid  emission  of  light  and  formation 
of  silica.  It  is  not  attacked  by  any  acid.  A  strong  solution  of  potash  or  soda 
dissolves  it  slowly,  with  evolution  of  hydrogen.  Heated  to  commencing  redness 
in  dry  chlorine  gas,  it  burns  completely,  and  forms  chloride  of  silicon. 

Octahedral  or  Diamond  Silicon.  —  When  vapour  of  chloride  of  silicon  is 
passed  over  aluminium  kept  in  a  state  of  fusion  in  an  atmosphere  of  hydrogen, 
part  of  the  aluminium  is  converted  into  chloride,  which  volatilizes,  and  the  silicon 
thereby  separated  dissolves  in  the  remaining  aluminium,  which  thus  becomes  more 
and  more  saturated  with  silicon;  and  at  length  a  point  is  attained  at  which  the 
excess  of  silicon  separates  from  the  melted  aluminium  in  large  beautiful  needles, 

*  Ann.  Ch.  Pharm.  c.  82.  f  Ann.  Chem.  Phys.  [3],  xlix.  62. 

J  Compt.  rend.  xlii.  48. 


CHLORIDE    OF    SILICON    AND    HYDROGEN.  777 

having  a  dark  iron-grey  colour,  reddish  by  reflected  light,  and  exhibiting  irides- 
cence like  that  of  iron-glance.  These  crystals  are  derived  from  the  regular  octo- 
hedron,  and  often,  like  the  diamond,  exhibit  curved  faces;  they  are  very  hard, 
and  are  capable  of  scratching  and  of  cutting  glass  (Deville). 

Atomic  weight  of  Silicon.  — It  is  still  a  disputed  question  whether  the  atomic 
weight  of  silicon  should  be  21-35  or  14-1,  and  accordingly,  whether  the  formula 
of  the  oxide,  chloride,  &c.,  should  be  Si03,  SiCl8,  &o.,  or  Si02,  SiCla,  &c.  The 
vapour-density  of  the  chloride,  5-939  according  to  Dumas,  is  in  favour  of  the 
formula  SiCla,  which  gives  a  condensation  to  2  volumes  (or  rather  Si2Cl4,  giving  a 
condensation  to  4  vols.),  whereas  the  formula  SiCl3  would  involve  the  very  unusual 
condensation  to  3  volumes.  An  argument  in  favour  of  this  latter  formula  has 
been  drawn  from  the  difference  between  the  boiling  points  of  the  bromide  and 
chloride  of  silicon  (153°  —  59°  C  =  94  =  3  x  32  nearly),  inasmuch  as  the 
earlier  researches  of  H.  Kopp  had  led  him  to  conclude  that  the  boiling  points  of 
analogous  chlorides  and  bromides  generally  differ  by  multiples  of  32°  C.  Kopp 
has,  however,  more  recently  shown  that  this  law  is  very  far  from  being  a  general 
expression  of  observed  results,  and  that  the  difference,  23-5°  or  its  multiples, 
occurs  quite  as  frequently.  Now  the  difference  94  between  the  boiling  points  of 
bromide  and  chloride  of  silicon,  is  just  4  X  23'5,  and  is  therefore  so  far  con- 
sistent with  the  formulae  Si2Br4  and  Si2Cl4. 

Colonel  Yorke*  has  endeavoured  to  determine  the  formula  of  silicic  acid,  by 
ascertaining  the  quantity  of  carbonic  acid  displaced  from  excess  of  an  alkaline 
carbonate  by  fusion  with  a  given  weight  of  silica.  Experiments  with  carbonate 
of  potash  gave,  as  a  mean  result,  30-7  for  the  equivalent  of  silicic  acid,  agreeing 
with  the  formula  Si02  (14-1  +  2x8  =  30-1).  Experiments  with  carbonate  of 
soda  gave  21-3  for  the  equivalent  of  silicic  acid,  agreeing  nearly  with  half  that 
which  is  represented  by  the  formula  Si03  (21-35  +  3x8==  45-35).  Experi- 
ments with  carbonate  of  lithia  gave  the  number  14-99,  agreeing  nearly  with  the 
formula  SiO.  By  fusing  23  parts  of  silica  with  54  parts  of  carbonate  of  soda, 
dissolving  the  fused  mass  in  water,  and  evaporating  the  solution  in  vacuo,  a  crys- 
tallized salt  was  formed  containing  (besides  5  per  cent,  of  carbonate  of  soda)  the 
salt  NaO.Si02  +  7HO.  These  results  seem  to  show  that  silicon  is  capable  of 
uniting  with  oxygen  in  more  than  one  proportion,  a  conclusion  in  accordance  with 
the  results  obtained  by  other  experimenters. 

Wohler  and  Buff,"j"  by  heating  silicon  to  low  redness  in  a  current  of  dry  hydro- 
chloric acid  gas,  have  obtained  a  new  chloride  of  silicon,  which  is  a  mobile  fuming 
liquid,  more  volatile  than  the  terchloride.  Water  decomposes  this  liquid,  forming 
hydrochloric  acid,  and  a  new  oxide  of  silicon,  which  is  a  white  substance,  slightly 
soluble  in  water,  but  dissolving  very  easily  in  alkalies, — even  in  ammonia,  with 
evolution  of  hydrogen  and  formation  of  silicic  acid.  When  heated  in  the  air,  it 
burns  with  a  white  flame.  This  compound  is  evidently  a  lower  oxide  of  silicon, 
but  its  exact  composition  has  not  yet  been  determined. 

Fuchs  has  obtained  two  hydrates  of  silicic  acid  ;  one  containing  between  9-1 
and  9-6  per  cent,  of  water,  the  other  between  6-6  and  7  per  cent.  The  former 
might  be  denoted  by  either  of  the  formulae,  2Si03.HO  or  3Si02.HO,  according 
to  the  atomic  weight  of  silicon  chosen;  but  the  latter  agrees  only  with  the 
formula,  4Si02.H04 

The  true  formula  of  silicic  acid  and  atomic  weight  of  silicon  must  then  be 
considered  as  still  undecided ;  the  balance  of  evidence  seems,  however,  to  incline 
in  favour  of  the  formula,  Si02,  making  the  atomic  weight  of  silicon  14-1.  The 
analogy  between  silicic  acid  and  titanic  acid  points  to  the  same  conclusion. 

Chloride  of  Silicon  and  Hydrogen,  Si2Cl8.2HCl. — This  is  the  compound 
which  Wohler  and  Buff  obtained  by  heating  crystalline  silicon  in  a  current  of  dry 
hydrochloric  acid  gas.  It  is  a  colourless,  very  mobile  liquid,  of  sp.  gr.  1-65,  and 

*  Proceedings  of  the  Royal  Society,  viii.  140.  -j-  Compt.  reud.  xliv.  834. 

Ann.  Ch.  Pharm.  Ixxxii.  119. 


iib  SILICON. 

boiling  at  42°  C.  It  has  a  very  pungent  odour,  and  fumes  strongly  in  the  air. 
Its  vapour  is  as  inflammable  as  ether-vapour,  and  burns  with  a  faint  greenish 
flame,  diffusing  vapours  of  silica  and  hydrochloric  acid.  When  passed  through  a 
red-hot  tube,  it  is  decomposed,  yielding  hydrochloric  acid,  terchloride  of  silicon, % 
and  a  specular  deposit  of  amorphous  silicon.  The  compound  is  decomposed  by 
water  with  formation  of  a  corresponding  oxide. 

The  compounds  Si2Br3.2HBr,  and  Si2I3.2HI,  are  obtained  in  a  similar  manner. 
The  former  is  liquid,  the  latter  solid,  at  ordinary  temperatures. 

Hydrated  Oxide  of  Silicon. — Si203.2HO,  is  formed  by  the  action  of  water  on 
either  of  the  preceding  compounds,  but  most  easily  from  the  chloride.  It  is  a 
snow-white  amorphous,  very  bulky  powder,  which  floats  on  water.  It  is  insoluble 
in  all  acids  except  hydrofluoric  acid.  Alkalies,  even  ammonia,  dissolve  it 
readily,  with  evolution  of  hydrogen  and  formation  of  an  alkaline  silicate. 

It  may  be  heated  to  300°  C.  without  alteration ;  but  at  higher  temperatures,  it 
glows  brightly,  and  gives  off  spontaneously  inflammable  hydrogen  gas  (containing 
siliciuretted  hydrogen.) 

A  lower  oxide  of  silicon  (SiO  ?)  and  the  corresponding  chloride  appear  also  to 
exist.* 

Siliciuretted  Hydrogen.  A  remarkable  gaseous  compound  of  silicon  and 
hydrogen  is  produced  when  a  bar  of  aluminium  containing  silicon  is  connected 
with  the  positive  pole  of  a  Bunsen's  battery  of  8  to  12  cells,  and  made  to  dip  into 
a  solution  of  chloride  of  sodium.  The  aluminium  then  dissolves  in  the  form  of 
chloride,  a  considerable  quantity  of  gas  is  evolved  at  its  surface,  and  many  of  the 
gas-bubbles,  as  they  escape  into  the  air,  take  fire  spontaneously,  burning  with  a 
white  light  and  diffusing  a  white  fume.  When  the  gas  is  collected  in  a  tube  over 
water,  and  bubbles  of  oxygen  are  passed  up  into  it,  each  successive  bubble  pro- 
duces at  first  a  brilliant  white  light  and  a  copious  white  fume;  but  this  effect 
gradually  diminishes  in  intensity,  and  at  last  the  remaining  gas  will  no  longer 
burn  spontaneously  by  contact  with  oxygen.  This  residual  gas  is  hydrogen;  the 
spontaneously  inflammable  gas,  which  forms  but  a  small  portion  of  the  mixture,  is 
siliciuretted  hydrogen.  When  the  gaseous  mixture  is  made  to  escape  from  a  glass 
jar  provided  with  a  stop-cock,  it  burns  in  a  jet,  and  deposits  silica  round  the 
orifice.  A  piece  of  white  porcelain  held  in  the  flame,  becomes  stained  with  a 
brown  deposit  of  silicon ;  and  if  the  gas  be  made  to  pass  through  a  narrow  glass 
tube,  and  heated  till  the  glass  softens,  a  deposit  of  silicon  is  likewise  obtained, 
and  the  gas  which  issues  from  the  tube  is  no  longer  spontaneously  inflammable. 
The  compound  has  not  yet  been  analyzed  quantitatively. 

The  formation  of  siliciuretted  hydrogen  appears  to  be  due  to  a  secondary  action 
accompanying  the  electrolysis  of  the  saline  solution.  The  aluminium,  forming 
the  positive  pole  of  the  battery,  combines  with  the  chlorine  and  dissolves ;  but  the 
quantity  of  aluminium  removed  is  about  one-fourth  greater  thaa  that  which  is 
equivalent  to  the  quantity  of  chlorine  eliminated  from  the  solution.  This  excess 
of  aluminium  is  found  to  be  removed  in  the  form  of  alumina,  uniting  with 
oxygen  derived  from  the  water  of  the  solution.  The  equivalent  quantity  of 
hydrogen 'is  of  course  evolved,  and  part  of  it  enters  into  combination  with  the 
silicon  contained  in  the  aluminium.  The  compound  has  not  yet  been  obtained  by 
a  purely  chemical  reaction ;  but  it  has  been  observed  that  the  hydrogen  evolved, 
when  aluminium  dissolves  in  hydrochloric  acid,  burns  with  a  brighter  flame  than 
pure  hydrogen,  and  yields  a  small  deposit  of  silica  (Wohler  and  Buff.)f 

Estimation  of  Silicon  and  Silicic  acid.— When  silica  exists  in  solution,  it  may 
be  completely  separated  from  all  the  other  substances  present,  by acidulating  the 
solution  with  hydrochloric  acid,  evaporating  to  dryness,  and  boiling  the  residue 
with  water  containing  hydrochloric  acid,  which  will  dissolve  everything  excepting 

*  Ann.  Ch.  Pharm.,  Oct.  1857,  p.  94.  f  Ann.  Ch.  Pharm.  ciii.  218. 


„  ANALYSIS    OF    SILICATES.  779 

the  silica.  The  residue  may  then  be  dried,  ignited,  and  weighed.  The  complete- 
ness of  this  separation  depends  on  the  perfect  drying  of  the  silica  before  it  is  boiled 
with  the  acidulated  water.  Now,  to  ensure  this  complete  dryness,  the  silica  must 
be  heated  somewhat  above  the  temperature  of  the  water-bath,  the  drying  being 
completed  on  a  sand-bath  or  over  a  lamp.  In  doing  this,  it  sometimes  happens 
that  too  much  heat  is  applied,  and,  in  that  case,  certain  other  substances,  espe- 
cially alumina  and  oxide  of  iron,  may  also  be  rendered  insoluble  in  the  dilute  acid. 
To  obviate  this  source  of  error,  the  dried  residue  must  be  moistened  all  over  with 
strong  hydrochloric  acid,  then  left  to  stand  for  half  an  hour,  and  afterwards  boiled 
with  water.  Everything  will  then  dissolve  excepting  the  silica. 

Analysis  of  Silicates.  —  Some  natural  silicates,  cerite,  for  example,  are  com- 
pletely decomposed  by  hydrochloric  acid.  In  that  case,  it  is  sufficient  to  boil  the 
pulverized  mineral  with  strong  hydrochloric  acid  as  long  as  anything  continues  to 
be  dissolved ;  then  evaporate  to  complete  dryness.  and  treat  the  residue  as  above. 
The  liquid  filtered  from  the  insoluble  silica  contains  the  bases  of  the  mineral, 
which  may  be  separated  and  estimated  by  methods  already  described. 

Silicates  which,  like  felspar,  resist  the  action  of  hydrochloric  acid,  are  decom- 
posed by  fusion  with  an  alkaline  carbonate.  The  mineral,  very  finely  powdered, 
is  mixed  in  a  platinum  crucible  with  three  or  four  times  its  weight  of  dry  carbo- 
nate of  soda ;  the  platinum  crucible,  placed  within  an  earthen  crucible  linked  with 
magnesia,  and  heated  to  bright  redness  in  a  furnace  for  about  twenty  minutes ;  the 
fused  mass,  when  cold,  removed  from  the  crucible  by  digestion  in  dilute  hydro- 
chloric acid  with  the  aid  of  heat;  the  whole  evaporated  to  dryness;  and  the  silica 
separated,  and  the  bases  determined  as  above.  Some  silicates,  zircon  for  example, 
resist  the  action  of  alkaline  carbonates,  and  must  be  decomposed  by  fusion  with 
hydrate  of  potash  or  soda  in  a  silver  crucible. 

By  this  process,  not  only  the  silica,  but  all  the  bases  of  silicate  may  be  deter- 
mined, excepting  the  alkalies.  To  determine  these,  the  mineral,  reduced  to  an 
almost  impalpable  powder,  is  very  intimately  mixed  with  five  times  its  weight  of 
pure  carbonate  of  lime,  and  the  mixture  exposed  in  a  platinum  crucible,  protected 
as  above,  to  the  strongest  heat  of  an  air-furnace  for  about  half  an  hour.  The 
mass,  which  is  not  fused,  but  sintered  together,  is  then  digested  in  dilute  hydro- 
chloric acid;  the  silica  separated  as  before;  the  greater  part  of  the  lime  and  like- 
wise the  bases  of  the  silicate  precipitated  by  carbonate  of  ammonia  and  free  am- 
inonia ;  the  filtrate  evaporated  to  dryness,  and  the  ammoniacal  salts  expelled  by 
ignition;  the  residue  redissolved  in  water;  the  remainder  of  the  lime  precipitated 
by  oxalate  of  ammonia;  and  the  ammoniacal  salts  again  expelled  by  evaporation 
and  ignition.  The  residue  then  contains  nothing  but  the  chlorides  of  the  fixed 
alkalies  and  magnesia,  if  that  substance  was  contained  in  the  mineral.  Carbonate 
of  baryta  may  also  be  used  instead  of  carbonate  of  lime,  and  the  excess  of  baryta 
removed  by  sulphuric  acid. 

Another  method  of  obtaining  the  alkalies  in  a  silicate,  is  to  decompose  it  with 
hydrofluoric  acid  aided  by  a  gentle  heat.  The  acid  must  be  added  by  small  por- 
tions to  the  finely  pulverized  niin'eral  contained  in  a  platinum  dish,  till  the  action 
ceases  and  the  whole  is  reduced  to  a  pasty  mass.  This  mass  is  then  heated  with 
strong  sulphuric  acid,  which  expels  fluoride  of  silicon  and  hydrofluoric  acid ;  the 
residue  is  heated  to  low  redness  to  expel  the  excess  of  sulphuric  acid ;  the  dry 
mass,  when  cold,  moistened  with  strong  hydrochloric  acid,  and,  after  standing  for 
about  half  an  hour,  digested  with  water.  The  whole  then  dissolves,  provided  the 
decomposition  by  the  hydrofluoric  acid  has  been  complete.  The  solution  contains 
the  alkalies  and  the  other  bases  in  the  state  of  sulphates. 


780  SULPHUR. 

f 

SULPHUR. 

Allotropic  Modifications  of  Sulphur  (p.  292).  — Among  the  various  modifica- 
tions of  sulphur,  there  are,  according  to  Berthelot,*  two  principal  states  which 
are  more  stable  than  the  rest,  and  are,  in  fact,  the  limits  to  which  all  the  others 
may  be  reduced.  These  are,  first,  the  octohedral,  or  electro-negative  sulphur, 
which  acts  as  a  supporter  of  combustion,  and  the  electro-positive,  or  combustible 
sulphur,  which  is  generally  amorphous  and  insoluble  in  bisulphide  of  carbon, 
alcohol,  &c. 

Allied  to  octohedral  sulphur  are  two  conditions  of  inferior  stability,  viz.,  the  pris- 
matic variety,  which  crystallizes  from  melted  sulphur,  and  the  soft  emulsionable 
sulphur  (milk  of  sulphur),  precipitated  from  the  solution  of  an  alkaline  polysul- 
phide  by  the  action  of  acids.  Both  these  varieties  of  sulphur  are  soluble  in  bi- 
sulphide of  carbon,  and  change  spontaneously  into  octohedral  sulphur  after  a  cer- 
tain time. 

Electro-positive  sulphur,  properly  so  called,  is  that  which  is  obtained  when  sul- 
phur separates  from  any  of  its  compounds  with  oxygen,  chlorine,  bromine,  &c., 
the  chloride  or  bromide  yielding  the  most  stable  variety.  It  is  amorphous  and  in- 
soluble in  solvents  properly  so  called,  that  is  to  say,  in  liquids  which  do  not  act 
upon  it  chemically,  such  as  water,  alcohol,  ether,  bisulphide  of  carbon,  &c. 

To  this  electro-positive  sulphur  are  allied  several  modifications  more  or  less  dis- 
tinct, which  may  perhaps  be  reduced  to  three  principal  varieties,  all  amorphous, 
but  less  stable  than  the  one  just  mentioned,  viz.,  the  soft  sulphur  precipitated 
from  solutions  of  the  hyposulphites ;  the  insoluble  sulphur  obtained  by  exhaust- 
ing flowers  of  sulphur  with  alcohol  and  bisulphide  of  carbon ;  and  the  insoluble 
sulphur  obtained  by  exhausting  with  bisulphide  of  carbon  the  soft  sulphur  pro- 
duced by  the  action  of  heat.  These  varieties  are  distinguished  one  from  the 
other  by  the  greater  or  less  facility  with  which  they  are  transformed  into  soluble 
crystallizable  sulphur,  either  by  a  temperature  of  100°  C.,  or  by  contact  with  cer- 
tain electro-positive  bodies,  such  as  the  alkalies  and  their  sulphides,  an  alcoholic 
solution  of  hydrosulphuric  acid,  &c.  By  the  contrary  influences,  that  is  to  say, 
by  contact  with  bodies  having  a  decided  electro-negative  character,  they  may  all 
be  reduced  to  the  most  stable  insoluble  variety,  viz.,  that  which  is  deposited  from 
the  chloride  or  bromide  of  sulphur. 

The  particular  modification  which  sulphur  assumes  when  separated  from  any  of 
its  compounds,  depends  essentially  on  the  nature  of  that  compound.  It  is  alto- 
gether independent  of  the  state  of  the  sulphur  previous  to  combination,  and  like- 
wise of  the  reagent  which  produces  the  separation,  provided  that  reagent  has 
neither  a  decided  electro-positive  character,  such  as  the  alkalies,  nor  a  decided 
electro-negative  or  oxidizing  character,  and  provided  that  it  acts  rapidly  and  with- 
out any  considerable  evolution  of  heat.  The  influence  of  these  latter  conditions, 
is  due  chiefly  to  the  unequal  stability  of  the  several  modifications  of  sulphur. 
Of  all  these  varieties,  the  octohedral  sulphur  is  the  most  stable,  and  that  to  which 
all  the  others,  even  the  most  electro-positive,  tend  to  return,  especially  under  the 
influence  of  heat.  (Berthelot). 

Sulphur,  deposited  at  the  positive  pole  of  the  voltaic  battery  in  the  electrolysis 
of  an  aqueous  solution  of  hydrosulphuric  acid,  is  soluble  in  bisulphide  of  carbon 
arid  crystallizable ;  but  that  which  is  deposited  at  the  negative  pole  in  the  electro- 
lysis of  sulphurous  or  sulphuric  acid,  is  insoluble  in  bisulphide  of  carbon. 
(Berthelotf). 

Magnus  |  obtained  a  black  modification  of  sulphur  by  repeatedly  heating  sul- 
phur to  300°  C.,  cooling  suddenly,  and  exhausting  with  bisulphide  of  carbon  ;  and 
this  black  sulphur,  heated  to  a  temperature  between  130°  and  150°,  passed  into  a 

*  Ann.  Ch.  Phys.  [3J,  xlix.  430.  f  Pogg.  Ann.  xcii.  308. 

Ann.  Ch.  Pharm.  ci.  58. 


SULPHIDE    OF    NITROGEN.  781 

red  modification.  According  to  Mitscherlich,  however,  pure  sulphur  does  not 
exhibit  these  modifications,  but  when  sulphur  is  melted  with  small  quantities  of 
fatty  matters,  various  highly  coloured  products  are  obtained.  Even  the  grease 
imparted  by  touching  sulphur  with  the  fingers,  is  sufficient  to  alter  its  colour 
considerably  when  melted. 

Vapour  of  sulphur,  when  it  comes  in  contact  with  cold  bodies,  condenses  in  the 
form  of  utricles,  that  is  to  say,  of  globules  composed  of  a  soft  external  pellicle  filled 
with  liquid  sulphur.  They  sometimes  retain  their  liquid  form  for  a  considerable 
time.  This  utricular  condition  has  also  been  observed  in  selenium,  iodine,  phos- 
phorus, and  arsenious  acid.  (Brame*). 

Respecting  the  melting  point  of  sulphur,  the  observations  of  different  experi- 
menters vary  from  104-5°  to  112-2°  C.  This  discrepancy  is  attributed  by  Pro- 
fessor Brodie  f  to  the  fact  that  the  melting  point  of  sulphur  varies  according  to  its 
allotropic  state.  According  to  the  observations  of  that  chemist,  rhombic  or  octo- 
hedral  sulphur  (crystallized  from  bisulphide  of  carbon,  alcohol,  or  benzol)  melts 
at  114-5°  C.;  but,  between  100°  and  114-5°,  it  is  transformed  into  the  oblique 
prismatic  modification,  which  melts  at  120°,  and  if  not  afterwards  more  strongly 
heated,  solidifies  at  nearly  the  same  point.  If,  however,  its  temperature  be  further 
raised,  it  does  not  solidify  till  cooled  to  111-5°,  and  if  it  be  then  heated,  melts  at 
a  point  very  little  higher.  In  fact,  above  1£0°,  sulphur  begins  to  pass  into  the 
plastic  state,  which  is  more  fusible.  The  variety  insoluble  in  bisulphide  of  carbon 
has  a  melting  point  considerably  above  120°.  The  gradual  loss  of  transparency 
of  the  prismatic  sulphur  crystallized  from  fusion,  arises,  according  to  Brodie,  from 
the  hardening  of  plastic  sulphur  mechanically  enclosed  within  the  crystals.  When 
crystals  which  have  thus  lost  their  transparency,  are  digested  in  bisulphide  of 
carbon,  a  portion  always  remains  undissolved.  If  sulphur  which  has  been  fused 
and  strongly  heated,  be  suddenly  cooled  by  a  mixture  of  solid  carbonic  acid  and 
ether,  it  solidifies  in  a  hard,  perfectly  transparent  mass,  which  becomes  soft  and 
elastic  at  ordinary  temperatures.  This  appears,  indeed,  to  be  the  solid  state  of 
plastic  sulphur. 

Formation  of  Anhydrous  Sulphuric  acid. — When  a  dry  mixture  of  2  vols.  sul- 
phurous acid  and  1  vol.  oxygen  or  atmospheric  air,  is  passed  through  a  red-hot 
glass  tube  containing  certain  metallic  oxides,  e.  g.  cupric,  ferric,  or  chromic  oxide, 
the  gases  unite  and  produce  dense  white  fumes  of  anhydrous  sulphuric  acid.  A 
mixture  of  the  oxides  of  copper  and  chromium  induces  the  combination  with  pecu- 
liar facility.  These  oxides  appear  to  be  capable  of  inducing  the  combination  of 
unlimited  quantities  of  sulphurous  acid  and  oxygen.  Spongy  metallic  copper  pro- 
duces the  same  effect  when  heated,  but  not  till  the  copper  has  become  oxidized. 
Clean  polished  platinum  foil,  or  spongy  platinum,  produces  the  combination  con- 
siderably below  a  red  heat,  but  not  at  ordinary  temperatures.  (Wb'hlerJ). 

Sulphide  of  Nitrogen  (p.  309). — This  body  was  discovered  by  Soubeiran,  who 
assigned  to  it  the  formula  NS3;  but  it  has  since  been  more  minutely  examined  by 
Fordos  and  Gelis,§  who  have  shown  that  its  true  formula  is  NS2-  The  best  mode 
of  preparing  it  is  to  pass  dry  ammoniacal  gas  into  a  solution  of  protochloride  of 
sulphur,  SCI,  in  eight  or  ten  times  its  volume  of  bisulphide  of  carbon.  Crystals 
of  sal-ammoniac  are  then  deposited,  and  the  solution  becomes  darker  in  colour, 
and  deposits  cochineal-coloured  flakes,  which  soon  decompose  and  turn  brown. 
An  excess  of  ammonia  decomposes  this  brown  compound.  The  current  of  gas 
must  be  continued  till  the  solution  acquires  an  orange-yellow  colour,  and  contains 
only  very  slightly  coloured  flakes,  which  may  be  separated  by  filtration.  The 
filtrate,  when  left  to  evaporate,  deposits  crystals  of  sulphur,  while  the  sulphide  of 

*  Compt.  rend.  xxix.  657;  xxxiii.  538,  579.  %  Ann.  Ch.  Pharm,  Ixxxi.  255. 

f  Proceedings  of  the  Royal  Society,  vii.  24.  \  Compt.  rend.  xxxi.  702. 


782  SULPHUR. 

nitrogen  remains  in  the  mother  liquid,  and  may  be  obtained  by  further  evapora- 
tion  of  the  decanted  liquid.  The  reaction  is  as  follows  :  — 

3SC1  -f  4NH3  =  NS2  +  S  +  3NH4CL 

At  the  same  time,  however,  there  are  a  number  of  intermediate  products  formed 
(the  brown  flocculent  matters  above-mentioned),  consisting  of  compounds  of  sul- 
phide of  nitrogen  with  chloride  of  sulphur,  viz.,  SCI .  NS2;  SCI .  2NS2;  and  SCI . 
3NS2;  but  these  are  all  ultimately  decomposed  by  excess  of  ammoniaN  Sulphide 
of  nitrogen  forms  similar  compounds  with  dichloride  of  sulphur,  SaCl. 

Sulphide  of  nitrogen  is  insoluble  in  water,  slightly  soluble  in  alcohol,  wood- 
spirit,  ether,  and  oil  of  turpentine  ;  bisulphide  of  carbon  dissolves  it  to  the  amount 
of  15  parts  in  1000,  and  the  solution  deposits  the  compound  in  small  elongated 
prisms  derived  from  the  right  rhoniboi'dal  prism,  and  terminated  with  dihedral 
summits;  they  are  transparent  and  of  a  golden  yellow  colour.  The  solution  must, 
however,  be  evaporated  immediately,  for  it  decomposes  after  a  short  time,  yielding 
hydrosulphocyanic  acid,  and  a  yellow  substance  like  that  which  is  commonly  called 
sulphocyanogen.  Water  slowly  decomposes  sulphide  of  nitrogen,  yielding  free 
ammonia,  together  with  hyposulphurous  and  trithionic  acids  :  — 

4NS2  +  15HO  =  NH40 .  S202  -f  2(NH40 .  S305)  -f  NH3. 

• 

Protosulphide  of  Carbon,  CS. — This  compound  is  obtained  :  1.  By  passing  the 
vapour  of  bisulphide  of  carbon  over  spongy  platinum  or  pumice-stone  heated  to 
redness ;  sulphur  is  then  deposited,  and  the  protosulphide  liberated  in  the  form, 
of  gas.  2.  In  the  preparation  of  the  bisulphide,  and  simultaneously  therewith. 
3.  By  decomposing  the  vapour  of  the  bisulphide  at  a  red  heat  by  means  of  lamp- 
black, wood-charcoal,  and  especially  by  animal  charcoal  in  fragments.  4.  By 
decomposing  the  vapour  of  the  bisulphide  at  a  red  heat  with  hydrogen.  5.  By 
calcining  sulphide  of  antimony  with  excess  of  charcoal.  6.  By  the  action  of  car- 
bonic oxide  on  hydrosulphuric  acid  at  a  red  heat !  — 

CO  +  HS  =  HO  -f  CS. 

7.  By  the  action  of  sulphurous  acid,  or  chloride  of  sulphur,  on  olefiant  gas  at  a  red 
heat.  8.  In  the  decomposition  of  sulphocyanogen  by  heat,  &c. 

The  first  process  yields  the  gas  tolerably  pure ;  that  which  is  obtained  by  the 
other  processes  is  mixed  with  hydrosulphuric  acid,  and  carbonic  oxide.  It  is 
purified  by  passing  it  rapidly  through  solutions  of  acetate  of  lead,  and  dichlo- 
ride of  copper  dissolved  in  hydrochloric  acid,  and  then  dried  and  collected  over 
mercury. 

Protosulphide  of  carbon  is  a  colourless  gas,  having  a  strongly  ethereal  odour, 
resembling  that  of  the  bisulphide,  but  not  disagreeable.  When  breathed  in  too 
large  a  quantity,  it  appears  to  be  powerfully  anaesthetic.  It  burns  with  a  fine 
flame,  producing  carbonic  and  sulphurous  acids,  and  a  little  sulphur.  Its  density 
is  somewhat  greater  than  that  of  carbonic  acid.  It  does  not  liquefy  at  the  tem- 
perature of  a  mixture  of  ice  and  salt.  Water  dissolves  nearly  its  own  volume  of 
this  gas ;  but  decomposes  it  somewhat  quickly  into  hydrosulphuric  acid  and  car- 
bonic oxide.  It  is  scarcely  more  soluble  in  alcohol  or  ether.  It  is  not  absorbed 
by  a  solution  of  dichloride  of  copper.  Acetate  of  lead  is  slowly  blackened  by  it. 
It  is  rapidly  decomposed  by  solutions  of  caustic  alkalies.  With  lime-water,  it 
yields  sulphide  of  calcium,  and  a  volume  of  carbonic  oxide  equal  to  its  own  :  — 

CaO  +  CS  =  CaS  +  CO. 

This  reaction  establishes  its  composition,  which  is  further  confirmed  by  the  fact, 
that,  when  exploded  with  oxygen,  it  yields  equal  volumes  of  carbonic  and  sul- 
phurous acids.  At  a  red  heat,  it  is  slightly  decomposed  :  1.  By  spongy  platinum; 
2.  By  aqueous  vapour,  into  IIS  and  CO  ;  3.  More  readily  by  hydrogen  into  HS 
and  a  hydrocarbon ;  4.  Completely  by  copper,  yielding  sulphide  of  copper,  and 


ESTIMATION    OF    SULPHUR.  783 

graphitoidal  carbon ;  5.  By  an  equal  volume  of  chlorine  in  sunshine,  with  for- 
mation of  products  not  yet  examined.  (Baudrimont.*) 

Bisulphide  of  Carbon.  —  By  the  action  of  nascent  hydrogen  (generated  by 
slowly  decomposing  hydrochloric  acid  with  zinc)  upon  bisulphide  of  carbon, 
Girardf  has  obtained  a  compound,  CHS,  which  is  neutral  to  vegetable  colours, 
has  a  powerful  odour,  is  insoluble  in  water,  dissolves  sparingly  in  alcohol,  ether, 
and  rock-oil,  more  readily  in  chloroform  and  bisulphide  of  carbon,  but  most  readily 
in  benzol ;  crystallizes  from  its  solutions  in  square  prisms;  sublimes  undecomposed 
at  150°  C.  in  long  needles  ;  but  decomposes  at  200°.  It  is  not  altered  by  alkalies ; 
dissolves  in  warm  hydrochloric  acid ;  and  is  decomposed  by  nitric  and  by  strong 
sulphuric  acids.  It  forms  crystalline  compounds  with  nitrate  of  silver,  and  with 
the  chlorides  of  platinum,  gold,  and  mercury. 

Bisulphide  of  carbon,  enclosed  with  water  in  a  sealed  tube,  and  heated  for  three 
or  four  hours  to  150°  C.,  is  resolved  into  carbonic  and  hydrosulphuric  acids. 
Many  metallic  oxides  and  salts,  treated  in  a  similar  manner  with  bisulphide  of 
carbon,  yield  carbonic  acid  and  a  metallic  sulphide.  (Schlagdenhauffen.J) 

Quantitative  estimation  of  Sulphur  and  its  compounds.  —  Sulphur  is  almost 
always  estimated  in  the  form  of  sulphuric  acid.  To  determine  the  quantity  of 
sulphur  in  a  metallic  sulphide,  the  compound  is  heated  with  nitric  acid,  aqua- 
regia,  or  sometimes  with  a  mixture  of  hydrochloric  acid  and  chlorate  of  potash, 
till  the  metal  is  oxidized,  and  the  sulphur  converted  into  sulphuric  acid.  The 
solution  is  then  treated  with  chloride  of  barium  or  nitrate  of  baryta,  and  the  pre- 
cipitated sulphate  of  baryta  collected  on  a  filter,  washed,  dried,  and  ignited. 
Before  adding  the  baryta-solution,  however,  the  liquid  must  be  considerably  diluted 
with  water,  because  the  nitrate  and  chloride  of  barium  are  themselves  insoluble 
in  strong  nitric  and  hydrochloric  acids.  The  liquid  is  then  boiled,  and  afterwards 
left  to  stand  till  the  precipitate  has  completely  settled  down  ;  after  which  the  clear 
liquid  is  first  passed  through  the  filter,  and  then  the  precipitate  thrown  upon  it; 
if  the  precipitate  be  poured  upon  the  filter  before  it  has  settled  down,  it  will  be 
sure  to  run  through.  As  the  oxidation  of  the  sulphur  is  very  slow,  the  metal 
being  completely  oxidized  and  dissolved  long  before  it,  and  a  portion  'of  the  sul- 
phur separated  in  the  free  state,  it  is  sometimes  convenient  to  collect  this  portion 
on  a  small  weighed  filter,  determine  its  amount  by  direct  weighing,  and  after- 
wards estimate  the  dissolved  portion  as  above. — In  the  sulphides  of  gold  and  pla- 
tinum, from  which  the  sulphur  is  completely  expelled  by  ignition,  its  quantity 
may  be  at  once  determined  by  weighing  the  residual  metal.  The  sulphides  of  the 
alkali-metals  and  alkaline  earth-metals  are  sometimes  analyzed  by  decomposing 
them  with  hydrochloric  acid,  receiving  the  evolved  hydrosulphuric  acid  in  a  solu- 
tion of  acetate  of  lead,  oxidizing  the  precipitated  sulphide  of  lead  with  fuming 
nitric  acid,  weighing  the  sulphate  of  lead  thus  produced,  and  thence  calculating 
the  quantity  of  sulphur. 

The  sulphur  in  organic  compounds  may  likewise  be  estimated  by  oxidizing  the 
compound  with  fuming  nitric  acid,  and  precipitating  the  resulting  sulphuric  acid 
with  a  baryta-solution.  Another  method,  given  by  Dr.  W.  J.  Russell, §  is  to  burn 
the  substance  in  a  combustion-tube  with  oxide  of  mercury,  carbonate  of  soda 
being  added  to  take  up  the  sulphuric  acid  produced,  and  a  small  bent  tube  dip- 
ping under  water  fitted  into  the  open  end  of  the  combustion-tube,  so  that  any 
acid  vapours  that  escape  may  be  condensed  in  the  water.  At  the  end  of  the  com- 
bustion, this  liquid  is  acidulated  with  hydrochloric  acid ;  the  tube  washed  out 
with  the  acid  solution ;  the  liquid  filtered ;  and  the  sulphuric  acid  precipitated  by 
chloride  of  barium. 

The  quantity  of  sulphuric  acid  in  a  soluble  sulphate  is  estimated  by  precipi- 

*  Compt.  rend.  xliv.  1000.  f  Compt.  rend.  xlih.  396. 

J  J.  Pharm.  [3],  xxix.  401.  \  Chem.  Soc.  Qu.  J    fli.  212. 


784  SELENIUM. 

tating  the  aqueous  solution  with  chloride  of  barium.  Some  sulphates  which  are 
insoluble  in  water  may  be  dissolved  in  hydrochloric  or  nitric  acid,  and  the  baryta- 
solution  then  added.  The  sulphates  of  lime,  strontia,  and  lead  may  be  decom- 
posed by  boiling  with  a  solution  of  carbonate  of  soda  (p.  736),  and  the  sulphuric 
acid  precipitated  by  chloride  of  barium  from  the  filtered  solution,  previously  aci- 
dulated with  nitric  or  hydrochloric  acid.  Sulphate  of  baryta  must  be  decomposed 
by  fusion  in  a  platinum  crucible  with  three  times  their  weight  of  carbonate  of 
soda;  the  fused  mass  digested  in  water;  the  filtered  soda-solution  acidulated; 
and  the  sulphuric  acid  precipitated  as  above. 

Sulphurous  and  hyposulphurous  acid  may  be  estimated  by  oxidation  with  nitric 
acid,  whereby  they  are  converted  into  sulphuric  acid,  or  by  Bunsen's  iodometric 
method  (p.  801). 

SELENIUM. 

Preparation  of  Selenium  (p.  311).  —  This  element  is  extracted  from  natural 
selenides,  and  principally  from  the  seleniferous  ores  of  the  Harz,  by  the  following 
process: — The  pulverized  ore  is  treated  with  hydrochloric  acid,  to  remove  the 
earthy  carbonates  with  which  it  is  mixed.  The  residue,  after  being  well  washed 
and  dried,  is  mixed  with  its  own  weight  of  black  flux,  and  calcined  for  an  hour 
at  a  red  heat.  Selenide  of  potassium  is  thus  formed,  which  is  separated  by  wash- 
ing the  cooled  and  rapidly  pulverized  residue  with  boiling  water.  A  brown-red 
solution  is  thus  obtained,  and  the  insoluble  matter  which  remains  on  the  filter  re- 
tains the  metals  (copper,  lead,  and  silver)  which  were  combined  with  the  sele- 
nium. The  solution  of  selenide  of  potassium  oxidizes  gradually  on  exposure  to 
the  air,  potash  being  formed,  and  the  selenium  collecting  in  a  grey  mass,  which  is 
carefully  washed,  dried,  and  distilled. 

When  the  selenium  contains  sulphur,  it  is  converted  into  seleniate  and  sulphate 
of  potash  by  calcination  with  a  mixture  of  nitre  and  carbonate  of  potash.  The 
calcined  mass  is  dissolved  in  hydrochloric  acid,  and  the  liquid  saturated  with  sul- 
phurous acid  gas,  and  heated  to  the  boiling  point.  The  selenic  acid  is  thereby 
reduced,  and  the  selenium  precipitated  in  red  flakes,  while  the  sulphate  of  potasli 
remains  in  solution.  (Wohler.*) 

Modifications  of  Selenium.  —  Berzelius  found  that  selenium  solidifies  in  the 
amorphous  state  by  sudden,  and  in  the  crystalline  state  by  slow  cooling.  Hittorff 
finds  that  crystalline  (or  granular)  selenium  melts  at  211-5°  C.  (412-6°  F.),  with- 
out previous  softening.  The  mass,  when  left  to  cool  slowly,  remains  fluid  below 
that  temperature,  and  solidifies  very  gradually  in  the  amorphous  state ;  a  ther- 
mometer immersed  in  it  during  the  cooling  does  not  remain  stationary  at  any 
point,  or  indicate  any  temperature  at  which  the  latent  heat  of  the  selenium  is  set 
free.  Amorphous  selenium  retains  its  condition  for  a  long  time  at  ordinary  tem- 
peratures; but  between  80°  and  217°  C.  (176°  and  412-6°  F.),  it  becomes  crys- 
talline and  gives  out  great  heat,  most  quickly  between  125°  and  180°  C.  (257° 
and  356°  F.),  and  when  pulverized.  When  amorphous  selenium  is  heated  in  an 
air-bath  to  between  125°  and  130°  C.,  a  thermometer  immersed  in  it  rises  sud- 
denly to  between  210°  and  215°  C.  Selenium,  as  precipitated  in  the  red,  finely 
divided  state  from  selenious  acid  by  sulphurous  acid  and  other  reducing  agents,  or 
from  an  aqueous  solution  of  seleniuretted  hydrogen  by  exposure  to  the  air,  is 
amorphous,  and  exhibits  the  above-mentioned  spontaneous  rise  of  temperature 
when  heated.  Selenium  deposited  from  solutions  of  selenide  of  potassium  or  am- 
monium by  exposure  to  the  air,  is  crystalline,  and  has  a  sp.  gr.  of  4-808  at  60°  F. 
These  modifications  of  selenium  are  analogous  to  those  of  sulphur  (p.  780). 
Berthelot  finds  that  selenium  deposited  at  the  positive  pole  in  the  electrolysis  of 
hydroselenic  acid,  is  soluble  in  bisulphide  of  carbon ;  but  that  which  is  deposited 

*  Trait6  de  Chimie  g6n6rale,  par  Pelouze  et  Frerny,  2me.  edition,  i.  430. 


PHOSPHORUS.  785 

f»t  the  negative  pole  in  the  electrolysis  of  selcnious  acid  is  insoluble.  Amorphous 
selenium  does  not  conduct  electricity;  crystalline  selenium  conducts  it  much 
better,  and  its  conducting  power  increases  rapidly  with  its  temperature.  (Hittorff.*) 
Quantitative  estimation  of  Selenium.  —  The  methods  for  the  estimation  and 
separation  of  selenium  are  similar  to  those  which  are  applied  to  tellurium  (p.  529). 
When  in  the  form  of  seleniou®  acid,  it  is  precipitated  in  the  free  state  by  sul- 
phurous acid.  Selenic  acid  must  first  be  reduced  to  selenious  acid  by  heating 
with  hydrochloric  acid ;  it  may  also  be  precipitated  as  a  baryta-salt,  like  sulphuric 
acid.  Selenious  and  selenic  acid  may  be  separated  from  certain  metals,  iron,  zinc, 
&c.,  by  hydrosulphuric  acid,  which  throws  down  sulphide  of  selenium  ;  from 
others,  such  as  copper,  silver,  and  lead,  by  sulphide  of  ammonium,  which  dis- 
solves sulphide  of  selenium.  Metallic  selenides  may  be  decomposed  by  heating 
them  in  a  current  of  chlorine  gas,  the  volatile  chloride  of  selenium  being  received 
in  water,  which  decomposes  it  and  precipitates  the  selenium. 

PHOSPHORUS. 

Red  or  amorphous  Phosphorus  (p.  314).  —  When  phosphorus  is  subjected  to 
the  action  of  the  sun's  rays,  or  to  a  high  temperature  in  vacuo,  or  in  a  gas  which 
does  not  act  upon  it  chemically,  it  quickly  assumes  a  red  colour,  and  becomes  com- 
pletely altered  in  its  properties.  This  modified  phosphorus  may  be  obtained  in 
considerable  quantity  by  heating  ordinary  phosphorus  to  230° — 250°  C.  (446° — 
482°  F.)  in  a  retort  filled  with  nitrogen  or  carbonic  acid,  and*  having  adapted  to 
its  beak  a  bent  tube  which  dips  under  mercury.  Part  of  the  phosphorus  con- 
denses on  the  neck  of  the  retort  in  the  ordinary  state,  but  the  rest  is  transformed 
in  the  course  of  a  few  hours  into  a  dark  red  mass,  which  is  a  mixture  of  amor- 
phous and  ordinary  phosphorus.  On  treating  this  mixture  with  bisulphide  of 
carbon,  the  latter  is  dissolved,  and  the  amorphous  phosphorus  remains  in  the  form 
of  a  red  powder. 

This  amorphous  phosphorus  differs  remarkably  from  ordinary  phosphorus,  both 
in  its  physical  and  in  its  chemical  properties.  Its  sp.  gr.  at  10°  C.  (50°  F.)  is 
1-964,  while  that  of  ordinary  phosphorus  is  between  1-826  and  1-840;  it  sinks  in 
melted  phosphorus,  the  density  of  that  liquid  at  45°  C.  being  1-88.  It  melts  at 
250°  C.,  and  at  260°  is  reconverted  into  ordinary  phosphorus.  Red  phosphorus 
is  much  less  energetic  in  its  chemical  affinities  than  ordinary  phosphorus.  At 
ordinary  temperatures  it  has  no  perceptible  odour,  and  may  be  exposed  to  the  air 
without  alteration.  It  does  not  become  luminous  in  the  air  till  heated  to  200°  C., 
or  take  fire  below  260°.  It  does  not  combine  with  melted  sulphur.  It  combines 
with  chlorine  without  emission  of  light;  with  bromine,  however,  it  exhibits  that 
phenomenon.  It  is  insoluble  in  bisulphide  of  carbon,  alcohol,  ether,  rock-oil,  and 
terchloride  of  phosphorus.  Oil  of  turpentine  and  a  few  other  liquids  dissolve 
small  quantities  of  it  (Schrotterf). 

Amorphous  phosphorus  may  be  obtained  in  the  compact  state  by  keeping  phos- 
phorus for  several  days  at  a  temperature  a  little  below  260°  C.  It  is  then  con- 
verted into  a  brittle,  easily  friable,  reddish-brown  mass,  having  a  conchoidal  frac- 
ture, and  exhibiting  on  the  fractured  surface,  an  iron-grey  colour  and  imperfect 
metallic  lustre.  As  thus  prepared,  however,  it  is  not  quite  pure,  but  contains  a 
small  quantity  of  ordinary  phosphorus,  which  causes  it  to  oxidate  at  ordinary  tem- 
peratures. The  density  of  this  compact  red  phosphorus  was  found  to  be  between 
2-089  and  2-106;  if  quite  pure,  it  would  be  still  denser  (SchrotterJ). 

Phosphorus  may  also  be  brought  to  the  amorphous  state  by  heating  it  with  a 
small  quantity  of  iodine.  When  phosphorus  is  melted  in  a  glass  vessel  filled  with 


50 


*  Pogg.  Ann.  Ixxxiv.  214. 
Wieu.  Akad.  Ber.  1848, 
Pogg.  Anu.  Ixxxi.  299;  Compt.  rend.  xxxi.  13 


f  Wieu.  Akad.  Ber.  1848,  130;   Ann.  Ch.  Phys.  [3],  xxiv.  406. 

is. 


786  PHOSPHORUS. 

carbonic  acid  gas,  and  a  small  quantity  of  iodine  introduced  through  an  upright 
glass  tube  reaching  nearly  to  the  phosphorus,  a  violent  action  takes  place,  attended 
with  great  rise  of  temperature,  and  a  hard,  black,  semi-metallic  mass  is  produced, 
which  yields  a  red  powder.  The  same  result  is  obtained  when  phosphorus  is 
melted  under  strong  hydrochloric  acid,  and  a  small  quantity  of  iodine  added; 
under  water  the  experiment  does  not  succeed.  The  product  thus  obtained  is 
nearly  pure  amorphous  phosphorus,  containing  only  a  trace  of  iodine;  when 
strongly  heated,  it  distils  over  almost  without  alteration,  the  distillate  containing 
only  a  trace  of  ordinary  phosphorus.  The  mode  of  its  formation  appears  to  be 
this  : — An  iodide  of  phosphorus  is  first  formed,  probably  PI2,  and  the  phosphorus 
contained  in  it  passes  into  the  amorphous  state ;  this  compound  is  then  decom- 
posed, the  amorphous  phosphorus  separated,  and  a  more  volatile  iodine  compound 
formed,  which  acts  upon  another  portion  of  phosphorus  with  the  same  final  result, 
so  that  by  repetition  of  these  processes  a  large  quantity  of  phosphorus  may  be 
brought  into  the  amorphous  state  (Brodie*).  Amorphous  phosphorus  thus  pre- 
pared differs  in  some  respects  from  that  which  is  obtained  by  the  action  of  heat, 
being  more  readily  attacked  by  potash,  and  precipitating  certain  metallic  solutions 
(e.  (j.  sulphate  of  copper),  an  effect  which  may  perhaps  be  due  to  the  small  quan- 
tity of  iodine  contained  in  it.  The  sp.  gr.  of  this  amorphous  phosphorus  is  2-23. 

The  formation  of  amorphous  phosphorus  under  the  influence  of  iodine  shows 
that  it  possesses  an  electro-positive  character,  like  amorphous  sulphur;  a  conclu- 
sion which  is  further  confirmed  by  its  formation  in  a  similar  manner  under  the  in- 
fluence of  bromine  and  chlorine,  and  by  the  imperfect  combustion  of  phosphorus 
or  phosphuretted  hydrogen  (Berthelot).  According  to  Schrotter,  the  substance 
usually  regarded  as  oxide  of  phosphorus,  P20,  is  nothing  more  than  amorphous 
phosphorus. 

Atomic  weight  of  Phosphorus.  —  By  burning  amorphous  phosphorus  in  oxygen 
gas,  Schrotter  finds  that  the  atomic  weight  of  phosphorus  is  31.*j" 

Modifications  of  Meta  phosphoric  acid  (p.  654).  — Thi^  acid  appears  to  be  sus- 
ceptible of  five  polymeric  modifications,  viz. : 

Monometaphosphoric  acid HO.P05. 

Dimetaphosphoric  acid 2H0.2P05. 

Trimetaphosphoric  acid 3 H0.3P05. 

Tetrametaphosphoric  acid 4H0.4P05. 

Hexainetaphosphoric  acid 6 H 0 . 6P05. 

The  formulae  of  these  several  modifications  are  deduced  chiefly  from  the  relative 
numbers  of  atoms  of  the  two  bases  in  the  double  salts  which  they  form. 

Monometaphosphoric  acid  is  the  variety  discovered  by  Maddrell.  It  is  pro- 
duced in  combination  with  potash,  when  that  alkali  and  phosphoric  acid  are 
ignited  together  in  equivalent  proportions,  —  and,  in  combination  with  oxide  of 
ammonium,  by  heating  dimetaphosphate  of  ammonia  to  250°  G.  (482°  F.).  'It 
does  not  form  any  double  salts,  and  probably  therefore  contains  only  one  atom  of 
acid  and  base  :  MO.P05. 

Dinu-taphosphoric  acid  is  produced  when  phosphoric  acid  is  heated  with  oxide 
of  copper,  zinc,  or  manganese  in  equal  or  nearly  equal  numbers  of  atoms.  The 
copper-salt,  which  serves  for  the  preparation  of  all  the  others,  is  obtained  by  heat- 
ing to  350°  C.  (66'2°  F. )  a  solution  of  phosphoric  acid  and  oxide  of  copper  in  the 
proportion  of  5P05  to  4CuO.  It  is  a  crystalline  powder,  insoluble  in  water,  but 
soluble,  with  the  aid  of  heat,  in  sulphuric  acid  and  in  ammonia.  The  dimeta- 
phosphates  of  the  alkalies,  which  are  obtained  by  treating  the  copper-salt  with 
sulphide  of  potassium,  &c.,  are  soluble  in  water,  crystallizable,  and  converted  by 
heat  into  insoluble  salts.  Dimetaphosphoric  acid  has  a  strong  tendency  to  form 

*  Chem.  Sec.  Qu.  J.  v.  289.  f  Ann.  Ch.  Phys.  [3],  xxxviii.  131. 


SULPHIDES    OF    PHOSPHORUS.  787 

double  salts,  all  of  which  contain  equal  numbers  of  atoms  of  the  two  bases; 
(MO.M'0).2P05;  hence  its  composition  is  inferred.  For  example,  on  mixing  a 
concentrated  solution  of  the  potash-salt  with  chloride  of  sodium,  or  of  the  soda-salt 
with  chloride  of  potassium,  a  crystalline  double  salt  is  obtained,  having  the  com- 
positi3n  (NaO.KO).2P05  +  2HO ',  and  by  mixing  2  at.  ditmetapfiosphate  of 
ammonia  with  1  at.  chloride  of  copper,  in  tolerably  concentrated  solutions,  and 
adding  alcohol,  blue  needle-shaped  crystals  are  formed,  containing  (CuO.NH40). 
2P05  +  4HO. 

Trimetaphosphoric  acid  is  produced  in  the  form  of  a  soda-salt  by  slowly  cooling 
a  fused  mixture  of  1  at.  P05  and  1  at.  soda.  Its  double  salts  contain  2  atoms  of 
one  base  to  1  atom  of  the  other,  (2MO.M'0).3P05. 

Tetrametaphosphoric  acid  is  formed  by  heating  phosphoric  acid  with  oxide  of 
lead,  bismuth,  or  cadmium,  or  with  a  mixture  of  equal  numbers  of  atoms  of  soda 
and  oxide  of  copper.  The  lead-salt  is  easily  decomposed  by  alkaline  sulphides, 
and  yields  the  corresponding  salts  of  the  alkalies.  The  soda-salt  in  combination 
with  water  is  viscid  and  elastic,  and  forms  with  a  larger  quantity  of  water  a 
gummy  mass,  which,  will  not  pass  through  a  filter.  The  double  salts  of  this  acid 
contain  equal  numbers  of  atoms  of  their  two  bases,  like  those  of  dimetaphosphoric 
acid ;  but  as  they  differ  in  physical  properties  from  those  of  the  latter,  it  is  proba- 
ble that  they  are  composed  according  to  the  formula  (2M0.2M'0).4P05,  e.g.  the 
copper  and  sodium  salt  =  (2CuO .  2NaO).4P05. 

Hexameto phosphoric  odd  is  the  first  discovered  modification  of  metaphosphoric 
acid  (see  page  321).  It  is  formed  by  igniting  the  hydrate  of  phosphoric  acid, 
by  the  sudden  cooling  of  the  soda-salt,  and  by  igniting  phosphoric  acid  with  oxide 
of  silver.  It  forms  double  salts,  the  quantities  of  base  in  which  are  nearly  in  the 
proportion  of  5  at  :  1  at. ;  hence  the  composition  of  these  salts  is  inferred  to  be : 
(5MO.M'0).6P05;  thus  the  soda  and  lime  salt  is  (5CaO .  NaO) .  6P05  (Fleit- 
mann).* 

Action  of  Water  at  high  temperatures  on  the  Pyrophosphates  and  Metaphos- 
phates.  —  These  salts  heated  with  water  in  sealed  tubes  to  280°  C.  (536°  F.), 
are  decomposed,  with  formation  of  tribasic  phosphates.  If  the  base  of  the  pyro- 
phosphate  forms  an  insoluble  tribasic  phosphate,  the  latter  is  precipitated,  and  an 
acid  phosphate  remains  in  solution.  Thus,  with  pyrophosphate  of  silver : 
2(2AgO .  P05)  +  2HO  =  3AgOP05  +  (Ag0.2HO).P05. 

If  the  base  of  the  pyrophosphate  forms  a  soluble  tribasic  phosphate,  the  product 
is  a  neutral  tribasic  phosphate  :  thus 

2KO .  P05  +  HO  =  (2KO .  HO)  .  P05. 

The  metaphosphates  similarly  treated  yield  insoluble  phosphates  and  free  phos- 
phoric acid,  which  dissolve  small  quantities  of  the  precipitated  phosphates;  thus 
with  lime : 

3(CaO.P05)  +  6HO  =  3CaO.P05  .+  2(3HO.P05). 

The  metaphosphates  of  potash  and  soda  yield  acid  phosphates  : 
NaO.P05  +  2HO  =  Na0.2HO.P05.f 

Sulphides  of  Phosphorus.. — These  compounds  are  easily  obtained  by  fusing 
sulphur  with  amorphous  phosphorus  in  an  atmosphere  of  carbonic  acid ;  a  violent 
action  takes  place,  but  no  explosion  (Kekule).J 

rP02 
Amides  of  Phosphoric  acid.  —  1.    Triphosphamide,  N3H6P02  =  NJ    H3. — 

I   H3 
When  dry  ammoniacal  gas  is  slowly  passed  into  oxychloride  of  phosphorus  (chlo- 

*  Pogg.  Ann.  Ixxviii.  233,  238.  f  A.  Reynoso,  Compt.  rend,  xxxiv.  795 

J  Proc.  Roy.  Soc.  vii.  38. 


788  PHOSPHORUS. 

ride  of  phosphoryl,  P02.C13),  and  the  product  afterwards  treated  with  water,  a 
solution  of  sal-ammoniac  is  obtained,  together  with  a  snow-white,  amorphous 
insoluble  substance,  which  is  triphosphamide : 

P02C13  +  6NH3  =  3NH4C1  +  N3H6P02. 

This  compound  is  scarcely  attacked  by  continued  boiling  with  water,  potash-ley, 
or  dilute  acids.  It  is  very  slowly  decomposed  by  boiling  with  strong  nitric  or 
hydrochloric  acid,  more  readily  by  aqua-regia.  Strong  sulphuric  or  nitro-sulphuric 
acid  dissolves  it  easily  at  a  gentle  heat,  forming  a  solution  which  contains  ammonia 
and  phosphoric  acid.  It  is  not  completely  decomposed  by  heating  with  soda-lime. 
When  fused  with  hydrate  of  potash,  it  gives  off  a  large  quantity  of  ammonia,  and 
leaves  phosphate  of  potash.  Heated  alone,  out  of  contact  of  air,  it  also  gives  off 
ammonia,  and  leaves  monophosphamide,  which,  on  being  heated  with  potash, 
evolves  more  ammonia,  and  leaves  phosphate  of  potash.  The  compound  may  be 
regarded  as  tribasic  phosphate  of  ammonia  minus  6  at.  water :  — 


By  the  action  of  anhydrous  aniline,  N  .  (C,2H5)  .  H  .  H,  on  oxychloride  of  phos- 


phorus, the  homologous  compound  triphenylphosphamide,  N3.P02.(C12H5)3.H3,  is 
obtained;    it   is   a  white  mass,  more  easily  decomposable  than  triphosphamide. 

Trinaphtylphosphamide,  N.P02.(C20H7)3.H3,  is  obtained  in  like  manner  by  the 
action  of  naphtylamine,  N  .  (C^Ri)  -  H  .  H,  on  oxychloride  of  phosphorus. 

SulphotriphospJiamide,  N3.PS2.H3.H3,  is  obtained  by  treating  sulphochloride  of 
phosphorus,  PS2C13,  with  ammoniacal  gas  ;  it  is  also  a  white  mass,  which  is  de- 
composed by  water,  with  evolution  of  hydrosulphuric  acid  gas.  Sulphotriplienyl- 

phosphamide,  N3.  PS2.  (C,2H5)3H3,  is  obtained  in  like  manner,  by  the  action  of 
aniline  on  sulphochloride  of  phosphorus.     (Hugo  Schiff).* 

2.  Biphosphamide,  N2H3P02  =  N2.P02.H3.  (Gerhardt's  Phosphamidetf.— 
Obtained  by  saturating  pentachloride  of  phosphorus  with  ammoniacal  gas,  and 
then  boiling  with  water.  Chlorophosphamide,  N2H4PC13,  appears  to  be  first  formed, 
and  afterwards  resolved  by  water  into  hydrochloric  acid  and  biphosphamide  : 


and  — 


PC1S  +  2NH3  =  N2H4PC13  +  2HC1; 
N2H4PC13  +  2HO  =  N2H3P02  +  3HC1. 


The  product  is  purified  by  boiling,  first  with  caustic  potash,  then  with  nitric  or 
sulphuric  acid,  and,  finally,  by  washing  water.  It  is  a  white  powder,  insoluble  in 
water,  alcohol,  and  oil  of  turpentine.  When  heated  without  access  of  air,  it  gives 
off  ammonia,  and  leaves  monophosphamide  ;  but  if  moisture  be  present,  it  yields 
ammonia  and  metaphosphoric  acid.  Fused  with  hydrate  of  potash,  it  gives  off 
ammonia  and  leaves  phosphate  of  potash.  It  resists  the  action  of  most  oxidizing 
agents  ;  but  is  slowly  oxidized  by  fusion  with  nitre,  and  deflagrates  with  chlorate 
of  potash.  It  may  be  regarded  as  bi-ammoniacal  phosphate  of  ammonia  (the  so- 
called  neutral  phosphate,)  minus  6HO  :  — 


Liebig  and  Wohler,  who  discovered  this  compound,  supposed  it  to  be  a  bihy- 
drate  of  phosphide  of  nitrogen,  PN2.2HO. 

*  Ann.  Ch.  Pharm.  ci.  300.  f  Ann.  Ch.  Phys.  [3],  xviii.  188. 


AMIDES    OF    PHOSPHORIC    ACID.  789 

3.   Monophosphamide,  N.P02.    (Gerhard?  s  BipJiosphamide).  —  Obtained   by 
heating  triphosphamide  or  biphosphamide,  without  access  of  air  :  — 

N3H6P02  —  2NH3  =  N.P02, 
and:  N2H3P03—   NH3  =  N.P02. 

It  is  a  pulverulent  substance,  resembling  triphosphamide  in  its  reactions,  but  still 
more  difficult  to  decompose  (Gerhardt,  Schiff).  It  may  be  regarded  as  ammonia, 
NH3,  in  which  the  3  at.  hydrogen  are  replaced  by  the  tribasic  radical,  P02,  or  as 
mono-ammoniacal  phosphate  of  ammonia  (the  so-called  acid  phosphate),  minus 
6HO:— 


N    TT    T>(\ 

4.  Phosphamic  acid,  NH2P04  =        ^      2}02.  —  This  compound,  which  may 


be  regarded  as  hydrated  oxide  of  ammonium,     jj4}02  in  which  3  at.  hydrogen 

in  the  ammonium  are  replaced  by  P02,  is  obtained  by  the  action  of  ammoniacal 
gas  on  anhydrous  phosphoric  acid  :  — 


P°*  j  06  +  2NH3  =  2N'I*IP°2  1  02  +  2HO. 

Great  heat  is  evolved,  and  the  product,  when  cold,  is  a  fused  mass,  consisting 
of  phosphamic  acid  and  phosphamate  of  ammonia,  generally  mixed  with  red 
phosphorus.  On  dissolving  this  mass  in  water,  and  filtering,  a  solution  is 
obtained,  from  which  the  other  salts,  most  of  which  are  insoluble,  may  be  formed 
by  double  decomposition.  The  free  acid,  which  may  be  obtained  by  decomposing 
the  lime-salt  with  sulphuric  acid,  is  a  semi-solid,  amorphous  mass,  which  dissolves 
easily  in  water  and  alcohol,  and  when  heated,  gives  off  ammonia,  and  leaves 
phosphoric  acid. 

The  phosphamates  of  the  earths,  and  heavy  metals,  are  insoluble  in  water,  and 
very  sparingly  soluble  in  acids,  a  character  which  distinguishes  them  from  the 
phosphates.  The  ammonia-salt  gives  white  precipitates  with  salts  of  barium, 
strontium,  calcium,  magnesium,  iron,  manganese,  zinc,  lead,  mercury,  and  silver, 
rose-coloured  with  cobalt,  greenish-white  with  nickel,  light-blue  with  copper,  and 
dirty  green  with  chromium  salts.  The  iron  salt,  NHFeP04,  dissolves  in  ammonia, 
forming  a  deep  purple  solution,  which  on  evaporation  leaves  a  crystalline  salt,  the 

NH  PO 

phosphamate    of  f  err  ammonium,    ^H  F  a£02.     The  phosphamates    of  cobalt, 

nickel,  zinc,  copper,  mercury  and  silver  likewise  dissolve  in  ammonia,  apparently 
with  formation  of  analogous  salts.     (Schiff.)* 

5.  Phospham,  N2P.H.  —  When  anhydrous  phosphoric  acid,  saturated  as  com- 
pletely as  possible  with  ammoniacal  gas,  is  heated  in  a  dry  current  of  that  gas,  it 
is  decomposed,  and  on  treating  the  mass  when  cold  with  water,  phosphoric  acid 
dissolves,  and  there  remains  a  small  quantity  of  a  yellowish  red  residue,  which 
gives  off  ammonia  when  fused  with  potash,  and  exhibits  in  other  respects,  the 
characters  of  phosphani  (Liebig  and  Wohler's  phosphide  of  nitrogen,  p.  328). 
This  compound  is  the  nitrile  of  phosphamic  acid,  being  related  to  it  in  the  same 
manner  as  aceto-nitrile,  N.C4H3,  to  acetic  acid  (Schiff)  :  — 

NH  (NH4)  P04  —  4HO  =  N2PH. 

Gladstone,*)"  by  the  action  of  alkalies  on  chlorophosphide  of  nitrogen  (p.  796), 
obtained  two  acids,  azophosphoric  and  deutazophosphoric  acids,  which  he  regarded 

*  Ann.  Ch.  Pharm.  ciii.  168.  f  Chem.  Soc.  Qu.  J.  iii.  135,  353. 


790  PHOSPHORUS. 

ns  phosphoric  acid  conjugated  with  one  and  two  atoms  of  the  group  PN.  Thus 
phosphoric  acid,  =  P05;  azophosphoric  acid,  =  PN.P05;  deutazophosphoric 
acid,  =  (PN)2.P05.  These  acids,  according  to  Gladstone's  analyses,  are  both 
tribasic,  the  formula  of  the  azophosphates  being  3MO.P2N06  =  P2NM308;  and 
that  of  the  deutazophosphates,  3MO.P3N205  =  P3N2M308.  It  is  probable,  how- 
ever, that  deutazophosphoric  acid  is  the  same  as  Schiff's  phosphamic  acid. 

The  formation  of  deutazophosphoric  acid   from    chlorophosphide  of  nitrogen 
(N2P3C1S),  is  represented,  according  to  Gladstone,  by  the  equation  — 

N2P3C15  +  5HO  =  5HC1  +  P3N205- 

Laurent,  however,  has  shown  that  the  formula  of  chlorophosphide  of  nitrogen  is 
more  probably  NPC12  ',  and  from  this  it  is  easy  to  deduce  the  formation  of  phos- 
phamic acid  :  — 

NPCla  +  4HO  =  2HC1  +  NII2P04. 

Moreover  the  analysis  of  the  deutazophosphates  of  baryta  and  silver  agree  with 
the  formulae  of  the  phosphamates  NHMP04  quite  as  well  as  with  Gladstone's 
formula.  By  decomposing  chlorophosphide  of  nitrogen  with  ammonia,  Gladstone 
obtained  in  three  experiments,  181,  183,  and  177  per  cent,  of  an  ammoniacal  salt. 
Regarding  this  as  phosphamate  of  ammonia,  and  representing  its  formation  by 
,the  equation  — 


NPC12  +  34}02  =        H'}0,  +  2NH4C1  +  2HO, 

the  quantity  should  be  175  per  cent.,  which  agrees  nearly  with  the  experimental 
result. 

Azophosphoric  acid,  which  appears  to  be  a  product  of  the  decomposition  of 

•vr  TT    ~p  f\ 

deutazophosphoric  acid,  is  most  probably  pyrophosphamic  acid,     3   JT  2   6  j  06, 
the  tribasic  amidogen  acid  of  quadribasic  pyrophosphoric  acid,  P2H40,4. 

Quantitative  estimation  of  Phosphorus  and  its  compounds.  —  Phosphorus  is 
always  estimated  in  the  form  of  phosphoric  acid.  When  it  occurs  in  combination 
with  a  metal,  or  in  an  organic  compound,  or  as  phosphorous  or  hypophosphorous 
acid,  it  is  brought  to  the  highest  state  of  oxidation  by  treatment  with  nitric  acid, 
aqua-regia,  or  a  mixture  of  hydrochloric  acid  and  chlorate  of  potash. 

The  precipitation  of  phosphoric  acid  (tribasic)  from  an  aqueous  solution,  in 
which  it  exists  in  the  free  state  or  combined  with  an  alkali,  is  best  effected  by  the 
addition  of  sulphate  of  magnesia  and  excess  of  ammonia,  chloride  of  ammonium 
being  likewise  added  to  prevent  the  precipitation  of  magnesia  in  the  form  of 
hydrate.  The  phosphoric  acid  is  then  precipitated  as  phosphate  of  magnesia  and 
ammonia,  NH4O.2MgO.P06.  The  precipitate  does  not  settle  down  at  once,  but 
its  deposition  may  be  accelerated  by  leaving  the  vessel  in  a  warm  place.  Care 
must  be  taken,  however,  not  to  allow  the  liquid  to  become  very  hot,  as  in  that 
case  hydrate  of  magnesia  will  be  precipitated,  and  will  be  very  difficult  to  re- 
dissolve.  The  precipitate,  after  standing  for  about  two  hours,  is  collected  on  a 
filter  and  washed  with  water  containing  ammonia,  as  pure  water  decomposes  it. 
It  is  then  dried  and  ignited,  whereby  it  is  converted  into  pyrophosphate  of 
magnesia,  2MgO.P05,  containing  63*67  per  cent,  of  phosphoric  acid,  P05,  and 
27  '98  per  cent,  of  phosphorus. 

If  the  phosphoric  acid  is  in  the  monobasic  or  bibasic  modification,  it  must  first 
be  converted  into  the  tribasic  acid  by  fusing  the  salt  with  five  or  six  times  its 
weight  of  carbonate  of  soda,  or,  better,  with  a  mixture  of  carbonate  of  potash  and 
carbonate  of  soda  in  equivalent  proportions.  The  mixture  may  then  be  fused 
over  a  lamp,  whereas  if  carbonate  of  soda  or  carbonate  of  potash  alone  be  used, 


SULPHITE    OF    PERCIILORIDE    OF    CARBON.  791 

the  heat  of  a  furnace  will  be  required.  By  this  fusion  with  excess  of  an  alkaline 
carbonate,  the  phosphoric  acid  is  in  most  cases  completely  separated  from  any 
other  base  with  which  it  may  be  combined,  and  converted  into  a  tribasic  phos- 
phate of  the  alkali,  which  may  then  be  treated  as  above. 

Phosphates  which  are  insoluble  in  water,  may  be  dissolved  in  nitric  or  hydro- 
chloric acid ;  and  from  these  solutions,  the  bases  may  in  some  cases  be  precipitated 
by  hydrosulphuric  acid,  in  others  by  sulphide  of  ammonium,  and  the  phosphoric 
acid  subsequently  precipitated  from  the  filtered  solution  in  the  form  of  the  amrno- 
nio-magnesian  phosphate  in  the  manner  above  described. 

To  separate  phosphoric  acid  from  the  earths^  other  methods  are  required.  From 
baryta  it  is  easily  separated  by  sulphuric  acid,  .which  throws  down  the  baryta ; 
from  strontia  and  lime,  also,  by  sulphuric  acid  with  addition  of  alcohol.  From 
maynesia  it  may  be  separated  by  fusion  with  a  mixture  of  carbonate  of  potash  and 
carbonate  of  soda  in  equivalent  proportions.  From  alumina  it  is  most  readily 
separated  by  dissolving  the  compound  in  hydrochloric  acid,  adding  sufficient  tar- 
taric  acid  to  keep  the  alumina  in  solution  when  the  liquid  is  neutralized  by  an 
alkali,  and  then  adding  excess  of  ammonia  and  sulphate  of  magnesia,  whereby  a 
precipitate  of  ammonio-magnesian  phosphate  is  produced,  which  may  be  treated  a? 
already  described.  This  method  may  also  be  applied  to  the  separation  of  phos- 
phoric acid  from  iron. 

When  phosphoric  acid  exists  in  combination  with  several  earthy  bases  together, 
it  may  be  separated  by  dissolving  the  compound  in  nitric  acid,  adding  metallic 
mercury  in  slight  excess,  evaporating  over  the  water-bath  to  perfect  dryness,  and. 
treating  the  residue  with  water.  The  whole  of  the  phosphoric  acid  then  remains 
undissolved  in  the  form  of  mercurous  phosphate,  while  the  bases  pass  into  the 
solution  as  nitrates.  (H.  Hose).  This  method,  however,  requires  attention  to  a 
number  of  details  and  precautions  which  cannot  here  be  given. 

Another  method  of  separating  phosphoric  acid  from  a  mixture  of  bases,  by 
means  of  acetate  of  uranium,  has  already  been  described  (p.  557). 

The  salts  of  phosphorous  and  hypophosphorous  acid  may  be  oxidized  by  nitric 
acid,  the  former  being  thereby  converted  into  pyrophosphates,  the  latter  into  meta- 
phosphates.  These  salts  must  then  be  converted  into  tribasic  phosphates  in  the 
manner  above  described. 

Phosphorous  and  hypophosphorous  acid  may  also  be  estimated  by  their  power 
of  precipitating  gold  in  the  metallic  state  from  its  solutions,  or,  better,  by  their 
reducing  action  on  mercuric  chloride,  which,  when  present  in  excess,  is  reduced 
to  mercurous  chloride. 

CHLORINE. 

Chloride  of  Nitrogen  (p.  345). — According  to  Bineau,*  this  compound  is  NC13, 
that  is  to  say,  ammonia  in  which  all  the  hydrogen  is  replaced  by  chlorine  Bineau's 
analysis  gives  10-6  p.c.  N,  and  89-3  01;  the  formula  requires  11-65  N,  and  88-35 
01.  According  to  Porrett,  Wilson,  and  Kirk,t  it  is  NHC13;  according  to  Glad- 
stone,J  NgHCl.,  or  NHC12  +  NC13. 

Sulphite  of  Per  chloride  of  Carbon,  C2C14.  2S02 — This  body  was  discovered  by 
Berzelius  and  Marcet,  who  obtained  it  by  the  action  of  aqua-regia  on  bisulphide 
of  carbon  j  but  a  better  mode  of  obtaining  it  is  the  following:  —  A  bottle,  capable 
of  holding  about  three  pints,  is  half  filled  with  a  mixture  of  peroxide  of  manga- 
nese and  hydrochloric  acid ;  about  800  grains  of  bisulphide  o£  carbon  are  then 
added  j  the  vessel  quickly  closed,  and  left  for  some  days  in  a  cool  place.  It  is 
then  exposed  for  several  days  longer  to  a  temperature  of  30°  G.  (86°  F.),  or  in 
summer  to  direct  sunshine,  and  frequently  shaken,  till  the  greater  part  of  the 
bisulphide  of  carbon  is  converted  into,  the  new  compound.  The  action  may  be 

*  Ann.  Ch.  Phys.  [3],  xv.  71.  f  Gmelin's  Handbook,  ii.  472. 

Cueui.  Soc.  Qu.  J.,  vii.  51. 


792  CHLORINE. 

greatly  accelerated  by  adding  a  quantity  of  nitric  acid  equal  in  weight  to  twice 
that  of  the  bisulphide  of  carbon  used.  The  mixture  is  then  distilled, "whereupon 
11  n  decora  posed  bisulphide  of  carbon  first  passes  over,  together  with  chloride  of  sul- 
phur and  a  peculiar  yellow  liquid  (C4S4C14),  and  afterwards  the  sulphite  of  per- 
chloride  of  carbon  condenses  in  the  solid  form  in  the  neck  of  the  retort.  The 
formation  of  this  compound  is  represented  by  the  following  equation  :  — 

2CS2  +  8C1  -f  4HO  =  C2C14 .  2S02  +  4HC1  +  28. 

Sulphite  of  perchloride  of  carbon  is  a  white  crystalline  solid  having  a  highly 
pungent  odour,  and  exciting  tears.  It  melts  at  135°  C.  and  boils  at  170°;  may 
be  sublimed,  and  forms  small  rhombohedral  crystals,  It  is  soluble  in  alcohol, 
ether,  and  bisulphide  of  carbon ;  insoluble  in  water.  It  is  decomposed  at  a  dull 
red  heat,  yielding  chlorine,  sulphurous  acid,  and  protochloride  of  carbon  :  — 

2(C2C14.  2S02)  =  401  +  4S02  +  2C2C12. 

It  decomposes  slowly  in  contact  with  water  or  moist  air,  yielding  sulphurous,  sul- 
phuric, carbonic,  and  hydrochloric  acids.  Heated  with  a  large  excess  of  strong 
sulphuric  acid,  it  gives  off  sulphurous  acid,  anhydrous  sulphuric  acid,  hydro- 
chloric acid,  and  phosgene  gas  :  — 

C2C14.  2S02  +  2S04H  =  2S02  -f  2S03  +2HC1  +  2COC1.* 

Ohlorosulphide  of  Carbon,  C4S4C14. — The  liquid  distillate  obtained  in  the  prepa- 
ration of  the  preceding  compound  contains  this  substance,  which  may  be  obtained 
from  it  in  a  state  of  purity  by  repeated  distillation  with  water  and  hydrate  of  mag- 
nesia, which  decomposes  the  chloride  of  sulphur.  It  may  also  be  prepared  by 
exposing  bisulphide  of  carbon  to  sunshine  in  an  atmosphere  of  dry  chlorine  — 

CS2  +  2C1  =  SCI  -f  CSC1, 

and  purified  as  above.  Also  by  passing  a  mixture  of  hydrosulphuric  acid  gas  and 
vapour  of  perchloride  of  carbon  through  a  red-hot  tube :  — 

2C2C14  +  4HS  =  4HC1  +  C4S4C14. 

It  is  a  yellow  liquid,  not  miscible  with  water;  has  a  peculiar  and  powerful  odour, 
and  irritates  the  eyes  very  strongly ;.  Sp.  gr.  1-46.  It  boils  at  70°  C.  (158°  F.)  It 
is  not  decomposed  by  water  or  acids,  not  even  by  nitric  acid.  Bisulphide  of 
carbon  and  caustic  potash  decompose  it  gradually.  It  absorbs  ammoniacal  gaa 
(Kolbef). 

Sulphite  of  Protochloride  of  Carbon,  C2C12 .  2S02.  —  Formed  by  the  action  of 
reducing  agents,  viz.,  sulphurous  acid,  hydro-sulphuric  acid,  zinc,  iron,  proto- 
chloride of  tin,  &c.,  on  the  sulphite  of  perchloride  of  carbon.  It  has  not  been 
obtained  in  the  anhydrous  state.  It  dissolves  in  water  and  alcohol,  and  is  best 
prepared  in  the  state  of  solution,  by  passing  sulphurous  acid  gas  through  an  alco- 
holic solution  of  sulphite  of  perchloride  of  carbon.  The  solution  is  colourless  and 
inodorous,  has  an  acid  reaction,  and  absorbs  oxygen  rapidly,  forming  sulphuric 
acid  and  phosgene  :  — 

C2C12.2SO2  -f-  40  =  2S03  -I-  2COC1. 

Chlorine  converts  it  into  C2C14.2S02.     (Kolbe). 

Perchlorocarbosulphurous  acid,  C2C130.2S02.HO. —  Formed  by  the  action  of 
caustic  alkalies  on  sulphite  of  perchloride  of  carbon : — 

C2C14.2S02  +  2KO  =  C2C130.2S02.KO  -f  KC1. 

The  hydrated  acid  is  obtained  by  decomposing  the  baryta-salt  with  sulphuric  acid. 
It  crystallizes  in  small  deliquescent  prisms,  which  may  be  partially  sublimed  with- 
out decomposition.  They  contain  2  at.'  water  of  crystallization,  their  formula 

*  Kolbe,  Ann.  Ch.  Pharm.  liv.  148.  f  Ibid.  xlv.  53- 


CHLORIDES    OF    SULPHUR.  793 

being  C2C130.2S02.HO  -f  2HO.  The  acid  is  not  decomposed  by  fuming  nitric 
acid  or  aqua-regia,  and  is  so  powerful  an  acid  that  it  expels  hydrochloric  acid  from 
its  combinations.  Its  salts  are  all  soluble  in  water  and  alcohol,  and  crystallize 
with  facility.  When  heated  they  are  resolved  into  phosgene,  sulphurous  acid, 
and  a  metallic  chloride ;  e.  g. 

C2C130.2S03.KO  =  2COC1  +  2S02  +  KC1. 

Chlorocarbosulphurous  acid,  C2C12.2S02.2HO. — Formed  by  the  action  of  alka- 
lies on  sulphite  of  protochloride  of  carbon,  or  by  the  action  of  zinc  on  the  pre- 
ceding acid.  Resembles  the  preceding  in  most  of  its  properties.  Its  salts,  when 
heated,  give  off  phosgene,  sulphurous  acid,  and  water,  and  leave  a  residue  of  me- 
tallic chloride  and  charcoal. 

Chloromethylomlphurous  acid,  C2HC1.2S02.2HO.  —  Formed  by  the  continued 
action  of  nascent  hydrogen  on  chlorocarbosulphurous  acid  : — 

C2C12.2S02.2HO  +  H  =  C2HC1.2S02.2HO  +  HC1. 

When  zinc  is  immersed  in  an  aqueous  solution  of  chlorocarbosulphurous  acid,  it 
dissolves  with  evolution  of  hydrogen;  and  the  hydrogen,  as  it  is  set  free,  con- 
verts part  of  the  acid  into  chloromethylosulphurous  acid ;  but  complete  transfor- 
mation can  only  be  obtained  by  subjecting  an  acidulated  solution  of  a  perchloro- 
carbosulphite  or  chlorocarbosulphite  to  the  action  of  the  galvanic  current.  The 
hydrated  acid  is  a  viscid,  strongly  acid  liquid,  which  bears  a  heat  of  140°  C. 
without  decomposition ;  at  — 16-6°  C.  it  becomes  syrupy ;  in  other  respects  it  re- 
sembles perchlorocarbosulphurous  acid.  All  its  salts  are  soluble  in  water,  and 
crystallizable. 

Metht/losulphurous  acid,  C2H30.2S02.HO.  —  Formed  when  a  neutral  solution 
of  perchlorocarbosulphite  of  potash  is  decomposed  by  the  electric  current,  the 
electrodes  being  formed  of  amalgamated  zinc  plates  : — 

C2C130.2S02.KO  -f  6Zn  +  6HO  =  C2H30.2S02.KO  +  6ZnO  +  3HC1. 
Also  when  an  amalgam  of  potassium  is  immersed  in  the  same  solution, 

G2C130.2S02.KO  +  6K  +  3HO  =  C2H30.2S02.KO  +  3KC1  +  3KO. 

The  concentrated  solution  of  the  hydrated  acid  is  a  sour,  inodorous,  viscid  liquid, 
which  maybe  heated  to  nearly  130°  C.  without  decomposition,  but  at  that  tempe- 
rature begins  to  turn  brown  and  decompose.  It  does  not  crystallize  when  pure. 
It  is  equal  to  perchlorocarbosulphurous  acid  in  stability  and  in  affinity  for  bases. 
Its  salts  are  soluble  and  crystallizable.  (Kolbe*). 

Intermediate  Chloride  of  Sulphur,  S4C13.  —  Protochloride  of  sulphur  is  readily 
decomposed  by  heat,  its  boiling  point  rising  quickly  from  64°  to  78°  C.,  where  it 
remains  stationary.  The  deep  orange-yellow  liquid  thus  obtained  appears  to  be 
composed  of  S4C>3  =  S2C1  -f  2S01. 

Terchloride  of  Sulphur,  SC13.  —  Not  known  in  the  separate  state,  but  exists  in 
the  compound,  SC13.5S03,  obtained  by  mixing  the  protochloride  of  sulphur,  SCI, 
with  Nordhausen  sulphuric  acid,  and  distilling.  Sulphurous  acid  and  anhydrous 
sulphuric  acid  pass  over  first,  then  the  compound  SC13.5S03,  while  monohydrated 
sulphuric  acid  remains  in  the  retort.  The  compound  SC13.5S03  is  a  colourless 
oily  liquid  having  a  peculiar  odour,  and  fuming  slightly  in  the  air,  Its  density 
is  1-818,  and  that  of  its  vapour  4-481.  Boils  at  145°  C.  (283°  F.).  Water  de- 
composes it  rapidly,  forming  sulphuric  and  hydrochloric  acids.  (H.  Rose.) 

Chlorosulphuric  acid,  S02C1,  is  regarded  by  some  chemists  as  a  bisulphate  of 
terchloride  of  sulphur,  SCl3.2S03.f 

*  Ann.  Ch.  Pharm.  liv.  143. 

f  See  page  301,  line  25,  where,  however,  there  is  a  misprint,  the  formula  being  given  as 
3S03.SC13  instead  of  2S03.SC13. 


794  CHLORINE. 

Sulphate  of  Bichloride  of  Sulphur,  SC]2.S03=S2C1203.— Formed  by  the  action 
of  moist  chlorine  gas  on  pro toch Wide  of  sulphur.  Large  transparent  colourless 
crystals,  which  are  decomposed  by  alcohol  and  water,  or  even  by  exposure  to  damp 
air.  Enclosed  in  a  sealed  glass  tube,  they  change  in  the  course  of  a  few  months 
into  a  very  mobile,  slightly  yellow  liquid,  which  has  the  same  composition  as  the 
crystals,  but  does  not  solidify  at —  18°  C.  (0°  F.).  It  is  dissolved  by  water,  with 
formation  of  sulphuric  and  hydrochloric  acids.  The  compound  S2C1203  may  be 
regarded  as  hyposulphuric  acid  in  which  2  at.  0  are  replaced  by  chlorine. 
(Millon.*) 

Ohlorosulphide  of  Phosphorus,  PS,0C14. — Besides  the  chlorosulphide  of  phos- 
phorus described  on  page  849,  another  compound  of  these  elements,  having  the 
formula  just  given,  is  obtained  by  passing  a  stream  of  phosphuretted  hydrogen 
into  dichloride  of  sulphur.  This  compound  is  a  yellow  syrupy  liquid,  which  is* 
decomposed  by  water,  with  evolution  of  hydrosulphurfc  acid  and  deposition  of  sul- 
phur. It  may  be  regarded  as  a  compound  of  dichloride  of  sulphur  with  a  pecu- 
liar sulphide  of  phosphorus,  not  yet  isolated  : — 

4S2C1  +  PS2  ==  PS10C14. 

This  compound  was  discovered  by  H.  Rose. 

Sulphide  of  Pentachloride  of  Phosphorus,  PC15.S4. — "When  a  mixture  of  3  pts. 
pentachloride  of  phosphorus  and  1  pt.  of  sulphur  is  melted,  a  colourless  liquid  is 
obtained,  which  boils  at  about  100°  C.  It  dissolves  large  quantities  of  penta- 
chloride of  phosphorus  and  sulphur,  the  latter  of  which  it  deposits  in  crystals;  it 
is  very  difficult  to  purify.  Water  decomposes  it  immediately,  with  formation  of  a 
great  number  of  products  (Gladstone. )•(•  The  compound  may  be  regarded  as 
PS2Cl3+Cl2S2(SchiffJ). 

Action  of  acids  on  Pentachloride  of  Phosphorus.  —  Persoz.  and  Bloch,§  by 
passing  dry  sulphurous  acid  gas  over  pentachloride  of  phosphorus,  obtained  a 
volatile,  strongly  refracting  liquid  which  they  regarded  as  PC15.2S02.  According 
to  Schiff||,  however,  this  liquid  is  decomposed  by  fractional  distillation,  being  re- 
solved into  oxychloride  of  phosphorus  which  boils  at  110°  C.  (230  F.),  and  a 
more  volatile  liquid,  which  passes  over  at  82°  C.  (147'6  F.).  This  latter  is  the 
chloride  of  thionyl.  S202.C12,  the  name  thionyl  denoting  the  biatomic  radical,  S20:, 

Q  C\ 

of  sulphurous  acid  and  its  salts,  hydrated  sulphurous  acid  being  Vr2  \  04,  and  an- 
hydrous sulphurous  acid,  S202.02.  Chloride  of  thionyl  is  a  volatile  liquid  of  great 
refracting  power,  and  having  a  suffocating  odour  like  that  of  sulphurous  acid.  It 
is  decomposed  by  water,  and  more  readily  by  alkalies,  into  hydrochloric  and  sul- 
phurous acids.  With  alcohol,  it  yields  hydrochloric  and  ethylosulphurous  acids. 

Q  r\ 

Thionamide,  N2  J  rr  2,  is  produced  when  chloride  of  thionyl  is  brought  in  con- 
-tl4 

tact  with  dry  ammonia  : 

S202.  01,  +  4NH3  =  2NH4C1  +  N2(S802)H4. 

The  action  is  very  violent,  but  may  be  moderated  by  cooling.  The  product  is  a 
white,  non-crystalline  solid,  which  gives  up  sal-ammoniac  when  digested  in  water, 
and  is  afterwards  completely  decomposed. 

Anhydrous  sulphuric  acid  acts  upon  pentachloride  of  phosphorus  in  the  same 
manner  as  anhydrous  sulphurous  acid,  producing  a  liquid  which  Persoz  and  Blocli 
regarded  as  PC15 .  2S03,  but  which,  according  to  Schiff,  is  resolved  by  distillation 

*  Ann.  Ch.  Pharm.  Hi.  230 ;  Ixxvi.  235.  t  Chem.  Soc.  Qu.  J.  iii.  5. 

%  Ann.  Ch.  Pharm.  ci.  309.  \  Compt.  rend,  xxvii.  86. 

j|  Ann.  Ch.  Pharm.  cii.  111. 


SULPHOBROMIDE    OF    PHOSPHORUS.  795 

into  oxychloride  of  phosphorus,  and  chloride  of  sulphuryl  or  chlorosulphuric  acid, 
S204-C12. 

With  hydrated  sulphuric  acid,  pentachloride  of  phosphorus  forms  chlorohy- 
dratcd  sulphuric  acid,  S2HC106  : 

S404  +  PC15  =  °2  +  HC1  +  PO.C13. 


And  this  compound,  by  the  further  action  of  the  pentachloride,  is  converted  into 
chlorosulphuric  acid,  S204  .  C12  (p.  709).  Chlorohydrated  sulphuric  acid  is  a 
liquid  which  boils  at  145°  C.,  is  decomposed  by  water,  yielding  hydrochloric  and 
sulphuric  acids,  and  dissolves  chloride'  of  sodium  at  a  gentle  heat,  with  evolution 
of  hydrochloric  acid  and  formation  of  the  compound  S2NaC106.  It  effervesces 
with  melted  nitre,  giving  off  a  vapour  (probably  N04C1)  which  smells  like  aqua- 
regia,  and  when  passed  into  water,  forms  nitric  and  hydrochloric  acids.  The 
compound  i?2HC106  is  probably  identical  with  that  which  H.  Rose  obtained  by  the 
action  of  sulphuric  acid  on  pentachloride  of  sulphur,  and  regarded  as  S203C1.  It 
is  likewise  obtained  in  small  quantity  by  the  action  of  strongly  heated  platinum- 
black  on  an  imperfectly  dried  mixture  of  chlorine  and  sulphurous  acid.  (Wil- 
liamson*). 

Tunystic  acid  treated  with  pentachloride  of  phosphorus  yields  pxychloride  of 
phosphorus  and  an  oxychloride  of  tungsten,  W204C12.  Similarly  with  molybdic 
acid. 

Hydrated  antimonic  acid  heated  with  pentachloride  of  phosphorus  yields  hydro- 
chloric acid  and  oxychloride  of  phosphorus,  with  a  residue  of  anhydrous  antimonic 
acid. 

Anhydrous  phosphoric  acid  and  pentachloride  of  phosphorus  form  oxychloride 
of  phosphorus  : 

P20IO  +  3PC16  =  5P02C13. 

When  strong  nitric  acid  is  cautiously  added  to  pentachloride  of  phosphorus, 
hydrochloric  acid  is  evolved  ;  and  if  the  escaping  vapour  be  passed  through  a  good 
refrigerating  apparatus,  a  blood-red  liquid  condenses,  which  when  distilled  yields 
yellowish-red  vapours,  probably  N04C1,  and  distillate  of  oxychloride  of  phosphorus. 
(Schiff). 

Chlorophosphide  of  Nitrogen  ,P2N2C15  according.  to  Wohler  and  Liebig,  who  dis- 
covered it  ;  P3N2C13  according  to  Gladstone  ;  PN»C12  according  to  Laurent.  It  is 
formed  by  the  action  of  ammonia  on  pentachloride  of  phosphorus.  On  treating 
the  crude  product  with  ether,  the  chlorophosphide  of  nitrogen  is  alone  dissolved, 
and  may  then  be  crystallized.  It  is  also  produced  by  distilling  a  mixture  of  1  pt. 
pentachloride  of  phosphorus  with  2  pts.  sal-ammoniac.  It  may  be  purified  by 
distillation  with  water,  being  carried  over  by  the  vapour  of  water,  and  then  only 
requires  to  be  dried.  It  crystallizes  in  rhomboidal  prisms;  melts  at  110°,  and 
boils  at  240°  C.  It  is  insoluble  in  water,  but  dissolves  in  alcohol,  ether,  and  oil 
of  turpentine.  Alkalies  decompose  it,  with  formation  of  phosphamic  acid  (p.  790). 

BROMINE. 

Bromine  of  Nitrogen.  —  When  chloride  of  nitrogen  is  gently  heated  with  bro-  - 
mide  of  potassium,  double  decomposition  takes  place,  and  a  brown,  very  heavy, 
oily  liquid  is  formed,  which  appears  to  be  bromide  of  nitrogen.  It  is  very  vola- 
tile, has  an  offensive  odour,  and  irritates  the  eyes  strongly.  It  detonates  easily, 
and  is  decomposed  by  hydrochloric  acid,  hydrubromic  acid,  and  ammonia.  Its 
composition  appears  to  be  NBr3.  (Millon). 

Oxybromide  of  Phosphorus,  PBr302.  —  Produced  by  the  decomposition  of  the 

*  Proceedings  of  the  Royal  Society,  vii.  11. 


796  IODINE. 

pentabiomide  in  moist  air.  "When  the  thick  reddish  liquid  thus  formed  is  heated, 
to  drive  off  the  hydrobromic  acid  which  it  contains,  and  then  distilled  at  about 
180°  C.  (366°  F.),  the  oxybromide  passes  over  in  the  form  of  a  colourless  heavy 
liquid,  which  boils  between  170°  and  200°  C.  It  does  not  mix  with  water,  but 
is  slowly  decomposed  by  that  liquid,  with  formation  of  phosphoric  and  hydro- 
bromic acids.  It  dissolves  in  oil  of  turpentine,  ether,  and  strong  sulphuric  acid, 
and  is  precipitated  from  the  last-mentioned  solution  by  water.  Nitric  acid  decom- 
poses it,  with  evolution  of  bromine.  Another  body,  apparently  of  the  same  com- 
position, but  solid  and  crystalline,  is  sometimes  obtained  as  a  residue  in  the  dis- 
tillation of  pentabromide  or  oxybromide  of  phosphorus,  and  by  the  action  of  moist 
air  on  the  pentabromide  in  an  imperfectly-closed  vessel.  It  is  decomposed  by 
water,  melts  and  volatilizes  when  heated,  but  on  cooling  remains  as  a  liquid, 
exhibiting  the  characters  of  the  oxybromide.  (Gladstone*). 

Sulphobromide  of  Phosphorus. — Pentabromide  of  phosphorus  is  decomposed  by 
hydrosulphuric  acid,  with  formation  of  a  heavy  liquid,  which  boils  without  decom- 
position at  200°  C.,  and  appears  to  have  the  composition  3PBr3.PS3;  it  may, 
however,  be  a  mixture  of-  two  compounds  having  nearly  the  same  boiling  point. 
(Gladstonef). 

IODINE. 

Natural  sources  of  Iodine. — According  to  Chatin,J  iodine  exists  in  the  air,  in 
nearly  all  water,  and  in  a  great  number  of  plants,  land  and  fresh-water  as  well  as 
marine ;  also  in  coal,  in  various  chemical  products,  viz.,  commercial  potash,  soda, 
and  sal-ammoniac,  in  wine,  cider,  perry,  &c.,  in  milk  and  eggs.  He  finds  also 
that  iodine  is  least  abundant  in  the  air  and  water  of  those  localities  in  which 
goitre  and  cretinism  prevail.  Similar  results  have  been  obtained  by  other  che- 
mists. On  the  other  hand,  Macadam, §  Lomeyer,||  and  others  have  not  been  able 
to  detect  iodine  in  the  air  or  in  rain-water.  Macadam,  however,  found  iodine  in 
commercial  potash,  in  numerous  samples  of  alkaline  carbonates  (used  as  reagents), 
in  the  ashes  of  wood-charcoal,  in  coal,  and  in  numerous  plants.  Lomeyer  exam- 
ined particularly  the  air  and  water  of  various  localities  where  goitre  is  scarce,  but 
found  no  trace  of  iodine.  Chatin  ^f  attributes  the  negative  results  obtained  by 
Macadam  and  Lomeyer  to  defective  methods  of  analysis,  but  does  not  give  any 
exact  description  of  his  own  process. 

Hypoiodic  acid,  I04,  and  Sub-hypoiodic  acid,  I60,9  =  4I03  +  I07.  —  When 
one  part  of  iodic  acid  and  5  parts  of  mouohydrated  sulphuric  acid  are  heated  in  a 
platinum  crucible,  till  oxygen  gas  and  afterwards  vapours  of  iodine  are  evolved,  a 
green  solution  is  obtained ;  and  on  leaving  this  for  some  days  in  a  dry  atmosphere, 
a  yellow  crystalline  crust  is  deposited,  which,  when  freed  from  the  excess  of  sul- 
phuric acid  and  washed  with  water  and  alcohol,  yields  sub-hypoiodic  acid;  and 
this  compound  heated  to  150°  C.  gives  off  vapour  of  iodine,  and  is  converted  into 
hypoiodic  acid.  The  latter  is  a  sulphur-yellow  amorphous  powder,  which  at  180° 
C.  is  resolved  into  iodic  acid  and  iodine.  Water  and  nitric  acid  decompose  it  in 
a  similar  manner.  Sulphuric  acid  dissolves  it  with  the  aid  of  heat,  and  on  cool- 
ing deposits  a  compound  consisting  of  I04 .  4SH04.  Aqueous  alkalies  decompose 
hypoiodic  acid,  forming  iodates  and  the  other  compounds  which  result  from  the 
action  of  iodine  on  alkalies. 

Sub-hypoiodic  acid  bears  a  considerable  resemblance  to  hypoiodic  acid,  both  in 
physical  and  chemical  properties.  When  heated,  it  gives  off  iodine  and  leaves 
hypoiodic  acid.  (Millon.) 

*  Phil.  Mag.  [3],  xxxv.  345.  f  Ibid. 

J  Compt.  rend.  xxx.  352;  xxxi.  280;  xxxii.  669;  xxxiii.  519,  529,  581. 

|  Chem.  Soc.  Qu.  J.,  vi.  166.  ||  Phil.  Mag.  [4],  vii.  237. 

f  .J.  Phann.  [3],  xxv.  192. 


IODIDE    OF    NITROGEN.  797 

Iodide  of  Nitrogen  (p.  358). — Gladstone*  has  analyzed  this  compound  (as 
prepared  by  precipitating  an  alcoholic  solution  of  iodine  with  excess  of  ammonia 
and  washing  with  water),  and  arrived  at  results  which  accord  with  Bineau's 
formula,  NHI2.  By  decomposing  the  compound  with  hydrosulphuric  acid,  he 
finds  that  it  contains  21  to  IN,  while  its  decomposition  by  aqueous  sulphurous 
acid  agrees  with  the  equation  — 

NHI2  +  4S02  +  4HO  =  NH3  +  2HI  +  4S03. 

Gladstone  suggests  for  the  compound  the  name  iodimide.  He  also  finds  the 
above  formula  to  be  in  accordance  with  the  formation  of  the  compound  by  the 
action  of  hypochlorite  of  lime  on  iodide  of  ammonium  (observed  by  Playfair), 
that  reaction  being  attended  with  evolution  of  ammonia,  according  to  the 
equation  — 

2(CaO.C10)  +  2NH4I  =  NHI2  +  2CaCl  +  4HO  +  NH3. 

Bunsen  takes  a  different  view  of  the  constitution  of  iodide  of  nitrogen.  He 
observes  :  1.  That  the  mode  of  formation  of  this  compound  from  iodine  and 
ammonia,  with  hydriodic  acid  as  the  only  secondary  product,  shows  that  it  must 
be  a  substitution-product  of  ammonia,  of  the  form  NI3,  NHI2  or  NH2I,  associated 
at  most  with  ammonia  or  hydriodic  acid ;  2.  That  it  cannot  contain  hydriodic  acid, 
because  it  dissolves  in  hydrochloric  acid  without  evolution  of  gas,  and  forms  a 
solution  containing  ammonia  and  protochloride  of  iodine,  but  no  hydriodic  acid; 
8.  That,  to  determine  its  composition,  it  is  sufficient  to  ascertain  how  much  101 
and  how  much  NH3  it  yields  with  hydrochloric  acid,  and  to  see  which  of  the 
following  equations  agrees  with  the  results  : — 

(a)  NI,  +  3HC1  =  3IC1  +  NH3. 

(b)  NHI2  +  2HC1  =  2IC1  +  NH3. 

(c)  NH2I  +  HC1  =  IC1  +  NH3. 

(d)  NH2I  +  NH3  +  HC1  =  IC1  +  2NH3,  &c. 

Preparations  obtained  by  mixing  cold  and  more  or  less  saturated  anhydrous 
alcoholic  solutions  of  iodine  and  ammonia,  which  were  not  decomposed  by  washing 
with  absolute  alcohol,  gave,  when  dissolved  in  hydrochloric  acid,  quantities  of 
ammonia,  iodine,  and  chlorine,  in  the  atomic  proportion  of  2:3:3,  showing  that 
the  constitution  of  the  compound  is  NI3  +  NH3.  A  preparation  obtained  by 
adding  ammonia  to  a  solution  of  iodine  in  aqua-regia  diluted  with  water,  and 
washed  as  quickly  as  possible  with  cold  water,  gave,  with  hydrochloric  acid, 
quantities  of  ammonia  and  protochloride  of  iodine  in  the  atomic  proportion  of 
5  : 12,  showing  that  its  formula  was  4NI3  -f-  NH3.  When  washed  with  water  for 
any  length  of  time,  even  till  the  greater  part  of  the  compound  was  decomposed, 
with  separation  of  iodine  and  nitrogen,  the  undecomposed  portion  still  yielded 
more  than  1  at.  ammonia  to  3  at.  chloride  of  iodine,  a  proof  that  ammonia  enters 
essentially  into  its  constitution.  Bunseu  is  of  opinion  that  there  exist  two  distinct 
compounds,  NI3.NH3  and  4NI3.NH3,  formed  in  the  manner  shown  by  the 
equations  — 

2NH3  +  61  =  (NI..NH,)  +  SHI; 
4(NI3.NH3)  +  3HO  =  4NI3.NH3+  3NH4O. 

The  formation  of  the  so-called  iodide  of  nitrogen  by  the  -action  of  ammonia  on  a  . 
solution  of  iodine  in  aqua-regia,  would  be  inconsistent  with  this  view,  if  that 
solution  contained,  not  IC1,  but,  as  is  commonly  supposed,  IC13,  because  NI3 
could  not  be  formed  by  the  action  of  ammonia  upon  the  latter.  Experiment, 
however,  shows  that  the  solution  of  iodine  in  aqua-regia  contains  only  101.  The 
formation  of  the  so-called  iodide  of  nitrogen  from  IC1  is  explained  by  the 
equation  —  \ 

2NH3  +  3101  =  (NI..NH,)  +  3HC1. 

«  Chem.  Soc.  Qu.  J.  v.  34. 


798  IODINE. 

The  immediate  products  of  its  explosion  are  nitrogen  and  hydriodic  acid : 

NI3.NH3  =  2N  +  SHI, 

which  latter  is  for  the  most  part  resolved  by  the  high  temperature  into  iodine  and 
hydrogen,  while  another  portion  unites  with  the  ammonia  of  the  compound,  form- 
ing iodide  of  ammonium,  thereby  setting  free  quantities  of  iodine  and  nitrogen 
equivalent  to  this  ammonia.* 

Gladstone,  in  a  subsequent  communication,*)"  remarks  that  his  mode  of  prepar- 
ing the  iodide  of  nitrogen  differs  essentially  from  that  of  Bunsen,  and  that  his 
formula  NHI2  may  be  written  2NI3  -f-  NH3,  which  shows  it  to  be  intermediate 
between  the  two  formulae  given  by  Bunsen.  He  concludes,  from  further  experi- 
ments, that  the  formula  NHI2  is  true,  not  only  for  the  preparation  obtained  by 
the  method  described  in  his  former  paper,  but  likewise  for  that  obtained  by  preci- 
pitation from  solutions  of  iodine  and  ammonia  in  absolute  alcohol. 

Iodides  of  Phosphorus  (p.  358).  —  These  compounds  are  best  prepared  by  dis- 
solving iodine  and  phosphorus  together  in  bisulphide  of  carbon,  and  cooling  the 
solution  till  it  crystallizes.  There  appear  to  be  only  two  iodides  of  phosphorus, 
viz.  PI2  and  PI3,  which  are  prepared  by  dissolving  the  two  substances  as  above, 
in  the  respective  atomic  proportions ;  if  they  be  mixed  in  any  other  proportions, 
the  same  compounds  crystallize  out,  together  with  the  excess  of  iodine  or 
phosphorus. 

The  biniodide,  PI2,  is  a  light-red  solid  body,  which  melts  at  110°  C.,  forming  a 
red  liquid.  Water  decomposes  it,  with  formation  of  hydriodic  and  phosphorous 
acid,  and  deposition  of  yellow  flakes.  When  melted  with  excess  of  phosphorus 
and  decomposed  by  water,  it  jaelds  red  phosphorus.  It  dissolves  in  bisulphide 
of  carbon,  and  is  deposited  from  the  solution  in  flattened  prismatic  crystals,  of  a 
light-orange  colour. 

The  teriodide,  PI3,  forms  dark-red  six  sided  laminae,  which  dissolve  very  readily 
in  bisulphide  of  carbon,  and  rapidly  absorb  moisture  from  the  air.  It  melts  at 
55°  C.,  and  crystallizes  in  well-defined  prisms  on  cooling.  At  a  higher  tempera- 
ture, it  is  decomposed,  giving  off  vapours  of  iodine.  Water  decomposes  it,  with 
formation  of  hydriodic  and  phosphorous  acids,  and  formation  of  an  orange-yellow 
flaky  deposit.  (Gorenwinder.)J 

Estimation  and  separation  of  Chlorine,  Bromine,  and  Iodine.  —  Chlorine,  in 
the  form  of  hydrochloric  acid  or  a  soluble  chloride,  is  estimated  by  precipitation 
with  nitrate  of  silver,  the  precipitate  being  treated  in  the  manner  described  at 
page  600.  The  fused  chloride  contains  24-72  per  cent,  of  chlorine,  equivalent  to 
25'42  of  hydrochloric  acid. 

Many  chlorides,  chiefly  basic  or  oxychlorides,  which  are  insoluble  in  water  dis- 
solve in  nitric  acid.  The  chlorine  in  such  compounds  may  be  precipitated  by 
adding  nitrate  of  silver  to  the  nitric  acid  solution.  Care  must,  however,  be  taken 
not  to  heat  the  compound  with  excess  of  nitric  acid,  as  in  that  case  a  portion  of 
the  chlorine  may  be  lost.  Some  chlorides,  as  the  chloride  of  silver  and  dichloride 
of  mercury,  are  insoluble  even  in  nitric  acid.  Chloride  of  silver  may  be  decom- 
posed, either  by  ignition  in  a  current  of  hydrogen,  by  heating  it  in  a  porcelain 
crucible  with  a  mixture  of  the  carbonates  of  potash  and  soda,  in  equivalent  pro- 
portions, till  the  salt  just  begins  to  melt,  or  by  treating  it  with  dilute  sulphuric 
acid  in  contact  with  a  piece  of  pure  zinc  (p.  597).  Dichloride  of  mercury  is 
easily  decomposed  by  caustic  alkalies. 

Chlorates  and  other  oxygen-salts  of  chlorine  may  be  reduced  to  chlorides,  by 
ignition,  or,  better  in  most  cases,  by  the  action  of  sulphurous  or  hydrosulphuric 
acid.  The  chlorine  is  then  precipitated  by  nitrate  of  silver,  as  above,  after  the 

*  Chem.  Soc.  Qu.  J.  vi.  90.  f  Ibid.  vii.  51. 

I  Ann.  Ch.  Phys.  [3],  xxx.  242. 


ESTIMATION   OF   CHLORINE,    BROMINE,   AND   IODINE.  799 

excess  of  the  reducing  agent  has  been  removed  by  means  .of  nitric  acid  or  a  ferric 
salt.  [For  the  methods  of  determining  the  quantity  of  chlorine  in  bleaching 
powder  and  other  hypochlorites  for  commercial  purposes,  see  p.  437,  and  p.  801  ; 
also  Bunsen's  volumetric  method,  p.  413.] 

The  quantity  of  chlorine  in  an  organic  compound  is  determined  by  igniting  the 
compound  with  excess  of  pure  quick-lime  in  a  combustion-tube,  whereby  the 
chlorine  is  converted  into  chloride  of  calcium.  The  contents  of  the  tube  are  then 
dissolved  in  dilute  nitric  acid,  and  the  chlorine  precipitated  by  nitrate  of  silver. 

Bromine  is  estimated  in  the  form  of  bromide  of  silver  (containing  42-55  per 
cent,  of  bromine),  in  exactly  the  same  manner  as  chlorine.  Bromates  are  also 
reduced  to  bromides  in  the  same  manner  as  chlorates  to  chlorides. 

When  bromine  and  chlorine  occur  together,  they  may  both  be  precipitated  by 
treating  the  solution  with  excess  of  nitrate  of  silver.  The  precipitate  of  chloride 
and  bromide  is  then  ignited  and  weighed  ;  and  a  known  portion  of  it  is  after-  • 
wards  heated  in  a  current  of  chlorine  gas.  The  bromide  of  silver  is  thereby  con- 
verted into  chloride,  the  bromine  passing  off  in  vapour.  The  resulting  chloride 
of  silver  weighs  less  than  the  mixture  of  chloride  and  bromide  by  the  difference 
(w)  between  the  weight  of  the  bromine  which  has  escaped  and  the  chlorine  which 
has  taken  its  place  ;  moreover,  these  weights  are  to  one  another  as  the  equivalent 
weights  of  bromine  and  chlorine,  that  is,  as  80  to  35*5.  Hence,  to  determine  the 
quantities  of  Br  and  Cl  in  the  mixed  silver-salts,  we  have  the  two  equations, 


whence  Br  =  1-8  w;  Cl  =  0-8  w. 

If  the  quantity  of  bromine  is  very  small,  as  in  sea-water  and  salt-springs,  in 
comparison  with  that  of  the  chlorine,  this  method  does  not  give  very  exact  re- 
sults. In  such  cases  it  is  best  to  mix  the  solution,  after  due  concentration,  with 
only  enough  nitrate  of  silver  to  precipitate  about  one-sixth  of  the  chlorine,  and 
treat  the  precipitate  thus  formed,  —  which  is  sure  to  contain  the  whole  of  the 
bromine,  —  in  the  manner  just  described.  The  remainder  of  the  chlorine  is  then 
determined  by  treating  the  filtered  liquid  with  excess  of  nitrate  of  silver. 

According  to  Mr.  F.  Field,*  chloride  of  silver  is  completely  decomposed  by 
agitating  it  with  excess  of  bromide  of  potassium  in  solution,  the  silver  being  con- 
verted into  bromide,  and  the  whole  of  the  chlorine  passing  into  the  solution. 
This  -mode  of  decomposition  might  therefore  be  used  instead  of  the  ignition  of  the 
mixed  precipitate  in  a  current  of  chlorine.  The  chloride  and  bromide  of  silver 
are  also  completely  decomposed  by  iodide  of  potassium. 

Iodine  in  soluble  iodides  is  estimated  by  precipitation  with  nitrate  of  silver,  in 
the  same  manner  as  chlorine  and  bromine;  100  pts.  of  iodide  of  silver  contain 
54  025  pts.  of  iodine. 

It  may  also  be  precipitated  as  iodide  of  palladium  by  mixing  the  solution  with 
nitrate  or  chloride  of  palladium.  A  black  precipitate  then  falls,  which  settles 
down  slowly  but  completely,  and  when  ignited,  leaves  metallic  palladium,  100  pts. 
of  which  are  equivalent  to  23-83  pts.  of  iodine;  or  the  precipitate  may  be  col- 
lected on  a  weighed  filter,  dried  at  100°  C.  and  weighed;  100  pts.  of  it  coutain 
7-04  pts.  of  iodine  ;  but  the  method  by  ignition  is  to  be  preferred. 

This  method  of  precipitation  serves  also  to  separate  iodine  from  bromine  and 
chlorine.  If  the  chlorine  is  also  to  be  estimated,  the  precipitation  must  of  course 
be  made  with  nitrate  of  palladium,  not  with  the  chloride.  If  bromine  is  present 
without  chlorine,  the  iodine  must  be  precipitated  with  chloride  of  palladium,  be- 
cause the  nitrate  would  precipitate  bromine  as  well  as  iodine  :  the  precipitation  of 
the  bromine  may,  however,  be  prevented  by  the  addition  of  a  soluble  chloride. 
To  estimate  the  chlorine  and  bromine  in  the  filtered  liquid,  the  excess  of  palladium 

*  Chem.  Soc.  Qu.  J.  x.  234. 


800  FLUORINE. 

must  be  removed  by  hydrosulphuric  acid,  and  the  excess  of  the  latter  by  means 
of  nitric  acid  or  a  ferric  salt.  The  bromine  and  chlorine  may  then  be  precipitated 
by  nitrate  of  silver,  and  the  precipitate  treated  in  the  manner  already  described. 

The  methods  of  treating  insoluble  iodides  are  similar  to  those  already  given  for 
chlorides  (p.  798). 

lodates  and  periodates  are  reduced  to  iodides  by  the  action  of  sulphurous  or 
hydrosulphuric  acid.  To  decompose  them  by  ignition  would  not  give  accurate  re- 
sults, because  a  portion  of  the  iodine  is  thereby  expelled. 

Iodine  and  bromine  in  organic  compounds  are  estimated  in  the  same  manner  as 
chlorine  (p.  799). 

FLUORINE. 

Sources  of  Fluorine.  —  Professor  Gr.  Wilson,  of  Edinburgh,  has  discovered 
fluorine  in  a  great  number  of  plants,  especially  in  the  siliceous  stems  of  grasses 
and  equisetaceous  plants,  always  however  in  very  small  and  variable  quantities. 
He  supposes  that  soluble  fluorine-compounds  diffuse  themselves  through  the  rising 
sap  of  the  plant,  and  are  converted,  by  the  silica  therein  contained,  into  insoluble 
silico-fluorides.  Traces  of  fluorine  also  occur  in  the  trap-rocks  near  Edinburgh 
and  in  the  neighbourhood  of  the  Clyde,  in  the  granites  of  Aberdeenshire,  and  in 
the  soils  formed  by  the  disintegration  of  such  rocks.*  The  same  chemist  has 
likewise  found  fluorine  in  the  ashes  of  ox-blood,  milk,  cream-cheese,  and  very 
slight  traces  in  the  ash  of  the  whey.f  For  the  detection  of  small  quantities  of 
fluorine  in  rocks,  ashes,  &c.,  Professor  Wilson  heats  the  substance  (mixed  with 
silica  if  that  body  be  not  already  present)  with  strong  sulphuric  acid  in  a  glass 
vessel;  passes  the  evolved  fluoride  of  silicon  into  water;  supersaturates  the  hydro- 
fluosilicic  acid  thus  formed  with  ammonia;  evaporates  to  dry  ness;  exhausts  the 
residue  with  water;  again  evaporates  the  nitrate;  and  tests  the  residue  in  the 
ordinary  way  by  treating  it  with  sulphuric  acid  in  a  platinum  vessel  covered  with 
a  waxed  glass  plate.  f 

Isolation  of  Fluorine.  —  Fremy,  by  submitting  fused  fluoride  of  potassium  to 
the  action  of  the  voltaic  battery,  has  eliminated  a  gas  which  rapidly  attacks  pla- 
tinum, decomposes  water  with  formation  of  hydrofluoric  acid,  and  displaces  iodine 
from  its  combinations  with  metals.  By  decomposing  fluoride  of  calcium  at  a  red 
heat  with  dry  chlorine  or  oxygen,  he  likewise  obtains  a  gas  which  rapidly  attacks 
glass.  This  gas  appears  to  be  fluorine.  § 

Anhydrous  hydrofluoric  acid  may  be  obtained  by  heating  the  fluoride  of  potas- 
sium and  hydrogen  in  a  platinum  vessel,  or  by  decomposing  fluoride  of  lead  on  a 
layer  of  charcoal  in  a  platinum  tube  by  dry  hydrogen  gas.  It  is  gaseous  at  ordi- 
nary temperatures;  but  at  the  temperature  of  a  mixture  of  ice  and  salt,  it  con- 
denses into  a  very  mobile  liquid,  which  acts  violently  on  water,  forms  white  fumes 
in  the  air,  and  attacks  glass.  (Fremy.  ||) 

Estimation  of  Fluorine.  —  The  solid  compounds  of  fluorine  are  decomposed  by 
heating  them  in  a  platinum  crucible  with  strong  sulphuric  acid,  the  heat  being 
continued  till  all  the  fluorine  is  expelled  in  the  form  of  hydrofluoric  acid,  and  the 
excess  of  sulphuric  acid  is  likewise  drawn  off.  The  residual  sulphate  is  then 
weighed,  and  the  quantity  of  metal  in  it  calculated  ;  this  quantity  deducted  from 
the  original  weight  of  the  fluorine  gives  the  quantity  of  fluorine.  Or,  supposing 
no  other  volatile  acid  to  be  present,  if  the  difference  in  the  weight  of  the  fluoride 
and  the  sulphate  formed  from  it  be  d,  the  quantity  of  fluorine  may  be  found  by 
means  of  the  equations, 

SO,        48 
,04-  d,    -r' 


*  Edinb.  Phil.  J.  liii.  356.  f  Chem.  Gaz.  1850,  366. 

J  Chem.  Soc.  Qu.  J.  v.  151.  |  Compt.  rend,  xxxviii.  393;  xl.  966. 

J  Ibid,  xxxviii.  393. 


BUNSEN'S  GENERAL  METHOD.  801 

The  second  mode  of  calculation  is  equally  applicable,  whether  the  fluorine  be  com- 
bined with  one  metal  or  with  several. 

Fluorides  frequently  occur  in  nature  in  conjunction  with  phosphates,  as  in 
apatite  and  in  bones.  To  analyze  such  a  compound,  it  is  first  heated  with  sul- 
phuric acid  to  expel  the  fluorine ;  the  residue  digested  with  alcohol  to  dissolve  the 
phosphoric  acid  which  has  been  set  free ;  the  quantity  of  that  acid  determined  by 
precipitation  with  ammonia  and  sulphate  of  magnesia;  and  the  metals  now  remain- 
ing in  the  form  of  sulphates  determined  by  methods  already  given.  Lastly,  the 
total  weight  of  these  metals,  together  with  that  of  the  phosphoric  acid,  or  rather 
of  the  corresponding  salt-radical  (P08,  if  the  phosphates  are  tribasic),  is  deducted 
from  the  original  weight  of  the  mineral ;  and  the  difference  gives  the  quantity  of 
fluorine. 

From  solutions,  fluorine  is  generally  precipitated  as  fluoride  of  calcium,  from 
the  weight  of  which,  if  pure,  the  quantity  of  fluorine  may  be  immediately  calcu- 
lated ;  but  if  other  substances  are  precipitated  at  the  same  time,  the  quantity  of 
fluorine  must  be  determined  in  the  manner  above  described. 

BUNSEN'S  GENERAL  METHOD  OF  VOLUMETRIC  ANALYSIS. 

This  method,  which  is  applicable  to  a  great  number  of  analyses  depending  upon 
oxidation  and  reduction,  is  founded  on  the  principle  of  liberating  a  quantity  of 
iodine  equivalent  to  the  substance  which  is  to  be  estimated,  and  determining  the 
amount  of  this  iodine  by  means  of  a  standard  solution  of  sulphurous  acid. 

Iodine  and  sulphurous  acid,  in  presence  of  water,  form  hydriodic  and  sulphuric 
acids; 

S02  +  I  +  HO  =  S03  +  HI, 

each  equivalent  of  sulphurous  acid  thus  transformed  corresponding  to  1  eq.  of 
iodine,  or  32  parts  by  weight  of  anhydrous  sulphurous  acid  to  123-36  parts  of 
iodine. 

For  this  reaction,  however,  it  is  necessary  that  the  liquids  be  very  dilute ;  for, 
at  a  certain  degree  of  concentration,  the  opposite  change  takes  place,  sulphuric 
and  hydriodic  acids  decomposing  each  other  in  such  a  manner  as  to  yield  sulphur- 
ous acid,  water,  and  iodine.  The  solution  of  sulphurous  acid  used  for  the  esti- 
mation of  iodine  must  never  contain  more  than  from  0-04  to  0-05  per  cent,  of 
iodine. 

The  method  requires  three  standard  test-liquids  :  a  solution  of  iodine,  a  solution 
of  sulphurous  acid,  and  a  solution  of  iodide  of  potassium.  To  prepare  the  first,  a 
weighed  quantity  of  iodine,  as  pure  as  can  be  obtained,  is  dissolved  in  a  concen- 
trated solution  of  iodide  of  potassium  (which  must  be  perfectly  free  from  free 
iodine  and  iodate  of  potash,  and  therefore  must  not  exhibit  any  brown  colour, 
either  by  itself  or  on  addition  of  hydrochloric  acid),  and  the  liquid  diluted  to  such 
a  degree  that  200  cubic  centimeters  may  contain  1  gramme  of  iodine,  so  that,  if  a 
division  of  the  burette  contains  half  a  cubic  centimeter,  each  degree  may  contain 
4- J0  or  0-0025  of  a  gramme  of  the  iodine  used.  But  as  a  commercial  iodine,  even 
the  purest,  contains  traces  of  chlorine,  it  is  necessary  to  determine  the  real  value 
in  iodine  of  a  degree  of  the  burette  by  special  experiment.  The  method  of  doing 
this  will  be  presently  described  (p.  804). 

Of  the  second  test-liquid,  the  dilute  sulphurous  acid,  it  is  best  to  prepare  a  con- 
siderable quantity,  20  or  30  litres,  at  a  time,  so  that  the  alteration  produced 
in  it  by  the  oxidizing  action  of  the  air  during  the  course  of  an  experiment, 
or  even  in  a  day,  may  be  imperceptibly  small.  To  give  the  acid  the  proper 
degree  of  solution,  20  or  30  litres  of  water  are  mixed  with  a  small  measure-glass- 
ful of  concentrated  sulphurous  acid ;  the  liquid  shaken ;  200  burette-degrees,  or 
100  cubic  centiin.  of  it  measured  off;  this  portion  of  liquid  mixed  with  starch, 
and  the  standard  solution  of  iodine  added  from  the  burette,  till  the  liquid  just 
51 


802  BUNSEN'S  GENERAL  METHOD 

exhibits  a  perceptible  blue  colour.  If  the  number  of  burette-degrees  of  the  iodine- 
solution  required  for  this  purpose  be  t,  and  the  quantity  of  iodine  in  one  degree 
be  a,  the  quantity,  x,  of  anhydrous  sulphurous  acid,  S,  in  100  degrees  of  the  acid 
solution  will  be 

8  32 

x  =  =- .  at  =  T^-™  .  at. 
1  12b*3b 

The  most  convenient  strength  of  the  sulphurous  acid  solution  is  about  0-03 
anhydrous  sulphurous  acid  to  100  water.*  It  must  be  tested  at  the  commencement 
of  each  day's  work,  and  will  require  renewal  after  three  or  four  days.f 

The  third  test-liquid  is  a  solution  of  pure  iodide  of  potassium,  containing  about 
1  grm.  of  the  iodide  to  10  cubic  centimeters  of  water. 

1.  Determination  of  the  amount  of  pure  iodine  in  a  commercial  sample. — The 
weighed  sample  is  dissolved  in  the  solution  of  iodide  of  potassium,  in  the  propor- 
tion of  about  0-1  grm.  to  4  or  5  cub.  centim.  of  liquid.     To  the  resulting  brown 
solution,  as  many  measures,  n,  of  the  standard-solution  of  sulphurous  acid  are 
added  as  are  required  to  destroy  the  brown  colour  completely.     The  next  step  is 
to  determine  the  quantity  of  iodine,  xt  by  which  this  quantity  of  sulphurous  acid 
has  been  partially  decomposed.     This  is  effected  by  adding  three  or  four  cubic 
centimeters  of  clear  and  very  dilute  starch-solution,  and    then  dropping  in  the 
standard-solution  of  iodine  from  the  burette,  till  a  blue  colour  begins  to  appear. 
If  t'  degrees  of  the  iodine-solution  are  required  for  this  purpose,  and  the  quantity 
of  iodine  in  each  degree  is  a,  the  quantity  required  to  decompose  completely  the 
n  measures  of  sulphurous  acid  is  x  +  aff.     Further,  if  we  determine  the  quantity 
of  iodine,  a  t,  required  to  decompose  one  measure  of  the  sulphurous  acid  solution, 
we  shall  obtain  the  equation  x  -f  at?  =  nat ;  whence 

x  =B  a  (nt  —  f). 
If  the  weight  of  the  sample  of  iodine  be  A,  the  quantity  expressed  as  a  per  centage 

will  be  — —  (nt  —  ^) ;  and  if  — j-  =  1,  that  is,  if  the  quantity  weighed  out  is 
^i  jA. 

exactly  100  a  (4  grms.  if  a  =  T^  grm.),  the  difference  of  the  two  measurements, 
nt  —  ^,  gives  at  once  the  per  centage  of  iodine  in  the  sample. 

The  same  method  may  be  applied  to  determine  the  quantity  of  free  iodine  con- 
tained in  any  liquid. 

2.  Determination  of  Chlorine.  —  Chlorine  decomposes  a  solution  of  iodide  of 
potassium  instantly  and  completely,  without  the  aid  of  heat,  setting  free  an  equiva- 
lent quantity  of  iodine.     If  this  quantity  of  liberated  iodine  be  determined  in  the 
manner  just  described,  the  quantity  of  chlorine  will  be  given  by  the  equation, 

Cl 
x  =  •=-  a  (nt  —  ^). 

5.  Similarly  for  Bromine : 

x  =  -y-  •  a  (nt  —  ^). 

4.  Chlorine  and  Bromine  together. — To  estimate  the  quantity  of  chlorine  con- 
tained in  a  sample  of  bromine,  a  quantity,  A,  of  the  bromine,  throughly  dried,  is 
dissolved  in  a  solution  of  iodide  of  potassium,  and  the  quantity  of  iodine,  a(nt  —  t') 
thereby  separated,  is  determined  as  above.  Then,  denoting  the  quantity  of  bromine 
by  x,  and  that  of  chlorine  by  y,  we  have  the  equations  :  — 

*  As  a  cubic  centimeter  of  water  weighs  a  gramme,  this  is  the  same  as  0-03  grm.  in  100 
cubic  centimeters  or  200  burette-divisions. 

f  A  modification  of  this  method,  in  which  hyposulphite  of  soda  is  used  instead  of  sulphur- 
ous acid,  has  been  introduced  by  Mr.  E.  0.  Brown.  (See  page  484.) 


OF    VOLUMETRIC    ANALYSIS.  803 

x  -f  y  =  A] 


~A  —  a(nt  —  tf)  a  (nt  —  f)  —  = 

whence  a;  =  —  -       —  --       =  -  - 


CI    ~"~     Br  Ci     ~~     "Br 

If  the  chlorine  and  bromine  are  in  a  state  of  combination,  they  may  be  set  free  by 
distilling  the  mixture  or  compound  with  bichromate  of  potash  and  sulphuric  acid, 
the  evolved  gases  being  passed  into  the  solution  of  iodide  of  potassium. 

A  similar  method  may  be  applied  to  a  mixture  of  chlorine  and  iodine,  the  equa- 
tions then  becoming  — 

x  +  y  =  A',^x  -fy  —  a(nt  —  (f). 

5.  Chlorites  and  Hypochlorites.  —  A  solution  of  the  salt  is  mixed  with  solution 
of  iodide  of  potassium,  and  hydrochloric  acid  added  in  slight  excess.  From  the 
quantity  of  iodine,  a  (nt  —  t)  thus  separated,  the  quantity  of  chlorous  acid,  xr,  or 
hydrochlorous  acid,  x",  may  be  determined  from  the  equations 

ci 


It  must  be  remembered  that  1  eq.  CIO  decomposes  2  eq.  Kl,  and  1  eq.  C103 
decomposes  4KI. 

This  method  is  well  adapted  to  the  estimation  of  chloride  of  lime  for  commercial 
purposes.  If  A  be  the  weight  of  the  sample,  the  percentage  of  chlorine  will  be 

-  —  —  a  (nt  —  f)  j  and  if  A  be  equal  to  —  -  —  a,  the  difference  of  the  two  mea- 
-4.1  1 

surements,  nt  —  if,  gives  directly  the  bleaching  power  of  the  product  in  percentage 
of  chlorine. 

6.  Ghromates.  —  When  a  chromate,  e.  g.  bichromate  of  potash,  is  boiled  with 
excess  of  fuming  hydrochloric  acid,  every  2  eq.  chromic  acid  eliminate  3  eq. 
chlorine  :  — 

2O03  +  6HC1  =  Cr2Cl3  +  6HO  +  301  ; 

and  the  3  eq.  of  chlorine  passed  into  a  solution  of  iodide  of  potassium,  liberate  3 
eq.  of  iodine,  which  may  be  estimated  volumetrically  as  above.  Hence  the  quan- 
tity x  of  chromic  acid  contained  in  a  known  weight  A  of  bichromate  of  potash,  or 
any  other  chromate,  will  be  given  by  the  equation  — 

2  Cr 
x  =     10ra^"""0j 

200  Or 
or  in  100  parts  :  x  —  a  (nt  —  0- 

ja.  .  ol 

If  A  =  —  ——  a,  that  is,  if  the  sample  taken  weighs  exactly  this  quantity,  the 
difference  of  the  two  measurements,  nt  —  *',  gives  directly  the  percentage  of  chromic 

acid.     Similarly,  for  A  —  100  -  ^=  -  a,  this  difference  would  give  the  per- 

ol 


804  BUNSEN'S  GENERAL  METHOD. 

centage  of  pure  bichromate  of  potash,  and  for  A  =  200 ^ a,  the  percent- 
age of  pure  chromate  of  lead  in  these  respective  salts. 

The  analysis  is  made  by  introducing  a  weighed  quantity  of  the  chromate  into  a 
small  flask  holding  about  40  cubic  centimeters,  filled  about  two-thirds  with  fuming 
hydrochloric  acid,  and  having  a  gas-delivery  tube  adapted  to  its  neck  by  means 
of  a  tube  of  vulcanized  caoutchouc.  The  glass  tube  is  inserted  into  the  neck  of  an 
inverted  retort,  of  the  capacity  of  about  160  cubic  centim.,  containing  a  solution 
of  iodide  of  potassium.  The  middle  of  the  neck  of  the  retort  is  blown  out  into  a 
bulb  to  receive  any  liquid  that  may  be  thrown  up.  A  piece  of  vulcanized  caout- 
chouc is  tied  tightly  over  the  open  end  of  the  glass  tube,  and  a  slit  cut  in  it  with 
a  sharp,  wet  penknife.  This  slit  opens  when  pressed  from  within,  but  closes 
tightly  when  pressed  in  the  opposite  direction,  thus  forming  an  excellent  valve. 
The  liquid  in  the  flask  is  now  boiled  for  three  or  four  minutes,  by  which  time  the 
whole  of  the  chlorine  is  expelled,  and  an  equivalent  quantity  of  iodine  liberated. 

The  volumetric  analysis  of  pure  bichromate  of  potash  affords  an  easy  method  of 
determining  the  value  of  a,  or  the  quantity  of  pure  iodine  contained  in  a  burette 
degree  of  the  standard  solution  (p.  802).  For  if  the  bichromate  of  potash  be  pure, 

its  weight  A  is  exactly  equal  to — a  (nt  —  ^)  ;  therefore, 

3L4 
a  = 


(K  +  2  Or)  (nt  —  t") 

7.  Peroxides.  —  The  quantity  of  oxygen  in  the  peroxides  of  lead,  manganese, 
&c.,  may  be  estimated  in  a  similar  manner  to  chromic  acid.  Thus,  the  percentage 
of  oxygen  in  binoxide  of  lead  Pb02  is  given  by  the  formula  — 

9O 

(nf-_  0; 


and  the  percentage  of  pure  binoxide  of  manganese  in  a  commercial  sample  of  the 
black  oxide  by  the  formula  — 

100  Mn 
x  =    A     t    a(n<  —  0- 

* 

Besides  the  preceding  and  a  great  number  of  other  bodies  which  give  rise  to  a 
separation  of  free  chlorine,  the  iodometric  method  may  be  applied  to  the  estimation 
of  substances  which  are  raised  by  chlorine  to  a  higher  degree  of  oxidation.  These 
substances  are  heated  with  fuming  hydrochloric  acid  and  a  known  weight,  p,  of 
pure  bichromate  of  potash;  the  evolved  chlorine  is  passed  into  iodide  of  potassium; 
and  the  liberated  iodine  estimated  as  above.  The  quantity  thus  separated,  viz. 

a  (nt  —  tf),  is  equal  to  the  quantity  of  iodine,  ~—  -  -.,  equivalent  to  the  bichro- 

K  -f-  2Cr 

mate  used  minus  the  quantity  t,  equivalent  to  the  protoxide  to  be  estimated.    The 
latter  is  therefore, 


Thus,  to  determine  the  amount  of  protoxide  of  iron  in  a  given  sample  of  iron- 
ore,  it  must  be  remembered  that  each  equivalent  of  iodine  or  chlorine  converts  2 
eq.  of  protoxide  into  sesquioxide  :  — 

2FeO  -f  I  +  HO  =  Fe203  -f-  HI. 
If  then  i  be  the  quantity  of  iodine  required  to  convert  the  protoxide  of  iron  in 


POTASSIUM.  805 

a  given  sample  into  sesquioxide,  the  quantity  c  of  protoxide  in  this  sample  will 

2  TV 
be  e  =  i  .  —  ;  and  substituting  for  i  its  value  above  given,  we  have 

6  Fe  2  F'e  . 

-  —  *<•«-'>''  . 


and  hence  it  is  easy  to  calculate  the  equivalent  quantities  of  metallic  iron  and 
sesquioxide. 

Various  other  applications  of  the  method,  will  be  found  in  Professor  Bunsen's 
memoir.* 


METALS  OF  THE  ALKALIES  AND  EARTHS. 

POTASSIUM. 

Preparation  of  Potassium. — The  process  of  obtaining  this  metal  by  igniting  a 
mixture  of  carbonate  of  potash  and  charcoal,  has  received  considerable  improve- 
ments from  the  researches  of  Maresca  and  Donny.f  The  ordinary  form  of  the 
process,  which  is  that  devised  by  Brunner,  is  dangerous,  and  gives  very  uncertain 
results,  the  quantity  of  metal  obtained  by  it  being  often  very  small,  and  some- 
times, even  when  the  greatest  care  is  taken,  absolutely  nothing.  The  danger 
arises  from  the  obstruction  of  the  connecting  tube  by  the  black  substance  formed 
by  the  action  of  carbonic  oxide  on  the  potassium  there  deposited ;  and  the  loss  of 
product  is  due,  partly  to  the  formation  of  this  black  substance,  and  partly  to  the 
escape  of  portions  of  the  metal  in  the  form  of  vapour.  The  first  of  these  incon- 
veniences can  only  be  obviated  by  keeping  the  entire  length  of  the  connecting 
tube  at  a  red  heat  during  the  whole  operation.  But  in  that  case,  if  the  large 
receivers  invented  by  Brunner  (see  fig.  152,  p.  370,  and  153,  p.  371,)  are  used, 
not  a  particle  of  the  metal  condenses,  the  whole  escaping  in  the  form  of  vapour. 
Hence  it  is  necessary  to  use  much  smaller  receivers ;  and  the  form  which  the 
authors  find  to  give  the  best  results,  is  that  of  a  shallow  rectangular  box,  12  cen- 
timeters long,  6  wide  and  4  deep.  Another  source  of  failure  in  the  operation  is 
the  want  of  a  due  proportion  between  the  carbonate  of  potash  and  charcoal  in  the 
calcined  tartar.  To  obtain  the  best  result,  the  quantity  of  charcoal  should  be 
neither  more  nor  less  than  that  which  is  theoretically  required  for  the  complete  re- 
duction of  the  potash  present.  Whether  this  is  the  case,  can  only  be  ascertained 
by  a  previous  analysis  of  the  burnt  tartar ;  and  any  excess  or  deficiency  of  char- 
coal, must  be  remedied  by  mixing  samples  of  tartar  of  different  qualities.  Lastly, 
to  prevent  the  perforation  of  the  iron  bottle  during  the  ignition,  it  should  be 
coated,  not  with  clay  luting,  but  with  fused  borax.  Such  a  coating  is  easily 
formed  by  sprinkling  pulverized  borax  on  the  bottle  when  it  is  at  a  dull  red  heat. 

Preparation  of  Potassium  by  Electrolysis A  mixture  of  1  at.  chloride  of 

potassium  and  1  at.  chloride  of  calcium  (which  mixture  is  used  because  it  melts 
at  a  much  lower  temperature  than  chloride  of  potassium  alone),  is  melted  in  a 
small  porcelain  crucible  over  a  lamp,  and  subjected  to  the  action  of  a  Bunsen's 
battery  of  six  elements  with  carbon  poles,  the  heat  being  so  regulated  that  a  solid 
crust  forms  round  the  negative  carbon  pole,  while  the  mixture  remains  fused  and 
allows  the  free  evolution  of  chlorine  at  the  positive  pole.  When  the  decomposi- 
tion has  been  continued  in  this  manner  for  about  twenty  minutes,  and  the  cooled 

*  Ann.  Ch.  Pharm.  Ixxxvi.  265 ;  Chem.  Soc.  Qu.  J.  viii.  218. 
f  Ann.  Ch.  Phys.  [3],  xxxv.  147. 


806  SODIUM. 

crucible  is  opened  under  rock-oil,  a  large  quantity  of  potassium,  almost  chemically 
pure,  is  generally  obtained.  If  the  same  experiment  be  repeated  at  a  white  heat 
over  a  charcoal  fire,  with  an  iron  wire  as  negative  pole,  small  globules  of  potassium 
are  seen  burning  on  the  surface;  and  these,  when  analyzed,  are  found  to  be  almost 
pure.  (Matthiessen.)* 

Preparation  of  pure  Hydrate  of  Potash.  —  Wbhler  recommends  for  this  pur- 
pose the  decomposition  of  pure  nitre  by  metallic  copper  at  a  red  heat.  1  pt.  of 
nitre  and  2  or  3  pts.  of  thin  copper  plate  cut  into  small  pieces,  are  arranged  in 
alternate  thin  layers  in  a  covered  copper  crucible,  and  exposed  for  half  an  hour 
to  a  moderate  red  heat.  The  cooled  mass  is  then  treated  with  water,  the  liquid 
left  to  stand  in  a  tall  covered  cylindrical  vessel  till  the  oxide  of  copper  has  com- 
pletely settled  down,  and  the  pure  solution  of  potash  then  decanted  with  a 
siphon. 

With  the  above  proportions  of  nitre  and  copper  part  of  the  latter  is  converted 
only  into  suboxide.  It  may,  therefore,  be  used  for  a  second  preparation  of  potash, 
by  mixing  1  pt.  of  it  with  1  pt.  of  nitre  and  1  pt.  of  metallic  copper. 

Iron  may  also  be  used  to  decompose  the  nitre ;  but  the  potash  thereby  obtained 
is  contaminated  with  small  quantities  of  carbonic  acid,  silica,  &c.  The  same 
objection  applies  to  the  use  of  an  iron  crucible,  if  a  perfectly  pure  product  be 
required,  f 

Estimation  of  Potassium.  Potassium,  when  it  occurs  in  a  compound  not  con- 
taining any  other  metal,  may  be  estimated  either  as  sulphate  or  as  chloride.  All 
potassium-salts  containing  volatile  acids,  are  decomposed  by  heating  them  with 
sulphuric  acid,  the  excess  of  which  may  afterwards  be  expelled  by  a  stronger 
heat,  and  the  quantity  of  potassium  or  potash  calculated  from  the  weight  of  the 
residual  neutral  sulphate.  It  is  difficult,  however,  to  expel  the  last  traces  of  free 
sulphuric  acid  by  mere  ignition;  but  they  may  be  completely  driven  off  by 
dropping  a  lump  of  carbonate  of  ammonia  into  the  crucible,  and  repeating  the 
ignition  with  the  cover  on ;  the  sulphuric  acid  then  diffuses  into  the  atmosphere 
of  ammonia  in  the  crucible,  and  a  perfectly  neutral  sulphate  remains.  It  contains 
54-06  per  cent,  of  potash,  KO. 

In  estimating  potassium  as  chloride,  the  only  precaution  to  be  observed  is  to 
ignite  the  chloride  in  a  covered  crucible,  as,  when  strongly  heated  in  contact  with 
the  air,  a  portion  of  it  volatilizes.  The  chloride  contains  52-47  per  cent,  of 
potassium,  equivalent  to  63-19  per  cent,  of  potash. 

The  separation  of  potassium  from  all  soluble  substances  except  ammonia,  is 
easily  effected  by  precipitating  it  with  bichloride  of  platinum,  adding  alcohol  to 
complete  the  precipitation  of  the  chloroplatinate  of  potassium,  collecting  the  pre- 
cipitate on  a  weighed  filter,  washing  with  alcohol,  and  drying  it  at  100°  C.  It 
contains  16-04  per  cent,  of  potassium,  equivalent  to  19-31  of  potash. 

SODIUM. 

Preparation. — Deville  finds  that  the  reduction  of  this  metal  from  the  carbo- 
nate, by  ignition  with  charcoal,  is  greatly  facilitated  by  the  addition  of  some  sub- 
stance, such  as  chalk,  which  retains  the  mass  in  a  pasty  state  during  ignition. 
The  best  product  is  obtained  with  a  mixture  of  717  pts.  of  dry  carbonate  of 
soda,  175  charcoal,  and  108  chalk.  With  regard  to  the  form  of  apparatus,  and 
the  mode  of  conducting  the  process,  Deville  follows  exactly  the  directions  given 
by  Maresca  and  Donny  (p.  805),  for  the  preparation  of  potassium. £ 

Sodium  may  be  readily  obtained  by  electrolysis,  in  a  manner  similar  to  that  de- 
scribed for  potassium  (p.  805),  using,  however,  a  mixture  of  1  at.  chloride  of 
Bodium,  and  2  at.  chloride  of  calcium.  (Matthiessen.) 

*  Chem.  Soc.  Qu.  J.  viii.  30.  t  Ann.  Ch.  Pharm.  Ixxxvii.  373. 

%  Ann.  Ch.  Phys.  [3],  xliii.  5. 


SULPHATE    OF    SODA.  807 

Carbonate  of  Soda.  —  Solutions  of  carbonate  of  soda  are  capable  of  assuming 
the  state  of  supersaturation,  and  exhibiting  phenomena  similar  to  those  of  the 
sulphate  (p.  391).  An  aqueous  solution  of  the  salt,  saturated  at  a  high  tempera- 
ture, and  enclosed  while  boiling  hot  in  sealed  tubes  or  well-corked  flasks,  remains 
supersaturated  at  ordinary  temperatures,  and  frequently,  even  when  cooled 
several  degrees  below  0°  C.,  not  depositing  any  crystals.  Keeping  the  air  in  con- 
tact with  the  liquid  from  agitation  (as  by  covering  the  hot  solution  with  a  glass 
receiver),  is  often  sufficient  to  prevent  the  formation  of  crystals  at  ordinary 
temperatures  ;  but  free  access  of  air  causes  immediate  solidification,  attended 
with  rise  of  temperature.  The  passage  of  an  electric  current  through  a  super- 
saturated solution,  does  not  induce  any  change  of  state. 

The  supersaturated  solutions  of  carbonate  of  soda  contain  a  salt  having  less 
water  of  crystallization  than  the  ordinary  10-hydrated  salt.  The  salt  contained  in 
them  is,  in  fact,  a  7-hydrated  salt,  NaO .  C02  +  7HO,  and  of  this  salt  there  are 
two  modifications,  differing  in  crystalline  form  and  in  degree  of  solubility.  One 
of  them  (a)  crystallizes  in  rhombohedral  crystals;  the  other  (6),  in  square  tables 
or  low  prisms :  both  these  salts  absorb  water  rapidly.  The  salt  b  was  first  ob- 
tained by  Thomson,  who,  however,  supposed  it  to  contain  8  at.  water.  When  a 
solution  saturated  at  the  boiling  heat,  and  containing  a  slight  excess  of  the  solid 
salt,  is  enclosed  in  a  flask,  which  is  corked  immediately  after  the  boiling  has 
ceased,  no  crystals  are  deposited  from  it  for  a  long  time  on  cooling  down  to 
between  25°  and  18°  C. ;  but  on  cooling  below  8°,  it  deposits  chiefly  the  salt  b. 
When  cooled  to  between  16°  and  10°,  it  yields  the  salt  a,  which  redissolves 
between  21°  and  22°,  forms  again  on  cooling  to  19° ;  and  on  cooling  from  10°  to 
4°,  becomes  opaque,  and  passes  into  the  salt  b.  After  cooling  to  a  lower  tempe- 
rature, and  for  a  longer  time,  when  the  state  of  supersaturation  ceases,  the  whole 
is  converted  into  a  mass  of  crystals  of  the  ordinary  salt  NaO  .  C02  +  10  aq.  The 
following  table  gives  a  comparative  view  of  the  quantities  of  the  10-hydrated  and 
of  the  two  varieties  of  the  7-hydrated  salt,  contained  in  100  parts  of  the  saturated 
solutions  at  different  temperatures  :  — 

Temperature 0°  10°  15°  20°         25°  30°  38°  104°. 

10-hydrated  salt 7-0  12-1  16-2  21-7  28-5  37-2  51-7  45-5. 

7-hydrated  (b) 20-4  26-3  29-6  38-6  38-1  43-5  —            — 

7-hydrated  (a)..... 31-9  37-9  41-6  45-8         — 

Hence,  it  appears,  that  carbonate  of  soda  exhibits  a  maximum  of  solubility,  at 
38°  C.  The  decrease  of  solubility  above  this  point  arises  from  the  formation  of 
another  hydrate,  NaO .  C02  -f  HO.  This  hydrate,  which  separates  out  when  a 
solution  saturated  at  104°  C.  is  concentrated  by  boiling,  is  more  soluble  in  cold 
than  in  hot  water,  and  the  crystals  which  have  been  separated  by  boiling,  redis- 
solve  in  the  mother  liquor,  when  left  to  cool  in  a  closed  vessel.  (H.  Loewel.)* 

Besides  the  hydrates  above-mentioned,  two  others  have  been  discovered  by 
Jacquelain,f  viz.  NaO  .  C02  +  15HO,  which  crystallizes  below  —  20°,  and  when 
dried  in  vacuo  gives  off  5  atoms  of  water,  and  is  converted  into  the  ordinary  ten- 
hydrated  salt;  and  NaO  .  CO  -f-  9 HO,  obtained  by  repeatedly  crystallizing  a  solu- 
tion which  at  first  contains  a  portion  of  bicarbonate  of  soda.  Jacquelain  also  finds 
that  carbonate  of  soda  gives  off  carbonic  acid  when  melted,  even  in  a  stream  of 
pure  and  dry  carbonic  acid. 

Sulphate  of  Soda.  —  This  salt  appears  to  be  capable  of  existing  in  solution  in 
three  different  states,  viz.  as  anhydrous  salt,  NaO .  S03,  as  the  seven-hydrated  salt, 
NaO .  S03  +  7HO,  and  as  the  ten-hydrated  salt,  NaO .  S03  +  10HO,  which  is 
the  ordinary  Glauber's  salt.  The  following  table  shows  the  solubility  (as  deter- 
mined by  LoewelJ)  of  the  anhydrous  salt,  and  of  the  two  hydrates,  in  water,  at 
various  temperatures ;  also  the  quantity  of  anhydrous  salt  corresponding  in  each 

*  Ann.  Ch.  Phys.  [3],  xxxiii.  334.  f  Compt.  rend.  xxx.  106. 

J  Ann.  Ch.  Phys.  [3],  xlix.  32. 


808 


AMMONIUM. 


case  to  the  hydrate  dissolved.     The  numbers  in  the  table  are  the  quantities  of 
salt  dissolved  in  100  parts  of  water. 


SOLUBILITY  OF  SULPHATE  OF  SODA. 


Temp. 

NaO-SCK 

NaOSOg  +  10HO. 

NaO.SO,+  7HO. 

Anhydrous. 

Anhydrous. 

Hydrate. 

Anhydrous. 

Hydrate. 

0°C. 

5-02 

12-16 

19-62 

44-84 

10 

Q-nn 

23-04 

30-49 

78-90 

15 

12-20 

35-96 

37-43 

105-79 

18 

52-25 

16-80 

48-41 

41-63 

124-59 

20 

52-76 

19-40 

58-35 

44-73 

140-01 

25 

51-53 

28-00 

98-48 

52-94 

188-46 

26 

51-31 

30-00 

109-81 

54-07 

202-61 

30 

50-37 

40-00 

184-09 

33 

49-71 

50-76 

323-13 

34 

49-53 

55-00 

412-22 

40-15 

48-78 

50-40 

46-82 

59-79 

45-42 

70-61 

44-35 

84-42 

42-96 

103-17 

42-65 

Sulphate  of  Soda  and  Potash.  —  Gladstone*  has  obtained  a  salt  containing 
NaO  \  ^^3)  kv  fusing  the  neutral  or  acid  sulphate  of  potash  with  chloride  of 
sodium,  or  sulphate  of  potash  with  sulphate  of  soda,  dissolving  the  fused  mass  in 
hot  water,  and  leaving:  it  to  crystallize,  or  by  mixing  the  two  salts  in  hot  aqueous 
solution.  The  salt  which  crystallized  out  was  anhydrous,  and  exhibited  the  crys- 
talline form  of  sulphate  of  potash.  H.  Rosef  had  previously  obtained  the  same 
salt,  but  had  not  assured  himself  of  its  definite  constitution. 

Estimation  of  Sodium. — This  metal,  like  potassium,  may  be  estimated  either 
as  chloride  or  as  sulphate.  The  sulphate  contains  32-54,  and  the  chloride  39-53 
per  cent,  of  sodium. 

Sodium  is  separated  from  potassium  by  means  of  bichloride  of  platinum,  with 
addition  of  alcohol,  which  precipitates  the  potassium,  and  leaves  the  sodium  in 
solution.  The  quantity  of  potassium  may  then  be  determined  from  the  weight  of 
the  precipitate,  and  the  sodium  estimated  by  difference.  Or  if  a  direct  estimation 
of  the  sodium  be  desired,  the  filtered  liquid  may  be  freed  from  excess  of  platinum 
by  means  of  hydrosulphuric  acid,  and  the  sodium  in  the  filtrate,  which  then  con- 
tains no  other  metal,  determined  as  sulphate. 

If  the  potassium  and  sodium  are  in  the  form  of  chlorides,  the  method  just 
described  may  be  applied  immediately ;  if  not,  it  is  best  first  to  convert  them  into 
chlorides,  which  may  in  some  cases  be  done  by  merely  heating  the  mixed  salts 
with  excess  of  hydrochloric  acid,  or,  in  case  of  sulphuric  or  phosphoric  acid  being 
present,  by  precipitating  the  acid  with  chloride  of  barium,  removing  the  excess 
of  barium  with  carbonate  of  ammonia,  and  expelling  the  ammoniacal  salts  from  the 
filtrate  by  evaporation  and  ignition.  The  residue  is  a  mixture  of  the  chlorides  of 
potassium  and  sodium. 

AMMONIUM. 

A  compound  radical  consisting  of  ammonia  with  an  additional  atom  of  hydro- 
gen, was  first  supposed  to  exist  in  the  ordinary  salts  of  ammonia  by  Berzelius,  and 


*  Chem.  Soc.  Qu.  J.  vi.  106. 


f  Pogg.  Ann.  lii.  452. 


CARBONATES    OF    AMMONIUM.  809 

termed  ammonium.  This  body  has  never  been  insulated,  but  is  supposed  to 
appear,  in  a  certain  experiment,  in  combination  with  mercury,  and  possessed  of 
the  metallic  character  (p.  167).  The  compounds  of  ammonium  are  always  strictly 
isomorphous  with  the  corresponding  compounds  of  potassium. 

Chloride  of  ammonium,  Hydrochlorate  or  Muriate  of  ammonia,  Sal-ammo- 
niac, NH4 .  01.  —  This  salt  is  formed  when  ammonia  is  neutralized  by  hydrochloric 
acid ;  NH3  4-  HC1  =  NH4 .  01.  It  is  prepared  in  large  quantity  from  the  am- 
moniacal  liquor  obtained  in  the  distillation  of  bones,  in  the  manufacture  of  animal 
charcoal,  and  from  the  liquor  which  condenses  in  the  distillation  of  coal  for  gas. 
These  liquors  contain  ammonia  principally  in  the  state  of  carbonate  and  hydrosul- 
phate,  which  may  be  converted  into  chloride  of  ammonium  by  the  addition  of 
hydrochloric  acid.  The  salt  is  purified  by  crystallization,  and  sublimed  in  vessels 
of  iron  or  earthenware,  in  the  upper  part  of  which  it  condenses  and  forms  a  solid 
cake,  the  condition  in  which  sal  ammoniac  is  always  met  with  in  commerce. 

Sal-ammoniac  is  tenacious  and  difficult  to  reduce  to  powder;  its  sp.  gr.  is  1  45. 
It  has  a  sharp  and  acrid  taste,  and  dissolves  in  2-72  parts  of  cold,  and  in  an  equal 
weight  of  boiling  water;  it  is  also  soluble  in  alcohol.  It  generally  crystallizes 
from  solution  in  feathery  crystals,  which  are  formed  of  rows  of  minute  octohe- 
drons  attached  by  their  extremities.  At  a  red  heat  it  volatilizes  without  previous 
fusion. 

A  corresponding  bromide,  iodide,  and  fluoride  of  ammonium  may  be  formed  by 
neutralizing  ammonia  with  hydrobromic,  hydriodic,  and  hydrofluoric  acids. 

Sulphides  of  Ammonium. — When  4  volumes  of  ammonia  combine  with  2  of 
hydrosulphuric  acid  gas,  the  sulphide  of  ammonium  is  produced ;  NH3  -f-  HS  = 
NH4 .  S.  Ammonium  combines  with  sulphur  in  several  other  proportions,  which 
are  obtained  on  mixing  and  distilling  the  various  sulphides  of  potassium  with  sal- 
ammoniac.  In  the  reciprocal  decomposition  which  occurs,  the  potassium  com- 
bines simply  with  chlorine,  and  the  ammonium  with  sulphur.  The  following  com- 
pounds are  generally  enumerated:  NH4  .  S;  NH4  .  S  +  HS;  NH4  .  S3  and 
NH4 .  S6.  The  protosulphide  has  long  been  formed  by  distilling  a  mixture  of 
quicklime,  sulphur,  and  sal-ammoniac,  and  known  under  the  name  of  the/wmin^ 
liquor  of  Boyle.  It  is  a  volatile  liquid,  the  vapour  of  which  is  decomposed  by 
oxygen,  and  thus  fumes  produced.  The  second  compound,  which  is  a  sulphide 
of  hydrogen  and  ammonium,  is  formed  by  transmitting  hydrosulphuric  acid  gas 
through  solution  of  ammonia  to  saturation.  This  liquid  is  generally  called  the 
hydrosulphate  of  ammonia,  and  is  a  very  useful  reagent  in  chemical  analysis.  All 
the  sulphides  of  ammonium  are  soluble  in  water  and  alcohol  without  decom- 
position. 

Nitrate  of  Ammonium,  NH40  .  N05.— When  nitric  acid  is  saturated  with  am- 
monia, a  salt  is  obtained  which  crystallizes  in  six-sided  prisms,  and  is  isomorphous 
with  nitrate  of  potash.  Besides  the  elements  of  anhydrous  nitric  acid  and  am- 
monia, this  salt  contains  an  atom  of  water  which  cannot  be  separated  from  it, 
which  is  also  found  in,  and  is  equally  essential  to,  the  salts  formed  by  neutralizing 
all  other  oxygen-acids  by  ammonia,  such  as  sulphurous  acid,  sulphuric,  carbonic, 
&c.,  in  contact  with  water.  The  hydrogen  of  this  water  is  assigned  to  the  am- 
monia, to  form  ammonium,  which  the  oxygen  converts  into  oxide  of  ammonium , 
so  that  the  product  is  nitrate  of  the  oxide  of  ammonium ;  or  NH3  -f-  HO  .  N05  = 
NH40  .  N05.  This  salt  deflagrates  with  flame  when  thrown  upon  red-hot  coalts 
When  decomposed  between  300°  and  400°,  it  is  resolved  into  water  and  nitrous 
oxide  (p.  597). 

Carbonates  of  Ammonium. — The  neutral  carbonate  of  oxide  of  ammonium 
appears  not  to  exist  in  the  free  state,  but  by  distilling  the  sesquicarbonate  of  am- 
monia of  the  shops  at  a  gentle  heat,  Rose  obtained  a  volatile  crystalline  salt,  which 
may  be  viewed  as  a  compound  of  anhydrous  carbonate  of  ammonia  with  carbonato 
of  ammonium  :  NH3 .  C02  +  NH40  .  CO;.  When  the  commercial  salt  is  exposed 
to  the  air,  it  loses  its  pungent  odour,  and  a  white  friable  mass  remains,  which  is 


810  AMMONIUM. 

the  bicarbonate  of  ammonium,  or  carbonate  of  water  and  oxide  of  ammonium  : 
HO  .  C02  +  NII40  .  C02.  This  is  a  stable  salt,  and  may  be  dissolved  and  crys- 
tallized without  change. 

The  sesquicarbonate  of  ammonia  of  the  shops  is  a  crystalline  transparent  mass, 
which  Rose  finds  to  have  generally,  but  not  always,  the  composition  assigned  to  it 
by  Mr.  Phillips,  or  to  contain  3C02  with  2NH3  and  2HO.  Rose  is  disposed  to 
consider  it  a  compound  of  anhydrous  carbonate  of  ammonia  and  bicarbonate  of 
oxide  of  ammonium,  or  NH3C02  -t-  (HO  .  C02  4-  NH40  .  C02).  Mr.  Seanlan 
has  shown  that  a  small  quantity  of  water  dissolves  out  the  carbonate  from  this 
salt,  and  leaves  the  bicarbonate,  which  is  the  least  soluble.  This  observation  does 
not  prove  the  commercial  salt  to  be  a  mechanical  mixture  of  the  two  salts  derived 
from  it,  as  many  undoubted  compounds  of  two  salts  are  decomposed  by  water, 
when  one  of  the  constituent  salts  is  much  more  soluble  than  the  other.  Another 
salt  was  obtained  by  Rose,  in  well-formed  crystals,  of  which  the  ammonia  and 
carbonic  acid  are  in  the  proportions  of  the  sesquicarbonate,  but  with  three  ad- 
ditional atoms  of  water.  No  fewer  than  twelve  different  carbonates  of  ammonia 
are  described  by  that  chemist.* 

Sul/phate  of  Ammonium,  NH40  .  S03  -f  HO.  —  This  is  a  highly  soluble  salt, 
which  possesses  an  atom  of  water  of  crystallization,  in  addition  to  the  atom  which 
is  essential  to  its  constitution.  It  appears  also  to  crystallize  without  this  water. 

Phosphates  of  Ammonium.  —  The  biammoniacal  tribasic  phosphate,  (2NH4 
O  .  HO)  .  P05,  analogous  to  ordinary  phosphate  of  soda,  is  obtained  by  decom- 
posing the  acid  phosphate  of  lime  with  carbonate  of  ammonium.  It  forms  large 
transparent  crystals,  belonging  to  the  oblique  prismatic  system,  which  effloresce  on 
the  surface  when  exposed  to  the  air,  and  give  off  a  portion  of  their  ammonia,  even 
at  ordinary  temperatures.  The  salt  dissolves  in  4  parts  of  cold,  and  a  smaller 
quantity  of  hot  water.  (Mitscherlich.) 

The  monoammoniacal  phosphate,  (NH40  .  2110) .  P05,  is  formed  by  adding 
phosphoric  acid  to  the  solution  of  the  preceding  salt,  till  the  liquid  becomes 
slightly  acid.  It  forms  crystals  belonging  to  the  square  prismatic  system,  and 
somewhat  less  soluble  than  the  preceding.  (Mitscherlich.) 

A  basic  phosphate  is  also  formed  by  mixing  a  concentrated  solution  of  the  biam- 
moniacal salt  with  ammonia ;  but  it  quickly  gives  off  ammonia,  and  is  reconverted 
into  the  biammoniacal  salt. 

Pyrophosphate  and  Metaphosphate  of  Ammonium  may  also  be  formed  by  adding 
ammonia  to  the  aqueous  solutions  of  the  respective  acids ;  but  they  are  converted 
by  evaporation  into  the  corresponding  tribasic  phosphates.  (Graham.) 

Oxalates  of  Ammonium.  —  The  neutral  oxalate,  C4(NH4)208  (regarding  oxalic 
acid  as  a  bibasic  acid,  p.  702),  is  obtained  by  neutralizing  the  aqueous  acid  with 
ammonia  It  crystallizes  in  long  prisms  united  in  tufts  and  belonging  to  the  right- 
prismatic  system  :  they  contain  2  eq.  of  water,  which  they  give  off  at  a  moderate 
heat.  The  acid  oxalate,  C4(H  .  NH4)08,  is  precipitated  in  the  crystalline  form, 
when  the  solution  of  the  neutral  salt  is  mixed  with  oxalic,  sulphuric,  or  hydro- 
chloric acid.  It  is  much  less  soluble  than  the  neutral  salt. 

A  superoxalate,  C4(H  .  NH4)08  -f  C4H208,  separates  from  a  solution  of  equal 
parts  of  oxalic  acid  and  the  acid  oxalate,  in  crystals  resembling  those  of  the  pre- 
ceding salt,  and  containing  4  eq.  of  water. 

Neutral  oxalate  of  ammonium,  when  strongly  heated,  gives  off  4  at  water,  and 
yields  a  sublimate  of  oxamide  (p.  713) : 

C4N2H808  — 4HO  =  C4N2H404. 

Neutral  oxalate  Oxamide. 

of  ammonium. 

*  Scientific  Memoirs,  ii.  98. 


LITHIUM.  811 

The  acid  salt,  when  heated,  gives  off  2  at.  water,  and  leaves  oxamic  acid  (p. 
704): 

C4NH508  —  2110  =  C4NH306. 

Acid  oxalateof  Oxamic  acid. 

ammonium. 

All  amides  and  amidogen-acids  may,  indeed,  be  regarded  as  ammonium-salts 
minus  water.  But  few  of  them,  however,  are  produced  by  the  actual  abstraction 
of  water  from  the  corresponding  ammonium-salts  ',  they  are  more  generally  pro- 
duced by  the  action  of  ammonia  on  anhydrous  acids,  acid  chlorides,  or  compound 
ethers  (pp.  704,  713,  715). 

The  compounds  formed  by  the  action  of  dry  ammonia  on  the  anhydrous  acids, 
sometimes  called  anhydrous  salts  of  ammonia,  and,  by  H.  Rose,  ammon-salts,  are 
all  either  amides  or  aniidogen-acids.  Thus,  2  vols.  ammoniacal  gas,  and  1  vol. 
carbonic  acid,  unite  and  form  the  compound  NH3C02,  which,  doubling  the  atomic 

C  O 
weight,  is  carbamide,  N2  \  A  2,  or  2  at.  ammonia  in  which  one-third  of  the  hydro- 

1 

gen  is  replaced  by  the  biatomic  radical  carbonyl,  C202.     With  anhydrous  sulphu- 

.ric    acid,    ammonia    forms    two   compounds,  viz.    NH3S03,  Rose's    sulph-atam- 

S  O 
mon,  or   sulphamide,  =  N2  j  |j  4  +  2HO  ;    and  sulphamic   acid,  NH3S206  = 

a    2   4  Similarly,  with   anhydrous   sulphurous   acid,  ammonia   forms 


thionamide,  NH3S02  =  N2  j        2,  and  thionamic  acid,  NH3S206  = 

[For  the  amides  of  phosphoric  acid,  see  page  787.] 

All  salts  of  ammonium,  heated  with  fixed  caustic  alkalies,  give  off  ammonia, 
which  may  be  absorbed  by  hydrochloric  acid,  and  its  quantity  then  determined 
either  by  evaporating  the  solution  of  chloride  of  ammonium  over  the  water-bath, 
or,  more  exactly,  by  precipitation  with  bichloride  of  platinum  (p.  619). 

LITHIUM. 

Preparation.  —  Pure  chloride  of  lithium  is  fused  over  a  spirit-lamp,  in  a  small 
porcelain  crucible,  and  decomposed  by  a  zinc-carbon  battery  of  four  or  six  cells. 
The  positive  pole  is  a  small  splinter  of  gas-coke  (the  hard  carbon  deposited  in  the 
gas-retorts),  and  the  negative  pole  an  iron  wire  about  the  thickness  of  a  knitting- 
needle.*  After  a  few  seconds,  a  small  silver-white  regulus  is  formed  under  the 
fused  chloride,  round  the  iron  wire  and  adhering  to  it,  and  after  two  or  three 
minutes  attains  the  size  of  a  small  pea.  To  obtain  the  metal,  the  wire  pole  and 
regulus  are  lifted  out  of  the  fused  mass,  by  a  small,  flat,  spoon-shaped  iron 
spatula.  The  wire  may  then  be  withdrawn  from  the  still  melted  metal,  which  is 
protected  from  oxidation  by  a  coating  of  chloride  of  lithium.  The  metal  may 
now  be  easily  removed  from  the  spatula  with  a  penknife,  after  having  been  cooled 
under  rock-oil.  These  operations  may  be  repeated  every  three  minutes  ;  and  thus 
an  ounce  of  the  chloride  may  be  reduced  in  a  very  short  time. 

Lithium,  on  a  freshly-cut  surface,  has  the  colour  of  silver,  but  quickly 
tarnishes  on  exposure  to  the  air,  becoming  slightly  yellow.  It  melts  at  180°  C. 

*  The  decomposing  power  of  an  electric  current  depends  chiefly  upon  its  density,  i.  e. 
upon  the  quotient  obtained  by  dividing  the  strength  of  the  current  by  the  surface  of  the 
pole  at  which  the  electrolysis  takes  place.  Thus,  a  current  of  constant  strength  passed 
through  an  aqueous  solution  of  terchloride  of  chromium,  eliminates,  as  its  density  is  suc- 
cessively diminished  (or  the  cross-section  of  the  reducing  pole  increased),  metallic  chromium, 
chromous  oxide,  chromic  oxide,  and,  lastly,  hydrogen.  (Bunseu,  Pogg.  Ann.  xci.  619.) 


812  BARIUM. 

(356°  F.),  and  if  pressed  at  that  temperature  between  two  glass  plates,  exhibits 
the  colour  and  brightness  of  polished  silver.  It  is  harder  than  potassium  or 
sodium,  but  softer  than  lead,  and  may,  like  that  metal,  be  drawn  out  into  wire. 
It  tears  much  more  easily  than  a  lead  wire  of  the  same  dimensions.  It  may  be 
welded  by  pressure  at  ordinary  temperatures.  It  swims  on  rock-oil,  and  is  the 
lightest  of  all  known  solids,  its  specific  gravity  being  only  0-5986.  Taking  the 
atomic  weight  at  6*5,  its  atomic  volume  is  therefore  1-06,  being  nearly  the  same 
as  that  of  calcium. 

Lithium  is  much  less  oxidable  than  potassium  or  sodium.  It  makes  a  lead-grey 
streak  on  paper.  It  ignites  at  a  temperature  much  higher  than  its  melting  point, 
burning  quietly,  and  with  an  intense  white  light.  It  burns  when  heated  in 
oxygen,  chlorine,  bromine,  iodine,  or  dry  carbonic  acid,  and  with  great  brilliancy 
on  boiling  sulphur.  When  thrown  on  water,  it  oxidizes,  but  does  not  fuse  like 
sodium.  Nitric  acid  acts  on  it  so  violently,  that  it  melts  and  often  takes  fire. 
Strong  sulphuric  acid  attacks  it  slowly;  dilute  sulphuric  acid  and  hydrochloric 
acid,  quickly.  Silica,  glass,  and  porcelain  are  attacked  by  lithium  at  temperatures 
even  below  200°  C.  (Bunsen.)* 

According  to  Dr.  Mallett,f  the  atomic  weight  of  lithium  is  6-95;  and  accord- 
ingly that  of  sodium  is  exactly  the  mean  between  those  of  lithium  and  potassium. 

Nitrate  of  Lithia.  —  This  salt  has  a  strong  tendency  to  form  supersaturated 
solutions.  Above  10°  or  15°  C.,  it  crystallizes  in  rhombic  prisms,  resembling  those 
of  common  nitre,  but  below  10°  in  rhombohedrons }  both  kinds  of  crystals  are 
deliquescent.  The  crystals  which  separate  from  the  supersaturated  solution  at  1°  C. 
are  slender  needles.  (Kremers.)J 

Phosphate  of  Lithia.  —  According  to  W.  Mayer,§  the  precipitate  formed  on 
adding  phosphate  of  soda  to  the  solution  of  a  lithia-salt,  is  not  a  double  phosphate 
of  lithia  and  soda,  as  commonly  supposed,  but  a  tribasic  phosphate  of  lithia, 
3LiO.P05  The  same  precipitate  is  also  produced  when  a  lithia-salt  is  treated 
with  phosphate  of  potash  or  phosphate  of  ammonia,  mixed  with  free  alkali. 

Estimation  of  Lithium. — This  element,  when  separated  from  other  metals, 
may  be  estimated  in  the  form  of  sulphate  or  chloride,  in  the  same  manner  as 
potassium  or  sodium.  From  potassium  it  is  separated  by  precipitating  the  latter 
with  bichloride  of  platinum ;  and  from  sodium,  by  converting  the  two  bases  into 
chlorides,  and  treating  the  dried  chlorides,  in  a  well-closed  bottle,  with  a  mixture 
of  absolute  alcohol  and  ether,  which,  after  a  few  days,  dissolves  the  whole  of  the 
chloride  of  lithium,  and  leaves  the  chloride  of  sodium  undissolved. 
,  •  • 

BARIUM. 

Bunsen  has  obtained  this  metal  by  subjecting  chloride  of  barium,  mixed  up  to 
a  paste  with  water  and  a  little  hydrochloric  acid,  at  a  temperature  of  100°  C.,  to 
the  action  of  the  electric  current,  using  an  amalgamated  platinum  wire  as  the 
negative  pole.  In  this  manner,  the  metal  is  obtained  as  a  solid,  silver-white, 
highly-crystalline  amalgam,  which,  when  placed  in  a  little  boat  made  of  thoroughly 
ignited  charcoal,  and  heated  in  a  stream  of  hydrogen,  yields  barium  in  the  form 
of  a  tumefied  mass,  darkly  tarnished  on  the  surface,  but  often  exhibiting  a  silver- 
white  lustre  in  the  cavities. ||  Matthiessen  has  obtained  barium  by  a  method 
similar  to  that  adopted  for  strontium  (p.  690),  but  only  in  the  form  of  a  metallic 
powder. 

Binoxide  or  Peroxide  of  Barium.  —  A  solution  of  this  oxide  in  dilute  hydro- 
chloric acid  acts  as  a  reducing  agent  on  various  metallic  oxides,  a  portion  of  its 
oxygen  uniting,  at  the  moment  of  separation,  with  the  oxygen  of  the  other  metallic 

*  Ann.  Ch.  Pharm.  xciv.  107;  Chem.  Soc.  Qu.  J.  viii.  ]43. 

f  Sill.  Ann.  J.  [2],  xxii.  349.  J  Pogg.  Ann.  xcii.  520. 

\  Ann.  Ch.  Pharm.  xcviii.  193.  ||  Pogg.  Ann.  xci.  619. 


CARBONATE    OF    BARYTA.  813 

oxide  (p.  689).  When  peroxide  of  barium  is  introduced  into  a  solution  of  bi- 
chromate of  potash  acidulated  with  hydrochloric  acid,  oxygen  is  abundantly  evolved 
(its  evolution  being,  however,  preceded,  in  the  case  of  cold  dilute  solutions,  by  the 
formation  of  a  blue  compound,  first  observed  by  Barreswil,  and  supposed  by  him 
to  be  a  perchromic  acid,  O207) ;  and  according  to  Brodie's  experiments,  the  re- 
action, when  a  great  excess  of  bichromate  of  potash  is  present,  takes  place  as 
shown  by  the  equation  — 

2Cr03  +  4Ba02  =  O203  +  70  -f  4BaO, 

the  chromic  acid  being  reduced  to  sesquioxide  of  chromium.  The  quantity  of 
oxygen  evolved  affords  the  means  of  calculating  the  per  centage  of  real  Ba02  in 
the  sample  used.  Oxide,  chloride,  sulphate,  or  carbonate  of  silver  introduced  into 
an  acid  solution  of  a  peroxide  of  barium,  is  partly  reduced  to  metallic  silver,  the 
quantity  of  metal  thus  reduced  being,  however,  always  less  than  that  which  is 
equivalent  to  the  oxygen  which  exists  in  the  peroxide  together  with  baryta. 
The  quantity  reduced  increases  with  the  amount  of  the  silver  compound  used, 
and  diminishes  as  the  temperature  is  higher.  A  small  quantity  of  the  silver- 
compound,  or  of  any  similar  substance,  is  capable  of  decomposing  a  large  quantity 
of  the  peroxide.  Iodine,  on  the  other  hand,  decomposes  only  an  equivalent 
quantity,  according  to  the  equation  — 

Ba02  +  I  =  Bal  +  02  (Brodie*). 

[For  the  separation  of  oxygen  from  the  air  by  first  converting  baryta  into  the 
peroxide,  and  then  decomposing  the  latter,  see  p.  759.] 

Peroxide  of  barium,  heated  over  a  large  spirit-lamp  in  a  rapid  current  of  car- 
bonic acid  gas  becomes  white-hot,  and  at  the  same  time  small  white  flames  burst 
out  from  its  surface,  probably  arising  from  the  evolution  of  oxygen  from  the  still 
undecomposed  peroxide.  A  similar,  but  much  more  brilliant  appearance  is  pre- 
sented when  the  peroxide  is  heated  in  sulphurous  acid  gas.  (Wohlerf). 

Carbonate  of  Baryta,  mixed  with  carbonate  of  lime  and  charcoal,  and  heated 
to  redness  in  a  stream  of  aqueous  vapour,  is  decomposed,  and  yields  caustic 
baryta.  This  process  is  recommended  by  JacquelainJ  for  the  preparation  of 
caustic  baryta. 

According  to  Boussingault,§  a  solution  of  chloride  of  barium,  mixed  with  the 
native  sesquicarbonate  of  soda  called  Uras,  yields  a  precipitate  of  2BaO .  3C02- 
Laurent  assigns  to  this  precipitate  the  formula  2BaO .  3C02  +  HO.  H.  Eose,|| 
on  the  other  hand,  finds  that  the  chloride  of  barium  and  bicarbonate  of  soda 
always  yield  a  precipitate  consisting  merely  of  BaO .  C02,  and  similarly  with  lime. 

Recently-precipitated  sulphate  of  baryta,  enclosed,  with  a  solution  of  bicarbo- 
nate of  soda,  or  with  dilute  sulphuric  acid,  in  a  sealed  glass  tube,  and  heated  for 
60  hours  to  250°  C.  (472°  F.),  dissolves  to  a  slight  extent,  and  separates  out  on 
the  sides  of  the  tube  in  microscopic  crystals,  whose  form  agrees  with  that  of 
heavy  spar.  Pure  water,  or  a  solution  of  sulphide  of  sodium,  does  not  perceptibly 
dissolve  sulphate  of  baryta  under  similar  circumstances.  (Senarmont^f). 

Estimation  of  Barium. — Barium  is  almost  always  estimated  in  the  form  of  sul- 
phate, the  precipitation  and  filtration  being  performed  in  the  manner  already 
described  for  the  estimation  of  sulphuric  acid  (p.  784). 

Precipitation  with  a  soluble  sulphate  likewise  serves  to  separate  barium  fom  all 
other  metals  except  strontium,  calcium,  and  lead. 

*  Phil.  Trans.  1850,  759.  f  Ann.  Ch.  Pharm.  Ixxviii.  175. 

%  Ann.  Ch.  Phys.  [3],  xxxii.  421.  |  Ibid.  xxix.  397. 

||  Pogg.  Ann.  Ixxxvi.  293.  \  Ann.  Ch.  Phys.  [3],  xxxii.  129. 


814  STRONTIUM. 

Barium  is  also  sometimes  estimated  as  carbonate,  being  precipitated  by  carbo- 
nate of  ammonia  with  addition  of  caustic  ammonia,  and  the  liquid  boiled  to  render 
the  precipitation  complete.  The  carbonate  is  not  decomposed  by  ignition. 


STRONTIUM. 

Preparation. — This  metal  is  also  obtained  by  the  electrolysis  of  its  chloride  in 
the  fused  state.  A  small  crucible,  with  a  porous  cell  in  the  middle,  is  filled  with 
anhydrous  chloride  of  strontium,  mixed  with  a  little  chloride  of  ammonium,  and 
in  such  a  manner  that  the  level  of  the  fused  chloride  within  the  cell  may  be  much 
higher  than  in  the  crucible.  The  negative  pole  placed  in  the  cell  consists  of  a  very 
fine  iron  wire  wound  round  a  thicker  one,  and  then  covered  with  a  piece  of 
tobacco-pipe  stem,  so  that  only  y'gth  of  an  inch  of  it  appears  below ;  the  positive 
pole  is  an  iron  cylinder,  placed  in  the  crucible  round  the  cell.  The  heat  should 
be  regulated  during  the  experiment,  so  that  a  crust  may  form  in  the  cell ;  the 
metal  will  then  collect  under  this  crust  without  coming  in  contact  with  the  sides 
of  the  crucible.  In  this  manner,  pieces  of  the  metal  weighing  half  a  gramme  are 
sometimes  obtained. 

Strontium  resembles  calcium  in  colour  (p.  815),  being  only  a  shade  darker;  it 
oxidizes  much  more  quickly  than  that  metal.  Its  specific  gravity  is  2-5418.  Its 
place  in  the  electrical  series,  with  water  as  the  exciting  liquid,  is  as  follows  : 

+  — 

K,     Na,     Li,     Ca,     Sr,     Mg,     &c. 

Strontium  burns  like  calcium,  and  acts  similarly  to  it  when  heated  in  chlorine, 
oxygen,  bromine,  or  iodine,  or  on  boiling  sulphur,  or  when  thrown  on  water  or 
acids.  (Matthiessen*). 

Estimation  of  Strontium.  —  Strontium,  like  barium,  may  be  estimated  in  the 
form  of  sulphate ;  but  as  sulphate  of  strontia  is  slightly  soluble  in  water,  it  is 
necessary,  in  order  to  ensure  complete  precipitation,  to  add  alcohol  to  the  liquid, 
which  may  be  done  if  there  are  no  other  substances  present  which  are  insoluble 
in  alcohol. 

Generally  speaking,  however,  it  is  better  to  precipitate  strontium  in  the  form 
of  a  carbonate,  by  adding  carbonate  of  ammonia  and  caustic  ammonia,  and  heating 
the  liquid.  The  precipitation  of  strontia  in  this  form  is  more  complete  than  that 
of  baryta.  The  precipitate  may  be  ignited  on  a  lamp  without  giving  off  carbonic 
acid.  It  contains  59-27  per  cent,  of  strontium,  and  70-14  of  strontia. 

The  same  mode  of  precipitation  serves  to  separate  strontia  from  the  alkalies. 

The  separation  of  strontia  from  baryta  is  best  effected  by  means  of  hydrofluo- 
silicic  acid,  which  precipitates  barium  in  the  form  of  a  crystalline  silicofluoride, 
leaving  the  strontium  in  solution.  The  precipitate  must  be  left  to  settle  down  for 
two  or  three  hours ;  and  its  deposition  may  be  accelerated  by  a  gentle  heat.  It 
may  then  be  collected  on  a  weighed  filter,  washed  with  water,  and  dried  at  100°  C. 
The  filtrate  containing  the  strontium  is  then  mixed  with  sulphuric  acid,  evaporated, 
and  ignited,  whereby  it  is  converted  into  sulphate. 

The  quantities  of  barium  and  strontium  in  a  mixture  may  likewise  be  determined 
by  an  indirect  method,  viz.  by  weighing  them,  first  in  the  form  of  chlorides  or 
carbonates,  and  afterwards  as  sulphates.  Thus,  suppose  them  to  be  first  precipi- 
tated as  carbonates,  the  united  weight  of  which  is  found  to  be  w,  then  converted 
into  sulphates,  the  weight  of  which  is  w'.  Then,  to  determine  the  quantity  of 
baryta,  x,  and  strontium,  y,  in  the  mixture,  we  have  the  equations 

*  Chem.  Soc.  Qu.  J.  vii.  107. 


CALCIUM.  815 

BaC  SrC  BaS  S'rS          , 

— -  x  H r-  y  =  w  ;     —r-  x  -\ —  =  w  ; 

Ba  Sr  Ba  Sr 

98-7          73-7  116-7       91-7 

OT'7fr7a!+5F7y==f';    T6-7*  +  5F7y  = 

A  similar  method  may  be  applied  in  all  cases  in  which  two  substances  in  a  mix- 
ture can  be  weighed  in  two  distinct  forms.  Such  methods,  however,  give  exact 
results  only  when  the  quantities  of  the  substances  to  be  determined  are  not  very 
unequal. 

CALCIUM. 

Preparation. — A  mixture  of  2  at.  chloride  of  calcium  and  1  at.  chloride  of 
strontium,  with  a  small  quantity  of  chloride  of  ammonium  (this  mixture  being 
more  fusible  than  chloride  of  calcium  alone),  is  melted  in  a  small  porcelain  cruci- 
ble, in  which  a  carbon  positive  pole  is  placed,  while  a  thin  harpsichord  wire  wound 
round  a  thicker  one,  and  dipping  only  just  below  the  surface  of  the  melted  salt, 
forms  the  negative  pole.  The  calcium  is  then  reduced  in  beads,  which  hang  on 
to  the  fine  wire,  and  may  be  separated  by  withdrawing  the  negative  pole  every 
two  or  three  minutes,  together  with  the  small  crust  which  forms  round  it.  A 
surer  method,  however,  of  obtaining  the  metal,  though  in  very  small  beads,  is  to 
place  a  pointed  wire  so  as  merely  to  touch  the  surface  of  the  liquid ;  the  great 
heat  evolved,  owing  to  the  resistance  of  the  current,  causes  the  reduced  metal  to 
fuse  and  drop  off  from  the  point  of  the  wire,  and  the  bead  is  taken  out  of  the 
liquid  with  a  small  iron  spatula.  Or,  thirdly,  the  disposition  of  the  apparatus 
may  be  the  same  as  that  for  the  reduction  of  strontium  (p.  814). 

Properties. — Calcium  is  a  light  yellow  metal,  of  the  colour  of  gold  alloyed  with 
silver ;  on  a  freshly  cut  surface,  the  lustre  somewhat  diminishes  the  yellow  colour, 
which  becomes  more  apparent  when  the  light  is  reflected  several  times  from  two 
surfaces  of  calcium,  or  when  the  surface  is  slightly  oxidized.  It  is  about  as  hard 
as  gold,  very  ductile,  and  may  be  cut,  filed,  or  hammered  out  into  plates  having 
the  thickness  of  the  finest  paper.  Its  specific  gravity  is  1-5778.  In  dry  air  the 
metal  retains  its  colour  and  lustre  for  a  few  days,  but  in  damp  air  the  whole  mass 
is  slowly  oxidized.  Heated  on  platinum-foil  over  a  spirit-lamp,  it  burns  with  a 
very  bright  flash.  It  is  not  quickly  acted  upon  by  dry  chlorine  at  ordinary  tem- 
peratures ;  but  when  heated,  burns  in  that  gas  with  a  most  brilliant  light ;  also  in 
iodine,  bromine,  oxygen,  sulphur,  &c.  With  phosphorus,  it  combines  without  ig- 
nition, forming  phosphide  of  calcium.  Heated  mercury  dissolves  it  as  a  white 
amalgam.  Calcium  rapidly  decomposes  water,  and  is  still  more  rapidly  acted  on 
by  dilute  nitric,  hydrochloric,  and  sulphuric  acids,  nitric  acid  often  causing  igni- 
tion. Strong  nitric  acid  does  not  act  upon  it  below  the  boiling  heat.  In  the  vol- 
taic circuit,  with  water  as  the  liquid  element,  calcium  is  negative  to  potassium 
and  sodium,  but  positive  to  magnesium.  It  is  not,  however,  reduced  by  potassium 
or  sodium  from  its  chloride  by  electrolysis.  On  the  contrary,  a  fused  mixture  of 
CaCl  with  KC1  or  NaCl,  in  certain  proportions,  yields  potassium  or  sodium,  when 
subjected  in  a  certain  manner  to  electric  action  (p.  806);  hence  it  appears  that 
the  metal  formerly  obtained  by  reducing  chloride  of  calcium  with  potassium  or 
sodium,  could  not  be  calcium,  but  was,  probably,  a  mixture  of  potassium  or  sodium 
with  aluminium,  silicon,  &c.  (Matthiessen.*) 

Lime.  —  According  to  Wittstein,f  1  part  by  weight  of  lime  dissolves  in  729  to 
723  pts.  of  water,  at  ordinary  temperatures,  and  in  1310  to  1569  pts.  of  boiling 
water.  The  carbonate  of  lime  deposited  from  lime-water  on  exposure  to  the  air  is 
really  the  neutral  carbonate,  CaO.C02. 

Marchand  and  Scheerer  find  that  calcspar  begins  to  give  off  carbonic  acid  at 

*  Chem.  Soc.  Qu.  J.  viii.  28.  f  Repert.  Pharm.  [8],  i.  182. 


816  CALCIUM. 

200°  C.,  but  that  a  certain  quantity  of  that  acid  remains  with  the  lime,  even  after 
the  most  violent  ignition.* 

Sulphate  of  Lime  dissolves  in  water  containing  sal-ammoniac  more  abundantly 
than  in  pure  water,  part  of  it  appearing  to  be  decomposed  into  chloride  of  calcium 
and  sulphate  of  ammonia.  The  presence  of  nitrate  of  potash  likewise  increases 
the  solubility  of  gypsum.  (A.  Vogel,  jun.f) 

Sulphate  of  Lime  and  Potash,  KO.S03  -f  CaO.S03  +  HO.  —This  salt  is  ob- 
tained as  an  accessory  product  in  the  manufacture  of  tartaric  acid  from  cream  of 
tartar.  The  latter  salt  is  converted,  by  treatment  with  carbonate  of  lime,  into 
tartrate  of  lime  and  neutral  tartrate  of  potash ;  and  by  the  action  of  sulphate  of 
lime,  all  the  tartaric  acid  is  obtained  in  combination  with  lime,  together  with  an 
impure  solution  of  sulphate  of  potash.  This  solution,  when  evaporated,  yields  a 
hard  deposit,  and  in  slowly  evaporating  large  quantities  of  it,  transparent  lami- 
nated crystals  are  obtained,  having  the  composition  expressed  by  the  above  for- 
mula ;  they  are  sparingly  soluble  in  water,  more  easily  in  dilute  hydrochloric  acid. 
The  non-crystalline  deposit  contains  about  65  per  cent,  of  this  double  salt,  toge- 
ther with  sulphate,  carbonate,  and  phosphate  of  lime,  carbonate  of  magnesia, 
silicate  of  potash,  oxide  of  iron,  alumina,  water,  and  traces  of  organic  matter 
(J.  A.  Phillips.!) 

Phosphate  of  Lime.  —  According  to  H.  Ludwig,§  the  precipitate  produced  by 
ordinary  phosphate  of  soda  in  a  solution  of  chloride  of  calcium  mixed  with  ammo- 
nia, has,  after  washing  and  drying  in  the  air,  the  composition  3CaO.P05-f  5|HO ; 
after  keeping  for  two  years  in  a  loosely-stoppered  bottle,  it  is  reduced  to  3CaO.P05 
+  3£HO,  and  of  these  3£HO,  2£  go  off  below  100°.  The  precipitate  was  free 
from  chlorine,  but  contained  a  trace  of  ammonia. 

According  to  Forchhammer,||  apatite,  may  be  artificially  crystallized  by  fusing 
tribasic  phosphate  of  lime,  or  bone-ash,  with  four  times  its  weight  of  chloride  of 
sodium,  and  leaving  the  fused  mass  to  cool  slowly.  The  mass  when  cold  exhibits 
cavities  containing  numerous  delicate  six-sided  prisms,  having  the  composition  of 
apatite. 

Estimation  of  Calcium.  —  This  metal  may  be  estimated  either  as  carbonate  or 
as  sulphate.  The  best  method  of  precipitating  it  is,  in  most  cases,  by  means  of 
oxalate  of  ammonia,  the  oxalate  being  the  least  soluble  of  all  the  salts  of  calcium. 
If  the  solution  contains  an  excess  of  any  strong  acid,  such  as  nitric  or  hydrochlo- 
ric acid,  it  must  be  neutralized  with  ammonia  before  adding  the  oxalate  of  ammo- 
nia, because  oxalate  of  lime  is  soluble  in  the  stronger  acids.  The  precipitate, 
after  being  washed  with  hot  water  and  dried,  is  heated  over  a  lamp,  care  being 
take  not  to  allow  the  heat  to,  rise  above  redness.  It  is  thereby  converted  into  car- 
bonate of  lime,  containing  40-15  p.  c.  of  calcium  and  56-12  of  lime. 

If,  however,  the  solution  contains  any  acid  which  forms  with  lime  a  compound 
insoluble  in  water,  phosphoric  or  boracic  acid  for  example,  this  method  of  preci- 
pitation cannot  be  adopted ;  because,  on  neutralizing  with  ammonia,  the  lime 
would  be  precipitated  in  combination  with  that  acid,  and  would  not  be  converted 
into  oxalate  on  addition  of  oxalate  of  ammonia.  In  such  a  case,  the  lime  may  be 
precipitated  as  sulphate  by  adding  pure  dilute  sulphuric  acid  and  alcohol.  The 
sulphate,  when  dried,  contains  41-25  per  cent,  of  lime.  Phosphate  of  lime  may, 
however,  be  precipitated  from  its  acid  solutions  by  oxalate  of  ammonia,  with  addi- 
tion of  acetate  of  ammonia,  because  oxalate  of  lime  is  insoluble  in  acetic  acid, 
which  dissolves  the  phosphate  with  facility. 

From  the  alkalies,  lime  is  easily  separated  either  by  oxalate  of  ammonia,  or  by 
sulphuric  acid  and  alcohol. 

*  J.  pr.  Chem.  1.  237.  f  Repert.  Pharm.  [3],  v.  342. 

I  Chem.  Soc.  Qu.  J.  iii.  348.  §  Pharm.  Centr.  1862,  345. 

Tl  Pogg.  Ann.  xci.  688. 


MAGNESIUM.  817 

Lime  is  separated  from  baryta  by  precipitating  both  the  earths  as  carbonates, 
dissolving  the  carbonates  in  nitric  acid,  evaporating  to  dryness,  and  digesting  the 
residue  in  absolute  alcohol,  which  dissolves  nitrate  of  lime,  but  not  nitrate  of 
baryta.  They  may  also  be  separated  in  this  manner  in  the  form  of  chlorides,  but 
the  separation  is  less  complete,  because  chloride  of  barium  is  not  quite  insoluble 
in  absolute  alcohol. 

From  strontia,  lime  is  separated  in  the  same  manner,  nitrate  of  strontia  being 
likewise  insoluble  in  absolute  alcohol. 

When  baryta,  strontia,  and  lime  occur  together,  the  baryta  is  first  separated  by 
hydro-fluosilicic  acid  ;  the  s-trontia  and  lime  in  the  filtrate  are  then  converted  into 
sulphates;  these  sulphates,  after  being  weighed,  converted  into  carbonates  by 
fusion  with  carbonate  of  soda,  or  by  boiling  with  the  aqueous  solution  of  that  salt 
(p.  736)  ;  the  carbonates  weighed  ;  and  the  quantities  of  strontia  and  lime  deter- 
mined from  the  equations  : 

91-7          68 
5Ff*  +  28*  =  W7 
73-7         50 


in  which  x  is  the  weight  of  strontia,  y  that  of  the  lime,  w  that  of  the  sulphates, 
and  w'  that  of  the  carbonates  of  the  two  bases.  Or  the  carbonates  may  be  dis- 
solved in  nitric  acid,  and  the  nitrates  separated  by  absolute  alcohol. 

MAGNESIUM. 

Bunsen  prepares  this  metal  by  the  electrolysis  of  the  fused  chloride.  A  porce- 
lain crucible  is  divided  in  its  upper  part  into  two  halves  by  a  vertical  diaphragm 
(made  out  of  a  thin  porcelain  crucible-cover),  and  fitted  with  a  cover  (filed  from 
a  tile),  through  which  the  extremities  of  the  carbon-poles  of  a  galvanic  battery 
are  introduced  into  the  two  halves  of  the  crucible.  The  crucible  is  then  heated 
to  redness,  together  with  the  cover  and  the  poles  ;  filled  with  fused  chloride  of 
magnesium  (p.  415)  ;  and  subjected  to  the  action  of  a  battery  of  10  zinc-carbon 
elements.  The  negative  pole  is  cut  like  a  saw,  so  that  the  magnesium,  as  it 
separates,  may  lodge  in  the  cavities,  and  not*  float  on  the  surface  of  the  specifically 
heavier  liquid.*  According  to  Matthiessen,f  the  metal  may  be  much  more  easily 
obtained  from  a  fused  mixture  of  4  at.  chloride  of  magnesium  and  3  at.  "chloride 
of  potassium,  which  is  prepared  with  more  facility  than  the  pure  anhydrous 
chloride  of  magnesium.  The  two  salts  mixed  in  the  proper  proportions  J  with  a 
little  chloride  of  ammonium  may  be  fused  and  electrolyzed  in  Bunsen's  apparatus 
just  described,  the  cutting  of  the  negative  pole  being,  however,  dispensed  with, 
as  the  metal  is  heavier  than  the  fused  mixture.  A  very  simple  and  convenient 
way  of  reducing  the  metal,  especially  for  the  lecture-table,  is  to  fuse  the  mixture 
in  a  common  clay  tobacco-pipe  over  an  argand  spirit-lamp  or  gas-burner,  the 
negative  pole  being  an  iron  wire  passed  up  the  pipe-stem,  and  the  positive  a  piece 
of  gas-coke,  just  touching  the  surface  of  the  fused  chlorides.  (Matthiessen.) 

Magnesium  may,  however,  be  obtained  in  much  larger  quantity,  by  heating  a 
mixture  of  600  grammes  of  chloride  of  magnesium,  100  grms.  fused  chloride  of 
sodium,  and  100  grms.  of  pulverized  fluoride  of  calcium,  with  100  grins,  of 
sodium,  to  bright  redness,  in  a  covered  earthen  crucible.  The  magnesium  i? 
thereby  obtained  in  globules,  which  are  afterwards  heated  nearly  to  whiteness  in 
a  boat  of  compact  charcoal,  placed  within  an  inclined  tube  of  the  same  material, 
through  which  a  stream  of  dry  hydrogen  is  passed.  The  magnesium  then  vol?- 

*  Ann.  Ch.  Pharm.  82,  137.  fChem.  Soc.  Qu.  J.  viii.  107, 

J  The  solution  of  the  chloride  of  magnesium  may  be  evaporated  almost  to  dryness,  and 
analyzed  to  find  the  proportion  of  anhydrous  salt  present. 

52 


818  ALUMINIUM. 

tilizes  and  condenses  in  the  upper  part  of  the  tube.  Lastly,  it  is  remelted  with  a 
flux  composed  of  chloride  of  magnesium,  chloride  of  sodium,  and  fluoride  of  cal- 
cium, and  is  thus  obtained  in  large  globules.  (II.  Deville  and  Caron.)* 

Magnesium  on  the  recently-fractured  surface  is  sometimes  slightly  crystalline 
and  coarsely  laminated;  sometimes  fine-grained.  In  the  former  cases  it  is  silver- 
white  and  shining;  in  the  latter,  bluish  grey  and  dull.  Its  specific  gravity  is 
1-7430  at  4-  5°  C.  (Bunsen)  :  1-75,  according  to  Deville  and  Caron.  It  is  about 
as  hard  as  calcspar,  and  may  be  easily  filed,  bored,  sawn,  and  flattened  to  a  certain 
extent,  but  is  scarcely  more  ductile  than  zinc  at  ordinary  temperatures.  It  melts 
at  a  moderate  red  heat  (Bunsen) ;  melts  and  volatilizes  at  about  the  same  tempe- 
rature as  zinc  (Deville  and  Caron).  It  does  not  alter  in  a  dry  atmosphere,  but  in 
damp  air  soon  becomes  covered  with  a  film  of  hydrate  of  magnesia.  Heated  to 
redness  in  the  air,  or  in  oxygen  gas,  it  burns  with  a  dazzling  white  light,  and 
forms  magnesia.  It  decomposes  pure  cold  water  but  slowly,  acidulated  water  very 
quickly  ;  when  thrown  on  aqueous  hydrochloric  acid,  it  takes  fire  momentarily ; 
strong  sulphuric  acid  dissolves  it  but  slowly ;  a  mixture  of  sulphuric  acid  and 
fuming  nitric  acid  does  not  act  upon  it  at  ordinary  temperatures.  It  burns  when 
heated  in  chlorine  gas;  also  in  bromine-vapour,  though  with  less  facility;  in 
sulphur  and  iodine-vapour  very  brilliantly  (Bunsen). 

Estimation  of  Magnesium. — When  magnesia  occurs  in  a  solution  not  contain- 
ing any  other  fixed  substance,  its  quantity  may  be  determined  by  evaporating  to 
dryness,  igniting  the  residue,  then  moistening  it  with  sulphuric  acid  slightly 
diluted  with  water,  and  expelling  the  excess  of  that  acid  at  a  low  red  heat ;  sul- 
phate of  magnesia  then  remains,  containing  38-7  per  cent,  of  magnesia. 

If  the  solution  contains  other  fixed  substances,  the  magnesia  must  be  precipi- 
tated by  the  addition  of  ammonia  in  excess  and  phosphate  of  soda.  The  precipi- 
tated ammonio-magnesian  phosphate  is  then  treated  in  the  manner  described  at  p. 
790.  The  pyrophosphate  of  magnesia  obtained  by  igniting  it  contains  36-33  per 
cent,  of  magnesia. 

From  baryta  and  strontia,  magnesia  is  separated  by  sulphuric  acid ;  from  lime, 
by  oxalate  of  ammonia,  with  addition  of  chloride  of  ammonium  to  prevent  the 
precipitation  of  the  magnesia. 

From  the  alkalies,  magnesia  may  be  separated  by  converting  the  bases  into 
sulphates,  and  adding  baryta-water.  *The  magnesia  is  then  precipitated  in  the 
form  of  hydrate,  together  with  sulphate  of  baryta.  The  precipitate,  after  wash- 
ing, is  digested  with  dilute  sulphuric  acid,  which  extracts  the  magnesia  in  the 
form  of  sulphate ;  and  the  filtrate  containing  the  alkalies,  together  with  the  excess 
of  baryta,  is  also  treated  with  sulphuric  acid,  which  precipitates  the  baryta,  and 
converts  the  alkalies  into  sulphates. 


Preparation.  —  This  metal  is  now  obtained  in  considerable  quantity  by  decom- 
posing the  chloride  or  fluoride  with  sodium.  The  chloride  of  aluminium  is  pre- 
pared on  the  large  scale  by  passing  chlorine  over  a  previously  ignited  mixture  of 
clay  and  coal-tar  in  retorts  like  those  used  in  the  preparation  of  coal-gas,  and  is 
either  made  to  pass  into  a  chamber  lined  with  plates  of  earthenware,  where  it  con- 
denses into  a  compact  crystalline  mass ;  or  the  vapour  is  made  to  pass  over  chlo- 
ride of  sodium  at  a  red  heal,  whereby  it  is  converted  into  the  double  chloride  of 
aluminium  and  sodium.  To  effect  the  reduction,  400  pts.  of  this  double  salt, 
200  pts.  of  chloride  of  sodium,  200  pts.  of  fluor-spar  (or  better,  of  cryolite),  all 
perfectly  dry  and  finely  pounded,  are  mixed  together,  and  the  mixture  placed, 
together  with  75  or  80  parts  of  sodium,  in  an  earthern  crucible,  the  saline  mixture 

*  Ann.  Ch.  Pharm.  ci.  359. 


ALUMINIUM.  819 

and  the  sodium  being  deposited  in  alternate  layers.  The  crucible  is  then  mode- 
rately heated  till  the  action  begins,  afterwards  to  redness,  the  melted  mass  stirred 
with  an  earthenware  rod,  and  afterwards  poured  out.  Twenty  parts  of  aluminium 
are  thus  obtained  in  a  compact  lump,  and  about  5  parts  in  globules  encrusted  with 
a  grey  mass.  (H.  Ste-Claire  Deville.)* 

Aluminium  may  also  be  prepared  in  a  similar  manner  from  cryolite,  the  native 
fluoride  of  aluminium  and  sodium,  which  is  now  imported  in  large  quantities  from 
Greenland.  (H.  Rose.)"|"  Instead  of  this  natural  mineral,  an  artificial  cryolite 
may  be  used,  prepared  by  mixing  1  part  of  burnt  clay  with  3  parts,  or  rather 
more,  of  anhydrous  carbonate  of  soda,  supersaturating  the  mixture  with  hydro- 
fluoric acid,  then  drying  and  fusing  it  at  a  red  heat.  A  fluoride  of  aluminium 
and  potassium  possessing  analogous  properties  may  be  prepared  .by  a  similar  pro- 
cess. (Deville.)J 

Aluminium  may  likewise  be  obtained  by  the  electrolysis  of  the  double  chloride 
of  aluminium  and  sodium,  the  process  being  similar  to  that  adopted  by  Bunsen 
for  the  electrolysis  of  chloride  of  magnesium.  (Deville,  Bunsen.) 

Pure  aluminium  is  a  white  metal,  with  a  faint  bluish  iridescence  ;  when  recently 
fused,  it  is  soft  like  pure  silver,  and  has  a  density  of  2.56;  but  after  hammering 
or  rolling,  it  is  as  hard  as  iron,  and  has  a  density  of  2.67.  A  bar  of  it  is  very 
sonorous.  It  conducts  electricity  eight  times  as  well  as  iron,  arid  is  slightly  mag- 
netic. Its  melting  point  is  between  those  of  zinc  and  silver :  when  solidified 
from  fusion,  or  reduced  by  electrolysis,  it  exhibits  crystalline  forms,  apparently 
regular  octohedrons.  It  does  not  oxidize  in  the  air,  even  at  a  strong  red  heat ; 
neither  does  it  decompose  water,  excepting  at  the  strongest  red  heat, — and  even 
then  but  slowly.  It  does  not  dissolve  in  nitric  acid,  either  dilute  or  concentrated, 
at  ordinary  temperatures,  and  but  very  slowly  in  boiling  nitric  acid ;  dilute  sul- 
phuric acid  scarcely  attacks  it  at  ordinary  temperatures,  even  after  a  long  time ; 
but  hydrochloric  acid,  at  any  degree  of  concentration,  dissolves  it  readily,  even  at 
low  temperatures,  with  evolution  of  hydrogen.  It  is  not  attacked  by  hydrosul- 
phuric  acid,  or  by  the  fused  hydrates  of  the  alkalies.  It  does  not  combine  with 
mercury,  and  when  fused  with  lead,  takes  up  only  traces  of  that  metal.  With 
copper  it  unites  in  various  proportions,  forming  light,  very  hard,  white  alloys,  and 
it  combines  also  with  silver  and  iron.  (Deville.) 

Alumina.  —  The  specific  gravity  of  alumina  ignited  over  a  spirit-lamp  is  from 
3.87  to  3.90;  after  6  hours'  ignition  in  an  air-furnace,  3.75  to  3.725;  and  after 
ignition  in  a  porcelain  furnace,  3.999,  which  agrees  very  nearly  with  that  of 
naturally  crystallized  alumina  as  it  occurs  in  the  ruby,  sapphire,  and  corundum. 
(H.  Rose.§) 

Bihydrate  of  Alumina,  soluble  in  water,  A1203  -f  2HO.  When  a  dilute  solu- 
tion of  biacetate  of  alumina  (see  page  820),  is  exposed  to  heat  for  several  days, 
the  whole  of  the  acetic  acid  appears  to  become  free,  and  the  alumina  passes  into 
an  allotropic  state  in  which  it  is  soluble  in  water,  and  is  no  longer  capable  of 
acting  as  a  mordant,  or  of  entering  into  any  definite  combination.  This  allotropic 
alumina  retains  2  at.  water  when  dried  at  100°  C.  Its  solution  is  coagulated  by 
mineral  acids  and  by  most  vegetable  acids,  by  alkalies,  by  a  great  number  of 
neutral  salts,  and  by  decoctions  of  dye-woods.  It  is  insoluble  in  the  stronger 
acids,  but  soluble  in  acetic  acid,  unless  it  has  been  previously  coagulated  in  the 
manner  just  mentioned.  Boiling  potash  changes  it  into  the  ordinary  terhydrate. 
Its  coagulum  with  dye-woods  has  the  colour  of  the  infusion,  but  is  translucent, 
and  entirely  different  from  the  dense  opaque  cakes  which  ordinary  alumina  forms 
with  th«*same  colouring  matters.  (Walter  Crum.||) 

*  Ann.  Ch.  Phys.  [3],  xlvi.  415;  see  also  Compt.  rend,  xxxviii.  279;  xl.  1298. 
f  Pogg.  Ann.  xcvi.  152.  J  Ann.  Ch.  Phys.  [3],  xlix.  83. 

§  Pogg.  Ann.  Ixxiv.  430.  ||  Chem.  Soc.  Qu.  J.  vii.  225. 


820  ACETATES  OF  ALUMINA. 

According  to  Phillips,*  hydrate  of  alumina  when  kept  after  precipitation  in  a 
moist  atmosphere,  or  under  water,  becomes  after  a  few  days  difficult  to  dissolve  in 
acids. 

Alum. — By  fusing  ignited  alumina  with  four  times  its  weight  of  bisulphate  of 
potash,  a  mass  is  obtained,  which  when  treated  with  warm  water,  leaves  an  in- 
soluble residue,  consisting  of  thin  microscopic  six-sided  tables,  which  refract  light 
singly.  They  contain  23  per  cent,  potash,  30.7  sulphuric  acid,  and  46.3  alumina, 
and  appear  to  consist  of  crystallized  anhydrous  alum.  (Salm-Horstmar.f) 

Nitrate  of  Alumina.  —  According  to  Ordway,^  a  concentrated  and  somewhat 
acid  solution  of  alumina  in  nitric  acid,  deposits  colourless,  flattened,  oblique 
rhombic  prisms,  containing  A1203.  3N05  +  18HO.  These  crystals  melt  at  72.8° 
C.  into  a  colourless  liquid  which  solidifies  in  the  crystalline  form  on  cooling;  they 
are  deliquescent,  and  dissolve  in  water  and  in  nitric  acid.  Half  an  ounce  of  the 
pulverized  crystals  mixed  witk  an  equal  weight  of  bicarbonate  of  ammonia,  lowered 
the  temperature  from  10.5°  to  — 23.3°  C.  By  the  action  of  this  salt  upon  hydrate 
of  alumina,  basic  salts  appear  to  be  formed.  Salm-Horstmar,§  by  evaporating 
and  cooling  a  solution  of  hydrate  of  alumina  in  nitric  acid  of  26.3  per  cent.,  like- 
wise obtained  a  salt  which  crystallized  in  rhombic  prisms  and  (by  truncation)  in 
hexagonal  tables;  but  after  repeated  solution  in  water,  it  no  longer  crystallized 
distinctly;  and  its  aqueous  solution  was  decomposed  by  evaporation  at  a  somewhat 
elevated  temperature. 

Acetates  of  Alumina.  —  By  decomposing  tersulphate  of  alumina  (p.*  421),  with 
neutral  acetate  of  lead,  a  solution  is  formed,  consisting  apparently  of  a  mixture  of 
biacetate  of  alumina  with  1  at.  free  acetic  acid. 

When  this  aluminous  solution  is  evaporated  at  a  low  temperature  and  with  suf- 
ficient rapidity, — as  by  spreading  the  concentrated  solution  very  thinly  over  sheets 
of  glass  or  porcelain,  exposing  it  to  a  temperature  not  exceeding  100°  F.,  and,  as 
it  runs  together  in  drops,  rubbing  it  constantly  with  a  platinum  or  silver  spatula, 
—  a  dry  substance  is  obtained  which  may  be  redissolved  easily  and  entirely  by 
water.  This  is  the  biacetate  of  alumina,  A1203 .  2C4H303  -f  4HO  :  the  alumina 
contained  in  it  retains  all  its  usual  properties. 

When  the  first  aluminous  solution,  containing  not  less  than  4  or  5  per  cent,  of 
alumina,  is  left  for  some  days  in  the  cold,  a  salt  is  deposited  in  the  form  of  a  white 
crust,  which  is  an  allotropic  biacetate  of  alumina  insoluble  in  wafer.  Heat  effects 
the  same  change  in  the  aluminous  solution  more  rapidly,  and  the  insoluble  biace- 
tate then  separates  in  the  form  of  a  granular  powder.  At  the  boiling  temperature, 
the  liquid  is  thus  deprived,  in  half  an  hour,  of  the  whole  of  its  alumina,  which 
goes  down  with  f  of  the  acetic  acid,  leaving  J  in  the  liquid. 

The  soluble  biacetate  of  alumina  is  decomposed  by  heat,  yielding  the  bihydrate 
of  alumina  soluble  in  water  already  described  (p.  820).  The  insoluble  biacetate 
of  alumina,  when  digested  in  a  large  quantity  of  water,  is  gradually  changed  into 
the  soluble  biacetate,  part  of  which,  however,  is  decomposed  during  the  process 
into  acetic  acid  and  the  allotropic  bihydrate  of  alumina. 

The  precipitate  which  is  formed  on  the  application  of  heat  to  a  mixed  solution 
of  acetate  of  alumina  and  sulphate  of  potash,  and  which  is  soluble  in  cold  acetic 
acid,  is  a  bibasic  sulphate  of  alumina,  2A1203 .  S03  -f  10 HO. 

Common  salt  added  to  a  solution  of  teracetate  of  alumina  forms,  on  the  appli- 
cation of  heat,  a  very  finely  divided  white  precipitate,  containing  44-66  per  cent, 
alumina,  21-96  acetic  acid,  5-51  hydrochloric  acid,  25-90  water,  and  1-97  chloride 
of  sodium.  A  similar  precipitate  is  formed  by  nitrate  of  potash  (Walter  Grum.||) 

Estimation  of  Alumina. — Alumina  is  precipitated  from  its  solution*  in  the 
form  of  hydrate  by  ammonia,  carbonate  of  ammonia,  or  sulphide  of  ammonium ; 

*  Chem.  Gaz.  1848,  349.  f  J.  pr.  Chem.  Hi.  319. 

J  Sill.  Am.  J.  [2],  ix.  30.  g  J.  pr.  Chem.  lix.  208. 

||  Chem.  Soc.  Qu.  J.  vii.  217. 


GLUCINUM.  821 

the  precipitate  when  ignited  yields  pure  anhydrous  alumina,  containing  53-26  per 
cent,  of  the  metal. 

Precipitation  with  ammonia  or  sulphide  of  ammonium  serves  also  to  separate 
alumina  from  the  preceding  bases.  In  thus  separating  it  from  the  alkaline  earths, 
care  must  be  taken  not  to  expose  the  liquid  to  the  air;  otherwise  carbonic  acid 
will  be  absorbed  by  the  excess  of  ammonia,  and  the  alkaline  earths  precipitated  as 
carbonates.  From  baryta,  alumina  is  most  readily  separated  by  sulphuric  acid. 

GLUCINUM. 

This  metal  and  its  compounds  have  been  minutely  examined  by  Debray.*  The 
metal  may  be  obtained  from  the  chloride  by  reduction  with  sodium.  It  is  a  white 
metal,  whose  density  is  2-1.  It  may  be  forged,  and  rolled  into  sheets  like  gold. 
Its  melting-point  is  below  that  of  silver.  It  may  be  melted  in  the  outer  blowpipe- 
flame,  without  exhibiting  the  phenomenon  of  ignition  presented  by  zinc  and  iron 
under  the  same  circumstances ;  it  cannot  even  be  set  on  fire  in  an  atmosphere  of 
pure  oxygen,  but  in  both  experiments  becomes  covered  with  a  thin  coat  of  oxide, 
which  seems  to  protect  it  from  further  change.  It  does  not  appear  to  combine 
with  sulphur  under  any  circumstances,  but  unites  directly  with  chlorine  and 
iodine  with  the  aid  of  heat.  Silicon  unites  readily  with  glucinum,  forming  a  hard 
brittle  substance  susceptible  of  a  high  polish ;  this  alloy  -is  always  formed  when 
glucinum  i$  reduced  in  porcelain  vessels.  Glucinum  does  not  decompose  water  at 
a  boiling  heat,  or  even  when  heated  to  whiteness.  Sulphuric  and  hydrochloric 
acid  dissolve  it,  with  evolution  of  hydrogen.  Nitric  acid,  even  when  concentrated, 
does  not  act  upon  it  at  ordinary  temperatures,  and  dissolves  it  but  slowly  at  a 
boiling  heat.  Glucinum  is  not  attacked  by  ammonia,  but  dissolves  readily  in 
caustic  potash. 

The  above-mentioned  properties  differ  considerably  from  those  of  the  metal 
which  Wohler  obtained  by  igniting  chloride  of  glucinum  with  potassium  in  a  pla- 
tinum crucible ;  the  metal  thus  obtained  being  a  grey  powder,  very  refractory  in 
the  fire,  but  combining  with  oxygen,  sulphur,  and  chlorine  much  more  energeti- 
cally than  Debray' s  metal.  The  differences  appear  to  be  due,  partly  to  the  differ- 
ent states  of  aggregation,  and  partly  to  the  contamination  of  Wohler's  metal  with 
platinum  and  potassium. 

Glucina.  —  Debray  prepares  this  earth  from  the  emerald  of  Limoges  by  the  fol- 
lowing process.  The  mineral,  finely  pounded  (levigation  with  water  is  quite 
superfluous),  is  fused  with  half  its  weight  of  quicklime  in  an  air-furnace,  and  the 
glass  thus  obtained  is  treated,  first  with  dilute,  and  then  with  strong  nitric  acid, 
till  it  is  reduced  to  a  homogeneous  jelly.  The  product  is  then  evaporated  to  dry- 
ness,  and  heated  sufficiently  to  decompose  the  nitrates  of  alumina,  glucina,  and 
iron,  and  a  small  portion  of  the  nitrate  of  lime ;  and  the  residue,  consisting  of 
silica,  alumina,  glucina,  sesquioxide  of  iron,  nitrate  of  lime,  and  a  small  quantity 
of  free  lime,  is  boiled  with  water  containing  sal-ammoniac,  which  dissolves  the 
nitrate  of  lime  immediately,  and  the  free  lime  after  a  while,  with  evolution  of 
ammonia.  (If  no  ammonia  is  evolved,  the  calcination  has  not  been  carried  far 
enough  and  must  be  repeated.)  The  liquid  is  then  decanted;  the  precipitate, 
after  thorough  washing,  treated  with  boiling  nitric  acid ;  and  the  resulting  solu- 
tion of  alumina,  glucina,  and  iron  poured  into  a  solution  of  carbonate  of  ammonia 
mixed  with  free  ammonia.  The  earths  are  thereby  precipitated  without  evolution 
of  carbonic  acid,  and  the  glucina  redissolves,  after  seven  or  eight  days,  in  the 
excess  of  carbonate  of  ammonia.  As  the  carbonate  of  ammonia  may  also  dissolve 
a  small  quantity  of  iron,  it  should  be  mixed  with  a  little  sulphide  of  ammonium 
to  precipitate  the  iron  completely.  Lastly,  the  carbonate  of  ammonia  is  distilled 
off,  and  the  carbonate  of  glucina  which  remains  yields  pure  glucina  by  calcination. 

*  Ann.  Ch.  Phys.  [3] ,  xliv.  5. 


822  GLUCINUM. 

Glucina  is  not  hardened  by  heat  like  alumina,  but  merely  rendered  less  soluble 
in  acids.  Ebelmen  has  obtained  it  in  hexagonal  prisms  by  exposing  a  solution  of 
glucina  in  fused  boracic  acid  to  a  powerful  and  long-continued  heat.  It  may  be 
more  easily  obtained  in  microscopic  crystals,  apparently  of  the  same  form,  by 
decomposing  the  sulphate  at  a  high  temperature  in  presence  of  sulphate  of  potash, 
also  by  calcining  the  double  carbonate  of  glucina  and  ammonia. 

Hydrate  of  glucina  dissolves  in  potash  like  alumina,  but  is  reprecipitated  by 
boiling  when  the  solution  is  diluted  with  water  to  a  certain  extent.  It  is  likewise 
soluble  in  carbonate  of  potash  or  soda,  sulphurous  acid,  and  bisulphite  of  ammonia. 
When  precipitated  by  ammonia,  especially  from  the  oxalate  or  acetate,  it  is  com- 
pletely redissolved  by  prolonged  ebullition. 

Glucina  was  regarded  by  Berzelius  as  a  sesquioxide,  G1203,  while  Awdejew  and 
others  regard  it  as  a  protoxide,  G1O.  The  latter  formula  appears  preferable,  first 
because  it  gives  more  simple  formulae  for  the  salts  of  glucina  than  the  former,  and 
secondly,  because  glucina,  on  the  whole,  exhibits  a  closer  resemblance  to  known 
protoxides,  such  as  magnesia,  than  to  sesquioxides,  such  as  alumina.  The  greater 
simplicity  of  the  formulae  derived  from  the  formula  G10,  will  be  seen  from  the 
following  table : 


AT         i      i  ^  *     f   i     •  f         G10.SO- 

Neutral  sulphate  of  glucina.... |  Qr  Qj^Kj        12HO. 

Sulphate  of  glucina  and  potash {  or  g^Jgj^-  <»0. 

Carbonate  of  glucina  and  an^nia { 

f    i     •                      -u  /          KO.C2034-G102Co03 

Oxalate  of  glucina  and  potash j 


The  reasons  which  induced  Berzelius  to  regard  glucina  as  a  sesquioxide,  were 
founded  on  the  resemblance  of  glucina  and  alumina  in  the  hydrated  state,  from 
the  volatility  of  the  chlorides,  and  from  the  supposed  capability  of  glucina  and 
alumina  to  replace  one  another  in  minerals,  as  in  cymophane  and  in  emerald. 
This  last  point  has  been  completely  settled  by  the  researches  of  Awdejew  and  of 
Damour,  from  which  it  appears  that  cymophane,  the  native  aluminate  of  glucina, 
has  always  the  same  composition  (G10.A1203),  from  whatever  locality  it  may  be 
derived.  With  regard  to  the  hydrates,  it  is  true  that  alumina  and  glucina  are 
precipitated  under  the  same  circumstances;  but  there  the  resemblance  ends. 
Glucina,  when  dried  in  the  air,  absorbs  carbonic  acid  and  forms  a  carbonate,  which 
alumina  does  not.  The  existence  of  a  definitely  crystallized  carbonate  of  ammonia 
and  glucina  (obtained  by  boiling  a  solution  of  glucina  in  carbonate  of  ammonia, 
stopping  the  ebullition  as  soon  as  turbidity  appears,  then  filtering,  and  adding 
alcohol)  constitutes  another  important  difference  between  that  earth  and  alumina. 
The  anhydrous  oxides  likewise  differ  essentially.  Glucina  volatilizes,  like  mag- 
nesia, without  melting,  whereas  alumina  fuses  under  the  same  circumstances. 
Glucina  cannot  be  fused  with  lime,  like  alumina,  the  presence  of  another  body, 
such  as  silica  or  alumina,  being  required  to  enable  the  fusion  to  take  place.  In 
this  respect  again  glucina  resembles  magnesia.  The  identity  of  crystalline  form 
which  has  been  observed  between  glucina  and  alumina  is  merely  an  isolated  fact, 
which  would  be  important  if  the  two  bodies  possessed  similar  chemical  properties, 
but  not  otherwise. 

Chloride  of  glucinum  exhibits  at  first  sight  considerable  resemblance  to  chloride 
of  aluminium,  and  is  prepared  in  a  similar  manner;  but  the  resemblance  does  not 
go  far.  Chloride  of  glucinum  is  less  volatile  than  chloride  of  aluminium  :  thus, 
when  a  mixture  of  finely  powdered  emerald  and  charcoal,  made  into  a  paste  with 
oil,  is  calcined  in  a  crucible,  then  powdered,  and  heated  in  a  porcelain  tube 
through  which  chlorine  gas  is  passed,  chloride  of  glucinum  and  chloride  of 
aluminium  are  formed  together;  but  the  chloride  of  glucinum  passes  over  first, 
and  may  be  separately  condensed.  Chloride  of  glucinum  is,  in  fact,  about  as 


GLUCINA.  823 

volatile  as  chloride  of  zinc.  Chloride  of  aluminium  unites  with  the  alkaline  chlo- 
rides, forming  compounds  which  may  be  called  spmelles,  and  are  represented  by 
the  general  formula  MCI  +  A12C13;  but  chloride  of  glucinum  does  not  form  any 
similar  compound. 

It  must,  however,  be  remembered  that  glucina  does  not  exhibit  any  very  close 
analogy  to  the  class  of  protoxides.  It  is  not  isomorphous  with  lime  or  magnesia. 
Cymophane  may  be  represented  by  the  general  formula  of  the  spinelles,  G10.  A1203 ; 
but  the  dissimilarity  of  its  crystalline  form  prevents  it  from  being  included  in  that 
class  of  minerals.  The  emerald  also  differs  completely  in  crystalline  form  from 
the  generality  of  silicates  of  the  same  composition,  whose  general  formula  is 
MO.Si03  +  M2'03.3Si03.  Neither  is  there  any  greater  analogy  between  the  double 
sulphates,  carbonates,  and  oxalates  of  glucina  and  those  of  lime  or  magnesia.  On 
the  whole,  glucina  appears  to  be  intermediate  in  its  properties  between  the  prot- 
oxides and  sesquioxides. 

Grlucina  is  precipitated  from  its  solutions  for  quantitative  analysis  in  the  same 
manner  as  alumina.  From  the  latter  it  is  separated  by  carbonate  of  ammonia. 


824 


MEASURES    AND    WEIGHTS. 


TABLE   A. 

FOR   CONVERTING   FRENCH    DECIMAL    MEASURES   AND   WEIGHTS   INTO   ENGLISH    MEASURES   AND 

WEIGHTS. 

1  Meter  =    1-0936331  English  yards. 

==     3-2808992       «        feet. 
=  39-37079  "        inches. 

1  Liter  =  0-2209687  Imperial  gallons. 

=  1-7677496        »        pints. 

=  0-35317      cubic  feet. 

=  61-02710          "    inches. 

1  Kilogramme  —    0-0196969  cwt. 

=    2-20606      Ib.  (avoird.) 
=     2-68098      Ib.  (troy.) 

1  Gramme        =     15-44242    grains. 

These  values  are  taken  from  the  "  Table  of  Constants  "  at  the  end  of  the  Tables  of  Logarithms  published  by 
the  Society  for  the  Diffusion  of  Useful  Knowledge. 
The  Imperial  Gallon  is  equal  to  277-24  cubic  inches,  and  contains  10  Ibs.  avoirdupois  of  water  at  60°  Fah. 


TABLE   B. 

BAROMETER   SCALE   IN   MILLIMETERS   AND   INCHES. 


Mm.     In. 

Mm.     In. 

Mm.     In. 

700  =  27-560 

730  =  28-741 

760  =  29-922 

701  =  27-599 

731  =  28-780 

„  761  =  29-962 

702  =  27-639 

732  =  28-820 

762  =  30-001 

703  =  27-678 

733  =  28-859 

763  =  30-040 

704  =  27-717 

734  =  28-899 

764  =  30-080 

705  =  27-756 

735  =  28-938 

765  =  30-119 

706  =  27-795 

736  =  28-977 

766  =  30-159 

707  =  27-835 

737  =  29-017 

767  =  30-198 

708  —  27-875 

738  =  29-056 

768  =  30-237 

709  =  27-914 

739  =  29-096 

769  =  30-277 

710  =  27-954 

740  =  29-135 

770  =  30-316 

711  -=  27-993 

741  =29-174 

771  =  30-355 

712  =  28-032 

742  =  29-214 

772  =  30-395 

713  =  28-072 

743  =  29-253 

773  =  30-434 

714  =  28-111 

744  =  29-292 

774  =  30-474 

715  =  28-151 

745  =  29-332 

775  =  30-513 

716  =  28-190 

746  =  29-371 

776  =  30-552 

717  =  28-229 

747  =  29-411 

777  =  30-592 

718  =  28-269 

748  ==  29-450 

778  =  30-631 

719  =  28-308 

749  =  29-489 

779  =  30-671 

720  =  28-347 

750  =  29-529 

780  =  30-710 

721  =  28-387 

751  =  29-568 

781  =  30-749 

722  =  28-426 

752  =  29-607 

782  =  30-788 

723  =  28-466 

753  =  29-647 

783  =  30-828 

724  =  28-505 

4  754  =  29-686 

784  =  30-867 

725  =  28-544 

755  =  29-725 

785  =  30-907 

726  =  28-584 

756  =  29-765 

786  =  30-946 

727  =  28-623 

767  =  29-804 

787  =  30-985 

728  =  28-662 

758  =  29-844 

788  =  31-025 

729  =  28-702 

759  =  29-882 

789  =  31-064 

28  inches  =  711-187  millimeters. 

29  "      =736-587 

30  "      =761-986  " 

31  "      =  787-386 

1  millimeter  =  0-03937079  inch.          |          1  inch  =  25-39954  millimeters. 


CENTIGRADE    THERMOMETER. 


825 


TABLE   C. 

FOR   CONVERTING    DEGREES    OF    THE    CENTIGRADE    THERMOMETER   INTO    DEGREES    OF    FAHREN- 
HEIT'S   SCALE. 


Cent. 

Fah. 

Cent. 

Fah. 

Cent. 

Fah. 

—  100° 

..  —  148-0° 

—  44°  ... 

—  47-2° 

-f  12°  ... 

-f  53-6° 

99 

146-2 

43  ... 

45-4 

13   ... 

55-4 

98 

144-4 

42  ... 

43-6 

14  ... 

57-2 

97 

142-6 

41  ... 

41-8 

15  ... 

59-0 

96 

140-8 

40  ... 

40-0 

16  ... 

60-8 

95 

139-0 

39  ... 

38-2 

17  .. 

62-6 

94 

137-2 

38  ... 

36-4 

18  ... 

64-4 

93 

135-4 

37  ... 

34-6 

19  ... 

66-2 

92 

133-6 

36  ... 

32-8 

20  ... 

68-0 

91 

131-8 

35  ... 

31-0 

21  ... 

69.8 

90 

130-0 

34  ... 

29-2 

22  ... 

71-6 

89 

128-2 

33  ... 

27-4 

23  ... 

73-4 

88 

126-4 

32  ... 

25-6 

24  ... 

75-2 

87 

124-6 

31  ... 

23-8 

25  ... 

77-0 

86 

122-8 

30  ... 

22-0 

26  ... 

78-8 

85 

121-0 

29  ... 

20-2 

27  ... 

80-6 

84 

119-2 

28  ... 

18-4 

28  ... 

82-4 

83 

117-4 

27  ... 

16-6 

29  ... 

84-2 

82 

1156 

26  ... 

14-8 

30  ... 

86-0 

81 

113-8 

25  ... 

130 

31  ... 

87-8 

80 

112-0 

24  ... 

11-2 

32  ... 

89-6 

79 

110-2 

23  ... 

9-4 

33  ... 

91-4 

78 

108-4 

22  ... 

7-6 

34  ... 

932 

77 

106-6 

21  ... 

5-8 

35  ... 

95-0 

76 

104-8 

20  ... 

4-0 

36  ... 

96-8 

75 

103-0 

19  ... 

2-2 

37  ... 

98-6 

74 

101-2 

18  ... 

0-4 

38  ... 

100-4 

73 

99-4 

17  ... 

+  1-4 

39  ... 

102.1 

72 

97-6 

16  ... 

3-2 

40  ... 

104-0 

71 

95-8 

15  ... 

6-0 

41  ... 

105-8 

70 

94-0 

14  ... 

6-8 

42  ... 

107-6 

09 

92-2 

13  ... 

8-6 

43  ... 

109-4 

68 

90-4 

12  ... 

10-4 

44  ... 

111-2 

67 

88-6 

11  ... 

12:2 

45  ... 

113-0 

66 

86-8 

10  ... 

14-0 

46  ... 

1148 

65 

85-0 

9  ... 

15-8 

47  ... 

116-6 

64 

83-2 

8  ... 

17-6 

48  ... 

118-4 

63 

81-4 

7  ... 

19-4 

49  ... 

120.2 

62 

79-6 

6  ... 

21-2 

50  ... 

122-0 

61 

77-8 

5  ... 

23-0 

51  ... 

123-8 

60 

76-0 

4  ... 

24-8 

52  ... 

125-6 

59 

74-2 

3  ... 

26-6 

53  ... 

127-4 

58 

72-4 

2  ... 

28-4 

54  ... 

1292 

57 

70-6 

1  ... 

30-2 

55  ... 

131-0 

56 

68-8 

0  ... 

32-0 

56  ... 

132-8 

55 

67-0 

4-  i  ... 

33-8 

57  ... 

134-6 

54 

65-2 

2  ... 

35-6 

68  ... 

136-4 

63 

63-4 

3  ... 

37-4 

59  ... 

138-2 

52 

61-6 

4  ... 

39-2 

60  ... 

140-0 

61 

59-8 

5  ... 

41-0 

61  ... 

141-8 

60 

58-0 

6  ... 

42-8 

62  ... 

143-6 

49 

56-2 

7 

44-6 

63  ... 

145.4 

48 

64-4 

8  ... 

46-4 

64  ... 

147-2 

47 

52-6 

9  ... 

48-2 

65  ... 

149-0 

46 

50-8 

10  ... 

50-0 

66  ... 

150-8    | 

45 

49-0 

11  ... 

61-8         67  ... 

152-6 

826 


CENTIGRADE    THERMOMETER. 
TABLE    C.  —  (continued.} 


Cent 

Fab. 

Cent. 

Fah. 

Cent. 

Fah. 

+  68°  ... 

+  154-4° 

+  130°  ... 

+  266-0° 

+  192°  ... 

+  377-6° 

69  ... 

156-2 

131  ... 

267-8 

193  ... 

379-4 

70  ... 

158-0 

132  ... 

269-6 

194  ... 

381-2 

71  ... 

159-8 

133  ... 

271-4 

195  ... 

383-0 

72  ... 

161-6 

134  ... 

273-2 

196  ... 

384-8 

73  ... 

163-4 

135  ... 

275-0 

197  ... 

386-6 

74  ... 

165-2 

136  ... 

276-8 

198  ... 

388-4 

75  ... 

167-0 

137  ... 

278-6 

199  ... 

390-2 

76  ... 

168-8 

138  ... 

280.4 

200  ... 

392-0 

77  ... 

170-6 

139  ... 

282-2 

201  ... 

393-8 

78  ... 

172-4 

140  ... 

284-0 

202  ... 

395-6 

79  ... 

174-2 

141  ... 

285-8 

203  ... 

397-4 

80  ... 

176-0 

142  ... 

287-6 

204  ... 

399-2 

81  ... 

177-8 

143  ... 

289-4 

205  ... 

401-0 

82  ... 

179  6 

144  ... 

291-2 

206  ... 

402-8 

83  ... 

181-4 

145  ... 

293-0 

207  ... 

404-6 

84  ... 

183-2 

146  ... 

294-8 

208  ... 

406-4 

85  ... 

185-0 

147  ... 

296-6 

209  ... 

408-2 

86  ... 

186-8 

148  ... 

298-4 

210  ... 

410-0 

87  ... 

188-6 

149  ... 

300-2 

211  ... 

411-8 

88  ... 

190-4 

150  ... 

302-0 

212  ... 

413-6 

89  ... 

192-2 

151  ... 

303-8 

213  ... 

415-4 

90  ... 

194-0 

152  ... 

305-6 

214  ... 

417-2 

91  ... 

195-8 

153  ... 

307-4 

215  ... 

419-0 

92  ... 

197-6 

154  ... 

309-2 

216  ... 

420-8 

93  ... 

199-4 

155  ... 

311-0 

217  ... 

422-6 

94  ... 

201-2 

156  ... 

312-8 

218  ... 

424-4 

95  ... 

203-0 

157  ... 

314-6 

219  ... 

426-2 

96  ... 

204-8 

158  ... 

316-4 

220  ... 

428-0 

97  ... 

206-6 

159  ... 

318-2 

221  ... 

429-8 

98  ... 

208-4 

160  ... 

3200 

222  ... 

431-6 

99  ... 

210-2 

161  ... 

321-8 

223  ... 

4334 

100  ... 

212-0 

162  ... 

323-6 

224 

435-2 

101  ... 

213-8 

163  ... 

325-4 

225  '.'.'. 

437-0 

102  ... 

215-6 

164  ... 

327-2 

226  ... 

438-8 

103  ... 

217-4 

165  ... 

329-0 

227  ... 

440-6 

104  ... 

219-2 

166  ... 

330-8 

228  ... 

442-4 

105  ... 

221-0 

167  ... 

332-6 

229  ... 

444-2 

106  ... 

222-8 

168  ... 

334-4 

230  ... 

446-0 

107  ... 

224-6 

169  ... 

336-2 

231  ... 

447-8 

108  ... 

226-4 

170  ... 

338-0 

232  ... 

449-6 

109  ... 

228-2 

171  ... 

339-8 

233  ... 

451-4 

110  ... 

230-0 

172  ... 

341-6 

234  ... 

•  453-2 

an  ... 

231-8 

173  ... 

343-4 

235  ... 

455-0 

112  ... 

233-6 

174  ... 

345-2 

236  ... 

456-8 

113  ... 

235-4 

175  ... 

347-0 

237  ... 

458-6 

114  ... 

237-2 

176  ... 

348-8 

238  ... 

460-4 

115  ... 

239-0 

177  ... 

350-6 

239  ... 

462-2 

116  ... 

240-8 

178  ... 

352-4 

240  ... 

464-0 

117  ... 

242-6 

179  ... 

354-2 

241  ... 

465-8 

118  ... 

244-4 

180  ... 

356-0 

242 

467-6 

119  ... 

246-2 

181  ... 

357-8 

243  ... 

4694 

120  ... 

248-0 

182  ... 

359-6 

244  ... 

471-2 

121  ... 

249-8 

183  ... 

361-4 

245  ... 

473-0 

122  ... 

251-6 

184  ... 

363-2 

246  ... 

474-8 

123  ... 

253-4 

185  ... 

365-0 

247  ... 

476-6 

124  ... 

255-2 

186  ... 

366-8 

248  ... 

478-4 

125  ... 

257-0 

187  ... 

368-6 

249  ... 

480-2 

126  ... 

258-8 

188  ... 

370-4 

250  ... 

482-0 

127  ... 

260-6 

189  ... 

372-2 

251  ... 

483-8 

128  ... 

262-4 

190  ... 

374-0 

252  ... 

485-6 

129  ... 

264-2 

191  ... 

375-8 

253  ... 

487-4 

BAUME  S    HYDROMETER, 
TABLE    G.— (continued.) 


827 


Cent. 

fth. 

Cent. 

Fah. 

Cent. 

Fah. 

+  254°  ... 

+  489-2° 

+  286«  ... 

•f  546-8° 

+  318°  ... 

+  604  4° 

255  ... 

491-0 

287  ... 

548-6 

319  ... 

606-2 

256  ... 

492-8 

288  ... 

550-4 

320  ... 

608-0 

257  ... 

494-6 

289  ... 

552-2 

321  ... 

609-8 

258  ... 

496-4 

290  ... 

554-0 

322  ... 

611-6 

259  ... 

498  2 

291  ... 

555-8 

323  ... 

613-4 

260  ... 

500-0 

292 

557-6 

324  ... 

615-2 

261  ... 

501-8 

293  ... 

559-4 

325  ... 

617-0 

262  ... 

503-6 

294  ... 

561-2 

326  ... 

618-8 

263  ... 

505-4 

295  ... 

563-0 

327  ... 

620-6 

264  ... 

507-2 

296  ... 

564-8 

328  ... 

622-4 

265  ... 

509-0 

297  ... 

566-6 

329  ... 

624-2 

266  ... 

510-8 

298  ... 

568-4 

330  ... 

626-0 

267  ... 

5126 

299  ... 

570-2 

331  ... 

627-8 

268  ... 

514-4 

300  ... 

572-0 

332  ... 

629-6 

269  ... 

516-2 

301  ... 

573-8 

333  ... 

631-4 

270  ... 

518-0 

302  ... 

575-6 

334  ... 

633-2 

271  ... 

519-8 

303  ... 

577-4 

335  ... 

635-0 

272  ... 

521-6 

304  ... 

579-2 

336  ... 

636-8 

273  ... 

523-4 

305  ... 

581-0 

337  ... 

638-6 

274  ... 

525-2 

306  ... 

582-8 

338  ... 

640-4 

275  ... 

527-0 

307  ... 

584-6 

339  ... 

642-2 

276  ... 

528-8 

308  ... 

586-4 

•340  ... 

644-0 

277  ... 

530-6 

309  ... 

588-2 

341  ... 

645-8 

278  ... 

532-4 

310  ... 

590-0 

342  ... 

647-6 

279  ... 

534-2 

311  ... 

691-8 

343  ... 

649-4 

280  ... 

536-0 

312  ... 

593-6 

344  ... 

651-2 

281  ... 

537-8 

313  ... 

595-4 

345  ... 

653-0 

282  ... 

539-6 

314  ... 

597-2 

346  ... 

654-8 

283  ... 

541-4 

315  ... 

599-0 

347  ... 

656-6 

284  ... 

543-2 

316  ... 

600-8 

348  ... 

658-4 

285  ... 

545-0 

317  ... 

602-6 

349  ... 

660-2 

TABLE   D. 

COMPARISON  OF   THE  DEGREES  OF   BAUME*'s  HYDROMETER  WITH  THE  REAL  SPECIFIC  GRAVITIES. 

1.  for  Liquids  heavier  than  Water. 


Degrees. 

Specific  Gravity. 

Degrees. 

Specific  Gravity. 

Degrees. 

Specific  Gravity. 

degrees. 

Specific  Gravity. 

0 

1-000 

20 

1-152 

39 

1  -345 

58 

1-617 

1 

1-007 

21 

•160 

40 

1-357 

59 

1-634 

2 

,    1-013 

22 

•169 

41 

1-369 

60 

1-652 

3 

1-020 

23 

•178 

42 

1-381 

61 

1-670 

4 

1  027 

24 

•188 

43 

1-395 

62 

1-689 

5 

1-034 

25 

•197 

44 

1-407 

63 

1-708 

6 

1-041 

26 

.    -206 

45 

1-420 

64 

1-727 

7 

1-048 

27 

•216 

46 

1-434 

65 

1-747 

8 

1-056 

28 

•225 

47 

1-448 

66 

1-767 

9 

1.063 

29 

1-235 

48 

1-462 

67 

1-788 

10 

1.070 

30 

1-245 

49 

1-476 

68 

1-809 

11 

.1-078 

31 

1-256 

50 

1-490 

69 

1-831 

12 

1-085 

32 

1-267 

51 

1-495 

70 

1-854 

13 

1-094 

33 

1-277 

52 

1-520 

71 

1-877 

14 

1-101 

34 

1-288 

53 

1-535 

72 

1-900 

15 

1-109 

35 

1-299 

54 

1-551 

73 

1-924 

16 

1-118 

36 

1-310 

55 

1-567 

74 

1-949 

17 

1-126 

37 

1-321 

56 

1-583 

75 

1-974 

18 

1-134 

38 

1-333 

57 

1-600 

76 

2-000 

19 

1-143 

828 


WEIGHT    OF    ALCOHOL. 

TABLE    D.  — (continued.) 

2.  Baume's  Hydrometer  for  Liquids  lighter  than    Water. 


Degrees. 

Specific  Gravity. 

Degrees. 

Specific  Gravity. 

Degrees. 

Specific  Gravity. 

Degrees. 

Specific  Gravity. 

10 

1-000 

23 

0-918 

36 

0-849 

49 

0-789 

11 

0-993 

24 

0-913 

37 

0-844 

50 

0-785 

12 

0-980 

25 

0-907 

38 

0-839 

51 

0-781 

13 

0-980 

26 

0-901 

39 

0-834 

52 

0-777 

14 

0-973 

27 

0-896 

40 

0-830 

53 

0-773 

15 

0-967 

28 

0-890 

41 

0-825 

54 

0-768 

16 

0-960 

29 

0-885 

42 

0-820 

55 

0-764 

17 

0-954 

30 

0-880 

43 

0-816 

56 

0-760 

18 

0-948 

31 

0-874 

44 

0-811 

57 

0-757 

19 

0942 

32 

0-869 

45 

0-807 

58 

0-753 

20 

0-936 

33 

0-864 

46 

0-802 

59 

0-749 

21 

0-930 

34 

0-859 

47 

1  0-798 

60 

0-745 

22 

0-924 

35 

0-854 

48 

0-794 

Bauine's  hydrometer  is  very  commonly  used  on  the  Continent,  especially  for  liquids  heavier  than  water. 

In  the  United  Kingdom,  Twaddell's  hydrometer  is  a  good  deal  used  for  dense  liquids.  This  instrument  is  so 
graduated  that  the  real  specific  gravity  can  be  deduced  by  an  extremely  simple  method  from  the  degree  of  the 
hydrometer,  namely,  by  multiplying  the  latter  by  5,  and  adding  1000 ;  the  sum  is  the  specific  gravity,  water 
being  1000.  Thus  10°  Twaddell  indicates  a  specific  gravity  of  1050°,  or  1-05 ;  90°  Twaddell,  1450,  or  1-45. 


TABLE   E. 


SHOWING   THE   PROPORTION    BY   WEIGHT,  OF   ABSOLUTE    OR   REAL   ALCOHOL,  IN  100   PARTS    OF 
SPIRITS    OF   DIFFERENT    SPECIFIC    GRAVITIES.       (FOWNES.) 


Sp.Gr.  at 
60°  F. 

Percentage  of 
real  Alcohol. 

Sp.  Gr.  at 
60°  F. 

Percentage  of 
real  Alcohol. 

Sp.  Gr.  at 

60°  F. 

Percentage  of 
real  Alcohol. 

Sp.  Gr.  at 
60°  F. 

Percentage  of 
real  Alcohol. 

•9991 

0-5 

•9638 

26 

•9160 

51 

•8581 

76 

•9981 

1 

•9623 

27 

•9135 

52 

•8557 

77 

•9965 

2 

•9609 

28 

•9113 

53 

•8533 

78 

•9947 

3 

•9593 

29 

•9090 

54 

•8508 

79 

•9930 

4 

•9578 

30 

•9069 

55 

•8483 

80 

•9914 

5 

•9560 

31 

•9047 

56 

•8459 

81 

•9898 

6 

•9544 

32 

•9025 

57 

•8434 

82 

•9884 

7 

•9528 

33 

•9001 

68 

•8408 

83 

.  -9869 

8 

•9511 

34 

•8979 

59 

•8382 

84 

•9855 

9 

•9490 

35 

•8956 

60 

•8357 

85 

•9841 

10 

•9470 

36 

•8932 

61 

•8331 

86 

•9828 

11 

•9452 

37 

•8908 

62 

•8305 

87 

•9815 

12 

•9434 

38 

•8886 

63 

•8279 

88 

•9802 

13 

•9416 

39 

•8863 

64 

•8254 

89 

•9789 

14 

•9396 

40 

•  -8840 

65 

•8228 

90 

•9778 

15 

•9376 

41 

•8816 

66 

•8199 

91 

•9766 

16 

•9356 

42 

•8793 

67 

•8172 

92 

•9753 

17 

•9335 

43 

•8769 

68. 

•8145 

93 

•9741 

18 

•9314 

44 

•8745 

69 

•8118 

94 

•9728 

19 

•9292 

45 

•8721 

70 

•8089 

95 

•9716 

20 

•9270 

46 

•8696 

71 

•8061 

96 

•9704 

21 

•9249 

47 

•8672 

72 

•8031 

97 

•9691 

22 

•9228 

48 

•8649 

73 

•8001 

98 

•9678 

23 

•9206 

49 

•8625 

74 

.7969 

99 

•9665 

24 

•9184 

50 

•8603 

75 

•7938 

100 

•9652 

25 

INDEX. 


ABSOLUTE  Expansion  of  Mercury,  37. 
Absorption,  Coefficients  of,  764. 

of  Gases  by  Liquids,  763 

Water,  Heat  evolved 

in  the,  756. 
Acetate,  Ferrous,  451. 

Mercurous,  579. 
Acetates  of  Alumina,  820. 
Copper,  482. 
Lead,  492. 
Acid,  Anhydrous  Sulphuric,  157. 

Antimonic,  542. 

Antimonious,  539. 

Antitartaric,  669. 

Arsenic,  532. 

Arseriious,  530. 

Azophosphoric,  789. 

Azoto-sulphuric,  302. 

Bismuthic,  550. 

Bisul-hyposulphuric,  305. 

Boracic,  288,  774. 

Bromic,  351. 

Carbonic,  270. 

Chloric,  116,  340. 

Chlorocarbosulphurous,  793. 

Chloromethylosulphurous,  793. 

Chloronitric,  344. 

Chloronitrous,  345. 

Chlorochromic,  513. 

Chlorosulphuric,  301,  708,  795. 

Chlorous,  343. 

Chromic,  510. 

Cobaltic,  463. 

Columbic,  572. 

Colurnbous,  571. 

Deutazopliosphoric,  780. 

Ferric,  455. 

Fluoboric,  361. 

Fluosilicic,  362. 

Hydriotic,  355. 

Hydrobrornic,  351. 

Hydrochloric,  335. 

Hydroferricyanic,  454. 

Hydroferrocyaiiic,  448. 

Hydrofluoric,  359. 

Hydrofluosilicic,  362. 

Hydrotelluric,  528. 

Hydrosulphuric,  306,  322. 

Hypochloric,  343. 

Hypochlorous,  338. 

Hypoiodic,  796. 


Acid,  Hypophosphorous,  316. 
Ilyposulphuric,  302. 
Hyposulphurous,  107,  303. 
lodic,  356. 
Manganic,  439. 

Mellitic,  Croconic,  Rhodizonic,  276 
Metaphosphoric,  324,  786. 
Metastannic,  498. 
Methylosulphurous,  793. 
Molybdic,  522. 
Monosul-hyposulphuric,  305. 
Nitric,  259. 
Nitroprussic,  457. 
Nitrosulphuric,  301. 
Nitrous,  257. 
Osmiamic,  629. 
Osmic,  628.' 
Osmious,  628. 
Oxalic,  276. 
Oxamic,  811. 
Penta-iodic,  357. 
Pentathionic,  305. 
Perchloric,  107,  341. 
Perchlorocarbosulphurous,  792. 
Perchromic,  513. 
Periodic,  357. 
Permanganic,  439. 
Phosphamic,  789. 
Phosphoric,  318. 
Phosphoric,  Amides  of,  787. 
Phosphorous,  315. 
Pyrophosplmmic,  790. 
Racemic,  (>70. 
Radicals.  Hydrides  of,  718. 
Kuthenic,  Oo5. 
Seleuic,  312. 
Selenioux,  312. 
Silicic,  292,  778. 
Stannic,  497. 
Sulphamic,  81 1. 
Sulphuric,  295. 
Sulphurous,  294. 
Sulphantimonic,  544. 
Tantalic,  567. 
Tantalous,  567. 
Thionamic,  811. 
Telluric,  527. 
Tellurous,  626. 
Tetrathionic,  305. 
Titanic,  502. 
Trisul-hyposulphuric,  305. 

(829) 


830 


INDEX. 


Acid,  Trithionic,  805. 
Tungstic,  517. 
Vanadic,  515. 
Acids,  Action  of   Ammonia   on   Anhydrous, 

713. 

Anhydrous,  704. 
Aromatic,  701. 
Basicity  of,  700. 
Bibasic.  701. 
Conjugated,  703. 
Fatty,  Boiling  Points  of,  729. 
Fatty,  Table  of,  701. 
Heat  evolved  in  the  Combination  of, 

with  Water,  756. 
Monobasic,  701. 
or  Negative  Oxides,  700. 
Oxygen,  156. 
Sulphur,  706. 
Theory  of,  156. 

Tartaric  and  Antitartaric,  669. 
Tribasic,  702. 

with  Bases,  Heat  produced  by  Com- 
bination of,  755. 
Affinity,  Chemical,  176,  730.       \ 
of  Solution,  177; 
Order  of,  180. 
Tables  of,  181. 
Air,  Analysis  of,  249. 

Composition  of  dry  Air  by  Volume,  252. 
Air,  Diffusion  of  Vapours  into,  90. 

Extraction    of  Oxygen  from  Atmosphe- 
ric, 759. 

Researches  on  the  Expansion  of,  40. 
Weight  of,  245. 

Alcohol,  Action  of  Sulphuric  Acid  on,  738. 
Alcoholic  Nitrides,  Secondary  and  Tertiary, 

711. 

Sulphides,  706. 

Alcohol-metals,  derived  from  Type  HH,  718. 
Alcohol-radicals,  690,  697. 

Action  of  Ammonia  on  the 
Bromides  and  Iodides  of, 
710. 

Chlorides  of,  707. 
Cyanides  of,  709. 
Hydrides  of,  716. 
Primary  Nitrides  of,  716. 
Alcohols,  Biatomic,  698. 

Boiling  Points  of,  729. 
Classification  of  Primary,  697. 
Secondary,  or  Ethers,  699. 
Triatomic,  699. 
Aldehyde-radicals,  Hydrides  of,  717. 

Nitrides  of,  712. 
Aldehydes,  699. 
Alkalamides,  716. 
Alkalies,  Estimation  of  in  Silicates,  779. 

Separation  of  Magnesia  from,  755. 
Alkalimetry,  386. 

Gay-Lussac's  Method  of,  388. 
Allotropy,  150. 
Alloys  of  Antimony,  545. 
Bismuth,  552. 
Cadmium,  475. 
Copper,  483. 
Gold,  606. 
Lead,  493. 


Alloys  of  Mercury,  589. 
Nickel,  468. 
Silver,  599. 
Tin,  501. 
Zinc,  473. 
Alum,  422,  820. 
Basic,  423. 
Stone,  422. 
Alumina,  419,  819. 

Acetates  of,  820. 

and  Potash,  Sulphate  of,  108. 

Estimation  and  Separation  of,  820. 

Hydrates  of,  420.  820. 

Nitrate  .of,  420,  424. 

Phosphate  of,  424. 

Salts  of,  421. 

Silicates  of,  424. 

Silicates  of  Lime  and  of,  240. 

Sulphate  of,  421. 

and  Potash,  Alum,  422. 
Aluminium,  419. 

Chloride  of,  421. 
Fluoride  of,  421. 
Preparation  of,  419. 
Properties  of,  419. 
Sulphide  of,  421. 
Sulphocyanide  of,  421. 
Amalgam  of  Gold,  606. 
Amalgamation  of  Silver,  592. 

of  the  Zinc  Plate  of  the  Vol- 
taic Battery,  194. 
Amalgams,  589. 

Amides  of  Phosphoric  Acid,  787. 
Primary,  712. 
Secondary,  714. 
Tertiary,  715. 

Amido-chloride,  Mercuric,  583. 
Amidogen-Acids,  708. 
Salts,  715. 
and  Amides,  167. 
Ammon-compounds,  811. 
Ammonia,  Action  of,  on  Anhydrous  Acids,713. 
Acid  Chlorides,  713. 
Compound  Ethers,  713. 
Bichloride   of  Mercury, 

578. 

the  Bromides  and  Iodides 
of  the  Alcohol-radi- 
cals, 710. 

and  Glucina,  Carbonate  of,  822. 
Antimoniates  of,  544. 
Aurate  of,  603. 
Chromates  of,  511. 
Estimation  of,  619,  811. 
Molybdate  of,  523. 
Nessler's  Test  for,  586. 
Phosphate  of,  396. 
Preparation  of,  264. 
Properties  of,  265. 
Salts  of,  166. 
Why  is  it  a  Base  ?  1 69. 
Ammoniacal  Amalgam,  167. 

Compounds  of  Iridium,  625. 
Compounds  of  Palladium,  621. 
Platinum  Salts,  (J 12— 618. 
Salts,  Decomposition  of,  168. 
Salts  of  Cobalt,  463. 


INDEX. 


831 


Ammonia-salts,  Anhydrous,  811. 
Ammonia  type,  693 — 710. 
Ammonio-Bichlovide  of  Tin,  499. 

Compounds  of  Nickel,  468. 
Nitrate  of  Silver,  534—598. 
t  Nitrates,  Mercuric,  588. 

Platinic  Compounds,  615. 
Platinous  Compounds,  613. 
Sulphate  of  Copper,  534. 
Ammonium  and  Bismuth,  Terchloride  of,  551. 
Chloride  of,  809. 
Carbonates  of,  809. 
Chloroplatinate  of,  612. 
Nitrate  of,  809. 
Oxalates  of,  810. 
Phosphates  of,  810. 
Sulphate  of,  810. 
Sulphides  of,  809. 

Ammo-platammonium,  Bisalts  of,  616—618. 
Pro  to- salts     of,    614, 

615. 

Amphigen,  or  Leucite,  426. 
Amylic  Alcohol,  active  and  inactive,  670. 
Analcime,  426. 

Analysis  of  Organic  Bodies,  277 — 771. 
Sea-water,  242. 
Silicates,  779. 
Volumetric,     Bunsen's    general 

Method  of,  801. 

Anhydrides,  or  Anhydrous  Acids,  704. 
Anhydrous  Acids,  Action  of  Ammonia  on,  713. 
Nitric  Acid,  766.  , 

Sulphuric    Acid,    Formation    of, 

296—750. 

Sulphuric  Acid,  Action  of,  on  the 
Pentachloride  of  Phosphorus, 
709—794. 

Telluric  Acid,  527. 
Tellurous  Acid,  526. 
Animal  Charcoal,  269. 
Anthracite,  267. 

Antidotes  to  Arsenious  Acid,  536. 
Antimoniate  of  Antimony,  544. 
Antimoniates  of  Lead,  544. 

Ammonia,  544. 
Potash,  542. 
Antimonic  Acid,  542. 
Oxide,  539. 
Acid,  Action  of,  on  Pentachloride 

of  Phosphorus,  795. 
Antimonides,  716. 
Antimonious  Acid,  539. 
Antimoniuretted  Hydrogen,  544. 
Antimony,  Sources  and  Extraction  of,  589. 
Alloys  of,  545. 

and  Arsenic,  Separation  of,  547. 
Potash,  Oxalate  of,  541. 
Tartrate  of,  541. 
Tin,  Separation  of,  547. 
Oxide  of,  539. 
Pentachloride  of,  544. 
Pentasulphide  of,  544. 
Estimation  and  Separation  of,  545. 
Separation  of,  from  Arsenic  and 

Tin,  546. 
Sulphate  of,  541. 
Terchloride  of,  541. 


Antimony,  Tcrflnoride  of,  541. 

Tersulphide  of,  540. 
Antitartaric  Acid,  669. 
Antithetic,  or  Polar  Formulae,  168. 
Aqueous  Vapour.  Tension  of,  316. 
Argentiferous  Copper,  Liquation  of,  592. 
Aridium,  459. 
Arseniate  of  Cobalt,  462. 

Didymium,  566. 
Uranyl,  557. 
Arsenic  and  Antimony,  Separation  of,  547. 

Hydrogen,  533. 
Acid,  532. 

considered  Tribasic,  170. 
Chlorides  of,  533. 
Estimation  and  Separation  of,  537. 
Reduction,  Test  for,  535. 
Persulphide  of,  533. 
Separation    of,   from  .Antimony  and 

Tin,  546. 

Sources  and  Extraction  of,  530. 
Sulphides  of,  533. 
Testing  for,  534. 
Arsenides,  716. 
Arsenious  Acid,  530. 

Antidotes  of,  536. 
Ash,  Analysis  of  Black,  394. 
Aspartic  Acid,  active  and  inactive,  670. 
Assay  of  Gold,  608. 

Silver,  600. 
Atmosphere,  245,  246. 

Density  of  the,  245. 
Temperature  of  the,  246. 
Atomic  Motion,  738. 

Representation    of  a  double  Decom- 
position, 189. 
Theory,  119. 

Volume,    dependent    upon     rational 
Formula,  727.   ^ 
of  Liquids,  720. 

Solids,  171—728. 
and  Specific  Gravity  of  Elements, 

172. 
of  Salts,  173. 

Oxides,  175. 
Weights,  Gerhardt's,  687. 

Relations  between  the,  and 
Volumes  of  Bodies  in  the 
Gaseous  State,  125. 
Atoms  and  Equivalents,  685. 
Specific  Heat  of,  120. 
Table  of  Specific  Heat  of,  121. 
Aurate  of  Potash,  603. 
Auric  Bromide,  605. 
Chloride,  605. 
Iodide,  605. 
Oxide,  602. 

and    Soda,     Hyposulphite    of, 

606. 

Sulphide,  605. 

Aurosulphite  of  Potash,  603. 
Aurous  Chloride,  602. 
Oxide,  602. 

and   Soda,    Hyposulphite   of. 
606. 

Baryta,  60G. 
Sulphide,  602. 


832 


INDEX. 


Azophosphoric  Acid,  789. 
Azoto-sulphuric  Acid,  302. 

BARILLA,  395. 
Barium,  403—812. 

Binoxide  of,  404—812. 
Chloride  of,  405. 
Class  of  Elements,  145. 
Decomposition    of  Peroxide    of,   by 
.     Aqueous  Vapour,  759. 
Estimation  and  Separation  of,  813. 
Formation  of  Peroxide  of,  759. 
Protoxide  of,  403. 
Baryta  and  Aurous  Oxide,  Hyposulphite  of, 

606. 

Carbonate  of,  405—813. 
Chromate  of,  512. 
Estimation  of,  813. 
Hydrate  of,  404. 
Molybdate  of,  524. 
Nitrate  of,  405. 
Sulphate  of,  405. 

Bases  and  Acids,  Heat  developed  by  Combi- 
nation of,  755. 
Nitrile,  711. 

Proper  or  "Metallic  Oxides,  697. 
Basic  Alum,  423. 
Basicity  of  Acids,  700. 
Basyl  Class  of  Compound  Radicals,  155. 
Battery,  Bird's,  220. 

Bunsen's,  220. 
Daniell's,  218. 
Grove's,  209,  218. 
Beilstein's  Experiments  on  Liquid  Diffusion, 

745. 

Benzoate,  Ferric,  456. 
Beryl,  or  Emerald,  428. 
Beryllia,  or  Glucifl*,  428. 
Beryllium,  428. 
Biamides,  Primary,  or  Diamides,  713. 

Tertiary,  715. 

Bi-ammonio-platinic  Compounds,  616,  618. 
Bi-ammonio-platinous  Compounds,  614,  615. 
Bibasic  Phosphate  of  Water,  320. 

Salts,  161. 

Biborate  of  Soda,  397. 
Bicarbonate  of  Potash,  378. 

and  Magnesia,  416. 
Soda,  389. 
Bicarburetted  Hydrogen,  of  Faraday,  286. 

Preparation  of,  286. 
Bichloride  of  Bismuth,  550. 
Iridium,  625, 
Lead,  489. 
Osmium,  627. 
Platinum,  611. 

Tin  with  Oxychloride  of  Phos- 
phorus, 500. 

Tin  with  Pentachloride  of  Phos- 
phorus, 499. 
Titanium,  503. 
Tin,  499. 

Tin  and  Potassium,  500. 
Tin  and  Sulphur,  499. 
Bichromate  of  Bismuth,  552. 

Chloride  of  Potassium,  511. 
Potash,  511. 


Bifluoride  of  Titanium,  503. 
Bihydrusulphate  of  Potash,  374. 
Bimercurammonium,  Chloride  of,  584. 

Nitrate  of,  589. 

Binoxide  or  Bioxide  of  Barium,  404. 
Hydrogen,  242. 

Manganese  and  Hydrochloric 
Acid,  Preparation  of  Chlorine 
from,  330. 

Nitrogen,  Compound  of,  with 
Chlorine,  340. 

Properties  of,  256. 
Preparation  of,  255. 
Strontium,  406. 
Cobalt,  463. 
Bismuth,  549. 
Iridium,  624. 
Lead,  487. 
Manganese,  437. 
Platinum,  611. 
Ruthenium,  634. 
Tin,  497. 
Vanadium,  515. 

Bird's  Battery  and  Decomposing  Cell,  220. 
Bi-salts      of      Ammo-platammonium,      616. 

617. 

Platammonium,  615,  616. 
Bismuth    and    Ammonium,    Terchloride    of, 

551. 

Bichloride  of,  550. 
Bichromate  of,  552. 
Bioxide  of,  549. 
Bisulphide  of,  550. 
Carbonate  of,  551. 
Nitrates  of,  551. 
Quadroxide  of,  550. 
Selenide  of,  550. 
Sources  and  extraction  of,  553. 
Subnitrates  of,  552. 
Sulphates  of,  551. 
Terchloride  of,  551. 
Teriodide  of,  551. 
Teroxide  of,  549. 
Tersulphide  of,  550. 
Bismuthic  Acid,  550. 
Bisul-hyposulphuric  Acid,  305. 
Bisulphate  of  Soda,  395. 
Bisulphide  of  Bismuth,  550. 
Carbon,  309. 

Action  of  Chlorine  on, 

792. 

Action  of  Nascent  Hy- 
drogen on,  783. 
decomposed   by  heat- 
ing with  Water  and 
with  Salts  in  sealed 
tubes,  783. 
Hydrogen,  3U8. 
Iron,  453. 
Platinum,  611. 
Titanium,  503. 
Tin,  499. 
Bittern,  383. 
Black  Sulphur,  780. 
Black's  Views  on  Fluidity,  60. 
Bleaching  Powder,  413. 
Bodies,  Compound,  106. 


INDEX. 


833 


Codies,  Relation  between  the  Atomic  Weights 
and  the  Volumes  of,  in  the  Gas- 
seous  State,  125. 
Boilers,  Construction  of.  72. 
Boiling  Point  and  Chemical  Composition,  Re- 
lations between,  728. 
Points  of  Acids,  728. 

Alcohols,  728. 
Compound  Ethers,  728. 
Homologous     Compounds, 

730. 

Table  of,  66. 
Boracic  Acid,  Estimation  of,  775. 

Reactions  of,  774. 
Boracite,  418. 
Borate  of  Magnesia,  418. 
Borates,  289. 
Borax,  397. 

Borofluoride  of  Potassium,  776. 
Boron,  Chloride  of,  347. 

Allotropic  modifications  of,  773. 
Estimation  of,  775. 
Fluoride  of,  361. 
Nitride  of,  775. 

its  Preparation,  Properties,  288. 
Boutigny,  Experiments  on  the  Ebullition  of 

Water,  64. 

Brewster  on  Light,  246. 
Brix,  Experiments  of  Vaporization  on,  69. 
on  the    Latent    Heat   of    Vapour    of 

Water,  68. 
Bromic  Acid,  675. 
Bromide,  Auric,  605. 

Mercuric,  585. 

Mercurous,  or  Dibromide  of  Mer- 
cury, 578. 

of  Alcohol-radicals,  Action  of  Am- 
monium, 710. 
Cadmium,  475. 
Iodine,  358. 
Lead,  489. 
Nitrogen,  795 
Phosphorus,  351, 
Silver,  795. 
Silicon  352. 

and  Hydrogen,  777. 
Sulphur,  351. 
Tantalum,  569. 
Titanium,  503. 
Bromides,  709. 

Atomic  Volume  of  Liquid,  725. 
Bromine,  Chloride  of,  351. 

Preparation  of,  350. 

Properties  of,  350. 

Separation  of  from  Chlorine,  799. 

Iodine,  799. 

Volumetric  Estimation  of,  802. 
Bude  Light,  Gurney's,  287. 
Bunsen,  Carbo-zinc  Battery,  220. 
Eudiometers,  282. 
Experiments  on  the  Absorption  of 

Gases,  763. 
Experiments   on    the   influence    of 

Mass  on  Chemical  Action,  731. 
General  Method  of  Volumetric  Ana- 
lysis, 801. 

53 


Bunsen,  and   Roscoe,    Measurement   of  the 

chemical  Action  of  Light,  675. 
Burette,  Description  of,  388. 
Bussy,   Table  of  the  Efficiency   of  different 
Charcoals,  269. 

CADMIUM,  Alloys  of,  475. 

Chloride,    Bromide,    Iodide,    and 

Sulphate  of,  475. 

Estimation  and  Separation  of,  475. 
Oxide,  475. 

Sources  and  Extraction  of,  479. 
Sulphide  of,  475. 
Calcium,  407. 

Binoxide,  Protosulphide,  Phosphide, 

Chloride  of,  4p9. 
Estimation  of,  816. 
Fluoride  of,  410. 

Hydrate  of  the  Binoxide  of.  409. 
Preparation  and  Properties  of,  815. 
Separation    of,    from    Barium    and 

Strontium,  817. 
Separation  of,  from  Magnesium  and 

the  Alkali-metals,  816,  818. 
Calomel,  Bichloride  of  Mercury,  or  Mercu- 
rous Chloride,  577. 
Caloric,  33. 
Calorimeters,  752. 

Canary-glass,  Fluoresence  of,  556,  672. 
Capillary  Tubes,  42. 
Carbamide,  713 — 811. 
Carbides,  270. 

Carbon  and  Hydrogen,  Compounds  of,  278. 
Nitrogen,  Cyanogen,  286. 
Sulphur,  309. 

Bisulphide  of,  309,  783,  791. 
Chlorides  of,  345. 
Class  of  Elements,  148. 
from  Wood,  268. 
Estimation   of,  by  Combustion   with 

Oxide  of  Copper,  &c.,  771. 
Hydrogen,      and     Oxygen,     Atomic 
Volume  of  Liquids  containing,  448. 
Perchloride  of,  347. 
Protochloride  of,  346. 
Protosulphide  of,  782. 
Relation  between  Heat  of  Combustion 

and  Specific  Heat  of,  754. 
Solid  Sulphide  of,  311. 
Specific  Heat,  and  Heat  of  Combus- 
tion of  Varieties  of,  123,  754. 
Subchloride  of,  347. 
Sulphides  of,  309,  782,  783. 
Sulphite  of  Perchloride  of,  79.1. 
Sulphite  of  Protochloride  of,  792. 
Uses  of,  270. 
Volatility  of,  768. 
Carbonate  of  Baryta,  405 — 813. 

Bismuth,  551. 
Cerous,  560. 
Chromous,  506. 
Mercurous,  578. 
of  Cobalt,  461. 
Copper,  480. 
Didymium,  565. 
Glucina,  822. 
Glucina  arid  Potash,  822. 


834 


INDEX. 


Carbonate  of  Iron,  450. 

Lanthanum,  563. 
Lead,  489. 
Lime,  410. 
Lithia,  403. 
Magnesia,  416. 
Manganese,  434. 
Potash,  377. 
Silver,  597. 
Soda,  384. 

Hydrates  of,  807. 
Soda,  Preparation  of,  from  the 

Sulphate,  392. 
Solubility  of,  807. 
Strontia,  406. 
Zinc,  472. 
Carbonates,  274. 

Decomposition   of  insoluble,  by 

soluble  Sulphates,  736. 
Decomposition  of  insoluble  Salts 

by  Alkaline,  736. 
of  Ammonium,  809. 
Table  of,  173. 

Carbonic  Acid,  Composition  of,  272. 
Estimation  of,  771. 
Preparation  of,  271. 
Properties  of,  271. 
Uses  of,  274. 
Vapour,  Tension  of,  80. 
Oxide,  absorption  of  by  Dichloride 

of  Copper,  770. 
Estimation  of,  772. 
Preparation,  274. 
Properties,  275. 
Carburet  of  Iridium,  625. 
Carburets  or  Carbides,  270. 
Cast-iron,  444. 

Catalysis  or  Decomposition  by  contact,  186. 
Cavendish,  Experiments  on  Hydrogen,  237. 
Celsius's  Thermometer,  44. 
Ceric  Oxide,  560. 
Cerium,  556. 

Estimation  and  Separation  of,  561. 
Metallic,  559. 
Protochloride  of,  560. 
Protofluoride  of,  560. 
Protosulphide  of,  560. 
Protoxide  of,  559. 
Sesquichloride  of,  560. 
Sesqui  oxide  of,  559. 
Ceroue  Carbonate,  560. 
Oxalate,  560. 
Oxide,  559. 
Phosphate,  561. 
Sulphate,  560. 
Ceruse,  489. 
Chalybeate  Waters,  241. 
Charcoal,  268. 

Animal,  269. 
as  a  Disinfectant,  769. 
Platinized,  770. 
Chemical  Action,  Development  of  Heat  by, 

752. 
Influence     of     Mass     on, 

730. 

of  Light,  Measurement  of, 
675. 


Chemical  Affinity,  176,  730. 

and  Magnetic  Actions  of  the  Cur- 
rent compare^!,  680. 
and     Optical     Extinction     of    the 

Chemical  Rays,  678. 
Composition     and    Boiling    Point, 

Relations  between,  728. 
Composition  and  Density,  Relations 

between,  720. 

Compounds,  Classification  of,  695. 
Decomposition,  Cold  produced  by, 

757. 
Functions,  Classification  of  Bodies 

according  to  their,  696. 
Nomenclature,  109. 

Notation  and  Classification,  102 

685. 

Rays,  Extinction  of,  678. 
Chlorate  of  Lead,  491. 

Potash,  380. 
Chlorates,  341. 
Chloric  Acid,  340. 

Composition  of,  341. 
Resolution  of,  into  Peroxide  of 
Chlorine    and    Hyperchloric 
Acid,  342. 
Chloride,  Auric,  605. 

Aurous,  602. 
v     Chromic,  508. 
Chromous,  506. 
Cupric,  480. 
Cuprous,  478. 
Ferric,  675. 
Ferrous,  454. 
Merc-uric,  582. 
Mercurous,  577. 
Platinic,  611. 
Platinous,  610. 
Stannic,  499. 
Stannous,  495. 
Uranous,  555. 
of  Aluminium,  421. 
Ammonium,  808. 
Barium,  405. 
Bimercurammonium,  583. 
Boron,  347. 
Bromine,  351. 
Cadmium,  475. 
Calcium,  409. 
Carbon,  314. 
Cobalt,  461. 
Didymium,  565. 
of  Gold,  602. 

and  Potassium,  605. 
Iodine,  358. 
Lanthanum,  563. 
Lead,  488. 
Lime,  413. 

Volumetric  Estimation  of 

413,  803. 
Magnesium,  415. 
Mercurammonium,  584. 
Mercury  with  Ammonia,  582. 
Mercury,  Double  Salts  of,  584. 
Nickel,  468. 
Nitrogen,  345,  791. 
Phosphorus,  349. 


INDEX. 


835 


Chloride  of  Phosphoryl,  709. 
Potassium,  375. 

<«         Bichromate  of,  511. 
Rhodium  and  Potassium,  632. 
Silicon,  347. 

and  Hydrogen,  777. 
Silver,  595. 
Sodium,  383. 
Strontium,  406. 
Sulphuryl,  708,  795. 
Tantalum,  569. 
Tetramercurammonium,  584. 
Thionyl,  794. 
Uranyl,  556. 

and  Potassium,  556. 
Zinc,  472. 
Chlorides,  491,  661,  707. 

Acid  or  Negative,  708. 

Action  of  Ammoniaon  Acid,  713. 

and  Oxides  of  Osmium,  627. 

Atomic  Volume  of  Liquid,  725. 

Basic  Metallic,  707. 

Classification  of,  707. 

of  Alcohol-Radicals,  708. 

Tables  for  Atomic  Volumes  of  1st 

and  2d  Class  of,  174,  175. 
of  Arsenic,  533. 

Bibasic  Acids,  702. 
Iridium,  624. 

Manganese,  434,  436,  440. 
Palladium,  620,  621. 
Platinum,  610. 
Tellurium,  528. 
Tribasic  Acids,  702. 
Tungsten,  520. 
Chlorimetry,  414. 
Chlorine,  106,  329. 

Action  of,  on  Potash,  341. 
and  Binoxide  of  Nitrogen,  344. 
Oxygen  Compounds  of,  338. 
Sulphur,  348. 
Class  of  Elements,  146. 
Estimation  of,  798. 
Heat  of  Combination  of  Metals  with, 

754. 

Peroxide  of,  343. 
Preparation  of,  329. 
Process  for,  from  Hydrochloric  Acid 
and  Binoxide  of  Manganese,  330. 
Process  for,  from  Chloride  of  So- 
dium,   Binoxide   of   Manganese, 
and  Sulphuric  Acid,  332. 
Properties  of,  332. 
Separation  of,  from  Iodine,  800. 
Uses  of,  334. 

Volumetric  Estimation  of,  802. 
Chlorite  of  Lead,  491; 
Chlorites,  Volumetric  Estimation  of,  803. 
Chlorocarbosulphurous  Acid,  793. 
Chlorochromic  Acid,  513. 
Chloromethylosulphurous  Acid,  793. 
Chloronitric  Acid,  344. 
Chloronitrous  Acid,  345. 
Chlorophosphate  of  Lead,  492. 
Chlorophosphide  of  Nitrogen,  795. 
Chloroplatinate  of  Ammonium,  612. 
Potassium,  612. 


Chloroplatinate  of  Sodium,  612. 

Chloroplatlnite    of  Potas- 
sium, 611. 
Chlorosulphide  of  Phosphorus,  349,  794. 

Tin,  499. 

Chlorosulphuric  Acid,  708,  795. 
Chlorous  Acid,  343. 
Chloroxicarbonate  Gas,  347. 
Chloroxide  of  Phosphorus,  349. 
Chromate  of  Baryta,  512 
Lead,  512. 
Lime,  512. 
Magnesia,  512. 
Potash,  611. 
Silver,  513. 
Soda,  511. 
Chromates  and  Tungstates,  Table  of,  174. 

Compounds,  of  Mercuric  Chloride 

with  Alkaline,  585. 
Decomposition    of    Insoluble,    by 

Alkaline  Carbonates,  737. 
of  Ammonia,  512. 
Volumetric  Estimation  of,  803. 
Chrome  Iron,  510. 
Chromic  Acid,  510. 

Chloride,  508. 
Oxide,  506. 

Salts,  Reactions  of,  507. 
Sulphate,  508. 

Chromium  and  Potassium,  Oxalate  of,  509. 
Estimation  and  Separation  of,  513. 
Protochloride  of,  506. 
Protoxide  of,  505. 
Sesquichloride  of,  508. 
Sesquioxide  of,  506. 
Sesquisulphide  of,  508. 
Sources  and  Extraction  of,  506. 
Terfluoride  of,  513. 
Chromoso-chromic  Oxide,  506. 
Chromous  Carbonate,  506. 
Chloride,  506. 
Oxide,  505. 
Sulphate,  506. 
Sulphite,  506. 
Chrysoberyl,  428. 
Cinnabar,  581. 
Circular  Polarization,  662. 

in  Organic  Bodies,  664. 
Claudet,  Analysis  of  Black  Ash,  394. 
Clay,  424,  425. 

Iron  Stone,  Smelting  of,  442. 
Classification  and  Notation,  Chemical,  685. 

of    Bodies   according   to   their 

Chemical  Functions,  695. 
of  Elements,  144. 
Coal  Gas,  280. 

Henry's  Analysis  of,  282. 
Cobalt,  Ammoniacal  Salts  of,  463. 
Arseniate  of,  462. 
Bioxide  of,  463. 
Carbonate  of,  461. 
Estimation  and  Separation  of,  466. 
Chloride  of,  461. 
Nitrate  of,  401. 
Phosphate  of,  462. 
Phosphide  of,  463. 
Protoxide  of,  460. 


836 


INDEX. 


Cobalt,   Separation  of,  from  Nickel,  468. 
Sesquicyanide  of,  463. 
Sesquioxide  of,  462. 
Sources  and  Extraction  of,  459. 
Sulphide  of,  463. 
CobaltSc  Acid,  463. 

Oxide,  462. 
Cobaltous  Oxide,  460. 
Cobalt-yellow,  461. 
Coefficients  of  Diffusion,  744. 

Gas-absorption,  763. 
Cohesion,  176. 

Axes  of,  in  Wood,  651. 
Cold   produced  by  Chemical  Decomposition, 

757. 

Columbia  Acid,  572 
Columbium,  570. 
Columbous  Acid,  571. 
Columbites,  571. 

Coloured  Media,  Spectra  exhibited  by,  674. 
Combining  Measure,  127. 
Numbers,  686. 
Proportions,  111-119. 
Combustion,  Heat  of,  229,  751. 

in  Air,  230. 
Common  Salt,  383. 
Compound  Ethers,  705. 

Action  of  Ammonia  on,  713. 
Boiling  Points  of,  729. 
Compounds,  Formation  of,  by  Substitution, 

182. 

Formulae  of,  109. 
Condensing  Tube,  73. 
Conduction  of  Heat,  51,  650. 
Conjugate  Metals,  719. 

Radicals,  695. 
Conjugated  Acids,  703. 
Contraction    of    Liquids   from    the    Boiling 

Point,  37,  638. 
Water,  38. 
Copper,  Acetates  of,  482. 

Action  of  Nitric  Acid  upon,  256. 
Alloys  of,  483. 
Ammonio-sulphate  of,  534. 
and  Potash,  Oxalate  of,  482. 
Dichloride  of,  478. 
Dicyanide  of,  478. 
Diniodide  of,  478. 
Dioxide  of,  477. 
Disulphide  of,  478. 
Estimation  and  Separation  of,  483. 
Hydride  of,  478. 

Liquation  of  Argentiferous,  592. 
Nitrates  of,  482. 
Protochloride  of,  480. 
Protoxide  of,  479. 
Sources  and  Extraction  of,  476. 
Sulphate  of,  481. 
Volumetric  Estimation  of,  484. 
Cordier,  Investigation  on  Heat,  58. 
Corrosive  Sublimate,  582. 
Crichton's  Thermometer,  43. 
Cryophorus,  Dr.  Wollaston's,  75. 
Crystalline  Form  and  Rotatory  Power,  Rela- 
tions between,  668. 

Crystallized  Bodies,  Conduction  of  Heat  in, 
650. 


Cupellation  of  Silver,  600. 
Cuprammonium,  167,  480. 
Cuproso-cupric  Cyanide,  479. 
Cuprous  Chloride,  Iodide,  and  Cyanide,  478. 
Hyposulphite,  479. 
Oxide.  477. 
Carbonate,  481. 
Chloride,  480. 
Nitrate,  482. 
Oxide,  479. 

Salts,  Reactions  of,  479. 
Sulphate,  482. 
Sulphite,  479. 

Current,  Heating  Power  of  the  Voltaic,  684. 
Reduction  of  the  Force  of  the,  to 
absolute  Mechanical  Measure,  684. 
Regulator,  683. 

Electric,  Measurement  of,  679. 
Cyanide,  Cuproso-cupric,  479. 
Cuprous,  478. 
Ferric,  454. 
of  Lead,  489. 
Mercury,  586. 

Mercury  and  Potassium,  587. 
Palladium,  620. 
Potassium,  376. 
Silver,  597. 
Cyanides,  Compound,  165. 

of  the  Alcohol-radicals,  709. 
of  Platinum,  611,  616 
Cyanogen,  253.  ZLpp 

DALTON  on  Evaporation  of  Water,  475. 
Dalton's  Atomic  Theory,  119. 

Law  of  the  Dilatation  of  Gases,  40 
Miscibility  of  Gases,  87 
Daniell's  Constant  Battery,  218. 
Hygrometer,  93. 
Pyrometer,  45. 
Debus'  Experiments  on  the  Influence  of  Mass 

on  Chemical  Action,  732. 
Decomposition,  181. 

by  Contact,  186. 
Cold  produced  by,  757. 
Circumstances    which    affect 
the  order  of,  541,  733-740. 
Decompositions,  Secondary,  205. 
Delarive  and  Marcet,  Hay  craft,  Dulong,  Ap- 
john,    Suermann,   Delaroche,    Berard,    on 
Specific  Heat  of  Gases,  49. 
Density  and  Chemical  Composition,  Relations 

between,  720. 

Deutazophosphoric  Acid,  789. 
Deuto-hydrate  of  Phosphoric  acid,  320. 
Dew,  Deposition  of.  57. 

Well's  Experiments  on,  58. 
Diamagnetic  Bodies,  217. 
Diamides,  or  Primary  Biamides,  713. 
Diamond,  267. 

-boron,  774. 
-silicon,  776. 
Diaphragm,  Two  Polar  Liquids  separated  by 

a  Porous,  205. 
Dibromide  of  Mercury,  578. 
Dichloride  of  Mercury,  577. 

Action   of  Ammonia 
on,  578. 


INDEX. 


837 


THcyanide  of  Copper,  478. 
Didymium,  Arseniate  of,  566. 
Carbonate  of,  565. 
Chloride  of,  565. 
Estimation  of,  564. 
Metallic,  564. 
Nitrate  of,  566. 
Oxalate  of,  565. 
Peroxide  of,  564. 
Phosphate  of,  566. 
Protoxide  of,  564. 
Salts  of,  564. 

Sources  and  Extraction  of,  564. 
Sulphate  of,  565. 
Sulphide  of,  565. 
Sulphite  of,  566. 
Diffusion-coefficients,  744. 
Diffusion  of  a  Salt  into  the  Solution  of  another 

Salt,  743. 
Gases,  87. 

through  Porous  Septa,  751. 
Liquids,  740. 
Liquids   through   Porous  Septa, 

746. 

Dilatation  of  Solids  by  Heat,  34,  637. 
Dimetaphosphoric  Acid,  786. 
Dimorphism,  150. 
Diniodide  of  Copper,  478. 

Mercury,  578. 
Dioxide  of  copper,  477. 
Diplatosamine  and  Diplatinamine,  618. 
Disinfecting  Properties  of  Charcoal,  769. 
Dissipation  of  Heat,  53. 
Distillation,  Natural  Sequel  to  Vaporization, 

72. 
Disulphide  of  Copper,  478. 

Mercury,  577. 
Dolomite,  407. 
Double  Decomposition  of  Salts,  183,  733. 

regarded  as  the  Type 
of  Chemical  Action 
in  general,  691. 

Refraction,  Polarization  by,  659. 
Salts,  163. 
Dutch  Liquid,  286. 
Dynamical  Theory  of  Heat,  654. 

EARTHENWARE  AND  PORCELAIN,  426. 
Elasticity,  Axes  of,  in  Wood,  651. 
Electric  Current,  Heating  Power  of,  684. 

reduced    to    absolute   Me- 
chanical Measure,  684. 
Currents,  Measurement  of  the  Force 

of,  679. 

Resistance  of  Metals,  682. 
Electricity,  679. 
Electro-gilding,  607. 
Electrolysis,  203. 
Electro-silvering,  607. 

Elementary  Bodies,  Atomic  Weights,  and 
Formula  of,  in  the  free  State, 
689. 

Substances,  Table  of,  102-104. 
Elements,  Arrangement  of,  in   Compounds, 

154. 

Atomic  Volume  and  Specific  Grav- 
ity, of,  Table  I.,  172. 


Elements,  Barium  Class  of,  145. 
Carbon  Class  of,  148. 
Chlorine  Class  of,  146. 
Classification  of,  144. 
Gold  Class  of,  148. 
Magnesian  Class  of,  145. 
Metallic,  363. 
Non-metallic,  223,  759. 
Phosphorus  Class  of,  147. 
Platinum  Class  of,  148. 
Potassium,  Class  of,  145. 
Sulphur,  Class  of,  144. 
Symbols  of  the,  109. 
Tin,  Class  of,  148. 
Tungsten,  Class  of,  148. 
Emerald,  or  Beryl,  428. 
Enamel,  401. 

Endosmose  and  Exosmose,  747. 
Equivalent  of  Heat,  Mechanical,  652. 

Values  of  Radicals   693. 
Equivalents  and  Atoms,  685. 

Table  of,  102. 
Erbia,  429. 
Erbium,  429. 
Etherification   explained  by  Atomic  Motion, 

739. 
Ethers,  699. 

Action   of  Ammonia  on  Compound, 

713. 

Boiling  Points  of  Compound,  729. 
Compound,  705. 

Sulphur,  707. 
Hydrosulphuric,  706. 
of  Bibasic  Acids,  702. 
Tribasic  Acids,  702. 
Ethylene,  717. 
Euchlorine  Gas,  340. 
Euclase,  428. 
Eudiometers  for  Measuring  Gases,  283. 

of  Bunsen,  283,  284. 
Evaporation  in  Vacuo,  74. 

Spontaneous,  90. 

Dalton  and  Reguault  on  the,  of 

Water,  91. 

Expansion  and  the  Thermometer,  33. 
of  Gases,  40. 
Liquids,  35,  638. 
Mercury,  absolute,  639. 
Solids,  33,  539. 
Water,  639. 
Extinction  of  the  Chemical  Rays,  678. 

FAHL-ORES,  595. 

Faraday,  on  the  Liquefaction  of  Gases,  79. 
on   Relation    between    Light    and 

Magnetism,  216,  671. 
Fatty  Acids,  701. 

Boiling  Points  of,  729. 
Felspar,  427. 
Ferric  Acid,  456. 

Compounds,  451. 
Oxide,  451. 
Sulphide,  453. 
Ferrocyanide  of  Iron,  450. 

Potassium,  449. 

and  Iron,  44S. 
Ferroso-ferric  Oxide,  453. 


838 


INDEX. 


Ferroso-ferric  Sulphate,  455. 
Ferrous  Compounds,  448. 
Oxide,  448. 

Volumetric  estimation  of,  804. 
Fick's  Experiments  on  Liquid  Diffusion,  744. 
Flame,  Structure  of,  263. 
Fluidity,  as  an  effect  of  Heat,  59. 
Black's  Views  on,  60. 
Table  of,  59. 
Fluoboric  Acid,  361. 
Fluoboride  of  Silicon,  362. 
Fluorescence,  671. 
Fluoride  of  Aluminium,  421. 
Boron,  361. 
Calcium,  410. 
Manganese,  434. 
Silver,  597. 
Tantalum,  569. 
Fluorides,  709. 
Fluorine,  682. 

Detection  of  minute  quantities  of, 

800. 

Estimation  of,  801. 
Isolation  of,  800. 
Sources  of,  800. 
Fhior-Spar,  360,  410. 
Fluosilicic  Acid,  362. 
Formulae,  Rational,  692. 
Formulae,  Antithetic  or  Polar,  168. 

of  Compounds,  109. 
Freezing  Apparatus,  410. 
of  Water,  75. 
Mixtures,  391. 
Fulminating  Gold,  603. 
Functions,  Classification  of  Bodies,  according 

to  their  Chemical,  696. 
Fusco-cobaltia  Salts,  464. 

GALVANOMETER,  222,  679. 

Garnet,  426. 

Gas-Battery,  Grove's,  209. 

Gases  and  Vapours,  Specific  Heat  of,  642. 

Air  and,  are  imperfect  Conductors,  53. 
Absorption  of,  by  Liquids,    81,    240, 

763. 

Dalton  on  Miscibility  of,  87. 
Density  of,  83,  84.  * 
Determination  of   the   Specific   Heat 

of,  49. 
Diffusion  of,  87. 

through    Porous    Septa, 

751. 

Effusion  of,  83. 
Expansion  of,  40. 
Faraday's  Experiments  on,  78. 
Heat  evolved   by  the   Solution  of,  in 

Water,  756. 

Passage  of,  through  Membranes,  90. 
Permanent,  77. 
Priestley,  on  Diffusion  of,  87. 
Table  of  the  Specific  Gravity  of,  and 

Vapours,  130,  136. 

Thilorier's  Machine  for  the  Liquefac- 
tion of  Carbonic  Acid,  77. 
Transpiration  of,  85. 
Gerhardt's  Atomic  Weights,  688. 
Formulae  of  Salts,  166. 


Gerhardt's  Theory  of  the  Ammoniacal   Pla- 
tinum Compounds,  617. 
Types,  619. 
Unitary  System,  687. 
German  Silver,  468. 
Gilding  and  Silvering,  607. 
Glass,  399. 

Analysis  of,  400. 
Bohemian,  401. 

Composition  of,  Varieties  of,  400. 
Crown,  400. 
Crystal,  401. 
Devitrification  of,  402. 
Flint,  401. 

Green  or  Bottle,  401. 
Window,  400. 
Glauber's  Salts,  391. 

Glucina  and  Ammonia,  Carbonate  of,  822. 
Potash,  Oxalate  of,  822. 
Carbonate  of,  822. 

Glucina,  Estimation  and  Separation  of,  823. 
Properties,  Rational   Formula   auii 

Preparation  of,  821. 
Glucinum,  428,  821. 
Gladstone's  Experiments  on  the  Influence  of 

Mass  on  Chemical  Action^  622. 
Glycerines,  699. 
Glycols,  698. 
Gold,  Alloys  of,  606. 

Amalgam  of,  606. 
and  Potassium,  Chloride  of,  605. 
Class  of  Elements,  148. 
Estimation  and  Separation  of,  607. 
Extraction  of,  601. 
Oxide  of,  602. 
Fulminating,  603. 
Properties  of,  601. 
Sesquichloride  of,  605. 
Sesquioxide  of,  602. 
Sesquisulphide  of,  605. 
Sources  of,  601. 
Graham's  Experiments  on  Liquid  Diffusion, 

740. 

Researches  on  Osmose,  748. 
Graphite,  267. 

Preparation  of  pure,  finely  divided, 

770. 

Graphitoi'dal  Boron,  774. 
Silicon,  776. 
Gunpowder,  379,  380. 
Gurney's  Bude  Light,  284. 
Gypsum,  412. 

HAIL,  249. 

Heat,  Absorption  and  Reflection  of  Radiated, 

54. 
Bache's  Experiments  on  the  Radiation 

of,  54. 

Capacity  of  Different  Bodies  for,  48. 
Central,  58. 
Conduction  of,  51,  650. 
Developed   by  Chemical  Combination, 

751. 

Dilatation  of  Solids  by,  34,  637. 
Distribution  of  the  Rays  of,  101. 
Despretz  and  Dulong's  Experiments  on 

Latent,  69. 


INDEX. 


839 


Heat,  Dynamical  Theory  of,  654. 

Evolved   by  the   Solution  of  Gases  in 

Water,  756. 

Effects  of,  on  Glass,  35. 
Evolved  in  the  Combination  of  Acids 

with  Water,  756. 

Experiments  of  Melloni  on  the  Trans- 
mission of,  55,  642. 
Fluidity,  as  an  Effect  of,  59. 
Latent,  69,  642. 
Mechanical  Equivalent  of,  652. 
Nature  of,  96,  97,  654. 
of  Combination  of  Acids  with  Bases, 

755. 
Combinations      of      Metals      with 

Chlorine,  754. 
Combination   of   Metals,  &c.,  with 

Oxygen,  752. 
Combustion  and  Specific  Relations 

between,  754. 
or  Cold  produced  by  Solution  of  Salts 

in  Water,  756. 
Radiation  of,  53. 
Regnault's   Table  of  the  Capacity  of 

Bodies  for,  49. 

Rumford's  Experiments  on  the  Radia- 
tion of,  53. 
Specific,  48,  640.     . 
Table  of  the  Conduction  of,  by  Build- 
ing Materials,  51. 
Transmission  of,  55. 

Radiant,  through  Media 
and  the  Effects  of 
Screens,  55. 

Transparency  of  Bodies  to,  56. 
Heating  Power  of  the  Voltaic  Current,  684. 
Hedyphan,  413. 
Hemihedry,  668. 
Hexametaphosphoric  Acid,  787. 
Henry,  on  Coal  Gas,  282. 
Hepar  Sulphuris,  374. 
Homologous  Compounds,  Boiling  Points  of, 

730. 

Homologous  Series,  698. 
Horse-chestnut   Bark,    Fluorescence   of,  In- 
fusion of,  672. 
Humboldite,  276. 
Hydracids,  337. 
Hydrate  of  the  Binoxide  of  Calcium,  409. 

otash,  Preparation  of,  from  the 
Nitrate,  806. 
Hydrated  Bisulphate  of  Potash,  378. 

Sesquisulphate  of  Potash,  378 
Tantalic  Acid,  567. 
Hydrates  of  Alumina,  420,  819. 
Copper,  478. 
Silicic  Acid,  291. 
Sulphuric  Acid,  300. 
the  Alcohol-radicals,  716. 
Aldehyde-radicals,  717. 
Metals  Proper,  716. 
Hydraulic  Mortar,  409. 
Hydride  of  Phosphorus  (Liquid),  327. 
Hydrides  of  Carbon,  278. 
Hydriodic  Acid,  355. 
Hydroboracite,  418. 
Hydrobromic  Acid,  351. 


Hydrochl  orate  of  Ammonia,  809. 
Hydrochloric   Acid    and    Binoxide  of    Man- 
ganese, process  for 
preparing   Chlorine 
from,  657. 
Preparation  of,  335. 
Table     of    the     Specific 

Gravity  of,  336. 
Type,  693,  707. 
Hydrocyanic  Acid,  377. 
Hydroferricyanic  Acid,  454. 
Hydroferrocyanic  Acid,  449. 
Hydrofluoric  Acid,  683. 

Anhydrous,  800. 
Hydrofluosilicic  Acid,  362. 
Hydrogen  and  Arsenic,  533. 

Nitrogen,  Ammonia,  264. 
Phosphorus,  326. 
Sulphur,  306. 
Antimoniuretted,  544. 
Bicarburetted,  285. 
Binoxide  of,  242. 
Bisulphide  of,  308. 
Cavendish's  Experiments  on,  237. 
Peroxide  of,  232. 
Preparation  of,  232. 
Properties  of,  234.' 
Protocarburetted,  278. 
Protoxide  of,  237. 
Quantitative  Estimation  of,  762. 
Siliciuretted,  778. 
Teroxide  of,  760. 
Hydrogen-type,  693,  716. 
Hydrosulphate  of  Ammonia,  809. 
Hydrosulphuric  Acid,  306. 

Ethers,  706. 
Hygrometer,  91. 

Condensing  (Regnault's),  94. 
Daniell's,  93. 
Differential,  92. 
Wet  Bulb,  92. 
Hyperchloric  Acid,  342. 
Hypochloric  Acid,  343. 
Hypochlorite  of  Lime,  413. 
Hypochlorites,  340. 

Volumetric  Estimation  of,  803. 
Hypochlorous  Acid,  338. 
Hypo-iodic  Acid,  796. 
Hypophosphorous  Acid,  316. 

Analysis  of,  318. 
Hyposulphate  of  Magnesia,  417. 
Hyposulphate  of  Manganese,  435. 

Silver,  597. 
Hyposulphite,  Cuprous,  479. 

of  Auric  Oxide  and  Soda,  606. 
Aurous  Oxide  and  Soda,  606. 
Baryta,  606. 
Silver,  597. 
Strontia,  407. 
Hyposulphuric  Acid,  302. 
Hyposulphurous  Acid,  303. 

Estimation  of,  784. 
Hydrotelluric  Acid,  528. 

ILMENIUM,  572. 

Imides,  714. 

Inactive  Tartaric  Acid,  670. 


840 


INDEX. 


Induction,  Photo-chemical,  677. 
Insolubility,  influence    of,   on   Chemical  De- 
composition, 182,  738. 
Insoluble  Salts,  Decomposition  of,  by  Soluble 

Salts,  736. 

lodate  of  Potash,  381. 
lodates,  357. 
lodic  Acid,  356. 
Iodide,  Auric,  591. 

Cuprous,  478. 
Platinous,  611. 
of  Cadmium,  475. 
Lead,  489. 
Nitrogen,  358,  797. 
Palladium,  620,  799. 
Potassium,  375. 
Sulphur,  358. 
Stannous,  497. 
Silver,  596. 

Tetramercurammomum,  586. 
Zinc,  472. 
Iodides,  679,  709. 

Atomic  Volume  of  Liquid,  725. 
Ferric  and  Ferrous,  449,  454. 
of  Alcohol-radicals,  Action  of  Am- 
monia on,  710. 
Mercury,  578,  586. 
Phosphorus,  358,  798. 
Iodine,  Bromides  of,  359. 
Chlorides  of,  358. 
Compounds  of,  355. 
Estimation  of,  799. 
Preparation  of,  352. 
Properties  of,  353. 
Separation    of,    from    Bromine    and 

Chlorine,  800. 
Sources  of,  352,  796. 
Uses  of,  355. 

Volumetric  Estimation  of,  801. 
lodo-aurate  of  Potassium,  606. 
Ions,  Transference  of  the,  206. 
Iridic  Sulphate,  625. 

Iridium,  Ammoniacal  Compounds  of,  625. 
Carburet  of,  625. 
Chlorides  of,  626. 
Oxides  of,  624. 
Properties  of,  623. 
Sources  and  Extraction  of,  622. 
Sulphides  of,  624. 

Iron  and  Potassium,  Ferrocyauide  of,  449. 
Bisulphide  of,  453. 
Black  or  Magnetic  Oxide  of,  453. 
Carbonate  of,  450. 
Cast,  444. 

Ferricyanide  of,  450. 
Malleable,  445. 
Metallurgy  of,  442. 
Ores  of,  442. 

Passive  condition  of,  447. 
Properties  of,  446. 
Protoacetate  of,  451. 
Protochloride  of,  449. 
Protocompounds  of,  448. 
Protocyauide  of,  448. 
Protiodide  of,  449. 
Protonitrate  of,  451. 
Protosulphate  of,  451. 


Iron,  Protosulphide  of,  449. 

Protoxide  of,  448. 

Puddling  of,  445. 

Pyrites,  453. 

Quantitative  Estimation  of,  457. 

Scale  Oxide  of,  453. 

Separation  of,  from  other  Metals,  458. 

Sesquichloride  of,  454. 

Sesquicompounds  of,  451. 

Sesquicyanide  of,  454. 

Sesquiiodide  of,  454. 

Sesquioxide  or  Peroxide  of,  451. 

Sesquisulphide  of,  453. 

Sources  of,  441. 

Subsulphide  of,  449. 

Volumetric  Estimation  of,  458,  804. 
Isomerism,  152. 
Isomorphism,  139. 
Isomorphous  relations  of  Manganese,  440. 

KELP,  395. 

LANTHANUM,  Carbonate  of,  563. 

Chloride  of,  563. 

Estimation  of,  564. 

Metallic,  563. 

Nitrate  of,  563. 

Protoxide  of,  563 

Sources  and  Extraction  of,  562. 

Sulphate  of,  503. 
Latent  Heat,  61,  642. 
Lead,  Acetates  of,  492. 
Alloys  of,  493. 
Antimoniates  of,  544. 
Bichloride  of,  489. 
Bioxide  or  Peroxide  of,  487. 
Bromide,  Iodide,  and  Cyanide  of,  489. 
Carbonate  of,  489. 
Chlorate  of,  491. 
Chloride  of,  488. 
Chlorite  of,  491. 
Chlorophosphate  of,  492. 
Chromate  of,  512. 
Estimation  and  Separation  of,  493. 
Minium  or  Red,  487. 
Nitrate  of,  490. 
Nitrites  of,  491, 
Oxychloride  of,  488. 
Perchlorate  of,  491. 
Phosphate  of,  491. 
Protosulphide  of,  488. 
Protoxide  of,  486.  * 

Salts,  Reactions  of,  491. 
Sesquibasic  acetate  of,  492. 
Sesquioxide  of,  487. 
Sources  and  Extraction  of,  485. 
Suboxide  of,  485. 
Sulphate  of,  490. 
Sulphide  of,  487. 
Tribasic  subacetate  of,  492. 
Leslie,  Radiation  of  Heat,  53. 
Leucite,  or  Amphigen,  426. 
Liebig's  Condensing  Tube,  78. 
Light,  Brewster  (Sir  D.)  on,  100,  246. 
Change  of  Refrangibility  of,  671. 
Common,  99. 
Decomposition  of,  100. 


INDEX. 


841 


Light,  Difference  of  Chemical  Power  in  Morn- 
ing and  Evening,  679. 
Double  Refraction  of,  99,  659. 
Forbes  on,  246. 
Gurney's  Bude,  284. 
Measurement  of  the  Chemical  Action 

of,  675. 

Polarization  of,  99,  658. 
Faraday's  Experiments  on    the  Rela- 
tions between  Magnetism  and,  216, 
671. 
Lime,  407. 

and  Alumina,  Silicates  of,  745. 

Potash,  Sulphate  of,  816. 
Carbonate  of,  410. 
Chromate  of,  512. 
Estimation  of,  816. 
Hydrate  of,  407. 
Hypochlorite  of,  413. 
\  Hyposulphite  of,  412. 

Nitrate  of,  412. 
Phosphate  of,  412,  816. 
-    Salts  of,  410. 
Separation  of,  from  Baryta  and  Stron- 

tia,  816. 
from  Magnesia  and  the 

Alkalies,  816. 
Solubility  of,  815. 
Sulphate  of,  412,  816. 
Volumetric  Estimation  of  Chloride  of, 

414,  803. 

Liquation  of  Argentiferous  Copper,  328. 
Liquefaction,  59,  642. 
Liquids,  Absorption  of  Gases  by,  763. 
Atomic  Volume  of,  720. 
Circular  Polarization  in,  664. 
Contraction    of,    from    the    Boiling 

point,  37,  639. 
Diffusion  of,  740. 

through  porous  Septa, 

746. 

Expansion  of,'  36,(  638. 
Latent  Heat  of,  643. 
Specific  Heat  of,  640. 
Tension  of  Vapours  of  mixed,  648" 
Vaporization  of,  66. 
Lithia,  402. 

Carbonate  of,  403. 

«          Estimation  and  Separation  of,  812. 
Hydrate  of,  403. 
Nitrate  of,  812. 
Phosphate  of,  812. 
Sulphate  of,  403. 
Lithium,  402,  811. 

Chloride  of,  403. 
Luteo-Cobaltia  Salts,  464. 

MADDER- STOVE,  95. 
Magnesia,  415. 

Alba,  416. 

Bicarbonate  of  Potash  and,  416. 

Borate  of,  418. 

Carbonate  of,  416. 

Chromate  of,  512. 

Estimation  and  Separation  of,  818. 

Hyposulphate  of,  417. 

Nitrate  of,  418. 


Magnesia,  Phosphate  of  and  Ammonia,  418. 
Silicates  of,  418. 
Sulphate  of,  417. 

Magnesian  Class  of  Elements,  145. 
Magnesium,  415,  817. 

Chloride  of,  415. 
Magnetic  Action,   Rotatory   Power   induced 

by,  671. 

and  Chemical  Actions  of  the  Cur- 
rent compared,  680. 
Oxide  of  Iron,  453. 
Magnetic  Polarity,  187. 
Malaguti's   Experiments   on  the  Reciprocal 

Action  of  Salts,  734. 
Malic  Acid,  Active  and  Inactive,  670. 
Malleability,  364. 
Malleable  Iron,  444. 

Manganese,  Bioxide  or  Peroxide  of,  436. 
Black  Oxide  of,  436. 
Carbonate  of,  434. 
Estimation   and   Separation   of, 

441. 

Fluoride  of,  434. 
Hyposulphate  of,  435. 
Isomorphous  relations  of,  440. 
Molybdate  of,  524. 
Oxides  of,  432. 
Perchloride  of,  440. 
Phosphide  of,  433. 
Protochloride  of,  433. 
Protocyanide  of,  434. 
Protosulphide  of,  433. 
Protoxide  of,  432. 
Protosulphate  of,  434. 
Reactions  of,  432. 
Red  Oxide  of,  436. 
Sources  and  Extraction  of,  431. 
Sesquichloride  of,  436. 
Sesquicyanide  of,  436. 
Sesquioxide  of,  435. 
Valuation  of,  Bioxide  of,  437. 
Manganic  Acid,  439. 
Oxide,  435. 
Sulphate,  435. 
Manganous  Oxide,  432. 

Sulphate,  434. 
Margueritte's  Experiments  on  the  Reciprocal 

Action  of  Salts,  736. 
Mariotte,    Deviation    from   the   Law  of    in 

Gases,  82. 

Law  of  Compression  of  Gases,  81. 
Marsh  Gas,  717. 
Marsh's  Test  for  Arsenic,  535. 
Mass,  Influence  of,  on  Chemical  Action,  730. 
Measurement  of  the  Force  of  Electric  Cur- 
rents, 679. 

Mechanical  Equivalent  of  Heat,  652. 
Mechanical  Measure  of  the  Electric  Current, 

684. 

Mellon  (Liebig),  287. 
Melting  Point  of  Sulphur,  292,  781. 
Mercaptans,  706. 
Mercurammonia,  581. 
Mercurammonium,  Chloride  of,  584. 
Mercuric  Amido-chloride,  583. 

Ammonio-nitrates,  589. 
Bromide,  585. 


842 


INDEX. 


Mercuric  Chloride,  582. 

Compounds,  579. 
Iodide,  585. 
Nitrates,  588. 
Oxide,  578. 

Seleniate  and  Selenite,  588. 
Sulphate,  588. 
Sulphide,  581. 
Sulphites,  588. 

Mercuroso-mercuric  Iodide,  586. 
Mercurous  Acetate,  579. 

Bromide,  or  Dibromide  of  Mer- 
cury, 578. 
Carbonate,  or  Carbonate  of  Black 

Oxide  of  Mercury,  578. 
Chloride,  Bichloride  of  Mercury, 

or  Calomel,  577. 
Compounds,  576. 
Iodide,  or  Biniodide  of  Mercury, 

578. 
Nitrates,   or    Nitrates    of    Black 

Oxide  of  Mercury,  579. 
Sulphates,  or  Sulphate  of  Black 

Oxide  of  Mercury,  578. 
Seleniate,  578. 
Selenite,  679. 
Mercury,  Absolute  Expansion  of,  639. 

Action  of  Ammonia  on  Bichloride 

of,  578. 

Alloys  of,  and  Potassium,  589. 
Calorimeter,  752. 
Chloride  of,  with  Ammonia,  582. 
Cyanide  of,  586. 
Bibromide  of,  578. 
Bichloride  of,  577. 
Biniodide  of,  578. 
Bioxide  of,  576. 
Bisulphide  of,  577. 
Bouble  Salts  6*f  Chloride  of,  584. 
Estimation  and  Separation  of,  590. 
Nitride  of,  681. 
Nitrochloride  of,  583. 
Oxy chloride  of,  109,  584. 
Oxycyanide  of,  587. 
Protobromide  of,  585. 
Protochloride  of,  582. 
Protoxide  of,  579. 
Protosulphide  of,  581. 
Sulphochloride  of,  584. 
Metalloids  or  Acid  Metals,  719. 
Metals,  Alcohol,  718. 

Combinations  of,  366. 

Conduction  of  Heat  in,  649. 

Conjugate,  719. 

Biamagnetic,  217. 

Electric  Resistance  of,  682. 

Found  in  Native  Platinum,  369,  608. 

General  Observations  on,  363. 

Heat,      of     Combination      of,     with 

Chlorine,  754. 
Heat  of  Combination  of,  with  Oxygen. 

752. 
Isomorphous  with  Phosphorus,  369, 

530. 

in  Native  Platinum,  608. 
Mixed,  719. 
Noble,  573. 


Metals,  of  the  Alkalies,  368,  804. 

Alkaline  Earths,  368,  812. 
Earths  Proper,  368,  822. 
Oxidability  of,  366. 
Physical  Properties  of,  364. 
Proper,    having    Isomorphous    "Rela- 
tions with  the  Magnesian  Family, 
369,  494. 
Proper,  having  Protoxides  isomorph- 

ous  with  Magnesia,  368,  431. 
Proper,  Hydrides  of,  716. 
Proper,  of  which  the  Oxides  are  re- 
duced   by    Heat   to   the~  Metallic 
state,  369,  573. 
Protoxides  of,  366. 
Table  of  the,  363,  364.  * 

Fusibility  of  different 

365. 

Metameric  Bodies,  154. 
Metaphosphates,  320. 

Action  of  Water  on  the,  787. 
Metaphosphoric  Acid,  324,  786. 
Metastannates,  498. 
Metastannic  Acid,  498. 
Methylosulphurous  Acid,  793. 
Microcosmic  Salt,  396. 
Minium,  487. 
Mitchell's  Experiments  on  Biffusion  of  Gases, 

90. 
Mixed  Liquids,  Tension  of  Vapours  of,  648. 

Metals,  719. 
Molybdate  of  Lead,  524. 

Manganese,  524. 
Molybdates  of  Ammonia,  523. 
Baryta,  524. 
Potash,  523. 
Soda,  523. 
Molybdenum,  Chlorides  of,  525. 

Estimation  and  Separation  of, 

525. 

Sources  of,  521. 
Sulphides  of,  524. 
Molybdic  Acid,  522. 

Oxide,  522. 

Molybdous  Oxide,  521. 
Monobasic  Salts,  161. 
Monometaphosphoric  Acid,  786. 
Monophosphamide,  789. 
Monosul-hyposulphuric  Acid,  305.  • 

Motion,  Atomic,  738. 

NEUTRAL  Metantimoniate  of  Potash,  543. 
Nichol's  Prism,  660. 
Nickel,  Ammonio-Compounds  of,  468. 
Chloride  of,  468. 

Estimation  and  Separation  of,  468. 
Oxides  of,  467. 

Sources  and  Extraction  of,  466. 
Sulphate  of,  468. 
Niobium,  570. 
Nitrate,  Cupric,  482. 
Ferric,  455. 
of  Alumina,  424. 
Ammonium,  810. 
Argentamrrionium,  598. 
Baryta.  405. 
Bimercarummonium,  589. 


INDEX. 


843 


Nitrate  of  Cobalt,  401. 

Didymiuvn,  560. 
Lanthanum,  5t)3. 
Lead,  490. 
Lime,  412. 
Lithia,  812. 
Magnesia,  418. 
Palladium,  620. 
Potash,  379. 
Silver,  598. 
Soda,  395. 
Strontia,  407. 

Tetramercurammonium,  589. 
Trimereurammonium,  589. 
Uranyl,  556. 
Zinc,  473. 
Stannous,  497. 
Uranic,  556. 
Nitrates,  Mercuric,  588. 
Mercurous,  579. 
of  Bismuth,  551. 
Table  of,  379. 
Nitre,  378. 

valuation  of,  768. 

Nitric  Acid,  Action  of,  upon  Copper,  256. 
Anhydrous,  766. 
Mode  of  preparation  by  M.  De- 
ville,  and  properties,  described, 
259. 

Battery  (Grove's),  218. 
Estimation  of,  767. 
Preparation  of,  260. 
Properties  of,  256. 
Uses  263. 

Nitric  Oxide,  Preparation  of,  766. 
Nitride  of  Boron,  775. 

Mercury,  581. 
Nitrides,  Intermediate,  715. 

Negative  or  Acid,  712. 

of    the    Alcohol-radicals,    primary, 

710. 
Alcohol-radicals,  secondary 

and  tertiary,  711. 
Aldehyde-radicals,  712. 
Titanium,  503. 
Positive,  710. 
Nitrile  Bases,  711. 
Nitrite  of  Silver,  598. 
Nitrides  of  Lead,  490. 
Nitrochloride  of  Mercury,  583. 
Nitrogen,  113. 

and  Hydrogen,  Ammonia,  264. 
Phosphorus,  329. 
Sulphur,  309. 
Binoxide  of,  256. 
Bromide  of,  795. 
Chloride  of,  345,  791. 
Chlorophosphide  of,  795. 
Compounds,    Atomic    Volume    of 

Liquid,  779. 
Compounds  containing  Phosphorus 

and,  787. 

Iodide  of,  358,  797. 
Peroxide  of,  258. 
Preparation  of,  244,  765. 
Properties  of,  244. 
Protoxide  of,  253. 


Nitrogen,  Quantitative  Estimation  of,  766. 

Sulphide  of,  309,  781. 
Nitrocyanide  of  Titanium,  504. 
Nitroprussic  Acid,  450. 
Nitropvussides,  457. 
Nitrosulphuric  Acid,  301. 
Nitrous  Acid,  257. 
Oxide,  766. 
Noble  Metals,  573. 
Non-metallic  Elements,  223,  759. 
Normal  Acid  Fluid,  388. 
Notation   and  Chemical  Nomenclature,  101- 

106. 
Classification,  Chemical,  685. 

OCTOHEDRAL  BORON,   774. 

Silicon,  776. 
Ohm's  Formulae,  681. 
Oil  Gas,  286. 

of  Vitriol,  297. 

Specific  Gravity  of  the  Vapour 

of,  138. 

Olefiant  Gas,  or  Ethylene,  285,  717. 
Optical  and  Chemical  Extinction  of  the  Chemi- 
cal Rays,  678. 
Organic  Compounds,  Circular  Polarization  in, 

664. 

Estimation    of    Carbou 

and  Hydrogen  in,  771. 

Estimation  of   Chlorine 

in,  799. 
Estimation  of  Nitrogen 

in,  766. 
Estimation   of   Sulphui 

in,  783. 

Osmiamic  Acid,  629. 
Osmic  Acid,  628. 

Sulphate,  627. 
Osmious  Acid,  628. 
Osmium.  Bichloride  of,  627. 

Estimation  and  Separation  of,  629. 
Oxides  and  Chlorides  of,  627. 
Sources  and  Extraction  of,  626. 
Sesquioxide  of,  627. 
Sulphides  of,  629. 
Terchloride  of,  628. 
Osmose  through  Membrane,  748. 

Physiological  Action  of,  750. 
through  Porous  Earthenware,  748. 
Jolly's  researches  on,  747. 
Graham's  researches  on,  748. 
Oxalate,  Cerous,  560. 
Ferric,  456. 

of  Chromium  and  Potassium,  509. 
Copper  and  Potash,  480. 
Didymium,  565. 
Glucina  and  Potash,  822. 
Potash  and  Antimony,  541. 
Silver,  599. 

Oxalates,  Decomposition  of  Insoluble  by  Al- 
kaline Carbonates,  737. 
of  Ammonium,  810. 
Oxamide,  713,  810. 
Oxalic  Acid,  276. 

Estimation  of,  772. 
Oxamic  Acid,  704,  810. 
|  Oxide,  Antimonic,  539. 


844 


INDEX. 


Oxide,  Auric,  602. 
Aurous,  602. 
Ceric,  560. 
Cerous,  559. 
Chromic,  506. 
Chromoso-chromic,  506. 
Chromous,  505. 
Cobaltic,  462. 
Cobaltous,  460. 
Cupric,  479. 
Cuprous,  477. 
Mercuric,  579. 
Molybdic,  522. 
Molybdous,  521. 
of  Antimony,  539. 
Cadmium,  445. 
Gold,  601. 
Iridium,  623,  624. 
Iron,    Volumetric    Estimation    of, 

804. 

Manganese,  432,  435,  436. 
Khodium,  630. 
Silver,  594. 
Phosphorus,  315. 
Potassium,  Salts  of,  377. 
Vanadium,  515. 
Zinc,  472. 
Palladous,  620. 
Platinic,  611. 
Platinous,  610. 
Rhodic,  630. 
Ruthenic  634. 
Stannic,  497. 
Stannous,  495. 
Tungstic,  517. 
Uranic,  555. 
Uranoso-uranic,  555. 
Uranous  554.  . 

Oxides  and  Chlorides  of  Osmium,  627. 

Atomic  Volume  and  Specific  Gravity 

of,  175. 

Intermediate,  or  Oxygen  Salts,  705. 
Metallic,  Classification  of,  697. 
Negative  or  Acid,  700. 
Positive,  697. 
Oxychloric  Acid,  341. 
Oxybromide  of  Phosphorus,  796. 
Oxychloride  of  Lead,  488. 

Mercury,  584. 
Oxycobaltia-salts,  463. 
Oxycyanide  of  Mercury,  587. 
Oxygen,  113. 
Oxygen-Acids,  156. 

Active  Modification  of,  760,  762. 
Compounds  of  Chlorine  and,  338. 
Extraction  of,  from  Atmospheric  Air, 

759. 
Heat  produced  by  combination  with, 

752. 

Preparation  of,  223. 
Properties  of,  227. 
Quantitative  Estimation  of,  762. 
Oxygenated  Water,  155. 
Oxygen-Salts  or  Intermediate  Oxides,  705. 
Ozone,  232,  759. 


PACKFONG,  468. 

Palladium,  Ammoniacal  Compounds  of  621— 

622. 

Chlorides  of,  620-621. 
Cyanide  of,  620. 

Estimation  and  Separation  of,  622. 
Nitrate  of,  620. 
Properties  of,  619. 
Protoxide  of,  619. 
Reactions  of,  620. 
Sources  and  Extraction  of,  619. 
Sulphide  of,  620. 
Passive  condition  of  Iron,  447. 
Pearl-Ash,  377. 

Pentachloride  of  Antimony,  544. 
Phosphorus,  349. 

Action  of  Acids 

on,  794. 

Pentaiodic  Acid,  357. 
Pentasulphide  of  Antimony,  544. 
Pentathionic  Acid,  305. 
Perchlorate  of  Lead,  491. 

Potash,  381. 
Perchloric  Acid,  341. 
Perchloride  of  Carbon,  347. 

Sulphite  of.  816. 
Manganese,  440. 
Periodates,  358. 
Periodic  Acid,  357. 
Permanganic  Acid,  439. 
Permeability  to  Liquids,  Axes  of,  in  Wood, 

651. 

Persulphide  of  Arsenic,  533. 
Peroxide  of  Chlorine,  343. 
Didymium.  564. 
Iron,  451. 
Lead,  487. 
Manganese,  436. 
Nitrogen,  258. 
Potassium,  374. 
Silver,  599. 

Peroxides,  Volumetric  Estimation  of,  804. 
Phospham,  789. 
Phosphamic  Acid   789. 
Phosphate,  Cerous,  561. 

of  Alumina,  424. 
Cobalt,  462. 
Didymium,  567. 
Lead,  491. 
Lime,  412,  816. 
Lithia,  812. 
Magnesia,  418. 

and  Ammonia,  418. 
Phosphates,  321. 

Analysis  of,  325,  791. 
Bibasic,  322. 

of  Ammonium,  810. 
of  Uranyl,  556. 

Ziuc,  473. 
Tribasic,  321. 
Uranic,  556. 
Phosphide  of  Cobalt,  463. 

Manganese,  433. 
Nitrogen,  328,  790. 
Tungsten,  520. 


INDEX. 


845 


Phosphides,  716. 

Phosphites,  817. 

Phosphocerite,  561. 

Phosphoric  Acid,  Analysis  of,  325. 

Action  of,  on  Pentachloride 

of  Phosphorus,  795. 
Amides  of,  787. 
considered  Tribasic,  170. 
Deuto-hydrate  of,  Acid  or 
Bibasic     Phosphate     of 
Water,  320. 
Estimation  of,  790. 
Separation  of,  from  Bases, 

791. 

Preparation  of,  318. 
Protohydrate  of,  320. 
Terhydrate  of,  or  Tribasic 
Phosphate  of  Water,  320. 
Phosphorous  Acid,  Analysis  of,  318. 
Estimation  of,  791. 
Preparation  of,  317. 
Properties  of,  317. 
Phosphorus,  313. 

Atomic  Weight  of,  786. 
and  Hydrogen,  326. 

Nitrogen,  328,  788. 
Sulphur,  328. 
Bromide  of,  351. 
Chloride  of,  349. 
Chlorosulphide  of,  349. 
Chloroxide  of,  349. 
Class  of  Elements,  147. 
Estimation  of,  791. 
Iodides  of,  338,  798. 
Liquid  Hydride  of,  327. 
Oxide  of,  315. 
^xybromide  of,  795. 
Pentachloride  of,  349. 
Properties  of,  313. 
Red,  314. 

or  Amorphous,  785. 
Solid  Hydride  of,  326. 
Sulphides  of,  328,  787. 
Sulphobromide  of,  796. 
Terchloride  of,  349. 
Phosphoryl,  Chloride  of,  709. 
Phosphuretted  Hydrogen  Gas,  326. 
Photo-Chemical  Induction,  677. 
Platinic  Chloride,  611. 

Oxide,  611. 

Platinized  Charcoal,  770. 
Platinocyanides,  610. 
Platinous  Chloride,  610. 
Cyanide,  611. 
Iodide,  611. 
Oxide,  610. 
Platammonium,  Bisalts  of,  615-616. 

Proto-salts  of,  613-614. 
Platinum  Black,  609. 

Bichloride  of,  611. 
Bioxide  of,  611. 
Bisulphide  of,  611. 
Class  of  Elements,  615. 
Estimation  and  Separation  of,  618. 
Extraction  of,  608. 
Inflammation  of  Mixed  Oxygen  and 
Hydrogen  by,  209. 


Platinum,  Metals  in  Native,  608. 

Process  of  rendering  malleable,  609. 
Protochloride  of,  610. 
Protosulphide  of,  610. 
Protoxide  of,  610. 
Residues,  New  Method  of  treating, 

635. 

Salts,  Ammoniacal,  612-618. 
Sources  of,  608. 
Spongy,  609. 
Sulphocyanides  of.  612. 
Platosamine  and  Platinamine,  618. 
Polar  Chains,  42.  , 

Formulas,  168. 
Liquids,  Separation  of,  205. 
Polarity,  Chemical,  187. 

Illustrations  from  Magnetical,  187. 
of  Arrangement,  192. 
Polarization,  Circular,  662. 

of  Light,  99,  216,  658. 
by  Reflection,  658. 
Refraction,  Single  and  Double, 

658. 

Tourmalines,  660. 
Polarized  Light,  Nature  of,  660. 
Polybasite,  595.  . 
Polythionic  Series,  304. 
Porcelain  and  Earthenware,  413. 
Potash,  372. 

Acid  Antimoniate  of,  543. 

Metantitnoniate  of,  543. 
Action  of  Chlorine  upon,  341. 
Antimoniates  of,  542. 
and  Antimony,  Oxalate  of,  541. 
Tartrate  of,  541. 
Glucina,  Oxalate  of,  822. 
Lime,  Sulphate  of,  816. 
Soda,  Carbonate  of,  391. 

Sulphate  of,  808. 
Aurate  of,  603. 
Aurosulphite  of,  603. 
Bicarbonate  of,  378. 
Bichromate  of,  511. 
Bihydrosulphate  of,  374. 
Chlorate  of,  380. 
Chromate  of,  511. 
Estimation  of,  806. 
Felspar,  425. 
Hydrate  of,  372,  806. 
Hydrated  Bi sulphate  of,  378. 

Sesquisulphate  of,  378. 
Hydriodate  of,  375. 
lodate  of,  381. 
Ley,  373. 

Molybdates  of,  523. 
Neutral  Metantimoniate  of,  543. 
Nitrate  of,  378. 
Valuation  of,  768. 
Perchlorate  of,  381. 
Preparation  of  Hydrate  of,  from  the 

Nitrate,  806. 
Red  Prussiate  of,  376. 
Sulphate  of,  378. 
Tellurate  of,  628. 
Terchromate  of,  511. 
Yellow  Prussiate  of,  375. 
Potashes,  377. 


846 


INDEX. 


Poiassa,  372. 

Potassio-ferrous  Tartnito.  451. 
Potassium,  Chloride  of,  375. 

and  Gold,  Chloride  of,  605. 

Iron,  Ferrocyanide  of,  449. 
Mercury,  Cyanide  of,  587. 
Rhodium,  Chloride  of,  632.. 
Chloroplatinate  of,  612. 
Chloroplatinite  of,  611. 
Class  of  Elements,  145. 
Compounds  of,  372. 
Cyanide  of,  376. 
Estimation  of,  806. 
Ferricyanide  of,  376. 
Ferrocyanide  of,  375. 
Improvements  in  the  Preparation 
of,  by  Maresca  and  Donny,  805. 
Iodide  of,  375. 
lodo-aurate  of,  606. 
Pentasulphide  of,  374. 
Peroxide  of,  374. 
Preparation  of,  369. 

by    Electrolysis, 

805. 

Properties  of,  372. 
Protosulphide  of,  374. 
Salts  of  Oxide  of,  377. 
Separation  of,  from  Sodium,  808. 
Sulphides  of,  374. 
Sulphocyanide  of,  377. 
Telluride  of,  528. 
Trisulphide  of,  374. 
Priestley  on  Diffusion  of  Gases,  87. 
Prism,  NichoPs,  660. 
Proto-acetate  of  Iron,  451. 
Protobromide  of  Mercury,  585. 
Protocarburetted  Hydrogen  :  —  Experiments 

on,  282. 

•Preparation  and,  279. 
Properties  of,  279. 
Protochloride  of  Carbon,  346. 

Sulphite  of,  792. 
Cerium,  560. 
Chromium,  506. 
Copper,  480. 
Iridium,  624. 
Iron,  449. 
Mercury,  582. 
Platinum,  610. 
Rhodium,  631 
Ruthenium,  634. 
Sulphur,  349. 
Tin,  496. 

Tin  and  Potassium,  497. 
Uranium,  555. 
Protocyanide  of  Iron,  449. 
Protofluoride  of  Cerium,  560. 
Proto-hydrate  of  Phosphoric  Acid,  320. 
Protiodide  of  Mercury,  585. 
Protosulphurets,  123. 
Protoxide  of  Cerium,  559. 

Chromium,  505. 
Cobalt,  460. 
Copper,  479. 
Didymium,  564. 
Iridium,  624. 
Iron,  448. 


'rotoxule  of  Lanthanum,  563. 
Lead,  486. 
Mercury,  579. 
Nickel,  467. 
Nitrogen,  253. 
Palladium,  619. 
Platinum,  610. 
Ruthenium,  633. 
Tin,  495. 
Titanium,  502. 
Silver,  594. 
Uranium,  554. 
Vanadium,  515. 

rotoxides  of  Metals,  366,  688,  697. 
'rotosalts    of    Ammo-platammonium,    614, 

615. 

Platanmionium,  613,  614. 
5rotosulphate  of  Iron,  451. 
Protosulphide  of  Carbon,  782. 
Cerium,  560. 
Iron,  449. 
Mercury,  581. 
Platinum,  610. 
Tiii,  496. 
Prussian  Blue,  454. 
Prussine,  165. 
Psychrometer,  93. 
Purple  of  Cassius,  604. 
Pyrites,  Iron,  453. 

Pyrometer,  Daniell's  and  Wedgwood's,  45. 
Pyrophosphamic  Acid,  790. 
Pyrophosphate  of  Soda,  322. 
Pyrophosphoric  Acid,  321. 

QUADROXIDE  of  Bismuth,  550. 
Quartation  of  Gold  and  Silver,  601. 
Quartz,  Loft  and  Right-handed,. 662. 
Quinine,  Fluorescence  of  Salts  of,  671. 

RACEMIC  Acid,  Composition  of,  670. 
Radiant  Heat,  55. 
Radicals  and  Types,  692. 
Conjugate,  694. 
Equivalent  Values  of,  693. 
Rain,  Mean  Fall  of,  in  London,  248. 

in  Northern  Europe,   Central  Europe, 

and  in  South  Europe,  248. 
in  York,  248. 

Rational  Formula  and  Atomic  Volume,  Rela- 
tion between,  727. 

Formulae,  692. 
Rays,  Chemical,  101. 

Deoxidizing,  101. 
Reaumur,  Thermometer  of,  44. 
Reciprocal  Action  of  Salts,  705. 
Red  Lead,  487. 

Oxide  of  Copper,  477. 
Phosphorus,  785. 
Sulphur,  781. 

Reduction  of  the  Force  of  the  Electric  Cur- 
rent  to   absolute    Mechanical 
Measure,  690. 
Test  for  Arsenic,  535. 
Reflection,  Polarization  by,  658. 
Refraction,  Polarization  by,  659. 
Refrangibility  of  Light,  Change  of,  671. 
Regnault,  Condenser-Hygrometer,  94. 


INDEX. 


847 


Regnault,  Experiments  on  Gases,  82. 

Oxygen,  227. 
on  Atomic  Heat,  123. 

Evaporation  of  Water,  91. 
the  Weight  of  Air,  245. 
Table  of  Specific  Heat,  49. 

the,8pecific  Heat  of  Com- 
pounds, 124,  125. 
Gases,  642. 
Tension    of  Vapour   of  Water   in 

Vacuo,  74,  646. 

Resistance  of  Metals,  Electric,  682. 
Respirators,  Charcoal,  769. 
Rheometers,  679. 
Rheostat,  683. 
Rhodic  Acid,  630. 
Rhodium  and  Potassium,  Chloride  of,  632. 

Estimation  and  Separation  of,  632. 
Oxides  of,  630. 
Protochloride  of,  631. 
Sesquichloride  of,  631. 
Sources  and  Extraction  of,  630. 
Sulphate  of,  632. 
Sulphide  of,  631 
Kose's  Fusible  Metal,  39. 
Roseocobaltia  Salts,  464. 
Rotatory  Power  and  Crystalline  Form,  Rela- 
tions between,  668. 
Power  induced  by  Magnetic  Action, 

216,  671. 

Power,  Specific,  664. 
Ruthenic  Acid,  634. 
Oxide,  634. 
Sulphate,  634. 
Ruthenium,  Bioxide  of,  634. 

Bichloride  of,  634. 

Estimation   and    Separation    of, 

635. 

Protochloride  of,  634. 
Protoxide  of,  633. 
Sesquichloride  of,  634. 
Sources  and  Extraction  of,  633. 
Sesquioxide  of,  634. 
Sulphides  of,  635. 
Rutherford's  Thermometer,  21. 

SACCHARIMETRY,  664. 

Saccharine  Solutions,  Table  for  the  Analysis 

of,  668. 

Safety  Lamp,  Davy's,  280. 
Sal-alembroth,  585. 
Saline    Solutions,    Tension   of   Vapours   of, 

647. 

Waters,  241. 
Sal  prunelle,  700. 
Salt,  Microcosmic,  396. 
Saltpetre,  378. 

Valuation  of,  168. 
Salt-radical  theory,  156. 

objections  to,  159. 
Salts  of  Cobalt,  Ammoniacal,  463. 

Tin.  496. 
Salts,  117. 

Acid,  Neutral,  and  Basic,  705. 
Amidogen,   or   Intermediate   Nitrides, 

715. 
Analysis  of  (Wenzel),  118. 


Salts,  Atomic  Volume    and    Specific  Gravity 

of,  Table  11.,  173. 
Bibasic,  161. 
Calorific    Effect    of    Solution    of,    in 

Water,  756. 

Constitution  of,  156,  166. 
Decomposition  of  Ammoniacal,  168. 

Insoluble,  by  Soluble, 

736. 

by  Diffusion,  745. 
Derivations  of  Double  by  Substitution, 

164. 

Diffusion  of,  740. 
Double,  163. 

Double  Decomposition  of,  183,  186. 
Formation  of,  by  Substitution,  166. 
Glauber's,  391. 
Heat   produced  in  the  Formation  of, 

755. 
Monobasic,  160. 

the  Type  of  Red  Chromate 

of  Potash,  163. 

Oxygen,  or  Intermediate  Oxides,  705. 
Reciprocal  Action  of,  733,  740. 
Solubility  of,  in  100  parts   of  Water, 

178. 

Solution  of,  177. 
Sulphur,  708. 
Table  of,  124. 
Tribasic,  161.  , 

usually  denominated  Subsalts,  162. 
Scale-oxide  of  Iron,  453. 
Scales  of  Chemical  Equivalents,  117,  118. 
Schweitzer,  Analysis  of  Sea-water,  241,  242 
Sea-salt,  162. 

Sea-water,  Analysis  of,  242. 
Secondary  Decomposition,  205. 
Seleniate  and  Selenite,  Mercuric,  591. 
Mercurous.  579. 
of  Baryta,    Decomposition    of,    by 

Alkaline  Carbonates,  737. 
Selenic  Acid,  312. 
Selenide  of  Bismuth,  550. 
Selenides,  706. 
Selenious  Acid,  312. 

Selenium,  Allotropic  Modifications  of,  784. 
Estimation  of,  785. 
Preparation  of,  784. 
Properties  of,  311. 
Sesquicarbonate  of  Soda,  590. 
Sesquichloride  of  Carbon,  545. 
Cerium,  560. 
Chromium,  508. 
Gold,  605. 
Iridium,  624. 
Iron,  454. 
Ruthenium,  634. 
Sesquicompounds  of  Iron,  451. 
Sesquicyanide  of  Cobalt,  463. 

Iron,  454. 
Sesquioxide  of  Cerium,  559. 

Chromium,  506. 
Cobalt,  462. 
Gold,  603. 
Iron,  451. 
Lead,  487. 
Manganese,  455. 


848 


INDEX. 


Sesquioxide  of  Nickel,  467. 
Osmium,  627. 
Ruthenium,  634. 
Titanium,  502. 
Tin,  497. 
Uranium,  555. 

Sesquisulphide  of  Chromium,  508. 
Iron,  453. 
Gold,  605. 
Silica  or  Silicic  Acid :  — 

*    Dissolved  by  Acids,  290. 
Hydrates  of,  291,  777. 
Preparation  and  Properties  of,  290. 
Silicate  of  Soda  and  Lime,  400. 

Zinc,  473. 
Silicates,  291. 

Analysis  of,  779. 

of  Alumina,  401,  424. 

Lime  and  of  Alumina,  426. 
Magnesia,  418. 
Potash  and  Lead,  401. 
Soda,  379. 

Silicic  Acid  dissolved  by  Acids,  290. 
Estimation  of,  778. 
Formula  of,  777. 
Hydrates  of,  777. 
Siliciuretted  Hydrogen,  778. 
Silicon  or  Silicium,  Allotropic  Modifications 

of,  776. 

Atomic  Weight  of,  777. 
Estimation  of,  778. 
Silicon   and    Hydrogen,    Chloride,    Bromide, 

and  Iodide  of,  777. 
Silicon,  Hydrated  Oxide  of,  778. 

Chloride  of,  348. 
Bromide  of,  352. 
,  Preparation  of,  289,  776. 

Properties  of,  289. 
Silver,  Alloys  of,  599. 

Ammonio-nitrate  of,  534. 
Assay  of,  600. 
Bromide  of,  596. 
Carbonate  of,  597. 
Chromate  of,  513. 
Cupellation  of,  600. 
Cyanide  of,  597. 

Estimation  and  Separation  of,  599. 
Fluoride  of,  597. 
Hyposulphate  of,  597. 
Hyposulphite  of,  597. 
Iodide  of,  596. 
Metallurgy  of,  592. 
Nitrate  of,  598. 
Nitrite  of,  598. 
Oxalate  of,  599. 
Peroxide  of,  599. 
Properties  of,  593. 
Protoxide  of,  594. 
Sources  of,  592. 
Suboxide  of,  593. 
Sulphate  of,  597. 
Sulphide  of,  595. 
Silvering,  607. 

Silver-ores,  Treatment  of,  592. 
Silver-salts,  Reactions  of,  595. 
Simmler  and  Wilde's  Researches   on  Liquid 
Diffusion,  745. 


Six's  Thermometer,  46,  47. 
Soda,  373,  382. 

and  Auric  Oxide,  Hyposulphite  of,  606. 
Aurous   Oxide,  Hyposulphite   of, 

606. 
Potash,  Carbonate  of,  391. 

Sulphate  of,  808. 
Ash,  386. 
Alum,  423. 

Biborate  of  (Borax),  397. 
Bicarbonate  of,  389. 
Biphosphate,  396. 
Bipyrophosphate  of,  397. 
Bisulphate  of,  395. 
Carbonate  of,  384. 
Chlorate  of,  396. 
Chromate  of,  511. 
Furnace,  393. 

Hydrates  of  Carbonate  of,  807. 
Hyposulphite  of,  391. 
Metaphosphate  of,  322,  397. 
Molybdates  of,  523. 
Nitrate  of,  395. 
Phosphates  of,  396. 
Preparation  of  Carbonate  of,  from  the 

Sulphate,  392. 

Preparation  of  Sulphate  of,  393. 
Pyrophosphate  of,  322,  396. 
Salt,  386. 

Sesquicarbonate  of,  390. 
Silicates  of,  399. 
Solubility  of  Carbonate  of,  807. 
Sulphate  of, '808. 
Solution  of  Caustic,  382. 
Subphosphate  of,  396. 
Sulphate  of,  391. 
Sulphite  of,  391. 
Sodium,  382. 

Chloride  of,  383. 
Chloroplatinate  of,  612. 
Compounds  of,  382. 
Estimation  and  Separation  of,  808. 
Preparation  of.  382,  806. 
Salts  of  Oxide  of,  384. 
Sulphides,  383. 
Telluride  of,  529. 

Solid  Bodies,  Atomic  Volume  of,  171,  728. 
Expansion  of,  33,  539. 
Specific  Heat  of,  640. 
Soluble  Glass,  399. 
Solution,  Density  of  Salts,  737. 

of  Salts  in  Water,  Calorific  Effect, 

756. 

Soils,  Estimation  of  Nitrates  in,  768. 
Spectra  exhibited  by  Coloured  Media,  673. 
Specific  Heat,  48,  640. 

and  Heat  of  Combustion,  Re- 
lations between,  754. 
of  Gases,  50. 
Atoms,  120. 
Carbon,  123. 
Gravity  of  Gases  and  Table  of,  130- 

136. 

Rotatory  Power,  664. 
Stannic  Acid,  497. 

Chloride,  499. 

Salts,  Reactions  of,  498. 


INDEX. 


849 


Stannic  Oxide,  497. 

Oxide,  Sulphate  and  Nitrate  of,  500. 
Sulphide,  499. 
Stannous  Iodide,  497. 
Oxide,  495. 

Salts,  Reactions  of,  495. 
Sulphate  and  Nitrate,  497. 
Steam  as  a  Moving  Power,  70. 
Latent  Heat  of,  69,  644. 
Steel,  446. 
Stoneware,  427 
Strontia,  726. 

Estimation  of,  814. 

Separation  of,  from  Baryta,  814. 

Lime,  817. 
Sulphate,  Hyposulphite,  and  Nitrate 

of,  Carbonate  of,  406,  407. 
Strontium,  Binoxide  and  Chloride  of,  406. 

Preparation    and   Properties    of, 

406,  502. 

Subchloride  of  Carbon,  347. 
Subnitrates  of  Bismuth,  651. 

Copper,  482. 

Suboxide  or  Bioxide  of  Bismuth,  549. 
Lead,  486. 
Silver,  594. 
Subsalts,  162. 

Substances,  Table  of  Elementary,  102-105. 
Substitution,  Formation  of  Compounds  by, 

182. 

Subsulphide  of  Iron,  449. 
Succinate,  Ferric,  456. 

Sugars,  Optical  Rotatory  Power  of,  664-669. 
Sulphamide,  811. 
Sulphantimonic  Acid,  544. 
Sulphate  and  Nitrate  of  Stannic  Oxide,  500. 
Ceroso-ceric,  560. 
Cerous,  560. 
Chromic,  508. 
Chromous,  506. 
Cupric,  481. 
Ferric,  455. 
Ferroso-Ferric,  455. 
Ferrous,  451. 
Iridic,  625. 
Manganic,  435. 
Manganous,  434. 
Mercuric,  588, 
Mercurous,  579. 
of  Alumina,  421. 
Ammonium,  810. 
Antimony,  541. 
Bismuth,  551. 
Cadmium,  475. 
Didymium,  565. 
Didymium,  Solubility  of,  565. 
Lanthanum,  563. 
Lead,  490. 
Lime,  412. 

and  Potash,  816. 
Magnesia,  417. 
Nickel,  468. 
Potash,  378. 

and  Soda,  808. 
Rhodium,  632. 
Silver,  597. 
Soda,  Solubility  of,  808. 

54 


Sulphate  of  Strontia,  406. 

Titanic  Acid,  503. 
Uranyl,  556. 
Zinc,  472. 
Osmic,  627. 
Potassio-Ferric,  455. 
Stannous,  497. 
Ruthenic,  634. 
Uranic,  556. 
Uranous,  555. 
Sulphates,  300. 

Earthy,  decomposition  of,  by  Al- 
kaline Carbonates,  736. 
Formulae  of  Neutral,  158. 
Atomic    Volume    of    First    and 

Second  Class,  174. 
Sulphide,  Auric,  605. 

Aurous,  602. 
Cuprous,  478. 
Ferric,  453. 
Ferrous,  449. 
*•  Merdhric,  581. 

Mercurous,  577. 
Stannic,  499. 
Stannous,  496. 
of  Aluminium,  421. 
Carbon,  solid,  311. 
Didymium,  565. 
Lead,  488. 
Manganese,  433. 
Nitrogen,  309,  781. 
Rhodium,  631. 
Silver,  595. 
Tantalum,  569. 
Zinc,  472. 
Sulphides,  Alcoholic,  706. 

Classification  of,  706. 
of  Ammonium,  809. 
Arsenic,  533. 
Carbon,  309,  782. 
Cobalt,  463. 
Iridium,  624. 
Molybdenum,  524. 
Osmium,  629. 
Phosphorus,  328,  787. 
Potassium,  374. 
Ruthenium,  635. 
Tellurium,  528. 
Tungsten,  519. 
Sulphite,  Chromous,  506. 
Cuprous,  479. 
of  Cadmium,  475. 
Didymium,  566. 
Perchloride  of  Carbon,  791. 
Protochloride  of  Carbon,  791. 
Soda,  391. 

Sulphites,  Mercuric,  588. 
their  uses,  295. 

Sulphobromide  of  Phosphorus,  796. 
Sulphocarbonic  Acid,  309. 
Sulphochloride  of  Mercury,  584. 
Sulphocyanide  of  Aluminium,  421. 
Platinum,  612. 
Potassium,  377. 
Sulphur,    Allotropic   modifications   of,    292, 

780. 
and  Carbon,  309,  782. 


850 


INDEX. 


Sulphur,  and  Chlorine,  348,  793. 
Hydrogen,  306. 
Nitrogen,  309,  781. 
Phosphorus,  328,  787. 
Bromide  of,  351. 
Chlorides  of,  348,  793. 
Class  of  Elements,  144. 
Estimation  of,  783. 
Heat  of,  Combustion  of,  in  various 

states,  754. 
Iodide  of,  358. 
Melting  Point  of,  292,  781. 
Properties  of,  292. 
Protochloride  of,  349. 
Uses  of,  293. 
Sujphur-Acids,  706. 
Sulphur-Compounds,     Atomic    Volume     of 

Liquids,  725. 

Sulphur-Ethers,  Compound,  704. 
Sulphur-Salts,  707. 
Sulphuric  Acid   Action  of,  on  Pentachloride 

of  Phosphorus,  794.    « 
Density  of,  299. 
Estimation  of,  783. 
Formation    of,    Anhydrous, 

781. 
Heat  evolved  in  the  Hydra- 

tion  of,  755. 
Hydrates  of,  300. 
Manufacture  of,  297. 
Preparation  of,  296. 
Properties  of,  298. 
Uses,  300. 
Sulphurous  Acid,  Action  of.  on  Pentachloride 

of  Phosphorus,  794. 
Estimation  of,  783. 
its  Preparation,  294. 
Properties  of,  295. 
Series,  295. 
Volumetric  Estimation  of, 

801. 

Water,  300. 

Sulphuryl,  Chloride  of,  708,  795. 
Supersaturated   Solutions   of  Carbonate   of 
Soda,  807. 

Sulphate  of,  391. 
Symbols,  110. 

TANOENT-Compass,  679. 
Tantalic  Acid,  567. 

Hydrated,  567. 
Reactions  of,  571. 
Tantalous  Acid,  564. 
Tantalum,  566. 

Bromide  of,  569. 
Chloride  of,  669. 
Estimation  and  Separation  of, 

569. 

Fluoride  of,  569. 
Sulphate  of,  569. 
Tartar-emetic,  541. 

Tartaric  Acid,  Circular  Polarization  of,  669. 
Inactive,  670. 
Pyro-electricity  of,  670. 
Tartrate  of  Potash  and  Antimony,  641. 

Potassio-ferrous,  451. 
Tartrate  of  Tin  and  Potassium,  497. 


Telluretted  Hydrogen,  528. 
Telluric  Acid,  527. 

Anhydrous,  527. 
Tellurides,  528,  706. 
Tellurium,  525. 

Chlorides  of,  628. 

Estimation    and    Separation    of, 

529. 

Sulphides  of,  528. 
Tellurous  Acid,  626. 

Anhydrous,  526. 

Temperature,  Capt.  Parry  and  Back  on,  59. 
Equilibrium  of,  57. 
of  the  Atmosphere,  246. 
Table    of  interesting   Circum- 
stances in  the  Range  of,  47, 
48. 

Tension  of  Vapours,  645. 
Terbia,  429. 
Terbium,  429. 

Terchloride  of  Antimony,  541. 
Bismuth,  551. 
Bismuth     and     Ammonium, 

551. 

Iridium,  625. 
Osmium,  628. 
Phosphorus,  349. 
Terchromate  of  Potash,  511. 
Terfluoride  of  Antimony,  541. 
Chromium,  513. 
Teriodide  of  Bismuth,  551. 
Teroxide  of  Bismuth,  549. 
Hydrogen,  760. 
Iridium,  624. 
Tersulphide  of  Antimony,  540. 

Bismuth,  550. 
Test-Acid,  389. 

Tetramercurammoniura,  Chloride  of,  584. 
Iodide  of,  581. 
Nitrate  of,  588. 

Tetrametaphosphoric  Acid,  787. 
Tetrathionic  Acid,  305. 
Tetartohedry,  668. 
Thenardite,  392. 
Thionamic  Acid,  801. 
Thionamide,  794,  801. 
Theory  of  Heat,  Dynamical,  654. 
Thermometer,  Celsius,  43. 

Crichton's,  43. 
Description  of  the,  41. 
Regnault's   and  Pierre's    Re- 
marks on  the,  43. 
Reaumur's,  44. 
Rutherford's,  46. 
Sanctorio's     and     Sir     John 

Leslie's,  41. 
Six's,  46. 

Thermo-multiplier,  55. 
Thionyl,  Chloride  of,  794. 
Thorina,  429. 
Thorium,  428,  429. 
Tin,  494. 

Alloys  of,  500. 
Ammonio-Chloride  of,  499. 
and  Antimony,  Separation  of,  547. 
Potassium,  Bichloride  of,  500. 

Protochloride  of,  496. 


INDEX. 


851 


Tin,  and  Potassium,  Tartrate  of,  497. 
Sulphur,  Bichloride  of,  499. 
Bichloride  of,  with  Oxychloride  of  Phos- 
phorus, 500. 
Bichloride    of,    with    Pentachloride    of 

Phosphorus,  499. 
Bioxide  of,  497. 
Bisulphide  of,  499. 
Chlorosulphide  of,  499. 
Class,  148. 

Estimation  and  Separation  of,  501. 
Protochloride  of,  496. 
Protiodide  of,  496. 
Protoxide  of,  495. 
Protosulphate  of,  497. 
Protosulphide  of,  496. 
Separation     of,     from     Antimony    and 

Arsenic,  546. 
Sesquioxide  of,  497. 
Volumetric  Estimation  of,  501. 
Tinkal,  397. 

Titanic  Acid,  Sulphate  of,  503. 
Titanic  Oxide,  502. 
Titanium,  501. 

Bichloride  of,  503. 

Bifluoride  of,  503. 

Bisulphide  of,  503. 

Bromide  of,  503. 

Estimation     and     Separation    of, 

504. 

Nitrides  of,  503. 
Nitro-cyanide  of,  504. 
Protoxide  of,  502. 
Sesquioxide  of,  502. 
Touchstone,  608. 

Tourmalines,  Polarization  by,  660. 
Transpiration  of  Gases,  85. 
Triamides,  Primary,  714. 
Tribasic  Phosphate  of  Water,  320. 

Salts,  161. 

Trimetaphosphoric  Acid,  787. 
Tritnercurammonium,  Nitrate  of,  589. 
Triphosphamide,  787. 
Trisul-hyposulphuric  Acid,  305. 
Trithionic  Acid,  305. 
Tungstates,  518. 

and  Chromates,  Atomic  Volume 

of,  174. 
Tungsten,  517. 

Class  of  Elements,  148. 
Chlorides  of,  520. 
Estimation  and  Separation  of,  520. 
Phosphides  of,  520. 
Sulphides  of,  519. 
Tungstic  Acid,  517. 

Action  of,  on  Pentachloride  of  Phos- 
phorus, 795. 
Oxide,  577. 
Turnbull's  Blue,  450. 
Type-Metal,  545. 
Types  and  Radicals,  692. 

ULTRAMARINE,  402. 

Unitary  System.  Gerhardt's,  687. 

Uranic  Nitrate,  556. 

Oxide,  655. 

Oxide,  Compounds  of,  with  Bases,  557. 


Uranic  Phosphates,  556. 

Salts,  Fluorescence  of,  556,  672. 
Sulphate,  556. 

Uranium,  Estimation  and  Separation  of,  557. 
Sources  and  Extraction  of,  653. 
Protochloride  of,  555. 
Protoxide  of,  554. 
Sesquioxide  of,  555. 
Uranoso-uranic  Oxide,  555. 
Uranous  Chloride,  555. 
Oxide,  554. 
Sulphate,  555. 

Uranyl  and  Potassium,  Chloride  of,  556. 
Arseniate  of,  557. 
Chloride  of,  556. 
Nitrate  of,  556. 
Phosphates  of,  556. 
Sulphate  of,  556. 
Utricular  Sulphur,  781. 

VANADIC  ACID,  515. 
Vanadium,  515. 

Bioxide  of,  515. 

Estimation  and  Separation  of,  516. 
Protoxide  of,  515. 
Vaporization,  62-76. 

Brix's  Experiments  on,  69. 
Despretz's  Experiments  on,  69. 
Table     of   Elastic    Force    of 

Steam,  68. 
Vapour,  248. 

of  Water,  238. 
Vapours  and  Gases,  Specific  Heat  of,  642. 

Table   of  the   Specific   Gravity   of 

Gases  and,  130-136. 
Latent  Heat  of,  642. 
Tension  of,  645. 

of  Saline  Solutions,  Tension  of,  647. 
Vapour-volume,  Uniformity  of,  689. 
Varvicite,  437. 
Ventilators,  Charcoal,  679. 
Voltaic  Circle,  Application  of  the,  to  Chemi- 
cal Synthesis,  206. 
(Compound),  197. 
Liquid  Elements  of  the,  202. 
(Simple),  191. 
Solid  Elements  of  the,  200. 
without  a  Positive  Metal,  208. 
with  the  Connecting  Wire  un- 
broken, 193. 
with     the     Connecting    Wire 

broken,  196. 
Theoretical  Considerations  on, 

211. 

Battery,  198. 

Current,  Heating  Power  of,  684. 
Endosmose,  207. 
Instruments,  218 
Protection  of  Metals,  201. 
Secondary  Decomposition,  205. 
Transference  of  Ions,  206. 
Volta-meter,  221. 
Volume,  Atomic,  of  Liquids,  720. 
Volume,  Atomic,  of  Solids,  173,  728. 
Volumetric      Analysis,      Bunsen's      Genera 

Method  of,  801. 
Volatility  of  Carbon,  679. 


852 


INDEX. 


WATER,  ABSORPTION  OF  GASES  by,  81,  239, 
763. 

Boutigny's  Experiments  on  the  Ebul- 
lition of,  64. 

Calorific  Effect  of  Solution  of  Salts 
in,  756. 

Calorimeter,  752. 

Capacity  of,  for  Heat,  48. 

Chalybeate,  241. 

Circulation  of,  39. 

Constitutional,  162. 

Contraction  of,  38. 

Ebullition  of,  63. 

Estimation  of,  762. 

Expansion  of,  39,  639. 

Estimation  of  Nitrogen  in,  768. 

Evaporation  of  (Dalton),  91. 

Filter,  240. 

Heat  evolved  in  the  combination  of 
Sulphuric  Acid  with,  756. 

Latent  Heat  of,  61,  642. 

Vapour  of,  61,  644. 

Leslie's  Process  for  Freezing  of,  75. 

Oxygenated,  155. 

Properties  of,  238. 

Saline,  241. 

Schweitzer's  Analysis  of  Sea-Water, 
241. 

Specific  Heat  of,  641. 

Sulphurous,  241. 

Table  of  Boiling  Point  of,  66. 

Tension  of  Vapour  of,  74,  646. 


Water,    Tribasic  Phosphate  of,  320- 

Type,  693,  697. 

Uses  of,  240. 

Vapour  of,  238. 
Wedgwood's  Pyrometer,  45. 
White  Lead,  489. 
Williamson's   Theory   of    Chemical    Action, 

738. 

Winds,  246. 
Wood,  Heat-conducting  Power  of,  651. 

YELLOW  PRUSSIATE  OF  POTASH,  375. 
Yttria,  429. 
Yttrium,  428,  429. 

ZINC,  116,  200,  470. 

Alloys  of,  473. 

Carbonate  of,  472. 

Chloride  of,  472. 

Estimation  and  Separation  of,  473. 

Iodide  of,  472. 

Nitrate  of,  473. 

Oxide  of,  472. 

Phosphate  of,  473. 

Plates,  Amalgamation  of  the,  194. 

Silicate  of,  473. 

Sources  and  Extraction  of,  470. 

Sulphate  of,  472. 

Sulphide  of,  472. 
Zincoid,  200. 
Zirconia,  430. 
Zirconium,  428,  430. 


THE   END. 


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